battery charging - Page 1
Forum section: electronics / projects

author: pete g
author_rank: Regular Contributor
timestamp: May 13, 2023, 03:53:21 pm
content: hi all, can i use a nicad battery charger to charge nmh batteries?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 13, 2023, 03:59:00 pm
content: Short answer, no. Charging modern batteries requires monitoring slope of the voltage rise, temperature, time and probably other things. Best to buy a dedicated charger or, if you have various types, a more sophisticated RC charger. I'm not convinced that old ways of charging NiCads were all that great, as most test equipment that used them killed them rather more quickly than it should have. The old schemes were mostly trickle and voltage based. It's bad to charge too slowly or too fast. Long term float seems to be bad for most types other than Pb.This site isn't perfect but does have a lot of good info-https://batteryuniversity.com/

author: Benta
author_rank: Super Contributor
timestamp: May 13, 2023, 07:44:38 pm
content: Even shorter answer: yes. NiCd and NiMH cell characteristics are almost the same.My chargers take both.

author: CaptDon
author_rank: Super Contributor
timestamp: May 13, 2023, 11:35:55 pm
content: Thinking about the AA chargers I have much experience with, It seems they are designed to safely charge NiCads which were originally around 650mah. The unit is stated as "Safe for NiCad and NIMH battery charging and as you might expect just takes about 4 times longer to charge 2000mah NIMH batteries. I have some Sanyo NiCads (650mah yellow wrapper) probably 20 years old and charged thousands of times and I think they are as strong today as when I bought them.

author: bdunham7
author_rank: Super Contributor
timestamp: May 14, 2023, 12:14:32 am
content: Best answer: it dependsIf you use a slow (trickle or timed) charger and the NiMH cell has a larger capacity than the original NiCd you may be OK. If you use a rapid charger that depends on sensing the voltage drop that occurs at full charge, then a NiCd-calibrated charger may miss the much smaller ▲V of NiMH cells and keep going until it cooks the cell.

author: floobydust
author_rank: Super Contributor
timestamp: May 14, 2023, 12:55:54 am
content: Most of my devices did not have a problem going from NiCd to NiMH.The ones that did have a problem - one does not do a (NiMH) "top up charge" where you go to 1.5Vpc, so it never fully charges- unless I manually intervene.Another, the software coulomb counter gets confused because the new NiMH has so much more capacity and it cries the battery is dead but it really isn't yet.Lastly, NiMH hates being left on a charger too much, it just ruins them and they have a short life, whereas NiCd could tolerate it.

author: IanB
author_rank: Super Contributor
timestamp: May 14, 2023, 01:36:00 am
content: Quote from: pete g on May 13, 2023, 03:53:21 pmWhere did you get a nicad battery charger? Did you arrive here in a time machine from the 1970's?To get a more useful answer: instead of saying "a nicad battery charger", how about giving more details about the specific make, model, purpose, and date of manufacture? You cannot possibly get a good answer to your original question since it leaves so much unsaid.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 14, 2023, 03:32:23 am
content: QuoteNo need for thejokeinsult. If you want to do that go play on Twitter of Facebook.

author: IanB
author_rank: Super Contributor
timestamp: May 14, 2023, 05:18:20 am
content: Quote from: JustMeHere on May 14, 2023, 03:32:23 amIt's not a joke or an insult. You try answering what "a nicad battery charger" is? Is it a trickle charger or a fast charger? Is it a wall wart with a diode and resistor, or does it have electronics inside it? Is it for AA or AAA cells, or is it for a portable tool like a drill or a screwdriver? Is it for a single cell, or for a pack? Was it manufactured in 1980 or in 2000? Can you show a picture of it? What does it say on the label?

author: tooki
author_rank: Super Contributor
timestamp: May 14, 2023, 09:20:10 am
content: Quote from: Benta on May 13, 2023, 07:44:38 pmShort answer is actually no. The little difference in characteristics makes the difference in the charger.A NiMH charger can be safely used on NiCd, but not the other way around. A NiCd charger can’t detect the tiny -deltaV that happens when the NiMH battery is full (the -deltaV in NiCd is much larger), and so it will overcharge the NiMH.

author: tooki
author_rank: Super Contributor
timestamp: May 14, 2023, 09:22:24 am
content: Also, most NiMH don’t like being trickle-charged. They make special NiMH that can be trickle-charged, but in the long run it would damage standard and LSD NiMH cells.

author: pete g
author_rank: Regular Contributor
timestamp: May 14, 2023, 04:19:01 pm
content: worx 18v nicad battery charger part #C1817A005. I think it shuts off when a certain volt is reached?

