# Pulse Charging SLA Batteries

Discussion in 'The Projects Forum' started by survivalsys, May 19, 2011.

1. ### survivalsys Thread Starter New Member

Apr 15, 2010
3
0
I have scoured the net, sites like battery university and nowhere can I find any real info on what voltage, current, charge, discharge times to create a pulse charger for a 12V SLA battery.

I have a need since after replacing my UPS batteries, I have a number of 2nd hand that I want to charge. Conventional chargers take too long.

The locally import battery chargers we get from China are expensive and they don't do what they claim should happen ie multi stage charging.

From some docs downloaded from Wikipedia and other sites, it seem that PULSE CHARGING SHOULD DO THE TRICK if high current/voltage pulses could be managed ie: magnitude, pulse rate etc. and it won't damage the batteries.

I've rewound a transformer to deliver 500V DC pulses using a 555 timer but from a previous reply from one of the senior forum members this is too high.

My question: Is there ballpark specs I can target on to start experimenting without blowing things up ? Will say a 50 - 60 volt pulse of short duration and @ 6.9A be sufficient ?

Battery Specification:

Cells Per Unit = 6
Voltage Per Unit =12
Normal Operating Temperature Range = 25oC±5oC
Capacity = 20Ah@20hr-rate to 1.75V per cell @25oC
Weight = Approx. 5.90 Kg
Max. Discharge Current = 200 A (5 sec)
Internal Resistance = 14m ohm
Operating Temperature Range = Discharge: -20 ~60 Charge: 0oC~50oC Storage: -20oC~60oC
Float charging Voltage = 13.7 to 13.9 VDC/unit Average at 25oC
Recommended Maximum Charging Current Limit = 6A
Equalization and Cycle Service = 14.6 to 14.8 VDC/unit Average at 25oC

2. ### Kermit2 AAC Fanatic!

Feb 5, 2010
4,165
1,120
Pulse or steady. A battery will only hold 'X' amount of energy. Calculate the amount of current you are putting in the battery 'over time', with the pulses and it should be almost the equivalent of the same amount of 'amps per hour', if done with a steady, non pulsing current.

The ENERGY delivered should be the same no matter which way you charge it.

3. ### Kermit2 AAC Fanatic!

Feb 5, 2010
4,165
1,120
why do you want to pulse the energy into the battery? You want to create a chemical reaction between the lead sulfate, sulfuric acid, and water in the battery using electricity.

If I was hungry and wanted to eat. I think I would prefer to take alot of small bites of food over a long period of time. Your method would be like a person sitting at the table getting hamburgers served up by a Major league pitcher. 100 mile per hour big macs aimed at my head does deliver 'food' to me, but not really how I want it.

You understand? Pulses CAN be used to break up clumps of hardened sulfate crystal(according to the patents on the subject) but as for charging a GOOD battery I think you will find it is a less than ideal method of charging. LA battery tech has been around for a long long time. If pulsing was a superior method of charging we would already be using it.

4. ### t06afre AAC Fanatic!

May 11, 2009
5,939
1,224
If you still have not looked at these sites, please do so
http://www.chem.hawaii.edu/uham/bat.html
I did mention this in PM, but this is to bring other members up to speed. As I said before you are mixing terms. Battery desulphator is one thing http://home.comcast.net/~ddenhardt201263/desulfator/lowpower.htm And this has nothing to do with a Battery impulse charger. You say you want to use high voltage but why do you want to this. from the first link
So using 60 volt on a 12 volt SLA is asking for a battery explosion and damge. And 500 volt . A battery desulfator may produce perhaps up to 80 volt. But the energy is deliverd in a very short puls. So the energy over time is very small.
It is also a limit how much current you can charge a SLA without risking problems like overheating and damage. The energy not used in the chemical process of charging. Will be converted to heat. The vendor of the battery will give you recomended max charge current.
The best way to build a charger is not some device just bashing voltage and current into the battery. But rather build a circuit that monitor both battery voltage and charge current and keep the values inside recommended values. You can get circuits that do this. One of them is the UC3906 from TI. You can find more about this circuit here http://focus.ti.com/docs/prod/folders/print/uc3906.html#technicaldocuments
I think you will find the app notes interesting

5. ### #12 Expert

Nov 30, 2010
17,840
9,178
There. Two other people have said what I said before your previous post got banned for mentioning an overunity scam. I'm glad you learned not to mention that, but you still seem to be chasing "How to do it completely wrong". What in the world has got you fixated on blowing up a battery with 500 volt arcs?

