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Extending Receiver NiMH 6V pack leads

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Andy C16/06/2019 16:24:23
146 forum posts

In a desperate attempt to minimise additional nose weight on my slow poke (it needs a lot!) I have moved the battery pack to just behind the engine and now need to extend the lead to reach the receiver. Initial thoughts was simply a 30cm servo extension lead, but now am wondering whether I would need to increase wire size for that distance. What are the rules on this please? Plane is running spektrum receiver and 5 standard size futaba servos.

cymaz16/06/2019 16:30:58
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8489 forum posts
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Running a thick wire will reduce any resistance, that's a good thing. I use twisted wires to cut down any RF interference.

Andy C16/06/2019 16:51:34
146 forum posts

Thanks C.

Only options I have in my current spares are some twisted 22awg leads or some 14awg wire which I could solder in to extend. Will the 22awg be acceptable or should I order something in between 22 and 14?

Frank Skilbeck16/06/2019 17:49:56
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From the net, awg 22 servo wire is approx 16.2 ohms per 1000ft, so lets say thats 0.02 ohms for 30 cm, if the total servo current was 3 amps then that's an 0.06v voltage drop..........

If you are using AA cells then the voltage drop across them at 3 amps will be much much higher.

Andy C16/06/2019 22:38:31
146 forum posts

Thanks Frank but what does that actually mean. Can a 5 cell NiMH receiver pack lead needing an additional 12" of wire be done with 22AWG?

cymaz17/06/2019 06:48:06
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Servo plugs and pin connections probably account for more wire resistance than the extension lead itself. I had a 5cell eneloop with a 30 cm twisted extension lead. I couldn’t tell if there was any voltage drop when flying.

Andrew Ray17/06/2019 06:56:26
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Andy, extending the lead by that much shouldn’t be a problem. Worth getting a multimeter if you don’t have one then you can measure the voltage before and after for peace of mind.

Frank Skilbeck17/06/2019 07:37:08
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4383 forum posts
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Posted by Andy C on 16/06/2019 22:38:31:

Thanks Frank but what does that actually mean. Can a 5 cell NiMH receiver pack lead needing an additional 12" of wire be done with 22AWG?

Andy, I should have been clearer, AA cells typically have a fairly high internal resistance, which would typically be 0.1 to 0.2v per cell at 3 amps. So total voltage drop would be 0.5 to 1.0v over the battery, so the 0.06v drop along the extra cable is negligible.

Andy C17/06/2019 08:10:04
146 forum posts

Thanks Frank. Understand now. yes

Peter Robinson 917/06/2019 08:35:30
15 forum posts

Hi

For info, What I tend to do is not use the connector on ex leads cut the plug off (battery and ex lead)and solder directly to the lead on the battery to make one lead, or open the heatshrink and solder to the tags on the battery. Saves on connections.

Peter

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