The Cessna 120-140 Association Forum

Good afternoon ladies and gents. I just went through an electrical system upgrade on my 140, and thought I would share the results.

First off, the “before”. My plane was equipped with a 35 amp Delco generator and had previously been upgraded to a Concorde battery. It had all original wiring, voltage regulator, fuses, etc.

I replaced the battery with an Odyssey. I removed the top half of the battery box, leaving just the tray in which to mount the Odyssey. I used the PMA approved battery box, which is quite stout. I left all primary wiring to the battery in place.

Next, I removed the generator and voltage regulator, replacing them with the plane power alternator, of 50 amps. I did not rewire the entire plane, but most of the wiring behind the panel, excluding the original fuse block, was redone, and all wiring in the engine compartment was replaced. I swapped to a new voltmeter. The voltmeter would not fit in the existing location so I placed it in the far right instrument hole, which was open on my aircraft. I made a blank and mounted the warning light for the alternator in the original volt meter location. I left the original fuse block intact, and added a set of 6 Tyco (several switchable) breakers to manage my TC, alternator field, dummy light, intercom, USB port, master, and a spare for future use.

I weighed EVERYTHING very carefully. I ended up cutting 17 lbs - 11.3 oz. I could have gotten a little more by removing the original fuses, as several are not really being used, as I have all LED lighting, only one landing light and my TC and cigar lighter circuits are in the breaker set.

All in all, I am pretty pleased. Better functionality, modern wiring, and almost 18 lbs pretty evenly distributed front to rear. I was hoping for 20lbs and I thing I could have shortened or rerouted some wiring and removed the fuse block and gotten there pretty easily but this is good enough until I upgrade to a Garmin com/intercom unit and remove the portable intercom. If you are really wanting to put some effort, relocating the Odyssey to the firewall (ala C170 STC) would cut a TON of heavy cable and you could probably use a powersports version of the battery box that has lightening holes - my box is over 1.5 lbs. I also added a long run of 8 wire across the panel to the Volt meter.

Feel free to reach out to me with any questions you might have. All in, I had about 17 hours in it, including fabricating a little breaker panel. The cost was pretty painful but my generator and alternator both had to be rebuilt anyways so that was $400 that I had to spend anyways. I had about $1350 with all the wiring, breakers etc. plus I have to pay my mechanic something for the sign off and filing paperwork so I will be around $1500 or so when it’s all over. Again, $4-500 of that was going to be spent regardless so I am calling it a $1000 upgrade. Haven’t flown yet so keeping my fingers crossed.

Hello Meloosifah

Congratulations for your nice job !

I did more or less the same last year, with some differences:

I kept the DC Delco dynamo and starter, I removed the fuses completely and installed a sub panel respecting the 6 original circuits and adding three to protect new device lines as Xpdr, for instance.

The only original wires I did not yet changed are the two Nav lights on the wing tips, and the Grimes wires on the left wing.

Yesterday I was looking on the right wing and saw how the old cloth covered wire is passed thru the ribs. Perhaps soldering the new cable to the old one and carefully moving both could allow to install the new one in place, but is a big risk in my opinion, without having previous experience.

Best regards,
Horacio

Wow, this is great! Im curious to see if you have any interference between the alternator and the compass. The previous owner of my 140 did the plane power conversion. Whenever I turn on the alternator my compass swings about 30 degrees. All the wiring on my plane from stem to stern is new. I’ve been scratching my head as to what I can do to either fix the interference or block it somehow.

Congrats on a very nice upgrade!

Lance

Have had the compass swing problem as well. No one seems to have an answer for me. Would appreciate any info you might find.

Only thing you can realistically do is swing the compass with the alternator on, and an average load, then just know that the landing light etc will cause greater issue.
Some aircraft back in the day had some interesting fixes, like mounting the compass on the ceiling behind the pilot and he viewed it with a series of mirrors, MD80 I think?

I have not checked the compass but was able to confirm that the alternator does NOT create any radio or intercom noise, as some have reported. No shielded wire but I paid close attention to grounding and power wire routing. I will report on the compass issue soon.

I have an LED Grimes landing light and have seen no compass swing with it.

a64pilot wrote: ↑Thu Dec 31, 2020 6:00 pm Some aircraft back in the day had some interesting fixes, like mounting the compass on the ceiling behind the pilot and he viewed it with a series of mirrors, MD80 I think?

You flipped up a small mirror on glare shield to position it to read mag heading from a second mirror that reflected off aft facing compass above copilots head. Nice flying plane.

Hello,

I have the Delco Remy original DC generator, and no swing at all in the compass.

That being said, I would check:

Is compass in the original position ?

Did you re-route wires Number 10 (Regulator to fuse or CB), Number 12 (Starter to Ammeter) or Number 13 (Ammeter to BUSS) ?
Wire numbers taken from Charles Kimball diagram.

Have you used any shielded wire in the alternator installation ? If affirmative, take care to ground only one end.

Finally, if that checks do not solve the issue, you can try magnetic MU-metal shielding or electric shielding that are available at Aircraft Spruce.

Good luck !
Horacio

My mag compass swings about 30 degrees when I turn on the master switch? In flight it checks out pretty closely in all quadrants when compared with section lines and the readings from my AVARE gps.