Generator low voltage - no AVR

[lponcet]

Hi all,
I'm new to this forum, but couldn't find anything that related precisely to my problem, so here goes:
Generator is an SDMO zephyr 8000. It has 120 and 240 vac ouputs. Was working fine until the other day when, in the middle of a welding run, the voltage dropped and my weld turned to birdsh*t. The 240 output is now 160 and the 120 output is around 70 v. When I put a big load on, the voltage drops even further. Manually accelarating the engine can bring the the voltage up to 210 v, but it's really screaming away and the voltage still drops a lot when a big load comes on.
It's pretty simple inside. There is no AVR, it's just the engine speed that changes the voltage, but that is still normal. Four wires come out of the alternator: earth, common, 120 and 140. two pairs of smaller wires also come out and attach to two capacitors. There are some diodes inside, which I have not been able to test as access is terrible. I'm a pretty practical person, but I don;t know a lot about the inner workings and windings of generators. Are there simple tests I can do at least figure out what's gone wrong (it's either the capacitors, diodes or windings as the AC wiring has nothing else connected to it).

[wellandpower]

Hi, nice of you to join. Have you asked SDMO for a diagram, if you get one someone might be able to help you with it better.
The voltage will not be controlled by the engine at all, it must be controlled by something else soemwhere along the line, but the voltage will always depend on the engine speed.

You can test the main stator winding, by testing the insulation, but sounds like it is probably OK.

You can test that the diodes are OK by testing the resistance in both directions. One direction it should be high (ie it should be offering high resistance, the other way it will depend on the current. Tested with a multimeter it might be several kohms.

A diagram will certainly offer us a better ability to assist you futher.

[lponcet]

Hi, thanks for replying. I've asked SDMO for a wiring diagram or any ideas on what may have happened and am waiting for a reply.
I'd be very surprised if any of the components on the control panel control the voltage or current. If there is an AVR or something similar, it must be deep inside the alternator. All I can see in there are a few diodes, which I can't actually get at to test. Is it possible that the AVR is the alternator housing?

[wellandpower]

It might be capacitor controlled, i think that is normal when there is no AVR. I believe the capacitors control the voltage in the rotor, hence the main stator voltage.

We only use AVR controlled machines here, so sorry to be a bit sketchy on this.

[lponcet]

Thanks for that. SDMO replied eventually. They also thought it was either capacitors or diodes, so it's good to get confirmation. I will try to get hold of replacement capacitors to see if that does the trick. Thanks again for your advice.

[wellandpower]

No problem. Do you know the alternator make?

[lponcet]

The alternator make is MECC ALTE SPA. I've now got a PDF with information and wring diagrams, but can't figure out how to upload it to this forum. One question: each capacitor has two wires connected to it. The wires are the same colour and size and have no distinguishing features. Would it matter which wire connects to which terminal on the capacitor or are they interchangeable?

[merryengineer]

Mostly capacitors are non directional. Some types of ELECTROLYTIC CAPACITORS are directional and you need to connect these the right way round, otherwise you will get a bang!

Normally the directional ones will have -VE marked on them.

I know Welland sell Mecc Alte spares and they are usually available in a couple of days. If you have all the details now of your alternator, i suggest you email the spares team and they will no doubt be able to get them for you.