| |
The
difference between a battery charger
and a power supply. |
There is a
problem that a battery charger has to
solve that a power supply does not.
When you apply 4.6 volts to a 4V lead
acid battery it is impossible to know
how much current the battery will suck
up. A 1000AH battery one would probably
take 100s of amps if it was fully
discharged. So a battery charger has a
"constant current" circuit that cuts
back the voltage until the battery is
asking for exactly what the charger
wants to supply. Then, as the battery
fills up, that voltage is increased so
that the current stays constant.
Eventually the voltage will top out and
then the current slowly drops as the
battery fills up. Some benchtop power
supplies have the constant current
limit feature, and if you are trying to
charge an odd-voltage lead acid or
lithium battery they are the simplest
alternative. |
Another
bad idea for energy
harvesting
  |
Here is another one from
the same source. The idea is to put a
couple of scoops in front of the
electric or hybrid car to run a
generator to charge the battery.
Ignoring the fact that squirrel cage
fans work on centrifugal force and
therefore don't run backwards by
pushing air at them, this is another
example of putting more load on the
car's motor by adding extra drag on the
car. Therefore you are going to lose
energy rather than harvest some wasted
energy. |
A bad idea
for energy harvesting |
We get passed a lot of
interesting ideas for alternative or
free energy generation. I thought about
creating a web page based on these,
showing the fallacies, but of course
most of these are closely held secrets
and the inventor would be upset and
probably litigious if we divulged
them.
However, I just got an
e-mail from an invention promotion
company that has public links, so I can
discuss it. The invention can be found
here
http://www.sellidea.com/?id=6239
Here
is why this is a bad idea. It is
usually useful to ask "where is the
energy coming from?" In this case he
proposes a generator analogous to a
linear motor to be run along elevator
or conveyer belts to extract energy in
the form of electricity. The conveyer
belt is the easiest to debunk.
Obviously, the only source of energy in
the conveyer belt is the motor that
drives it. Any energy extracted from
the belt's motion will add to the
motor's load, and therefore cost more
energy than is generated.
The
elevator has to deal with gravity,
however, which is more mysterious.
There are counter-weights in the
elevator that compensate for the weight
of the elevator and cables, so for an
empty elevator the motor is just
overcoming friction, no actual
potential energy is being generated
when the elevator moves to the top
floor. (I know that this is a
simplification of what must be a lot of
counterweight engineering, but it is
true enough). When a load is added to
the elevator, there is potential energy
stored as the elevator moves up, and
lost as the elevator moves down. If
there is energy to be extracted from
the downward motion, the motor is still
in the circuit, and could be used for
that purpose if practical. There is no
energy available for extraction as the
elevator moves up, since any generator
added will add to the load of the
motor, consuming more energy.
|
| Mystery Battery |
An antique 6V lead acid battery was recently unearthed in Washington State. The finder is looking for more information about this. Take a look.
|
| Shock voltage |
Q:
Hello, I was just reading how to design
battery packs on your website, and I
just have a few questions. I'm wanting
to build some 7.2volt Nicd packs for RC
cars. I've read how to do it, but was
just wondering if I could get shocked
while doing it? I read that you can
short the battery if you touch the +
and - wires together, but what if you
just held in each hand the positive and
negative wires at the same time? Would
that complete the circuit and I get
shocked? I'm asking because with rc
packs, there really isn't any
insulation for the battery tabs,
because we use discharge trays in
racing to always keep the cells
matched, and the trays have to touch
each cell tab.
A: Engineers
use the rule-of-thumb that anything
under 60 volts isn't likely to shock
you. |
| Replacement lithium
polymer cells. |
Q:
I am in search for a Walkman NW-S202F
MP3 player replacement battery.
Original is a polymer 116mAh
1-756-686-11 manufactured in
2006.
A: All you need is to find
one that will fit into the space of
that battery. Here is our list, the
ones with "add to cart" are the ones we
have in stock. You need to find whether
the existing battery has a protection
circuit board mounted on the flange
where the leads come out. It is a small
circuit board under the tape, but
outside the battery pouch.
http://www.powerstream.com/li-pol.htm
|
| Video-eye |
Yes,
the man with the video-cam eye is using
a PowerStream battery in his eye
socket. For more information about the
eye, plus borgeye video here is a
link:
http://www.physorg.com/news/2011-08-eyeborg-vision-future-video.html
We did donate a
few cells to that project. Too wild to
resist.
http://eyeborgproject.com/partners/
Don't try this
at home!
|
| The patent office does
another disservice to the investing
public |
I just got an
e-mail invitation to invest in a
company based on patent number 7615876.
Look it up, it is a fairly
straightforward perpetual motion
machine which purports to use a gear
box to increase the torque and
horsepower of a motor before it powers
a generator, which then powers the
motor and a load.
So the lessons
to carry away from this is that the
attorney, primary examiner, and
possibly the inventor should have known
better than to let this slip through.
And no investor can depend on the
patent office to evaluate the technical
merit of anything. I can't fault an
inventor for trying to raise money on
an patented idea that he sincerely
believes in, but I can fault the patent
attorney, and especially the patent
office, which should have technical
education enough to pull the plug on
this. Investigative reporter
alert! |
| Excess power consumption
in home appliances? |
Q: Recently
I've been a bit concerned about the
power consumption of my home
appliances. I have a notebook power
supply that says: Input: 100-240V~ 1.7A
50-60Hz Output: 19V 3.42A Does this
mean that it consumes 187 watts if
connected to 110 V and 374 watts if
connected to 220 volts? Is it possible
for it to consume twice the amount of
watts if connected to a 220 current?
Thanks.
