Generator blowing fuses

[MichDoc]

Okay, I'm not very experienced with generators since this is my first one, but I have an Onan 4000 watt Microquiet, mounted in my Class C. It's about 8 years old now. I don't use it often, so I fire it up once a month for an hour or so, and run my A/C to exercise it.
I had a problem where it got progressively harder to start. It would crank, but not start, and finally wouldn't crank, so I took it to an RV place near where we were staying in Texas. They found a bad ground wire and replaced that, along with the fuse block just before (or after) the battery. It worked great until I got it home to Michigan where I started blowing fuses. The fuse block is an ANL, with a 125 amp fuse, and it lets me try starting two or three times before it blows. I prime for about 45 seconds, crank for 5 seconds, and then wait for two minutes before I prime for about fifteen seconds more, and crank again. The third time, the starter sounds very slow like the battery is getting weak, and then the fuse blows, cutting off all of my 12 volt power. After replacing the fuse, I can usually try once or twice more and then get it started. I don't know if they put in a fuse that is too small (125 amps) because I don't know what was in it before they replaced the fuse and holder, and I can't tell the wire size to check because only about 2" of cable is exposed, and I can't see any wire size markings on it.
Any thoughts? By the way, I'm not much of a mechanic, and definitely not an electrician, but figured I'd check here for any obvious thing that you might suggest that I look for, or do, before taking it in to a dealership.
Thanks for any help.

[MichDoc]

Dutch_12078 wrote:
My Onan Marquis 7kw was blowing ANL 145 amp fuses when I bought the coach. The fuse blew almost instantly when the start switch was pressed. The fix was a new starter motor.

Thanks for the info. It seems like several people are suspecting the starter, so I guess that's where I'll have to begin. I just wonder why it takes several attempts before my fuse blows. Your situation sounds more of what I would typically expect from a bad starter.

[Dutch_12078]

My Onan Marquis 7kw was blowing ANL 145 amp fuses when I bought the coach. The fuse blew almost instantly when the start switch was pressed. The fix was a new starter motor.

[MichDoc]

The connections all seem okay, but I'll check them again. However, it would seem to me that if there was a short, the fuse would blow the first time I tried starting the generator, rather than waiting.
I'll also check into a new starter if I can't find anything else wrong.
I appreciate all the suggestions, because I'm kinda at a loss right now.

[TEXAS]

Could be that you have a shorted battery. If you are blowing a 125 amp fuse. You have a major problem. Have you checked all your DC connections.

[gatorcq]

Sounds like this is the fuse for the starter, which you mention after third time starter sound weak. Possible it is a bad starter.

[MichDoc]

TEXAS wrote:
I hope you ment 12.5 fuse. 125Amps for a DC control fuse is a bit much. Which shop did you go to here in Texas. Sounds to me that you have a bad starter. Very common problem on the KY units. The bendix falls apart jamming up the starter. Not hard to change,just a pain to get to.You have to remove it from the RV. Then remove the cover. To get to the starter.

No, it's really a 125 amp. It's in line with the main battery cable, so it's not just for the generator, it apparently protects the battery and associated cables. This is the one that's blowing. The starter seems okay (to me, at least), and cranks very smoothly until it blows the fuse. When I try to start it the third time, it sounds like the battery is low, and I'm wondering if that would cause the generator starter to try and draw more power for starting. This last time I plugged into shore power for about an hour, after which the generator started. I don't know if it was because there was now more power available in the battery, or if it had enough of a prime to start.

[TEXAS]

I hope you ment 12.5 fuse. 125Amps for a DC control fuse is a bit much. Which shop did you go to here in Texas. Sounds to me that you have a bad starter. Very common problem on the KY units. The bendix falls apart jamming up the starter. Not hard to change,just a pain to get to.You have to remove it from the RV. Then remove the cover. To get to the starter.

[MichDoc]

Thanks pianotuna. I've decided to find someone (more flexible than me!) to try and crawl under there and see if they can locate the wire to determine its size. The circuit breaker is a good idea, especially since I've probably already invested more in fuses than the circuit breaker would cost.
I'm still wondering why its always popping the fuse though.
Thanks again for the response.

[pianotuna]

Hi,

Try to find out the size of the wire. Then replace that blowing fuse with an appropriately sized DC circuit breaker.