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LyleM

Active Member
I'm putting an Odyssey ES PC680 battery in the back behind the rear baggage compartment in my -8. I've heard some people use 2 AWG battery cable, and some use 6 AWG. I sure would like to use the 6 AWG battery cable. Anyone with experience with this battery and wire gage, I would like to hear how it worked out. Thanks
 
2 for the starter and an 8 for the buss is fairly common. A 6 is to light for the starter load.
 
LyleM said:
I'm putting an Odyssey ES PC680 battery in the back behind the rear baggage compartment in my -8. I've heard some people use 2 AWG battery cable, and some use 6 AWG. I sure would like to use the 6 AWG battery cable. Anyone with experience with this battery and wire gage, I would like to hear how it worked out. Thanks
Click to expand...

I think you misunderstood what you were told. #2 AWG is used for the battery cables on a rear mounted battery. #6 AWG is used as the positive cable from the main contactor to the fuse block/bus [assuming you mount the contactor near the battery].
With a firewall mounted battery, #4 is used for the battery main cables. #8 AWG is generally used for the fuse block/bus feed wire with a front mounted battery.
Charlie
 
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As above, from recollection #2 is "correct" for main cable. #4 you might want to try if you are desperate to save weight, and willing to possibly have starting issues / have to upgrade later on. It's not the #4 cable will "melt" or catch fire on you, just might cause too much voltage drop to turn engine well.

We used #2, aft battery, 180 engine turns v well on Odyssey...

Andy & Ellie Hill
RV-8 G-HILZ
RV8tors
 
CCA Wire

RV8RIVETER said:
If weight is what you are concerned about, I used this, very light.

http://www.periheliondesign.com/fatwires_files/fatwire2flyer.pdf
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I considered using perihelion's CCA "Super 2" wire in my RV-8 but decided against it for the following reasons:

1. The weight savings is only about 12 oz for a 15' run (less when considering the added weight of bigger lugs and cusion clamps.
2. The insulation is only rated to 105C vs 150C for tefzel.
3. At 0.562" OD, the CCA wire is much fatter than standard 2AWG @ 0.392". This is an issue through the spar and the gear towers where space is limited. This also requires larger Adel clamps.

Skylor

Skylor
 
Welding Cable

Skylor,

I used #2 welding cable as the sheath is extremely durable and the cable itself is very flexible. My battery is in the back. My cable route is up the right side, over the spar, and into the switch/breaker panel located on the right. It is barely visible under the right side ledges.
This route worked for me to get power to the main buss. I have a single stud terminal post below the switch breaker panel. Number 6 cable feeds the buss from there.

The #2 cable continues thru the bottom holes in the gear tower, thru the firewall, and to the starter. Lot's of wire for lots of juice.

Sorry I don't have a pick for you.

Don
 
Silly place to worry about weight.

The #2 battery lead that goes from my aft battery box to the starter contactor on the firewall weighs.....get ready for it........2.2 lbs.

Much ado about nothing.
 
skylor said:
I considered using perihelion's CCA "Super 2" wire in my RV-8 but decided against it for the following reasons:

1. The weight savings is only about 12 oz for a 15' run (less when considering the added weight of bigger lugs and cusion clamps.
2. The insulation is only rated to 105C vs 150C for tefzel.
3. At 0.562" OD, the CCA wire is much fatter than standard 2AWG @ 0.392". This is an issue through the spar and the gear towers where space is limited. This also requires larger Adel clamps.

Skylor

Skylor
Click to expand...

Not trying to sell anyone, but just for the record, the 0.562" OD of the CCA Super 2 wire fits perfectly in the 5/8 x 3/4 bushings from Van's, and goes through the spar and gear towers with no problems.
As for the weight savings, I look at the percentage change as well as the absolute weights. In this case it is about 30%. I like that.
105C is about 221F, and is the same rating as the welding cable I have. For this particular run, I'm ok with that as well, and would buy it again.
To each their own!
 
Thanks guys for your input. I now know that I will use the #2 AWG battery cables. I'm going to run the positive cable through some conduit to the front, and was going to run the ground cable in the same conduit to a single point ground, but that would not have been possible with that heavy cable. So checked with Van's and they said grounding to the airframe should work just fine. So I think all is good.
 
The #2 battery lead that goes from my aft battery box to the starter contactor on the firewall weighs.....get ready for it........2.2 lbs.

Much ado about nothing
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Sorry - disagree Steve. If as William says it is 30% then that is a saving of nearly 0.7lbs.

If you want your aircraft to be 50lbs lighter than it could be (and everyone should IMHO), you will not achieve that by finding an engine that is 50lbs lighter. It will be via 500+ items where you can shave off 0.05 - 1.0 lbs.

On the RV-3, the "lightening" holes in the entire set of wing ribs saved 0.77lbs. I am not sure the builder / Vans would go to the trouble if designing and drilling out all those holes to save ~0.8lbs to then "blow it away" with an unnecessarily heavy battery cable.

On the RV-3 we certainly will examine a #4 cable for weight. And be willing to "experiment" and see if it works (or alternatives).

I am not saying #4 will be OK, but worth researching (as is the "Super 2" or whatever).

Andy
 
AWG 2 not needed in your RV3

Andy Hill said:
snipped

On the RV-3 we certainly will examine a #4 cable for weight. And be willing to "experiment" and see if it works (or alternatives).

I am not saying #4 will be OK, but worth researching (as is the "Super 2" or whatever).

Andy
Click to expand...

