I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

James Sweet wrote:

I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.


Brand? Model?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

James Sweet wrote:
I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

I don't understand why you think an alternator would need brushes or
slip rings. An alternator is an AC generator. The diode rectifies
its output (serving a function similar to what brushes would do in
a DC generator).

BTW, in some sense all good capacitors are "open circuits." However,
an ohm-meter should initially show a low "resistance" (until the
capacitor charges).

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Just honing in on your post - you say the capacitor is open circuit - how did
you determine that? And how did you determine the diode is OK?

Just wondering whether you actually checked the capacitor with a proper
capacitor tester or just a multimeter?

And did you check the diode in both forward and reverse modes? ie with the
meter leads one way it should read almost a short circuit, and with the meter
leads reversed it should read almost infinity

David - who is very sus about the diode



CJT wrote:

James Sweet wrote:
I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

I don't understand why you think an alternator would need brushes or
slip rings. An alternator is an AC generator. The diode rectifies
its output (serving a function similar to what brushes would do in
a DC generator).

BTW, in some sense all good capacitors are "open circuits." However,
an ohm-meter should initially show a low "resistance" (until the
capacitor charges).

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

I don't understand why you think an alternator would need brushes or
slip rings. An alternator is an AC generator. The diode rectifies
its output (serving a function similar to what brushes would do in
a DC generator).


How is the field current controlled? Automotive alternators use a pair
of slip rings to power the rotor, regulation is achieved by adjusting
the current through the rotor as needed to keep the output voltage
constant. I've never seen one that was brushless.

BTW, in some sense all good capacitors are "open circuits." However,
an ohm-meter should initially show a low "resistance" (until the
capacitor charges).


I'm very familiar with testing capacitors, I've been repairing
electronics as a hobby for around 15 years now. I checked it with an ESR
meter as well as compared it to a similar motor run cap I had on hand.
The capacitor is bad, besides, the diode is good, there's no other
active components I can see and it stopped producing power suddenly
while under load so it isn't a matter of flashing the field.

quietguy wrote:
Just honing in on your post - you say the capacitor is open circuit - how did
you determine that? And how did you determine the diode is OK?

Just wondering whether you actually checked the capacitor with a proper
capacitor tester or just a multimeter?

And did you check the diode in both forward and reverse modes? ie with the
meter leads one way it should read almost a short circuit, and with the meter
leads reversed it should read almost infinity

David - who is very sus about the diode



CJT wrote:


James Sweet wrote:

I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

I don't understand why you think an alternator would need brushes or
slip rings. An alternator is an AC generator. The diode rectifies
its output (serving a function similar to what brushes would do in
a DC generator).

BTW, in some sense all good capacitors are "open circuits." However,
an ohm-meter should initially show a low "resistance" (until the
capacitor charges).




I checked the diode out of circuit with my Fluke multimeter's diode
function, so far it's never let me down, though the check does only pass
a few volts through it.

As I said in another post, the capacitor was thoroughly and properly
tested, trust me, it's open circuit. As far as I know, these oil filled
caps are internally fused so my guess is the plates shorted and blew the
fuse.

Michael A. Terrell wrote:
James Sweet wrote:

I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.



Brand? Model?




Does it matter? I'm just asking for general principals here, not advice
on fixing this particular unit. Surely brushless alternators of this
sort must be widespread and likely don't vary much from unit to unit.

In article oRJkh.5859$6f4.5807@trndny08,
James Sweet wrote:
What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

Presumably the rotor is a series of magnets? Rotate any magnet(s) within a
coil(s) and you can get a form of AC output. DC dynamos have commutators
to give 'pulsed' DC from this. The slip rings in a car alternator are
there so the current in the field windings can be varied thus the output.

--
*Work is for people who don't know how to fish.

Dave Plowman London SW
To e-mail, change noise into sound.

On Thu, 28 Dec 2006 06:53:08 GMT, James Sweet wrote:

I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

Have you tried Google? Searching on schematic "brushless alternator" yields a
lot of hits, including a simplified description and schematic of a three phase
brushless alternator at:

http://www.ee.qub.ac.uk/power/fyp/pd...e_tlittler.pdf

and more info at:

http://www.pearen.ca/dunlite/BrushlessAlternators.pdf

On Thu, 28 Dec 2006 01:36:21 -0600, CJT wrote:


James Sweet wrote:
I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

I don't understand why you think an alternator would need brushes or
slip rings. An alternator is an AC generator. The diode rectifies
its output (serving a function similar to what brushes would do in
a DC generator).

