Desulfator for 12V Car Batteries, in an Altoids Tin

Picture of Desulfator for 12V Car Batteries, in an Altoids Tin
Hello Everybody!

After a year or so of reading and drooling over other people's wonderful projects in these pages I decided to finally make one of my own. Here is my first instructable, a version of the ever popular Battery Desulfator, which I built in an Altoids tin.

First, some background:

My urge to build this project came when my wife's car refused to turn over after a three day weekend away. Here in Tokyo, during winter, the temperature can drop to the low 20's (F) at night and since we have no garage, her car just has to endure the cold as best it can. Many people don't realize that you don't have put up with repeated jump-starts or run to the nearest garage and plunk down 7,500 yen ($85) for a new battery every time this happens. Your old battery may just have built up a layer of lead sulphate crystals on its plates and that is preventing the acid from contacting them over their full surface area. This is caused by subjecting the battery to long periods of insufficient charge, as in the cases of unplugged golf carts over the winter, infrequently used automobiles, and PV systems that don't get enough sunlight to charge their batteries. The result is a great reduction in the battery's ability to produce electricity.

With a desulfator circuit you can reverse this process and rejuvenate the battery to like new condition. You can also save money and prevent water and ground pollution at the same time by keeping your old battery out of the local landfill. As long as nothing is seriously wrong with the battery it can last many times the two or three years that people typically use them. You can even get free batteries from garages that routinely throw them away, desulfate them, and never buy another battery again. Save money and help the environment - now there's a green ecology scheme I can get into!

Most DIY desulfator circuits in use today can trace their roots back to an article in issue # 77 of Home Power magazine written by Alistair Couper in June/July of 2000. Many versions were spawned by his design but they all accomplish the same thing, that is, they use various pulsing circuits to force the lead sulphate crystals back into the electrolyte thus rejuvenating the battery and restoring its lost capacity. The version I chose uses an NE555P timer chip for the multivibrator front end and two coils, a low ESR cap, a fast diode, and an N-channel MOSFET (hereafter referred to as a FET) to generate the high voltage (50V) spikes in the output. Credit goes to Ron Ingraham for changing the design to use an N-channel FET instead of the harder to find and more expensive P-channel types in the earlier versions. Along the way I couldn't resist adding a few tricks of my own to make the design more convenient. See this link for a description of the theory and other information on desulfators.

This circuit can be used three ways - as a standalone device powered by the battery under test; as a standalone device but used in parallel with a battery charger; or built into a charger so that the two work together as one. I chose the third option for my circuit but added a switch so I can use either device independently. Mounting the device onto my charger also allowed me to use the charger's output cables for both functions and avoid the tangle of wires that inevitably results at the battery.

Once properly adjusted, the desulfator can be left on permanently whenever the charger is charging. Just be aware that no matter what configuration you choose, the desulfator is powered by the battery under test so if you use it without a charger care must be taken to avoid deep discharging the battery.

High power versions of these circuits can be built for off-grid solar-cell systems as well where many batteries are typically arranged in series/parallel banks and attached to inverters to produce 120V AC. These battery banks can be desulfated en-masse while being charged by their solar arrays for a truly self-maintaining system minus the periodic checks for electrolyte level, as long as the desulfator circuit is scaled up in size sufficiently.

The Altoids can is the perfect box for this project as the circuit neatly fits inside it and the metal construction can shield much of the RFI that may be emitted by the output stage. You can't beat the price of these tins, and they even come with free mints, or do the mints come with a free tin, I forget... ?

So with the background out of the way, let's get to work!
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DanH418 days ago

AS you say 15 year old technology, antique in electronics terms. Some of the latest desulfators are much more efficient, the technology being driven by the solar industry needing to reduce the battery replacement costs to try to keep up with the fall in solar panel prices. have a look at this website at these prices it is not worth trying to build your own.

Hi. I am aware thet last comment was 5+ years ago and I might never get an answer, but still ready to try.

I wonder if longer spike would give better results ? Or then maybe higher frequency ? I just have laying around few IGBT-s with 400V and 600A power limits. If I would use one of them in place of Q1 and maybe high current L1 and L2 (I do have toroids from the same 30KW 3 phase UPS system) I might get faster results ?

yaly3 months ago

Hello, the inductors are unavailable localy, can I use the big inductor/toroid from a PC power supply unit ? And can I use the IRFZ44 instead ?, I know the L in IRLZ44 stands for logic level input.

yaly3 months ago

Hello, the inductors are unavailable localy, can I use the big inductor/toroid from a PC power supply unit ? And can I use the IRFZ44 instead ?, I know the L in IRLZ44 stands for logic level input.

