Charging SLA Battery in car

I have a 7ah SLA battery. Can I charge it directly from the 12v cigarette plug? I want to build a 12v cigarette plug to alligator clip adapter and just hook them up to the battery. I know I would have to watch and not leave it there all the time. Will it harm the battery?

Thanks for the info.

I wouldn't recommend it.

A lighter socket is usually 10amp , and if the sla battery has a low voltage you could easily exceed this as the current rushes through the wiring to equalise (as current wouldn't be limited). This would likely blow a fuse or possibly melt wiring.

There also the chance that you will short the clips with the same result. Better solution is to fit a female socket on the sla and get a 'lighter-lighter charger' which will limit current and be fused.

I would second that: Don't do it.

Even a "lighter-lighter charger" probably isn't going to be current limited to the point where it's appropriate for a little 7Ah battery. (If you don't care about your SLA battery, well that's another matter.)

you really don't want to charge 7ah battery with 10 amps, usually sla of that capacity charged with 500ma for 18 hours, slas don't take fast charge well.
boosters that have 7-15ah batteries inside can be charged with cigarette plug, (car chargers are included in the box) but usually there is a big sand resistor in there to limit current, or in good quality boosters circuit board.

one other thing even worse.... charging an SLA while running the engine it would be like a 100 amp alternator trying to charge a 7amp battery. Think about charging a nimh AA at a 30 amp rate or a 4 minute fast charger and you will get the idea.

Lynx_Arc said:

one other thing even worse.... charging an SLA while running the engine it would be like a 100 amp alternator trying to charge a 7amp battery. Think about charging a nimh AA at a 30 amp rate or a 4 minute fast charger and you will get the idea.

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Well the 100A alternator isn't a problem, but the increased voltage (say 14.5V instead of 12.6V) will result in a higher charge current on top of it all, yes.

core said:

Well the 100A alternator isn't a problem, but the increased voltage (say 14.5V instead of 12.6V) will result in a higher charge current on top of it all, yes.

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I realize you won't probably won't get 100 amp into it but... if the battery for some reason is damaged and shorted it has the potential to draw a lot more current at 15v than directly off a car battery at ~12.6v.

Ready said:

I have a 7ah SLA battery. Can I charge it directly from the 12v cigarette plug? I want to build a 12v cigarette plug to alligator clip adapter and just hook them up to the battery. I know I would have to watch and not leave it there all the time. Will it harm the battery?

Thanks for the info.

Click to expand...

Can't you just use a 12 volt charger or a trickle charger at home.

Some people with caravans use a system that will charge a second 12V battery that can be used to power lights etc in the caravan ... They use a diode in the circuit to prevent the caravan from discharging the vehicle battery ... Perhaps a visit to a caravan shop will provide you with the necessary parts.
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march.brown said:

Some people with caravans use a system that will charge a second 12V battery that can be used to power lights etc in the caravan

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Caravan? I actually had to look that one up just now. (Caravan == Recreational Vehicle for you USA people) Yeah, the setup you're talking about I would call a "house battery". I'm not sure any RV charge controllers can be set to such a small current limit though. I could be wrong.

To the original poster: I think your best bet is to just get a compact hobby charger (they all accept 12V input) and do it right. What's that little Accucell going for now, maybe $20?

How do you charge your SLA at home? It's quite likely whatever you use to charge it runs on 12V, no?

march.brown said:

Can't you just use a 12 volt charger or a trickle charger at home.

Some people with caravans use a system that will charge a second 12V battery that can be used to power lights etc in the caravan ... They use a diode in the circuit to prevent the caravan from discharging the vehicle battery ... Perhaps a visit to a caravan shop will provide you with the necessary parts.
.

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you could use one but there is a chance it charges at too high of a rate to be good for the SLA in the long run as it may be designed for charging large lead acid batteries instead of smaller ones.

I can't imagine you don't have at least ONE 12V wall wart, it it puts out 100mA-1A you'll be set. Just stick it on there over night, THough I'd do it outside, I've smelled SLA's leak not nice.

Hrmmm...

Are we talking about needing to charge a 7Ah SLA from a vehicle or do you just need a way to charge it period, and you thought going out to the car would be the easiest way?

Hello Ready,

I do it all the time...

I have a jump pack that has a gel cell battery in it. I use the compressor to charge up my tires. After using it a few times, I check the voltage and when the battery gets low, I hook up the 12 volt adapter and charge the pack battery while I am driving.

Your battery is smaller than mine, but if you watch things it should be OK. Mine tests out to 16 Ah, and it takes 4 - 5 hours to charge it. I estimate the charge rate to be in the 2.5 - 3 amp range. This may be a little high for you battery, but other than reduced cycle life you should be OK, as long as the charging system on your car is in good condition.

Do I recommend doing this? NO. Look at all the reasons that others have posted to understand why. However, if you pay attention to the charge it is possible to do it and do it with some safety. A good place to start thinking about this is to evaluate what would happen if something went wrong, and take measures to contain any possible damage.

Tom

SilverFox said:

I do it all the time...

I have a jump pack that has a gel cell battery in it. I use the compressor to charge up my tires. After using it a few times, I check the voltage and when the battery gets low, I hook up the 12 volt adapter and charge the pack battery while I am driving.