A: No, the current
listed is the highest possible, so that
would be at 100 volts. As the voltage
goes up the current goes down to keep
the watts the same. Also, note that the
testing agencies (UL) require that you
put the highest possible surge current
on the label, so you cannot have any
possible chance to calculate the
efficiency or power consumption of the
device based on the label. best regards
mark |
| At what voltage is a 9V
battery dead? |
I'm trying to
find info on when a 9 volt battery is
sub par for use. I have a voltage
meter, but the problem is that I don't
know the cut-off point where a battery
loses effectiveness. For instance, in a
regular, non-rechargeable, Alkaline
type battery, does a reading of 8.9
volts mean it's still has over 75%
original capacity? What's the point
where battery should be replaced--at
what voltage reading? I feel like I
keep replacing batteries installed in
devices for back-up purposes should
power fail, when perhaps they would
still do the job at a lower reading,
but have no idea what the readings
really mean.
Thanks,
Terri
Sorry Terri, there is no
good answer to this question. First of
all, the voltage you measure is in
large part due to the chemistry
voltage. The battery could have very
little charge left and still read high
voltage when it is "open circuit." You
have to measure the battery under some
load to get an idea of its state of
charge. The load that you would use
would be drawing the same power as the
gadget under power. Next, it depends on
the device the battery is powering.
These transistor radio batteries are
usually used to power gadgets that
don't take much power. Also, some
devices are designed to run over a wide
range of voltages, so even if the 9
volt battery is only putting out 5
volts they would still operate. Lastly,
9 volt batteries consist of several
cells in series. I have seen them use 6
cells in series, and 5 cells in series.
So a 9 volt battery could be nominally
7.5 volts. Using 5 cells gives you less
voltage, but the cells are bigger, so
they give more run time if the device
it is running can use the lower
voltage.
The answer to your
question can only be "When the device
can't operate, then the battery needs
to be replaced." I know that this isn't
much help in your case, where the
batteries are used for emergency
purposes, sorry again.
best regards
mark |
| Why can't you charge a
lithium ion battery when it is too
cold? |
Mark, I've read
(and heard you say) that a LiPo battery
should not be charged at low temps
(e.g. -20C). Why is this? Is there a
safety reason for this or will it just
degrade the capacity? --
Damien
The thermodynamics of the
lithium-ion intercalation change below
about zero degrees C, and make it
favorable to deposit lithium metal onto
the graphite. This seals the graphite
and kills the battery, and lithium
dendrites have the chance to short the
cells and cause a fire.
best
regards, mark |
| Time to recharge the
battery after starting the
car. |
Hi,
There is
a lot of discussion in my group about
how many miles you have to drive your
car to recharge the battery after
starting. Can you shed some
light?
Tonk
Dear Tonk,
I
can do a back-of-the-envelope estimate.
Typical car batteries are rated for
cold cranking amps, and the one I use
has 800 CCA. So being very conservative
lets assume that it takes 800 amps. I
have three cars, 22 years old, 9 years
old, and 10 years old, they all start
in less than 3 seconds, but to be
conservative let's assume 10 seconds.
So 10 seconds times 800 amps is 8000
amp-seconds (8000 coulombs for you
physicists) or 2.2 amp-hours.
Now let's look at the charger.
All of my cars have alternators greater
than 60 amps, so 2.2AH/60A = 0.03
hours, or 2 minutes to recharge the
battery.
More realistically,
lets say that it takes 300 amps to
start the car for 3 seconds, that would
take 0.25 AH, and the recharge time is
15 seconds.
Now the Karman Ghia
that I had in college usually took 2
minutes to start and had a 65 amp
alternator. It would have taken about
10 minutes to recharge.
best
regards
mark |
| Charging lithium ion in
parallel |
Hello Dr. Mark,
I'm glad I found your web log. I
have a question about charging Li-ion
and Li-polymer cells in parallel. I
have searched for and found others who
have opinions about this. Some say
absolutely don't do it because the
cells won't charge equally. I know that
is an issue with cell in series, but
does it apply to cells in parallel?
Others say it's safe because cells in
parallel naturally balance because
power will flow from the stronger cell
to the weaker cell. Can you shed some
light in this?
Thanks
Bruce
Dear Bruce,
The
answer is that since lithium ion
chemistries are charged with voltage
control they can be charged in parallel
with no problem. The same with lead
acid batteries.
The nickel
based chemistries are charged with
current control and they don't like to
be charged in parallel.
I have
discussed this with many top battery
designers, and I have seen dozens of
designs that charge lithium ion in
parallel with no problem, so I have
high confidence in this answer.
However, it is rare for one battery to
have enough voltage to charge another,
nature just doesn't work that way. What
happens is that the battery with the
lowest charge state will take most of
the current until their equivalent
impedances are equal. Since the lithium
chemistries use a specific float charge
voltage, if you connect a fully charged
battery with an uncharged battery very
little current will flow between the
two. Then putting this combo on a
charger the fully charged battery will
accept no current while the uncharged
battery is being filled.
best
regards
mark |
| Mysterious
Instrument |
A correspondent sent me pictures of something she found in her parent's attic. Any idea what it is?
Click on the picture for
more views.
|
| Switchmode or
Switching? |
Q; What do the words
'Switchmode mean? My experience with
switching power supplies is that they
only work well if there is some minimum
load.
A: There are various
topologies used in switchmode aka
switching power supplies. Some need to
supply some output current in order for
the housekeeping circuitry to work,
others have a separate bootstrap
circuit to make it operate. The former
system is used in ATX computer power
supplies, the latter in almost
everything else. best regards mark |
| AAA
versus AA Capacity |
Q: Alkaline AA vs AAA
amphours comparison question for your
battery guru: For Alkaline batteries
what is the comparison between AA and
AAA batteries 1.5v in the amp hours
output for say the 100ma discharge rate
(or any other rate for that matter). We
want to know how many AAA 's = 1 AA
cell? what is the difference in
amphours. thanks
A: Depending
on which ones you are comparing an AA
has about 2 to 3 times an AAA.
http://www.powerstream.com/BET.htm
best regards,
mark
|
| Mystery
with battery tender |
Q: I found your website
while trying to solve a problem. You
seem very knowledgeable and I'm hoping
that you wont mind helping me (a
newbie) solve a problem... I can't seem
to charge a new 12V 18AH sealed lead
acid battery. I thought it would be a
simple matter to connect my 750mah
Deltran Battery Tender however the
voltage quickly runs up to 13.5v and
the Battery Tender discontinues output.
