Thursday, June 18, 2009

Homemade DIY Battery Desulfator / Charger


I had posted a video on youtube.com a few weeks ago showing my first very crude and simple battery charger/desulfator. Someone commented on how well it worked for repairing nicads. I'd like to explain that a bit. The nicads don't get sulfated like lead acid, but they do degrade. Little microscopic filaments that look like hair build up and eventually short out the plates. When you hook up a regular charger and it is trying to charge at half an amp, it does that by putting out a fixed voltage. The battery plates are so "fuzzy" that it never takes a charge.

But the desulfator / charger is a constant current device. If you set it for half an amp by using a 12 microfarad "Run" capacitor, then it will push half an amp at whatever voltage it needs. It can go as high as 170 volts DC. And then it pulses it 120 times a second. Believe me, that fries those little hairs pretty quickly. Then the voltage drops down to normal and you can charge for a few hours after that. I normally put a timer on it so it doesn't overcharge.

If you have a nicad pack that is charged at half an amp, don't set up the charger to push 3 amps into it. (or if you do, don't do it for too long) That is bad for the battery and could be dangerous. You change the amps by putting in a different capacitor. A 24 MFD capacitor will charge at 1 amp. A 50 MFD would be just over 2 amps.

You can see the post here that talks about making one. http://poormanguides.blogspot.com/2009/05/updated-chargerdesulfator.html

There are so many old nicad battery packs out there just waiting to be fixed.

Richard

41 comments:

  1. Just arrived and new here, but... I find all those things simply like what I was caring and looking for for a while!! Thanks!!

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  2. Dario, welcome aboard. I'll try to keep it up. There is a lot of info out there and it feels like new ideas are infinite. I'll keep digging and trying to think outside the box.

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  3. Hi, sounds great. Is it possible to use this on a system with 6 2Volt Batteries connected in line with each 1080 Amps?
    How can I build one myself?
    Please contact me using http://ralfengel.com/contact

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  4. Hi, sure it can charge any battery or cell up to about 150 volts or so. It puts out 170 volt or so DC pulses. Check here to see how to make it. http://poormanguides.blogspot.com/2009/05/updated-chargerdesulfator.html
    I have charged nicads, nimh, lead acid, and gel cells. Don't do lithium ion though. Just change your capacitor to the appropriate size for your battery.

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  5. Richard, I have a question about desulfating batteries for you. I have 4 6V batteries, and while I know that the IDEAL way would be to desulfate battery 1 first, then battery 2 and so on, I'd like to cut down on the length of time it takes by hooking up all 4 batteries at once. Do you think that hooking them up in series or parallel would be better? How about hooking them up in two 12V banks and paralleling the banks? I know that it'll handle large banks, but I'm wondering which configuration is better.
    I'm new to this desulfating stuff, but I've built myself a 25/175 desulfator according to your design and am eager to try it out on these "dead" batteries.

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  6. Doug,

    Hi, thanks for the comment. I would recommend putting all 4 batteries in series and after a few days, take the 2 in the middle and put them on the end. Watch the voltage, if it hovers at 30 volts or a little more, then you need a smaller cap than a 25 mfd. But you should be ok. And the voltage may go pretty high when you first hook it up, that just means you have a pretty bad battery. Make sure you hook to the battery and then turn on. And turn it off before removing or even adjusting the power leads.

    After a few days, let the batteries sit over night with no charger or desulfator hooked up. Then check voltages the next day. They should all stabalize at 6.3 to 6.4 volts.

    Richard

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  7. My power supply is 230/40v so would the capacitor etc need to be different?

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  8. If I remember correctly, you can use 16 MFD for each amp.

    Richard

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  9. Hi Richard, please excuse my ignorance here. In New Zealand mains power 230v plus or minus 6% and 50 Hz. Need to know what adaptations to make if any. From your last answer I assume a 16uF cap for low power would give 1 amp and then two more 50uF in parallel would give approx 7.25amps. what wattage isolating trannie required? Would a 35amp rectifier be OK? Are any changes needed for the shunt? Would it be simpler to keep your specs and step my voltage down to 120v?