Nic-SMD5 months ago


I built this circuit followed all instructions. However I am not sure if it is working properly. Probably not. Even I connected the circuit itself either with an external charger, there is no current pass through the circuit.
Thus I made some measurements but I do not know what are the correct values should be. I measured the output of 555 IC. from pin 3 to ground and from D3 to ground and both measures 0.5V. Are that 0.5V enough to trigger the FET?
Also when I connect the battery, there is a very quiet noise on the circuit (which maybe it is normal).
Any ideas what may goes wrong?

I used 60n03gp FET

Thank you

kmpres (author)  Nic-SMD5 months ago

The instructible gives clear instructions on what voltages to expect. However, most of the circuit's signals have a short duty cycle so they are best viewed with an oscilloscope. I'f you're using a voltmeter on the 555 you'll likely get an incorrect reading. On a scope you should see a 12V p-p pulse pattern similar to the picture in step 4. This is plenty for the FET as it only needs about 5V to trigger properly, but it must be a clean signal or it will overheat. The 1,000 Hz whine coming from the coils is a good indicator that the FET is working and the signal is reaching the coils. Way down in the comments (about 5 years ago) I posted two scope images that clearly show the pulses as they reach the battery, but you'll need a fast scope to see them. I'm not familiar with the 60n03gp, though it appears to be a low voltage type (output voltage 1.2V) and is therefore unsuited for this application.

Lase7 months ago

great design , I am wondering if you would know what would be needed to make this work for 5 x 12 or 60 v sla pack as I would like to add this to my e scooter which is 60 v


kmpres (author)  Lase7 months ago

The indestructible had a link to a high power version, but that was five years ago and it has since gone offline. You might find one by searching for a similar device used for Photo-Voltaic arrays online. Basically, if I remember correctly, you need to increase the voltage/current capacity of the major components and see to it that the 555 chip runs on 15 volts or less. You could also make separate desulfators for each 12V pack. Be aware that though readers have reported that the device has worked on SLAs, it may take some experimentation on your part to get it to work as well on them as it does on wet cells.

Lase kmpres7 months ago
Thanks have been looking
astral_mage7 months ago

u have a web site that i can buy these from yet?

kmpres (author) 11 months ago
I can't tell you how low "low ESR" should go. I only used one kind and it worked.
larry_too11 months ago
Just wondering how low an ESR is adequate, ie., what was the ESR rating of the one you used? If it was adequate, I need not incur the size/price bogy of a lower one.
I'm unable to read the part number that you used on the annotated schematic.
larry_too11 months ago
Newby here,
Looking at digikey, I find several low ESR capacitors and am wondering "how low to go".
I would expect the lower to be larger as well as more expensive. Any ideas here?
I have found the numbers that I asked for below, I think:
220uH 3.6A M8875-ND 3.48
1000uH 2.4A M8895-ND 3.46
100uF 25V LO ESR 493-6631-1-ND 2.95 or
100uF 25V LO ESR PCE4929CT-ND 1.32

Any suggestions before I punch off the order? feel free to e-mail if you would rather. That 8D deep cycle battery awaits my attention.
kmpres (author)  larry_too11 months ago
Larry, you did exactly what I did before I built my prototype. You checked the specs according to the schematic and they all look good.  In the end your choices becomes a matter of convenience.  Ask yourself:  Assuming the parts specs are similar enough to be within say, 5% of the schematic, ask yourself:  Are the parts small enough to fit an Altoids can?  Are the prices acceptable?  Are you willing to do a little experimenting with a few different manufacturers, types, packages, or slightly different specs?  It can be a bit of a gamble but that's part of the fun of electronic experimenting. Your parts choices are very close to mine, spec-wise, so I don't think you'll have any trouble.  But I can't test them for you to be sure. That's up to you.
buzza1 year ago
Hmmm. I did a pre build on a bread board and it seemed to work fine; coil nice high hum. Soldered it up, it gets very hot, put a bigger fuse in, it is drawing about 3.5 amps, so I thought maybe the FET was staying on- oh and no hum from the coils. However, I did a quick test, the two coils in series across 12v draws about 1.5 amps. So now I am stumped, I am not sure if the circuit is working ruffly ok, but I should put a in a pot as discussed and try tweaking the 555, or if I should replace the FET. Anyone else had high current draw issues?
larry_too buzza11 months ago
Jumping in late here but I sure could use an updated set of part numbers for the coils, FET, low ESR cap, and the FRED diode. I'm unable to find some of the numbers in the current Digikey online catalogue. Any help would be appreciated as I have a large motorhome battery needing attention.
jamiemudry1 year ago
I'm curious to see a little more about the waveform that is transmitted to the battery, has anyone scoped this at all? I have this running on an AGM battery and it seems to be working, but I had to wind my own coils, substitute components, and it's currently built on a breadboard....
kmpres (author)  jamiemudry1 year ago
Deep down in the comments are two images I posted taken with a fast scope.
career7071 year ago
OK, thanks kmpres, I've built the peak detection circuit, placed it in parallel with my desulfator and DVM, reads about 1.6v(mind you at one stage it did read 15.??v). now the batteries i'm testing are a 55A Optima Yellow Top AGM Type been desulfating for about 6 days Standing charge before was 12.22v, now has climbed to 12.55v taken off charge last night and left, then tested about 9 hours later.

