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To repair my "crispy" wires from the PMA to the R/R connector I ordered a prewired connector from the UL distributor (Wicks Aircraft). Keith is very helpful and is starting to have good inventory of parts on hand. Upon receipt, I noted that the wire size for the output pos and neg leads to the aircraft seemed to be undersized for a 30A load. The wire size are 12ga and I'm thinking they should be 10ga . In the latest install manual the wiring diagram shows those wires as an 8ga to gnd and 10ga to the aircraft system.
For those running a 350iS what are typical amp draws during high power cruise flight conditions? I have a dual ECU setup and draw approx 20A while cruising at 2600 rpm with all equipment functioning except pitot heat. With the Dynon pitot heater on and cycling I draw an additional 8 amps. When initially (after takeoff) topping off the batteries due to ground (non-flight use) I suspect that I am maxing out the capacity of the alternator for a while and have at least 30A going thru the 12ga output wires.
The prewired connector consists of the three phase wires with 1/4" crimped female spade terminals, and two output wires with 5/16" crimped female spade terminals. I am considering removing the output wires, and replacing with 10ga and new crimped terminals. In the meantime, Ray Lawrence is going to ask UL in Belgium their thoughts and if those do need to be 10ga wires.
Any thoughts or questions regarding this anybody?
My cursory review suggests you are right to be concerned. You may want to review Bob Nuckolls white paper on wire sizing here:
The length of the wire, continuous/intermittent duty and the temperature of the wire are all related.
It's certainly true that many builders unnecessarily over-size wires. The only penalty for this is weight and possibly and difficulty in fab'ing terminals.
On the larger wires, with longer runs, the added weight of over-sizing can be significant. I had considered putting the battery in the rear fuse until I calculated the added weight of the cables was just over 7 lbs! Decided that a 4.1 lb EarthEx battery towards the front of the plane made a lot more sense.
Tom, thanks for the amp draw info. That seems a bit high when comparing to the UL charts for ECU and fuel pump electric load. Was that with the battery fully charged? Any other equipment drawing amps?
I plan on replacing the output wires from the prewired connector as soon as I can locate an appropriate pair of crimpers for the terminals and 10 ga wire size.
I think it was charging the battery at that time with the Skyview.ECU and pump. The only other draw is the lights which might be an amp.
Hello fellow UL flyers,
This response is for both recent posts about this issue.
I had 2 similar experiences with the connector on my 350i when I had the Reg/Rectifier mounted on a thin aluminum sheet on the motor mount with the blast air tube from the cylinder cooling box.
I duplicated the design from the firewall forward install instructions.
After failure #1, I made sure the electrical connector was absolutely tight to reduce any chance of heating due to arcing, resistance from incomplete engagement etc. at the plug.
After the 2nd episode, I moved the Reg/Rectifier to the firewall and placed some heat transfer paste between the two. The volume of metal in the firewall is able to dissipate a lager amount of heat.
Since then, I have had absolutely no change in the wires or connector and I am up to 320 hours.
This may be luck, coincidence or actual.
I believe the heat discharged by the Reg/Rectifier was more than could be dissipated by the air blast and the thin aluminum mounting plate. As the heat increased in the R/R, the plastic connector and wire insulation suffered and eventually failed.
I cannot explain why some installs have no troubles and others have.
This is purely my opinion and based only on my experience.
Best luck to my fellow builders.
What diagram shows the RR leads as 10 awg? Rev 13 pf the manual still shows 12 awg to the battery but I plan on upsizing them to 10 anyway.
I have LED lights and one screen full Skyview Classic system along with standard UL firewall forward (fuel pumps etc ).
If the sensor can be believed, my amp reading during cruise flight is 18 amps at 2500 RPM.
Hey David. Did you end up changing the leads to 10 awg? After discussions with Ray, I Decided to go with a 40 amp ANL fuse between the regulator and battery. This is a disaster scenario fuse designed soley to protect the battery and master bus during a what if failure in the regulator/alternator. I do not have a fuse between the battery and master bus as noted in the UL drawings.
I too think the 12awg leads are to close to the edge here.
Hi John, yes I did! I used the UL prewired connector and upsized the ground and output wires to 10 ga wire via soldering to terminals which I then inserted to the plastic connector. At the same time I also replaced the R/R and applied fresh heat paste on the backside. Over 50 hours on that mod and everything looks good so far.
Mine came with the prewire plug already in the regulator. That connector is really tight. I have been reluctant to pull it out but may give it a try tomorrow. Standard spade connectors I suppose?
I seem to recall most distinctly that I needed 5/16 for those two versus 1/4...NOT 100% positive though...