Introduction: Simplest Charger/desulfator Ever

Picture of Simplest Charger/desulfator Ever

This charger can charge almost any battery type at any voltage. It desulfates lead acid batteries as well. It works quite well. Be warned tho, it contains lethal voltages. If powered by 120vac it can get up to 170 volts and 340 volts on 220vac.

Step 1: Materials:

Ac run capacitor Rectifier or 4 diodes Switch(optional) Electrical cord

Step 2: Schematic

Picture of Schematic

Step 3:

Picture of

As you can see it is quite simple. The capacitor couples the battery to the mains as well as limiting the current. At 120vac it charges at 1 amp for ever 22uf in capacitance, 13 uf at 240. The switch is merely convenience so i dont have to unplug and replug. Then the diode bridge rectifies it to dc.

Step 4: Usage

it works in a way that if the battery is sulfated or weak etc. it will always charge at the preset amps. So if the battery is only taking 5 amps at 12 volts and u have it set for 10 amps, it will raise its voltage until it is charging at 10 amps. At 120vac the charging voltage could go up to 170vdc. 340 with 240. It also pulses at 120 herts which desulfates the lead acid batteries. It should also be noted that this is a universal charger and will charge any voltage battery. It should also be noted that the is no protection against over charging and if it is left on the charger when the battery is already charged it could damage the battery.


ARON751A (author)2017-08-08

Capacity lead battery charger /desulfator can charge from 0v to full charge

CyberR (author)2016-10-29

I've now rebuilt this desulfator with a switch that disconnects both the live and neutral mains lines and added a small PSU board from an old phone charger that runs an LED. I now plug this into a 24hr timer set to turn on for 30mins then off for 1 hour.

I'm currently looking into adding a temperature activated switch that will sound an alarm and cut power to the desulfator side if the temp rises too much. I am however trying to keep it as simple as posible with as little cost and electronic assembly as possible.

willdbill (author)2016-09-24

This thing dose it work and how long a charge do you nead to discharg recharg how many times if i dont get a reply i will asume the op has friyed hime shelf

chris2u (author)2016-09-23

This circuit is LIVE and highly DANGEROUS !!

Full mains voltage is available at the battery terminals unlike chargers that use a mains frequency or switch mode transformer..

Contacting any of the wiring or connections with a grounded body (human or otherwise) could prove fatal.

Maybe an experimental project for the lab.....But not where humans or animals could come in contact with it in any way..

CyberR (author)2016-06-30

erm... another update. I... err... I may have killed the batteries, used them in an R/C car in parallel for more amps. Long story short, the rear drive of the R/C got bust/destroyed so the car in storage till i could rebuild. took it out today to check something out and, like a Doofenshmirtz, had forgot to disconnect the SLAs.

Going to have to scrounge parts and rebuild defulfator (stripped it for another project) and a try a few other techniques first then this. fingers crossed.

StephanM20 (author)2016-06-08

I love simple designs. However, I see some things I don't like:
Protection: If the capacitor fails with a shortcut, -I don't even want to imagine that. A fuse it the minimum you should integrate.

Ripple current of capacitor not regarded. Standard capacitors will can ripple currents about 2A. You want 5-10A. Make sure you don't cook the capacitor.

Nobody guarantees that the battery is charged by nominal current! The current will be mainly determinded by battery resistance and resistance of the rest of the circuit.

No overload protection. Yes it might remove reversable sulfatation, because this is usually done by applying overvoltage by a limited time. Overvoltage for a longer time will kill the battery quickly.

rmargate (author)2015-11-06

can i use it to charge a 48v sla battery pack of my ebike?

blackalic (author)rmargate2016-02-17

Yes,12v,24v,36v,48v etc...

Lionhearmatrix (author)2015-12-10

Hi guys. I'm on 240V here and have cap from an old microwave (0.97uF, 2400VAC). Which rectifier or which diodes should I use? Thanks

CyberR (author)2015-09-29

can't get hold of a starter cap however I do have a cap from a microwave. Would I be able to use this instead? We use 240v 60Hz mains which is also what the caps rated at?

CyberR (author)CyberR2015-09-30

Gone ahead and created the circuit using the high-voltage microwave cap rated @ 0.72uF 2100v ac I have and a bridge rectifier from a dead PSU board and added a light so can see instantly if circuit is live.

The results
No bang!!! That's a first.

2 x 12v 2.9Ah SLAs
3hrs on charge : not charging.
3hrs on this circuit : now charging.

I'm now alternate the batteries 1hr on 1hr off.

Oh and I never have more than one battery hooked up at anytime when charging or desulphating. I'm not that stupid lol

CyberR (author)CyberR2015-10-11

A quick update. I still don't know the history of the 2 SLA's other than they were stone dead when salvaged from a bust electric recliner. However they are now back up and running thanks to this simple circuit.

