Battery Charging NiMH & NiCd

[TheAmmoniacal]

I've just invested in a new set of rechargeable batteries (9-volt, AAA, AA, C size), some NiMH and some NiCd. I've never cared much about the chemistry of my rechargeables before, most cheap charger I have claim to charge both. But after looking for a higher quality one to "charge them all", I noticed they all just claim to charge NiMH. An example being this: http://www.en.varta-consumer.com/en/Products/Chargers/Details/LCD%20Smart%20Charger.aspx#

In the specifications: "System to charge:   Nickel Hydride (NiMH)" No mention of NiCd on the site or in the manual.

Why is this? And is it safe to charge NiCd in them?

[hayatepilot]

Why is this? And is it safe to charge NiCd in them?

Yes you can charge with a NIMH charger.
Modern Chargers detect the end of charge when the voltage of the battery stops rising. In this case, both NiCd and NiMH cells are fully charged.
NiCds are not mentioned in the manuals because they are banned in the EU. They are only allowed for medical and military applications.

Greetings

[ion]

The voltage dip when a NiMH cell is full tends to be weaker than that of a NiCd cell.  So any NiMH smart charger that terminates on -dV (like the one in the link) should be fine with NiCd, as long as the charging current is appropriate.

[helius]

The flip side is that NiCd cells will float charge happily, giving off the excess power as heat. Many devices with NiCd cells keep them charged that way. But that is disaster for NiMH: float charging them will eventually generate H₂ and make them blow up.

[HKJ]

Modern Chargers detect the end of charge when the voltage of the battery stops rising. In this case, both NiCd and NiMH cells are fully charged.

Some do, but many uses voltage termination.

[Robomeds]

Unless things have changed from when I was doing battery design (about 15 years back) NiMH really should be terminated on a dTemp, not dVoltage.  The dVoltage at the time wasn't reliable enough.  I doubt things have gotten better these days.  Still, I think my LaCrosse BC-1000 uses a type of -dV/dt termination. 

These guys have always been a good source of info (now that I no longer work for a battery maker). 
http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride

Some additional reading
http://www.powerstream.com/NiMH.htm

Here is an older thread that may be of interest
https://www.eevblog.com/forum/beginners/nimh-charger-best-life/

[hpapagaj]

Hi,

I just bought a cordless strapping tool with 14.4V 2.4A NiCd battery pack. The seller said that the battery is gone, so I am going to replace with new NiMh 3.0A batteries (with a local battery refurbish company). It is a step forward or backward? I can choose NiCd batteries too, but they are only 2.0A. +info: the tool will be not used on a daily basis, only every 3-4 weeks.

Back to the original topic: I want to try out original NiCd batteries too, but the tool comes without original charger. I already ordered an universal charger (Imax B6), but it takes some time to delivery from Gearbest. Until then, can I charge the battery with my bench power supply? If yes, on what voltage/current?

Thank you

[macboy]

Hi,

I just bought a cordless strapping tool with 14.4V 2.4A NiCd battery pack. The seller said that the battery is gone, so I am going to replace with new NiMh 3.0A batteries (with a local battery refurbish company). It is a step forward or backward? I can choose NiCd batteries too, but they are only 2.0A. +info: the tool will be not used on a daily basis, only every 3-4 weeks.

Back to the original topic: I want to try out original NiCd batteries too, but the tool comes without original charger. I already ordered an universal charger (Imax B6), but it takes some time to delivery from Gearbest. Until then, can I charge the battery with my bench power supply? If yes, on what voltage/current?

Thank you

Slow charge at 1/10 capacity, so 240 mA in your case, for 14 hours. Then drop current to about 50 mA  (Trickle charge) for as long as you want until you use them, even days or weeks later. Old weak cells may want to self-discharge, so the trickle will keep the whole pack topped up until you use them. Otherwise, some will self discharge to near zero and others will be near full, and the pack will be useless in that state.  Nicd is extremely tolerant of continuous trickle charge.

Edit: so you use the constant current mode of the supply. Set voltage to much higher than pack full charge voltage (20 V +) and set current limit to 240 mA.  Then connect to the pack.