3.5 lb alternator

[brown bear]

I have been running the permanent magnet alt. from the little john deere for 1665 hours , I pulled if off today the check it over before a trip to Alaska and found the bearings worn and needing replaced. The windings look like new. not much else to go wrong. Not bad for 1665 hours !
Doug

[Kalibr]

I'd like to revive this thread to solicit more feedback on using a permanent magnet PM (John Deer, or rather, Yanmar style) alternator on the front/belt driven end of a Lycoming. I am trying to make my setup as light as possible and this alternator may let me remove 2-3 pounds from the very front v using the lightest traditional alternator. My electrical needs will be small and 20 amps will cover it for sure. Other than the weight saving, Inlike the simplicity of the alternator itself and the slightly simpler wiring it will require in my application.
I noticed that the gentleman who originally started this thread subsequently mentioned eksewhere that this setup didn't work for him as the regulator couldn't hold back the voltage due to the alternator spinning too fast with the existing pullley. I am wondering if other people had better luck perhaps with a larger pulley and/or different regulator?
Thanks!

[SHIPCHIEF]

Doug (brown bear) posted success with the Deere alternator when regulated via a B&C adjustable regulator.
I didn't try that. I used an auto parts replacement regulator for the alternator, as used on a garden tractor. It looks like the one used on the RV-12.
I would consider trying the Deere alternator on my RV-8 again, using the B&C regulator, if I have trouble with the Denso Mini.
I have the flywheel with smaller diameter belt pulley on my Lycoming, this would run the alternator at a higher RPM than the original application.
The Alternator output must have exceeded the current capacity of the original regulator when running at high RPM. They regulate by sinking extra current to ground. Maybe 2 of the original regulators could be mounted in parallel?
The alternator's pulley is welded to the magnet housing, so converting it to a larger diameter pulley does not look easy.
I removed the 22.5 pound (90 amp!) generator from my Yak-55 and installed the B&C BC422 10 amp alternator for a 21 pound savings. I also removed the lead acid batteries in fiberglass 'lunchboxes' and replaced them with LiFePO4 powersport batteries for a 10 pound savings. I can feel the difference flying aerobatics !!

[Kalibr]

Scott, thank you! I didn't realize the pulley is welded -- might be too much hustle to try to replace it.

[rv7charlie]

Don't know about the model you have, but at least some of the PM alts are made with the front of the rotor being the back half the pulley, and what amounts to a tapered washer making up the front half. With some machine shop work and the right length bolt, you should be able to mount whatever pulley you desire by removing the 'front half' of the original pulley.

If you have the smaller flywheel pulley on the engine, it should turn the alt *slower*; not faster, than the large pulley flywheel.

[Mich48041]

There are at least 3 ways to regulate the output from a permanent magnet alternator (dynamo).
1. Shunt excess current to ground.
2. Add series resistance to limit current.
3. Turn the current on and off to allow only needed current to pass. The regulator turns on for part of each AC cycle.
-
The voltage regulator in the RV-12 uses method 3. The larger the electrical load is, the more heat is emitted from the regulator. Regulators should be mounted with heat conductive paste.

[hohocc]

If you have the smaller flywheel pulley on the engine, it should turn the alt *slower*; not faster, than the large pulley flywheel.[/quote]

I suspect the op was meaning the small pulley runs the alternator faster than in it's original JD tractor, but slower than with the large pulley would.

Interesting point you raise about the possibility of changing pulley on some models, that could be a very useful change.

[SHIPCHIEF]

hohocc is correct, I have the smaller Lycoming pulley, it turns the PM alternator faster than the John Deere application.
The link in my signature opens pictures of my RV-8 build. The first page, near the bottom has 2 pictures of the alternator and regulator mounted to the plane.

[rv7charlie]

Sorry Scott; I went through your message a bit too fast, & misread it.

[SHIPCHIEF]

Based on Joe Gores point 3, that the regulator operates by turning output current on and off during a portion of each AC cycle to regulate the output. I wonder if the original regulator can't control the higher forward bias caused by higher RPM. The B&C regulator might work where the original fails by having higher spec output transistors?