hobbico nicad -deltaV safe for ni-mh packs?

[VegasF6]

Hello, I was digging through some of my ancient RC stuff and I came across another charger I had retired. It is the Hobbico Accu-Cycle Plus, Pro series.

I have read other threads of people wanting to charge ni-mh on ni-cad chargers and the answer is usually no. Generally because of too high peak voltage rates, or perhaps the chargers simply were dumb timed chargers.

But, this charger does specify that it is a -deltaV charger. In addition, the discharge cycle limits to 1.05V for cell. So, it sounds like it might be safe to use on ni-mh cells? As I recall, no one was really talking about ni-mh at the time when I was using this stuff, I am not even sure it existed, or at least in the RC world. I simply used it for charging TX and RX ni-cad packs as my cars were all nitro.

Here is a passage from the manual:

Accu-Cycle Plus utilizes the "-deltaV" method for detecting peak
charge. By this method, the cycler monitors battery voltage during
charge, specifically noting when the maximum battery voltage occurs
and then terminates fast charge. In fact, once a NiCd battery has
reached peak charge, or maximum total voltage, the voltage will then
begin to DECREASE if left in charge mode. The "-deltaV" method
of detecting peak charge notes when this decrease in voltage occurs
and terminates peak charge when the voltage PER CELL decreases
by 32mV. If a condition exists causing peak charge to be
undetectable (perhaps caused by a defective battery pack),
Accu-Cycle Plus has two safety features which should terminate
fast charge:
1. If the voltage of the battery reaches the equivalent of 1.74V
PER CELL, fast charge will terminate.
2. If after 120 minutes peak charge has not been detected, fast​

charge will terminate.

A few things concern me. If the charger misses termination, will the 1.74V per cell be too high for ni-mh to survive?

At a charge rate of only 1A and a 2 hour timer circuit, high capacity pack will require multiple charge cycles. Possible over heating of the charger may at least require a fan. Will multiples charge cycle adversely effect charging?

Charge is designed to look for a 32mV change in charge rate. I have seen chargers that this was adjustable, termination could be as low as 5mV change. Will this #, 32mV be ok?

Thanks

 

[Mr Happy]

It's a bit of a problem to use a NiCd charger for NiMH as the -dV is smaller with NiMH. Typically the -dV setting for NiMH should be about 5-10 mV per cell. In this case, if the charger is looking for -32 mV per cell it will likely miss termination.

 

[SilverFox]

Hello Vegas,

That charger, left to its default settings, will cook your cells.

It is looking for a -dV much higher than what is used with NiMh chemistry. This will result in excessive battery heating as the voltage is finally driven down to the termination value.

If that value is adjustable, normal -dV values for NiMh chemistry is 3 - 10 mV per cell. Sanyo publishes using 10 mV, but most RC people use 3 - 5 mV.

The 1.74 volt reference is a peak voltage shut off. If the cell gets to 1.74 volts, the charge will terminate. I don't recall ever seeing a NiMh cell reach that high a voltage (especially when being charged at 1A), so that safety feature won't be used when charging NiMh cells.

The timer and limited charge rate limit the chargers usefulness, but you may be able to find some use for it. However, if you can't adjust the -dV value, I would suggest only using it with NiCd cells.

Tom

 

[VegasF6]

Thank you for the replies. From what I find, only the elite model, which this isn't, has an adjustable termination point. But, I will keep looking.