Electrical issues

Archimago

Archimago

Pre-takeoff checklist
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Archimago
Hi all,
I have a Grumman AA5
I replaced the battery contactor and starter relay 3 years ago and then in February of this year I starting having battery contactor/relay/solenoid issues so replaced it. All was fine and haven’t had a hiccup until this evening when the problem returned again.
I started the plane just fine, taxied over to hose off bugs etc. preflighted to include checking lights and stall horn etc but when I went to start, the buss had no power.
I tapped the battery solenoid and it worked momentarily but then it didn’t. After multiple attempts I did get the buss energized but as soon as I pressed the starter button the buss dies again. It acts like the solenoid is bad but I just replaced it. What would cause a new solenoid to fail like this?.
Battery indicates 12.8volts
I get 12volts at the solenoid with master switch on (on the small terminals)
Terminals are clean and nothing feels loose or looks corroded
When I left I could not get any current to the buss.
Thanks
Richard
 
Does your starter or master contactor have a flyback diode as part of the design?
 
Archimago said:
I have a Grumman AA5
Click to expand...
Do you have a wire diagram for your aircraft that you can post or link to?
Archimago said:
I replaced the battery contactor and starter relay 3 years ago and then in February of this year I starting having battery contactor/relay/solenoid issues so replaced it.
Click to expand...
Why did you replace both relays 3 years ago?
Archimago said:
Battery indicates 12.8volts I get 12volts at the solenoid with master switch on (on the small terminals)
Click to expand...
Have you ever checked the rest of the electrical system as part of the relay replacements? Given you are losing .8 volts at the solenoid points more to the electrical supply side to the relays and not the relays themselves. However without more info cant offer much more but I would chase your voltage drops first (and grounding side) before throwing more parts at it.
 
Archimago said:
Hi all,
I have a Grumman AA5
I replaced the battery contactor and starter relay 3 years ago and then in February of this year I starting having battery contactor/relay/solenoid issues so replaced it. All was fine and haven’t had a hiccup until this evening when the problem returned again.
I started the plane just fine, taxied over to hose off bugs etc. preflighted to include checking lights and stall horn etc but when I went to start, the buss had no power.
I tapped the battery solenoid and it worked momentarily but then it didn’t. After multiple attempts I did get the buss energized but as soon as I pressed the starter button the buss dies again. It acts like the solenoid is bad but I just replaced it. What would cause a new solenoid to fail like this?.
Battery indicates 12.8volts
I get 12volts at the solenoid with master switch on (on the small terminals)
Terminals are clean and nothing feels loose or looks corroded
When I left I could not get any current to the buss.
Thanks
Richard
Click to expand...
With 12 volts at the master contactor coil terminals, it should work. HOWEVER:

If it has two small terminals, one of them is hot all the time, being connected to the battery side of the contactor. Measuring between that terminal and airframe ground at 12 volts doesn't prove anything other than that it's connection to the battery might be OK. Might. If there is resistance anywhere, it could drop to zero when the master switch is on.

The other terminal does the same thing that the single terminal on other contactors do: It goes to the master switch, which grounds it to complete the circuit and close the contactor. You might have a problem anywhere along that line, including a tired master switch, loose connections at the switch or contactor, or corrosion inside the crimp terminals.

The diode is not a factor. If it's open, it doesn't affect anything other than spike suppression when the master is switched off. If it's shorted, it will smoke instantly and open and take itself out of the circuit.

Having everything go dark when you hit the starter button implies bad master contactor contacts, loose cable from the contactor to the bus or to the battery, or simply a bad battery. The circuit suffers a massive voltage drop when the starter is actuated. Now you have to start measuring voltage drops across the master contactor and every cable connection, including the battery ground cable.
 
Thanks all. Looks like I need to carve out some more diagnostic time, I have some things to check
 
Could be the relay, could be a bad connection or broken wire. Need to chase it down, best with a Volt/Ohm meter and a test light.
 
Thanks to all!
I found the culprit. Corrosion where the battery contactor connects to the starter relay. Cleaned up and working beautifully.
This same cannection also supplies power to the main bus
My annual is coming up and I plan on combing throughmy connections one by one
 
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