This has probably been asked before but I couldn't find a thread on it. How low can you let the charge get down to on a NiMH battery in a DX7 transmitter and be able to safely fly? I have always been pretty conscientious about keeping it at a full charge, but as I add more planes to it and extend my flying time at the field it would be nice to know! Thanks!

Battery power does not affect range just in case you did not know.
Considering that at 7.2v the pack would be fully depleted I would stay around 9v - 9.6v before recharging. Thats only based on NiMh voltages and not DX7 experience so other may post more accurate info.

Based on the DX8's manufacturer alarm settings, for the DX7 NiMh 9.6v pack the alarm trigger would be at 8.6v hence why I said 9v and the minimal voltage for such a pack is 9.6v hence my recommendation.

When the indicated battery voltage gets down to the nominal voltage of an 8 cell battery, (9.6V) you're still safe, but it's time to think about charging up. I don't know what the DX7 low voltage warning level is, but it's not something you want to hear while flying. At 8.8V, the battery is outa gas. How fast your voltage drops from the nominal of 9.6V to the low voltage warning depends on the age, capacity and condition of the battery.
Pete
Go Yankees!!

Thank you guys for your response! I've never let it go below 10V in the past. Better safe than sorry!

I usually put my radios (one of them is a DX7) on the charger when the battery voltage drops to 9.4-9.5V. I'm using low self discharge NiMH 2000mAh cells ("hybrid", "eneloop", etc.) in the trannies. From a full charge I get around 5 hours of total on time and about 20% capacity left in the pack as safety margin.

Originally Posted by ctyankee

Thank you guys for your response! I've never let it go below 10V in the past. Better safe than sorry!

That's a good point at which to charge, but you've still got lots of reserve. So don't be afraid to go lower -- just keep your eye on the voltage, as at some point it will start to drop rapidly and you may have little time to land. I would set 9.6 as my minimum.

The various tx each present a specific "load" on the batt pack
An old PCM may deplete a given pack in under two hours
The very same pack in another later model tx may last twice as long
A case in point is the new 4 cell DX8 - they will run an entire day - and on ENELOOPS- even longer as starting voltage is higher and resting losses are extremely low . (such as on the shelf)

I talked to customer service at Horizon yesterday about this and they mentioned that there is actually an alarm at 9.6V. He mentioned that a fully charged pack should give several hours of flying. I am good with that!

Originally Posted by ivanc

I usually put my radios (one of them is a DX7) on the charger when the battery voltage drops to 9.4-9.5V. I'm using low self discharge NiMH 2000mAh cells ("hybrid", "eneloop", etc.) in the trannies. From a full charge I get around 5 hours of total on time and about 20% capacity left in the pack as safety margin.

Are you using the conventional transmitter charger to charge these?

Originally Posted by ctyankee

Are you using the conventional transmitter charger to charge these?

I have done that -no problem- NOT a quick charger - just the little wall wart.

I fairly recently switched to the 2000mAh Sanyo Eneloop TX pack. Love it! Charge seems to last forever and I just charge it with the wall wart. Simple and effective. I didn't want to go lipo, but I definitely wanted a longer TX run time.

I use a Hobbico Accu-Cycle Elite. Charge rate is 0.55A

i.

Originally Posted by ivanc

I use a Hobbico Accu-Cycle Elite. Charge rate is 0.55A

i.

If I remember right, the max amps for the fuse in the TX is 1.0A. Personally, I just use the included TX charger. It's no big deal to leave it plugged in overnight for a good, solid 12+ hours or so. It's not like it has to be done all that often and we don't discharge these packs all the way to zero, anyway. That's the biggest advantage...to me... More capacity, MUCH longer lasting pack due to the low self-discharge properties of Eneloops and it's still pretty much "stock". And, you don't have to take the battery out of the TX all the time to charge, as you would with lipos to be SAFE...

Originally Posted by mhunter

If I remember right, the max amps for the fuse in the TX is 1.0A. Personally, I just use the included TX charger. It's no big deal to leave it plugged in overnight for a good, solid 12+ hours or so. It's not like it has to be done all that often and we don't discharge these packs all the way to zero, anyway. That's the biggest advantage...to me... More capacity, MUCH longer lasting pack due to the low self-discharge properties of Eneloops and it's still pretty much "stock". And, you don't have to take the battery out of the TX all the time to charge, as you would with lipos to be SAFE...

The fuse is 3A but JR and/or Spektrum warn not to charge above about 1A with the battery in the Tx.

Just keep in mind that 12 hours at say 110 mA will only about half fill a 2000 mAh Eneloop. That's usual plenty for what we take out of the Tx in a normal flying session. But if the battery is really low it will need about twice that. If you have one of the old 50 mA wall warts (from a few years ago when packs were typically 600 mAh), you'll have to roughly double those numbers.

I'm a great fan of Eneloops and have also used RayoVac Hybrids from Walmart for my buddy box with good success. Same kind of chemistry.