If the armature has windings, you need to connect to them. The only
alternator that wouldn't require any brushes nor slip rings would be one
that had just a permenant magnet on the armature.

James Sweet wrote:
I'm working on a generator for someone that recently just quit producing
electricity.
Generators don't produce electricity they convert mechanical energy to
electrical energy.

On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

So replace the capacitor and find out.

What I'm curious though is how exactly does this thing work?
How do you think it works, you turn it and the magnets move and break
electrons free from their atoms and that creates a charge and therefore
electrical current.

The
armature has no connection at all to anything.
Maybe the armature is broken.

I imagine it must receive
power through induction but how is the output regulated?
You said generator not transformer.

Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

That generator sounds broken beyond repair.

On Thu, 28 Dec 2006 06:53:08 GMT, James Sweet
wrote:

I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

Search for "induction generators"

There's a common trick of using an ordinary induction motor as an AC
sine wave generator. It requires one cap across the winding and that
is usually a non-polar type with a low dissipation factor (oil filled
are ideal)

They won't start under load - have to be started then the load
applied. They balk at running other induction motors unless the motor
is ~1/6 the size of the generator.

No rectifier necessary. (but that may be part of some self-excitation
scheme, to insure the iron keeps some residual magnetism)

They can lose excitation and stop producing even without any defective
parts. They usually depend on some residual magnetism to kick things
off - and that may not be there - in which case you connect a DC
source to the generator when it is stopped to magnetize the iron.

http://www.linux-host.org/energy/einductge.html gives some info on
them.


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On Thu, 28 Dec 2006 12:34:23 -0500, default
wrote:

The capacitor is open circuit so that's an obvious problem

I would also question that . . . oil filled caps don't incorporate
fuses, real oil filled caps are "self-healing" and damn near
indestructible. It is possible, but not likely.

And all caps are open with a DC ohm meter - except lossy electrolytic
types.

Electrolytic caps can also be used in induction alternators and they
can and do fail - the caps have to withstand a high circulating
current - uses no power (ideally) but the current has to flow through
the cap and the cap has to be able to handle that current.

Home power alternators look similar to induction generators and work
similar but incorporate permanent magnets in the rotor - no regulator
except control the speed of the engine driving it to keep the
frequency correct.

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In article oRJkh.5859$6f4.5807@trndny08, wrote:

I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

James-

The field windings on the rotor have their own set of diodes (and
resistors), often two, sometimes four. I assume these are the diodes you
checked. There are no slip rings because the field coil generates AC, the
diodes rectify it for DC field current.

(Some generators also have a separate stator winding and rectifier for use
in charging a battery, in case that is the rectifier you checked.)

The capacitor is connected to an independent winding on the stator. I
don't understand how it works, but as load current increases the
capacitor's reactance shifts the magnetic field to increase generator
output. That is the only form of regulation on some simple generators.

If you are interested, one source of information is the search function at
http://www.smokstak.com

Fred

budgie wrote in
:

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must
receive power through induction but how is the output regulated? Is
there a trick to manufacturing these? Given there's no brushes or slip
rings I'd have thought all alternators would be made this way unless
there was a disadvantage.

Have you tried Google? Searching on schematic "brushless alternator"
yields a lot of hits, including a simplified description and schematic
of a three phase brushless alternator at:

http://www.ee.qub.ac.uk/power/fyp/pd...e_tlittler.pdf

and more info at:

http://www.pearen.ca/dunlite/BrushlessAlternators.pdf

Interesting topic. In brief, it's possible to make an alternator without
brushes, as follows:

On the same shaft, there are two separate rotor windings. In the case,
there are two separate stator windings.

The first stator gets its current from the battery. Its rotor generates
AC which is rectified by diodes which are rotating with it. This DC is
then wired to the second rotor winding, which is of course also rotating
with the diodes. Hence, no brushes.

