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Old 04-21-2016, 09:56 AM   #21
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Originally Posted by TouringDan View Post
I don't see a problem here. Any time you put a load on a battery you will get a voltage drop. The bigger the load, the higher the voltage drop.

Dan
Good point Dan.

The voltage read under load is not indicative of battery charge level, at least not accurately. To test the batteries, run the load for a specific amount of time related to the specified capacity of the batteries and then take the load off. An hour or so later, measure the voltage and compare it to a state of charge chart. This test will tell you if there is a battery capacity problem.

That said, I don't know what a good number for the internal resistance of a battery is. His is exhibiting (12.9-11.5)/17 or about 0.08 ohms. Maybe someone else has that data.

Al
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Old 04-21-2016, 11:34 AM   #22
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Voltage Drop when Fridge on DC

I would not think that a bank of 4 6 volt batteries would drop 1.4 volts with only a 17 amp load. I can see .5 volt drop but 1.4 seems like too much.
Are the readings being taken at the battery posts?
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Old 04-21-2016, 12:05 PM   #23
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Originally Posted by TG Twinkie View Post
Again; bad battery(s) or bad connection.
Have you checked the ground/common connection at the point where it connects to the frame or skin.
Yup, checked the ground connection and seems to be just fine. Bolted directly to the frame.

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Do the lights ever dim or flicker?
They don't flicker, but they will dim if I turn everything on at the same time.

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Originally Posted by TG Twinkie View Post
I would not think that a bank of 4 6 volt batteries would drop 1.4 volts with only a 17 amp load. I can see .5 volt drop but 1.4 seems like too much. Are the readings being taken at the battery posts?
The "seems like too much" is how I felt too, which is why I started this thread, but I'm not sure how to calculate what would be an acceptable drop. My fridge is a Norcold NX841 by the way.

The readings are from the Victron Battery Monitor, which is connected directly to the positive and negative battery posts (via a shunt for the negative).

Maybe a better question is this: has anyone else tried to run their fridge on DC only? If so, what sort of voltage drop are you getting from a cold start? Amp draw? Wattage?
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Old 04-21-2016, 01:50 PM   #24
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Good point Dan.

The voltage read under load is not indicative of battery charge level, at least not accurately. To test the batteries, run the load for a specific amount of time related to the specified capacity of the batteries and then take the load off. An hour or so later, measure the voltage and compare it to a state of charge chart. This test will tell you if there is a battery capacity problem.

That said, I don't know what a good number for the internal resistance of a battery is. His is exhibiting (12.9-11.5)/17 or about 0.08 ohms. Maybe someone else has that data.

Al
I did a little digging.
This reference talks about the use of golf cart batteries in RV's
http://yarchive.net/car/rv/golf_cart_batteries.html

This reference gives a real world measurement of internal resistance.
https://www.solarpaneltalk.com/forum...nal-resistance

Based on the second reference it seems possible that trekkerboy's problem is the batteries. The internal resistance I calculated above is 5 times higher than that measured in the second reference.

Al
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Old 04-26-2016, 07:27 AM   #25
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Quote:
Originally Posted by Al and Missy View Post
I did a little digging.
This reference talks about the use of golf cart batteries in RV's
http://yarchive.net/car/rv/golf_cart_batteries.html

This reference gives a real world measurement of internal resistance.
https://www.solarpaneltalk.com/forum...nal-resistance

Based on the second reference it seems possible that trekkerboy's problem is the batteries. The internal resistance I calculated above is 5 times higher than that measured in the second reference.

Al
Thanks for digging into this for me Al! Just ordered a battery hyrdrometer to determine which battery(ies) are the problem. Thanks again for all your wisdom and help!
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Old 04-26-2016, 08:58 AM   #26
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This should be a very easy troubleshoot.
175 Watts / 12 Volts DC = 14.6 amps (Volts X Amps = Watts).
I would grab my handy dandy multi meter with clamp on DC Amp reading;
(found one on ebay item 222032055360)
This should give a true and realistic Amp reading at the refer (providing adequate voltage is there (V X A = W).
If the voltage is low and the amp reading is relatively OK then go straight to the batteries. Most good battery sales will measure them for you, I just go to my Napa and get the guys to test them.
If the batteries are good then there is a wiring issue. You could try and wire them direct using another set of wires (but safety is always an issue!)
Good luck, 15 Amps X 8 Hours = 120 Amps! this would drain batteries rapidly
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Old 04-27-2016, 12:36 PM   #27
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Originally Posted by prairieschooner View Post
This should be a very easy troubleshoot.
175 Watts / 12 Volts DC = 14.6 amps (Volts X Amps = Watts).
I would grab my handy dandy multi meter with clamp on DC Amp reading;
(found one on ebay item 222032055360)
This should give a true and realistic Amp reading at the refer (providing adequate voltage is there (V X A = W).
If the voltage is low and the amp reading is relatively OK then go straight to the batteries. Most good battery sales will measure them for you, I just go to my Napa and get the guys to test them.
If the batteries are good then there is a wiring issue. You could try and wire them direct using another set of wires (but safety is always an issue!)
Good luck, 15 Amps X 8 Hours = 120 Amps! this would drain batteries rapidly
I got in touch with Thetford (which owns Norcold) and got an answer to this question...

The voltage drop I experienced is normal. Evidently, the 12v power mode of this fridge was only intended to maintain cold temps, not cool the fridge from warm. In my case, I was testing the 12v mode by trying to cool the fridge from the start, not just maintaining the existing cool temps.

So, there you go.
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Old 04-28-2016, 07:58 AM   #28
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Very interesting, Im planning on getting a 12V only or a 12/120v fridge. Possibly from dometic, i will have to investigate the capabilities of 12v only
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