Tried a second new battery tender, same
result. Tried a second sealed lead acid
battery (12V 7AH), same result. Hmmpf.
So I tried a 1 Amp fixed output
charging source. Voltage then quickly
ran up to 15v after ten seconds so I
disconnected it. If I put a moderate
load on either battery the voltage
quickly drops to 8v. So they definitely
are not charging. What the heck am I
doing wrong? Thanks for letting me lean
on you. -Mick
A: I can't see
that you are doing anything wrong. I
always assumed that those battery
tenders were like ours
http://www.powerstream.com/SLA-12V07.htm
and would charge a battery as well
as tend it. As for your fixed voltage
source, it won't hurt the batteries to
be charged at 15 volts until they are
near full or full. Sorry,
troubleshooting from this distance is
tough! Maybe one of our readers has
some insight.
best regards mark
|
| Battery
Capacity |
Q: When a
battery’s “Rated
Capacity” is 170mAh, does that
mean it is capable of delivering 170mA
continuously for one hour before the
entire battery is discharged?
A:
Yes, but with limitations. The rating
is measured over a specified time.
Usually for lead-acid batteries this
time is 20 hours. For lithium-ion it is
usually 5 hours. When discharging
quickly you always loose some capacity.
This is a very strong factor with
lead acid, where if you discharge at a
1C rate you only get 50% of the rated
capacity. It is not a big factor in
lithium ion, NiCad, and NiMH batteries,
unless you are discharging at very high
rates (above 1C to5C depending on the
design of the battery) |
| Battery
Capacity 2 |
Q: Is a battery’s
“Rated Capacity” linearly
proportional? In other words, if a
battery’s rated capacity is
170mAh, could it be assumed that it can
deliver 85mA for two hours, 42.5mA for
four hours, etc.?
A: Yes, with the
above limitation. mAH are proportional
to coulombs. 1 mAH = 3.6 coulombs.
Other than the problem discussed above
it is linear. The slower the discharge
the more linear it is. If you discharge
time is a period of months you will
start to run into the self-discharge
rate of the battery, so you will again
get less than the rated
amp-hours.
See our web page "
Engineering Design Notes on Battery Powered Devices
"
|
| Conservation of
Energy |
Q: Hello: I have a
question. I have a DC power supply that
is putting out 14 volts at 14 amps. And
I have a motor that is running at 14
volts but needs a higher amp rating.
Can a DC-DC converter increase the amp
output? If not is there anyway to
increase the amp output?
A:
Energy conservation means that "watts
in" must be more than or equal to
"watts out." Watts is volts times amps,
so if you increase the amperage you
have to decrease the voltage.
best
regards
mark |
| Current
limit of AC/DC adapters |
Q: I have heard that AC
adapters can output TWICE the current
as stated on the labels. Are there any
that limit the current?
A: The
old-style transformers could do that
and get hot, but the voltage would
drop, and eventually they would blow
the internal fuse.
Switchmode
power supplies can typically supply
120% with some loss in voltage
regulation (and they get hot), but
start hiccoughing (turning on to see if
the problem has been solved, then
turning back off again) when the
current goes too high.
If you
want a current-regulated power supply,
those are harder to find, they are what
battery chargers typically use.
I
don't know of any AC/AC power supplies
that are current limited (other than
the fuse).
best regards
mark |
| Battery
charging auxiliary batteries |
Q: I run a computer
repair business, and while most of my
work is done at the client’s site,
sometimes I have to bring their
equipment back to my office. I’d
like to set up a portable computer lab
in my van so I can do more work
on-site, and have bought a couple 750AH
deep-cycle batteries to power things.
I’d like to power the lab off
these batteries and not take any
chances of running down the vehicle
battery. I’ve looked at your
product list and wonder if your
PST-DC-UPS-1212 is the right product to
keep the batteries charged while on the
road.
A: For such big
batteries I would suggest the
http://www.powerstream.com/battery-isolator.htm
to charge while driving and then
isolate the deep-cycles from the
starting battery. The PST-DC-UPS-1212
would take a long time to charge a 1500
AH battery!
|
| Does
turning a fluorescent light on-and-off
waste energy? |
Q: How long does a
fluorescent light have to stay "off" to
pay for the energy required to start it
up again?
A: This is an urban
myth from my childhood, and it isn't
true now and I doubt that it was ever
true with the oldest iron ballasts. It
does take energy to start a bulb, but
very little, insignificant compared
with running the lamp for a few
seconds.
|
| Comments
on the Stanford Nanowire
battery |
This link discusses a
breakthrough at Stanford University.
http://news-service.stanford.edu/news/2008/january9/nanowire-010908.html
This is interesting, but weird.
Since silicon isn't used in any
batteries at the present time, the
article is somewhat misleading,
evidently the author missed some
important facts. Carbon is typically
used for the anode material to store
the lithium ions, and since silicon
doesn't have a graphite-like analog (Si
crystallizes in the diamond
structure)
Most puzzling is the fact
that the best lithium-metal batteries
only have 2-3 times the capacity of
lithium ion batteries per unit weight
or volume. Using lithium-plated silicon
nanowires you will have far less
density than a solid layer of lithium
metal, so how can they have 10x the
capacity? You can see from the pictures
that there is a lot of empty space in
the nanowire tangle.
