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blast tube on alt

miyu1975

miyu1975

Well Known Member
anyone have any good shots of who they affixed the blast tube towards the alt? I was trying to work through this today I didn't come up with anything I was satisfied with...

Also, where on the alt do you want the blast tube....front, back, side...??

IMAG0110.jpg
 
Ryan:
It looked like the air was being sucked in the middle and slung to the outsides so I put a reverse flow on the tube. sorry, no picture of it mounted.


Uploaded with ImageShack.us
 
Larry,
I like your idea. I did something similar, but used red RTV to "mold" the turn in place.
What I'm having trouble with is finding a way to support the end of the tube & hold it in place. How did you do it?

Thanks.
 
What I have found is that the part of the alternator that fails due to heat is the regulator - not the big moving parts. The reg is in that silver box on the back, so I cut the end of the hose on the diagonal and tie it close to the "open" front end of the regulator housing with a piece of thin safety wire. The wire sits in the goove of the hose, and through one of the slots in the alternator case.

Paul
 
miyu1975 said:
....where on the alt do you want the blast tube....front, back, side...??
Click to expand...
When Plane Power wrote its installation instructions, it would have been helpful to include an image. The information does however, include the following language:

"Supply outside ram air to rear of alternator by the use of 1" scat tube or other suitable ducting."

This is how I interpreted that particular instruction:

2wnmmw5.jpg
 
I had this same question when I went to mount my 60A, belt driven, Vans supplied PP alternator - so I called PP and asked them. Their answer surprised me - which was that blast tube cooling was not necessary unless you were consistently running the alternator at rated current for hours on end. As a result of this discussion, I did not install a blast tube. I might see 60A for 20 or 30 seconds after engine start, but during normal ops 20-30 amps is typical. Around 75 trouble free hours so far.

Would be interested in hearing if anybody has had to replace the diodes one of these alternators who did not use a blast tube.
 
Noah said:
Would be interested in hearing if anybody has had to replace the diodes one of these alternators who did not use a blast tube.
Click to expand...

This is hardly a scientific sample (sample size = "1"), but I didn't have a blast tube on my original ND alternator, and it lasted about 300 hours (if I remember correctly). Regulator failed. Added a blast tube to cool the reg on the second one, and it lasted 1,000 hours. Coincidence?

Like I said.....small sample size, probably anecdotal....:rolleyes:
 
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At the risk of sounding cynical (who me?)..I wouldn't bother with the blast tube cus the rear bearing will fail in 300 hours anyway!

My PP alt was an expensive waste of time.

Frank
 
blast tube

I installed a blast tube when I built my airplane. The ND alternator bearing failed at 124 hours. We were on the way to Oshkosh and ended up spending two days in Scottsboro, Alabama with a bunch of very helpful folks. We found an alternator shop in a neighboring town that took three alternators and made the one we have now. The bearing spun in the housing and ruined the rear housing. It also ripped some things loose that needed to be connected!!!!! I don't know how much blast tubes work to preserve bearing life.
 
DEWATSON said:
I installed a blast tube when I built my airplane. The ND alternator bearing failed at 124 hours. We were on the way to Oshkosh and ended up spending two days in Scottsboro, Alabama with a bunch of very helpful folks. We found an alternator shop in a neighboring town that took three alternators and made the one we have now. The bearing spun in the housing and ruined the rear housing. It also ripped some things loose that needed to be connected!!!!! I don't know how much blast tubes work to preserve bearing life.
Click to expand...

Something similar happened to a friend in my EAA chapter on his way back from Oshkosh this year. Someone mentioned to him, and I'd never thought about it, that the alternator blast tube turns into a downspout in heavy rain and can dump water right into the alternator. (Probably tough on bearings and other things)

Hmmmm, I have the same blast tube setup as most and wonder how much water actually gets down it.
 
