Where to mount resistors for P-leads?

[cassius]

Hello, new to the forum. I'm helping my son with his RV-7A project. We're using the AeroElectric wiring approach and are using two toggle switches for the magnetos. (Dual Slick). I have shielded 20AWG coming back from the P-leads to turn the mags off. I'm wondering where the best place to mount the 60K ohm resistors is; I'm considering putting them in heat-shrink and mounting them directly to the P-leads, and pulling the connection for the R-L RPM to the magnetos.

Am I asking for trouble with this? Should I connect the R-L RPM wires to the 60K ohm resistors behind the toggles and keep all that wiring behind the firewall? Pros/Cons anyone?

Oh by the way, I CAN'T FIND my resistors supplied - can someone tell me the wattage required?

Thanks
Cassius Smith
http://www.golfsierra.org/

 

[meljordan]

I did mine just as you are considering, in heat shrink directly to the mag P leads. I then run the wires through the firewall to the EMS. Has worked great for over 500 hours. Any resistor 30K to 100K will work, normally Dynon supplies 30K, but 60K is fine if that is what you have. 1/4 watt resistors will be fine.

By the way, to handle the engine vibration I soldered 22ga. wire to each end of the resistor, positioned so they overlaped the resistor inside the heatshrink. This gives you strain relief and about a 2 inch wire lead to connect to the P-lead makes it flexible. I used glue filled heat shrink also, but regular should work if that is all you have.

Of course, you can also wire to the mag switches, again, keep the resistors close to the swich and provide strain relief.

Best Regards,
Mel Jordan
RV-6A, Tucson

 

[dynonsupport]

Thanks for the help Mel.

The only other thing we'd mention is that the switches MUST switch the P-Lead directly, not through the resistors. The whole point of the resistors is so that if the EMS or EMS wiring fails, it can't turn off your mags. As far as hooking direct to the mags or to the back of the switches, the EMS doesn't care and they will both work fine. Totally up to you and how it works best for you to wire it.

 

[cassius]

Thanks everyone for the help. I have a secondary question - with this setup, do you see a dropout in the RPM signal when you are doing your mag check? I would think you wouldn't since you have redundancy and are still connected to the "other" mag.

My son had ordered a tach sender from Van's but it didn't fit, so instead of replacing it we are going with the direct connect approach. I'm just trying to figure out if there is a downside to this.

Thanks
Cassius Smith
http://www.golfsierra.org/

 

[dynonsupport]

The Dynon EMS is actually relatively unique in the aircraft engine monitoring world- most EMS systems only allow you to hook up one tach input. In this case, you don't see any RPM when you switch to one of your mags since it drops totally offline. The Dynon EMS hooks to both mags, so we can give you RPM when doing your mag check.

There's really no downside to hooking to the mags- it's our preferred connection method. In the future, we may even be able to tell you if one of your mags is acting up in flight if you hook up this way.

 

[cassius]

Thanks much for the great support! I really didn't expect such a quick answer on a SATURDAY! ;D