Question Regarding Magneto Wiring With ACS Ignition Switch

I have this ACS ignition (below) switch thinking this is sufficient to provide electrical control to the left mag with coupler and right Pmag. I have seen other panel setup that have additional switches for the Left and Right mag.

My question is that, are the additional magneto switches needed if I already have the ACS switch?

What is the advantage of having separate magneto switches? or is it important when I have 1 regular magnetos and 1 p_mag?

Thanks

You need to think about this. The P mag requires power at low RPM (start up), normal switches like shown ground a mag p-lead when "off", unground it when "on". To use it on a Pmag may require a relay of some kind to actually switch the power.
Disadvantage: these switches do not have the greatest reputation for reliability.
Advantage: if some kid gets in your plane and kills himself, when the parents sue you can at least claim you tried to mitigate the hazard, with a key.

Mag switch

You can use the ACS switch regardless of whether you have 1 or 2 P-Mags as you will still be switching the ‘P’ lead on or off as required. A lot of people just choose the ACS as it gives some ‘safety’ by needing the key for starting. Others prefer toggle switches & use different ways of locking out accidental or deliberate engine start by others.
Your choice on which way you go with this.

Thanks for the replies. I am trying to make the setup simple, just like most of the training airplanes and not to make the starting checklist more complicated.

ACS Switch with Right PMAG

I have the exact same situation. My engine was delivered from Lycoming with a PMAG on the right side and a non-impulse magneto on the left side.

Unfortunately the ACS switch is designed to have the Impulse-coupled magneto on the left side and the non-impulse coupled magneto on the right side. When you install the optional jumper at the “R” terminal this kills the right magneto during start.

I need to do just the opposite: kill the left magneto during start while using the PMag to start the engine. I wrote the manufacturer of PMags about this problem and they answered me:

———-

The ACS switch has a built-in feature that will defeat any non-starting ignition that is located on the right side.

"IF" as you state you will receive an engine as described, you can:

Leave the jumper on the back of the ACS switch installed and swap key switch attachments between L and R ignitions (i.e. the non-impulse magneto will be controlled by the R acs switch position). Or swap locations of the E-MAG and the magneto (left to right) in the back of the engine. This would retain correct labeling and switch operation.

You could, of course, replace the magneto with another E-MAG (which most people do) and remove the jumper on the ACS switch. Both ignitions would then be active at startup (i.e. better starting).
————
I’m not interested in swapping positions of the magneto and PMag, so I plan to switch the wiring on the switch and perhaps modify the label on the ACS switch.

Hope this is helpful!

Leonard Westermeyer
RV-7A “almost” complete.

LeonardWestermeyer said:

I have the exact same situation. My engine was delivered from Lycoming with a PMAG on the right side and a non-impulse magneto on the left side.
...

I need to do just the opposite: kill the left magneto during start while using the PMag to start the engine.

Click to expand...

I ordered the IO360-M1B engine with the same left magneto + right PMag configuration as yours. Can you explain about the reason for using the PMag as the starting magneto instead of using the traditional impulse coupler? I am planning to use the current magneto/PMag setup for the first flight. The magneto will be probably replaced with another PMag when it has reached the hours for overhaul. I am trying to keep the customization to a minimum for now.

Thanks.

Impulse Magneto for startup

My problem is that my engine was delivered with a non-impulse coupled magneto on the left. So I would need to use the PMag on the right for startup.

However other posts have stated that the PMag will do a better job than the magneto for starting the engine:

https://vansairforce.com/community/showthread.php?t=153320

A couple of quotes from that thread:

“ If you decide to install 1, please remove the impulse as it will do nothing to assist in the starting process as the P-Mag will provide impeccable starting on its own, and you can use auto plugs with it saving even more money.”

“ The P-Mag is producing max joules at the correct timing point irrespective of engine rotation speed. It can also be set up to pause to allow a couple of blades to pass so that any unburnt fuel in the inlet manifold is ingested and prevents induction fires from a backfire or indeed, prevents a starter kickback which will damage a lightweight starter.”

“ My setup with easy starts hot or cold.

* P-Mag on right
* Non-impulse mag on left
* Fine wire plugs on top (not a lot of clearance with a plenum)
* Auto plugs on bottom
* Toggle switches for mag control/grounding
* Circuit breaker for occasional testing of the P-Mag alternator
* Left side wired during build for second P-Mag or other EI (undecided)
* Push button from Steinair for starting
* No backup alternator or battery but planning for backup alt on the vac pump pad.
__________________
Ray”

In your case if you don’t want to take advantage of the PMag for starting, you could wire the ACS normally with the jumper on the “R” terminal so the PMag would be disabled and then the impulse coupled magneto would do the starting.

What is for sure is that you should not use both at the same time and that a non-impulse coupled magneto cannot start the engine by itself.

Hope this helps!

Leonard Westermeyer