Building voltage regulator for 3ph generator

regulator.
formatting link
Voltage ergulators for this application are cheap, and readily available. Sorry I don't know off the top of my head where. Trust me, cheap and available. They connect to the ouptut, and rectify it and output it to the field windings. A friend of mine generates his own electricity, and uses them.
Since the output is AC, and the field is DC, the polarity of the field can't possibly matter can it? It can't! It really can't.. Yet it does..... ???? This caused some _HUGE_ confusion, and an argument.
Here is why it matters, and what to watch out for. As the generator starts up, residual magnetism generates a very weak output. That weak output is enough to supply a little voltage output, for a little more field, and the generator bootstraps up to full outout in a matter of a couple of turns. The key here is residual magnetism is what starts the generator initially. If the polarity of the residual magnetism matches the output of the regulator, it will bootstrap up. If someone disconnects a working regulator, from an idle generator, and swaps the leads to the field, it will not come back on line. Everyone might think the regulator just went bad. What is happening is that the generator starts to output a weak voltage from the residual magnetism left over from the last time it ran. The regulator outputs a field current that now bucks the residual magnetism. It bootstraps the residual field down to zero.. And the perfectly good alternator and perfectly good regulaotr output zero volts. Even a zap from a AA cell will start it outputting full power. But talk about strange symptoms!!! Everthing was working perfect, the regulator is disconnected, reconnected, and everything is dead!
This scenario can also plague you if you build your own regulator. It was so "interesting" that I had to share it. Even though I hate typing.
So, your homemade regulator might not start up on its own. The comercial units that I saw did not have a stepdown transformer. This allows the residual startup voltage to be sufficient to initially bootstrap the field. The field might be pulse width modulated, toreduce power lost in the regulator, I don't know. The units were a little box the size of a mouse.
Pete
Reply to
3t3d
Loading thread data ...
I have an old 15 KW 3ph generator that is missing the voltage regulator.
The alternator has a 12 volt generator on the back that I assume
provided the dc current for the field winding.
I would like to get an idea of the level of difficulty of designing and
building a regulator, it would not have to be high performance as the
generator will be only be used to run shop motors.
I have a schematic for a homemade regulator used to control a car
alternator to provide 110 volts. (see link below)
formatting link

