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Starter/engine ground cable

SteveL

Active Member
Good evening!
RV7A, firewall mounted Odyssey Battery,Sky Tec light weight starter. Several of Van's electrical drawings show size 2 AWG from starter solenoid to starter. I don't have any 2 AWG but I have plenty of 4AWG with the appropriate connectors. Will the 4 be sufficient or should I order some 2 AWG?
Thanks!
SteveL
 
Battery cables

I have seen 4awg used on some aircraft, usually on short runs. 2awg would give you better service. Stronger crank longer life etc..
I personally am using 2awg. I do have over 40 years as an a&p. So just my humble opinion.

RD
 
Not answering your question directly....but I would spend the $ and go with 2 awg. The starter circuit typically does not have a fuse or circuit breaker to protect over current....and you want as much juice as possible going to the starter when it calls for power.
 
Welding cable often used for this, as the cable is much more flexible. I used that and soldered the terminals onto each end.
 
From Aero Electric Book

This is the Z11 Diagram from the book. The wire is 4AWG to the starter. Of course, it is ultimately down to you.
 

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4AWG wire

Are you guys (and gals) using Tefzel 4 AWG wire, or just the standard PVC coated stuff from Lowes?
 
I am using the welding grade cables. I was able to find a local electrical/electronic store that sells welding grade cable instead of the standard cable like Lowes.
 
I use Tefzel for the power and braided for the ground strap. Stein has both. Why cheap out for just a couple feet of each?
 
Good evening!
RV7A, firewall mounted Odyssey Battery,Sky Tec light weight starter. Several of Van's electrical drawings show size 2 AWG from starter solenoid to starter. I don't have any 2 AWG but I have plenty of 4AWG with the appropriate connectors. Will the 4 be sufficient or should I order some 2 AWG?
Thanks!
SteveL

On my 6/320, I ran #4 cable from the solenoid to the starter. Spins like a champ. IMO, Tefzel is not required FW fwd, so I used std PVC battery cables.

Larry
 
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4g Tefzel on mine for the past 4 years and no issues with starting. Also swapped the PC680 for EarthX for much better starter speed and improved hot starts. Same for battery/FW ground to engine. If it were going to the aft of the fuselage, I'd use 2g for both.
 
I can't say that I remember exactly but I'm pretty sure that I used 2 AWG Tefzel from the solenoid to the starter. It is VERY stiff wire. It's worked fine for 11 years and I re-used it when I did an engine swap a couple of years ago.

I would strongly consider welding cable if I had to do it again (or maybe the 4 AWG that you have on hand).

I used the braided straps for the ground. One from battery to engine block and a second from battery to firewall (forest of tabs bolt).
 
When I needed to replace the battery, starter and ground cables on my '48 Plymouth I used this vendor for custom-made cables:

https://www.batterycablesusa.com/battery-cables.html

The cable stock is very flexible (the 0 gauge has 1000 strands!) and the price is very reasonable with quick turnaround. They should be able to build cables in whatever length and gauge is needed with eyelet terminals on each end.
 
Van's sells 2AWG tefzel in 10 and 15 foot lengths. Yeah, it costs a bit more than welding cable, but given that this is the highest amperage and scariest power cable in the plane, paying $20 more for real aircraft cable that does the job right, can handle some bending during installation / maintenance, and is properly tinned and aircraft-grade doesn't really seem like a bank-breaking unnecessary expense to me.
 
Van's sells 2AWG tefzel in 10 and 15 foot lengths. Yeah, it costs a bit more than welding cable, but given that this is the highest amperage and scariest power cable in the plane, paying $20 more for real aircraft cable that does the job right, can handle some bending during installation / maintenance, and is properly tinned and aircraft-grade doesn't really seem like a bank-breaking unnecessary expense to me.

Gold plated stranding would be even better, as long as no expense is being spared here. While there is some benefit to tinned strands, I fail to see the need for tefzel coating forward of the firewall. I have seen cars sitting out in the elements for decades with straight copper strand cable and PVC jacket and held up nicely, minus the acid based corrosion near the battery and that doesn't apply to us with SLA batteries.

We each must make our own quality/cost decisions.
 
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I have Tefzel cable attached to my battery and I will replace this with Welding cable. A lot more flexible and still excellent fire characteristics. A little heavier than Tefzel. I also hesitate between no 4 and no 2... not for availability. I have both... but rather for weight and actual need.
 
The great things about Welding Cable is that it is uber-flexible and the jacket is tough-as-nails.

I've run 100s of feet of it in battery rooms, bus conversions, mega yachts and because it is so flexible it is easy to install and make the wire runs pretty.
 
One difference that I saw is the Tefzel wire is rated at 150C and the welding cable is 105C. Or at least the ones that I looked at. Maybe it matters, maybe it doesn't. I decided on the Tefzel for the starter and battery cable.
 
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B&C arguably makes the best starter. So I use the 4AWG cable they sell for the task. This may not be optimum for a 12ft cable on rear mounted battery.

I got a great idea here on the forum for grounding and that's a separate cable to the starter casting. Again, maybe not attractive for a 12ft cable.

Then, to assure more than one path home for ignition spark , I used the normal flat strap from engine case to forest of tabs on the firewall.

My 3 works well with a red cable to starter and flat strap to the case, but the separate ground cable to starter approach struck me as optimum performance and reliability.
 
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Ray, the main difference between Tefzel and Welding cable is not the temperature range. It is the flexibility. For attachments subject to movements, I always fear a tefzel wire will unscrew the attachment (I had this on an alternator). On a battery terminal, it is is much easier to attach the welding cable than the tefzel one.

Welding cable is very resistant to abuse. It is also a little bit heavier.
 
Michel,

I understand the benefits of each. I may actually use some welding cable for certain things that need a more flexible wire. I was just pointing a difference between the two for the group. In some instances having a more rigid wire actually be a benefit though.
 
Grounding to empty engine pad?

The studs holding the starter aren't easily accessible, nor are they extra long, so adding an additional ring terminal there feels questionable to me. However, there is a vacant mounting pad between the starter and the alternator on the starboard half of the engine case. It has three 5/16 X 18 threaded holes in line. I can't see why I wouldn't just create my own stud there for grounding.

When I went down the aviation aisle today at Ace Hardware, I found some studs with 5/16 X 18 threads on one end and 5/16 X 24 threads on the other end. They looked like cast iron, black and rather rough looking. Described as Automotive studs. Also, there is a non-threaded portion in the middle which might make it hard to thread a nut down to the engine case to hold the ground in place.

Am I looking at the right thing? Have I found my way off of the straight and narrow and into some odd corner?
 
The studs holding the starter aren't easily accessible, nor are they extra long, so adding an additional ring terminal there feels questionable to me. However, there is a vacant mounting pad between the starter and the alternator on the starboard half of the engine case. It has three 5/16 X 18 threaded holes in line. I can't see why I wouldn't just create my own stud there for grounding.

When I went down the aviation aisle today at Ace Hardware, I found some studs with 5/16 X 18 threads on one end and 5/16 X 24 threads on the other end. They looked like cast iron, black and rather rough looking. Described as Automotive studs. Also, there is a non-threaded portion in the middle which might make it hard to thread a nut down to the engine case to hold the ground in place.

Am I looking at the right thing? Have I found my way off of the straight and narrow and into some odd corner?


Why worry with a stud? Just use a coarse thread bolt, washer and lock washer. Be sure to clean any paint from the contact area to assure a good ground.
 
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