PowerStream's blog for power supplies and batteries

Dr. Mark's Power Supply and Battery Web Log (Blog)

Home: Power Supplies, Battey Chargers, Batteries, DC/DC Converters, custom and off-the-shelf

Click Here for the Dr. Mark Blog Archives!

Custom design and manufacture of state-of-the-art battery chargers, UPS, and power supplies

Table of Contents	Last updated 22 February 2008
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 is 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.

PowerStream Technologies: 140 South Mountainway Dr. Orem Utah 84058 Phone: 801-764-9060, 9062, 9063, or 9064 Fax: 801-764-9061
		PowerStream Technology 140 South Mountainway Dr. Orem, UT 84058 Phone: 801-764-9060, 9062, 9063, or 9064 Fax: 801-764-9061 Map & Directions
© Copyright 2000, 2002, 2003, 2005, 2006, 2007, 2008 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 derivative text using automatic thesaurus substitution software.