Tuesday 23 September 2008

P-mags and wiring

There has been lots of discussion recently on Vansairforce, as to how to wire P-mags.

I didn't really want to depart from E-mags wiring approach, but I did want to minimise the number of switches. I also wanted to keep it as similar as possible to the switching of normal Slick or Bendix mags for ergonomic reasons.

I decided to wire it exactly as E-mag proposed, but combined the functions of their two switches, into a single 2-50 type (expensive) switch.



The way it works is that when you are ready to start the engine, first you turn the master on. Now the electronics of both the P-mags are live. Then you move the levers for both the left and right P-mags from the lower position to the middle. Now the 'P-leads' are live. Then you press the starter.

If you want to test your mag drop. You run up to say 1800rpm (keep the stick back), or whatever speed suits you, and push the left lever to the bottom position. Monitor the drop. The electronics remains live but the 'p-lead' is off. Repeat for the right mag. This is just like the past so far.

To test the self generation you turn the 'p-lead' off on one mag, say the left, and lift the switch on the right mag into its upper position. This cuts the external power to the right mag. As long as the engine keeps running the right mag is generating. Vica versa for the left mag. The upper positions are spring loaded, so the switch will not stay up there by accident.

To test for the rpm where the self generation ceases, you do the same thing, except holding the switch in its upper position, you very slowly throttle back until it quits. Don't save it, let it come to a halt. I only do this from time to time at the end of the day when I am shutting down anyway.

If for any reason on the ground you want power to the P-mags removed, pull the fuses.

This has worked well for me for 27 hours now. The learned habits of the past are continued and the switching is simple. I told Brad at E-mag what I proposed to do and while he did not actively support it he did not appear to have any problems with it either.

If you want to make your wiring really complicated, there are all sorts of things you could do, but why not keep it simple? This way its just like the switches from the past and as long as you put the switches out of the way, you wont knock them off in flight. Just like the past!

The plug leads are standard automotive equipment that E-mag provide with adapters, so they fit the larger holes in the engine block. They are easy to make up and test if you just follow E-mag's instructions.