My plan was to wire in a small step down transformer across one of the
phases of the generators output, rectify it(to get a dc voltage
proportional to the desired output voltage) and feed it into the circuit
for the homemade regulator.
Other than the fact that my field winding will probably draw more
current than the homemade regulator's transistor is able to provide, is
this a workable plan?
Reply to
SBAER
I don't think it would be very hard to get your generator working, but I am not sure that your plan will work. One question is whether your generator is actually a generator or an alternator. Look to see if it has slip rings or a commutator. Depending on that answer there are more questions.
Dan
SBAER wrote:
regulator.
formatting link
Reply to
dcaster
I suggest you look for a bassler regulator. I bought one years ago and it only cost me about 75 bucks. These regulators use AC from the alternator to drive the field. I suspect your 12V winding is only intended for battery charging for the starting batteries.
Reply to
Charles A. Sherwood
Sbaer
If you think you can build a voltage regulator, I also think you can . The field current of your 15 KW alternator may not exceede that of some automotive alternators. I hope that you do build a voltage regulator and keep RCM informed about your progress. There are several RCM posters who are very well qualified to assist you with the design. I even think *I* could build one, but wouldnt even think about it without asking Don Foreman.
Jerry
Reply to
Jerry Martes
I'll note for the benefit of some of the other posters that a lot of older and larger generators did indeed have a separate PM DC exciter generator to provide power for the field. I have a vintage 1944 25KW unit that has a 1KW DC exciter on the end of it. It's not 12V though, so they may be correct that yours is designed for battery charging although usually you see that on single phase generators much smaller than 15KW.
The point about regulators being readily available and not too expensive is correct. You should be able to go to a local generator service place (Onan, Kohler, Etc.) and talk to someone who can help you select a suitable unit.
Pete C.
SBAER wrote:
Reply to
Pete C.
I seem to recall one version that was built around an LM317. There is a variant of that chip that will do 5 amps, also.
Jim
Reply to
jim rozen
formatting link
This circuit appears to be a linear regulator, and will likely dissipate a HUGE amount of power in your application. A much better circuit would use a PWM modulator and a power FET transistor in chopping mode, and a freewheeling diode to recirculate the field current. A 555 chip could probably be used as the PWM modulator, and an op amp could probably serve as a gain element to improve regulation.
Jon
Reply to
Jon Elson
LM338
Reply to
Don Foreman
Sure, but as other posters have noted we can do better than that ancient circuit. If you can find out what voltage and current the field winding needs, cooking up a regulator circuit should be no problem.
Reply to
Don Foreman
Stan
What RPM is needed to give you the frequency of the output voltage you require? Do you have an engine RPM controller? Where are the slip rings used? I suspect they are used to make comtact to the field circuit. I advise you to look very carefully at the clearances inside the generator before deciding to remove the bearing within it. I'm pretty sure I'd try to drive the generator with some sort of drive that allows you to keep the alternator assembled as it now is.
Jerry
Reply to
Jerry Martes
I certainly wouldn't consider removing any bearings. Use a large Lovejoy type "spider" coupling, they are inexpensive and will accommodate some misalignment. The genset I have uses one of these between the massive flywheel on the International UD9 engine and the generator. The whole thing is built on a heavy I beam skid. My particular unit uses a six pole generator and runs at 1,200 RPM.
Pete C.
Jerry Martes wrote:
Reply to
Pete C.
I made an error, the field voltage is actually 60 v as is the output of the exciter on the back. The unit does have slip rings. I had talked to my local generator service place but he was not too helpful. I also looked up the prices on the Basler website and they looked quite high (nothing in the under $200 range) but I will make some more inquiries.
The generator has two bearings and a drive shaft and mounting feet (it looks like an electric motor). I plan to drive it with a VW diesel engine. I think the easiest way to mate the two is to make a fairly stiff frame that would look like a big angle plate thst bolts to the back of the engine block and an adjustable plate (adjustable with jack screws) to mount the generator to. I would make an adapter to attach the generator shaft to the flywheel and use an dial indicator to set the two shafts in line. Once this was set up I thought I would remove the front bearing from the generator to prevent the bearings from being loaded by any misalignment in the shafts. How does this sound to you.
stan
Reply to
SBAER
I made a mistake when I said the field voltage was 12 volts, it is actually 60 volts as is the voltage on the name plate of the exciter on the back of the alternator. The current rating on the nameplate of the exciter is 6 amps.
stan
Reply to
SBAER
Thanks for the heads up on this problem, I will keep it in mind when I try to fire the thing up. The generator has sat idle for 30 years i bet, it may well have lost its residual magnetism.
stan
Reply to
SBAER
The thing looks like a big electric motor with another smaller one attached on the back to the same shaft. The large one has slip rings, the smaller one has brushes. I made a mistake when i said the field voltage was 12 volts it is actually 60 volts.
stan
Reply to
SBAER
The speed is 1800 rpm, I plan to govern it with a moified cruise control unit out of my wife's 1992 VW Golf, she never uses it anyway and won't miss it (the cruise control that is).
stan
Reply to
SBAER
That may be a better idea, although I may have to make a couple visits to the scrap yard to find one in my price range.
stan
Reply to
SBAER
OK. Those values sound reasonable. I'd measure the field resistance so we know what the field will draw at 60 volts rather than what the exciter is capable of supplying. They're probably similar but it's an easy measurement to make.
I don't think field current or voltage varies greatly from no-load to full-load. Jerry Martes, please chime in here.
PWM is an obvious solution here, but a simpler "brute force" approach would probably also work OK. I've seen such an approach used on several somewhat larger machines that Jerry Martes has successfully repaired.
PWM requires slightly more complex circuitry, but if you're comfortable with building elex from a schematic the parts required probably wouldn't cost $20.
If you'd like to proceed, measure the field resistance and reply either on-group or by email. If you can build elex from a schematic and care to do so, I'd be happy to work with you on this.
Reply to
Don Foreman
Hi
Thanks for the interest. Does PWM stand for pulse width modulation? I assume you would control the field of the exciter rather than the field of the alternator directly. Would you use the exciter's output to feed back into the exciter's field or would you use the the 12 volts from the battery? I appreciate any help, and am more than willing to try to build something from scratch as this project is as much about learning as it is about replacing my propane powered unit. It may take a while for me to report back about the regulator's effectiveness as I cannot test it until I make a mount to couple the generator to the engine.
stan
Reply to
SBAER

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.