Hello and help!

[phil.woodshed]

Hi all, I have finally got my VASOMAC running but still have no power at the alternator.... well there is a nominal 1.xxV and it has reached 6V +/_
there is a video on you tube with it running

[/youtube]      http://youtu.be/p6bOEne2QwQ

I have cleaned all the connections, checked the brushes and there are no wear marks on the rotor indicating a loose stator coil.

It spins on 24V (well it did some months ago and I stuck a 12V battery on it yesterday closed the solenoid and gave it a nudge and it made an effort to turn).

It doesn't seem to be producing DC either, certainly not at the battery terminals, only a variable ripple in mV.

I am not sure what type alternator it is, possibly BKB. the plates on the base don't give a make.

I have manuals and as can be seen in the switchgear control cubicle in the video, there is a wiring diagram...... minus the top right corner which is the alternator and brush layout.

Any advice on methods of checking what may be wrong please. I don't have a Wheatstone bridge nor a megger so its my trusty DVM only.

I am fairly electrics savvy but please don't assume I understand everything.

regards,

Phil

[ronmar]

Hey Phil
   If I am reading the meter correctly in the video, it was showing up to about 6V out at 60 HZ?  If that is the case, that output is probably the residual magnetism in the rotor exciting the stator. 

Generatror(alternator) 101:  The generator either takes some energy from the main stator windings, or pulls energy from a harmonic winding,  rectifies it to DC and feeds it back thru the brushes to the rotor field windings. THis energy builds the magnetic field to excite the stator. This energy is usually regulated in some way which controls the generator output voltage.

So that meter indication in the video looks to me like no energy is reaching the rotor windings. This could be bad brushes, an open rotor winding or wiring or the regulation circuitry or field energy source may be at fault.  Are you familliar with the troubleshooting term "half-stepping" It is where you try to break a faulty circuit in half and definitively determine which half is bad.  Then you take the bad half and again divide that half in half and try and determine which half is bad.  A good first halfstep point on a generator is to disconnect the field leads that feed down to the brushes.  With the engine running and your meter connected to the generator AC output, take a small 12V battery and momentarilly apply 12VDC to those field winding leads. If all is well with the field wiring,  windings and brushes, you should see a noticeable increase in AC output.  Watch the output voltage and don't let it exceed the rated AC output voltage, if it goes high, disconnect the 12V input.  This is known as "flashing the field" and is a good thing for anyone who tinkers with generators to know how to do.

No increase in AC out, means the problem is wiring, brushes or rotor field windings.  AC output means the issue is upstream in the regulator or source wiring/circuitry...
   

[phil.woodshed]

Generatror(alternator) 101:  The generator either takes some energy from the main stator windings, or pulls energy from a harmonic winding,  rectifies it to DC and feeds it back thru the brushes to the rotor field windings. THis energy builds the magnetic field to excite the stator. This energy is usually regulated in some way which controls the generator output voltage.

..Ok, with you so far,


So that meter indication in the video looks to me like no energy is reaching the rotor windings. This could be bad brushes, an open rotor winding or wiring or the regulation circuitry or field energy source may be at fault. 

..brushes seem ok, leastways they conduct

..open rotor winding..... DVM continuity or megger?

..regulation circuit.... in box attached to alternator?

..field energy source ??...... round here that's NPK to make the grass grow......

 Are you familliar with the troubleshooting term "half-stepping" It is where you try to break a faulty circuit in half and definitively determine which half is bad.  Then you take the bad half and again divide that half in half and try and determine which half is bad.  A good first halfstep point on a generator is to disconnect the field leads that feed down to the brushes. 

..I am now, thank you.
..Which are the field leads?.... indeed define field please

With the engine running and your meter connected to the generator AC output, take a small 12V battery and momentarilly apply 12VDC to those field winding leads. If all is well with the field wiring,  windings and brushes, you should see a noticeable increase in AC output.  Watch the output voltage and don't let it exceed the rated AC output voltage, if it goes high, disconnect the 12V input.  This is known as "flashing the field" and is a good thing for anyone who tinkers with generators to know how to do.

..Excellent,perfectly understood (pending "field" definition).
,.I keep hearing about flashers I was worried some of you spend too much time in your sheds.....

No increase in AC out, means the problem is wiring, brushes or rotor field windings.  AC output means the issue is upstream in the regulator or source wiring/circuitry...
   
[/quote]

Thank you
Phil

[ronmar]

The "field" is what is excited by the field current to build the magnetic field in the rotor(rotating part in the generator).  That field(magnetic field) is what excites the stator(stationary) windings which output the AC power to whatever electrical load you are powering.

There should be 2 wires connected to the two brushes.   The electric current that excites the field, flows down one wire, thru one brush, thru the rotor windings, back thru the other brush and back up the second wire to complete the circuit.   You disconnect those 2 wires that connect to the brushes and apply your DC test current to the two wires to build an electromagnetic field.  IF these parts are OK, the generator will output more AC voltage than it currently is...

AN ohmmeter can also be connected to these two wires to measure the resistance thru the brushes and the rotor windings...

[phil.woodshed]

Thank you, I did as you said but got nilch.

I am confused why I get a frequency from the output yet virtually no voltage, unless these windings are short.

There are also the second sets of brushes. At least 2 must be the 24V dynamo windings but these share the commutator with 4 additional brushes which I can't  figure out. The diagram inside the starter control box is missing the top right corner which is the DC circuit I guess. None of my manuals show a similar arrangement so I am confused.

If I get chance tomorrow I will pull the rotor from the case and try to trace all the wires. As It is everything is dirty and dark so impossible to decipher.

Any advice that will save me time or point me in the right direction would be gratefully received.

A winding resistance list would help as I can use a 6V battery and measure the current to calculate low resistances.

Does anyone know how to ID the alternator make?
It is no. 23837/15 4.25KVA but the 'type' was never stamped on any of the plates.
I know it's original and the engine is 872VA11 so was one of the first 1000 VAs manufactured and it's a 1961 the first year of manufacture.
I'm also reliably informed the alternator is a 5K unit rated at 4.25 for the 7.5HP VA output.

I really could do with getting it running before winter as my batteries have lost half their capacity and I can't afford to replace them so will be more reliant on a geny for the first time in the 11 yrs I've lived here

[ronmar]

Frequency is a factor of engine/generator RPM.  The core of the rotor is iron plates and has been exposed to the field so it has absorbed a magnetic field.  It is exciting the stator windings at the running RPM, but without a strong enough field to get much output voltage.

Sorry, I have no info for your specific generator...

[millman56]

The wire wound variable resistor which controls the field current can be problematic, the brass adjusting clamp may suffer from metal fatigue and crack,  also the resistor wire surface in contact with this can oxidise, both may result in no or intermittent alternator output.    The clamp may be silver soldered or bronze welded to repair breaks and a light rub with 300 grit paper cleans up the wire surface.

Mark. 

[millman56]

Forgot to say that Chris R has a wealth of experience with the VA SOMs, he kindly pointed me in the right direction when I was struggling with a problem.

Mark.

[phil.woodshed]

Thanks everyone. As far as I can tell the resistor is ok, ( we are talking about the one mounted on the frame I presume). I will do a low resistance check on it when time permits and determine the exact reading.

How do I raise Chris R ? I have scoured lots of previous posts before I posted this but failed to find any clues as to how the DC side works and why I have no power.

[millman56]

Just type "VA Startomatic" in the search box.