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  10. Brian, well it might be easier to just step down to 120 volts. But the 50 hertz might still make the numbers slightly off. But close enough and that could be your isolation transformer as well.

    You are right on your numbers above at 7.25 amps for your voltage. At that amperage, you would want 150 watt transformer per 12 volts that you are charging. So, for example, use 300 watt transformer if you are charging a 24 volt bank. And the 35 amp rectifier is more than enough and the shunt would stay the same.

    But if you step down the voltage and use the same capacitors, then that would be 4.6 amps instead of 7.2. In that case you would need at least about 100 watt transformer per 12 volt battery.

    Richard

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  11. Hi again Richard,
    Thanks so much for your help but I have one more question. Do the capacitors have to be run capacitors and do they need to be rated for my mains voltage of 230v or could voltage rating be higher than that? I purchased your "Poor Man's Guide to Welding with Batteries" a few days ago and am trying to get this desulfator going for that. Cheers

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  12. Brian,

    They have to be Run capacitors. If you use the start capacitors, they will smoke after about 30 seconds and eventually flame up. The rating should be higher than the mains. Just multiply the mains by 1.4. So, 230 volt mains needs a 330 MFD or better. If you don't have big enough capacitors, then you can put two in series to raise the voltage rating. Make sure they have the same MFD rating though.

    Thanks for reading my welding book. What did you think?

    You should've seen what happened when a friend and I used a 24 volt forklift battery to weld. The rod melted right through a 1/2 inch thick piece of plate steel. I think it was about 30,000 watts of raw power.

    Richard

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  13. Richard,
    Thanks for that. I am impressed with the welding book and believe it is just what I require for the small amount of welding I do. All I have to do first is get the desulfator going. I can get the required run capacitors at 440v so hope they will work OK.

    Currently looking at Kevin Dixons battery reconditioning book which I guess you are affiliate to so no real use asking for an unbiased opinion about it. Trying to decide between it and another. Seems to be some validity to both.

    Many thanks for your time and generous help.
    Regards

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  14. Hi Richard,

    In India, the mains power is 230v/60Hz. What will be the adaptations in this case.

    Haris

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  15. Hi, Haris.

    I found the AC capacitor equation.
    A=amps
    f=frequency in hz
    c=capacitance..24 MFD is 0.000024 (you can use capacitance in MFD and divide by 1,000,000)
    v=volts

    A=2*PI*f*c*v or c = A/(2*PI*f*v)

    example with 24 MFD at 120 volts 60hz
    A= 2 * 3.1416 * 60 * 0.000024 * 120
    A = 1.08 amps

    example with 230 volts 60 hz and 1 amp
    c = 1 / (2 * 3.1416 * 60 * 230)
    c = 11.5 MFD

    Same thing but if you use 50 hz then
    c = 13.8 MFD

    At 240 volts and 50 hz then
    c = 13.3 MFD

    Richard

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  16. Hi Richard
    Can you elaborate a bit more about the desulfating side? how long does it take to desulfate a severely sulfated battery (say 50 AH lead acid battery - assuming that plates are not corroded and no shorts inside the cells).
    I'm asking because from your explanation you mentioned that it gives 120 cycle / sec. , while normal desulfators uses 1 - 5 kHz and it needs about one month to repair such batteries.
    My second question if I may, can I replace the stainless steel rod (shunt) with a resistor(s) and what values do you recommend?

    Amr

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  17. quick question.

    I have 2 6 volt batteries and i would like ot hook up my 12 volt desulfator to them.
    I know they have to be wired in series but would i hook up the desulfator to the 1 open positive and 1 open negitive?

    Wouldn't that shortcuirit the battery?

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  18. Ranma,

    Yep, just hook in series and hook your desulfator to the two open terminals. Just make sure the polarity is correct. In other words, hook up positive to positive, etc.

    Richard

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  19. Amr,

    This kind of pulser is constant current but it will vary the DC pulses up to 170 volts or so if it has to in order to get the correct current to flow. The downside is that you have to watch it carefully and don't let it overcharge the batteries.