The other battery is a wet lead acid 44A, peering inside the vents I see that the lead plates appear to be clean(dark brown), there is like a paper seperation sheet which has what looks like a grey powder on it this is also 12.45v standing charge (has been standing for a while).

Am i correct in saying that as the desulfation process continues the peak voltage declines as the lead sulfate disolves (I'm sure I read that somewhere).

Changed the 220uH 2.4 Amp to a different unknown type runs much cooler (less turns but thicker magnetic wire than the old one) the tone produced at 0.70A (as in smoke test 1) sounds more pronounced
career7071 year ago
Gone to the trouble of rebuiling the circuit on a seperate board, dropped the Ampare output to half an AMP, The P600G Diode (D2 bought new rated at 6Amp) gets fairly hot, as does the 220uh inductor and the IRFZ44N Transistor everything else is cold, unit only on for a few minutes.

When I do a voltage test on the output section (eg on D2) of the circuit it never exceeds the voltage of the test battery being desulfated. I say this because other videos on youtube have had voltage output of inexcess of 46V(is this correct for this circuit also). Capacitor C4 (100UF Electrolytic LOWESR) did explode so replaced with a new 1000uF Electrlytic LOWESR type this is now cold.

R2 = 6.1K
R4 = 150K
AMPARES to battery as in smoke test 1 = 0.50A on multimeter.

Have tried to locate the diode noted in previous comments not found as yet, have also read your comment with regards to how the circuit works, makes excellent reading.

Any ideas from the overheating description i provide above. thank you for your help.
kmpres (author)  career7071 year ago
Looks like you're in the ballpark. You won't read anything more than nominal battery voltage if you're using a voltmeter. Only a scope can see the high voltage spike as it has a very short duration, much too short for a meter to pick up. Even most lower end scopes won't see it because it is too short for them to pick up and display. You need a 200 mHz scope to see the spike. Some people have been able to use a peak detection circuit with a meter to measure the spike, but I've not tried this so can't advise further. It is normal for the diode, C4 and coils (especially the smaller one) to get warm. Just be sure to adjust R2 so they don't get hot as they will burn up if left on too long. Normal spike voltage is around 50 volts. Mine seems to operate well at 55 volts p-p, but the parts get very warm at anything higher.
career7071 year ago
Thank you for your response, your build is excellent, unfortunately I do not have a scope (on my wish list), When I do a voltage test on the Positive side of the Diode (P600G/6A4) it reads between 12-13V, pin 3 of the NE555N reads only 1.60V I would have thought that this output would be higher,
Voltages on the Inductors also show only 13v max.
Parts used
Q1 = IRFZ44N
Q2 = 2N2907A
L1 = BOURNS - 2324-V-RC - INDUCTOR, TOROID V, 1000UH, 10%,2.4A
L2 = Inductor 220uH 2.4A Toroid Bourns 2116-V

Only been into electronics for a few months, a few small projects, this build certainly had me scratching my head a few times.
kmpres (author)  career7071 year ago
I'm not sure how you can read the voltage off your 555 output pin without a scope.  The duty-cycle is short and far from sinusoidal.  A voltmeter would likely give you a low reading.  Also, your diode may not be fast enough.  It needs to be a fast reacting type. As explained in the instructible, any old diode from your junk-box won't do in this case.   Someone wrote in and said that the FR602 went out of production some while ago but he found a replacement and listed it in the Comments.
career7071 year ago
Don't know if this instructible is still answered, but, I have built this desulfator, I have a few issues maybe you can help me with,

1/ smoke test 1, Ckecking the current with R2 as a Pot set at 15k, R4 Pot set to 270k, my multimeter is set at 10A, the reading is 0.07A, I was expecting 0.7A.

2/ I do get the tone once connected, I also get the Interference on my AM Radio.

3/ If I turn R2 Up to get 0.70A my 220Uh Inductor gets extremely hot so much so that I have had to fit a Cooling fan.

