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Marathon SE350/Basler BE350/AVC63 Failures Riding on UFRO

Marathon SE350/Basler BE350/AVC63 Failures Riding on UFRO

Marathon SE350/Basler BE350/AVC63 Failures Riding on UFRO


We have found a pattern failure in SE350 AVRs on Marathon generators with 3 cylinder diesels. They appear to be the same as the Basler units listed in the title so wondering if Basler is the manufacturer of all of them.

Units of all different ages and engine brands have done it.

What happens is that the output voltage becomes extremely frequency dependent.

Changing the UFRO pot has no effect when the failure is occurring. It can be run from min to max and voltage remains constant.

Slight adjustment to engine speed will send the voltage up or down proportionally even though the engine is running very close to 60 Hz. Like a few tenths of a cycle.

The voltage pot will still be functional although somewhat sensitive.

Calls to Marathon yielded a lot of talking but of course we were the only ones that ever had this problem, however it seems widespread to us.


RE: Marathon SE350/Basler BE350/AVC63 Failures Riding on UFRO

I'm not sure if Basler makes the SE350, but since they offer the retrofit version BE350, I wouldn't think so since most manufacturers who have Basler brand their AVR's don't let Basler sell an aftermarket version. I'm pretty sure originally most smaller Marathons used the AVC63-4 AVR. It functions the same as the two 350 AVR's but has different wiring, main difference as I remember is that the AVC63-4 has seperate input terminals for power and sensing, while both the 350 AVR's combine sensing and power internally.

I had a customer who had some similar issues about 4 years ago, with a fleet of about 40 small gensets, we took 5 units and installed the AVC63-4 AVR's, no problems with them for about 6 months, as far as I know he eventually converted the entire fleet. You may want to try the Basler version BE350, I have no experience with it.

I have used all of the AVC family of AVR's with very few problems.

A couple of other things you may want to take a closer look at,
Carefully inspect the V/Hz jumper, we found several where the wire was broken as it came out of the potting. Also found problems if the jumper connection got corroded, sometimes cleaning the jumper connection made the problem go away.

Check the field resistance, as I remember the Marathon AVR had a minimun field resistance of about 12-15 ohms, the Basler version about 20 ohms. We found over the years that lower than rated minimum field resistances caused some strange things to happen with the smaller AVR's, including instability and the V/Hz (or UFRO) not to work as expected.

Hope that helps, MikeL.

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