Still running strong even when they've been in heavy use and completely drained they've still recharged on a normal charger.

steve000 (author)CyberR2015-10-19

Many thanks for your update I'll attempt to make this myself now

ZoranKoco (author)2015-10-05

I have questions about your success too. I made this charger long time ago, and I was experimenting only with one lead acid battery, 12V 55 Ah witch wasn't in use for long time, but I'm not sure that I improved it from sulfatization. However it was charging with this charger, my question is does it really work like desulfator?? I would like to read more comments of your expirience.

Toga_Dan (author)2015-10-02

op, are you still following this? I have questions about your success rate. I'm also concerned about that much voltage on a 12v. Did you track battery temperature? Did you ever put this on an oscilliscope? I wonder what %of a second there is voltage to battery. I suppose that is contingent upon capacitance. A small cap only sending voltage thru for a brief moment., etc.

Jakob2803 (author)2013-06-07

OP: What about when the battery voltage rises? The current through the capacitor decreases, so the charger would get slower and slower, the fuller the battery got.

Jakob2803 (author)Jakob28032013-06-07

And I forgot to ask - what about the power dissipated in the capacitor? :)

Macattacku (author)Jakob28032013-06-08

Well from what i can tell, i would be dissapating ~100 watts of power through the cap, but i never had any real heat or warmth com off it. Run capacitors are built for that. They have metal cases.

blackalic (author)Macattacku2015-01-26

Hello, there's so many type of capacitors and i don't know what kind of capacitor is run with non polar.. you think this brand of capacitor is good for battery disulfator?

Uf (mfd):
370-440 V
50/60 Hz
Temperature range:
-40 to +85°C
+/- 5%
Capacitor type:
Construction Style:
Aluminum w/ Steel Cap

blackalic (author)blackalic 2015-03-10

hello, i used this type if capacitor and it works, but it takes to much time to charge the battery so i changed to 25uf..Now it's good enough to charge my 12v 12amp. .Next time i will try 2pcs. 50uf capacitor.. You think it's good for 36v 12amps electric scooter? thanks

shomas (author)blackalic 2015-09-08

Personally I would prefer slow trickle charge rather than quick charge. That way you can still benefit from the desulfating your battery without over charging it.

Macattacku (author)blackalic 2015-01-29

wow. i have not done anything with my account here for like a year. but yah that seems fine. just beware the voltage etc, etc. this charger is not safe by any means but it does work. im sorta used to it because ive worked with tube amps before, but i wouldn't do this unless you know how to act around high voltage. brand shouldnt really matter as long as its about 400 volts, nonpolarized, and with a metal case.

shomas (author)Macattacku2015-09-08

By dissipate I think you mean allows 100 watts of power to "flow through" rather than being converting to heat as can happen dialectric (material between the plates) heating. Dielectric heating at main's 60 hz is virtually unnoticeable.

whansard (author)Macattacku2014-05-05

I've been having fun with this for a few months now, first using 4 diodes, and now a bridge rectifier. when i run it hooked up through a kill-a-watt device, the charger seems to only pull about 5 watts from the wall socket when using a 5uf run capacitor. the past few days i've taken a bunch of film capacitors out of an old monitor, and they work fine. i have several that are well below 1uf. they don't even get warm when i'm charging a battery.

Macattacku (author)whansard2015-01-29

yah, i was a little less informed when i first wrote this. the capacitor isnt dissapating the excess energy, its merely limiting it thrrough capacitive reactance. this is a fairly common circuit in low power homebrewed transformerless power supplys. but since theres no way to reasonably ground this, it isnt terribly safe.

blackalic (author)Macattacku2015-01-26

Hello, there's so many type of capacitors and i don't know what kind of capacitor is run with non polar.. you think this brand of capacitor is good for battery disulfator?

Uf (mfd):
370-440 V
50/60 Hz
Temperature range:
-40 to +85°C
+/- 5%
Capacitor type:
Construction Style:
Aluminum w/ Steel Cap

Jakob2803 (author)Macattacku2013-08-14

I was also wondering if the cap wouldn't also draw current out of the battery on the negative half of the period. And 100W is pretty much! :O

Macattacku (author)Jakob28032013-08-14

Well it isnt built to be efficient, its built to be simple as well as an effective desulfator. Like i said that 100 watts doesnt appear to warm the metal case of the cap, which is roughly 2 inchs by 1 inch by 3 inchs. And no, it would not discharge the battery because it charges on both phases and the doide blocks reverse current. Without a full wave rectifier the capacitor wouldnt let any power through.

Macattacku (author)Jakob28032013-06-08

Wrong sir! The point of the capacitor is that it is a constant current charger. In a constant voltage charger the current tapers off, but in a constant current charger the voltage rises and no mattery how charged the battery is at whatever voltage it puts in the set amount of current. No matter what!

Jakob2803 (author)Macattacku2013-06-08

Yes but this is not a constant current charger. The current through the capacitor depends on the voltage across it and its reactance. If the battery is charged, the battery voltage rises, while the voltage from the wall socket remains the same, so the voltage over the capacitor is reduced and less current flows.

