Newage Stamford Data

[electrosteam]

Hi all, a new member and my first post.

I got here trawling through the web looking for information on a Stamford alternator that a good friend built into a nice compact Kubota gen-set.
My friend did a good job overhauling the engine, the alternator was bought-in as 'overhauled', and my task is to get the electrics to work.

When first completed, the gen-set worked fine under test, then the EDIC motor controlling throttle position failed with intermittent internal limit switch (contact disc)  problems.
It took a while to get the EDIC straightened out, but now we have output voltage above maximum limits.

The unit is: Stamford Type D8A, No. D53367/9, 5 kVA, 415 V 50 Hz, Excitation 155 V 1.15 A.

It appears to be a transformer regulated type.
The phases come off the rotor via brushes, and then (apparently) drive the transformer.
There is a diode bridge feeding the excitation on the stator.

At no-load, phases are about 250/245 to N (240 V required) with excitation about 70 V 0.7 A.

With a load, voltage goes up to 270/255 V, with excitation about 95 V 0.9 A.

I have tested the 4 diodes as OK and experimented with resistors in series with the excitation.
There are 4 studs that could be taps on the transformer as the bridge is connected to one of them.
I have experimented with moving the bridge to other studs.

Cannot make sense of it at the moment.
Can anyone point me to a wiring diagram and/or description of this alternator ?

Thanks in advance for any help,
John.

[mobile_bob]

if it is transformer controlled, you will have to adjust the transformer air gap to get the voltage regulated to within the spec
limits,

the transformer adds to the normal excitation current to boost the voltage under load as a regular alternator would normally droop.

for instance an ordinary harmonically excited alternator might start out at 255vac at no load and drop to around 240vac at part load and maybe down to 225-230 at full load, whereas

a transformer controlled unit is setup to be pretty much right on 240vac and as the load comes on the transformer starts to add to the excitation current in an effort to keep the droop down and the 240vac output steady.  it is not completely successful, but can be pretty good if setup properly.

what i don't recall is which way to go, but i think you will need to add a bit to the air gap of the transformer to drop the no load voltage to more near 240vac ,  and then see how it does as you add load.

all this assumes a steady state stable rpm from no load to full load operation, if you don't have that or nearly so, your results will vary.

does it look like anyone has had the frame apart on the transformer?  look carefully at the bolts and see if there is sign of them being in a slightly differing position as evidenced by paint marks.

also,  many of these units use fiber shims to set the air gap, you could use a manila folder paper stock, business cards or a cereal box paste board to try to alter the airgap... remember that there must be something to shim the gap as the magnetic forces are so great that it will suck back together and close the gap under full load, and in doing so change the excitation and by extension the output voltage.

fwiw
bob g

[mobile_bob]

just to add a bit, in case you are not sure of what you might have

that is assuming you have a transformer controlled generator/alternator

the excitation transformer is almost always made up of EI core, non interleaved, in that the E cores are what the coil is mounted on and the I core closes the magnetic circuit.

if you have such an animal, look carefully for some sort of shim between the E core and the I core laminations, there must be some shim in there and if there is not, then it has been either improperly assembled as new, or put back together without the shim as overhauled.

if you find you have no shim(s) you need to start by adding maybe .020" or so and see what happens, make sure to tighten the bolts tight after assembly and retest... then if you need to add more, do so, if the resulting voltage goes too far the other way, remove the shim and put in something less like maybe .010 or .015" 

without a manual for your specific alternator, you will have to trial and error, cut and fit, test and retest to get it right.

not as hard as it sounds

in my opinion the transformer controlled alternators are better than harmonic, nearly as good as electronically regulated but simpler and more robust.

do a google search for "winco transformer controlled generator" you should be able to find how they did it and the theory of operation is the same for all transformer controlled generator/alternators.

btw, welcome to the forum

bob g

[mobile_bob]

http://www.marathonelectric.com/generators/docs/manuals/GPN015.pdf

go to section 7 and read up on adjusting the air gap, shims, setting no load and full load voltages of transformer
controlled generator/alternators

while this info is not specific to your unit, it will however give you the theory of operation and a starting point to sort your unit out.

we had a similar discussion back in '12 here on the forum

http://www.microcogen.info/index.php?action=printpage;topic=3004.0

and in '11

http://www.microcogen.info/index.php?topic=1604.0

bob g