brushless alternator?

[James Sweet]

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.

 

[Michael A. Terrell]

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

 

[CJT]

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).

 

[quietguy]

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

 

[James Sweet]

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.

 

[James Sweet]

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:

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.

 

[James Sweet]

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.

 

[Dave Plowman (News)]

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.

 

[budgie]

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/pdf/Diode Failure_tlittler.pdf

and more info at:

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

 

[AZ Nomad]

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.

 

[Malissa Baldwin]

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.

 

[default]

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.

 

[default]

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.

 

[Fred McKenzie]

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

 

[Jim Land]

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/pdf/Diode Failure_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.

 

[James Sweet]

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.

 

[James Sweet]

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.

 

[James Sweet]

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.

 

[James Sweet]

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.

 

[Ancient_Hacker]

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.