is there a way of charging one of these or a smaller one from a car cigarette lighter
charging battery
- Thread starter 333rocky333
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Yes, but only when the vehicle engine is running.
That would be ok, it would charge between jobs, when needed, it dont need fully charging, just enough for the occasional use to test 12 volt Led strips, to determine they are ok before ordering new drivers
Why that approach (or do you perhaps also have other uses in mind?)? ... much smaller, lighter and cheaper than a lead-acid battery ...
Kind Regards, John
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I have loads of the batteries various sizes, from alarm panels and emergency light units, some still good, some are physically really small, rather than scrap them, I could keep 2 on the van, just for when i need instant 12 volt DC.
I also have loads of mains to 12 volt units, but its not always ideal to run mains leads around, or turn circuits off to wire one in, so would prefer something I can just crocodile clip on to the 12volt tails easily, as they are usually poorly accesible.
I dont want to run around getting drivers, to return and find the led strips faulty too.
I also have a 12 volt chargeable led light,that when flat i have a made up lead that i can plug these batteries in to use the light, till I get to charge it.
At the moment I use one battery till its dead then use another and on and on, but I would prefer to just use two smaller ones
what would happen if I used a fused plug in lead that outputs 12 volt fom the car lighter socket, maybe need a diode and a few bits
Im not fussed if it shortens the life of the battery as i can just use another one when it happens.
I also have loads of mains to 12 volt units, but its not always ideal to run mains leads around, or turn circuits off to wire one in, so would prefer something I can just crocodile clip on to the 12volt tails easily, as they are usually poorly accesible.
I dont want to run around getting drivers, to return and find the led strips faulty too.
I also have a 12 volt chargeable led light,that when flat i have a made up lead that i can plug these batteries in to use the light, till I get to charge it.
At the moment I use one battery till its dead then use another and on and on, but I would prefer to just use two smaller ones
what would happen if I used a fused plug in lead that outputs 12 volt fom the car lighter socket, maybe need a diode and a few bits
Im not fussed if it shortens the life of the battery as i can just use another one when it happens.
Last edited:
Fair enough.
I dont want to run around getting drivers, to return and find the led strips faulty too.
A diode would stop your battery discharging itself by trying to run anything in your car, but there would be little risk of that happening whilst the engine was running, anyway.
If you literally just connect your battery to the cigarette lighter, in the absence of any regulation/control circuitry you will be totally at the mercy of the voltage (at the lighter) whilst the alternator is running to determine what current will be pushed into your battery.
Kind Regards, John
Would that be a problem
I notice my rechargeble light seems to take 12 volt power from the lighter, it has an led on it, if left plugged in, when the ignitions off the led changes colour I asume from the feed back from the lamp, this also turns the radio on
Hard to say. If it resulted in the battery getting seriously overcharged, I suppose it may get hot (or worse), and it's life could be reduced (although I realise that doesn't really matter to you).
Exactly - that's what a diode would prevent happening. So long as the engine running, the 'supply voltage' is (because of alternator) almost inevitably always going to be higher than the voltage of your battery, so current would only be able to flow into the battery, even without a diode. When the engine is off, then, in the absence of a diode, your battery would be attempting to run anything that was still connected to the circuit (like your radio). A diode would prevent current running in that direction.I notice my rechargeble light seems to take 12 volt power from the lighter, it has an led on it, if left plugged in, when the ignitions off the led changes colour I asume from the feed back from the lamp, this also turns the radio on
Kind Regards, John
I value your opinion John, what I intend is using one of my old phone leads and fit just a 1 amp fuse, I will fit a diode in the plug somehow,what size/type do you suggest, I will limit plugging it in to about 10 minutes a week just to give it a boost and see how it goes.
Is that low risk do you think
Is that low risk do you think
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First thoughts on this suggestion. A cigar lighter socket generally has around a 20A fuse. I'm not aware of what protective circuitry there might be but lets say there is a bare car battery available, and you connect another to it. I'm not sure how much current can flow but it must be at least 20A we have to assume. This diode will have to be rated at say 40-60A for the fuse to stand any chance of protecting it. At 20A, and assuming it is a Schottky diode it will also be dissipating approaching 20W which you have to get rid of with a large heat sink.
I'm not saying I know the answer, but I think this may need a bit more thought. Such as a current limiting circuit.
I'm not saying I know the answer, but I think this may need a bit more thought. Such as a current limiting circuit.
You might want to first try to ascertain what are the current-supplying capabilities (and fusing) of the cigarette lighter socket. I suspect that (if the socket could provide it), in the absence of any current control the battery would probably draw a lot more than 1A if it were fairly flat, so you might need a significantly larger fuse than that. If I connect a fairly dumb cheapo charger to a fairly flat lead acid battery, the initial charge rate is often usually 4-5A.
Any power diode you can find will have an adequate voltage rating. In view of above comments, I'd be inclined to suggest a current rating of at least 5A, probably ideally 10A ... at a quick glance, maybe something like this (albeit only 6A). However, as I said, if you're never going to leave it plugged in without the engine running, you probably don't really need a diode.
Kind Regards, John
The plug that goes in the lighter socket, has a fuse in it usually a 20mm one, I was intending putting a 1 amp in that and the diode after that
Edit, john suggests a bit higher
As Detlef and I (even more so Detlef) have suggested, I think that a 1A fuse would probably blow immediately, particularly if the battery was anything approaching flat. Charging batteries without any current control/limitation is always going to be a bit iffy. Don't forget taht a fuse is merely a protective device - it can do nothing to limit current other than stopping it completely!
Kind Regards, John
Thinking about it can I just charge them at the weekend using a proper car battery charger
Also, don't forget Kirchoff's second law. "Around any closed circuit, the sum of the EMFs is equal to the sum of the IR products." Your car battery and the alarm battery both have internal resistances, and thus, when connected in parallel (via the lighter socket) and the engine not running, there will be a circuit between the two batteries. One will discharge the other, if your lighter socket is permanently live.
Going back to the comment regarding the radio, this could be because the alarm battery is allowing the radio to "see" +12V through the lighter socket (if it is ignition-switched) when the ignition is off.
Going back to the comment regarding the radio, this could be because the alarm battery is allowing the radio to "see" +12V through the lighter socket (if it is ignition-switched) when the ignition is off.
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