Click to expand...

Tom, have you assembled your own charging method for your jump pack, or what exactly are you connecting? Running 12V to the jump pack through its intended charging jack is a whole different ballgame than directly connecting 14+V directly to the terminals of a SLA battery!

Wow so many answers. Yes I was wanting to charge it from the vehicle while driving. I forgot about the high amps being a problem.

I don't have a hobby charger for them yet. I have been using a foldable solar 12v 6w panel to keep them charged.

I do have wall warts but I guess I would have to watch them and not leave them on there too long, since they don't have any trickle capability, is that correct.

I had been looking at this one:
http://www.batterymart.com/p-12v-1a-sealed-lead-acid-battery-charger.html

But I also wanted to have a way to charge in the vehicle to top them off before I get to a campsite or something.

Thanks for all the replies and help.

Hello Core,

My jump pack has a 12 volt adapter that attaches directly to the battery. One option for jumping a vehicle is to simply put the jump pack in the vehicle and hook up the packs 12 volt adapter to a 12 volt adapter in the vehicle. This put the jump packs battery in parallel with the vehicles battery. You wait for the charge to equalize between the two batteries and then start the vehicle.

The size of the wires and fuses in the vehicles 12 volt adapter circuit limit the amount of current that flows when using this method. It is quicker, and sometimes more effective, to use the heavy gauge jumper cables built into the jumper pack and hook them directly to the battery. After the vehicle starts, if you leave the jump pack hooked up, its battery will be charged by the vehicle charging system but there isn't usually enough room to leave the jump pack hooked up while driving down the road.

The jump pack also has a charger built into it that runs off of household AC, or you can charge its battery using another battery charger connected to either the jump cables or to the 12 volt adapter.

The jump pack battery charges to 14.1 volts when charged from my vehicle, and 14.4 volts when charged from its built in AC charger.

Tom

Sorry to bump this, but SilverFox mentioned charging his jumpstarter directly from the car, care to elaborate the setup?
I'm currently trying to figure out how to float [again, not charge but float] about 18AH worth of SLAs directly from the car. Currently the concept is simple, A fuse, a TVS, a 3A forward diode feeds a capacitor bank filled with everything from 0.01uF to 3300uF. That then feeds a 9-32Vin 15Vout Cincon DC/DC converter.
Since the converter is only 10W at 15V, two 1N4001 diodes are used to drop the voltage to around 13.4V. On paper it seems plausible, but on the car an array of problems is causing it not to work as intended. Namely the noise interference which I suspect is radiating from the converter.

Hello Illum,

My jump starter has a 12V plug receptacle built in and a cord that allows me to plug it into the cars 12V system. I simply plug it in and drive to top things off. I do NOT leave it hooked up beyond the time it takes to drive to my destination.

If the battery in the jump pack was discharged, I would first hook the jump pack to the cars battery with the engine off and let the two batteries equalize. This takes 15 - 20 minutes. I would then start the car and let it run for about 10 minutes. This would put a "quick" charge on the battery in the battery pack. This raises the voltage to a point where current drops off and there is no problem hooking up to the 12V receptacle in the car would present any problems.

After this "quick" charge, driving to my destination completes the charge.

Tom

Remember in the old days, we used a bulb in series with the charging circuit to limit current?

Norm

I do the same here that silverfox related, mostly when I have to, on the go. When I am home, i would use a normal charger or hobby charger. I have a Male-Male car cord, straight wired with fuses on both ends, so if there is any Tip (+) to ground connection that occurs, it is fused for it.

Then, I just connect it via the cigar lighter socket, and manually terminate. the cig socket is good for 10A usually, as long as the other battery is not Way low, it shouldnt be a problem. there is a lot of wire to get to the socket itself so there is already some resistance.

One of the cords I use has a Led light that is in the car cord connector, that one is much better, with the tiny led Indicator, I can tell if the connections are made, and if the fuse is broke or not. Another trick was to put one of those Car Cord Automotive testers on the end of the cord. That end plugs into the battery, and can give an estimate of the voltage or charge state.

This year, china has a Cig lighter automotive tester that actually shows a Voltage, would make a good end of a car cord. that and those cheap voltmeters that will run off the power that is already there. with stuff like that, seeing the charge state and voltage would be much better.
With a 6-10foot charge wire, and via the resitance in the car cig lighter already, if the "metering" device plugs into the small battery it will mostly read the battery itself while charging. so although it is reading Both the car voltage and the battery voltage, it is still closer to reading the battery, and works ok. If i then disconnect the One side going to the car, I can read the battery only.

the one i used before was the radioshack auto alternator charging thing , has 3 lights used in combo, red =low , red+yellow =med , Yellow=ok and green was charging or charged. Simple quick Interpretable idea of the charge.
A Pic of that one here http://www.google.com/imgres?imgurl...a-MK-jriwKvkIGwCQ&itbs=1&sa=X&ved=0CDcQrQMwBQ

And something like this , is what i would use now http://www.amazon.com/dp/B007CT6510/?tag=cpf0b6-20 Just as example pictures because they are not so easy to find using search http://www.amazon.com/dp/B0092KVYGI/?tag=cpf0b6-20