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Old 08-05-2013, 09:08 AM   #1
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Voltage gauge or alternator

So on my last trip the RV was plugged in as we loaded up, fridge on. Unplugged and headed out only to find a typical problem the fridge didn't light on lp. Seems spiders our whatever cause issues even if it sits for a week in between trips.
So rather than stop I just flipped on the inverter and kept the fridge on AC. About an hour later I notice my alt gauge is reading only 11.5v rather than the typical 13.8. (this is est cause its not a digital gauge)
So I start to worry that my alternator isn't working. So I started the Genny to charge up batteries so I could reach my destination. The next day I started the engine to check it out and it was back to 13.8v.

So question is: does the gauge read alternator output or actual battery voltage? Seems as its battery voltage to me.
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Old 08-05-2013, 09:14 AM   #2
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Dash gauges read alt output. Most likley your batteries were low. This can cause the alt output to read low at first and gradually climb back to normal.
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Old 08-05-2013, 09:31 AM   #3
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Quote:
Originally Posted by chief02 View Post
Dash gauges read alt output. Most likley your batteries were low. This can cause the alt output to read low at first and gradually climb back to normal.
Ditto. as for spiders in your propane burners, put a dog flea collar in there.
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Old 08-05-2013, 09:36 AM   #4
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A voltage gauge reads battery voltage and an amp meter reads alternator output. Chances are your fridge used more power than you alternator can output. Therefore, your battery voltage dropped.
Depending on how long your trip is, you could cool the fridge with AC voltage then turn it off till you reach your destination or... you could run your generator to keep it cool. If it were me, I would not run it strictly off my batteries.
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Old 08-05-2013, 09:36 AM   #5
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Were your headlights on at the same time?
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Old 08-05-2013, 10:36 AM   #6
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Your 160 amp alternator should keep up with the frig on ac and headlights as well as dash air. The fridge is on the house batteries and the dash gauge reads the chassis battery. Since your alt fail light is not on I would suspect bad chassis battery or perhaps diode isolator. One less likely choice would be a partially bad alternator. They have multiple diodes that if only one fails then output is reduced.
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Old 08-05-2013, 10:46 AM   #7
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First, if I understand you correctly you are talking about your voltage gauge on the dash so lets get that straight. If the motor is off and the ignition key is on then it reads the voltage of the CHASSIS batteries. If the motor is running then it is reading a combination of the ALTERNATOR output voltage and the CHASSIS batteries. If your batteries are real low then it may not read the full alternator output voltage until the chassis batteries are charged up. When charged up to some good level then you will read the alternator charge voltage which is as you said around 13.8 to 14.2 volts (there abouts). So after you have run the motor for some time and again shut the motor off and turn the key back on you will read the charge level of the chassis batteries which for a full charge should be around 12.7 volts but you really don't know because you are just eyeballing the gauge. It should stay at that level for a period of time but will drop if no charging system activated on the MH while not in use.

Ok so now let's understand that neither the fridge or the inverter run off the CHASSIS batteries. They run off the house batteries. So that dash voltage gauge has nothing to do with the inverter or fridge. Unless you have a selector switch the switch the gauge from one battery system to the other.

It appears that you either have bad chassis batteries and should both make sure your battery cables are clean and tight and have the batteries checked under load.

On a gas operated fridge if you turn off the propane with the fridge or water heater pilot still going it will use up any residual propane left in the lines so when you try and start the fridge after a period of storage it has air in the lines and will not fire off until after several resets and retries. I find it best to light the gas stove and get the propane flowing before lighting the fridge after a storage period. It clears the air out of the lines.

See if that helps understanding what is probably going on. It would help to use an accurate voltmeter across the chassis battery terminals and read the correct voltage and see how that matches what you are eyeballing on the gauge. Do it with the motor off and with the motor running. Let us know what you find out.
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Old 08-05-2013, 11:05 AM   #8
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Thanks mike and everyone else. Yes I was referring to the volt gauge on the dash and my batteries seem to be fine. I may have compounded the issue with running a ground wire between the house batteries and chassis batteries.
Reason for that was I was having an issue with grounding and in an attempt to resolve that issue added a common ground but did not connect the positives of the chassis and house batteries.
I plan to remove that wire as it did not resolve my ground problem.
This chassis is so corroded and I need to climb under it and clean up all the ground connections to the chassis.
After a quick clean of the fridge burner it fired up so for the ride home (3hrs) it ran on lp and without turning the inverter on gauge stayed right around 13.8v and never dropped.
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Old 08-05-2013, 11:16 AM   #9
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The wire you have on the negative sides of the batteries should not make any difference since they are both at the same potential on that negative/ground side. It sounds like the best thing you can do is wash all the battery cables and post with a baking soda solution then remove each cable terminal and wire brush all. It is easier to buy a battery cleaning wire brush to get inside the cable terminals. Yes and take the grounds loose and wire brush all until clean. I believe this is the first thing to do before anything else. Normally this is the problem when you have battery and charging problems
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Old 08-05-2013, 11:35 AM   #10
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Yea all the terminals on the batteries are clean as I remove them from the chassis during the winter to keep in the garage with a trickle charger on them.
My problem seems to be with the grounds to the chassis. Back in June the engine would not start and gave the typical symptoms of a dead batt (clicking but not turning over). Threw jumper cables on and saw no improvement. Everyone said starter was shot but after a thorough removal and cleaning of the cable ground to the starter everything was fine and it fired right up.
Think I still have some ground issues tho as my fuel gage works sporadically. But no other issues.
I was just really confused why my volt gauge would read so low as like you mentioned the inverter should run off house batteries. Just didn't make sense to me.
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Old 08-05-2013, 01:46 PM   #11
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Mike, great observation! I thought the alt charged both the house and chassis batteries. I guess I never checked.

Rob, when I run with my headlights on, my volt gauge reads just above 12 volts. If I adjust the brightness of the dash lights, the gauge will move slightly. However, when I use a multimeter and check voltage at the battery or on my "house" electrical panel, I show 13.5 - 14.2 volts depending on the state of the batteries. I'm not sure if this is what Jim Hitek was leading to, but I believe it to be a ground issue with my dash gauge causing my voltmeter to read incorrectly. So I'm wondering what voltage was really at your batteries when your gauge was reading low? Maybe if the voltage shows low again, you can check the voltage at the batteries to make sure the gauge in the dash is working correctly. Just a thought....
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Old 08-05-2013, 07:34 PM   #12
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Ron, yes on most motorhomes the alt will charge the house batteries also but because of a battery isolator the voltage gauge will only read the chassis battery/alt output voltage. I have also found that most volt meters on the dash read low because of the voltage drop in the length of wire from one of the mh to the other
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Old 08-05-2013, 08:25 PM   #13
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When your engine is running your alternator charges your chassis batteries. If you have a BIRD or IRD then the solenoid closes and all batteries are connected. If your batteries are good then your voltage should come back up in awhile.
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Old 08-06-2013, 05:25 PM   #14
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The fridge pulls 300-400 watts on A/C (Kind of hungry) and this translats to around 30-40 amps by the time you factor in inverter loss.. more when you factor in line loss in the wires from the alt to the battery.... The alternator is clearly NOT up to providing this kind of power.

By compairison,, Headlights are 30-50 watts.. So the fridge is like a dozen headlights.
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