Question For Electrical Guru's ;-)

[Dougal]

My large torch has a 6v (0.4Ah) lead acid rechargeable battery. Can I charge it with one of those little 12v > 6v gizmo's that plugs into the cigar lighter socket? It's got various voltage output settings from 1.5 up to 20 volts

 

[elton]

My large torch has a 6v (0.4Ah) lead acid rechargeable battery. Can I charge it with one of those little 12v > 6v gizmo's that plugs into the cigar lighter socket? It's got various voltage output settings from 1.5 up to 20 volts

No. Buy a 6V motorcycle battery charger.

 

[prv]

No. Buy a 6V motorcycle battery charger.

He doesn't want to charge it from 240v though.

Agree 6v won't push any charge into a 6v battery, but if his adaptor is adjustable then it ought to work. What would be a a suitable charging voltage for a 6v battery? 7.2?

Pete

 

[Fendant]

Think it is 7.2 Volt

 

[savageseadog]

It's fairly easy to drop a DC voltage down. Have a good look round ebay. There's two basic ways of doing the job by the way. You can use an analogue dropper which will generate a bit of heat, not efficient but simple electronics. The more complex way would be to use a switch mode or switching controller. Smaller, less heat, more efficient but more complex electronics.

 

[Jabs]

Set your adjustable voltage converter to 7.2v.
Feed the battery through a one ohm resistor.

Should work fine, but it may be slow to charge.

Does this matter?

Tony.

 

[JumbleDuck]

My large torch has a 6v (0.4Ah) lead acid rechargeable battery. Can I charge it with one of those little 12v > 6v gizmo's that plugs into the cigar lighter socket? It's got various voltage output settings from 1.5 up to 20 volts

Is it a sealed gel cell? If so, be very careful about charging it - use a proper charger if you possibly can. They only seem to come in 240V versions, so you may have to use an inverter too.

 

[Dougal]

It is a sealed battery. Its one of those Yuasa pale grey things. What a pain! Guess i should've just got a 12volt boat torch;-)

 

[JumbleDuck]

It is a sealed battery. Its one of those Yuasa pale grey things. What a pain! Guess i should've just got a 12volt boat torch;-)

I proper current-controlled multistage charger for 6V and 12V gel cells, running on a (nominal) 12V input would be a respectable seller, I think. YAPP?

 

[William_H]

The little SLA batteries can be recharged safely if you are prepared to give it a long charge time. ie small current. There are smart chargers for these with 3 stages of fast charge then float but sadly often only from 240vAC. I would suggest as said a regulator either switch mode or linear (LM 317T) will give a constant voltage set at about 7.2 volts or even less.
A simple series resistor from the 12v supply will give a constant current charge. The current is set by the resistor value. I would suggest 200ma charge current so about 35 ohms will give 200ma from a 12v battery on charge. This will give you 1AH in to the battery every 5 hours. This may be to slow for you. However you would still need to remove from charge when you reckon it has had enough. Faster rates make it more critical to turn off charge. A resistor and regulated voltage will give a safer but possibly even slower charge. Again depending on the series resistor value.
Whatever you do, do use your multimeter on amps to monitor charge current. Keep it a slow as you can. It is the overcharge and heating that will kill the battery. good luck olewill