6
\$\begingroup\$

I have a device with integrated NiCd charger. Would it be feasible to modify it to work with NiMH batteries? If necessary, I'm ready to rebuild the whole circuit.

Also what are main differences between NiMH and NiCd battery charging cycles?

\$\endgroup\$
4
\$\begingroup\$

Its possible but hard to answer without knowing the charger topology.

NiCd can be handle very high charge/discharge currents. Such charge currents could damage a NiMH battery.

Now it MAY be OK, not all NiCd chargers are of the high current/peak detect variety, sometimes called "Rapid Charge".

Some are simply timer based in which case they will very likely undercharge a NiMH battery.

Still other NiCd chargers are "trickle chargers" made to slow charge overnight, such a charger would work with NiMH but would likely take a very long time to charge since NiMH batteries generally have a much higher capacity.

Yet another charger type is the "smart charger" which monitors the battery as it charges and adjusts its charge rate, stopping or going into a trickle mode when the battery is determined to be full. The "full" trigger and charge profiles are different between NiCd and NiMH so I would assume this type would need to be modified (possibly with new firmware) to handle NiMH batteries.

EDIT: Ancillary question: are you sure switching battery chemistry is a good idea for this application? The mAh rating doesn't tell the entire story of battery life. If the device is high current then a NiCd battery may last much longer than a NiMH battery even though the NiMH battery likely has much higher mAh rating.

\$\endgroup\$
  • \$\begingroup\$ Vague question invites vague answers, so you're forgiven for not making a more accurate answer. :) Basically, I was asked to see if it's possible to modernize a 1983 RC car. It's got a good suspension and motors are fine, but the control circuit is a total mess of analogue electronics and I don't even know where to start analyzing it. It has two 9 V rails, a 12 V rail, and a 3 V rail. It uses 16(!!!) 1.5 V AA batteries and a 9 V battery. The manual said that the car has integrated charger which would charge NiCd batteries. unfortunately, I can't obtain NiCd batteries in AA size. \$\endgroup\$ – AndrejaKo Jun 11 '11 at 22:52
  • \$\begingroup\$ Since the motors probably take pretty large current, I'm most likely going to replace the whole circuit board and go with LiPo battery plus integrated charger. \$\endgroup\$ – AndrejaKo Jun 11 '11 at 22:53
  • \$\begingroup\$ @AndrejaKo I wouldn't think that using NiMH would be a problem for an RC car motor as long as your control circuity some some current surge protection. LiPo should work as well and likely is the best performer of all options. Do be careful with LiPo to provide adequate physical protection for the battery within the car, they tend to explode into flames if a cell is punctured. They also tend to explode if over charged so definitely use a purpose built LiPo charger. \$\endgroup\$ – Mark Jun 12 '11 at 2:02
2
\$\begingroup\$

NiCd and NiMH batteries do have similar voltage characteristics. A NiCd charger might do OK to charge NiMH batteries, but I wouldn't assume that without knowning what strategy the charger uses.

NiCd are a bit more forgiving than NiMH in charging. They can generally take higher charging currents and are more tolerant of trickle charging, although even most NiCd don't want to be trickle charged long term.

The end of charge is trickier to decide with a NiMH. Most NiMH chargers are therefore "smarter". I've seen some NiCd chargers be as dumb as a transformer, full wave bridge, and resistor. That's not so great for NiCd, but even worse for NiMH.

All in all, I'd not use a charger supposedly for one type of battery on another.

\$\endgroup\$
-2
\$\begingroup\$

nickel cadmium batteries can go anywhere. draw back is memory build up requiring reverse voltage across their contacts. this process will renew the battery as they age. great for radios ,but, beyond three years they will give you 2 more fair years and beyond your E.O.S.L. of 5 years is highly questionable. for more info look into your local amateur radio club in your area. also goto WWW.AARL.ORG in many cases this works for me.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.