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ellisjte

120 VAC Shuts Off When Running Both AC's On Genny

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Hi all, hoping someone can help me figure this out.

1997 safari sahara, 250hp CAT, 6.3kw Onan LP generator.

When running either AC on generator they seem to run fine.  Once I fire up the second they run fine for 15 minutes or so then all the 120 in the coach cuts off for a couple of minutes then comes back. AC's and all.  This cycle continues every 15 mins or so until I shut one of the AC's down.

All is well on shore power, no issues there.  I suspect an issue with the ATS, or an auto switching breaker off some sort on the genny.  

Any advice is appreciated!

Thanks,

Jason

Edited by ellisjte
Corrected generator

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Jason,

Welcome to the Forum. 

Did this just start or has it been a problem for a long time? Does the generator continues to run and you just loose a/c from the generator or does it ever just kill the generator all together?

One of your units  may be drawing too much amperage. Which would need a tech to look at it.

Herman 

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Hi Herman, It's been doing this since I bought it about 3 months ago. The generator keeps on going, the 120 comes back on after a few minutes too.

Some background, when I first bought the rig, the generator wouldn't start unless you jumped out at the posts.  Previous owner had taken it to camping world 3 times and they couldn't find it.  I was pretty sure we were dealing with a ground issue and sure enough I found a very loose chassis ground.  Once I tightened that down it fired right up.

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Jason,

Sounds like you may have more ground issues on the a/c output side. When it comes to the gen side a generator I bow to the experts. Onan shop.

Definition, EXPERT           an EX is a has been and a SPERT is a drip under pressure. :rolleyes::P

Herman

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Puzzling.

Obviously, it is not tripping the on-generator breakers, since they are manual reset only.

IF, repeat IF you are safe working around 120 VAC, open the ATS.  Next time this happens, check for voltage IN from the generator and voltage OUT to the main breaker box.

 

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Jason, what else is running at the same time that you are running the two AC's? Brett was typing at the same time as me so I deleted that part of my post. Well one other to add, while checking the ATS, be sure to check the voltage between the red and black connections.

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8 minutes ago, kaypsmith said:

 Well one other to add, while checking the ATS, be sure to check the voltage between the red and black connections.

Suspect the Onan 5.5 (I thought that model Safari came with a 6.5/6.3 propane Onan???) does not have two hots giving 240 VAC between them.  Just two separate 120 circuits.  If so, hot to hot SHOULD read 0.  I am not familiar with the 5.5, so someone please correct me if this is not correct.

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Brett, you are correct if this an RV generator, most 5500's are only 120 volt, that's why there is a 25 amp and a 30 amp breaker. I don't know what model he has, or if this a 30 or 50 amp coach. Onan does make a commercial model 5500 that is a true 240 volt, and if this one is, the breaker would be double gang attached together. The thought that I am having is that it is a 120 volt model, and that both AC's are on the same leg causing an overload condition, but that doesn't explain why the breaker on the generator isn't tripping. My only other guess is that there is some type of intelligent device that is supposed to shed loads is breaking down instead of doing it's job.

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2 hours ago, kaypsmith said:

Jason, what else is running at the same time that you are running the two AC's? Brett was typing at the same time as me so I deleted that part of my post. Well one other to add, while checking the ATS, be sure to check the voltage between the red and black connections.

Just the AC's.  I can fire up just about everything in the coach or just the AC's and the result seems to be the same.  I haven't thrown the microwave in the mix yet though.

Edited by ellisjte
Auto correct got me!

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Jason,

When your generator is running and you put a load on it, for example an air conditioner, does the generator sense the load and increase RPM's?  If not, you may have an issue with the demand controller. 

Blake

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The more I think about it my money is on the generator control board at this point.  

I'm pretty sure the grounding issues fried the board on the norcold fridge which caused intermittent issues. Seems logical I could be looking at a similar situation here.  Luckily my Dad has some good equipment (and expertise) I can borrow to diagnose this thing before I start buying parts.  I'll post an update when I can get time to grab Pops equipment and look at it again, might be a week or two.

Thanks for all the input!

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1 hour ago, ellisjte said:

When I put a load on it I hear the pitch change on the genny.  Not 100% sure it's faster.  I'll listen closer next time I'm at the RV.

A Frequency meter should offer some helpful information.

Rich.

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19 minutes ago, blakeloke said:

Ah....sounds good Jason....please let us know what you find.

Now I'm trying to figure out what you're shooting in the pic of you!

Blake

Hah, yeah that's my desert eagle!  It's a lot like a sports car.  Useless for most practical applications, expensive to operate, but it looks good and lots of fun!  Here's a better pic ?

IMG_7442.jpg

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Probably the Generator at this stage of the game.:rolleyes: Unless this is an inverter generator, the rpm should not change, but yes more fuel is required to keep at the same speed, therefore the governor does call up more fuel which will make a definite change in the sound. As Rich said a frequency counter would be helpful in determining that it remains at sixty cycles.

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Blake, my guess would be a 9mm or a .45, at a shooting range!  Military, Cop, Instructor or civilian personal carry permit...:D

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