This second rotor now has a DC current running through it, which makes it
the field coil for the second alternator. Its stator generates AC which
is rectified by diodes and is wired to the battery as usual.

One way to control the output is to regulate the current to the first
stator winding, which will regulate the current to the second rotor
winding.

Jim Land wrote:
budgie wrote in
:


What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must
receive power through induction but how is the output regulated? Is
there a trick to manufacturing these? Given there's no brushes or slip
rings I'd have thought all alternators would be made this way unless
there was a disadvantage.

Have you tried Google? Searching on schematic "brushless alternator"
yields a lot of hits, including a simplified description and schematic
of a three phase brushless alternator at:

http://www.ee.qub.ac.uk/power/fyp/pd...e_tlittler.pdf

and more info at:

http://www.pearen.ca/dunlite/BrushlessAlternators.pdf


Interesting topic. In brief, it's possible to make an alternator without
brushes, as follows:

On the same shaft, there are two separate rotor windings. In the case,
there are two separate stator windings.

The first stator gets its current from the battery. Its rotor generates
AC which is rectified by diodes which are rotating with it. This DC is
then wired to the second rotor winding, which is of course also rotating
with the diodes. Hence, no brushes.

This second rotor now has a DC current running through it, which makes it
the field coil for the second alternator. Its stator generates AC which
is rectified by diodes and is wired to the battery as usual.

One way to control the output is to regulate the current to the first
stator winding, which will regulate the current to the second rotor
winding.


Yeah I did and I saw that actually. This one is different though.
There's a single set of windings on the rotor which has a single diode,
though there may possibly be another diode buried at the motor end of
the rotor but looking through the vents I didn't see anything. I didn't
see any diodes in the stator either, though they might be hidden as
well. I have another motor run cap of similar but not the same rating on
hand which I'll try in the generator and see if it fixes the problem to
the extent of producing some power, I'm absolutely certain the original
cap is open but I'm not positive another problem doesn't exist.

Seems nobody here so far has a real solid understanding of how these
work but I'll figure it out. I was just hoping for a nice concise ready
made theory of operation to replace my deductions.

Presumably the rotor is a series of magnets? Rotate any magnet(s) within a
coil(s) and you can get a form of AC output. DC dynamos have commutators
to give 'pulsed' DC from this. The slip rings in a car alternator are
there so the current in the field windings can be varied thus the output.



No, the rotor is electromagnetic, it looks just like a very large DC
motor armature except it has only two poles and it is entirely self
contained with no electrical connection to any of the stationary parts.
The one diode I can find is mounted in the rotating assembly.

If the armature has windings, you need to connect to them. The only
alternator that wouldn't require any brushes nor slip rings would be one
that had just a permenant magnet on the armature.


So this one I'm looking at then doesn't exist? It clearly says
"Brushless Alternator" and there are clearly no brushes or slip rings,
just as there clearly *are* windings rather than permanent magnets on
the rotor. It's starting to sound like a magic trick.

default wrote:
On Thu, 28 Dec 2006 12:34:23 -0500, default
wrote:


The capacitor is open circuit so that's an obvious problem


I would also question that . . . oil filled caps don't incorporate
fuses, real oil filled caps are "self-healing" and damn near
indestructible. It is possible, but not likely.

And all caps are open with a DC ohm meter - except lossy electrolytic
types.

Electrolytic caps can also be used in induction alternators and they
can and do fail - the caps have to withstand a high circulating
current - uses no power (ideally) but the current has to flow through
the cap and the cap has to be able to handle that current.



Question it all you like, but the ESR meter shows this 35uF 370VAC
capacitor as open, and a similarly constructed 50uF 370VAC capacitor as
less than one ohm. Using the capacitance range on the DMM the 35 uF cap
reads 15 nF, while the 50 uF cap reads 50.2 uF. I can't imagine any
circumstances beyond an open connection, whether it be a fuse or just a
broken wire inside the capacitor can that would cause this.

James Sweet wrote:
I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator.

There's a way to do this, but it's rather inefficient.

You take your basic old furnace fan motor, which has stator windings,
and a rotor with pseudo-windings (actually just angled strips of copper
or aluminum.)

