Rigmaster APU problems

The Enemy · Dec 15, 2013

Hey folks, we have a 2007 Sterling with a 960 Bentz sleeper. The truck is equipped with a RigMaster APU and a Magnum industries power inverter. This morning we woke up to the inverter alarm going off and the display read "Battery Charging Failure". The APU shut itself off. After removing the inspection cover i noticed that the belt that drives the alternator was stretched and partially shredded. I replaced the belt and the APU fired up and ran fine for about 4 hours. After those 4 hours the charging failure message apeared again and the unit shut itself off. I checked the belt and its fine.

While the APU was working for those 4 hours the Magnun inverter display always said inverting, never charging, and the volts were between 12.6-12.1.

Anyone have any ideas as to what would be causing these problems? Any help would be appreciated as no working APU means no heat, wich means we have to idle the truck, which i hate doing.

zorry · Dec 15, 2013

Did you check to see if the alt pulley was spinning while you had the belt off ?

The Enemy · Dec 15, 2013

Yes, the pulley did spin when the belt was off.

golfournut · Dec 15, 2013

The Enemy said:
Yes, the pulley did spin when the belt was off.

Nick, do you have a plastic or metal antifreeze reservoir bottle?

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zorry · Dec 15, 2013

I believe the manuals are on line at the Rigmaster website.

golfournut · Dec 15, 2013

If you have the plastic reservoir bottle, check the lid to make sure it is not cracked. If cracked, after running for a while the cooling system sucks air. Also check that the little hole on top of the cap is not clogged. Becareful, do not enlarge that hole. Also might check the cover safety switch. Sometimes the rubber bands that hold them on get enough elasticity in them to trip the switch from vibration. One other place to check is the generator belt. To do that, you need to remove the rear housing. I think 4 or 5 screws. There are 2 adjusting bolts for that to keep it tight and aligned to the belt. Make sure that pully spins freely.

I had the same issue in mine when I had it. At one time or another, each of the 3 above was the culprit.

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zorry · Dec 15, 2013

My cover switch was such a pain I by-passed it. If the same switch I had, you can put a zip tie to keep it tripped.

This wouldn't be the problem today if it continued running without charging.

golfournut · Dec 15, 2013

Yep did that. Got tired of messing with that switch.

The plastic cap issue was the hardest to figure out. Wasn't losing antifreeze. After 3 or 4 hours of run time it would shut down. I forget the error code that came up. Replaced the radiator, hoses and clamps. Could not figure out how air was getting in there to cause a vapor lock. One day I took the cap off for something and it broke in half. Replaced the cap and never had that issue again.

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zorry · Dec 15, 2013

If I had one I'd upgrade to the metal tank.
They used a Chinese AC compressor the year they were going broke.
The new owner addressed the plastic overflow tank, went back to the high quality AC comp, improved belt and muffler issues.

The Enemy · Dec 15, 2013

All the belts are good, since i replaced the frayed one to the alternator. The safety switch is zip tied/bypassed. It has the metal cooling tank.

The error is a Charging Battery Fault, wich leads me to beleive there is eith a short in the Alt or a short in the speed sensor. But seeing as the Apu will run, i think i can possibly rule out the speed sensor. So i think it might be the ALT.

zorry · Dec 15, 2013

Thinking Alt. might poke around and find bad wire or a fuse.
Best hope of having heat tonight.
Unless 12 volt alt is out but you have 110.
Small electric heater will get you through til you get problem fixed.

highway star · Dec 15, 2013

Sounds like the alternator to me.

zorry · Dec 15, 2013

Would there be two wires from unit to battery box ?
One to starter, another to the charging circuit.
If you have 110, another option, though not as convenient, would be a small battery charger.

usafk9 · Dec 15, 2013

Large cable from battery to inverter, large fuse inline between, that should be in a plastic shroud screwed into the underside of your sleeper. That fuse has copper ends and the connections are not well protected.

Cup of coffee says those ends are corroded.

Remove cable from battery, remove fuse, wire brush all cable and fuse ends, re-attach.

Let us know how it comes out, please.

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highway star · Dec 15, 2013

Based on the damaged belt, I'm sticking with the alternator.

zorry · Dec 15, 2013

With Alt freewheeling, belt could just been worn out, and issue not addressed until another problem surfaced.

I wouldn't go to a shop and say replace alt.
I'd say correct my problem.
AJ may be onto something.

I know my rigmaster shook enough to loosen a wire now and then.

highway star · Dec 15, 2013

zorry said:
I wouldn't go to a shop and say replace alt.
I'd say correct my problem.

That's what I'd do. I'm over 19,000 hours on mine and I've had very, very little in the way of wiring kind of problems. I've had 1 blown fuse that kept the A/C compressor from kicking in, and I had to ground the safety shut off switch when it started randomly shutting the unit down. It's usually stuff breaking.