I can
imagine that the cycle life could be
10x because there is no wear-out
mechanism, maybe the author got that
confused. Or maybe the battery has 10x
the power output because so much
surface area is in contact with the
electrolyte. But it can't have 10x the
energy storage as stated in the
article.
|
| Replacement batteries
for emergency jumper packs |
Q: Who in US sells
replacement batteries for, Jumper
Battery packs used for emergency
starting? Can't figure it out. Steve
A: These typically use
standard-size sealed lead acid
batteries, such as those at
http://www.powerstream.com/BB.htm. If
you find one of the correct dimensions
it will work.
best regards
mark |
| Why are
lead acid batteries used in standby
applications? |
Q: Traditionally, lead
acid batteries have been used for
telecom and off-grid electrical
systems. If they can be damaged by deep
discharges, or by periods of partial
charge, why are they used for these
applications? Could you use a NiCd
battery in a UPS? Is there a better
battery chemistry for a renewable
energy system? Thanks! -Tim
A:
Their biggest advantage is that they
can be float charged, in other words
kept at a certain voltage without over
charging. This makes them very
convenient as batteries that are rarely
discharged, but are standing by for
most of their lives, such as telecom
standby power.
NiCad can be used
for UPS systems, but they can't be
float charged, so it takes a more
sophisticated charge controller.
Besides, they are more expensive than
the lead acid batteries.
For
batteries that are used in off-grid
situations nickel-iron batteries are
very nice. They are virtually
indestructible, can last for 50 years.
They have a low voltage and low energy
density, and aren't as easy to find, so
usually people use lead acid instead.
best regards mark |
| Battery
packs get hot |
Hi my name is
Jerimiah.
I read a lot of your tips
online and have run into a situation I
can’t figure out. I would
appreciate a little insight if
possible. I have two battery packs that
need to be connected. They hold 4 AA
batteries each. Unfortunately the
manufacturing company has gone out of
business and I have no way of buying a
new one. I have connected both the
packs exactly the same way they had
them connected. When I plug in the
batteries they start to heat up. What
do you think could be happening? Thank
you Jerimiah
You have some
polarity backwards, either one or more
of the AA cells is backwards or the
connection between the batteries is
backwards. If both wires from the one
pack are connected to the other pack
then you should be in parallel, plus to
plus and minus to minus. If only one
wire from one pack is connected to the
other then you are in series and you
should connect plus to minus.
best
regards mark |
| At what
discharge rate are LiPo batteries
measured? |
Mark,
For LiPo
cells, at what discharge rate is the
mA-hr rating based? I know for lead gel
cells it is based at 20 hr rate, with
the A-hr reduced significantly at
higher or faster discharge rates. Are
there published curves for given size
LiPo cells at different discharge
rates? Mike
Dear
Mike:
Typically it is the 5 hour
discharge rate that determines the
capacity rating of a lithium polymer
cell. Lithium cells don't lose their
capacity when discharged quickly as
much as lead-acid do. However, when the
discharge rate gets to a few minutes
they do lose some capacity. Some data
sheets will have the capacity versus
discharge time.
Also, lithium
polymer cells differ in their design.
Some are designed for rapid discharge
for the RC industry and some are
designed for slow discharge for more
sane applications. In the case of
fast-discharge (10C to 20C or 3 to 6
minutes) batteries the trend is to give
the capacity at fast discharge, since
the 5 hour discharge rate capacity is
irrelevant to the users.
best
regards mark |
| What is
the truth about silicone
batteries? |
There has been a bit of
flurry about a new lead battery, the
Silicone Power Battery. It is
advertized as new, green, and cool. To
quote it uses a "silicate salt
electrolyte that replaces the sulfuric
acid electrolyte of a normal lead acid
battery. This produces a battery that
is environmentally
friendly."
This excited the
materials scientist in me, since I know
that 99% of silicon compounds are
non-soluble, there must be something
cool going on. Besides, they say it is
still a 2 V per cell chemistry and is
compatible with automobile charging
systems.
Well, it turns out that
all this is just plain (mostly?) hype,
or hyperbole whichever you prefer. What
they do is to gel the sulfuric acid
with sodium silicates (a common way to
do it). So it is just a typical gel
cell. They may be making a better gel
cell, I don't know yet, but it is
nothing more or less than a lead acid
gel cell.
If you want to look up
the patent application it is USA
application 20040175623. |
| Smaller
rechargeable lithium ion coin
cells |
Many engineers have been asking for smaller rechargeable lithium ion coin-cells. We are happy to announce the new additions to our line of Li-ion LIR series cells, the LIR1220, which is 12 mm in diameter and 2 mm thick, and the LIR1024, which is 10 mm in diameter and 2.5 mm thick.
|
| Why are
non-rectifying contacts important in
CMOS? |
Dear Dr. Mark,
I
know you are a former JFET designer,
but I have a question in general about
metal contacts to semiconductors.
I've read that depending on the
n well process or the p well process it
is essential to diffuse p+ in a
p-region or n+ in a n-region so that an
ohmic contact is achieved. Then, it is
said that metal-semiconductor contacts
are rectifying, and that it is not
"good" for the operation of CMOS. Why
is that? why do you need an ohmic
contact so that current flows both ways
from metal to semiconductor?
What
is so "bad" about rectifying contacts?
Thanks. Andres.
A: Dear
Andres,
Rectifying junctions not
only prevent the current from flowing
both ways, but also present a voltage
drop for forward biassed operation.
This wastes power for simple circuits
and makes complicated circuits
impossible to make. So the p+ or n+
implants or diffusions are done to make
a metallic-like silicon to contact to,
which more closely matches the fermi
levels of the aluminum
contacts.
Best regards
mark |
| 6 to 12
volt converters for Volkswagens and
Porsches |
We finally have released a 6 to 12 volt converter that is 200 watts and fully isolated, so it can be used in either positive or negative ground cars. This opens the 12 volt world up to vintage cars that use 6 volt negative ground systems such as VWs and Porsches.
