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

 

 

 

 

[Ragsf15e]

21 hours ago, mikechaf said:

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?

I tried the same G5 in my F model. No fuse but i blew the CB before I realized that the G5 can draw up to roughly 12 AMPS.  You might need a dedicated circuit with a 15 amp or better circuit breaker. I did not do that, eventually I just bought the double battery for the G5 and ran it off that instead of ships power.

[PT20J]

My 28v M20J has a 10A cb, no fuse, and no dropping resistor to the original cigar lighter. If it is not in the schematic I would remove it. The cb protects the wire.

[Yetti]

If the most part if you have two 12V cigar plugs that is probably one more than the factory installed.  Same with cup holders. 

[mikechaf]

Digging through the logs, I found "installed aux power jack in panel." back in 2011, but no mention of fuses, what circuit breaker it was on, etc. Similarly no mention of these jacks during the more recent glass panel upgrade in 2019. Once I get some replacement fuses I'll play around with the circuit breakers to see where the two sockets are counted with a multimeter.

ragsf15e, where did you see that the Inogen G5 could draw 12.5A? If you can trust Google's AI, it says the highest setting (flowrate 6) consumes 61.5W. The single battery stores 46.1 W-Hr, and the spec sheet says 4 hours to charge. Putting that all together running off a 12V aircraft bus voltage (and assuming 90% charging efficiency) I get about 6.3A total power draw off the socket, which matches well with the 7.5A circuit capacity that Tom from Windblade suggested. 

Good to hear, PT20J. I'll see if I can verify the wire gauge before I jump to swapping out the fuse. Are there any other gotchas I should be worried about? I'm suspicious that the 2x 5A fuses could be explained by driving both of the sockets off of the 10A circuit breaker.

[1980Mooney]

2 hours ago, mikechaf said:

Digging through the logs, I found "installed aux power jack in panel." back in 2011, but no mention of fuses, what circuit breaker it was on, etc. Similarly no mention of these jacks during the more recent glass panel upgrade in 2019. Once I get some replacement fuses I'll play around with the circuit breakers to see where the two sockets are counted with a multimeter.

ragsf15e, where did you see that the Inogen G5 could draw 12.5A? If you can trust Google's AI, it says the highest setting (flowrate 6) consumes 61.5W. The single battery stores 46.1 W-Hr, and the spec sheet says 4 hours to charge. Putting that all together running off a 12V aircraft bus voltage (and assuming 90% charging efficiency) I get about 6.3A total power draw off the socket, which matches well with the 7.5A circuit capacity that Tom from Windblade suggested. 

Good to hear, PT20J. I'll see if I can verify the wire gauge before I jump to swapping out the fuse. Are there any other gotchas I should be worried about? I'm suspicious that the 2x 5A fuses could be explained by driving both of the sockets off of the 10A circuit breaker.

Yes 61 W on high is correct.   The charger supplied with the G5 or Rove6 output for simultaneous charging and operation is 24 VDC at 5.0 Amps.   So you should be good with 10 amp CB. on your 14 volt system.

Edited Sunday at 11:05 PM by 1980Mooney

[N201MKTurbo]

If you can’t find any other info for the lighter socket, just use the wire ampacity charts in 43-13.1B. 
 

As far as the socket is concerned, most are rated at 10A, some 15A. I found a specialty socket rated at 30A. 
 

Chief Aircraft has a PMA socket for $97 that is rated for 8A continuous and 10A peak.

[1980Mooney]

@mikechaf  BTW - the standalone Inogen BA-503 External Battery Charger (for the G5) draws 65 W.  Assuming the same charging circuitry in the G5 then operation on high and simultaneous battery charging can draw 125 W.  If power at the socket is 12.5 VDC, then your max draw is 10 Amps.

Edited Sunday at 11:14 PM by 1980Mooney

[N201MKTurbo]

FWIW, the buss voltage with the engine running is 13.6 to 14.1 depending on your regulator and how it is adjusted.

[N201MKTurbo]

If you do have a fuse, make it a slow blow.

[MikeOH]

1 hour ago, N201MKTurbo said:

If you do have a fuse, make it a slow blow.

Well, maybe if you expect a HUGE inrush current a slow-blow would be appropriate.

Thing is, it is not commonly understood that even a fast-blow fuse is really pretty damn slow at just over its rated current.  E.g., a 3AB fast acting 10 Amp fuse will take over 15 minutes to blow when at just over 10 Amps!  Even at 20 Amps it will take 4-5 seconds!

So, just how long do you really want to wait when the circuit is drawing over the fuse's rated current?

https://www.littelfuse.com/assetdocs/fuse-322-datasheet?assetguid=4716bb79-a4c9-46f8-a462-76ba7e6af5ae

 

[Yetti]

cigar lighters are horrible interfaces for delivering 12volts.     I would probably go with something like this:  https://www.amazon.com/PAEKQ-Sidewall-Weatherproof-Connector-Generator/dp/B0F61Q31RL/ref=sr_1_4?crid=FU86ZG3Q23KI&dib=eyJ2IjoiMSJ9.ONCGXK1t7jX7uyWkg4nWBgIHVAmm3QgjNp817H1jT5TnoxJbsLoK4ift99SE1isyEfkEJFCFsdPkUfbJi1_g-RAOqvjKEy31OMU7Z9OO_XjzszSH7e9kpq6E9dKkJvtwrayjTI3mu1MDaQbMBiIUmBNTI1949NLPFMxVb20w4cwve6bLBQBxHBl6auwUWqCeonINoEYljIUdV0cH8fyUfNnoNT7e8X1BpZuK6cgAPXg.G_rJHe5QGSdD8UP53YtQPApdq5S9VR6zH95ev7kB8L0&dib_tag=se&keywords=12v%2Bconnector%2Bsae%2Bpanel%2Bmount&qid=1756694253&sprefix=12v%2Bconnector%2Bsae%2Bpanel%2Bmount%2Caps%2C159&sr=8-4&th=1

 

the 12AWG is good for 25 amps at 12v

If you wanted to make it all certified wires, the plane end could be created with M22759 aircraft wire and crimp on bullet connectors. 

[N201MKTurbo]

2 hours ago, MikeOH said:

Well, maybe if you expect a HUGE inrush current a slow-blow would be appropriate.

Thing is, it is not commonly understood that even a fast-blow fuse is really pretty damn slow at just over its rated current.  E.g., a 3AB fast acting 10 Amp fuse will take over 15 minutes to blow when at just over 10 Amps!  Even at 20 Amps it will take 4-5 seconds!

So, just how long do you really want to wait when the circuit is drawing over the fuse's rated current?

https://www.littelfuse.com/assetdocs/fuse-322-datasheet?assetguid=4716bb79-a4c9-46f8-a462-76ba7e6af5ae

 

When I used to be an engineer at car audio company. The boss asked If we could make our own fuses. I said it can’t be that hard. I tried a zillion ways to make a fuse. I took tons of data. Making fuses is way harder than most people think.