Blown Cigar Lighter Fuse from Inogen G5- 12V M20J

[mikechaf]

I've been flying my new to me 1978 M20J for a few months now. I recently purchased a inogen G5 oxygen concentrator to increase comfort flying at and above 10k feet. My mooney has a 12v electrical system so I figured I could just plug it into the cigar lighter in the aircraft with the adapter for cars. Tom Laux of Windblade suggested that if I have >7.5A on the capacity plug, then it should be no problem. I reviewed the electrical diagram (http://mooney.free.fr/Manuels M20J/M20J/Mooney Service Manuel M20J Vol. 2 of 2.pdf page 4 for my s/n)and saw it is on the 10A circuit breaker (shared with ignition) and didn't see any fuses depicted (did I just miss it?).

During my first two flights with the G5 starting fully charged, the system successfully maintained 100% charge from the aircraft while running on the max flowrate. On my third flight, I started with the unit at ~80% state of charge before plugging it in. After a few seconds the device lost power, and I plugged it into the other socket which had the same result.

I dug around behind the panel and found a 5A fuse inline with the socket, which would make sense given my experience. I was surprised to find this given I had not found it on the service manual schematic. In the meantime, I intend to replace it with another 5A fuse, but I am curious for input from others as to why this fuse would be there if it wasn't in the schematic? I would love to swap it out for 7.5A or 10A fuse assuming the wiring and other systems are sized to handle that current draw. Does anyone have any insight they can offer?

[IvanP]

It is possible that the prior owner may have used the lighter plug for some portable device and he wanted to limit the current to 5A. Pure conjecture, though. Did you see any log entries related to changes in electrical system?  Does the plug go cold when the 10A C/B inicated on the diagram is pulled? Looks lik someone got creative with the wiring in that plane.  

[Aerodon]

It's not surprising that there is an inline fuse.  The M20K has Ign, Cigar and Tach on that CB, and you would not want the CB tripping because you have overloaded the Cigar.  I'm fairly certain I removed an inline fuse.

Another issue is that on 28V planes, the solution was to put a large resistor to drop the voltage for the 5A cigar lighter.  The problem is that when you plug in a 2A device, it probably sees 22V, not 14.  I put a proper inverter in to reduce the voltage from 28 to 14V.  And I had space for a new CB for the inverter,  I still put in an inline fuse on the 14V output from the inverter.

 

Aerodon

 

 

[MikeOH]

1 minute ago, Aerodon said:

I put a proper inverter in to reduce the voltage from 28 to 14V

Curious as to details on that inverter. My concern would be electrical interference from a SMPS.

[Aerodon]

5 minutes ago, MikeOH said:

Curious as to details on that inverter. My concern would be electrical interference from a SMPS.

It's a proper aviation inverter, KGS LT71A.  Lonestar also make them.  They are really expensive, but if you look around you will find a deal.

I mounted it on the nose gear well, where the avionics fan used to be.  My new avionics either don't need a fan, or have a built in fan or two.

Cessna used Astron 2412 inverters in late model 172's.  With a Cessna part number stuck on.  These are less than $100 on the used market, but a little big for my location.  These have an internal 3A fuse on the input side, so no need for another one.

Aerodon