Take a look at http://www.powerstream.com/dc6-12.htm
|
| Using
car batteries for deep
discharge |
Q: Car batteries are
the cheapest because of the high
quantity manufactured. Why does
everyone want to steer me toward an
expensive, special purpose, marine
battery for deep discharge
applications?
A: Car batteries
are mainly there for starting the car.
This takes a surprisingly high current,
up to 400 amps for a big engine on a
cold day. The way they accomplish this
is by having a lot of very thin plates
so there is a lot of surface area. This
allows them to discharge quickly, but
they are easily damaged by deep
discharging. Car batteries are normally
rated for only 5-10 deep discharges,
sustaining damage with every one of
them.
Deep discharge batteries are
designed to put out less peak current,
but they have thick plates that can be
charged and discharged many times
without corroding or falling to
pieces.
|
| Model
helicopter charging problems |
Hello, I'm Looking for
advice on charging NiMH batteries after
having problems, I came across your web
page - very informative and helpful and
answered some of my questions - many
thanks for that.
I do however still
have some queries and I wonder if you
could find the time to give me further
advice on this matter? My problem
concerns charging batteries for my
model helicopter which uses seven AA
NiMH batteries (8.4v).
When I
first purchased the model, the
instructions said to charge the
batteries for three hours with the
supplied charger. This I dutifully did
(using a timer), though the batteries
became increasingly hotter after each
charge, causing me to reduce the
charging time.
Within a very
short time, the batteries simply
wouldn't power the helicopter and very
little or no lift was generated. I
purchased new batteries, but the same
thing is happening again. I can't help
but feel that the supplied charger is
just not right for these batteries, it
is marked 12vdc and 300ma output and
furthermore it says on the side of the
charger, (if that's what it is!) 12v
adapter.
I would be happy to
buy a 'proper' charger, but I can't
find anything that will charge the
seven cells altogether. Any help or
advice that you can give would be much
appreciated, Regards, Phil
Dear Phil, It looks like you just have
a power supply that is overcharging the
batteries. I have used supplies like
this to charge NiMH, but you have to be
careful to make sure that the current
is less than 1/10 of the capacity when
the battery is full. So for a 1000 mAH
pack the current should be less than
100 mA when the battery is full. You
don't say what the capacity of your
batteries is, but I would be surprised
if a 12 volt power supply would work
well for this. We have a smart charger
at http://www.powerstream.com/NiMHWMm.htm
that will do it.
best
regards
mark |
| "Paper"
batteries from Rensselaer Polytechnic
Institute |
There has been a lot of
press lately about the Rensselaer
Polytechnic Institute's battery made of
cellulose and carbon nanotubes I
thought I would weigh in.
This
is a great technical achievement,
however don't look for these in your
cell phone soon, the cost of carbon
nanotubes is tremendous. Refined
nanotubes sell for $300 per gram,
unrefined soot containing nanotubes $20
per gram. A 8.5 x 11 inch sheet would
take $36 worth of nanotubes. Due to the
nature of nanotubes it is difficult to
imagine that they will ever be cheap
enough for a consumer battery.
I haven't been able to find the
original paper to find out how many
amp-hours per square meter. I'll weigh
in when I do. |
| Aircraft
batteries are they 24 volts or 28
volts? |
Q: I am confused about
the 28 volt airplane systems. Do they
use 28 volt batteries?
A: Cars
and trucks and other ground-based
equipment traditionally use the "2 volt
per cell" terminology. For example a 6
cell battery is a 12 volt battery even
though the open circuit voltage is 12.9
volts and the charging voltage can be
above 14.4 volts. This is because the
"average" voltage as a lead acid
battery is discharging is about 2 volts
per cell.
Aircraft have used a
different standard. They typically
quote the alternator voltage rather
than the battery voltage. This make
sense because (even for ground
equipment) most of the time the system
is running at the alternator voltage,
the battery itself never gets
discharged very much. The alternator
voltage is nominally 13.8 volts for a
"6 cell" system and 27.8 volts for a
"12 cell" volt system. This is
typically rounded to 14V and
28V.
Therefore a 28 volt
aircraft electrical bus will have a 24
volt lead acid battery in it.
So
the answer is "No, 28 volt aircraft use
24 volt batteries." |
| Parallel
and Series in pallet jack
batteries |
Q: Hello, I have a
quick question regarding pallet jack
batteries. We use Hyster, 24 volt
systems. When some of these came in,
they contained 4, six volt batteries,
wired in series. Some have 4, twelve
volt batteries, wired parallel.
How do you determine the amp -
hour capacity for the correct charger.
Wired parallel, do you add the capacity
of all four batteries or is it divided
by two? I have asked this question to
two people who work in the battery
industry and actually got two different
answers.
Dear David, When in
series the voltages add, but the amp
hours stay the same. When in parallel
the voltages stay the same but the amp
hours add.
If you have a 24
volt system with four 12 volt batteries
then you have two in parallel and two
in series, so the pack would have twice
the voltage and twice the AH of a
single 12V battery.
best regards
mark |
| What is
happening to Lead Acid Battery
Prices? |
Q: Why are lead acid
battery prices going
ballistic?
A: You are right,
prices for lead acid batteries are
going up faster than oil. There are a
couple of issues that have caused it.
The first was that China has taken the
VAT tax exemption for exports of lead
acid batteries off because lead acid
batteries are no longer a preferred
export.
Secondly, the price of
lead has been skyrocketing. Here is a
chart of the price of lead from August
2000 to August 2007. You can see that
the prices were fairly stable for
several years, then took a 100%
increase for a year or so. Now lead is
trading at 7 times what it did 4 years
ago.
The next chart is over
one year between August 2006 and August
2007.
This shows that over the
last year the price has gone up about
300%, this has really played havoc in
those industries that use lead,
particularly for lead acid
batteries.