More data

I have a few extra GRT temp sensors and connect via a multi-switch to the "coolant/H2O" circuit on my GRT eis. I have moved these to various spots in the engine compartment and monitored results for many flights. The sensor attached to the regulator housing shows a range of 120 to 130f in summer during cruise. It will rise inversely with the airspeed during approach. When I turn off the runway it will be above 150 f. A few minutes of taxi will bring it up to 180 f. I agree with Paul that the big parts do not normally experience excess heat. I have no cooling tube. I have tested many. I got more results from a heat deflector to keep the hot air coming from the #1 cyl fins off the back of the alternator during ground ops. After I refuel on trips the temp drops below 150 in a few minutes of climb. When I level off at 5000 msl it is below 140 f. I also experienced water problems when flying in rain with a common tube with no water baffle; regulator failure. Small sample here, just add to other reports. Now I have converted to external regulator, old Ford solid state. One more observation; my brushes wear much faster than those in cars. About 200-300 hrs.
Happy landings,
 
My RV-6 didn't have a blast tube, so I added one (corrugated black plastic tubing). I used a hot air gun to mold the curves into the tubing and used red hi-temp silicone RTV to help hold the curves and cut a boloney slice at the discharge end. I simply used the red RTV to glue the end to the back of the alternator with safety wire to hold it in place until the RTV cured. It's stuck on there pretty good now, and if I need to remove it, a razor knife will do the job.
 
I hate alt problems and I?m starting to wonder if Dale has the right idea, external regulator mounted in the cabin. I know they were old rebuild that had been rebuilt 20 dang times but, I put 3 on my Archer in 6 years. I really don?t want to be doing that again
 
I removed the regulator from my alternator and fitted a remote regulator in the cabin. Also mounted the regulator for the backup alternator in the cabin. No blast tubes on either alternator.:)
 
miyu1975 said:
anyone have any good shots of who they affixed the blast tube towards the alt? I was trying to work through this today I didn't come up with anything I was satisfied with...

Also, where on the alt do you want the blast tube....front, back, side...??

IMAG0110.jpg
Click to expand...

Ryan, I have a B&C and I was going to mount the air tube where you (and many others) have it. B&C advised me that this was not the correct position. According to B&C (and presumably the PP is the same) their alternator sucks in cooling air through the front and rear and exhausts heated air through the sides (centrifugal fans). In other words you are aiming your cooling air at the place where the hot air is being expelled and that is virtually useless.

I believe the cooling air needs to be directed to the housing at the very rear of the alternator. That will be effective in cooling the alternator, and most importantly the diodes in the rear.
 
Captain Avgas said:
Ryan, I have a B&C and I was going to mount the air tube where you (and many others) have it. B&C advised me that this was not the correct position. According to B&C (and presumably the PP is the same) their alternator sucks in cooling air through the front and rear and exhausts heated air through the sides (centrifugal fans). In other words you are aiming your cooling air at the place where the hot air is being expelled and that is virtually useless.

I believe the cooling air needs to be directed to the housing at the very rear of the alternator. That will be effective in cooling the alternator, and most importantly the diodes in the rear.
Click to expand...

Yes, that is also true for Plane Power alternators. I was told exactly that by Plane Power tech support.
 
Alt. blast tube

Quote:




Originally Posted by Captain Avgas

Ryan, I have a B&C and I was going to mount the air tube where you (and many others) have it. B&C advised me that this was not the correct position. According to B&C (and presumably the PP is the same) their alternator sucks in cooling air through the front and rear and exhausts heated air through the sides (centrifugal fans). In other words you are aiming your cooling air at the place where the hot air is being expelled and that is virtually useless.

I believe the cooling air needs to be directed to the housing at the very rear of the alternator. That will be effective in cooling the alternator, and most importantly the diodes in the rear.


roee said:
Yes, that is also true for Plane Power alternators. I was told exactly that by Plane Power tech support.
Click to expand...

I just installed a Plane Power and got the same information. Blast tube air to the rear of alt. Adding some stainless screen under the blast tube intake opening should keep bugs and some rain out.
 