author: tooki
author_rank: Super Contributor
timestamp: May 14, 2023, 04:38:42 pm
content: It's a 1h fast charger, so probably not.The key to NiCd and NiMH charging is that, as you apply the constant-current charging current, the voltage gradually rises and rises until the battery is full, at which point all subsequent charging current is converted to heat. The increased temperature in turn causes the battery's voltage todropa bit (negative voltage change, aka -dV)*. So the charging algorithm is to monitor the voltage and keep track of the peak, and once you detect the voltage falling rather than rising, you know you're charged. The issue is that the voltage drop in NiCd is quite pronounced, while in NiMH it's much more subtle. So if you design a charger expecting the generous voltage drop of NiCd, it won't detect the small voltage drop in NiMH. (Or it won't until the NiMH is horribly overcharged.)*because it's also wise to monitor the temperature with a sensor, chargers usually do both, known as -dV/dT charging. The temperature sensor will detect that the rate at which the temperature rises will jump, from the slow rise during charging, to a rapid rise when full.

author: pete g
author_rank: Regular Contributor
timestamp: May 14, 2023, 04:48:35 pm
content: is there a way to modify the nicad charger for nimh?

author: tunk
author_rank: Super Contributor
timestamp: May 14, 2023, 04:55:42 pm
content: Take it apart and post photos of the PCB (both sides).Then someone may be able say if it's (not) suitable.

author: IanB
author_rank: Super Contributor
timestamp: May 14, 2023, 04:58:14 pm
content: Quote from: pete g on May 14, 2023, 04:48:35 pmIt's always likely to be cheaper to buy a new and compatible battery charger rather than try to modify an old one.Also, tool batteries usually had NiCd cells inside them because they typically had better high power properties than NiMH cells. It would be unusual to find a tool battery with NiMH cells inside it. The technology generally jumped straight from NiCd to lithium.

author: bdunham7
author_rank: Super Contributor
timestamp: May 14, 2023, 05:40:17 pm
content: Quote from: pete g on May 14, 2023, 04:19:01 pmThose tool batteries typically have additional contacts for on-board circuitry (BMS) or temp sensors. Many of them will do NiCd or NiMH in packs that are specifically designed to work with the chargers. If your charger is NiCd only, what NiMH battery packs do you have that plug in to the proprietary slot? Or are you trying to charge battery packs that don't fit in the slot?

author: pete g
author_rank: Regular Contributor
timestamp: May 14, 2023, 07:50:51 pm
content: there is a fellow on the internet thats selling the worx battery charger shell and stuffing them with nimh batteries. thats what i'am using.

author: bdunham7
author_rank: Super Contributor
timestamp: May 14, 2023, 08:13:12 pm
content: Quote from: pete g on May 14, 2023, 07:50:51 pmMaybe ask him how the internals are set up on the battery packs? If the charger goes for a reasonable length of time and then shuts off without the NiMH cells getting more than warm, perhaps it works OK somehow. If it goes a long time and/or the cells get really hot, it's not working so well. FWIW, I have Makita tools with combination chargers for both chemistries. A non-OEM NiMH replacement I had actually caught fire while I was using it, but that wasn't during charging. Overall the NiMH versions seem to work OK, but they are not 'restuffed' and the chargers are originally intended to deal with both types.

author: pete g
author_rank: Regular Contributor
timestamp: May 14, 2023, 08:40:39 pm
content: when i use the nicad charger for nimh, they charge allright, the end of charge light comes on and the nimh batteries don"t get hot.

author: Benta
author_rank: Super Contributor
timestamp: May 14, 2023, 08:59:04 pm
content: "Chuckle" so much Black Magic about NiCd/NiMH cells here.I've worked with both over the last 30 years, mainly with Sub-C type cells, single or packs.1: you need an intelligent charger with staged charging, earlier expensive, cheap and standard today.2: you need fast charge, 1...2C.3: cutoff algorithm should be d2V/dt2.When that's in place, it doesn't matter a hoot if it's NiCd or NiMH cells. Only caveat is, that NiMH have a higher self-discharge and may need additional trickle-charging. Or even better: periodic boost charging.Cell temperature during charge: skin temperature, say 10...15 C above ambient.My cell packs (6...15 cells) live 10...15 years (weekly charge), at the end they're at 50% capacity, time for retirement.

author: Benta
author_rank: Super Contributor
timestamp: May 14, 2023, 08:59:49 pm
content: Quote from: pete g on May 14, 2023, 08:40:39 pmYep, like I said.