PMag issue

[eddieseve]

Hi Guys,

I looking for some suggestions for a possible cause for the issue I experienced.

Today I was going to change the oil and filter, so what better way to warm up the oil, than to take my wife for a fly. The RV was preflighted, master and alternator on and as I was getting settled I accidentally kicked one of the PMag power switches off, no big deal just turned it back on and then went through my normal startup procedure. Prime the engine for 5 seconds, mixture to idle cutoff, crack the throttle and engage the starter, for 2.5 years the engine has always fired after 2 blades, today nothing. My initial thought, not enough fuel, so I gave it another 2 seconds and cranked again, nothing.

Waited for about 1 minute and tried again, nothing, waited another 30 sec and tried again, nothing. By now the battery is starting to go a little flat so I gave up, pulled it back into the hangar and pulled the cowls and put the battery on charge.

I noticed the sniffle valve was dripping fuel, so that was not the issue.

Turned the master on again to see if the LEDs on the PMags where lit, no lights.

Grabbed the multi meter and checked for 12v at the connector, no power, so I checked the fuse, and it's blown, it's 5A as recommended, so I am wondering if de-powering and turning back on again without the engine running could cause this to happen?

I replaced the fuse, re-cowled pushed the RV outside and the engine fire right up.

Does anyone have any explanations for this?

One other question, I am running both PMags through the same fuse, could this eventually cause this to happen?

Cheers

[rwtalbot]

EMAG recommend a dedicated, pull-able 3A circuit breaker for each unit. They say if using a fuse it should be "slow blow". That implies there is some inrush current they are aware of. I would say it is possible you could blow a shared 5A fuse doing what you did and there may be nothing wrong with the units.

If it were me I would install two CB's so you can check and reset them, one to each bus if you have an E-bus. At a minimum don't share the fuse. If it blows you have no power to either ignition.

[RV10inOz]

Eddie??.what would Brownie say

Richard is right, two separate sources.

Do you still have a magneto on your workbench?

Give me a call if you get a minute. And Richard?.get to work on that -10 and stop reading VAF

[N941WR]

You need independent pullable breakers and engine case grounds for each P-mag. You do not want one component / wire to take both ignitions off line.

[eddieseve]

Thanks Guys

I'll rework the installation, I appreciate the feedback.

Cheers

[Bevan]

Some things on our aircraft are extremely important and critical systems. if you don't understand why a manufacturer has made their installation instructions for fuel, ignition, prop, engine etc the way they did, do not stray without full understanding and good reasons.

Bevan

[akarmy]

FYI, I'm using fuses just fine, but I did have to special order a couple of "SLOW BLOW" fuses from an electronics shop. They look quite different than normal auto blades and were quite a bit more expensive.

[Bevan]

Andy,

I've been told there is no such thing as "slow-blo" in an automotive blade style fuse. I'm talking about ATC fuses that fit into a traditional fuse block. If you have found a slow-blow for this type of block, I would like to know where you found them.

Bevan

[Bavafa]

Originally Posted by akarmy

FYI, I'm using fuses just fine, but I did have to special order a couple of "SLOW BLOW" fuses from an electronics shop. They look quite different than normal auto blades and were quite a bit more expensive.

Andy,
Where did you find the slow blow fuse? All I have seen are 5A x 250V and none for the 14v.

[billdianne]

http://www.mouser.com/ProductDetail/...87yhfudQ%3d%3d