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Charging NiMH AA batteries in a Tx

Charging NiMH AA batteries in a Tx

Old 12-13-2016, 06:01 PM
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Default Charging NiMH AA batteries in a Tx

I have a use for an el-cheapo Tx so I installed 8 Duracell NiMH 2450 mah batteries. Using the onboard charge port I hooked it up to an auto NiMH charger (hitec x2ac plus) @ .30 amps and monitored it. It was reaching 12.95 volts and the batteries were around 89 degrees F. The problem is it doesn't seem to sense the batteries are full and shut off.
Note: when testing with a volt meter the charge port will not show battery volts on the terminals? Seems to be a diode inside the Tx blocking outbound from the batteries.
Should I remove the diode or just scrap the idea?

Last edited by gmackhurry; 12-13-2016 at 06:17 PM. Reason: Typo
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Old 12-13-2016, 08:15 PM
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Charging the Nimh inside the transmitter is fine but don't charge for extended periods of time. Just like you stated, there is no way to sense when the pack is fully charged. You risk overcharging. 12v is pretty much fully charged.
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Old 12-14-2016, 01:44 PM
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Originally Posted by trigger View Post
Charging the Nimh inside the transmitter is fine but don't charge for extended periods of time. Just like you stated, there is no way to sense when the pack is fully charged. You risk overcharging. 12v is pretty much fully charged.
It's looking looking like that diode only has one job. To protect the batteries from an accidental short at the charge port. I'm assuming it will auto sense if I cut it out.
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Old 12-14-2016, 04:42 PM
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I regularly charge NiMH cells in one of my transmitters that has a diode in series with the charge jack. I set the charger for one more cell than the battery has (i.e. a 5-cell setting for a 4-cell battery) to compensate for the diode voltage drop, and use a reasonable current (700mA in this case) to not blow the diode. The charger detects the peak and turns off the charge current with no problems. Give it a shot.
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Old 12-15-2016, 01:33 PM
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Originally Posted by howardcano View Post
I regularly charge NiMH cells in one of my transmitters that has a diode in series with the charge jack. I set the charger for one more cell than the battery has (i.e. a 5-cell setting for a 4-cell battery) to compensate for the diode voltage drop, and use a reasonable current (700mA in this case) to not blow the diode. The charger detects the peak and turns off the charge current with no problems. Give it a shot.
That's absolutely a ridiculously smart idea for something I was making complex. Assuming it is a simple cheap 1 amp diode, 700mA should drop the voltage near 1 volt (.9 to be exact). So the charger should see peak just a smidge (.3v for a 1.2 v cell) high but probably not enough to hurt the cells. Ha! That's pretty good!
And I thought I was good at electronics, lol.
Thank you.
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