Is there any "smart" way to charge 8.4 V NiMh battery ? - Page 1
Forum section: electronics / projects

author: BravoV
author_rank: Super Contributor
timestamp: March 10, 2020, 08:05:18 pm
content: ... or just charge them as dumb old way using slow and low constant current ?As I'm aware, cmiiw, the peak detect just can be effective only in single cell charging, and if > 1 cells in series, it will not be reliable mechanism to terminate the charge.Any thought ?I am aware of 9V Lithium primary cell, its just just looking for 9V Alkaline alternative.Random image of 8.4 V NiMh battery grabbed from Google.

author: Nusa
author_rank: Super Contributor
timestamp: March 10, 2020, 08:16:58 pm
content: https://www.google.com/search?q=nimh+smart+charger

author: BravoV
author_rank: Super Contributor
timestamp: March 10, 2020, 08:21:39 pm
content: Quote from: Nusa on March 10, 2020, 08:16:58 pmThanks, but I guess u dont have any idea and understand what I am talking about.

author: magic
author_rank: Super Contributor
timestamp: March 10, 2020, 08:27:01 pm
content: I actually wondered about the same. I figured a slightly smarter solution than CC might be a 10V supply with limiting resistor. That's 1.43V per cell, which AFAIK is close to full capacity but not all the way there. It also charges empty batteries with higher current and then slows down to safe trickle charge.By the way, that VARTA battery doesn't have rounded corners and it may not fit into some equipment. Guess how I know.editThat's exactly how I charge one oddball triple-cell battery. 5V in series with 220Ω. Chosen to meet two constraints: maximum rated fast charging current into empty battery, maximum permissible trickle charge current into full battery. Luckily it's an "industrial" battery so there is a datasheet.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: March 10, 2020, 09:46:38 pm
content: I also found those rechargeable 9 V PP3's (7 or 8 1.2 V cells in series) really problematic and they never used to last more than a few cycles before failing. I think the main cause of failure with them is over-discharge of one of the cells (since they are not initially all equal or gradually become unbalanced over charging cycles) and then that discharged cell will get reverse charged (which damages NIMH cells) by the energized cells when used further. So the main thing with these is to never let them go empty before deciding to recharge , I now don't let mine get below about ~30% before they get a recharge .I decided the best charging strategy was to trickle charge them @ no more than 15 mA for 12 hours+ as at this charge rate I don't think they can be damaged by overcharging and you can leave them on and be sure ALL cells are charged up to max capacity. I Use these cheap plug-in trickle chargers as they deliver about the correct charging rate (16-22 mA) max trickle charge rate before damage is about 25mA I have read .https://www.ebay.co.uk/itm/Uniross-Compact-Charger-for-AA-AAA-9V-PP3-2x-Lloytron-9V-Rechargeable-Batteries/111581125510?epid=1439684832&hash=item19fac0db86:g:KOMAAOSw5UZY-LbS.I really don't use a lot of rechargeable PP3's so can't really vouch for my method yet but have had only one failure out of 5the other 4 are still going strong after about ~40 cycles.Regards .

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 10, 2020, 11:30:10 pm
content: http://www.ultrasmartcharger.com/Just adapt for a 9V pack. Or go for a lithium ion 9V, unless your application requires heat tolerance.

author: james_s
author_rank: Super Contributor
timestamp: March 10, 2020, 11:48:16 pm
content: I have a "9V" smart charger that I've been using for close to 10 years now, I bought it so long ago that I don't even know what brand it is but it's a plain silver box that looks a bit like a wall wart. You plug a battery into it and it beeps and the light turns red, when it's done it beeps again and the light turns green. If it detects an error it sits there beeping and refuses to try charging.I have NiMH 9V batteries that I've been using for years, I think the oldest is one of the first LSD types I bought at Harbor Freight to use in my DMM. I expected it to be crap but it has held up remarkably well.

author: markce
author_rank: Regular Contributor
timestamp: March 11, 2020, 12:19:00 am
content: I use an Opus NT-C900 to charge Tensai 8.4V NiMh, and it works fine for more than a year now.It's a pulse charger with dV/dt detection.For a in-depth review see:https://lygte-info.dk/review/Review%20Charger%20Opus%20BT-C900%20UK.html