4/ I think that it is working a little as the battery I fitted it to has has had an increase in Standing charge/Voltage.

5/ the 220uH Inductor I have is rated at 3.4A, the 1000Uh inductor is rated at 2.4A both toroid inductors.

I have checked and rechecked the build against the schematic and I believe that I have done everything correct, I am not an electronic guru, just started about 3 months ago, can read simple schematics,
kmpres (author)  career7071 year ago
I can't tell for sure, but it looks like you built it correctly.  The currents can vary significant;y depending on component values and impedances.  I would adjust the current until the toroids get noticeably warm but not overheat after prolonged use. The cooling fan is a good idea but you should adjust the pots so the circuit does not burn up if it stops working.  Check the noise level of the signal going into the FET.  A noisy signal will make the FET, C4 and coils overheat.  Also be certain that C4 is a low ESR type.  Finally, the acid test to see if the circuit is working properly is to hook it up to a fast scope.  The spike will climb or drop very quickly in response to slight changes in R2.  Down in the Comments are some pictures I took showing the output spike and ring as it should look.        
Fozzy Vis1 year ago
Hi, Wanted to build this to try to revive some batteries I got in an old UPS. After going through the parts list, I've sourced all the components except for the coils. I found these two coils that seem big enough to carry enough current, but the values are not quite like they are in the schematic. As you seem to mention that the values don't have to be exact, I was wondering if I could use these:

First (round) one is has two windings, each half of the toroid and 2.33 mH, with a measured 0.17 ohms.

The U-shaped one has even bigger gauged wire, is a single inductor, 873 uH and 0.07 ohms.
Both resistances measured with a regular multimeter, so DC.

I have a couple of the pcb's where these came from, so could easily use the U-shaped for both L1 and L2.
Or should I search for some other coils?

jbaker222 years ago
I only have a dc ammeter wiil that work for the tests? Also can I just use r3 and c2 instead of Q2? Thanks for your help :)
kmpres (author)  jbaker222 years ago
The instructible has instructions for using an ammeter, but an ammeter is of limited help in troubleshooting the circuit if it doesn't work properly. Not using Q2 will work only if your circuit is clean and has little to no noise. Noise will make the circuit overheat as others have found out. I have not built the circuit in this manner so can't comment on how well, or even if, it will work.
jbaker222 years ago
Do desolater rely on high voltage pulses, pulses, or current pulses? I built a simulation of the circuit and it is weird.
kmpres (author)  jbaker222 years ago
It's all in the instructible.   The comments give you a wealth of other information as well.   The circuit you linked is nearly identical to mine.  All desulfators work by converting battery current into very short high voltage pulses.  These pulses are seldom higher than 55 volts peak-to-peak, so they're not really high, just a few times higher than the nominal voltage of the battery under test.  That's all the circuit needs to do its work.  If your pulses are higher, it means the duty cycle of the output from the 555 is too long and needs to be reduced.  Otherwise you'll run the risk of overheating your components.
kmpres (author) 2 years ago
Excellent. I was just about to suggest you check your R values and wiring. A lot depends on the other components used, which is why I used pots for R2 and R4. Also, any cheap oscilloscope will let you see the pulse width from the 555 to the FET, but you'll need a fast one (100MHz or more) to see the spikes going to the battery. Some people have made peak detector circuits so they can at least tell how high the spikes go. As you adjust R2, the spike climbs or falls dramatically.
Testing my desulphator and it seems to get rather toasty hot (everything on the output side) with the 15k and 270k resistors, although I can hear the tone. Is it likely that I've made an error wiring up the timer? Dropping the size of R2 didn't seem to decrease the current all that much (seems to pull 15+A DC).

Nevermind, was using a 270 ohm resistor rather than a 270k ohm, hah. Now it works better. :)
didyman2 years ago
Another working one! Thank You for the instructable! It's a prototype, so design will surely change later. Especially for the location of C4. At first, i have forgotten to connect the enhancement circuits' PNP Base to the rest of the circuit, so there was no fast turn off and everything got warm too quick-finally the IRF2807 has gone.. So replaced with IRFZ44N and noticing the missing joint and....Works everything well. C4 and C1 also is a Yageo SC. It's low-ESR type, not the best available here, but i have some in spare. Gets so hot, but not that much. Some interesting notice. 555 output is fine, and so the output pulse. Everything is fine, and not very warm to the touch with a single 54Ah car battery, but after i tried it in my vehicle, with a 75Ah one. And there, it runs much hotter. And from the sounds intensity, it just turns lover at once and then climbing up louder slowly, then again, turns down. This also affects heat dissipation. What is interesting, the peak voltage reading is around 43V in both case (a 1N4148-100nF single peak detector is placed at the cables very end near to the battery).
The car is a Peugeot 205, no ECU in it, and the Pioneer radio seems unaffected, no 1kHz signal from the speakers in any mode, exept AM receiving, certainly :-)) . Now it's cyclic desulfating, as i don't like to leave alone this proto. Results-i will come back and tell!
Ahm, LED. I got a white one, and that works only in reversed. It shows that the FET opens, and i think its enough to state that pulses are generating. But i will try red ones later.
kmpres (author)  didyman2 years ago
Well done!  I'm glad you got it to work.  I have found that the circuit works best if attached to the battery with short cables, as you did.  In 1-2 months you should have a working battery again.