Feb 2, 2008
206
9
7. ### survivalsys Thread Starter New Member

Apr 15, 2010
3
0
Thankyou all for your advice specially t06fre and jerseyguy1966. Very informative. For the record I have not blown anything up yet, I am too cautious for that AND DO A LOT OF RESEARCH FIRST. Why I am fixated on pulse charging is the wikpedia comments and others saying it is OK and quicker and does not harm the battery. Some say that this is not main stream technology but more research is needed. The second problem I face is trying to find a decent 10A circuit that is not Nickel Cadmium.

Apparently pulse charging is working it's way into the marine world since mariners don't have the time to wait while batteries are charging. So the technology is out there and I just need to find it without importing expensive chargers.

I do have a multi stage charger but batteries get very hot and take very long. So I don't think it is doing what it is supposed to be doing. Tried building some circuits but all seem to be geared for lower Amp rated batteries.

Busy playing with x3 20A/H in series since the current in parallel needed is 6A (10%). The 2nd hand UPS batteries that was replaced with new are 100A/H. Current needed is 10A minimum.

There is a lot of chargers for Nickel Cadmium but very little for SLA since amps too high. The other problem is components. You guys don' realise what a privilege it is to live in countries where components are easy to get by. If I want something, either I have to make it myself or import it. So building battery chargers from a component list supplied is not that easy and can take months !!

I have studied all the links above and in previous posts on battery charging and chargers and if I can find a circuit that will charge my big SLA'S I'll go for it. It is not an option to charge my battries one by one and I am not buying the rubbish imports they sell in South Africa. I'll rather build my own circuit or circuits.

So anyone that knows anything about high amp chargers can help me build a 10A multistage charger without buying special chips which I cannot get anyway, please share. The best charger I build was a 6A but did not last very long. I just need the rudementary bits with current and voltage sense. I'll work out the rest. I am a hands on techie.

Some has suggested that I buy a 2nd hand UPS, take it apart and clone the multi stage charger secion if I can find the components. This could be an option if all else fails.

8. ### #12 Expert

Nov 30, 2010
17,840
9,178
Pulse charging is a perfectly reasonable thing to do. I built one 20 years ago, and it still works. It commonly throws 35 amps into a car battery and can survive a 200 amp surge...all with 15 volt transformers, but not with 500 volts!

If you want to get 500 volts on the terminals of an SLA battery, you will have to be ready to feed it several hundred amps. Do not be in the building when you do this because it will blow up instantly and the pieces will probably kill you.

You mentioned the batteries getting very hot. This is an inevitable side effect of fast charging. It does not mean something is wrong with the charger. It means you are charging so fast that you are getting close to warping the internal plates.

I already told you about using a 12 volt transformer and a rectifier to cause 16 volt pulse charging. This only requires a transformer, a rectifier, a power cord, and probably a fuse. You have already calculated the current you want. All that is left to get started is to buy a transformer and a rectifier. For good control and automatic operation, the other people here have given you good advice.

Good luck.

9. ### jerseyguy1996 Active Member

Feb 2, 2008
206
9
The BQ2031 is a controller so all you would have to do is design the drive circuitry to handle 10 amps. I built mine to charge at 2.5 amps and it is completely automatic. Qualifies the battery, bulk charges the battery, tops off the battery, and then maintains the charge if left plugged in. I even added a couple of analog volt and ammeters to it so that I could monitor the state of charge throughout the process. It is unnecessary though because it has LED outputs that will signal which stage of the charge it happens to be in as well.

10. ### survivalsys Thread Starter New Member

Apr 15, 2010
3
0
Thanks #12. Time to get to work with the advice given. The 500V transformer was an experiment I was conducting. I've imported EI laminations and bobbins and lately have the facility to build my own transformers.

Out of curiosity, I tapped the leads on the batteries just to do some measurements. I did series connect my big SLA's first giving close to 84V. Obviously I won't run it continuously at that voltage and started to rewind the transformer to give me a more acceptable voltage at a different guage wire for amps.

I am going to contact my suppliers to see if I can source the BQ2031 controller chip.

I think I now have enough info to move forward. Thanks to all.