Now this kind of motor works just fine, used in billions of
applications. You might wonder how it rotates with no permanent magnets
in the rotor and no slip rings. It's done by induction-- the stator
windings induce current in the rotor, which reflects back a magnetic
field. This requires a bit of slip, so these motors are typically
rated at "1725 RPM" instead of 1800.

You can do exactly the opposite-- rotate the motor and have the
generated current feed back a magnetic field. Only glitch, you need a
hefty capacitor across the stator windings to provide the out-of phase
current. And the efficiency isnt too wonderful. And there's no easy
way to adjust the current versus voltage versus hertz.

James Sweet writes:

If the armature has windings, you need to connect to them. The only
alternator that wouldn't require any brushes nor slip rings would be one
that had just a permenant magnet on the armature.

So this one I'm looking at then doesn't exist? It clearly says
"Brushless Alternator" and there are clearly no brushes or slip rings,
just as there clearly *are* windings rather than permanent magnets on
the rotor. It's starting to sound like a magic trick.

You've pretty much described it. The two pole armature gets current
induced in it by rotating inside the stator and that is made to be DC
by the diode or more likely, diodes. That then acts like the permanent
magnet rotating inside a stationary magnetic field. There doesn't need
to be a smoothing cap inside to make it pure DC. I'm not going to claim
any knowledge of the details but the scheme certainly seems plausible and
with care in designing the magnetic components seems like it should work
quite well.

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Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

James Sweet wrote:



If the armature has windings, you need to connect to them. The only
alternator that wouldn't require any brushes nor slip rings would be one
that had just a permenant magnet on the armature.



So this one I'm looking at then doesn't exist? It clearly says
"Brushless Alternator" and there are clearly no brushes or slip rings,
just as there clearly *are* windings rather than permanent magnets on
the rotor. It's starting to sound like a magic trick.
I'll put my 2 cents in ..
Brushless Alternators are like induction motors more or less.
if you take an induction more and spin the rotor having a AC volt
meter on the stator windings with no load, you will get electrical
energy, just not a lot. Now, since there is energy is in the field, you
take that little energy which is also being induced into the rotor
area. with the coil on the rotor, you do receive some current which
gets rectified to a shunt load, this causes a DC field to generate and
once this happens, the DC field just adds too and sums up and thus gives
more to the rotor etc, it's like it's own electro magnet (DC)
there is normally a cap in there somewhere on the stator circuit that
links the stator windows and causes current regulation depending on how
much load you're drawing from the alternator.
If this cap fails, you'll get very little current output, also,
sometimes the core needs to be demagnetized.
etc..
Ok, that was as simple of an explanation i could come up with.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

On Thu, 28 Dec 2006 22:35:09 GMT, James Sweet
wrote:

default wrote:
On Thu, 28 Dec 2006 12:34:23 -0500, default
wrote:


The capacitor is open circuit so that's an obvious problem


I would also question that . . . oil filled caps don't incorporate
fuses, real oil filled caps are "self-healing" and damn near
indestructible. It is possible, but not likely.

And all caps are open with a DC ohm meter - except lossy electrolytic
types.

Electrolytic caps can also be used in induction alternators and they
can and do fail - the caps have to withstand a high circulating
current - uses no power (ideally) but the current has to flow through
the cap and the cap has to be able to handle that current.



Question it all you like, but the ESR meter shows this 35uF 370VAC
capacitor as open, and a similarly constructed 50uF 370VAC capacitor as
less than one ohm. Using the capacitance range on the DMM the 35 uF cap
reads 15 nF, while the 50 uF cap reads 50.2 uF. I can't imagine any
circumstances beyond an open connection, whether it be a fuse or just a
broken wire inside the capacitor can that would cause this.


Don't get all defensive now. Oil filled caps have been around since
the, well, before I was born and they just don't die - and I've tried.
Got a few in my unreg choke input filter HV supply from the 40's still
going strong.

Some AC motor run caps look like oil filled types bur are dry and a
lot less permanent, and lighter weight - like one sees in microwave
ovens. I'm guessing you might have one of those. Crimped drawn
metal, aluminum case, with a plastic insulator - no elastomer seal, no
porcelain turret connectors and a quick connect, push on connector.
Looks similar to the old oil dielectric caps, but a lot more capacity
and a lot less rugged.

