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Low coach voltage

August 19, 2012, 10:02:16 am

I recently purchased a U300 with a 6V92TA. I've driven it on several long road trips and each time I discover new things. I just drove from Nashville to Maine and I noticed my coach voltage gauge fluctuates a lot. At night with the lights on the voltage gets really low, down to about 11 volts I'd say according to the dash gauge which is of unknown accuracy. The lights don't appear to be dim or anything. The air horn solenoid won't work when the voltage is too low. The engine dies at idle after startup when I turn on the auxiliary lights with the headlights. When I'm driving down the highway and turn the auxiliary lights on with the headlights the engine keeps running. No dashboard warning lights come on when the engine dies, so I suspect the DDEC computer shuts down when the voltage gets too low, possibly to prevent overheating from pulling high amperage across an automatic reset circuit breaker or something? I'm just speculating on all these things according to my very unscientific observations... so I'm wondering if my voltage regulator is messed up? The alternator did have loose belts, which I replaced and tightened a few times because they keep loosening. I kept the old belts as spares because there doesn't appear to be anything wrong with them and the new belts need to be tightened often too. I make it a standard practice to check the alternator belts before I start it up now, along with checking the oil, coolant, tire air pressure, and other usual stuff. I noticed a lot of posts on here about alternators and voltage regulators. I have an Hehr Powerline with a sticker on the side that says S.G.S. The wires are all tight and they show signs of corrosion or melting or anything unusual.

Scott

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Re: Low coach voltage

Reply #1 – August 19, 2012, 11:40:39 am

Scott,

The meter on the dash indicates the starting battery voltage but not at the battery but at the end of a long wiring harness with all its attendant voltage losses. If it shows 12vdc then the voltage is probably higher at the battery itself. You can correlate this with a digital voltmeter... just start the engine, turn on all the lights, note the indication on the dash meter and then go back and measure right at the battery terminals themselves.

Craig

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Re: Low coach voltage

Reply #2 – August 19, 2012, 08:14:31 pm

Do you think the DDEC computer is on an automatic reset circuit breaker? Do you think low voltage would cause high amperage and trip the breaker causing the computer and engine to shut down when I turn on the auxiliary lights? Maybe I should call Stewart & Stevenson or some other Detroit Diesel dealer and ask them this question? I presume they could plug their little hand held computer reader thingy into the DDEC computer and find out why it shut down if it's a circuit breaker that's built into the computer. If it's in the power line running to the computer it will probably only record a power loss though huh?... Here I am speculating again, I probably should call and ask them about it tomorrow... The alternator belts were slightly loose again this time, just enough so I could barely turn the alternator by hand, so I tightened the belts again. Those belts loosen a lot, but I never let them get loose enough that it would affect the voltage... or at least I don't think so

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Re: Low coach voltage

Reply #3 – August 20, 2012, 02:11:28 am

I do not know about your year but i had a 2000 that was on a resetable breaker and it was also the same one for the condenser fan. When I would turn on the dash AC the engine would die... till I replaced that fan.

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