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Audit Question

December 20, 2013, 07:39:06 pm

While driving we have the generator running with the  front furnace going. We've had the back furnace running to at times and the overhead heat strip at one time. I dont know what affects the VDC nor do I understand it....however, ive noticed that while sitting still it is pretty consistantly 13 or 12.9

When we were driving it was mostly 12.5/6 but did get as low as 12.3
At what point would I need to be concerned?

What makes it drop &  raise?

Will have my wife checking these 2 posts I just made as I want to get back on the road....just REALLY dont want to experience a set back.

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Re: Audit Question

Reply #1 – December 20, 2013, 07:44:48 pm

I would get a second reading, from a known accurate voltmeter or DVM connected directly to the battery terminals. Those numbers are low.

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Re: Audit Question

Reply #2 – December 20, 2013, 08:33:34 pm

I normally don't rely on voltage readings from the Audit monitor. I've not found that they correlate well to other readings. I use the dash gauge and a couple of digital gauges plugged to the 12VDC outlets in the dash. One of the outlets is wired to the house batteries and one is wired to the chassis batteries.

With headlights on, the values measured "in the cockpit" are always lower than with the headlights off. That is a function of voltage drop in the wiring rather than a drop in the voltage at the battery terminals. The readings for water temperature, oil pressure, and voltage all change a bit when I turn on the headlights.

As Lang suggests, check values AT THE BATTERIES with a reliable meter. Compare them with readings in the cockpit. Make the comparisons with lights, fans, heaters, etc., running as they would be on the road. Values will vary depending on what is turned on or off. Find out what are "normal" readings for your coach. Don't worry unless readings are outside the "normal" values for the current conditions.

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Re: Audit Question

Reply #3 – December 20, 2013, 09:01:53 pm

Carl, you don't need to run the generator in order to run the furnaces. You will need the generator to run the heat strip. Many times we have traveled all day in temperatures from 0-32F using the furnaces without running the generator. The charging system on the "big engine" is adequate to supply electricity for both furnaces.

On most coaches, the rear furnace supplies some heat to the basement. If you are traveling in temperatures below 32F, I recommend that you turn on the rear furnace in order to provide some heat for the basement.

The voltage readings in the cockpit area will go up and down depending on electric loads on the 12VDC systems. With more stuff running, e.g., dash heat fan, furnaces, headlights, the voltages will be lower than when those devices are not running.

Per my previous post, you'll need to see what is "normal" for your coach. If you notice lights getting unusually dim or gauges showing unusual values, suspect a problem. If the alternator on the "big engine" should fail, voltages will drop quickly. You will see big changes in lighting and gauges. You will see small changes as lights and appliances turn on and off. Don't worry about the small changes.

Watch for "normal." Try not to worry. Stay safe. People are eager to help.

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Re: Audit Question

Reply #4 – December 20, 2013, 09:11:53 pm

When I don't have a working generator this badly rub to the point I'm afraid to drive.  These why I run the generator - that's just been my experience.  I'll have to find my " normal".

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Re: Audit Question

Reply #5 – December 20, 2013, 09:13:50 pm

D'oh! Based on your recent post regarding a possible failure of the "new" alternator, you obviously know how to look for serious drops in chassis voltage. You also know how to use the generator and Boost switch to work around the alternator problem.

You may want to take advantage of emergency road service (if you have it) when you are near a good sized city and get some professional help.

Best wishes for a successful resolution and successful trip.

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Re: Audit Question

Reply #6 – December 20, 2013, 09:18:18 pm

I have posted on your other post on the isolator and left my phone number.

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Reply #7 – December 20, 2013, 09:38:25 pm

Yes Ron - I'll give you a call in the morning - Thanks buddy!

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Re: Audit Question

Reply #8 – December 20, 2013, 09:52:29 pm

Carl There is only one thing I can think might cause both problems. Loose belts. That CAT has about 4 pairs to run various functions.  The bottom pair off the crank shaft run every thing. When you were on wet roads , those could be slipping . When you turn on the lights, there is an added load to the system. Also, it is normal for the audit system to show lower voltage when running at night, with heater fans, and other loads on the dash circuit. If you are running your generator, run with your boost switch on. It will put less load on the battery isolator and you may see a slight increase in audit voltage. First chance, check belt tension. Especially the lower set. Hope this helps.

Gary O

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Re: Audit Question

Reply #9 – December 21, 2013, 01:45:41 am

I often worry that my belts are to tight although id rather have them to tight than to loose. If you can, discribe what I might physically expect to feell or notice about a properly tightened belt.

Thanks in advsnce

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Re: Audit Question

Reply #10 – December 21, 2013, 09:19:38 am

Anything more than 1/2" is too much.

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Re: Audit Question

Reply #11 – December 21, 2013, 10:44:51 am

That's deflection at center span.

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