Battery relocation

[Tim213]

Hi everyone, I know this has been discussed in the past but I am moving my battery location. My PC 680 has failed a couple of times in cold weather even after being on the charger. It just doesn’t seem to have the cranking power to turn the 3 bladed Trailblazer prop unless it’s warm. So I’m upgrading to a Earthx 900. My 680 was mounted on the firewall but not in a place to jumpstart without removing the top cowl. So I’m moving the new battery inside for better accessibility and heat protection the Earthx batteries seem prone to. It seems that under the seat is a common place so it will likely go there. My question is did you run the ground cable back to the firewall on a ground block or did you ground it near the battery to the steel frame, or how did you do it? Also any recommendations on how to best route the starter cable from the contractor to the battery under the seat is appreciated. Thanks

[marcusofcotton]

I'm of the camp that says to never use your frame as a current carrying device so as to avoid magnetizing it. That said, I'm also a weight weenie!

[jaredyates]

I am not opposed to airframe grounding but I would definitely not put the battery under the seat. Put it on the aft side of the firewall instead. Some folks put the heavy battery under the seat for weight purposes, but that is moot with the lithium. By putting the battery that far from everything, you will require more wire which means more weight, cost, resistance, and voltage drop. Also, you create the need to fabricate some robust short circuit protection from passenger feet and cargo. And you lose that space which is perfect for a tool bag or autopilot servo.

Also, the temperature rating on the Earthx is higher than the rating on your PC680. I ran the Earthx on the forward side of the firewall on our last plane and it held up better than the SLA batteries in the same spot. I never could get more than a year out of a lead battery on the forward side of the firewall.

If you get the vented version, you can route the vent right through the firewall and into the engine compartment.

[Battson]

The earth connection between the engine and battery is key.

If you are having trouble starting with a PC680, it's more likely an earth / circuit issue combined with a cold battery, than purely a battery issue. The starter draws hundreds of amps at 12V, a very low resistance circuit is required for this to work. There are many ways to have resistance in the circuit, e.g. is there paint between your starter and your engine block?

I think you get the point. You really want a huge and solid earth strap either direct from the engine block directly to the negative battery terminal, or at least to your star-point earth.

This means a battery on the firewall, or alternatively a lot of extra power cable. Remember, the longer the cable the heavier it needs to be. Originally I was quite optimistic about cable sizes (some 13 years ago). Now I would say 4 AWG is the absolute bare minimum, assuming a firewall battery run. I think 2 AWG or 1/0 AWG is a better choice. I had problems starting with 4G and upgraded to 0G cables, and moved the battery from under the seat to the firewall. This helped a lot.

If you have the battery high up the firewall, it will get hotter after engine shutdown (when things get the hottest). It also makes it harder to jump start. For anyone building anew, I suggest battery low on the engine side of the firewall, near the cowl door. My PC680 has lasted several years on the firewall, since the move from under the seat. They don't like being overheated.

[kestrel]

I'll second everything that Jared said.

I have my EarthX on the engine side of the firewall because it lives in the same box as all the PC680's that died before it. I insulated the battery box and ran a small cooling duct to it. The cooling duct is small enough diameter that it may not be helping anything, but I can't motivate myself to remove it.

Assuming that you move yours, Jared has the right advice.

[Nev]

What they said. My EarthX is mounted on the engine side of the firewall, with a vent in the cowling directly above it to help with cooling after engine shutdown.

During testing I ran a remote temperature sensor through to the battery compartment on the engine side of the firewall and sampled the actual temps during operation. The hottest temperature recorded under my cowling was approximately 13 minutes after engine shutdown, (but below the EarthX max operating temp). Inflight temps were relatively low.

[svyolo]

The problem with moving the battery farther aft is the required wire size goes up rapidly, as would the requried ground wire to the engine block which is probably necessary.

[Nev]

I also meant to say, it is relatively simple to add a ground power plug for charging and jump starting. Mine is located on the cockpit side of the firewall, between the rudder pedals. This enables me to use a jump pack if I need to, while remaining in the aircraft so it can be done by one person.

[svyolo]

I have a big 32AH lithium jump pack in the right boot cowl. Wired only as a battery back up on a switch, Easily removeable to jump start somebody else. I haven't put in a firewall plug like NEV said, but will. Seems like a great idea.

[jaredyates]

I also meant to say, it is relatively simple to add a ground power plug for charging and jump starting. Mine is located on the cockpit side of the firewall, between the rudder pedals. This enables me to use a jump pack if I need to, while remaining in the aircraft so it can be done by one person.

There is good wisdom here. If you need to make an extension cord, make one for the battery charger instead of the whole electrical system.

[noema]

I hung mine on the firewall after watching some yt videos on burning LiFe batteries. The burn down is more controlled than with LiPos but they still generate a ton of white smoke. This is presumably why EarthX has a VNT version with vent tubes that need to be routed to the outside.

[bearhawk2015]

I’ve had my earthx on the firewall for 7 years with no cooling tube and I’ve had no problems.

[Nev]

I’ve had my earthx on the firewall for 7 years with no cooling tube and I’ve had no problems.

This is good data point. Mine has a cooling tube, but I will likely remove it. I'd be better off having a slightly higher pressure above the cylinders that removing the cooling tube will give.