Stamford C20A single phase AVR?

[HutchSR3]

Hi,
This is my first post.
I have a alternator wiring question.
I recently purchased from auction a Lister SR3 with Stamford C20A alternator which was in pieces.
After assembly I trace everything out and realized the Fequency Unit and Voltage Control Unit were missing.
I have purchased a SX460 Automatic Voltage Regulator to replace the old components, according to the instuctions the exciter stator field xx- and x+ connect to the board, so can I remove the transformer-coil/rectifier assembly and replace with board?
Also I have one electronic component I can not identify it has 14 gauge wire and has one lead marked #2 photo 2012 014.
Please see photos and wiring lay out.
Any help is appreciated.
Thanks

[HutchSR3]

FYI.
more photos.

[mobile_bob]

this appears to me to be another one of the transformer controlled generators

the transformer is technically a compound transformer, wherein as the load goes up
it induces current into the secondaries which boost the field current.

this tells me that the field windings are probably wound heavier than a typical AVR or harmonic excited generator, so your new avr should be able to drive it hard under a surge condition without burning the field up. however the avr might or might not be capable of driving it as hard as the oem transformer does? i don't know.

wait and see what other members have to say on this one, maybe someone has a full schematic for this unit or one similar so we can get a better idea of what you need to do to get it functioning again.

btw, don't throw away anything !  especially that transformer!

bob g

[HutchSR3]

Thanks Bob,
I have never seen a transformer like that, L1 and L2 both have heavy windings as you mentioned, it's hard to trace being covered.
It's too bad all the control wiring was ripped out.
Even if I go to an AVR, I should probably leave it in then!
As you said hopefully some has seen or has drawings for this alternator.
Cheers

[mobile_bob]

have you tried the unit to see if it powers up?

most of these transformer controlled generators are pretty basic
i don't think i have seen one with a voltage control or frequency control unit?

frequency is a function of engine speed, and voltage is set by the airgap of that transformer.

are you referring to missing gauges/meters?

just curious

bob g

[HutchSR3]

Bob,
No, I have yet to fire it up, I have just finished putting it back together and wanted to get the wires in the alt put back.
The two wires for the exciter field were just hanging, not labelled, do you know if it matters about polarization, on the rectifier it has + and - .
From what I understand after the rectifier was the frequency control unit and on the other side was the voltage control unit, old tech. the new ones have the AVR.
These were missing! this was an old coast guard gen, they probably pulled them off for parts before sending to gov. sales.
Thanks

[mobile_bob]

if it were me, and i am not suggesting you do the same

i would connect one of the leads to one of the field posts
and connect the other via a switch to the other field post

polarity won't matter

then i would spin it up to speed, and connect a voltmeter to the outlet
and the flip the switch and see how high it climbs up,  if it is connected
for 240vac then i would get alarmed if it jumped up to 250-260vac.

this assumes you have the speed set at 1800 rpm for 60hz or 1500rpm for 50hz
and also assumes a 4 pole head.

if for whatever reason the voltage went above 260vac on a 240 connection
i would quickly flip the switch and deenergize the field.... then i would go looking for how the machine was setup for a voltage regulator.

i think the odds are good it will regulate, but i am not sure without a good schematic

it might be that there was some sort of voltage regulator that provided some excitation, and the transformer provided the boost for surge capacity?  i don't know for sure,  we don't have enough of the schematic to tell for sure.

the way you have it drawn i don't see how there would be any excitation coming off the transformer until there was a load across the L terminals, (L1 and L2, iirc your drawing)

there has to be a schematic out there somewhere for this machine,

you might try over at listerengine.com, member dieselgman might have access to a schematic for your machine, that would be a huge help with this problem.

bob g

[HutchSR3]

Thanks Bob,
I will give that a try, I wanted to get the wiring done before firing up the engine.
I have been in touch with dieselgman, and ordered parts for SR3.
Paul