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Heavy Duty Switch Recommendations?

Old 05-19-2003, 08:12 PM
Paul Cataldo
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Default Heavy Duty Switch Recommendations?

I am getting ready to build a Dave Patrick Edge 540. This will be my first big plane, and was wondering if I needed a Heavy Duty Switch Harness? What is the advantage of using one?
Do you generally use a HD harness with bigger planes?
I was considering the one Dave Patrick sells on their website. Not sure what brand, but it has a built in charge jack.
Any other recommendations on specific harnesses would be appreciated. Thanks fellas.
Old 05-20-2003, 02:08 AM
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Default Heavy Duty Switch Recommendations?

Yes, you want to use a good switch. I use Cermark HD switch (purchased from It has the builtin charging jack. I measured the voltage drop across a "standard" switch and across the Heavy duty switch when drawing a large current draw. I can't recall the exact numbers right now, but I remember convincing myself that the HD switch was measurably better.

Here's what I did: Set up on the bench a typical large capacity battery pack (e.g 2000 mAh 6.0 volt NiMh pack). routed this thru the switch and on to a car headlight. I think the headlight was drawing several amps. This was a "stress test" as your typical plane will not draw too many amps at one time.

(By the way, the current draw of the JR DS 8411 digital servos can each draw over one amp under heavy load. I have a theory that under extreme 3d conditions or perhaps in snap rolls, etc that the system might indeed draw several amps for brief periods of time).

I then measured the voltage across the headlight. For example with a HD switch, the voltage was around 5 volts. I then swapped out the switch and the voltage using the "standard" switch was 4.5 Volts.

I then put a "standard" aileron extension (I think 26 or 28 gauge wire) between the battery pack and the switch. The voltage measured at the headlight dropped another 1/2 volt I think.

The point is that everything between the pack and the servos has some resistance and by the time the power gets to the servos, it can be significantly less than at the pack.

So use a good switch and use larger gauge extensions (22 gauge wire).
Old 05-20-2003, 04:57 PM
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Default Heavy Duty Switch Recommendations?

Just as important and IMHO even more important to low-resistance to current (larger wire size = lower resistance to current) is reliability. The high-end switches from Cermak and MPI come with dual-pole connections. What this means is your hot lead is routed through the switch across 2 connections, instead of just one. That way if one of the connections fail, the other is probably OK. With larger, more expensive airplanes, I carry this one step further -- dual switches and dual batteries.

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