    You could replace the stainless steel with a resistor if you could find the right value. The one inch of that size stainless is exactly 0.001 ohms. It makes the math easy. 5 mA is equal to 5 amps for example. But you could use a resistor of higher value and do the conversion. But that interferes with the circuit and the stainless can handle hundreds of amps. So, really you can't beat stainless for this application. Even the professionally made shunts are usually 0.075 ohms and are meant for a digital shunt meter designed for that input. You could use a regular meter, but you would have to convert the numbers with a calculator.

    Richard

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  20. thanks for the reply i was thinking that but just wanted to make sure. Also keep up the good work on the blog.

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  21. sorry wrong account oh well.

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  22. very nice work , keep it up.

    How much it may take to desulfate a working but low gravity battery say 1200 all 6 cells

    Aruna

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  23. I have several battery packs for cordless tools that I believe are sulfated. Is there a way I can desulfate these closed types of batteries and reclaim them for use again (right now they will not take a charge?

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  24. for a cordless drill size battery, you can setup my desulfator to use a small capacitor, like 5 MFD or so. That gives about 0.2 amps and you can try that on the cell. Sometimes you have just one bad cell, so you charge the whole thing. Then take it apart and check voltage of each cell, when you find the bad one, hook up the desulfator directly to that one cell for awhile. There is another trick using a 6 volt cell, but kind of dangerous. I'd rather not explain that one.

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  25. hello i have 220 ac mains 50hz, i want to keep it very simple so dont want to use transformer to step down to 110.

    i tried with 2.5 mfd cap of fan to keep amps to very low since i wanted to use small diodes i dont have car diodes nor big 35 amp diodes. but my diodes shorted in both times in two attemps.

    i am confused why would normal diodes short at such low amp when cap is keeping the current constant .

    plese tell me solution by which i can use normal diodes i dont have high amp diodes.

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  26. Dextertec, the problem is the voltage rating of the diodes. The current is low, but the voltage exceeded the diodes rating. Whenever the power is turned on and the charger isn't connected to a battery, the voltage shoots up to 170 volts DC. One solution is to hook to the battery and then turn the power on to the charger. That is the only safe way anyway. You'll have to replace those diodes I'm afraid.

    Richard

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  27. i have been using capacitors for charging various of my batteries all the time now. before i used to have lots of problem with chargers, now i just put diffrent kind of capacitors from 2.5uf to 20uf on mains 220 v 50 hz, put 4 * IN5408 3Amp diodes for bridge and charge 12 batteries 6v batteries , will soon experiment 3*12 = 36 v batteri.

    it will be very ungratefull on my part not to say thanks this idea has helped me a lot and made my life better in many ways.

    there is one thing more that i need, i will apriciate a charge controller which would cut the supply 220 v when battery reaches 13.5 or 14 v peek charge

    putting in a timer is good for one time and once in a while but , not practical when i have to charge all the time diffrent batteries.

    thanks a lot

    DEXTERTEC AT YAHOO DOT COM

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  28. what is you're experiences in sulfated lead acid battery

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  29. I made your desulfator and am using it..it really did make a difference with several nicads that never held a charge long..even sitting over night they would be dead the next morning..after one charge they held them for days...and seem to have more power now..what do you think about always charging them with this device instead of the factory charger? seems to me this would be the perfect way to maintain them....
    Chaz

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  30. Hi,

    First, thank you for sharing such a valuable info.

    I've set up everything according to your diagram. And for the amperage
    I'm adding 15 uF or 50 uF Run capacitors (at 220 V 50 Hz).
    I started with a battery which is heavily sulphated (my first trial).
    I used three 15 uF/450 V then added two more 50 uF/450 V capacitors and I reached 6.1 Amps .
    Now at first the Voltage shoots up to 25-27 Volts and gradually drops down to 6 - 8 V. Sofar (within 1 week) the Battery came up from 1.9 V to 4.5 V and from time to time it drops back to 3 V.
    My question , since this is my first one, should I continue to try to desulphate or give up my hopes on this particular battery?

    Thanking you in advance.

