How to properly charge NiMh transmitter batteries?

[Quinton]

I have a Futaba 14SG and a 8FG and needed to buy a battery for the receiver.
The 8FG I bought 2nd hand and it was using a 2S Lipo

I called Ripmax to get the part number of the 8FG battery, and was told you can easily buy the battery, but the wall chargers can not be sold, as they have been removed for safety reasons as they do not pass some safety standard.

Now the 14SG battery is actually a 5 cell 6V NiMh battery 1800mA (10.8w) and on it, it says charging 170mA -15 hours
The 8FG battery is a 6 cell 7.2V NiMh battery 1800 mA with the same charging rate.

So a couple of questions.
When i first put the battery into the transmitter it said something like 5.4V
Obviously this is very low, and even below the recommended minimum of 1.1V/cell for NiMh, is this just because it is brand new, or should I be worried.

I plugged it into the Futaba wall charger for 2 hours, and now it says 8.4V which is a bit strange for only 2 hours.

The Futaba wall charger says sec: 4.8-6.0V - 600mAh, Im not even totally sure what that means, does it mean that it outputs 600mAh so should fully charge a battery within 3 hours?

Everything I have read says that I should be charging NiMh batteries at 0.1C which is about 180 mAh which should take 10 hours.
Can anyone enlighten me on the best way to charge the transmitter batteries, and what should the lowest/highest voltage be for these, I take it 1V for lowest and 1.4V-1.6V/cell for highest?

So in reality my tranmitter low voltage alarm should be set at 5.5V (1.1V/cell) for the 14SG and 6.6V for the 8FG?
If anyone can enlighten me of the dark new world of charging NiMh batteries I would be grateful.

 

[Bartman]

I have a Futaba 14SG and a 8FG and needed to buy a battery for the receiver.
The 8FG I bought 2nd hand and it was using a 2S Lipo

I called Ripmax to get the part number of the 8FG battery, and was told you can easily buy the battery, but the wall chargers can not be sold, as they have been removed for safety reasons as they do not pass some safety standard.

Now the 14SG battery is actually a 5 cell 6V NiMh battery 1800mA (10.8w) and on it, it says charging 170mA -15 hours
The 8FG battery is a 6 cell 7.2V NiMh battery 1800 mA with the same charging rate.

So a couple of questions.
When i first put the battery into the transmitter it said something like 5.4V
Obviously this is very low, and even below the recommended minimum of 1.1V/cell for NiMh, is this just because it is brand new, or should I be worried.

I plugged it into the Futaba wall charger for 2 hours, and now it says 8.4V which is a bit strange for only 2 hours.

The Futaba wall charger says sec: 4.8-6.0V - 600mAh, Im not even totally sure what that means, does it mean that it outputs 600mAh so should fully charge a battery within 3 hours?

Everything I have read says that I should be charging NiMh batteries at 0.1C which is about 180 mAh which should take 10 hours.
Can anyone enlighten me on the best way to charge the transmitter batteries, and what should the lowest/highest voltage be for these, I take it 1V for lowest and 1.4V-1.6V/cell for highest?

So in reality my tranmitter low voltage alarm should be set at 5.5V (1.1V/cell) for the 14SG and 6.6V for the 8FG?
If anyone can enlighten me of the dark new world of charging NiMh batteries I would be grateful.

A little history, RC Tx/Rx kits originally came with NiCd battery packs for the Tx and Rx with the Tx usually having 7 or 8 cells and the Rx usually having 4 cells. They almost always included a little wall charger with two long leads coming out of it so they'd reach your airplane sitting on the bench or floor by the electrical outlet.

Each year when we would start gathering our stuff for the flying season we'd go through the ritual of seeing if our batteries survived the months off as NiCd's were notorious for developing "set" where they'd develop crystals in the cells and they would no longer take a full charge. The hardcore guys had battery cyclers (I was a poor teenager at the time) and they'd cycle their packs multiple times throughout the winter making their packs last years. the guys, like me, that let them sit as is usually found one or two that were dead and needed to be replaced.

And then along came NiMh packs without the memory/set problem and able to use the same chargers as the NiCd. All was good in the world for slackers like me! No more dead packs in the spring.

NiCd and NiMh have similar discharge characteristics in that the voltage gradually drops off as the pack discharges with a final drop as the pack approaches empty. Our LiPo's hang in there much longer with a very flat voltage level until they're almost dead at which point they finally die and die hard they do!

For charging NiCd and NiMh packs the rule of thumb has always been charge them at 10% of their capacity which would be about ten hours for a full charge. Typically we would just put them on the charger and then pull them off in the morning before heading to the flying field. NiCd's don't hold a charge very well and will sag from a full charge, NiMh aren't quite as bad but they will also sag after a while.

NiCd and NiMh will both show voltage improvements shortly after being plugged in but they won't really deliver much until they've been fully charged.