1981 20KW Kohler 20ROP63 Issue

[MVCaprice]

Sams Forum,

We are having an issue with our Kohler 20KW Genset which we are hoping to run down. Given that these are somewhat common generators we thought this would be a good place to ask. So far some local shops have looked at it, but they have been unable to diagnose the issue.

The symptoms we are seeing is that if there is more than a 30 AMP load the voltage begins to drops from 220 to below 190 and even further if additional load is added. One potential diagnosis that was kicked around is that the generator unit itself is bad, but we are unsure.

The set has about 1500 hours on it.

Anyone have any suggestions?

 

[Boatsb]

fuel.

 

[Andy B]

Could be a weak capacitor,check frequency when the voltage drops if it stays around 60hz then problem is most likely in the back end.

 

[bigbill]

does it have a voltage regulator?
what about the governor? might not be keeping the engine up to the task

 

[MVCaprice]

Its not the engine dropping rpm, and its not fuel. There's no voltage regulator that I can find on it.

 

[davidwigler]

You're sure the rpm stays constant when voltage declines under load?

 

[MVCaprice]

No change in rpm that I can tell

 

[Andy B]

Frequency is directly related to rpm, if its low rpm is low,below 1800,if its high rpm above 1800.

 

[MVCaprice]

OK. Thanks guys. We'll take another look at the RPM and Frequency and post back.....

 

[carolinacoast]

we had a similar issue, and it was a dirty secondary fuel filter on the gen that was not actually changed until I changed it from suggestions from this board. Despite me having an invoice to the contrary.

 

[rwetherington]

Where is the yacht located? Now that I work as a rep for Kohler I will be glad to find you a tech in the area to look at your gen set.

 

[MikeP]

I agree with the suggestions that it's probably a fueling issue. But, as noted, the rpm would drop and you should be able to hear that as it occurs. Have you actually been sitting/standing next to the genny when additional load is applied so you could clearly hear whether the RPM is dropping? Being elsewhere in the boat it may not be so obvious.

FWIW A very handy device is an optical digital tachometer which can be used for this purpose as well as setting/verifying main engine idle/RPM as well as calibrating the tachometers.

 

[MVCaprice]

Where is the yacht located? Now that I work as a rep for Kohler I will be glad to find you a tech in the area to look at your gen set.

Its in Everett, Wa

 

[MVCaprice]

After looking into this more and redoing some of the wiring it appears that the voltage drop is indicative of a RE Rectifier (Bridge Rectifier aka Diode) malfunction. RPM on the other hand affects frequency .I am working on replacing the rectifier. It looks like the one we have was already replaced at some point.

 

[MVCaprice]

Update on this issue: I ended up purchasing a new rectifier from an electronics vendor. It ended up being a "VK648" which I was able to purchase for 18$. I was unable to source this part from Kohler and the price was right and was an identical part which it seems may have been updated at some point in the last 35 years.

After some other mechanical (cooling and exhaust system and wiring fixes) the generator is now working good. I also went through and replaced the primary and secondary (on engine) fuel filters and cleaned the water separator as well to make sure that wasnt a problem.

There is still a very slight voltage loss under load, but its still making well over 110 volts with an 80 amp load. I believe the rectifier was in fact the issue.

 

[MVCaprice]

I have had some PM questions on the rectifier so I wanted to post some more info about the part to help out others in the same situation.

The specific part number for the 20ROP63 rectifier is as follows:

VARO VK648 FNFP ​

I was able to source it from Radwell. Here is a link:

https://www.radwell.com/en-US/Buy/VARO/VARO/VK648