building microwind and microhydro generators

[Dominic-Luc Webb]

On Mon, 29 Dec 2008, Eeyore wrote:

Tim Wescott wrote:

My first guess at a quick & dirty generator would be a car alternator,
at least if you just want 12VDC from lead-acid batteries. It's very
best feature is that if you pick one that's common then replacement
parts can be found at the nearest junkyard (or the nearest neighbor with
the right vehicle, if you're not terribly scrupulous).

They're pretty inefficient. Permament magnet alternators can do much better.

Graham

I am not following this actually. From what I can find, the
conventional, at least classical, automomotive and marine
alternators are 3 phase brushless generators with no
commutators and the schematics I have been able to find for
these show a slotted stator with coils and a rotor with
permanent magnets. This looks essentially same as the
homemade wind generators I have seen so far. I know that
some "alternators" are actually DC generators with solid
state diodes. I do not know how to tell one from the other
when I am in the junkyard, but that is maybe a separate
question.

Is is not so that a true automotive/marine alternator uses
permanenent magnets? I know the marine ones are built to
not produce sparking that could ignite fires in engine rooms.

I now think 3 phase is my starting point, so let us assume
I will stay on this track. For wind generation, I note
that nearly all the small scale and home made wind generators
are using 12-18 slot stators (and 3 phase). As compared to
the 2 slot alternator, this implies the goal is to be able
to get 50/60 Hz at comparatively low RPM. The automotive
ones achieve their relative high RPM by using a pulley ratio
with the comparatively slower engine at idle, engine
have the larger pulley.

Is there any reason why I should not just use a car
alternator (if they have permanent magnets) and similarly
also use a pulley to get more RPM if needed?

Also, does anyone know how many poles or slots on a car
alternator and roughly how many RPM when the engine is at
idle (ballpark)?

Dominic

 

[Peter Bennett]

On Fri, 2 Jan 2009 12:34:09 +0100, Dominic-Luc Webb <dlwebb@canit.se>
wrote:

I am not following this actually. From what I can find, the
conventional, at least classical, automomotive and marine
alternators are 3 phase brushless generators with no
commutators and the schematics I have been able to find for
these show a slotted stator with coils and a rotor with
permanent magnets. This looks essentially same as the
homemade wind generators I have seen so far. I know that
some "alternators" are actually DC generators with solid
state diodes. I do not know how to tell one from the other
when I am in the junkyard, but that is maybe a separate
question.

The automotive (and marine) alternators that I am familiar with have a
field winding on the rotor, Any permanent magnetism in the rotor is
just residual magnetism remaining from the last time the field was
energized. The output current of the alternator is controlled by
controlling the field current.

Is is not so that a true automotive/marine alternator uses
permanenent magnets? I know the marine ones are built to
not produce sparking that could ignite fires in engine rooms.

Not in my experience (although one of the alternators on my boat
apparently has no external field current terminal - but I'm not going
to open it up to see why it works!)

I now think 3 phase is my starting point, so let us assume
I will stay on this track. For wind generation, I note
that nearly all the small scale and home made wind generators
are using 12-18 slot stators (and 3 phase). As compared to
the 2 slot alternator, this implies the goal is to be able
to get 50/60 Hz at comparatively low RPM. The automotive
ones achieve their relative high RPM by using a pulley ratio
with the comparatively slower engine at idle, engine
have the larger pulley.

I think that for your application, you do not need to worry about the
AC frequency produced by the alternator. You should use the DC output
to charge batteries, then use an inverter powered by those batteries
to produce AC when/if you need it. By using batteries, you can store
power generated on windy days for use on calm days.

I think the maximum RPM for many alternators is around 5000 RPM, and
the AC frequency will be 600 - 1200 Hz.

I suggest that you look at some alternator manufacturers' web sites,
such as http://www.balmar.net for information on alternators

Also, google for "off-grid power" to find web sites discussing
independent power systems.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

[Dominic-Luc Webb]

Thanks Peter!

I just found this, as a further answer to my question. It
is taken from an advert for a high output alternator in
Ebay:

This alternator will drop right in place of your existing
(factory) 90-amp unit and operates with the existing ecm
voltage regulator.

65-70 amps capability at 800 engine rpm
165 amps at 1600 engine rpm.

If a common truck alternator can actually generate 90 amp
at ~12 volt at the stated RPMs above, then it if a
homemade wind turbine can physically get it to turn at
this RPM, as with a pulley ratio, this would compete
extremely well with the very best homemade wind generators
I have been able to find online in which the actual
alternator components were handmade.

