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Desulfator for 12V Car Batteries, in an Altoids Tin

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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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inswlkes3 days ago

Hi @kmpres I'm having similar problems that @career707 reported of extreme heat at just 0.7A Wonder if you would explain your comment... "Check the noise level of the signal going into the FET". Thanks.

kmpres (author)  inswlkes2 days ago
The signal coming off the 555 should be clean, like the scope picture in Step 4. That square wave feeds the base of Q2 and the gate of the FET. If there's too much noise in the components or wiring then the FET won't turn off completely causing it, C4 and the coils to overheat. Q2 is there to help bring the gate voltage down to ground at the end of each pulse thus assuring that that FET will turn off completely. The square wave also has a short duty cycle and making it too wide will cause the output parts to overheat as well. It's best to use a scope, if you have one, to see these waveforms.
DanH45 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 www.recovermybatteries.com at these prices it is not worth trying to build your own.

kmpres (author)  DanH45 days ago
I disagree Dan. The point of this instructable was not to replace what is commercially available but rather to help educate people on how desulfators work and how to build them from easily available off-the-shelf components. People, particularly in less advanced countries where mass-produced versions are too expensive or not available, have even used recycled parts to build them helping to save their environment and costing them nothing. As the saying goes, the device may be inexpensive but the knowledge is priceless.
DanH4 kmpres5 days ago

What is the point of building something that is so out of date, inefficient and can damage the battery you are tying to save. This type of high voltage pulsing desulfator may provide some minor improvement in the short term, but long term it is proven that it does more damage than good. When this type of home build circuit board was first developed (15 years ago) commercial desulfators cost many hundreds of dollars, now like most modern electronic devices they are fraction of that, they work and they wont damage your battery.

kmpres (author)  DanH44 days ago

Dan, the point is to restore a battery that would otherwise have been thrown on the scrap heap thus avoiding unnecessary waste and pollution. If it is damaged beyond repair then this circuit won't help it, nor will any other. However, this circuit is so mild in its operation that it can do no harm to a battery as long as a trickle charger is left on with it. If you prefer, once a battery is restored to life then the circuit can be safely removed thus eliminating even that risk. When properly tuned it consumes only a few watts and is no less efficient than any of the commercial brands. And the fact that there are more and more desulfator products available in the marketplace speaks to its obvious success. Companies wouldn't be able to sell them if they were "proven" to do more harm than good.

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,
IMG-20130325-00272.jpg
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.        

Hi @kmpres I'm having similar problems that @career707 reported of
extreme heat at just 0.7A Wonder if you would explain your comment
"Check the noise level of the signal going into the FET". Thanks.

MamaM113 days ago

Wow very cool with an other one.. this is a very important invention that should be obligatory in al chargers i think. By enviromental law!

I just builded a very cheap and simple one without timer but with a self oscilating system. It' deviriated from the famus "Joul theif" and is called re-emf charger.

It takes the back emf from a bifilar coil and do the same kick thing. I have messured around 200v on a cap loaded with this one. Not to say this one is not good enough. The re-emf charger is quite easy to asemmble from scavanged parts indeed. (wery few parts indeed)

Important for it to work is fast diods to the battery + and feritecore in the toroid with atleast 30 winds and a snappy npn powertransistor. Yes and the bifilar strands should be conected in cross not paralell for it to work. I did that mistake :( and could not get it shaking how ever i shaked an hit the darn thing..

But what ever you build.. Do it.. Its the only resposible thing to do. Throwing batterys is.. bahhh.. Old 250ah batterys you can get by going to ask at lorry workshops. The transport industry throw batterys on first sign of weakness not to get in to trouble.. here in Finland its throwing seeson when the first -10c hits.. And in the local re-cykling center it's 10's of cubic metres of them in big greay boxes. I go there in the nights to go trough the electro junk container for fun electonics and and have a truely huge batterybank. Good luck for all you off gridders. And you all. Be sweet and do love mice! And your husbonds, children and wifes.. and your neighboures

DanH41 month 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 www.recovermybatteries.com at these prices it is not worth trying to build your own.

snakeman.est2 months ago

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 ?

yaly4 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.

yaly4 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-SMD6 months ago

Hello.

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-SMD6 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.

Lase8 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

Thanks

kmpres (author)  Lase8 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 kmpres8 months ago
Thanks have been looking
astral_mage8 months ago

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

kmpres (author) 1 year ago
I can't tell you how low "low ESR" should go. I only used one kind and it worked.
larry_too1 year ago
Understand,
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_too1 year 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
MOSFET N CH 60V 57A TO 220 IRFZ44VZPBF-ND 2.08
100uF 25V LO ESR 493-6631-1-ND 2.95 or
100uF 25V LO ESR PCE4929CT-ND 1.32
DIODE FAST 100V 6A PR6002-TDICT-ND 0.70

Any suggestions before I punch off the order?

Larry_too@yahoo.com feel free to e-mail if you would rather. That 8D deep cycle battery awaits my attention.
kmpres (author)  larry_too1 year 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?
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.

Larry_too@yahoo.com
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.
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?

Thanks!
DSC_0073.jpgDSC_0072.jpg
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. https://www.circuitlab.com/circuit/n47wvv/desulfater-2/
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.
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