View Single Post
Old Mar 20, 2011, 06:42 AM
abenn is offline
Find More Posts by abenn
Registered User
Letchworth, Great Britain (UK)
Joined Jul 2004
12,907 Posts
When a NiMh battery is fully charged it reaches a peak voltage, somewhere around 1.5v per cell, but can be as high as almost 1.6v per cell.

Because different brands and size have slightly different peak voltages (depends on condition too, I suppose), it's impossible to make the charger cutoff at a precise preset voltage, like we do with LiPos. Instead, NiMh chargers rely on the fact that after they're fully charged, if you keep on charging them, the voltage of an NiMh pack will actually drop slightly. This drop is referred to as the delta ("delta" means difference, in science-speak), and a delta-peak NiMh charger is programmed to stop the charge when it detects the peak voltage going down. On some chargers you can program how far the voltage has to drop before the charger will stop -- somewhere between 0.05 and 0.10v per cell are typical, I believe. Set the value too low and the charger may stop prematurely with a "false peak", and set it too high and it may overheat the battery due to over charging.

For my receiver and transmitter packs I only ever charge them at 1/10C, overnight, without any peak-detect. This may be what one of the charge modes is on your charger, but you'd better wait for someone who's familiar with it to confirm that.

I judge the condition of my NiMh packs partly on how much I can take out and put in, but also partly on how much they lose while sitting from one week to the next. So it might be worth cycling it again after a few days to see if you still get 700 out/700 in.

P.S. I've just found the manual for your charger on line, and here's what it says about the different charge modes for NiMh:

AUTOMATIC – Essentially ignores your setting for CURRENT, but charges at rate determined by the internal resistance of the battery pack. Especially useful when you don’t know what settings you should make due to lack of documentation.
LINEAR – Charges at whatever rate you have selected from start to finish (if the charger detects no problem with settings).
NORMAL – Charges according to your RATE setting but uses an intelligent algorithm to alter current as needed during charge.

I think it's self-explanatory. I've used an automatic setting on my 1210i charger when charging large packs, but I wasn't happy with it because it was heating my packs more than I was happy with. So I've always used the manual setting, setting it for a 1C rate. In the case of your charger, that would be the "linear", or maybe the "normal", setting.
abenn is offline Find More Posts by abenn
Last edited by abenn; Mar 20, 2011 at 06:58 AM.
Reply With Quote