Generator issues

[koliver]

My 4.4 kw Westerbeke is acting strangely.
When first started up, it will charge the batteries at the maximum that the charger, Xantrex MS2000 will permit. As the batteries get charged, dropping from Bulk to Acceptance, to Float, the generator will drop voltage, from the 125v that it starts with, to around 100v, which the Xantrex rejects, as that is too low. When that happens, charging stops altogether.

I notice this a few tries in, and then started adding other loads as the charger reduced loads. That kept the voltage up and allowed the charging to continue. Now, with a space heater drawing furiously, out on the foredeck, it works. Until the heater turns itself off. I might have one at home I can substitute, without an automatic overheat shutoff, but I digress.

I need to get this fixed, but I have already taken it in, which I did 2 years ago, but the tech, armed with test equipment, couldn't make it misbehave, so nothing was accomplished. Then I added solar, so the generator saw almost no use last year. This year I added significantly to electrical loads, so needed the generator, so now I have more incentive to get it fixed.

Which part of the genset is malfunctioning, to allow the voltage to drop as the load drops?

 

[Wood]

If you start the generator without the charger under low load - what is the voltage?

 

[High Wire]

Buy a Kill-A-Watt power monitor (about $25) and plug it into a wall outlet. It allows you to easily monitor output voltage on one leg and generator frequency from an accessible location.
Low frequency (engine speed) will lower the voltage as well as a voltage regulator problem.
Check your generator manual for generator output voltage troubleshooting.

 

[STB]

We need to do some more tests to get a better idea.

My first guess would that the problem is on the engine side of things with the governor.

Can you check the RPMs if the engine, e.g. with a tach gauge or phototach instrument? Do they go up and down with the voltage?

Can you check the AC output voltage frequency, for example with a multimeter frequency scale, a frequency counter instrument, or with an oscilloscope? Does it go up and down with the voltage?

If you happen to have an oscilloscope, does the waveform look right or change?

If it isn't on the mechanical side of things, it could be in the voltage regulator or regulator-exciter circuit. The answer could be as easy as a bad capacitor.

But, to make any real guess, I'd need to see the schematic for your generator or know the /exact/ model to see if I can find it online. Different generators work very differently in this respect, especially generationally.

 

[syjos]

Test the capacitor(s). Westerbekes come with one or two.

You'll need a multimeter with capacity measurement capabilities.

 

[Barking Sands]

I had this issue on my Westerbeke 4.4 when I purchased it. The Xantrex rejected the power and the voltage was low. I set my multimeter to hertz and plugged it in the nearest socket. I was getting low frequency. I cant remember exactly what it was but maybe high 40s. Come to find out, sometime in the recent past, someone had changed the stop solenoid. The stop solenoid is obviously connected to the fuel lever. Changing the stop solenoid requires a check and adjustment of the frequency to ensure it has not been altered during the R&R. This is also where the RPM is set. RPM= generator frequency. Just a few quick turns of the adjustment turnbuckle and I had it set to around 60.5 I think under no load. Then tested at high load to ensure it was around 59.9 to 60 hertz. Been fine ever since. Either the kilowatt mentioned above or a digital multimeter set to hertz and this check takes about 30 second. Adjusting takes a few minutes. I think you should rule this out before going down the line.