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Vacuum pad driven Alternators

S

SHIPCHIEF

Well Known Member
The 12/24 volt post got me thinking about weight again...
What about those vacuum pad drive alternators.
The first offerings were 8 amp permanent magnet jobs, and now 20A and bigger 'traditional' alternators are being offered.
The weight savings is substantial, several pounds! Also the weight moves aft.
With many planes going 'All Electric' the vacuum pump is not used, so why not? What is the current draw with Modern experimental avionics (Stein could give input ??)
A simple light plane could get by with 8 amps, more avionics if kept at home with a smart charger between flights. That alternator is advertised @ 2.75 lbs.
The larger 20A unit weighs 5.75 lbs, but you get to delete the belt, drive pulley, and brackets too. The smaller diameter models claim to clear specified oil system components on the back of the engine.
 
SHIPCHIEF said:
With many planes going 'All Electric' the vacuum pump is not used, so why not? What is the current draw with Modern experimental avionics (Stein could give input ??)
Click to expand...

With an all electric aircraft, why would you want vacuum pump? You're all electric, you don't need it.

The current draw on modern panels is all over the map. With everything on, my panel draws about 50a. However, I can shed things pretty quickly and a 20a alternator can keep more than enough going to get me home safely. Additionally, I have backup bateries that should last about hour if the backup alternator goes south too. Fortunately, it's highly unlikey for a multi-compenent failure.
 
I can't think of any reason a simple light airplane could not go with the vacuum pad mounted alternator as the primary/only alternator. My electrical draw is about the same as Bob's with everything on (even more with the Air Conditioner on), but I draw about 25 amps in normal cruise with strobes and nav lights on. My airplane is a full IFR machine. I think you could have your simple light airplane and you would have amps to spare with the 20 Amp pad mount.
 
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So Bob;
You have 2 alternators?
I suppose an RV-10 with all the Bells & Whistles would be right at home with such.
By the way, your site is nice, so is you plane.
I guess I'm thinking down a different path.
We're building a light weight Night VFR RV-9A for mountain flying. I'm trying to shed every pound possible, consistant with VAN's intent.
I was thinking about using the Vacuum Pad driven alternator as the sole source of ship's power to recharge the battery and run the avionics & lights.
 
SHIPCHIEF said:
So Bob;
You have 2 alternators?
I suppose an RV-10 with all the Bells & Whistles would be right at home with such.
By the way, your site is nice, so is you plane.
I guess I'm thinking down a different path.
We're building a light weight Night VFR RV-9A for mountain flying. I'm trying to shed every pound possible, consistant with VAN's intent.
I was thinking about using the Vacuum Pad driven alternator as the sole source of ship's power to recharge the battery and run the avionics & lights.
Click to expand...


Thanks!

Plane Power has a model that has even more amps than B&C. Be sure to fully understand how these alternators work as oppose to belt driven alternators. They tend not to put out much current unless at high rpm. This could be important while taxiing and during the landing phase with an idle throttle.
 
According to Sacskyranch http://www.sacskyranch.com/rapco.htm
The Lycoming 4 cyl vacuum pump is driven 1:1 engine speed.
So the alternator RPM will be low compared to the stock pulley & belt drive arrangement.
At low RPM the alternator output will be below 'rated output' at low idle it may be 'no output'. But at 2000 RPM, full output. So during runup, this could be checked.
On final approach, the landing lights may be sucking down the battery.
Just like in our old 1958 C-172 when it had a generator. ;)
On a short day trip, the low output 8 amp unit may not fully replenish the battery, but on a long cross country flight it could, if other loads are light enough.
If the plane is ordinarily kept in a hangar, it could be recharged with a 'smart charger'. Still beats hand propping.
I'm thinking along the lines of: Dynon Skyview (3.5 amp), Nav-com SL-30, < .2 amp), Transponder (Garmin 2.25 amp), Night VFR lighting (Avio, 1.35 amp), intercom & electric start. Total continuous load 7.3 amps. Landing lights and com transmit are intermittant loads.
Seems marginal...but doable.
David M is probably right with the 20 amp rated unit. More is always nice, but the weight, the weight......
 
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So get this

I have a full IFR stack, plus I don't have a mechanical fuel pump,..and for backup I run an SD8 on the vac pad...I can't say "vacuum" cus I get physically ill..:)

So for "fun" I ran the GNS 430, transponder, and primary radio (the Dynon and Pmags have their own back ups) and nav lights.

I took off on one high pressure fuel pump and set the RPM to 2600..Flew for nearly an hour and I swear the only way I could get the battery volts to dip below 12V was by hitting the transmit button on the primary radio.

That little alternator was putting out more than 8A for sure.

Thats more gear then I need to get home IFR if I had to..:)

Frank
 
I installed an SD8 on the vac pad and after 390 hours my belt driven alternator started to go. First indication on a cross country flight to Denver the Voltage started to drop below 13 and when it hit 11 I switched off the primary alternator and switched on the SD8. I also switched off the strobes. I flew the last hour on the SD8 with voltagee only dropping to 10, switched back over to the belt driven alternator for decent and found that after being off for an hour it was starting to send a full charge back to the battery. I turned the strobes back on, landed and three days later came back, cranked up the RV-10 and started back home. About an hour into the flight the voltage again started to drop and I swiched back over to the SD8 alternator for the balance of the flight home. Seems when the belt driven alternator started to get hot it started to fail. If I had not had both the SD8 and the belt driven alternator I would have been fourced to replace the alternator away from home and at a much higher cost. The SD8 is going on my other projects as well.
 
I have the SD8 as a primary on my Bucker. It is a very simple system with no avionics to speak of, so no issues with the total load.
However, if you are doing short hops, like flying Young Eagles, you do have to be careful as you can drain your battery on starts quicker than the SD8 can replenish the charge.
I have not had this problem as the Bucker will start on one blade and has no hot start problems, but if you have to sit there and crank between many short flights, it might be an issue.
 
frankh said:
I have a full IFR stack, plus I don't have a mechanical fuel pump,..and for backup I run an SD8 on the vac pad...I can't say "vacuum" cus I get physically ill..:)

So for "fun" I ran the GNS 430, transponder, and primary radio (the Dynon and Pmags have their own back ups) and nav lights.

I took off on one high pressure fuel pump and set the RPM to 2600..Flew for nearly an hour and I swear the only way I could get the battery volts to dip below 12V was by hitting the transmit button on the primary radio.

That little alternator was putting out more than 8A for sure.

Thats more gear then I need to get home IFR if I had to..:)

Frank
Click to expand...

That's what I'm building up as well. I'll have a primary bus with everything, and an essential bus with only right-now-critical items (fuel pumps, transponder, 430W) for a night IFR approach. The battery plus the SD-8 will get me down if my primary alternator goes Tango Uniform, even in worst case conditions.
 
All of the vac pad alternators are pretty decent, but the SD-8 is marginal for some applications...remember that transmitting on a radio can use almost 8A on it's own! It's definately a good addition, but the SD-20 isn't much more money in the scheme of things and gives you a lot more flexibility on an Ebuss or backups. We have some customers using the SD-20 as their sole alternator (day/vfr folks) without issue. I also don't yet have any first hand review of the PlanePower unit, but I hear it's supposed to be decent as well. Anyway, my point is that any of them are good add ons because if the fan is turning you're likely to have some power generation. Yes it costs more than a 2nd battery, but it usually weighs less and doesn't need replaced.. You can also wire the backups to be almost autmatic in their management of power (set the SD at a lower voltage than the main alternator).

My 2 cents as usual!

Cheers,
Stein
 
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