    Sadik Topaloglu
    fm Istanbul Turkey

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  31. you have sucsessfully restored some of cells, but some of those are hoplessly sorted. you can not desulfate sorted cells. If cell is empty then all of the acid is in lead plates and because acid harshness level is so high, it wil literally oxidize all of the lead to some sulfate powder (you can see that those sell are litle bit rounded out- visually). At this stage nothing helps. I f you have more or less right voltage but no capacity ,then desulfation helps most.

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  32. Hi Richard, I'm Richard as well. I'd like to build a capacitive charger for my electric car. It has 13 twelve volt lead-acid batteries connected in series for a 156 volt system. Resting voltage at a full charge is about 167 volts. I need to stay under 200 volts or risk damaging components.Could you help me at least figure which components to purchase for an output voltage between 170-180 volts? I've seen the YouTube videos and construct one once I know the exact components to buy. This won't be the primary charger, but I'd use it once a month to reduce sulfation. I probably won't be back on this site, but if you'd please email me at: rt66gv@yahoo.com I'd really appreciate it. Thanks much.

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    1. Hi, Richard. If you get up to 14.4 volts per battery, then you need a bank voltage of about 187 volts. So, to use this circuit, you would need 220 volts. I'm assuming that each battery is at least a 100 amps. At 220 volts at 60 hz, a 12 MFD cap will put one amp to the battery bank. So, if you were trying to charge for 50 amp hours, then a 15 MFD cap at 40 hours would do. Or an 80 MFD for about 7.5 hrs. Just depends on amp hours needed. This circuit has no auto-turn off function and it can overcharge if you let it.

      Also, it puts out full voltage when it isn't connected to the battery, so ALWAYS hook to the battery first and then turn ON! And ALWAYS turn OFF and then disconnect from battery!

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  33. Fantastic ebook on wind power! I've skimmed though it, and plan to go deeper into it and try my own setup at some point. Thanks for the thorough write-up!

    What drew me to the page was this DIY charger. I'm wanting to build a nice, high-power source to feed an electrolysis tank for rust removal. The car charger I used for a 5 gallon bucket just isn't cutting it with a 90 gallon tank. I know this is a completely different topic, but I'm desperate. If you think this might work for electrolysis, I'll put one together. Thanks in advance!

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    1. Robin, thanks for the compliment.

      It will work for electrolysis. Just remember, you set the amps by choosing the capacitance. Then the circuit will LIMIT the voltage to maintain that current. So, in conductive water, maybe that is 2 volts, for instance. Then, you feel safe with 2 volts and you go to move an electrode to a new spot. You take it out of the water for a second and the air has so much resistance, that the circuit allows 165 volts DC to exist until current starts flowing again. Very dangerous. NEVER TOUCH WHEN PLUGGED IN! Connect it to the circuit then plug in and it works fine.

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  34. Hi Richard,

    Can I use two 160uf photo flash caps back-to-back instead of run cap ?

    Haris

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  35. Haris, DON'T do it. You will have 6.5 amps going through those caps and smoke, fire, destruction will ensue! :) You need an oil filled/cooled capacitor. You have to use a RUN capacitor. Hopefully I'm not too late in my response.

    Richard

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  36. Hi..I filled my dead battery(12v 7.2ah UPS battery) with sterile water(which is used for injecting into body).

    Is it same as the distilled water?

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  37. hi Richard

    Sorry I have couple of questions plz give me answers I m very thankfull to you.

    1)For 220 @60 hz we can use 15mfd capacitor?
    ..and as the size of capacitor increase the amp increase and vice verse?
    2) what capacitor is suggested for wet lead acid 100ah battery?
    3)If only one cell is sulfates so how do I connect sulfator to that specific cell?
    4) Actually what is responsible for desulfating voltage,current or frequency?

    Thanks in advance

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  38. hello from Venezuela (excuse my english) tell me, this charger works with 120 volts rectified to DC? Direct 120V to 12 volt battery? I have some 12 volt batteries 17Ah sulfated, I can use this charger desulfating to repair? Thank you.

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  39. What about using half-bridge rectifier (and possibly double capacitor capacity) instead of full-bridge rectifier? That would make less frequent current peaks (which may be bigger if you alter capacitors). Giving battery some time to take a rest between these pulses… i think it could be better for the battery… Any ideas?

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