intelligent charger rejects some NiMH - Page 1
Forum section: electronics / general

author: whiskers
author_rank: Newbie
timestamp: January 16, 2020, 01:06:10 pm
content: Hello everyone,My intelligent battery chargers (Nitecore D4 and Nitecore New i4) rejects some NiMH rechargables. It charges for a few seconds to minutes, then rejects them by showing an error message (there are no details).This happens to somewhat used batteries and old ones, all kinds of brands (GP, memorex, ikea, ...).Other, seemingly similar batteries are no problem.The weird thing is those rejects charge well in a dumb charger, and thereafter are accepted just fine by the intelligent ones.What is happening here? Am I doing something wrong?Thanks in advance

author: ogden
author_rank: Super Contributor
timestamp: January 16, 2020, 01:25:13 pm
content: Usually it is high internal resistance and/or significant loss of capacity. If charger have battery capacity setting - try lowering it and try again. Other cause is overdischarge below 0.5V or so. When it happens - measure NiMh voltage. If cells are dropping voltage due to self-discharge, they are bad anyway. Otherwise your devices overdischarge batteries, thus are not compatible with NiMh.

author: Berni
author_rank: Super Contributor
timestamp: January 16, 2020, 02:10:16 pm
content: This does often happen with so called "fast chargers"These chargers use very large charging currents (3 to 10A) to charge them that quickly. But as batteries age there internal resistance slowly grows and eventually becomes too large to sustain such a large current. This makes the battery voltage rise very quickly once charging begins and the charger gives up.Its also possible that it is monitoring the temperature of the batteries (Hidden sensors in the chargers contact terminals) and determines the battery is heating up too quickly during charge.Only real fix for this is to charge the batteries at lower currents (Or use a different charger if your particular fast changer has no way to select the charge current). Yes it is more annoying to have to wait 3 to 10 hours for a battery to charge, but such gentle charging helps prolong the batteries life in the long run.

author: tszaboo
author_rank: Super Contributor
timestamp: January 16, 2020, 02:59:29 pm
content: It could be because they are very much discharged. Even though the fast charger doesnt seem to charge it, they run some 5mA current through it. When the voltage comes to a reasonable level, it charges normally. Leave it in the charger for an hour or two, and check again.

author: whiskers
author_rank: Newbie
timestamp: January 17, 2020, 06:35:24 pm
content: Thanks for your input.Slow-charging still won't work, I'll try to hook it up to a little power supply. Worst case I can have a little indoor barbecue?Are the cells recoverable in case of the internal resistance having grown or the cell being over-discharged? Or do they just appear to charge and will I be sorry later on?

author: Kilrah
author_rank: Unknown
timestamp: January 17, 2020, 06:41:36 pm
content: When they're toast they typically either have much lower capacity, high internal resistance or super high self-discharge, e.g. you charge them and they're empty in a month even without using them, in all cases they're basically useless.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 17, 2020, 07:36:55 pm
content: Quote from: whiskers on January 16, 2020, 01:06:10 pmAre the ones above that are old pre lsd nimh batteries?Do you have problems with lsd nimh like eneloops?I know my pre lsd nimh have lost capacity, but my lsd nimh charge fine.

author: David Hess
author_rank: Super Contributor
timestamp: January 20, 2020, 03:23:28 am
content: Quote from: ogden on January 16, 2020, 01:25:13 pmThat is my experience also. I have run some of my 2000mAH LSD cells down to 500mAH but it took almost 10 years at which point they are useless for some loads like cameras because of high internal resistance.Quote from: retiredcaps on January 17, 2020, 07:36:55 pmMy earlier pre-LSD NiMH cells all died with shorts and did so with maybe only 25% of the use of the later LSD cells I bought to replace them.

author: macboy
author_rank: Super Contributor
timestamp: January 20, 2020, 06:40:44 pm
content: I had plenty of good quality (Sanyo) non-LSD NiMH AA and AAA cells that exhibited this behavior. I could charge them in an old dumb NiCd charger (extending charging time proportionately) but they would usually not charge in the smart charger. When cells are inserted, my smart charger applies a high charge current (2 A or more) briefly, and measures cell voltage. A high internal resistance cell has a high voltage and fails the check. I found that holding them in my hand or pocket for a few minutes to warm them up, would sometimes reduce the internal resistance enough to allow the charge. Due to excessive self discharge, they have all since been recycled. I have a few much older NiCd cells which still work perfectly. Early NiMH cells were just terrible.

author: edpalmer42
author_rank: Super Contributor
timestamp: January 20, 2020, 06:50:08 pm
content: If your smart charger can do a charge/discharge cycle on the battery, you might be able to recover all or a substantial portion of the capacity by running it through a couple of cycles. I do this regularly with older cells.