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Firewall mount battery box

bryanflood

Well Known Member
Hello all,

thought some of you might find this helpful. I mounted a second battery on my firewall of the RV-10. When I test flew the set-up a stick on thermo-couple measured that the battery was getting too hot, so I tried a number of different combinations to cool it. In the stock configuration the battery would get to about 30F above the ambient in cowl air temperature. This heating was observed even with the alternator and battery isolated from the system, so the heating of the battery observed was due to radiant heat at least in part.

After some trial and error the best solution I found was this cooling shroud made from aluminum over the stock metal battery sleeve that came with the battery. (Odyssey battery metal sleeve like what comes in the stock vans battery mount kit) A 1" blast tube attaches to the box to provide cooling air from the back of the baffles. There is about 3/8 inch gap between the metal battery sleeve and aluminum cooling shroud. The cooling shroud is attached with bolts and standoffs through the metal sleeve that holds the battery. Half of the inlet to the 1" tube has been blocked off at the baffles with no noticeable affect.

With the new cooling shroud and a thermo-couple glued to the outside of the battery plastic shell in about the center of the largest face, the greatest battery temperature I have seen is about 90 F. The ambient cowl temperature, measured between the heater valves and the battery box (to the right of the battery), typically runs about 150F in cruise and up to about 200 on the ground after landing and taxing back to the runway for another take off on a hot summer day.

https://photos.app.goo.gl/4HuJRJTeYFp5SJBk6

https://photos.app.goo.gl/W88NSfZH6eSyrvpp8

Bryan
 
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cool

Thanks for sharing, looks like a nice install.

I'm still on EMP kit so have no deep knowledge in this space, but why do we want a battery up there? Aren't most already nose heavy?
 
Battery on firewall

Lonkelm,

I wanted a second battery for a second alternator and the firewall seems like the best place to put it to me. I have another battery in the stock location.

In some ways the RV-10 is nose heavy in another it's not. I depends how you use it. If you fly solo all the time with one passenger only and limited baggage, then it feels nose heavy on landing and I fly with Ballast in the baggage compartment for better feel even though I am in C.G. range.

If you want to load the plane up for more utility with 4 people and a full baggage compartment (family plane) it seems to makes more sense to shift some weight forward, this gives more flexibility and in some scenarios more capacity, but then you need more ballast to fly solo and be in C.G. range and or get the good landing feel. It's sort of a trade off thing. I guess different builds will come out with different C.G. ranges but I have talked to other 10 pilots who experience the same.

Best regards,

Bryan
 
I put a earthx backup battery on the firewall and initially was getting a high temp indication so put a y in the baffle scat over #5 cylinder to flow air onto the battery and that took care of any radiant heat overheating the battery.
 
Thanks for those insights!!

Lonkelm,

I wanted a second battery for a second alternator and the firewall seems like the best place to put it to me. I have another battery in the stock location.

In some ways the RV-10 is nose heavy in another it's not. I depends how you use it. If you fly solo all the time with one passenger only and limited baggage, then it feels nose heavy on landing and I fly with Ballast in the baggage compartment for better feel even though I am in C.G. range.

If you want to load the plane up for more utility with 4 people and a full baggage compartment (family plane) it seems to makes more sense to shift some weight forward, this gives more flexibility and in some scenarios more capacity, but then you need more ballast to fly solo and be in C.G. range and or get the good landing feel. It's sort of a trade off thing. I guess different builds will come out with different C.G. ranges but I have talked to other 10 pilots who experience the same.

Best regards,

Bryan
 
Dual Batteries

Thanks for sharing, looks like a nice install.

I'm still on EMP kit so have no deep knowledge in this space, but why do we want a battery up there? Aren't most already nose heavy?

If you're starting in with the idea of using dual batteries, I mounted two EarthX ETX900 batteries aft by modifying the mount for two batteries laterally mounted. It prevents any concerns over thermal issues, and the two lithium batteries are less than 10 pounds combined. It's a solid option, but does require running a second power wire forward; I have a 2ga for the main and 8ga for the aux battery running forward, along with a cross-connect contactor as well. The second wire is only 0.78 pounds added weight, so well worth it to me for the redundancy on my all electric installation.
 
This is what is penciled in my head, two in the back, but was considering the long wire run. I might think about primary up front and a backup in the rear to avoid two long runs. A shorter run will help with cranking power for primary use too.
 
Have you monitored battery temperature for the first 20 minutes or so after shutdown? I think that area gets hotter once all cooling air is removed, but have not made any measurements.
 
Battery temp

Bob,

after shutdown the in cowl air temperature rapidly rises and them starts to decay after a short period, like you suggest. The battery temp does not rise more than 10 degrees after shutdown, I am assuming this is due to the relatively cold thermal mass of the battery as compared to the air temp. Even in flight before the air blast tube install it would take some time for the battery to reach a steady state temp, something like 45 minutes to an hour.

Thanks,

Bryan
 
2 in the back

Like Ron pointed out, a better option would have been 2 batteries in the stock location behind the baggage compartment. Besides the benefit of having a few extra pounds as far aft is the obvious benefit of having the batteries in a cool location.
You are right about long wire runs but such decisions are always a compromise.
I have 2 installed at the stock aft location running 2 "fat" wire up each side of the fuselage to the front for starting and distribution.
I do monitor the temperature behind the fire wall, a sort of fire detector probe,
and I see temps from about 140F to 160F. my probe is located exactly where your battery is located.
Time will tell.
 
