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| Table of Contents |
Last updated |
| 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 altert! |
| 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) requires that you put the highest
possible surge current on the label, so you cannot have any possible chance to calculate the
efficiency 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.
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.
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 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.
|
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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.
|
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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!
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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. |
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PowerStream Technologies: 1163 S.
1680 West. Orem Utah 84058
Phone: 801-764-9060
Fax: 801-764-9061
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© Copyright 2000, 2002, 2003, 2005, 2006, 2007, 2008,
2009, 2010, 2011 Lund Instrument Engineering, Inc. All rights reserved This material
is copyrighted original work. It is forbidden to use this information, text, or graphics in
full or in part on another web site without written permission. This prohibition forbids making
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