We estimate that for
every $100 per metric ton increase you
can expect a 4% change in the cost of a
lead acid battery. This alone would say
that the price should have increased
80% over the last year.
This,
of course, plays havoc with those of us
in that industry. Some factories have
lead stockpiles that allow them to
smooth out the price increases, but
this means that even if lead plateaus
in price they will eventually run out
and need to raise their prices. Unless
the price of lead drops soon there will
continue to be increases in
prices.
I can also vouch for the
fact that no-one stockpiles raw
materials these days.
best
regards
mark |
| 24 volt
batteries |
Q: Hello, I'm just
curious why 24V batteries are not more
popular or even used, or available.
Thanks, Mark H.
A: Dear Mark,
24 volt batteries are very
popular, they are the standard for
wheelchairs, used on heavy earth moving
equipment, the standard for Semi's in
Europe, many electrical bicycles,
yachts etc.
But they are never,
ever sold as 24 volt. They are sold as
12 volt batteries, then connected
together in series by the user.
best regards
mark |
| Parallel
and Series lead acid batteries |
Q: Dear Sir or Ma'am, I
am considering purchasing one of your
sealed lead acid battery chargers, but
I have some questions that I'd like to
ask to make sure that I am buying the
right charger.
The batteries
that I am trying to charge are 6V 12AH
sealed lead acid batteries. Is is
possible and/or safe to connect two of
these 6V batteries in series
(essentially creating one 12V 12AH
battery) with either your 12V 6A car
battery charger or your 12V 35A car
battery charger?
Assuming that
is both possible and safe, would it
also be safe to charge two of those
composite 12V 12AH batteries with one
of those car battery chargers by
connecting the two 12V 12AH batteries
to the charger in parallel?
Is
it safe to place a load (12V, up to 10
Amp load) on the batteries while they
are being charged with one of those car
battery chargers? Is there a formula to
determine how long it will take for a
sealed lead acid battery to charge
based on the current output of the
charger and the amp-hour rating of the
battery? Thank you very much for your
assistance. Sincerely, Daniel
A: Dear Daniel, Thanks for your
letter. Yes, it is appropriate to
charge two 6 volt batteries in series.
It would be best if they were at the
same state of charge (or discharge)
before being connected in series and
either discharged or charged. You can
also charge two sets in parallel.
Again, if they aren't approximately at
the same state of charge it might
confuse a smart charger into slowing
down the charge prematurely.
A
10 amp load might confuse a smart
charger. Adding a load in parallel is
done all the time, but for best results
you need a charger that is designed for
continuous duty, most car chargers are
not, they will overheat if left on a 10
amp charge continuously. Also, smart
chargers might time out, or cycle on
and off under these conditions.
These chargers were designed for
this kind of application:
http://www.powerstream.com/charger-low-noise-high-power.htm
Amp-hours are just that, amps
times hours. So a 7 AH battery should
take 7 hours to charge if 1 amp is
applied to it. However, it typically
takes more time to get the last 5 or
10% into the battery because the
voltage of the battery goes up and
unless the charger has an accurate way
of determining the end-of-charge it
isn't safe for the battery to keep up
the constant current until it is full.
So it takes a little longer than you
would expect. Also there are some
charge inefficiencies that make the
amp-hour law a little inaccurate.
best regards
mark |
| Running LCD
TVs off RV Power |
A: Hello, I have a 15"
flat panel TV that I usually plug into
an AC wall outlet in my home. Instead,
I want to run this TV from a 12v
battery in my RV when I am camping in
an area where AC power is not
available. I know that I can purchase a
DC>AC inverter that will do this
but, is it really necessary since the
power adapter that came with the TV
shows that the set runs on 12v DC 4.16
amp. So, if my TV ultimately requires
12v DC 4.16 amp input, why wouldn't I
simply run it directly from the 12 volt
RV battery instead of converting
DC>AC and then back to DC? Is there
a simple solution to this problem?
Thanks, Frank
A: If the TV can
handle the range between 10 and 15
volts you can run it directly off the
RV battery. If not you need to
stabilize it to 12 volts.
http://www.powerstream.com/dc-buck-boost.htm
has the PST-DC/2812-8 which would do
the stabilizing. |
| Capacity at
end-of-rated-life for a battery |
Hi, I am writing a
report on batteries, and I had a
question regarding charging cycles. I
see that the battery comparison chart
specifies how deeply the battery is
discharged, and how many times that
battery can be charged. But what
exactly does it mean that the battery
can no longer be charged?
Does
that mean the battery no longer charges
beyond a certain capacity? For example,
if a battery has a nominal 1500mA-hr
and is said to be able to go through
700 cycles, then after the 700 cycles
what is the new amp-hour rating? Please
let me know what you know about this
topic, or if there's any good
literature. Thanks a lot > >
~James
Dear James,
The
industry standard is that the battery
is at its end of life when the
recoverable capacity reaches 80%. So a
10 AH battery would only have 8 AH when
considered to be at its end of life. Of
course the batteries can still be used
way beyond this 80% mark.
I
used to have a cell phone that would
only last for 2 calls per day, but that
was enough to get a call from my wife
to remind me to come home from the lab.
:) |
| Voltage of
a generator |
Hi, I found your
website to be very helpful.
Is
there any way I could convince you to
offer the same level of explanation to
this question: when I spin a 12V DC
motor backwards to generate
electricity, how is it possible to
generate voltage greater than 12V?
Thanks, Dave
A 12 volt
motor isn't really a "12 volt" motor.
It is just rated to rotate at a certain
speed when 12 volts is applied.
If more voltage is applied it
will spin faster, and if less is
applied it will spin slower.
The voltage generated when used
backwards is proportional to how many
wire loops are cutting how many
magnetic flux lines per second.
