Cordless charger question

[Timleech]

Following on from the Crimbo presents thread -

 

I have a cheap cordless multi-tool, with a '12 volt' battery.

Charger consists of a 'wall wart' with output listed as '12V DC 400mA' which plugs into the battery charging receptacle, this is a little box with one red LED, charging time is 4+ hours.

 

Question - what are the chances of it working OK, vs self-destructing, if I plug the charging receptacle into a 12V Dc supply on the boat? My boat is 24V, I have a '12V' socket fed from a 24-12 converter which gives a regulated 13.6V out, no doubt something else could be found to give closer to 12V for not too much money, if needed?

 

Thanks

 

Tim

[Nickhlx]

Following on from the Crimbo presents thread -

 

I have a cheap cordless multi-tool, with a '12 volt' battery.

Charger consists of a 'wall wart' with output listed as '12V DC 400mA' which plugs into the battery charging receptacle, this is a little box with one red LED, charging time is 4+ hours.

 

Question - what are the chances of it working OK, vs self-destructing, if I plug the charging receptacle into a 12V Dc supply on the boat? My boat is 24V, I have a '12V' socket fed from a 24-12 converter which gives a regulated 13.6V out, no doubt something else could be found to give closer to 12V for not too much money, if needed?

 

Thanks

 

Tim

 

 

I would say it is only likely to be a cheapo unregulated wall wart anyway and the current limiting is probably likely to be the internal impedance of the wall wart and a resistor... so charging at a slightly higher voltage will mean it gets charged a bit faster than at "12 volts"

 

If you were able, you could see what current it is being charged at ( put ammeter in series) by the wall wart, and see what it is when powered by the boats 13.6 volts ( or a bench power supply with volt / amp meters ?)

 

The "proper way" would be to open it up, see what cells are being used and their capacity e.g. AA cells and 1500 mAh and arranging to charge at say C/10 to C/20 via suitable series resistance. Slower would be better if left on 24/7 when not using, but faster would

be better if you use a lot and remember to remove from the charger when "charged" - i.e. when the cells begin to get warm

 

Nick

 

 

[Bob18]

I've taken two of those wall warts to bits.

One was nothing more than a transformer and a rectifier, with a protective fuse buried inside the transformer.

The second was a very clever "box of tricks", being a switched mode power supply, with both current and voltage control, and a fuse, not buried inside the transformer but sensibly placed so that it could be replaced (once you'd taken the wall wart to bits).

Both were for the same (expensive) manufacturer's power toys, and interestingly both the battery holders had a very similar current limiting circuit in them. Replacing the fuse in the "clever" wall wart allowed me to wear out the drill that went with the thick wall wart, its batteries were still up to scratch, but the gearbox was tatered so the drill went to the big drill-farm in the sky.....

 

Lesson, you can't be sure what sort of wall wart you've got....

 

Going back to the question, given the current limiting I found I would be fairly happy to use a boat "12V" supply, but only for short term re-charging and only then if I kept an eye on the battery temperature, not leaving it to cook somewhere for days (or even hours) on end.

[Timleech]

I've taken two of those wall warts to bits.

One was nothing more than a transformer and a rectifier, with a protective fuse buried inside the transformer.

The second was a very clever "box of tricks", being a switched mode power supply, with both current and voltage control, and a fuse, not buried inside the transformer but sensibly placed so that it could be replaced (once you'd taken the wall wart to bits).

Both were for the same (expensive) manufacturer's power toys, and interestingly both the battery holders had a very similar current limiting circuit in them. Replacing the fuse in the "clever" wall wart allowed me to wear out the drill that went with the thick wall wart, its batteries were still up to scratch, but the gearbox was tatered so the drill went to the big drill-farm in the sky.....

 

Lesson, you can't be sure what sort of wall wart you've got....

 

Going back to the question, given the current limiting I found I would be fairly happy to use a boat "12V" supply, but only for short term re-charging and only then if I kept an eye on the battery temperature, not leaving it to cook somewhere for days (or even hours) on end.

 

The wart is reasonably heavy, as these things go, so I suspect a transformer.

The battery receptacle, on the other hand, is as light as a feather (and is screwed together, so I might sneak a look inside. The wart is glued up).

 

 

Thanks

 

Tim

 

Edit - just had a quick peek.

 

There's a little PCB with three diodes, one transistor, an LED and four resistors. There are three connections to the battery. I can post a pic if anyone is really interested.

Tim

Edited November 4, 2012 by Timleech

[Nickhlx]

The wart is reasonably heavy, as these things go, so I suspect a transformer.

The battery receptacle, on the other hand, is as light as a feather (and is screwed together, so I might sneak a look inside. The wart is glued up).

 

 

Thanks

 

Tim

 

Edit - just had a quick peek.

 

There's a little PCB with three diodes, one transistor, an LED and four resistors. There are three connections to the battery. I can post a pic if anyone is really interested.

Tim

 

 

Three terminals on the battery suggests a temp sensing terminal, so, perhaps with the transistor, a crude end of charge device ?

 

Nick