While you're working at the alternator....a few well-placed dabs of silicone between case and rear cover will prevent the aluminum cover from vibrating, fracturing, and potentially shorting something.
 
No blast tube on my Plane Power, 450 hrs so far. The alternator that Vans supplied in their kits prior to the Plane Power, lasted 100 hrs with a blast tube.
I attribute that failure to improper operation though. I used to turn the alternator field on after engine start. After much discussion on these boards 5 or 6 years ago, I learned that, that was completely wrong. (Thanks GMC George), I now "gang" the alt field with the Master switch, On together, Off together. A relatively small sample, but, when I ask someone who has had early alternator problems, how they turn the alternator on, every one of them had been turning the alt field on AFTER starting the engine.
 
jthocker said:
No blast tube on my Plane Power, 450 hrs so far. The alternator that Vans supplied in their kits prior to the Plane Power, lasted 100 hrs with a blast tube.
I attribute that failure to improper operation though. I used to turn the alternator field on after engine start. After much discussion on these boards 5 or 6 years ago, I learned that, that was completely wrong. (Thanks GMC George), I now "gang" the alt field with the Master switch, On together, Off together. A relatively small sample, but, when I ask someone who has had early alternator problems, how they turn the alternator on, every one of them had been turning the alt field on AFTER starting the engine.
Click to expand...

The topic of switching on an alternator field after starting the engine is a complex issue and many "experts" disagree.

However Marc Ausman of Vertical Power claims that his solid state electrical control systems switch the alternator field on after the engine starts. This is his comment:

"IMO, there's no point in having the alternator field on prior to engine start. The alternator is not spinning so it won't generate any power. Since the voltage regulator is trying to bring the voltage up to 14 volts (from 12 volts), it is drawing current (typically 3-4 amps) and not producing any benefit with the engine stopped.

When the field is on, the alternator also generates a load on the engine proportional to the amount of electrical load needed. I haven't done any formal testing, but consider the electrical load during start.

After you start the engine, the Vertical Power VP-200 then automatically turns on the alternator field, then the avionics. Each device is turned on with a short delay (1/10 second) before the next device is turned on. This gives the voltage regulator plenty of time to adjust to each new load being turned on".

I'm certainly no expert in this field but my guess is that the biggest danger of starting the engine with the alternator field off is that you might then forget to turn it on. Some alternators used on RVs are internally regulated (Plane Power), others are externally regulated (B&C). When in doubt on this issue I'd suggest asking the manufacturer of the alternator what they recommend. That might be preferable to relying on anecdotal information. ;)
 
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If you use a blast tube, aim it at the rear compartment of the alternator where the diodes are. The internal windings get cooled by internal fan blades. I aim my black corrugated plastic tube with a piece of 12 gage solid wire from a section of romex. Leave the black or white insulation on and tie wrap it to the tube every inch or so. 12 gage is pretty stiff and when connected to the tube in this manner, will maintain the shape you make it. If the tube is long enough, you may need to stabilize it to something structural on the engine, but it will stay where you bend it for aiming purposes. I did both airplanes this way (-6 & -8) and both still work fine - 450 hours on the -8 and probably 600+ on the -6.
 
I thought I had posted this pic in this thread but I don't see it, here's how I did it. The tube is slotted between the tie wraps to direct the cooling air into the rear of the alternator.

IMG_4369b.jpg
 
I've never seen or had a failure that was induced by water. Possible, yes I suppose but I've not encounted one.
 
I had one. Torrential down pour IMC. Worst Ive ever been in. As soon as it went from heavy to stupid heavy, my alt went. Of course I have no way of knowing it was the exact cause. It is was I attributed it to. Blast tube right on regulator for cooling.

I never put a blast tube on again. Probably had even more failures as a result of no blast tube that I ever would or did with it. I know!:eek:
 
I used a blast tube similar to Walt's. To address water I drilled a 1/8 hole in the bottom cap...
 
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