This is what is penciled in my head, two in the back, but was considering the long wire run. I might think about primary up front and a backup in the rear to avoid two long runs. A shorter run will help with cranking power for primary use too.

As long as your primary wire is 2 gauge, you won’t have starting issues related to voltage drop. The voltage drop for a properly installed 2 gauge wire that is 12’ long (length from the battery to starter contactors), is about 0.19VDC. Assuming your battery is at least 12VDC to start, that will result in about 80A-100A cranking current for an IO-540. And if you’re using a B&C starter, the engine will still turn over at 9VDC with about 120A current draw. A second battery solves the failed main battery issue, and can also be used for additional voltage support as needed.

A 2 gauge wire at 12 feet will handle 100 cold cranking amps at 10ºC rise, or 150A at 30ºC temperature rise if you're excessively cranking a starter with worn brushes on a cold day, which is well above what the starter should draw when operating normally, but also well within the rating of M22759/16 wire, which is 150ºC (the current at that temp is much greater than 200A).

Somewhat off-topic is that issues that cause starter problems…may likely be anything from improper crimping, poor termination, failing starter, burned contacts (contactor), or failing battery - or any combination of the above. Although often blamed, the cable itself is unlikely to be the issue in this case when sized properly at 2 gauge.
 
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Hello all,

thought some of you might find this helpful. I mounted a second battery on my firewall of the RV-10. When I test flew the set-up a stick on thermo-couple measured that the battery was getting too hot, so I tried a number of different combinations to cool it. In the stock configuration the battery would get to about 30F above the ambient in cowl air temperature. This heating was observed even with the alternator and battery isolated from the system, so the heating of the battery observed was due to radiant heat at least in part.

After some trial and error the best solution I found was this cooling shroud made from aluminum over the stock metal battery sleeve that came with the battery. (Odyssey battery metal sleeve like what comes in the stock vans battery mount kit) A 1" blast tube attaches to the box to provide cooling air from the back of the baffles. There is about 3/8 inch gap between the metal battery sleeve and aluminum cooling shroud. The cooling shroud is attached with bolts and standoffs through the metal sleeve that holds the battery. Half of the inlet to the 1" tube has been blocked off at the baffles with no noticeable affect.

With the new cooling shroud and a thermo-couple glued to the outside of the battery plastic shell in about the center of the largest face, the greatest battery temperature I have seen is about 90 F. The ambient cowl temperature, measured between the heater valves and the battery box (to the right of the battery), typically runs about 150F in cruise and up to about 200 on the ground after landing and taxing back to the runway for another take off on a hot summer day.

https://photos.app.goo.gl/4HuJRJTeYFp5SJBk6

https://photos.app.goo.gl/W88NSfZH6eSyrvpp8

Bryan

My only battery is on the firewall on my 10. I also put a shroud on, but covered the top, since that's where the BMS electronics are housed. Not one problem since. I did put a heat shield below the bottom too, to keep the hot exhaust from convection heating the battery case after shutdown. My pictures are in this post:

https://vansairforce.net/community/showpost.php?p=1543464&postcount=10
 
Any reason not to mount in the sub-panel structure inside the cabin? Never heard of it on a -10 but I've seen EarthX batteries inside cabins of other RVs. That would allow for the forward location without ever getting too hot. As far as the need to occasionally charge the battery, I know you can attach pigtail charging wires to them.
 
Any reason not to mount in the sub-panel structure inside the cabin? Never heard of it on a -10 but I've seen EarthX batteries inside cabins of other RVs. That would allow for the forward location without ever getting too hot. As far as the need to occasionally charge the battery, I know you can attach pigtail charging wires to them.

I don't get it, why not just mount the battery, or batteries, aft of the baggage compartment on the mount as designed - and avoid temperature issues and the need to design and build a new mount?
 
It is possible

Any reason not to mount in the sub-panel structure inside the cabin? Never heard of it on a -10 but I've seen EarthX batteries inside cabins of other RVs. That would allow for the forward location without ever getting too hot. As far as the need to occasionally charge the battery, I know you can attach pigtail charging wires to them.

We recently mounted two EarthX ETX900-VNT batteries on the forward side of the subpanel aft of the firewall.We are using stock location aft of the baggage bulkhead for our built in oxygen bottle so that space wasn't available for battery mounting. We did install two of the Van's access panels on the forward fuselage skin. We also are installing a small panel in the engine bay with a door in the side of the cowling for charging as well as regulated power supply plug ins for use when needed. We do not have a full current capable external power port, since we are electrically dependent and have no intention of jump starting dead batteries.

I will say that access is limited and I'm not sure I can recommend this location to you. The batteries have to be fed in above the rudder pedals and then secured. I did it myself, but it would be easier with two people. I am hopeful we do not have to remove or access the batteries very often. Access to the battery terminals is somewhat limited, but doable.

For us the benefits were much shorter battery cables, favorable environment (compared to firewall forward) and help with CG since we have air conditioning and O2 located aft of the baggage bulkhead.

We had to run vent tubing for each battery out the bottom of the fuselage.
 
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