• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Lead-acid battery zapper

d4d4ng

New Member
I am a newbie in electronic, so please bear with me :)
I read an article at http://www.siliconchip.com.au/cms/A_104827/article.html about reviving an old lead-acid battery. The article discussed a way to get rid of lead-sulphate crystals on surface of battery cells that short-circuited those cells. It's using inductors to get a short pulse reverse polarity high voltage that will evaporate tha lead-sulphate crystals.
Instead of those inductors in that article, can I use a car ignition coil to produce high voltage to zap the lead-sulphate crystals.
I know that I have to be careful dealing with high voltage ;)
Thanks in advance.

Amri.
 

Oznog

Active Member
d4d4ng said:
Instead of those inductors in that article, can I use a car ignition coil to produce high voltage to zap the lead-sulphate crystals.
I know that I have to be careful dealing with high voltage ;)
No, because the goal is to create high current pulses. The pulses off an ignition coil have a lot of voltage but very little current capability- only a few mA. If you stick an ignition coil on a 12v battery, the battery load will clamp it down to only 12v and it receives basically the short circuit current of a few mA.

Those circuits I saw are pretty flawed- power inductors like that shouldn't be manually tweaked for peak current. YOu want to operate it in a peak current mode where a resistor senses the current and when it reaches a preset value under Isat it changes to kicking the output to the battery. You'll maximize the inductor current while being insensitive to changes in source voltage and timing cap deviations.
 

d4d4ng

New Member
Hi oznog,
Thanks for your info. Looks like I still have much to learn on electronic :oops: I thought that car ignition coil will do the same, but I'm wrong.
Anyway, thanks again :)
 

Someone Electro

New Member
Wodnt a capacitor rather be used to make high curent pulses.

I wired up a 40 000 Uf cap bank charged to 60V.Wen shorted whith an pencil tip,the tip exploded in a big flame.It also blows an 1 cm hole in aluminium foil and loses only 10V charge
 

pike

Member
ummm...does that circuit actually even work in reality?? sulphated batteries are a ****** to desulphate unless you take it apart, clean off the sulphate, and reassemble with fresh acid.
 

stevez

Active Member
I'd bet that there are some sites that discuss the desulfate process.

I'll share this -I just purchased a switched mode power supply for my RV. It takes a nominal 110 vac and provides 13.8 vdc to power some things and to charge the battery. This one is good for 45 amps. It works well even with inputs below 90 vac. It has a battery charge controller that is supposed to more properly manage the battery. One part of this is once every 24 hours it goes into "boost" mode which supplies a high level of charge current (presumably by raising the voltage) for about 15 minutes - said to desulfate the battery. I'd gather from this that desulfating is something that should be done regularly and might require substantial current.
 

Pommie

Well-Known Member
Most Helpful Member
I can vouch for the fact that SLAs can be rejuvenated with a pulsating current of some kind. I have 2 * 5AH 12V SLAs that have been used on an electric fence for the past 18 months. As it is left to my daughter to change them over, I usually get them when they are down to 2 or 3 volts. I used to get annoyed as I know that this sort of treatment will severely shorten there lives. This has not been the case, after many discharge/charge cycles and many of them being well below the sulphate causing level, they are both working fine and hold charge remarkably well.

The electric fence unit has a pulsed output that gives a pulse about every 2 seconds. If the unit is shorted to ground then a visible spark can be seen, if open circuit as intended then I assume that the energy outputed is dissipated back into the battery.

Oh, and why do I think that this does rejuvenate batteries. These batteries came from the UK in a shipping container and were about 5 years old when we started using them on the fence. As they were near the end of their lives I wasn't surprised they needed changing every week when we first used them. We now swap them about every 3 weeks.

BTW, I recharge them with a lab supply set at 14.5V and current limited to 400mA.

Mike.
 

Oznog

Active Member
There's enough people who seem to have had measurable results that I believe it.

I'm not sure I buy this stuff about "resonant frequency" of a battery. I suppose it's possible but I think it has more to do with sharp current pulses. Note that this is different from overcharging- just dumping in more current when it's already charged. We know that doesn't do anything to get rid of sulfation (sulphation?) which has already accumulated. The homebrew plans talk about resonant freq of 2 to 6 MHz but the output looks like a freq of 1KHz so I don't get it.

I suspect it is merely about putting sharp current pulses into the battery, in which case C6 is being counterproductive. My other theory is that alternating with sharp edges between discharge and charge would be more effective that simply alternating between charge and idle. I don't have anything to back that up and sadly it's going to be difficult to get real data on that issue.

Discharging caps into a battery- well you'd need some pretty big caps. If you dump many amps out of caps over and over many wear out quickly and the ESR increases.

I'd think the best way to do this would be to charge an inductor off the battery so it has like 10-20 amps and then reverse it so the current flows back charging the battery (of course this will always sum to a net discharge equal to the inductor, diode, and transistor losses). We can do that at 100kHz or whatever. That won't do this "resonant frequency" deal though, but I don't see where the "homebrew" desulf plans do that either. Those show a resonant freq of about 1KHz in the secondary stage as well as a misuse of C6 and L2, and they chose to specify a fast recovery std rectifier when it looks like a Schottky would be more appropriate.
 

Roff

Well-Known Member
Oznog, I agree with your resonance comment. I think he was seeing parasitic capacitance resonating with the inductance of his battery cable. I ran a sim of the circuit in question (see below), and there was ringing on the diode (which I didn't post) at about 600kHz. I don't think there is anything internal to a battery, or in this circuit, that would ring at 6MHz.
Note the current waveform into the battery. It is almost symmetrical about zero. I wonder if that is the ideal situation. I guess you don't want to have a net charge or discharge. Of course, since this is self-powered, the net has to be discharge.
Of course, this is only a simulation. If anyone builds this (fat chance), I would really like to see actual measured waveforms.
 

Attachments

bryan1

Well-Known Member
hiya Guy's,
Below is a link to a website that has a few de-sulphator circuits on it also it gives some pretty good info into de-sulphating
http://www.shaka.com/~kalepa/desulf.htm

Cheers Bryan :D
 

bryan1

Well-Known Member
Oop's sorry Ron I didn't realize you already gave the link to the same guy that does it.

:roll: :roll: Bryan :roll: :roll:
 

d4d4ng

New Member
Hi ante,
Thanks for your link. Your article needs a charger to construct the Pulse Charger that alas, I don't have yet :)
But anyway, I can learn the idea of desulfation for lead-acid battery.

Amri.
 

Latest threads

EE World Online Articles

Loading

 
Top