Best regards mark |
| Are silver
oxide cells "alkalines?" |
Hi. I was just looking
at some batteries on your website. I'm
writing because I have a basic question
as to how to categorize silver oxide
button cell batteries, and you seem
very knowledgeable. I would really
appreciate any clarification you can
offer.
My question is this: I
understand that a silver-oxide button
cell battery (like the SR1120W and
other SR batteries) has a silver oxide
cathode and uses an alkaline
electrolyte. Does the use of the
alkaline electrolyte (potassium
hydroxide or sodium) make these
batteries "alkaline batteries?" Or are
they not "alkaline batteries" because
they have a silver oxide cathode? Also,
what does the "W" at the end of a
battery designation (like SR1120W)
mean, as opposed to say an "X"? Thank
you so much for any help you can give
me! -
-- Andrew
Hi Andrew, A
battery engineer would say "this is an
alkaline battery" because it uses a KOH
electrolyte.
But a consumer
thinks that a manganese dioxide-zinc
battery with a KOH electrolyte is what
is meant by "alkaline" due to the
perpetual dumbing down of the populace
by marketing types.
This opens
up a confusion, because there are zinc
alkaline button cells with about the
same voltage and size as the silver
variety. But you can pretty much count
on the fact that when button cells are
advertised as "alkaline" they are the
lower capacity manganese-zinc alkaline
and not the silver-zinc alkaline. I
know about the prefix, S means
silver-oxide-zinc and R means round,
but I don't know what the suffixes
mean.
best regards mark |
| How low can
a NiCad or NiMH go? |
Hi,
Can you
discharge NiMH/NiCad cells to <1.0
volts and get away with it? Say down to
.3V-.4V..
Scott
Dear
Scott,
A single cell can be
discharged to zero volts without
damaging it. However in a pack there is
always the danger of reverse charging
one of the weaker cells when the pack
voltage gets too low. This causes
damage to the cell, which makes it
liable to be reverse charged even
deeper the next cycle, etc.
best regards mark |
| Corrosion from
NiMH |
Dear
Dr Mark,
A considerable number of
circuit boards fitted with NI-MH
batteries (not purchased from
PowerStream) are being returned with
severe corrosion of the copper tracks
and components within a 2” radius
of the battery, (gold plated pins have
a blue powdery corrosion).
The
corrosion also softens the plastic PCB
and causes capacitive leakage/breakdown
between the copper tracks. The
batteries are 3.6V 150mAh with an
average charge voltage of 4.1V and
retain their full charge even when
badly corroded. Most of the boards come
from petrol pumps but the problem also
exists on computer boards and POS
circuits. The corrosion effect
continues after cleaning the board and
replacing the battery.
Q
...Assuming the corrosion is caused by
gas coming from the battery can you
tell me what chemical is causing the
damage and recommend a treatment I can
apply to the circuit board to
remove/stop the corrosion process prior
to replacing the battery?
Thanks Tom
PS .. Brilliant
site
A: The electrolyte is
primarily potassium hydroxide solution
KOH, otherwise know as potash. It is
corrosive, but quickly reacts with
atmospheric CO2 to form potassium
carbonate which isn't corrosive, and
neither are poisonous.
The
batteries will only vent if they are
being over charged, which builds up gas
pressure in the cell. If this pressure
gets too high it is released by the
safety vent in the cell to prevent
explosions. Such pressure relief does
not kill the battery, it only reduces
the capacity slightly.
With the
gas some of the liquid comes out, which
contains the KOH. I wouldn't have
expected the corrosion to continue
after cleaning the board. KOH is
extremely soluble, so deionized water
should take it off.
Potassium
carbonate is harder to wash off, it
isn't as soluble, but it isn't
corrosive either. |
| Charging the starting
battery with a "house" battery |
Q:
Dear Dr. Lund:
I was wondering if
the
PST-BC1212-15 DCDC Charger
would be appropriate for the following
use: If I am carrying a house battery
on board my van being charged with a
battery to battery charger from the
start battery, and then the start
battery is inadvertently run down (say
I leave the headlights on)… can I
then reverse the wiring to use the
battery to battery charger to charge
the start battery from the reserve in
the house battery? I would use
sufficient gauge cable to prevent more
than 2-3% voltage drop. I am hesitant
to connect the house battery directly
to the start battery… is this
scenario a feasible solution? Am I
being too careful in not wanting to
make a “jumper” type
connection, instead using the battery
to battery charger?
A: Yes, this
would work, and not a bad idea at all.
Usually the house battery isn't
designed to put out enough current to
start the van, it is designed instead
to deep cycle. If it is large enough to
even give a partial charge to the
starting battery it could get the van
started.
You need more voltage to
charge a battery than another battery
would supply, which is why the
PST-BC1212-15 would be needed to do the
charging. It has a DC/DC converter to
boost the voltage.
And our
charger isolates the house battery from
the van so that it won't run down if
you leave the headlights on.
|
|
New Product, 24V to 48V DC/DC converter
|
Announcement
We just released the new DC/DC converter for running 48 volt equipment in 24 volt vehicles. This is useful for wireless routers and bridges on low voltage systems. This compliments the 12V to 48V converter we have sold for a couple of years.
|
|
Circular Mils
|
Q
: For transformers the current carrying
capability of wire is often listed in
"circular mils" What is a circular mil,
and how do I relate it to the real
world? Thanks a lot
A: The unit
"circular mils" is a strange unit. It
is a measure of area--the area of a
circle 0.001 inches in diameter, which
turns out to be 7.85 x 10^-7 square
inches, or 0.000507 square mm. So if
the criterion is 500 circular mils per
amp and you need 7 amperes you would
multiply 500 * 7 = 3500 circular mils,
multiply by 0.000507 to get 1.771
square mm, or a wire with diameter 1.5
mm, or about 14 AWG.
|
Free power from the
Phone Company!
