Engine Bay Air Temperature

[AKKen07]

There's enough discussion about the temperature limits for engine-side firewall-mounted EarthX batteries that I wondered how I could install some sort of sensor which would be incorporated into my EIS. Bingelis mentions temperature indicating stickers but I want something a little more real-time so I could see if I'm about to fry my expensive batteries. I would also know if I need to build a blast tube before I "blast" a battery. Today I thought of a CHT probe. It's the right temperature range, reasonably tough and might be easy enough to plug into an aux input for my EIS which I could then read on my EFIS. I haven't figured out if it would actually be compatible yet, but is there any reason it wouldn't work? I'd have to make some little mount near my batteries, but it seems like it would be simple enough. Any thoughts?

[PaulSA]

If you are using Dynon then you can add an extra OAT probe and connect to a general port. I have one fitted to the tunnel on my RV-10. IIRC, though, the max temperature it registers is 150F. I am sure a general purpose temperature probe could be configured.

[Nev]

I'm interested to follow this, I've got the same battery mounted on the forward side of the firewall too and agree, it would be nice to have a real time warning of a high temperature. I have added a blast tube, and the battery is housed in an insulated case with just the top exposed.

My main concern is on the ground after engine shutdown, when there is no cooling airflow. Having a temperature monitor might not work in this case because the aircraft could be turned off and unattended. (Large aircraft have a similar issue with the APU fire detection circuit when unattended on the ground and they rely on an automatic shutdown).

I also wondered about installing a vent in the top cowl above the battery, or it that vicinity. It would allow heat to rise out from the vent behind the baffled area during flight and on the ground, and shouldn't increase the pressure in that area. On the ground it may create a reverse cooling flow from the lower outlet, up the firewall area and out the vent.

During initial flying, my plan is to open the oil access door after shutdown until I get a feel for how hot it gets under the cowl after shutdown.

[AKKen07]

Nev, after talking with EarthX I’m confident enough that a lot of folks are putting their batteries where we are and getting away with it. And she (EarthX rep) said most don’t have blast tubes. So I’m betting you’re in great shape - I’m going to skip the tube at first and hopefully justify that with some sort of probe. I do have the insulated case though. I have been thinking about the blast tube logic too - and I think it would help with heating after shutdown just by virtue of being at a cooler temp when the prop stops and things start warming. Then the insulated case will hopefully slow the battery warming until enough heat escapes from the cowl to stop the whole process.

[BravoGolf]

Dynon’s EMS comes with a thermocouple to measure carb temperature, it connects to pin 23. I chose to mount it just above (1/4”) the EarthX battery on my firewall on my RV-7. Of course it’s measuring radiant heat but it gives me an idea of the temperature in that area. It shows up on the EFIS as carb temp. I’ve asked Dynon for the ability to alter the label, but I’m sure it’s not high on its priority list.

Look in the lower right corner of the display, it’s below the RPM and MP.

[AKKen07]

That’s a great idea. What’s the range on a carb temp gauge? I’ve never had one…

[BravoGolf]

The installation manual doesn’t give a range. It’s displayed on the EFIS screen so there isn’t a gauge, just a digital value. I’ve seen temps up to 115F but since I installed a larger blast tube it rarely goes above 100.

[whee]

If your using GRT stuff I’d just get their $26 OAT gauge and mount it where you want it. Their EIS is so user programmable I have no doubt you could set the parameters you want and feed them to the EFIS.

[jaredyates]

But it won't blink post-shutdown if the warning is run through the EMS, right?

[AKKen07]

So it might be worth running it to its own LED…?

[BravoGolf]

It is a wired off the battery but it only controls the ground to the light. So if the ship’s power is removed it won’t flash and if wired to the EFIS it won’t show up

[AKKen07]

GRT offered this to help me with this decision: The carb temp sensor has a limited range (127F I think). You could purchase an FT-1827-02 fluid temp sensor and use that to display air temp in your engine compartment. You can connected it to the coolant temp sensor input which will display from 59F to 314F.
So I'll do that

[Utah-Jay]

How many are putting the EarthX battery on the cockpit wide of the firewall?