Macattacku (author)Jakob28032013-06-08

I have used this and measured it. I have done much testing. On any battery or battery pack such as common ones 12v 24v 48v etc. it charges the same amperage no matter tge charge. It varies very very little. If a 12 volt battery is full i have accidently overcharged them. It will just crank it up to 20 volts or more to maintain the current. Charge doesnt matter it will forcefully shove its amperage in at 120 hertz. Thats what makes it good at desulfating.

Freddy_100 (author)2015-04-04

I have a 1,000,000 uf car audio capacitor. Can this work??

I am new to this and do not understand some of these things.

Any help would be appreciated. Thank you


NO! The cap you have is rated for less than 12 Volts DC? It will blow up if attached to 120VAC. It is also a DC capacitor. You need to use an AC run cap like those used with motors in heaters and an A/C systems. Get some local help if you don't understand what this all about. Otherwise this can be a dangerous setup. Really.

shomas (author)bill.harvey.1002015-09-08

Actually the rating is probably closer to 18 or 20 volts. but far less than the 120V AC actual instantanious peek voltage at 170V.

Furthermore, the real advantage in a setup like this is not the rate of charging. but its ability to desulfate batteries. Charge controlled battery chargers will give your batter much longer life. Desulfating a battery can some times breath new life into batteries suffering from sulfated plates. Having a large capacitance capacitor able to handle 2x the mains voltage would carry allow for too much current to flow and boil your battery.

harvie (author)2013-05-27

Why the capacitor? Is it really better than transformer? I think that transformer can do pretty much the same job... but many people are saying it can't... why?

shomas (author)harvie2015-09-08

The purpose of the capacitor is to limit current. Small capacitors don't store much charge so they will only allow a little current flow at 60hz. You can do the same with an Inductor because Inductors also limit AC current flow, but the more current you want to limit, the larger the inductor needs to be, The issue is made worse with at low frequencies like 60 hz. Furthermore, depending on the core, your likely to get a lot of losses through eddie currents and other resistance to changing magnetic fields in the core. A small capacitor rated at 2x your main voltage will be a lot cheaper and more energy efficent

Jakob2803 (author)harvie2013-06-07

The capacitor acts as a resistor to AC. You might as well use a big resistor instead. The point of it is to control the current.

Jose RomanT (author)Jakob28032015-05-29

You would require a resistor with a high power rating (expensive).

A better alternative would be an incandescent bulb.

Jakob2803 (author)Jakob28032013-06-07

And the transformer would let a lot of current flow, possibly damaging itself or the battery, that is the difference.

Macattacku (author)harvie2013-05-27

The capacitor limits the current. A 1:1 isolating transformer would perform a similar job but not the same. A capacitor allows the voltage to climb 170 volts if necessary. A transformer would only allow 120. This charger is by default inefficient, 120vac 1 amp in, 12volt, 24volt, 48volt etc at 1 amp out. I have used this charger for general purpose charging but its main purpose is battery desulfation. So to conclude, you can use a transformer but it wouldn't be as effective or cheap. It would also be less efficient. A capacitor has no losses besides the loss in voltage. A transformer has transformation losses.

Jose RomanT (author)2015-05-29

"The switch is merely convenience so i don't have to unplug and replug."

The switch will only give you a false sense of security as it turns off one half of the circuit, while the other half is still "live!". Unplugging and repluging this dangerous circuit is better than adding a switch for convenience. :-)

r2sail (author)2014-08-14

how do you know when a 12v battery is finished the desulfation process

Stefanovski (author)2013-09-15

I use this charger over a year it's OK I charge even 1.5v battery with small capacitor, BUT IT'S VERY DANGEROUS IT CAN KILL YOU EASY IF YOU DON'T BE CAREFUL.

Macattacku (author)Stefanovski2013-09-15

I typically use this to charge lead acids because its harder to danage them. Once something is charged the voltage can really climb. Thats why this is a charger that should supervised not just hook up and forget. Lead acid and nicad is what i recomend using this for but there is nothing stopping u from charging others. Do NOT charge lithium batteries with this, chance of explosion is very high if try and charge lithium batteries.

pmitch1400 (author)Macattacku2013-10-10

can you please tell me what cap to use i am on 120volts ac, sorry i am a beginner thanks

Macattacku (author)pmitch14002013-10-11

Mine is used for 120 vac. So 22 uf would give you about 1 amp. 44 for 2 amp, 66 for 3 amp. Etc. it goes smaller too 1 uf is about 40 ma. I cant say i recommend for a beginner considering the 170 volts dc present at the terminals. If you still want to do it thats up to u.

Macattacku (author)2013-06-08

Jacob to answer your other question, unless battery voltage is 160 volts, it will charge at the set anperage.

Macattacku (author)2013-06-08

Well a resister would also work but you would have serious heat problems. I have a 20 amp one of these and i still have no heat. Your gonna be dropping 2000 watts through that resistor. I dont think its easy to get a 6 ohm 2000 watt resistor. Its cheap to get a 440 uf motor run cap.

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