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Oct 20, 2017, 05:38 AM
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Ignition / RX Battery

Good Day,

I'm chasing some advise. I have never had a Gas engine before and I'm unsure of battery size / type for the ignition.

The plane is a .60 size trainer, Saito FG-14C, with 7 digital servos.

What would you do? I'm thinking a 7.4V lipo (2000mah) with SBEC for ignition and a separate 7.4V Lipo (2000Mah) with separate Sbec for RX, or 6v NiMH 2300mah (one for ignition and one for RX.

Any thoughts? Any idea of runtime?

I look forward to the responses.

Old Mate
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Oct 20, 2017, 04:49 PM
Oh...that's gonna leave a mark
capt kurt's Avatar
If it were me, I would use ONE Life battery for everything. This would require you to use something like Tech-aero opti switch to power your ign. As far as the battery size, I'm not sure if your model needs weight or not or how long your flights are, but I would think a Life 2100 would be plenty for you. The Life bat will also allow you to avoid using any regulators for your servos if not using HV servos.
Oct 20, 2017, 06:12 PM
Go fly a jet today
CARS II's Avatar
For a kill switch.

For a 2500 mha LIFE batt.

Crack it open and follow the instructions. On how to conver it to take power from the receiver.
Last edited by CARS II; Oct 20, 2017 at 06:20 PM.
Oct 21, 2017, 10:25 PM
Registered User
marmalade1's Avatar
I agree with the single 2100mAh LiFe battery with simple opto-kill switch.

Regarding mAh use, we tend to go overboard: double expected use is good and modern chargers allow us to know what we've used fairly accurately.

My 40+ 60 size glow planes (5 analogue servos) use about 65mAh per flight averaged over several 10m flights.

My 50cc Yak 55M (6 digital servos) use about 280mAh per 10m flight averaged over several flights.

DA suggests "a 700mAh battery is good for a days flying" of the DA50.

Select a battery and fly it. Charge it and see what you used. I bet it's less than you thought.

Allow double what you need as a margin e.g my 700mAh LiFe is good for over 10 glow flights, I charge it after 4-6 (end of each day) .

Oct 22, 2017, 04:32 AM
The great Brutufier
A single 5 cell 1900 mAh NiMH battery, regulated down to 5,1 V, provides me 90 minutes of safe flight time for a plane with an ignition and 3 analogue servo's.

Which type of battery you want to use, and whether you want to regulate the voltage, is up to everyone.
One thing I would want to advise on: these ignitions that are rated for higher voltages, they usually dump the excess voltage, so even if you have an ignition rated for 12V, it will consume less energy when you supply it with 5 Volts. At least, that is my experience.

In the case of the OP, I would suggest a single battery in the range of 2500 to 3000 mAh, since digital servos tend to drain more power.
In fact, if it had been analogue servos I would say 2000 to 2500 mAh would be sufficient in virtually all cases.

The RcExl opto-killswitch is a good one as well, and also comes with instructions how to modify it for single battery use. It is a 5 minute job....
Oct 24, 2017, 02:21 AM
Go fly a jet today
CARS II's Avatar
I'm using a single 2500 LIFE, a kill swith, 6 high torke analogs servos and two digital ones, I usually put back in somewhere around 360 mah after 3 flights.
Oct 24, 2017, 05:12 PM
Registered User
marmalade1's Avatar

Too much

Originally Posted by CARS II
I'm using a single 2500 LIFE, a kill swith, 6 high torke analogs servos and two digital ones, I usually put back in somewhere around 360 mah after 3 flights.
It's good to read actual mAh usage numbers. When I read of 2x 2500mAh rx batteries and a 2500mAh ignition battery for planes not much bigger than mine I sometimes think we're going over the top. Some redundancy for rx power is a fine idea for any plane, but the capacities is what amazes me.


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