Thorp Air Command - T18.net

I was wondering how many are using a Main Bus Diode like this:

http://www.periheliondesign.com/powerschottkydiodes.htm

The way I understand it. When the field collapses after energising (say a trim motor) you get an arc across the switch contacts. This causes early switch failure and a few other problems.

I was wondering how many Thorps are using a Diode? Is this fixing a real problem or creating another failure point. I haven't got to this point, but since there was a trim switch conversation. I thought I'd ask. I see D&C has them for about $20.

Cheap insurance or fixing something that isn't broke.

Bob MO

Bob,

I typically put a small diode across relay coils for the same reason. Some folks call that a free-wheeling diode. It's not for the relay contacts, but for the circuit that energizes the relay coil. It gives current a place to circulate as you let go of the switch.

I suppose that's also good for trim motors too and I'll consider that. For those that don't know, it might need two diodes in different arrangements if a reversing switch is used for the same motor. The layout is to provide a diode parallel to the inductor (i.e, motor or coil), so that when power is removed the residual energy can continue to flow through the inductor the same direction it did with power on. It's kind of a method to re-circulate left over "momentum". Eventually, the flow will damp out and cease when the field is fully collapsed. All in micro-seconds, of course.

I don't know that it's really important. It's probably suited for the same kind of people who spend $10,000 on the best quality hi-fi system because of personal taste. I'll throw them in just becuse it's easy and cheap. Trim motors don't use much current, you can get 3A 1N4001 diodes for $1 each. The 60A diodes on this web site are apparently sold for the main bus. I don't see the need for that ($20?) except for heavy loads like your starter or landing lights and those aren't even 60A. In that case, maybe I'll change the switch if it ever goes bad. I'm using surplus $3 switches.

Now that I think more about it, the bus bar diodes on the web site are for another reason like protection from charging cables backwards andover voltage protection. Nevertheless, the small free-wheeling diodes on inductors are still valid for reasons already stated.

Les Krumel