Cap could be all the problem . . . but a 50 uf cap would suggest it is
just there for sine wave smoothing and not a necessary generator part
- but I don't know what your load looks like to the gen either.
Try changing the cap with a new one - that may be all that's wrong.



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James Sweet wrote:

Does it matter? I'm just asking for general principals here, not advice
on fixing this particular unit. Surely brushless alternators of this
sort must be widespread and likely don't vary much from unit to unit.


You're so right. Why would you bother to see if you can find a
manual that might explain exactly how it works.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

default wrote:

Don't get all defensive now. Oil filled caps have been around since
the, well, before I was born and they just don't die - and I've tried.
Got a few in my unreg choke input filter HV supply from the 40's still
going strong.


They are paper or mylar film capacitors in metal, oil filled cans,
and they do fail. I have a military TS-382 audio generator similar to
the original Wein bridge HP 200 CD that is all oil filled or ceramic
capacitors, and every one of the oil filled capacitors is leaky.


"Oil filled capacitors don't fail" is a myth.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

James Sweet wrote:
I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

It works like a squirrel cage motor. An ac induction motor. That's why
it needs a little DC for the coil or else it won't generate. An
alternator is an AC generator, see the diodes? Those convert ac to dc.
Internal regulator? That's what keeps the battery from blowing up.

"James Sweet" wrote in message
newsRJkh.5859$6f4.5807@trndny08...
I'm working on a generator for someone that recently just quit
producing electricity. On the label it touted the fact that it's a
brushless alternator; this is actually the first time I'd worked on
one but I was expecting much more inside it, certainly some sort of
regulator module but in fact it seems the only parts are a stator very
much like that of a large induction motor, a simple 2 pole armature
with a diode mounted to a heatsink, and a capacitor connected to two
of the leads from the stator. The capacitor is open circuit so that's
an obvious problem, diode checks out fine as do the windings so I'm
assuming replacing the cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must
receive power through induction but how is the output regulated? Is
there a trick to manufacturing these? Given there's no brushes or slip
rings I'd have thought all alternators would be made this way unless
there was a disadvantage.

James,

This is one brushless 3-stage method - there are others.

1st stage. - pilot exiter

rotor = permanent magnet
stator = static coils

Rotate the rotor and AC power is induced in stator coils.
Output from stator coils is fed to second stage within the
stator.

2nd stage. - main exciter

stator = coils fed from 1st stage
rotor = coils

Output from 1st stage stator is rectified and fed to second
stage stator coils - regulation can be imposed here.
Rotate 2nd stage coils in 2nd stage magnetic field
- AC power is produced in rotor and output is fed to 3rd stage.

3rd stage. - output

rotor = coils fed from 2nd stage.
stator = coils

Output from 2nd stage rotor is rectified within the rotor body
and fed to 3rd stage rotor coils.
Rotating electromagnets cause induction of output in 3rd stage
stator coils
--
Regards,

C R Briggs.

Reply to address is munged. To reply, remove surplus spaces from:

btyguard-dontspam @ yahoo . co . uk

Michael A. Terrell wrote:
James Sweet wrote:

Does it matter? I'm just asking for general principals here, not advice
on fixing this particular unit. Surely brushless alternators of this
sort must be widespread and likely don't vary much from unit to unit.



You're so right. Why would you bother to see if you can find a
manual that might explain exactly how it works.




I have the service manual, it explains nothing of the theory of
operation, it just has a list of the components, shows where they mount,
part numbers, and torque specs for the bolts.

An alternator in a car is different. It has to have a battery to provide
its field with DC. An AC generator has permanet magnets in the rotor and
the current is induced in the field where the RPM of the rotor is
responsible for how much voltage is produced.



As I said before, this is not a permanent magnet generator, it has a
wound rotor and is more similar to a car alternator than you think.
Frequency is determined by the RPM, voltage is not, at least it is not
adjusted or regulated by varying the RPM.

At any rate, after doing some more research I think I have a pretty good
idea of how it works. It's the same principal as spinning an induction
motor to generate power except the armature with copper windings and a
rectifier are much more efficient for generating than the aluminum bars
in a motor armature. The service manual doesn't have an internal
schematic so I'm not sure how the capacitor connects but I can guess.
It's a clever concept at any rate, I'm not sure why they don't all work
this way but I've seen similar generators which had slip rings and a
circuit board to regulate the output much like a car alternator uses.

