SLA Battery Chargers?

[dat2zip]

Any good chargers for SLAs? I see the batteries in surplus and they seem to be good logical choices for battery backups for some of my lighting projects.

From what I've read, it seems that to get a fully charged battery requires a little more smarts than just a straight linear regulator hooked to the battery.

Anyone familiar with this:
http://www.batterymart.com/battery.mv?p=ACC-12BC1000D-1

I've got a 12V 4A/HR SLA and I'd like to leave the charger connected all the time. Any suggestions?

My total load is less than 1A at this time. Intermittent night time sentry mode for the front yard and some nightime fixed lighting. (All LEDs of course).

 

[Mr Ted Bear]

For years I kept/maintained a bunch of SLA's for my underwater video lights. Whether it was one or eight, I just hooked them in parallel (at times) and used a motorcycle battery tricke charger (nice and cheap).

the maufacture of the lights sold the same charger for $100 with a proprietary leeds; me.. i used aligator jumper clips

 

[zmoz]

That looks pretty good...nice price too. /ubbthreads/images/graemlins/grin.gif I'm not sure about this, but I think you are only suppost to charge SLA's at C/10, so you should charge a 4AH battery @ 400mah.

 

[dat2zip]

The TI IC UC3906 is designed specifically for this battery technology. I just picked up some of these.

Yeah, right, Like I have time to design, build and box one of these suckers. If one of the SLA chargers like the motorcycle chargers works for under $50.00 and I can find somewhere to get them. I'm sold...

 

[snuffy]

Here's a very good 1 amp kit using the UC 3906. smart battery charger
I've built a couple of them. It's a complete kit, case and all.
About an hour to build and you can set whatever charge current you want by choosing one resistor value.

 

[markus_i]

SLAs are pretty robust in that respect. I've been using them for a several years now on my bicycles (for lighting - yes, I have a good generator, but it's noisy and won't provide enough current for that 6W headlamp), and they haven't died on me from electrical failure (yet...). Usually, I don't care too much about it, voltage limit the lab supply to 2.3 (or so, usually written on the cell/battery) Volts per cell and maybe current limit to C/10.
Since I switched to Cyclon cells, I also invested in a dedicated (wall wart) charger for 6 V cells from Ansmann (German/European company, probably comparable to Maha from what I've heard). Makes handling a bit easier.
There are more complicated chargers out there (if you want to recharge a few hundred Amp-hours in less than 6 hours, things tend to get a little tricky), but for the small stuff and if you can tolerate 10+ hours of charging time, I wouldn't bother.

Bye
Markus

 

[Doug Owen]

Over the years I've worked with SLAs several times. The defribulators I used to service used 48 Volt batteries made of 6V 2.4 AH Globe batteries in series. Globe recommended a 'float charge' of 2.24 to 2.26 Volts per cell. This is the 'full time' voltage like you'd design into an emergency exit sign for instance.

As a one time electric car owner, I again got into LA battery chemistry. This time with the then industry leader, Exide. The goal here is fast charging without loss of electrolyte. There is a complex formula, temperature dependent, that determines the 'gassing potential' where water is split. You need to stay under that voltage (which means you need to measure battery temperature), but can push as much current as you can up to that point. Since the 'golf cart batteries' I was using can supply over 400 Amps (and can be recharged at least that fast), my maximum charge rate was limited by the 1500 Watts available at the wall outlet. Staying at that voltage after the current drops (all the lead has been converted back) is sucking around for sulfating your plates, however. Up to that point, all the current goes into chemical conversion (charging).

Lately, the Electron Microscope I work on uses a bank of Gates 18 25 AH cells in series parallel for 6 Volts which are recharged by a small M/G set (for isolation reasons) that's run to return 120% of charge used. A few times a year, the gun area is serviced and I charge cells individually to 2.26 Volts at that time to 'equalize the charge'. Again, supported by the maker of the cells.

I recommend a 317 type series regulator (includes internal power and current limits) set to 2.25 Volts per cell.

Doug Owen

 

[UK Owl]

Lead acid cells are 2.2 volt nominal, so your 12 volt battery is 6 x 2.2 = 13.2 volts nominal, however open circuit cell voltage is typically 2.3 volts per cell so you usually measure 13.8 volts on a fully charged battery. As long as you do not exceed this 13.8 volts with your trickle charge you should be okay.

I believe you aware your battery will be ruined is you let it go flat, or store it for extended times. You can prevent this by giving it a regular charge, or leaving on trickle charge.

For your trickle charge use between 2.25 volts and 2.3 volts per cell, this will vary slightly with variations on the lead/acid technology used buy the manufacturer, but use no more than 2.3 volts per cell or damage may be done.

Bear in mind this:

Whilst NiCd cells deteriorate with number of charge cycles, Lead Acid's will deteriorate with time even when kept on a trickle charge, that is why critical applications (such a as fire alarms / emergency lighting units) recommend replacing the batteries every few years. This replacement accounts for a large percentage of 'second hand' SLA batteries found in boot/jumble sales.

 

[Willmore]

For SLA cells, if you want to do it right, and you seem to, you need to get data sheet for the battery from the manufacturer. Due to the slightly different electrode construction from brand to brand and models within a brand, the specific per-cell voltages are different.

If you want a quick and dirty solution that will work perfectly 95% of the time, you will probably not go wrong with a LM317 as Doug said.

If you want to use the chips that you have, snuffy gave you a good lead, aa is a good place to go for boards/kits.

I have a box full of the gates D and X sized individual cells, so I built a charger for them years ago with a pair of 317s. One as a current limit and one as a voltage limit. Works fine. But, you need to know the exact cell voltages to limit to. Fortunately, Gates is really friendly and provides all of that information on their web site and will send you a nice pamplet if you call and ask. It shows the different voltage thresholds as well as each of their temperature coeficients. They also list a number of charging/charge mainentance schemes. Very much recommended even if you're not going to use their cells--just as beneral background and theory of operation.

Hamfests are a great source of SLAs. I got an 80Ah cell for under $1/amp. /ubbthreads/images/graemlins/smile.gif Smaller ones can be had for similar priceing. Oh, and that cell was *new*. Used, you can get better deals. As UK Owl points out, there are a lot of exit sign/emergency light swap-out cells available. The protocol for when they get swapped out is when they're estimated to be at 80% of new capacity. Since that's a conservative estimate.... /ubbthreads/images/graemlins/smile.gif