Blown Fuses Problem AFS2500 engine monitor

[lwfussell]

I am not an electronics technician and could really use some good troubleshooting advise. My 7A is ready to go with one exception. Every time I turn off the master switch while the engine is running it blows the 2Amp fuse protecting the engine monitor. If the engine is off there is no issue when powering the master switch up and down. There is only one 12V+ lead to the unit and I have checked it from end to end. The unit is powered by the A bus of a two bus system. I thought about moving the power lead to the avionics bus but then I would have no engine instruments until after engine start and system boot, not an acceptable alternative.

My only guess is that when the solenoid powers down it causes a spike that nails the small 2A fuse. If that is the case it could also be damaging other systems that have as of yet not exhibited any issues.


I really would like to have first flight on Memorial Day, any help would be greatly appreciated.

Thanks,

Larry

[dan]

Call Rob or the guys up at Advanced. I'm sure they'll help you sort this out.

[cytoxin]

sounds like you need a clamping diode across the offending load.

[Walt]

to shut of the master with the engine runnng. When shutting off the master you are disconnecting the battery from the sytem and alternators do not like to run without a battery (not sure if you are shutting off the alt when you turn off the master). Without the battery to effectively filter the output of the alternator you will cause damage to other components as well. Chances are you are blowing the fuse because the internal power supply capacitors of the monitor are now trying to supply the aircarft system current when the output from the alternator goes to zero (the alternator puts out AC which is rectified by diodes and filtered by the battery). If you are turning off the alternator with the master at the same time then I would first try installing a diode in the 12v supply line to the monitor to prevent a reverse current flow from the monitor to the aircraft system.

[N402RH]

Have you installed Van's protection diodes on the master contactor and starter relay? Make sure that you are not running the alternator without the battery connected to it.

You can always call me, my cell phone is (503) 701-5042

Rob Hickman
Advanced Flight Systems