Temperature inside cowlings

[Battson]

Does anyone know how hot it gets inside the cowling?

I am mounting a backup battery on the firewall, and I don't want to exceed the battery's maximum temperature limit.

[Battson]

My research has turned up this interesting fact -

"One thing to keep in mind is that most items under cowl don't see their highest temperatures until after engine shut down. The cylinders cool down and everything else heats up. The temperature rise after shut down for some components can be quite dramatic."

Given that fact, I could simply go flying and then check the temperature once I land & shutdown.

[jaredyates]

Let us know what you find out. I was just talking with a battery engineer a couple of days ago about this and he said the same thing about the temperature rise after shutdown.

[Battson]

It'll be a while before I'm back up and flying, a fair bit of modification and rework going on at the moment. I found that inside a Sonex cowl runs about 120-140F, in flight, but that's nothing like a Bearhawk.

I am rethinking the battery location I've chosen, because it's at the top of the firewall. Seeing as heat will simply rise when the engine is shut down, this is probably not the coolest place.

[Chris In Milwaukee]

What kind of battery is it? My primary battery is I the engine compartment, but it's the usual lead acid type. Are lithium batteries (presumed) extremely heat sensitive?

[jaredyates]

So far my research points to them being a little less heat sensitive than lead acid.

[Battson]

It's a Lithium metal hydride battery. LiPO4 I think.
I guess maybe it's their plastic case which limits them? Mine is limited to 60C or 140F. Supposedly they are more heat resistant than a normal battery, in terms of their chemical stability.

[jaredyates]

The thermal runaway temp is north of 500 degrees f for lithium iron phosphate, vs approx 300 for lithium cobalt. So the aforementioned limits are concerning the health of the battery, not the safety of it.

[Ed.Meyer]

I don't recall what the temperature limits are for the EarthX LiFePO4 batteries but we have two of them on the engine side of the firewall of our Patrol. I called EarthX before buying them asking if that was acceptable and they assured me it was and that many airplanes have them mounted in the engine compartment with no problems. We have only a little over 10 hours on the tach so far and no problems. I too had heard that the hottest is after shutdown.

[Battson]

I don't recall what the temperature limits are for the EarthX LiFePO4 batteries but we have two of them on the engine side of the firewall of our Patrol. I called EarthX before buying them asking if that was acceptable and they assured me it was and that many airplanes have them mounted in the engine compartment with no problems. We have only a little over 10 hours on the tach so far and no problems. I too had heard that the hottest is after shutdown.

I understand the EarthX battery share a common temperature limit with most other LiFePO4 batteries, 60C or 140F.