Are shallow discharges equivalent
to deep discharges?
Pee-powered battery, hype or
hoax?
How much voltage is required to charge a lead acid
battery?
|
Can you really steal power from the
telephone company?
There
is an infamous company (that I won't
link to for the world) that sells
appliances that run off of a telephone
outlet (even vacuum cleaners). Is this
real? Can you really “stick it to
the man” by tapping power off of
the greedy, faceless phone company?
Let’s
do the numbers:
It
turns out that there really is 48 volts
on your telephone outlet. The current
is limited to at most about 50 mA, and
most phones run on 20-30 mA. If you
draw more than 50 mA on a the phone
company will probably put you down for
a short and cut off your phone service
until the short is fixed. When you
start to draw any current at all from
the phone line the 48 volts sags
considerably, but we will use 48 volts
for our calculations just to be
conservative.
(Don't
forget that the ring tone is 90 volts,
20 Hz, and it can go up to 120 volts,
20 Hz, so don't get shocked while
messing around.)
So,
say you wanted to get free power. The
20 mA at 48 volts is about one watt.
Here in Utah we pay about $.07 per
kilowatt-hour. So by tapping power from
the phone line you could save seven
cents in 1000 hours, or 41 days. Now
you are sticking-it-to-the-man to the
tune of 61 cents per year.
The
company that makes these so-called
products sells a little voltage
converter for $70.00 to get you started
in the free-energy business. You can
pay for it with your savings, breaking
even in just 114 years. After that it
is all 100% pure savings.
Now,
just who is that “man” that
is getting the stick stuck
to?
Are shallow discharges equivalent to deep
discharges?
A recent blog posted on
Zdnet
implies that you can wear out your
laptop battery by leaving your battery
in the laptop and letting it recharge
every time you plug it in. This is
misleading. To paraphrase the poster,
he said that the battery is only good
for 300 charge-discharge cycles, so
leaving your battery installed every
time you boot up from AC power will
wear it out after only 300
boot-ups.
The truth is that a
lithium-ion battery that is rated for
300 full discharge cycles is also rated
for thousands of shallow discharge
cycles. A rule of thumb in battery
design is that the life of the battery
is related to the total number of
electrons drawn from it, therefore 300
full discharge cycles is equivalent to
600 half discharge cycles, or 3000 1/10
discharge cycles.
As with all
rules of thumb the relationship is only
approximate, in this case the cycle
life actually gets better than you
would expect for shallower
discharges.
You can verify this
from almost any cell data sheet, but
I'll just list one other witness to
this fact, this one from
Motorola
:
The relationship between
DOD [depth of discharge] and
cycle life is logarithmic. In other
words, the number of cycles yielded by
a battery goes up exponentially the
lower the DOD. Research studies have
shown that the typical cellular phone
user depletes their battery about 25 to
30 percent before recharging. Testing
has shown that at this low level of DOD
a lithium-ion battery can expect
between 5 and 6 times the cycle numbers
of a battery discharged to the one
hundred percent DOD level
continuously.
A recent science news story that I really
need to comment on:
The first urine-powered
paper battery has been created by
physicists in Singapore. The
credit-card sized unit could be a
useful power source for cheap
healthcare test kits for diseases like
diabetes, and could even be used in
emergency situations to power a
cellphone, they say. . .
The same story was repeated
all over, look it up on Google if you
want to read it. I am reluctant to
dignify it with a link.
The sad
thing about this is that the battery
does not take its power from urine, it
is just a dry-charged battery that
needs some water to activate it. I have
some 30+ year old army surplus
batteries somewhere squirreled away in
my "neat-science-stuff" collection that
work the same way, using the exact same
chemistry. The battery is completely
inert until you add water to it, and it
isn't too picky about what is also
dissolved in that water, or where (or
who) it came from.
Luckily the
article goes on to explain the
chemistry to us technical
types:
The battery is made of
a layer of filter paper steeped in
copper chloride, sandwiched between
strips of magnesium and copper. This
"sandwich" is then laminated in plastic
to hold the whole package together.
The resulting battery is just 1
millimetre thick and 60 by 30 mm across
– slightly smaller than a credit
card. To activate the battery, a drop
of urine is added and soaks through the
sandwiched filter paper. The chemicals
dissolve and react to produce
electricity. The magnesium layer acts
as the anode, losing its electrons. And
the copper chloride acts as the
cathode, mopping up the
electrons.
So it is just a
magnesium/copper chloride battery just
like my army surplus one. (Not
rechargeable, though the article from
New Scientist implies that another drop
will reactivate the battery). The claim
of "first" mentioned above is hard to
understand.
To learn more about
reserve batteries, go to
http://www.powerstream.com/BatteryFAQ.html#MgCu
Q: I am trying to charge batteries with "alternative energy"
which does not give a steady voltage. How much voltage is required to charge a
lead acid battery?
A: The minimum voltage
necessary to charge a lead acid battery
is 2.15 volts per cell, or 12.9 volts
for a 12 volt battery. This is what is
needed to get the battery chemistry
moving in the right direction. Anything
less than this will not do anything.
At this voltage the battery
won't accept very much current, or in
other words it won't charge very fast.
There is a band of voltage between 2.15
and the 2.39 volts gassing voltage when
the water starts to disassociate (12.9
and 14.4 volts for a 12 volt battery)
which is the charging range. The higher
the voltage the more current you can
stuff in the battery.
Some
schemes go way above 14.4 volts to get
a rapid charge, but drop their voltage
when the battery nears full charge.
Depending on the voltage range
of your energy source, you may need a
DC converter to efficiently use the
power generated, and possibly a full
buck-boost converter.
Don't stop, Click Here for the Dr. Mark Blog Archives!
|
.
Disclaimer: Information
presented here is the opinion of the
author. No warranties regarding the
correctness or value of this
information are implied or should be
assumed. |
|