During the winter my car's three year old battery decided it wasn't going to start my car on a cold morning so I jump started the car and took it to a battery dealer for his assessment.  Naturally he said it was toast and that I'd better replace it. Hah! I said. I put it on the desulator and two months later it was good as new.  Even tested it by leaving the car parked unattended for a week while I went on vacation. The car started right up when I got back.
didyman kmpres2 years ago
I have a client wich is an auto repair dept. I usually meet with this "don't think just throw it" mentality, but i always try to refuse. Original parts are horriblic in price, and the electronics aren't examples. And if it can be disassembled, there are good chances to repair (heh, cables, cheapo parts, relays, capacitors-everything that can go wrong in any regular product..). It's not only a value for-effort, but an environmental, too. And these batteries are take a much bigger toll than that the dealer asks for them at the shop. It's simply unbelievable, why there is no bigger efforts to save batteries with such a simple solution for a problem, that may be the main reason behind battery aging. I have measured 26V on the battery's terminals, 60V on the electronics (the measured 43V was on the fuse holder near the crocos) with the simple peak detector and the most voltage seems still loosing on the crocodiles, or on the wires attached to the battery-so further measures will take place, and maybe the mentioned ferrite ring will help more. Some not so important changes: I have BC556 at home for PNP, and BYW29F-150 for the FRED (as watching its forward characteristics, with 60A peak, developing only 1,2V on it, i can't believe it's enough for a red LED anyway with the currents the circuit is able to produce, but i will try it anyway-the FR602 has a noticably higher rdiff, so it easily can light up a lower Vf LED). Later, i will try to optimize circuit paths (but this probe-panel has two straight lanes in its middle, so i built up the higher current paths accordingly, and the FET's gate drive crosses it, but for this reason i placed the enhancement circ near the FET and let that crossing line see the low output impedance of the NE555. And it seems, as the peak is so narrow, the cabling has to be not only short, but free from narrow turns and parasite capacities. I think, these little thoughts may be useful, because we want to make sure the more energy reach the battery and not loosing on the path to it-again, some measurements will prove if they are valuable. And again, Your instructable is very kind, very practical and interesting, anybody could learn from it! And, some pics-may or may not interesting, but i show them :-) . It's a proto, so it looks like that (yes, i know: Things are made for temporary solutions tend to last for longer than anything else :-) ).
2009ee1952 years ago

I've made and assembled the circuit, made my own inductors as they were unavailable in the market. I can hear humming sound from the inductors, but have to place my ears very close. the led is also glowing but when i checked voltages and ampere with multimeter the dc voltage was 15v as i think because of zener diode and the current is just 0.1 amp this is not good can you tell me where i m going wrong?
kmpres (author)  2009ee1952 years ago
The zener should clamp the voltage to the 555 to no more than 15 volts, but under normal circumstances it should never get that high.  R1 takes down some of the voltage from the battery and acts as a current limiter for the zener and 555.  The voltage between pins 1 and 8 of the 555 should read around 12.5 V with a fully charged battery and the charger attached.   I'd check your charger first, then the 555 and zener section with S2 off.  Once you're satisfied the 555 and zener are wired and working properly, turn on S2 and check the output using the Smoke Tests.  Use a scope if you have one, or if not, follow the Smoke Test instructions and adjust R2 carefully watching for heat buildup in the coils, Q1, D2 and C4.  Try testing with a known good battery, too, to make sure it isn't your test battery that is causing the trouble.
2009ee1952 years ago
Hi Kmpres How r u?

Kmpres i was giving a look to charger section of your instructable, i was unable to to understand.

Did u attach the circuit parallel to charger and then attach it with battery?

If you attached parallely doesn't it affect the charger?

Or If u really attached parallely with charger can i use power diode to stop pulse going into charger, kind of insulating charger from the circuit output but on the same time using charger current as source?
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