So even if these alternators are not efficient, and even
if they are not of optimal design, as in lacking
permanent magnets, they are quite efficient compared
to the handmade alternators that do have permanent
magnets.

Having would coils by hand, I know this is a delicate
process and am not surprised if a factory made car
alternator is better than what I could make by hand
with what is theoretically superior design and
materials.

If there are no serious objections, I think I should
just go ahead and try the car alternator.

Dominic

 

[Jamie]

Dominic-Luc Webb wrote:

Thanks Peter!

I just found this, as a further answer to my question. It
is taken from an advert for a high output alternator in
Ebay:

This alternator will drop right in place of your existing
(factory) 90-amp unit and operates with the existing ecm
voltage regulator.

65-70 amps capability at 800 engine rpm
165 amps at 1600 engine rpm.

If a common truck alternator can actually generate 90 amp
at ~12 volt at the stated RPMs above, then it if a
homemade wind turbine can physically get it to turn at
this RPM, as with a pulley ratio, this would compete
extremely well with the very best homemade wind generators
I have been able to find online in which the actual
alternator components were handmade.

So even if these alternators are not efficient, and even
if they are not of optimal design, as in lacking
permanent magnets, they are quite efficient compared
to the handmade alternators that do have permanent
magnets.

Having would coils by hand, I know this is a delicate
process and am not surprised if a factory made car
alternator is better than what I could make by hand
with what is theoretically superior design and
materials.

If there are no serious objections, I think I should
just go ahead and try the car alternator.

Dominic

You most likely are talking about a brushless alternator.

Still functionally the same as the old style brush alternators
except for the method used to energize the rotor.

Instead of brushes, they use a DC coil that surrounds the
rotor into a slotted groove of the rotor or a side plate, in this
area, the rotor has a pick up coil that generates energy from the DC
magnetic field as its moving through it. This will excite the field and
not much current is needed for this.

This removes the need for brushes and also allows for a tighter
moister seal on the encasement of the coil..



http://webpages.charter.net/jamie_5"

 

[Jasen Betts]

On 2009-01-02, Dominic-Luc Webb <dlwebb@canit.se> wrote:

On Mon, 29 Dec 2008, Eeyore wrote:



Tim Wescott wrote:

My first guess at a quick & dirty generator would be a car alternator,
at least if you just want 12VDC from lead-acid batteries. It's very
best feature is that if you pick one that's common then replacement
parts can be found at the nearest junkyard (or the nearest neighbor with
the right vehicle, if you're not terribly scrupulous).

They're pretty inefficient. Permament magnet alternators can do much better.

Graham

I am not following this actually. From what I can find, the
conventional, at least classical, automomotive and marine
alternators are 3 phase brushless generators with no
commutators and the schematics I have been able to find for
these show a slotted stator with coils and a rotor with
permanent magnets.

often the rotor has an electromagnet which is powered by slip-rings
, and this power is switched to control the output of the altenator.

This looks essentially same as the
homemade wind generators I have seen so far. I know that
some "alternators" are actually DC generators with solid
state diodes. I do not know how to tell one from the other
when I am in the junkyard, but that is maybe a separate
question.

very few automotive altenators provide external AC terminals, most
have the rectifiers built-in, the aotomotice mechanics still call them
altenators though.

Is is not so that a true automotive/marine alternator uses
permanenent magnets? I know the marine ones are built to
not produce sparking that could ignite fires in engine rooms.

marine ones could be permanenent magnet, all the auto one's I've seen
had an electromagnet rotor.

On the other hand marine ones could have a stationary field
winding and a rotor that redistributes the field.

I now think 3 phase is my starting point, so let us assume
I will stay on this track. For wind generation, I note
that nearly all the small scale and home made wind generators
are using 12-18 slot stators (and 3 phase). As compared to
the 2 slot alternator, this implies the goal is to be able
to get 50/60 Hz at comparatively low RPM. The automotive
ones achieve their relative high RPM by using a pulley ratio
with the comparatively slower engine at idle, engine
have the larger pulley.

Is there any reason why I should not just use a car
alternator (if they have permanent magnets) and similarly
also use a pulley to get more RPM if needed?

vee pulleys have lots of friction. but it's possible a grooved of
toothed belt could work. chain or gears may be a better method,

Also, does anyone know how many poles or slots on a car
alternator

typically 5 or 6 of each north and south on the rotor, so
15 or 18 poles on the stator

and roughly how many RPM when the engine is at

idle (ballpark)?

idle RPM 500-1000 (larger engines are slower)