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brushless alternator?

S

Sam Goldwasser

Jan 1, 1970
0
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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J

Jamie

Jan 1, 1970
0
James said:
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.
 
D

default

Jan 1, 1970
0
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.
 
M

Michael A. Terrell

Jan 1, 1970
0
James said:
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
 
M

Michael A. Terrell

Jan 1, 1970
0
default said:
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
 
R

Roddy Meatstick..............

Jan 1, 1970
0
James said:
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.
 
M

Meat Plow

Jan 1, 1970
0
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.
 
C

C R Briggs

Jan 1, 1970
0
James Sweet said:
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
 
J

James Sweet

Jan 1, 1970
0
Michael said:
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.
 
J

James Sweet

Jan 1, 1970
0
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.
 
J

James Sweet

Jan 1, 1970
0
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.
 
M

Mark

Jan 1, 1970
0
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
 
R

Ross Herbert

Jan 1, 1970
0
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/download/770/3834/file/Installation_proc.pdf
 
J

Jamie

Jan 1, 1970
0
Meat said:
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.
 
M

Michael A. Terrell

Jan 1, 1970
0
James said:
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
 
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