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Electrical problem

tomkk

Well Known Member
I've been having an elecrtrical problem that I've been trying to shoot. Sometimes, with the Master switch on, if I turn on Ignition A or B, the Master relay picks momentarily, shutting down power. It's only momentary and the power comes back up immediately (the power is off probably for less than a second). Today, with all switches off except the Master, SkyView was showing 12.3V & -4A and the problem occurred. I put the battery on a charger, which charged for a short time then switched off, with the indicator light showing "Charged". After that, I was never able make the problem occur even though I'd disconnected the charger and run the system on the battery for probably 15 minutes. I've checked the connections and all seem to be good. I've dumped the SkyView data and the voltage does indeed go down to near zero before immediately recovering. The data showed voltage never actually reached zero before recovering which I think might mean the relay is actually off for a very short period of time. Any thoughts about this?

When I was checking the connections I noticed the bottom of the Master Relay was quite hot. Not enough to burn but enough so I wasn't anxious to keep my finger there for very long. Is it normal for the Master Relay to get hot?
 
Check part number of master relay

Is it normal for the Master Relay to get hot?
Warm, maybe, but hot? I don't think so. If you have the automotive type of master and starter relays - little metal cans with lugs sticking out the side - I'm sure you're aware that the starter relay is intermittent duty only and the master relay is rated continuous. Is it possible that somehow you got an intermittent duty relay in the master position? I think your first step should be to verify the part number of your master relay.
 
Thanks, but no, they're in correct positions - I've got about 230 hrs on the airplane and it's just started doing this recently.

It's not so hot that I can't hold my finger on it but hot enough so it's pretty uncomfortable.
 
Maybe the master switch is going bad. Try turning it on and off several times to wear away any corrosion. Make sure the arc suppression diode on the battery contactor is good. That diode minimizes arcing across the master switch contacts.
 
The vast majority of electrical problems are caused by bad connections. Check all wires going to the switches.
 
Sounds more like a loose connection, bad master switch or bad solder joint on the circuit board behind the master switch. Switching on (or off) ignition A and B might aggravate it through physical vibration since it's immediately adjacent. Just my 2 cents.

Alex
 
The RV-12 electrical system is a pretty low current system.
I doubt that it is a bad master sol.
I agree with looking at the master switch.

See if lightly tapping on the switch (vs switching one of the ign switches) causes the symptom.
I would also recommend that you confirm that the protection diode is installed on the master solenoid.
 
OK, plenty for me to check.

Several mentions of a possible bad Master Switch. Would a bad Master Switch cause a power cycle when one of the IGN switches was turned on?
 
The master switch and ignition switch are not related to each other electrically speaking. But since they are mounted in close proximity, vibration could cause a poor connection to open up. That poor connection could be inside of the master switch or, more likely, in the wire connections.
 
I was wrong to say that the master switch and ignition switch are not related electrically. They both are connected to the same ground. Assuming that you have the SkyView system, check the ground wire and also the the WHT/ORG wire between the AV-50002 and the AV-50000A.
A broken ground wire could result in always hot ignition.
 
I am constantly amazed at the wealth of information and help available on this site. Thanks
 
Do you have the Master relay wired to be activated by making the ground? if the Master relay is losing a momentary ground path when the IGN is turned on, (extra ground load from a shared ground of master and IGN switches) I would check your ground path from the master switch all the way to the battery ground.
 
Just to (hopefully) close this out ..

It's always hard to tell when an intermittent problem is fixed, but after a fairly small sample, I'm hopeful that my electrical problem is fixed. I replaced the Master Switch and that seems to have corrected it.
 
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