This is one brushless 3-stage method - there are others.

1st stage. - pilot exiter

rotor = permanent magnet
stator = static coils

Rotate the rotor and AC power is induced in stator coils.
Output from stator coils is fed to second stage within the
stator.

2nd stage. - main exciter

stator = coils fed from 1st stage
rotor = coils

Output from 1st stage stator is rectified and fed to second
stage stator coils - regulation can be imposed here.
Rotate 2nd stage coils in 2nd stage magnetic field
- AC power is produced in rotor and output is fed to 3rd stage.

3rd stage. - output

rotor = coils fed from 2nd stage.
stator = coils

Output from 2nd stage rotor is rectified within the rotor body
and fed to 3rd stage rotor coils.
Rotating electromagnets cause induction of output in 3rd stage
stator coils



That's most of what I found online, this is different though, it has
only one stage, unless other parts are cleverly buried within the
armature. It looks like a giant two pole DC motor armature except it has
no commutation, the free ends of the winding connect to each other
through a diode which is mounted to the rotating assembly. The only
external component is a single capacitor.

Don't get all defensive now. Oil filled caps have been around since
the, well, before I was born and they just don't die - and I've tried.
Got a few in my unreg choke input filter HV supply from the 40's still
going strong.
=----

I have had several oil filled caps used in ferroresonant transformers
go bad....

Mark

On Sat, 30 Dec 2006 04:07:10 GMT, James Sweet
wrote:



This is one brushless 3-stage method - there are others.

1st stage. - pilot exiter

rotor = permanent magnet
stator = static coils

Rotate the rotor and AC power is induced in stator coils.
Output from stator coils is fed to second stage within the
stator.

2nd stage. - main exciter

stator = coils fed from 1st stage
rotor = coils

Output from 1st stage stator is rectified and fed to second
stage stator coils - regulation can be imposed here.
Rotate 2nd stage coils in 2nd stage magnetic field
- AC power is produced in rotor and output is fed to 3rd stage.

3rd stage. - output

rotor = coils fed from 2nd stage.
stator = coils

Output from 2nd stage rotor is rectified within the rotor body
and fed to 3rd stage rotor coils.
Rotating electromagnets cause induction of output in 3rd stage
stator coils



That's most of what I found online, this is different though, it has
only one stage, unless other parts are cleverly buried within the
armature. It looks like a giant two pole DC motor armature except it has
no commutation, the free ends of the winding connect to each other
through a diode which is mounted to the rotating assembly. The only
external component is a single capacitor.


The DENSO brushless alternator service manual gives a brief
description of its operation. (I think the schematic fails to show
connection dots for the + and - side diodes)
http://www.denso.com.au/content/down...ation_proc.pdf

Meat Plow wrote:

On Thu, 28 Dec 2006 06:53:08 +0000, James Sweet Has Frothed:


I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.


An alternator in a car is different. It has to have a battery to provide
its field with DC. An AC generator has permanet magnets in the rotor and
the current is induced in the field where the RPM of the rotor is
responsible for how much voltage is produced.

Hmm, I won't get into it, but you're a little off.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

On Sat, 30 Dec 2006 09:55:50 -0500, Meat Plow
wrote:

SNIP


The DENSO brushless alternator service manual gives a brief
description of its operation. (I think the schematic fails to show
connection dots for the + and - side diodes)
http://www.denso.com.au/content/down...ation_proc.pdf

That link just shows how to install it.


Duh! wrong link. It should have been
http://www.denso.com.au/content/down...e/MAC-A581.pdf

James Sweet wrote:

Michael A. Terrell wrote:
James Sweet wrote:

Does it matter? I'm just asking for general principals here, not advice
on fixing this particular unit. Surely brushless alternators of this
sort must be widespread and likely don't vary much from unit to unit.



You're so right. Why would you bother to see if you can find a
manual that might explain exactly how it works.



I have the service manual, it explains nothing of the theory of
operation, it just has a list of the components, shows where they mount,
part numbers, and torque specs for the bolts.


It would have been helpful for you to have stated that to start with.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida