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Old 09-17-2012, 01:25 PM   #1
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Monitor Panel readings vs. voltage meter readings

I go out to the RV the night before we go campiing to start the refer. The Monitor panel shows the battery at "full" charge. When I return the next morning the Monitor panel shows the battery at "0" charge. But when I place a voltage meter on the battery posts it reads 12 volts.....what is happening? Thanks!!!
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Old 09-17-2012, 02:01 PM   #2
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This chart should help, 12.0 is pretty low. 12.6 is the lowest you probably want to go.

http://www.marxrv.com/12volt/voltchart1.gif
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Old 09-17-2012, 02:27 PM   #3
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Without more information I see this scenario. Also, Read your Voltage in Tenths of a volt (12._)

1. The 120volt cord to the motor home is not plugged in and the refrigerator is operating on 12v continuously all night trying to cool the refrigerator and freezer compartment and that uses up your battery charge.

2. The 120V cord is plugged in but your 120V to 12V converter is not operating.

3. The LP Gas supply wasn't turned on for the refrigerator.
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Old 09-18-2012, 08:03 AM   #4
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THANKS!!
When I do this I am not on Shore power. The refer and freezer work fine. So, I guess my question now is..."is it normal for the refer to use a "full battery charge" overnight or might I have some other drain on the battery?
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Old 09-18-2012, 11:38 AM   #5
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To save my battery's I operate my refrigerator on LP gas and 120v when available.
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Old 09-19-2012, 08:06 PM   #6
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yeah, 12volt operation of the fridge will run it down quick. use lpg or 120 volts.
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Old 09-19-2012, 08:58 PM   #7
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Battery voltage and state of charge - Energy Matters has a table that might help you see the relationship between what the monitor is telling you - from fully-charged down to no charge (meaning no safe usable charge left) - and what your meter is showing - from around 12.8V when fully charged (measured with no charge or discharge happening and after a "rest" of an hour or two) down to say 11.6V which is essentially dead flat (and actually well on the way to being dead period if you do it too often or don't get it charged back up asap).
At 12V your battery might only have less than 20% charge left in which is way less than the recommended limit of 40 to 50%. This safe limit is derived from the need to get an optimum life out of the batteries. If you never discharge they will last a long time, but of course you get no benefit. If you run them dead flat, you might get 100 cycles out of them but would always need to be replacing them. If you only go down to 50% and recharge properly and promptly, you might get 1000 cycles and somewhere around there will be optimum use per dollar cost.


And no, it isn't normal to flatten the batteries overnight unless you have only a small capacity battery installed, or it wasn't charged up properly in the first place, or it is faulty and won't hold a charge properly, or you left some large loads running overnight.
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Old 09-22-2012, 08:43 AM   #8
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W4MPG, what do you mean, 'lpg"?
to get my refer cold before a trip, i have to turn on the Master Battery switch for the refer to work, right? then i select propane vs. ac. but when i return the next day the refer has "shut down" because the battery has run down. we got a new deep-cell rv battery from a local rv dealer less than a year ago.
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Old 09-22-2012, 07:41 PM   #9
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How are you keeping the battery charged while it is parked.

Need to check that the fridge IS actually running on propane. Is the fridge a 2-way or 3-way unit. If a three-way, it could be reverting to whatever supply is available. If propane not available then perhaps switching to 12V which drags 10 Amps or more and that WILL flatten the battery very fast.

Note - a three-way unit has two 12V supplies - one light one to operate the electronics and a heavier one to operate the heater element.

If it is only a two-way fridge then the electronics can't be using that much power, so either your battery is not being charged properly in the first place (how do you keep it charged when not on shore power) or the battery is faulty and not holding a charge, or you have left a large 12V load switched on somewhere.
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Old 09-23-2012, 06:48 AM   #10
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Tony, thanks!
I go to the RV once a month and crank my vehicle engine and run my generator.
My refer is a two way. when i select "gas", it will shut off a couple of times until the gas can make its way from the tank to the refer. but then the "gas" light stays on...it does not switch to AC until be get to a CG and hook up to shore power...then we manually switch it to AC.

I guess I am gonna have to try to find out if there is a drain on my battery that I am not aware of.
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Old 09-23-2012, 07:08 AM   #11
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Do you have an inverter?? My Mh did the same thing twice. ran down the batteries overnight with just the fridge on. The fridge was selecting 120 volt, pulling it through the inverter to operate. With the inverter off, I never use it, the fridge selects 12 volt and works on gas.
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Old 09-23-2012, 09:10 AM   #12
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Sounds like a good excuse to buy a DC current clamp tester so you can check the various circuits to see what current is flowing.

Trouble is, assuming the batteries are in good condition and assuming they are fully charged (which can take many hours if they are fairly depleted), you need a reasonably high drain to get them down just overnight.

One drain that is often overlooked is the propane detector - if fitted. 100mA is 20 Ah a week, 80Ah a month and if the batteries aren't fully charged to begin with, is enough to make a big difference. Similarly, leaving a big inverter on can also add up, as can some battery chargers that put a load on the battery even though there is no mains connected. Storage compartment or engine bay lights are also another trap
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Old 09-24-2012, 07:14 AM   #13
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Thanks! 2 questions....
1. my inverter is under my bed, enclosed. i have a switch on my monitor panel to turn the inverter on/off. it indicates it is off. could it still be on and draining the battery?
2. my LP monitor comes on when the battery disconnect switch is turned on.....is there a way to turn it off ?
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Old 09-24-2012, 09:43 AM   #14
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Well, sounds like those two are off. Those two standby loads shouldn't add up enough to make a difference. Was just a thought because in some RVs that disconnect switch doesn't disconnect everything - ie on another post was reported the water pump remained on even with the disconnect off.

Sometimes really difficult to sort out these problems - sometimes because battery drain is a sum of several small drains that add up enough to make a difference when the battery is failing, or the monitor is reporting a charged battery when it is not, or ...

If this has only happened once and never happens again, then you might put it down to leaving something running, perhaps an unprimed pump running almost silently for a day or two or whatever.

If it happens again, you will need to do a methodical search to find out why.

One other thing - Rested battery voltage is quite a good indicator of how full or empty the battery is and the normal way is to fully charge the battery and then isolate it for say four hours minimum and then read the battery voltage. Reason I suggest it is your battery meter and a voltmeter would both read high if you had been charging the battery within the last 10 minutes or so and that might be giving you a false indication that the battery was fully charged.
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