Stealth MC60BP Battery Question

[PlayboyJoeShmoe]

I was very nicely given a MC battery Stick to play with.

I was going to seperate the batteries for charging, but have another idea.

If I make a cradle with contacts (like I did for some salvaged Lithiums) could I not charge the stick, using the right Walwart Votage/mAh and common sense?

And if so, what voltage/mAh would the superior brains here suggest???

 

[Ginseng]

PBJS,

I'm guessing something between a 6V150mA and 7.2V200mA wall wart might serve the purpose. Not sure though since the MC cradle uses a constant current circuit to give the pack the voltage it needs at 215mA.

Wilkey

 

[PlayboyJoeShmoe]

If I do it based on a time period based upon 1.5x the capacity (as I read on a linked website) that should work yes?

Since it's a 2.5aH stick, 250mA for 15 hours or so should do it?

Will I notice heat when it gets close to full?

 

[RussH]

PJS, I use 1.4 x C (or the percent of C that I think I have used) as a rough guide for a recharge time. That has been the standard for NiCad and NiMH for as long as I can remember (hence the 14hr. charging time recommended in most instructions for dumb chargers). That should be plenty, charging efficiency is normally assumed to be 80% or more, at least as long as you are not looking at really high recharge rates. That implies that 1.2x is enough, but also consider that the batteries are probably only 80% efficient in discharge also.

In reading manufacturer recommendations, it appears that charge rates below 10% C (like your 250ma for a 2500mah capacity) aren't very harmful even for NiMH. This is OK if you just can't use a smart charger. Even at .1C, the batteries should get warm when they are done. Sometimes they get warm for a while (30 mins.) and then cool off if the charger drops to a tricle charge. A lot of 'dumb' chargers have a low enough output voltage that the charge rate drops off above about 1.45 volts per cell. Then the cells may cool off again with the corresponding lower current.

My preference for this type of 'dumb' charging is a $7 Maha 2A4 which has either a 50ma or an 80ma charge rate depending on how you put the batteries in. Either rate is low enough to leave cells in all weekend to top them off. If they feel warm, it means they are fully charged but you can't always tell. IMHO, any overcharging will reduce the life of the cell somewhat, but it shouldn't be any great reduction in total life if only done occasionally or you are careful to keep it to a short period of overcharging.

I can't get too excited when the cells only cost $1. The problem is that mismatched cells (one damaged form overcharge, but the other 3 aren't) can result in one cell being reversed charged which causes problems in addition to ruining the reversed cell. I recently had one act like it was shorted and melt my 6AA holder. I thought it was a short, but I couldn't find anything wrong. The one battery had it's spring contact glowing cherry red.