move99

Hi,
I have a new NiMh 4 cell 4.8v 2000 mAh receiver battery and a Futaba charger (4.8v, 100 mAh output). How long should I charge the battery for the first time? I know I have to charge a new NiCd battery longer than the usual formula (capacity = output * hours). Does the same rule apply for the NiMH battery? Appreciate your input.
Move99

Rodney

You want to allow for at least a 120% charge time, i.e. 2000/100 * 1.2. A little longer (even a lot longer like 24 to 48 hours) will not damage the battery at that low a charge rate. This insures that all cells are at full capacity. It may take three or four cycles at this rate of charge to get full capacity from the cells. If you do a controlled discharge, stop the discharge at 1 volt per cell (4 volts for a 4 cell battery) to insure that you never let any one cell accept a reverse charge. Should one cell be of less capacity than the others, it gets a reverse charge if you discharge to to low a total pack voltage.

pilotpete2

+1 on that.
Using that 100mA wall wart charger is going to give you the best service life from that battery.
Pete

move99

Thanks for your tips! I'll go for 24 hrs first time. I have a fast charger, but, that one has a time limit being 1.5 hrs. I've been so far using that with 0.5 A of output current to charge NiCd batteries less than 1000 mAh capacity. For the 2000 mAh NiMh battery, I may have to repeat charging processes (or buy something better). By the way, my NiMh battery is a Hobbico HydriMAX. I came across a literature saying the battery doesn't have a memory effect. Is that true?
Move99

JPMacG

My Feedback: (2)

Regarding memory effect, yes that is true. NiMH does not suffer from memory effect.

Regarding fast charging, keep in mind that everything is a compromise. The price you pay for fast charging is reduced battery lifetime.

Rodney

NOT TRUE, both NiMh and NiCad can suffer from memory effect. However, the way they are use in our hobby, neither has a memory effect. What is often miss judged as memory problems is really voltage depression which can occur in both types of chemistry, it is just more common in NiCad. This can often be corrected by just charging at 0.1C for 15 to 16 hours. Just remember, both chemistries age and lose capacity as they get old because of deterioration of the the membrane separating the two plates.. I have some NiCad's that are 10 years old and still performing at about 75% capacity.
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JPMacG

My Feedback: (2)

Memory effect is virtually non-existent in both chemistries. Everyone is worrying about a problem that basically never existed except in a few special situations. We should stop nit-picking and let this old wive's tale die.

JPMacG

My Feedback: (2)

This Wikipedia article has a nice discussion on memory effect:

https://en.wikipedia.org/wiki/Memory_effect