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Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
hey ya'll, I have a 12V 3.4 Ah SLA battery, but my charger isn't working (it never really was made for high capacity batteries, but it worked for my other SLA which is dead now)
I'm going to see if the garage down the street will toss it on their charger for about 30 minutes tonight, but for future reference what is a good way to charge one of these things without a purchased charging unit? - from what I understand they need a lot of current, and ones at the store are expensive
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
I've liked this charger design I was using it on fairly old batteries so I wouldn't know how it would behave on newer ones. I just set it to supply between 13.8 and 14V and watched the current.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
I think there is nothing (except time) gained by charging lead-acid batteries at a high current.
Here's a description of a "smart charger" with about 2 active components, which kept my bicycle headlight battery in good shape for about 10 years. I'll follow up with a schematic, sooner or later.
1. Linear voltage regulator set for about 2.4 volts per cell, plus the drop of a series diode to protect the regulator against loss of input voltage. (I think the diode in Myke's link achieves the same goal).
2. Current is coarsely limited to about C/10, by choice of wallplug transformer and a series resistor upstream of the regulator.
3. Output current is sensed by voltage drop in, I think, a series resistor between negative supply and the regulator/battery negative. When charging current falls below about C/100, a comparator flips. That changes the state of an LED, and drops the regulated output voltage to a "float" level of about 2.25 V/cell, which can be maintained forever. Hysteresis is inherent.
Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
I have successfully built a L200 design very similar to the mike's link. The schematic I got from the datasheet of the L200. It's a voltage regulated power supply with current limit.
Slow charging is the way to go if you want you battery to last. Mine 12 V 7,2 Ah battery I charge with 0,5 A peak current.
I can recommend you the L200. It's very difficult to damage this IC and it proved to be reliable. But I had to supply 16 V to this charger work good, ending up with a 18 V 2 A transformer.
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
I'm just completing an intelligent SLA charger based on a UC3906N design - the base design is not mine (N5BiA, Bill Buoy) but I've reworked it for current parts and done a new PCB for it. It seems to be going well, I've just not got round to documenting it yet.
The reason? I have about 20 really nice 2yo SLAs from an APC UPS that was never used. They need TLC...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've always charged SLAs using a bench power supply with the current limit set to C/4 and the voltage set to 2.4 volts per cell. Leave it overnight and it'll be ready in the morning. This is similar to Klugesmith's recommendations, and I also got good service powering bike headlights. But you can't leave it on indefinitely because it doesn't have the voltage cut-back feature.
Don't use a car battery charger, that's the surest way to wreck them! Cheap car battery chargers are just a transformer and rectifier, there's no voltage regulation, and that will gas a SLA to death by overcharging it.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I use Hawker Cyclon 2V 5AH SLAs quite a lot, and do the same as Steve, charging from the variable constant current output on one of my bench PSUs. Besides not having any more room for yet more kit, the advantage of this option is that one can charge at rates dictated by mood and circumstance, so NiCADs, NiMH and what have you, can all drink from the same fountain, as slowly or as quickly as you please.
I'm sure that many rechargeable batteries and accumulators are sent to an early grave by 'quick charging' ready-to-wear battery chargers, so I like to charge just as slow as you please, so my sleep is not disturbed by gurgling electrolytes, hissing vents, and arcing between buckled plates.
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
Steve McConner wrote ...
I've always charged SLAs using a bench power supply with the current limit set to C/4 and the voltage set to 2.4 volts per cell. Leave it overnight and it'll be ready in the morning. This is similar to Klugesmith's recommendations, and I also got good service powering bike headlights. But you can't leave it on indefinitely because it doesn't have the voltage cut-back feature.
I've done this in the past, however the UC3906 drops back to float mode at the end of the charge, so that you can leave the charger and forget about it, i.e. it's happy to be permanently connected (designed for that).
My problem is that I've so many things on the go, I forget about stuff and to be honest, am just not in the workshop enough to keep an eye on things...
The design I ended up using conditions the batteries nicely and leaves then topped up all the time - I intend to put it in an old ATX PSU case. Total cost was about GBP 15 to build, including a small toroidal transformer, so not too bad.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Proud Mary wrote ...
I like to charge just as slow as you please, so my sleep is not disturbed by gurgling electrolytes, hissing vents, and arcing between buckled plates.
My sleep was once disturbed by a huge explosion and clouds of foul-smelling steam.
I was charging a big Ni-Cd pack made of eight 4/3D cells, inside a metal box that I built for it. One of the cells overheated and bulged, and this caused the rest of the pack to get jammed hard against the box, damaging the insulation, shorting it and exploding several other cells.
If I remember right, I put the smouldering mess out on the window sill and went back to sleep.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
Steve McConner wrote ...
I've always charged SLAs using a bench power supply with the current limit set to C/4 and the voltage set to 2.4 volts per cell. Leave it overnight and it'll be ready in the morning. This is similar to Klugesmith's recommendations, and I also got good service powering bike headlights. But you can't leave it on indefinitely because it doesn't have the voltage cut-back feature.
Don't use a car battery charger, that's the surest way to wreck them! Cheap car battery chargers are just a transformer and rectifier, there's no voltage regulation, and that will gas a SLA to death by overcharging it.
really? - I never had a problem with a car charger set at a low setting and watch the meter, at least with my former SLA which lasted me for over four years (and that was the only way I ever charged it, and it is how we charge similar SLAs on our farm for our lawn mowers, go-karts, etc) - I just always use between 2-5A depending on the battery (I used five for my former battery as it had a chigher capacity and I needed faster turn around) in this particular case I used two Amps for about 20 min. just to get enough charge to testm, but ironically I got a phone call which needed my attention and I left it running, so I have to charge again anyways! But, my school should have a charger so my form master can probably help me out
And thanks for all of the replies! - I'll need a more proper, and compact, charger for the future and always wanted to build one rather than spend the money on one
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SLA Battery Charging
Cheap car battery chargers are just a transformer and rectifier, there's no voltage regulation, and that will gas a SLA to death by overcharging it.
