NiMH Battery Charger as Dump Load

[DamonHD]

It's a little thing, but it pleases me because it avoids wasting some off-grid solar energy and helps ensure that we always have some AA/AAA cells charged up for gadgets...

I bought today a Maplin N42FK AA/AAA NiMH battery charger that can run from in a car (at 12V) and that has a timer and -deltaV cutoffs, ie should be safe to leave completely unattended with batteries in. It has a charge-state indicator which should help us know when the NiMH cells are full so that we can take them out and put them in out 'charged' box and rotate others in from out 'uncharged' set.

I have put this downstream of my LVD which was no longer being used for the laptop now that I am using the SheevaPlug for my server. The idea is that when the off-grid SLA battery is full-ish (and charging) then excess energy will be diverted to charging any NiMH cells in the charger. (Also the server will ramp up its consumption at its own chosen voltage thresholds as additional 'dump load'.)

This means that when there's excess off-grid solar energy available we can use a little of it recharging NiMH cells semi-automatically and when there are none there or they are charged then the server gets to use all that it can. In any case we waste less of what is available and 'free'!

Plus the charger came with some of the 'hybrid' NiMH cells, which have a lower-self discharge and that I want to try out.

Rgds

Damon

[DanG]

The new NiMH marketed now utilize a different separator membrane that takes up more room so the capacities have declined 15%~ but nothing for common consumer rechargeables compare!

I've retired all the NiCad & old style NiMH in this household, and now have:

1) Digital camera that always work.
2) C & D cell LED MagLites running off AA's w/ reducer sleeves that just keep lazing away hour after hour.
3) Solar yard & path lights that impress the neighbors even on the 8-hour-daylight cloudy days of winter.

Two things to be wary of is temperature and dropping cells. Its pretty common for NiMH's to vent steam and they have excess electrolyte provided for a few too-hot cycles but its a sure way to kill the cell. Fast chargers have 'token' built in cooling fans but the cooler you can keep them on the charge cycle the longer they will last. So far the only way I've seen my rechargeables meet end-of-life is by them managing a 4-foot suicide leap to a hard floor - fumbling a handful and dropping them won't kill them outright but a few weeks later they get rejected by 'smart chargers'...

[DamonHD]

Thanks for the tips: I would not have guessed that dropping NiMH cells would be terminal!

I have just a couple of devices that insist on 1.5V cells and will not function properly or at all on NiMH, but the rest seem fine.

Rgds

Damon