Well I have the NiMh high power cells coming this week, too late for the eneloops. BTW Do they come in Sub C?
The charger is the Sunpak original n I was told by others that have upgraded to NiMh it works just fine.
Anyway, I'll just keep an eye on the temp as I time it to see how long it takes to get em up to 100°F, I was told that is the cut off threshold for these cells.
A smart charger is another posability n adapt it to my cell pack configuration?... That's a great idea!
Thanks for the ideas.
If you don't use a smart charger, you *will* destroy the cells from overcharging. Temperature protection is one factor only; you need to cease charging at the correct time, which is when the cell voltage reaches its peak and then drops by 5mV. If charging doesn't cease then, the cells will be reduced in capacity and the pack will have a short life. If you charge at a low rate (12-hour), the cells should barely warm at all and that will give them the longest life. If you charge rapidly (1-hour rate), the cells will heat a lot, their life will be shortened and they will receive only a fraction of their full charge before hitting 37C.
You can build a higher-voltage smart charger to charge the whole pack but for balancing reasons, it's much much better to do it cell-by-cell. Since you're already into hacking up battery packs, I suggest you put a little 8-pin plug in there that allows you to wire the four cells individually into a 4-cell smart charger with a cable. The pack will last a lot longer and hold a lot more energy.
If I were building a battery pack now, I'd use 18650 lithiums.
Last night I was looking at a smart charger I have laying around. I opened her up n was surprised how much electronics there are in this thing.. very impressive system.
It's a 4 cell meant for C size NiMh batteries that does em as 2/pair, not 4 in series. I also noticed it doesn't have any temp sensors in the compartment, it must have a different feedback system based on load n voltage. Well my batteries are arranged as 2/pair so I'm going to hot wire the outputs to the original charger's holder where my cube fits (disconnect the internal jumper) and do em like that.
Hi Paul! Like Polygot said I read the document at the Energizer website they do recommend to charge cell by cell individually rather than charge them in series. The charger does several things to monitor the amount of charge. It checks to see if the voltage started to fall then it's full and also if the temperature raise rapidly then it's full. They do say that if you do not have the ability to monitor the charge like these smart charger then charge them at 10 hr rate so that there is less chance of over charging them. I wonder the sub C cells that you're getting what's the mA rating on them? I have found a lot of C and sub C NiMH cells that the capacity is about the same as AA cells although they are much bigger.
If you have a 2x2 smart charger you can directly wire up to the pack, that'd be the perfect option - no need to have jumpers/switches to separate the pairs for charging.
All that electronics is usually a microcontroller running a PWM buck converter (current control) and ADC (voltage monitoring) for each set of cells. Actually there are some neat integrated charger-in-a-chip solutions you can buy now that do everything but a lot of the good chargers still do it all explicitly: bit of a combination of manufacturers selling stuff on fancy features like mAh logging and not-invented-here syndrome.
The cells I ordered are 3300mAh NiMh...
They are tack welding the tabs for me as well in pairs so all I have to do is drop em in. I wire4d up the smartcharger I have to my cube n that will work out just fine. This charger has a very populated circuit board, no doubt computerized.. looks way too advanced except the standard transformer and rectifiers, standard entrance power source although with regulators before the PCB. I'm impressed. I had this thing in my closet for years, never used it.. actually never knew I had it till now.
Problem solved! Always good to work these things out with others.