OT: Rechargeable battery pack for toy

[Mark]

Hi,

I've bought a toy train for my son and am having trouble getting it to work so maybe someone can shed some light on the matter ;-)

I'm sure it's the battery pack that is causing the trouble. The batteries (NiHM) come in a pack which plugs into a charger and then into the train. Judging from the appearance and the voltage of the pack I am sure it contains 4x standard AA size NiMH cells. There is some corrosion on one terminal which looks like the end of a cell that has leaked some of its contents. Therefore it is unlikely to work as is.

The charger and the pack have three terminals - one labelled (+) and one labelled (-), no suprises there! However there is a third unlabelled terminal. Can anyone tell me what this is for? The charger has contacts for all three but the train receptacle only has contacts for +/-.

I am thinking of pulling the pack apart and placing some new cells in there but I was hoping to retain the charging method for convenience.

TIA, Mark

[Nick]

Hi Mark,

The cells have probably leaked - you can buy tagged NiMH cells to replace and just solder up (or get someone else to. The third terminal is for the charger to sense when charging is complete - there is a device in the battery pack which provides a suitable signal to the charger to tell it to switch off or drop to trickle. Transfer this device to the new cells / pack - its probably just a thermal switch but could be a semiconductor device - either way, use it and check you have it the correct way round in case it is a semiconductor device.

Nick

[Dave Plowman (News)]

Commonly a heat sensor - the charger looks at that to avoid over cooking the batteries.

[Mark]

Thanks for the info. I'm not sure what "tagged" NiMH cells are - is there a difference from ordinary AA ones?

I did get the pack to work in the end however - I guess there was a bad contact with the train and the charger.

I've never had rechargeables leak before - is this unusual?

Cheers, Mark

[chris_doran]

Tagged cells have little metal strips spot-welded to the ends instead of the flat end/button of those intended to go into sprung holders. It's much easier to solder to the tags than the huge thermal mass of the body. IME soldering to the body has a good chance of destroying the cell no matter how you try to cool it. Tagged cells are hard to come by, though.

Chris

[Bob Eager]

CPC have them....BT03140.

[john2]

o cool it. Tagged cells are hard to come

Or Maplin have them in their retail shops. £2 each approx.

[Dave Plowman (News)]

Maplin sell tagged AA cells - even my local one has them in stock.

[Mark]

Mark

[Bob Eager]

CPC ones are 1550.

[Mark]

What about the Maplin ones?

Mark

[Chris Bacon]

>> What capacity are they (mAh)?

Up to 2 Ah:

[Mark]

>>> What capacity are they (mAh)?

with size 'AA' and different capacities.

Lower down there is a list of stock and prices but it does not say which is which.

Mark

[Bob Eager]

Dunno. I gave up on Maplin when they went 'consumer'. Was just following up my bit!