[AKKen07]

I will have one on each side.

[Bcone1381]

I am on the cockpit side.

[Battson]

I kept mine cockpit side for this reason.
My Oddessey battery under the cowl has the same temperature limits with the metal jacket installed. Funny how the Oddessey tech needs a metal jacket to be safe at 60*C (140F), whereas the Li battery just goes straight to the same 60*C temp with plastic...

[zkelley2]

How many are putting the EarthX battery on the cockpit wide of the firewall?

I put mine on the cockpit side.

[Utah-Jay]

I am planning on putting the battery on the cockpit side of the firewall

[svyolo]

I have a hot side firewall mounted Earthx in one of their boxes with a ventilation tube. I am not sure if that is the same as a blast tube. It 1/2 inch, mounted low on their SS box. I burned in a matrix of cooling flow in their foam padding. I would not describe it as "air cooled". I would describe it as a slight positive pressure, keeping out hot air. I did the same with my dual EFI fuel pumps, in a housing on the firewall. I will configure one of my EIS ports with a sensor to sense temp at first. Both are temporary just to make sure they work.

[Nev]

I'm probably going to install a small vent in the engine cowl door beside/above the battery and aft of the high pressure area. I think this will draw cooling air upwards past the PMAGS and battery, and discharge it overboard on the right side. It should be very effective on the ground after shutdown too. It won't need to be very big - I'm thinking a couple of square inches.

[Nev]

Engine bay temps

I rigged up a temp probe yesterday near the battery and ran the wire through the FW into the cockpit. I've got an EarthX battery in the engine compartment, in an insulated battery mount, and a vent in the cowl above the battery. I also have two additional vents, one on each side of the lower cowling. All 3 vents help to increase the pressure differential while inflight. The one above the battery was added to provide an outlet for hot air while on the ground.

I did a series of flights, allowing the aircraft to stand out of the wind after each flight with the engine shut down. While inflight, the aft compartment showed around 35c on each flight and never really got much hotter. This made me realize that the cooling air blast tube on the battery was not really necessary and I've removed it.

After the first flight the temperature gauge recorded its highest reading 15 minutes after shutdown of 52°c.

I then taped the 3 vents shut and flew again. This caused the CHT's to run 10° hotter, but no change to the aft engine engine compartment. This time the highest reading was also 15 minutes after shutdown and was 56°c.

After that I returned everything to normal but left the temperature gauge in place and flew some circuits. The ambient temperature was 25c, and the CHT's always get on the warm side in the circuit, although they all stayed below 200c (390f). The real eye opener was when I put the plane in the hanger and was about to remove the temp probe and saw it was showing 64°c ! The battery is rated to 60c. That was where it peaked, and I assume it was a function of slow flight heating the engine hotter than normal and not much chance to cool down before stopping the engine. I guess opening a cowl in these warmer conditions would provide immediate relief.

I plan to repeat the same exercise once more now that I've made a few changes and will report if the results are different.

5F586552-5A07-41B9-99C3-7EB1002F5136.jpg

[Bcone1381]

I like how you collect real scientific data!!

[Battson]

I guess opening a cowl in these warmer conditions would provide immediate relief.

I had to open the cowl doors on a hot engine to fiddle with a loose EGT probe connection, having landed in the Nelson Lakes region this Tuesday. It caused the cylinders to chime like bells for a few minutes as they rapidly cooled, definitely not doing anything good for the engine.

[Richard E]

We routinely open the oil hatch on top of the cowling after shutdown.

Our LAME also refused to sign off lithium batteries so we stuck with two conventional lead/acid (24v) under the seats.

I did sneak one lithium backup battery into one Dynon screen, but often wonder what I would do in the event of it overheating.

[kestrel]

Our LAME also refused to sign off lithium batteries so we stuck with two conventional lead/acid (24v) under the seats

Lame indeed! EarthX even has an FAA approved/TSO model.

LiFePo4 are not the same is your laptop, phone or what Boeing used.