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Help! NI-MH wont work

#1
hi
i got an old futaba transmitter with a Ni-Mh battery and it is on 8,4 volts. but when i plug it in to the transmitter it only works for a second and then it turns off. i have tried charging it with 200 Ma, 3 volts for a hour but its still the same. Any idea why, and what can i do.
 

FastCrash45

Well-known member
#2
hi
i got an old futaba transmitter with a Ni-Mh battery and it is on 8,4 volts. but when i plug it in to the transmitter it only works for a second and then it turns off. i have tried charging it with 200 Ma, 3 volts for a hour but its still the same. Any idea why, and what can i do.
To charge 8.4v you need to put the voltage to the same to, or usually, higher voltage than what the pack voltage is. The 200ma is a good start on amps. How many Mah is the pack rated for? If its 2000mah youd divide by charge amps and that will tell you how long to charge it so 2000/200 = 10hrs. The 3 volts is barely enough to turn the radio on which is why it shuts down fast.
 

Piotrsko

Well-known member
#3
If it's older than a couple of years, stored uncharged, or allowed to develop memory then the batteries are toast. BTDTMO. Takes at least 4 hours to get above 8.4 using the futaba factory chargers since the charge around 30ma IIRC. back converted all mine to drycells since that was easier then trying to $$pend a small fortune for new packs. Could kludge up a 3S lipo pack plugged into the charge port with a banana plug, but your on your own for low battery warning since the factory warning would be disastrous for 3S lipo.

8 cells are 9.6v , my 70's vintage are 10 cell @12.5v the 6ex I have runs from 8.6 to 12.6 input voltage
 
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sprzout

Knower of useless information
Mentor
#4
Did you know that many of the cheapie voltage testers like this have buzzers?


You can actually set them for a voltage cutoff alarm with many of them, and they'll start freaking out when you get to a lower voltage. It's not ideal to hear in a plane that's 300 feet away, but it can help to give you an idea along with using a timer.
 

FDS

Well-known member
#5
I suspect that battery pack is dead. Cheap NiMh is not hard to get, lots available for airsoft etc in sub C size. Just change the plug to whatever one your old radio needs, do one lead at a time, don’t cut both together.
 
#7
To charge 8.4v you need to put the voltage to the same to, or usually, higher voltage than what the pack voltage is. The 200ma is a good start on amps. How many Mah is the pack rated for? If its 2000mah youd divide by charge amps and that will tell you how long to charge it so 2000/200 = 10hrs. The 3 volts is barely enough to turn the radio on which is why it shuts down fast.
The pack is rated for 210 ma for 5 hours, and 70 Ma for 15 hours
 

Merv

Well-known member
#8
With Ni-Mh batteries, the change rate is very slow, 1/10 C, that is if the pack was rated at 800 mah, then the change rate would be 80 mah. The change time was 10-12 hours. A small 9-12 volt wall wart could be used.
 
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#9
To charge 8.4v you need to put the voltage to the same to, or usually, higher voltage than what the pack voltage is. The 200ma is a good start on amps. How many Mah is the pack rated for? If its 2000mah youd divide by charge amps and that will tell you how long to charge it so 2000/200 = 10hrs. The 3 volts is barely enough to turn the radio on which is why it shuts down fast.
It's rated for 9,6 volt 210 Ma. Can I charge it with 1 amp and 17 volts?
 

Bricks

Well-known member
#15
Did some digging on that charger and could not really find any answers, you could just try and plug the battery into it try and start a charge and see if it will even accept the battery without showing a fault. NI-HM batteries at least do not have to worry about fire.
 

Bricks

Well-known member
#16
Did some digging on that charger and could not really find any answers, you could just try and plug the battery into it try and start a charge and see if it will even accept the battery without showing a fault. NI-HM batteries at least do not have to worry about fire.
 

Piotrsko

Well-known member
#18
Airborne packs are 4.2 to 6.2 vdc depending on battery chemistry. Transmitter packs are 7.2, 8.4, 9.6, 10.0 or 12.5 vdc depending on battery cell count, If they are semi-dead NIMH, that show some residual voltage, you could hit them with 7 volts at 1 amp for like 30 seconds making sure they don't get hot to the touch. Hot means they could steam explode (very messy and somewhat hazardous). That treatment could punch through the oxide layer on the cathode and allow a regular recharge, but my experiences say you have a trash bound package. If they show no voltage at all, don't bother charging, just go directly to disposal.

I'm curious: you have a current regulated laboratory grade power supply?
 
#19
Sky RC website.
Down the bottom of that page is a PDF manual.
That charger has to be for batteries larger than AA size. I've tried charging AA batteries at 1000mAh from dead flat (from digital camera) and they get so hot you can't hold them in your hand when fully charged.

@Moeller, you need a different/better battery charger.