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Cooling blast tube for alternator

JHartline

Well Known Member
I don't know for sure but I suspect my alternator gets pretty warm inside the cowl. Have any of you 14-drivers added a blast tube and if so, how did you plumb it? There's not a lot of real estate available for drilling a hole.

Suggestions, pictures?? Anything would be appreciated.
 
I don't know for sure but I suspect my alternator gets pretty warm inside the cowl. Have any of you 14-drivers added a blast tube and if so, how did you plumb it? There's not a lot of real estate available for drilling a hole.

Suggestions, pictures?? Anything would be appreciated.

I have had a blast tube to the alternator for all my three RVs and have never had any issues with alternator. I can't see a reason why not do it as B&C told me it is a good idea to have it. I don't have a picture handy but can take one next time I am at the airport.
 
Without before and after temperature measurement, no one knows if they really need a blast tube, or if adding one actually does anything useful.
 
Don't they have their own cooling fan? I guess what my question would be is...does it pull air through for cooling or push? Providing a source of outside air at the cooling inlet might be helpful.?
 
Most are designed for auto under hood installation and it is not a lot cooler there than in our planes. I have an ND alt in my 6 that has provided 850 hours of trouble free service with no blast tube. The most heat sensitive part is the VR circuitry (internally regulated) and I use externally regulated alternators to get that part into a cooler place (i.e. further away from an exhaust tube). The only other heat sensitive part are the diodes and they can take quite a bit of heat.

Pretty much every alternator has a fan. However, if you spin them backwards from the designed direction, they are no where near as effective at moving air. I buy alternator designed to run in the direction of the Lyc, which is opposite of 95% of auto engines.

Larry
 
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Alternator temps

I can’t speak for any other alternator brand but my B&C alternator fan ( front and rear fan location) pulls air nose to tail of the aircraft. I also have a thermocouple I can move around to test temperatures in different area FWF (normally is tucked in the primary battery box) and have never seen more than 35 degree F delta T to ambient in the front alternator location. The pad mount location is about 25 degree delta T. On a 14 the intake air skat tube runs right next to the alternator and maybe that helps.
 
Good points…I’m still researching if additional cooling is needed. Looking at the available space and access has me wondering how to do it should I decide it’s necessary. I had to do some post-OSH maintenance so I’m looking at options while I have the cowling off.

Data points are tough to define since there is no “max temp” on an alternator like there is on the P-Mags. At least none that I’m aware of. The delta-temp measurements are helpful to understand what relative differences i might be dealing with (thanks Dwight). I was going to stick a thermal sticker on or near the alternator and at least get a feel for an actual temperature under the hood. Anyway, it’s just a research project at this point.
 
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RV-10 PlanePower Alternator

Plane Power alternator in my RV-10, 700 plus hours and blast tube installed.
The tube is directed at the back of the alternator where the electronics are installed and where air is drawn in by the cooling fan. When you install the baffling it will be easy to install a 1/2" flange/nipple where you can attach a short scat tube and directed at the back of the alternator, plenty of room.
If later you feel you don't need it, it is a simple matter of capping the nipple.
The only downside I see is that of pumping additional air into the lower cowl and thus reducing the pressure differential and cooling effectiveness of the cylinders.
As an aside, my cylinder temps run in the low 300s with both a blast tube on the alternator and a blast tube on one of the mags.
I agree, some before and after data would be nice to have.
 
I agree with Ernest. I have already had to rebuild my Plane Power alternator on my -14. After the rebuild, I had installed a 1" flex tube. Drilled a hole in the front baffle, gooped it in place, zip-tied it to blow on the rear of the windings. My alternator still trips every so often but it resets easily. It is pretty warm here in Texas and even though my CHTs are between 280-350 most of the time, I suspect it's pretty warm under the #1 cylinder. I normally pull 11 amps without lights on. 18-22 with other systems on. Not excessive amount of power but that is still heat. Note: I was given the install paperwork when I bought the plane. Interesting that the alternator install shows putting a cooling tube in, but the builder of my plane saw fit not to. I guess being built in Oregon but flying in Texas there is a lot of differences. I even removed the complete cabin heat system to try and reduce the leaking hot air into the cockpit. I won't need it for quite awhile yet.
 
Might want to get some temperature measurements before choosing to feed water and dirt into the back of an alternator. And since it has fans at both ends, the blast tube is supplying something less than half the cooling air anyway.

Then consider the source of the heat, because it's always more efficient to reduce the source.

First convection; we know typical air temperatures in the lower cowl ballpark at 120F to 180F. Not insignificant, but arguably no warmer than cars, where the alternator lives in the outflow from (typically) two stacked heat exchangers, one of which is operating at 215F+.

There isn't a lot of metal to metal contact in the alternator mounting, so heating by conduction isn't likely to be significant. That leaves radiant heating.

Look at the photos below. What red hot thing is 6" to 10" from the back of the alternator? Does your red hot thing have a truly effective heat shield?

It's one of the goofy details of Lycoming design. The put the alternator on the side near the #1 headpipe. They put the starter on the cool side, where the headpipe is quite a lot more rearward.
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