Andy,
AWG 4 is the recommended starter/main cable size for RV3, 4, 6, 7, 8 & 9 models with the battery located in the front. I'm not familiar with all the possible locations for the battery on the 3. I do know that the stock location for the battery on the 4 [2 place variant of the 3] is in the front.
Vans only recommends AWG 2 cable for the 8 & 8A, IF you put the battery in the rear. This is done to offset the voltage drop during starting, caused by the longer cable.
Regarding using alternate types of cable. The welders cable mentioned by some, has one advantage. The rubber insulation is very thick and flexible. This is useful for use between the battery and main contactor and ground. The stiff Tefzel insulation in Mil Spec 22759-16 wire can cause failure of the battery terminals if it creates side loads on those terminals.
The downsides to welders cable are that it is heavier than Mil Spec wire and it's copper strands are not "tinned" [coated with solder] This lack of "tinning" would only be an issue for planes operated in or near salt water environments. For planes used in those environments, a better alternative would be marine cable. It also uses a soft insulation, but is "tinned".
The CCA wire offered by Perihelion Design does offer significant weight savings. That said, it also lacks the "tinned" strands of Mil Spec and marine wire. It's insulation does not offer the same resistance to damage that the Tefzel insulation of Mil 22759-16 wire offers. [FYI, the car manufacturers use Tefzel insulation on more and more parts in your car] I'm going from memory here [which is sometimes faulty]. While the CCA wire uses an insulation used previously on aircraft wire, I seem to remember that if exposed to flame, it creates a nasty smoke. Can someone who is using the CCA wire verify what it's insulation is made of?
Once you understand the advantages and disadvantages of each wire choice, you will be making an educated decision based on your needs and risk tolerances.
Charlie
 
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CCA Wire Insulation

From the spec sheet:

"Insulation material: Custom polyvinyl TPE proprietary
Flame retardant, 105 °C, fuel proof, oil proof, cut resistant, low smoke, non-cracking atlow temperature."​

I'm using an orange insulation ultra-flexible welder's cable for the battery to ground and battery to main contactor segments, CCA Super 2 from the main contactor up to the starter contactor, then likely tefzel on to the starter.

Thanks for jumping in on the weight savings, Andy, that's exactly my approach. If I can take a reasonable percentage of weight out of every little piece, even if it's only grams, the overall weight savings will come.
 
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LyleM said:
I'm putting an Odyssey ES PC680 battery in the back behind the rear baggage compartment in my -8. I've heard some people use 2 AWG battery cable, and some use 6 AWG. I sure would like to use the 6 AWG battery cable. Anyone with experience with this battery and wire gage, I would like to hear how it worked out. Thanks
Click to expand...

I realize this is an 8 forum, however I have a 6A with pc680 mounted on the firewall. For what it is worth, here is another perspective.

I used a #6 cable to my starter..... ostensibly to save weight. The problems I have had are...
  1. At any temperature, If I haven't started the plane in a week or so, I must "bump" the prop past the compression stroke.
  2. This past winter, it was about 40F. I couldn't get it past the compression stroke and had to give my battery a little extra charge. Then I could start it. This occured twice over the winter.
That being said, the general advice I have been given is to go to a #2 cable. I ordered this today and hope to install it before texas winter sets in... in december. :)
 
Andy Hill said:
...If you want your aircraft to be 50lbs lighter than it could be (and everyone should IMHO), you will not achieve that by finding an engine that is 50lbs lighter. It will be via 500+ items where you can shave off 0.05 - 1.0 lbs...
Click to expand...

This is the attitude we need to have as airplane builders! Hot rods and boats not so much...

The -8 in my hangar uses #4 from the rear to the firewall (still too big), but I stepped down to #6 to the starter to save a few ounces. No problem starting the 200 HP IO-360. Also, I have a rear mounted PC680 in the Hiperbipe which is similar in dimensions to the Vans side by side models. I run #6 the entire run and even after 5 years, the original battery has never had a problem turning the IO-360. Never! Could be 110 degrees and a hot start after refuel or in the teens on a cold morning - Just turn the key and it starts every time. I think that if I pulled the plugs out, I could fly the pattern on just the starter alone.

The key is the starter. If you have a good gear reduction starter vs the old direct drive unit, you will not pull anywhere near the load. There is a wire chart in AC43.13 that should be used to size your wiring - not what "Bubba" in the next hangar says.
 
Thinking only of the battery cable gives an incomplete picture.

The series resistance between the battery and the starter is the sum of the battery internal resistance, wire resistance, connector resistances, and the contactor resistance.

The difference in resistance for #6 vs #2 stranded cable gives about a 1/2 volt change for a ten-foot length at 200 amps (0.83 volts vs 0.33 volts). The battery internal resistance (7 milli-ohms for a PC 680) gives a 1.4 volt drop for comparison.

The battery internal resistance is fixed as is the contactor resistance.

You get to choose the cable size and different connectors.

Sloppy connector installation or use of the wrong connector for the cable chosen could easily make more difference than the size of the cable.
 
For you guys with rear mounted batteries, where are you landing the negative cable? Did you land it beside the battery, or did you also run it up to the firewall gound point? If you chose to land it in the back, did you use a smaller size cable than you did for the positive cable?
 
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Local Ground

Bill,

There is no need to run a negative ground forward. A local connection to airframe ground near the battery is quite sufficient. You should use the same size cable (or larger) as you use for the positive.

Don
 
We grounded it to the battery tray, and made efforts to get metal-metal contact between the battery tray and airframe, then sealed it. Seems to work well....
 
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