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Blown Starter Fuse
What would cause a starter fuse to blow? It is 7.5 amps in the Advanced Control Module used with a Quick Build panel. It is the older model before they went to logical breakers. I flew yesterday, no problem. But today it wouldn't turn over. Turns out the starter fuse was blown. But why? I examined it and it looks kind of cheap and flimsy. I put in a new one and everything is working fine. Would excessive cranking to start a hot fuel injected engine blow the fuse? Does 7.5 amps sound right for the starter motor? I was thinking it would be a 10 or 20 amp fuse. What else might cause the fuse to blow. I have only 38 hours on the airplane, RV-7A. Thanks
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The starter motor draws a huge current. The fuse in question most likely is for the starter solenoid (relay), and no, it should not blow from excessive cranking.
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starter contactor fuse
Bob
Thanks for your quick reply. Yes, I pulled the manual just now, it is the starter contactor fuse. That's interesting to think about. What would cause it to blow? Could it just be an old weak fuse? |
It could just be an old weak fuse. A bad fuse holder connection can generate heat which will blow a fuse.
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I seem to remember that when the voltage drops in a circuit, the amperage goes up.
You hit the starter and the volts drop way down because the battery is not 100% charged, that may cause the amperage of the starter solenoid circuit to rise enough to blow the fuse. Replace the fuse, charge the battery and it may be fixed. |
starter contactor fuse
Yen
interesting idea, because just before this happened I was running the panel and lights for awhile with the engine off. I was loading new database and trouble shooting a tail light that burned out. So I may have run down the battery just before trying to start it. Fuse is changed. I'll see how it goes. |
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There are lots of non-ohms law machines. e.g., motors often rely on induction to limit the current. If the voltage is low and the motor fails to turn, it can draw a large current.
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You should have a kickback diode or MOV between the contactor coil and ground to quench the voltage spike produced when the coil is de-energized.
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