Onan 45EM 15R Voltage Surge and Exciter Breaker Tripping

[mazdaboi]

Hello all,

Some time ago, I had posted about a mid 70's 45EM 15R that I was looking to buy. I did buy it a while back and got it shipped in. After various trials and tribulations, I got the generator running and generating power. It's configured for three phase wye, 120/240 VAC 60Hz. During my testing (with a small load), the voltage on all three phases was spot on, and the generator was acting as I'd expect.

Today, I figured it was time to try it on a larger load... The particular load I put on it can draw up to about 35 amps per phase. When this load is first turned on, it draws very little power. The next stage lasts for about a minute and it draws a handful of amps... The final stage comes on, and it will pull anywhere from 15 to 30-ish amps.

When the heavy load stage hit, the load ran for about 15 seconds then shut down. I checked the generator over and found that the exciter breaker had tripped. I disconnected the load, reset the exciter breaker, made sure the voltages were all sane, and powered the load back up.

This time I watched the voltmeter and ammeter on the generator. At first, during the low amperage stage, the voltage was 220VAC per leg, and the amperage was basically zero. When the high amperage stage hit, the ammeter was still basically zero, but the voltmeter was pegged at 300VAC.

At this point, I quickly threw the exciter breaker. I'm not sure if what I was seeing was accurate or not. I don't understand how the generator can be producing a solid 220VAC, and then suddenly peg the voltmeter when the load increases...

Hoping my load is okay, but I have no way to really check it at this point. I don't trust the generator now, and have no other source of three phase to test with.

I did some quick searching and found a post where someone had an exciter breaker tripping, and one of the individuals helping them asked if the voltage was going high at the same time. They didn't detail the failure mode, if that were the case (the original poster had no voltage surge).

Another page mentioned the possibility of bad diodes.

Does anyone have any thoughts on how the output voltage could swing high once a moderate load is put on the genset? Should I start by testing diodes?

Thanks,
Brad

[Wayne 440]

I suggest that you start by verifying the voltage that your set is configured for -
there is no "three phase wye, 120/240 VAC" connection. Common 3 phase connections in that voltage range are 120/240V, center tapped delta or 120/208V wye (Y).

Also if your load (do tell what it is) creates a leading power factor, it may cause problems with voltage regulation.

[Jim McIntyre]

^ Agreed.

Also, verify the set is making 60 Hz. Don't assume anything...

[Gunny]

A COMPLETE Model/Spec/Serial number would be a good starting point. Then we'll know exactly what you have.

My crystal ball is a little cloudy this morning.

[mazdaboi]

Thank you both for the advice.

I rechecked the generator head configuration and the voltage regulator connection a couple times before I started the set, and then again after I ran into this issue. Just looked it over again, in case I missed something yesterday, and it's configured as expected, according to the matrix displayed on the head cover panel.

You're correct that my description of the voltage regulator setting was incorrect. It's configured for 139/240, which is within the input specifications for the connected load. I have the voltage regulation control set for 220VAC output, which was what I had across all the phases, prior to the excursion. I need to be more careful in my descriptions. Sorry for the confusion.

The load in this case was a Coherent I70 mixed gas ion laser. I collect these old behemoths, and use them for light show projection. The I70 produces about 3.5 watts of output. They are horribly inefficient, water cooled beasts. The vast majority of the input power ends up going down the drain as warm water. There's certainly more modern technology to use for light show projection, but they don't interest me as much as the older technology. I suppose I'm a glutton for punishment.

The incoming power ends up being rectified, regulated, and placed across the plasma tube, so I suppose it could be a power factor issue. Before going down the generator route (versus RPC or VFD), I spoke with several other laserists. Two in particular also own generators for the same purpose. No power factor issues were brought up, but I also didn't ask directly. I'll see if I can get in touch with either of the individuals I'm thinking of, to ask the question.

Not quite sure how I'm going to diagnose this issue. I'd really like to put a large resistive load across the generator, to see how it behaves. That could go a long way in supporting or ruling out the idea of a power factor issue. At this point, the only loads I have are ion lasers, which don't grow on trees anymore. I can't risk damaging (another) one.

Assuming it turns out to be a power factor issue... I found a reference in one of the service manuals to additional filtering components that could be ordered and installed in the voltage regulation circuits, to help with such issues. Anyone happen to know about this kit and what it consisted of? Perhaps a choke and/or capacitors, to filter out switching harmonics?

Assuming its not a power factor issue... The service manual doesn't have a scenario that exactly describes what I'm seeing (voltage correct, until load increases, then voltage goes high, and exciter breaker trips). But, it does have scenarios for the voltage being too high, voltage being unstable, and exciter breaker tripping. I suppose I could go through all three scenarios and perform the testing indicated.

My first hurdle is getting a load to use for testing.

Again, would appreciate any thoughts you may have.

Thanks,
Brad

[Wayne 440]

Find a local HVAC shop and ask if the they have 2 or 3 removed "air handlers" with electric heat that you can get hold of. With about 30 minutes of work, they make serviceable load banks.

[Leon N.]

Wayne re your comment: [I suggest that you start by verifying the voltage that your set is configured for -
there is no "three phase wye, 120/240 VAC" connection. Common 3 phase connections in that voltage range are 120/240V, center tapped delta or 120/208V wye (Y). }

Onan offered a 120/240 3 phase, 4-wire configuration delta wound, one leg center tapped, to deliver 120/240 volt single phase power in capacities up to 2/3 of full rated 3 phase KVA.


I do not think we know what this guy has or is doing without first seeing his machines nameplate ratings let alone figure out what the heck he is loading it with. You are correct there is no 120/240volt 3 phase, 4 wire relationship unless it is delta wound as I mentioned. Agree?

[Wayne 440]

After my comment, the OP states that the 12 wire, "15" voltage code set is wye (Y) connected, adjusted to 220V phase to phase.

[Vanman]

Keeping history alive! I love it! I recall connecting power to a laser in a Hughes plant once. Supply was 480 volt, 3 phase, 60 amp. Also had connections for chilled water supply.

In the scenario where generator voltage goes high due to leading power factor on the line, the field breaker would not trip as the voltage regulator would have the exciting current down to minimum. Unless these have shunt trip field breakers, triggered by high voltage?? I'm dubious of that. But it would be a nice feature.

I think that this is (yet and still another) faulty electronic voltage regulator, or, possibly, an intermittent connection on the sense wires (assuming it has such).

[mazdaboi]

Gunny:
Onan 45.0 EM-15R/1140D 0374823022

Wayne 440:
Regarding the air handlers. Good idea. I was thinking of gathering up a bunch of electric stove elements and a furnace squirrel cage blower assembly, to build something. But, we recently had our (gas) furnace replaced. The company that installed the new furnace mentioned they'd take the old one to their bone yard. Will check with them to see if they may have some units that would serve this purpose.

Regarding keeping history alive: Someone has to, right? The laser you're referring to sounds like it could have been something like a Spectra Physics 171, which is about 5' long, glass and ceramic tube, and requires 480 three phase. Makes even my largest lasers look small! Would love to see one of them running.

Will work on rounding up a suitable test load. Will also study the voltage regulator diagnostic flowchart and steps, to get a better handle on how to diagnose a possibly bad regulator.


Thank you all for your input.


Brad