[Oeva-list] Anyone have experience with permanent magnet alternators?

[Myles Twete]

Tim-

Be careful with these PMAC specs---while they give more information than a
lot of ordinary alternator suppliers, the graphs presented by some
mfrs/vendors and the claims made can be out and out lies.  My experience
with these is from about 4 years ago or so.  Earlier, I had helped build and
did the wiring for a twin-engine steamboat
(http://www.northweststeamsociety.org/Pages/ProjectsBoats/Tortoise/NWSSBtor.
htm ), which we launched in 2001.  Well, it quickly became evident that this
was more like an electric boat since it required an average of 40-45amps at
12v to maintain power to the inverter, boiler, electric feed pump, etc.  The
plan was for electricity to be generated underway by using an alternator
driven by a twin-cylinder steam engine.  While that worked, all we could get
was about 15-18amps into 12v.  We tried another alternator, increased the
steam pressure to the engine, increased the pulley ratio, etc. and couldn't
get more than 20amps.  We even tried a "high output" alternator and one that
was "made for low RPM" applications--still not much better.  After a couple
years of running with what we had, and having read about these PMAC's, I
mentioned it to my friend, who pretty much ordered one without asking for
better information on them.  We received the PMAC, installed it easily
enough and gave it a whirl.  Once again, the amp gauge ended up rising to
20, then maybe to 24amps, then no more.  Worse, FAR WORSE, this PMAC device
was getting warm to HOT very quickly.  We quickly shut it down, removed the
unit and attempted to send it back to get money back.  When the supplier
would not accept return of the PMAC for our money back, I pointed out to the
supplier/manufacturer that his online specs was misleading AT BEST if not
blatantly fraudulent.  His claims were that this motor "loves" low or high
speeds and that high currents were no problem at all.  Our experience proved
these claims fraudulent.  We spun this motor AT MOST 1800 RPMs.  The no-load
voltage wasn't even 24v.  Loaded, the current delivered averaged 24amps,
max.  Yet the alternator quickly got warm-to-hot and was far from being able
to deliver the 100+ amps that they claimed.
In the end, my friend was out $300 and we pursued another, lower cost
solution: A surplus high efficiency Leeson DC permanent magnet 12/24v, 1.5HP
motor.  With this setup, not only can start the steam engine with the motor,
but as a generator, the Leeson will deliver 35amps into the 12v and barely
get warm---still not the 50amps that would be best, but at 35amps and at
$100 or so, it was a decent deal.

Bottom line: If your supplier won't give you better specs than they provide
online, ask them to.  The link you provide doesn't inform as to the internal
resistance.  It can kind of be inferred from the graph, e.g. this DC-500
from that WindBluePower site you mention:
http://www.windbluepower.com/Wind_Blue_Motor_Hydro_Permanent_Magnet_Alternat
or_p/dc-500.htm

At 2000RPM, they claim it can deliver 120amps into 12v.  The voltage curve
seems to indicate a Voc(2000RPM) of about 16v.  This means that at 120amps,
you should expect a loss of 4v*120amps or 480watts!  This is 75%
efficient---far less than an efficient PM DC Motor.  Further, their claims
are inconsistent---they claim that the graph shows Isc and Voc...yet then
they say that at 2000RPM, they get 120amps at 12v.  The graph shows about
115amps for Isc...not a chance you'd get 120amps into 12v if Isc is 115amps.

If you need high output and you find out this poor efficiency on your
bench---best of luck to you---you probably won't get your money back.
Bottom Line in my experience with these is they are only efficient at high
RPM, high voltage and relatively low current.  For efficiency, you need high
RPM and low current.  Hopefully you'll be dealing with a good vendor and one
who knows what they are selling.  But do your homework---don't let your
buddy order one without you being convinced.

Caveat emptor-

-Myles

-----Original Message-----
From: oeva-list-bounces at oeva.org [mailto:oeva-list-bounces at oeva.org] On
Behalf Of Tim Kutscha
Sent: Sunday, January 03, 2010 2:46 PM
To: oeva-list at oeva.org
Subject: [Oeva-list] Anyone have experience with permanent magnet
alternators?

Hi All,

I'm working with someone on a homebrew series hybrid car (similar to the
Chevy Volt).  We're looking to charge the main EV battery with a diesel
engine driving a PMA (permanent magnet alternator).  Neither of us has
experience with PMAs or how to properly select them for hybrid, micro-hydro
or micro-wind usage.

Does anyone in the OEVA have experience with PMAs that would be willing to
share their knowledge?  Ideally, we're looking for someone to provide
pointers on PMA selection and then be present during testing for a few hours
so we know what we're looking for in terms of performance (or things that
can go wrong).

Examples of the types of PMAs we're looking at are here:

http://www.windbluepower.com/category_s/1.htm
http://www.hydrogenappliances.com/powerpmas.html

Thanks for any and all suggestions!

Cheers,
Tim



      
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