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04-16-2016, 06:20 AM
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#1
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4 Rivet Member
1979 31' Excella 500
Charlevoix
, Michigan
Join Date: Aug 2014
Posts: 350
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Voltage Drop when Fridge on DC
We have a brand new Norcold NX841 3-way refrigerator in our AS and I was experimenting with running it purely off of DC. When I switched it over to just DC I noticed that the battery monitor went from 12.8v down to 11.2 right away (also noted fridge was drawing 15 amps and about 175 watts). I have 4 x 6v batteries ( Duracell EGC2 golf cart batteries) wired in series parallel (460 amp-hours capacity), and 6 gauge wire running about 10 feet from the battery to the refrigerator.
My question: is it normal for the battery bank voltage to drop that much under a big load (like refrigerator)? If so, what's the physics behind this behavior?
At any rate, the refrigerator flashes a "DC LO" message and won't function on DC alone due to low voltage, hence my question.
Thanks for any input!
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04-16-2016, 07:26 AM
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#2
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Rivet Master
1974 Argosy 26
Morrill
, Nebraska
Join Date: Nov 2009
Posts: 6,014
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Voltage Drop when Fridge on DC
I would check all of the connections. Sounds like you have a serious voltage drop.
Where is the monitor connected in the system?
Does the reading go back to 12.8 volts when you switch to propane?
11.2 volts is a dead battery in my book. But again it could be a bad connection.
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04-16-2016, 07:33 AM
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#3
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Rivet Master
1966 22' Safari
Hilltop Lakes
, Texas
Join Date: Jun 2008
Posts: 1,764
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Unless there is indeed a bad connection, which increases the resistance in the circuit, Ohm's Law says your voltage drop is normal. Gas absorption fridges running on DC draw a heck of a lot of current.
I think that DC fridge function is intended for when you're on the road with the TV's alternator supporting the current draw of the fridge. Even then, make sure it doesn't overload your alternator.
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04-16-2016, 12:15 PM
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#4
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Rivet Master
1974 Argosy 26
Morrill
, Nebraska
Join Date: Nov 2009
Posts: 6,014
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If you lose 1.6 volts. 11.2 down from 12.8 drawing only 175 watts. It's a bad connection or bad battery(s). Or perhaps the battery bank is not wired correctly and you don't have the full 4 battery capacity you think you have.
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04-16-2016, 12:31 PM
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#5
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Rivet Master
1991 34' Excella
Princeton
, New Jersey
Join Date: Aug 2003
Posts: 7,070
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Check the batteries with a hygrometer. You may have a bad cell.
__________________
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles
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04-16-2016, 12:56 PM
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#6
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4 Rivet Member
1979 31' Excella 500
Charlevoix
, Michigan
Join Date: Aug 2014
Posts: 350
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Quote:
Originally Posted by TG Twinkie
I would check all of the connections. Sounds like you have a serious voltage drop.
Where is the monitor connected in the system?
Does the reading go back to 12.8 volts when you switch to propane?
11.2 volts is a dead battery in my book. But again it could be a bad connection.
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Yup, goes back to 12.8 when the fridge isn't using DC.
Battery Monitor is connected to positive terminal of the battery bank and a shunt which is connected to the negative terminal of the battery bank.
Haven't found any bad connections...
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04-16-2016, 03:09 PM
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#7
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Rivet Master
2002 30' Classic S/O
Fleming Island
, Florida
Join Date: Nov 2013
Posts: 4,667
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Quote:
Originally Posted by trekerboy
Yup, goes back to 12.8 when the fridge isn't using DC.
Battery Monitor is connected to positive terminal of the battery bank and a shunt which is connected to the negative terminal of the battery bank.
Haven't found any bad connections...
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Measure the voltage between the plus and minus battery terminals. Sounds like you are getting too much drop across the shunt, or the shunt is wired wrong.
I think there should be two wires connected to the shunt, one on each side. The monitor should be measuring voltage between the positive and negative posts and calculating current from the shunt resistance and the voltage across it.
Al
__________________
“You cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO WBCCI 1322
2002 Classic 30 Slideout -S/OS #004
2013 Dodge 2500 Laramie 4x4 Megacab Cummins
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04-16-2016, 03:22 PM
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#8
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Rivet Master
1974 Argosy 20
2014 20' Flying Cloud
Kooskia
, Idaho
Join Date: Jul 2009
Posts: 4,591
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Was the original refrigerator a 3 way one, that is could it operate on 120 volts, 12 volts, or propane? 12 volt operation of absorption refrigerators takes a lot of power, 15 or more amps as you have noted.
I suspect your original refrigerator only used 12 volts for powering the electronics or even just the light in the refrigerator, and thus has only very small wires running to it, and they are not designed for the 15 + amp load you have put on them.
12 volt operation of the cooling portion of a refrigerator is a huge load on the trailer system, and will kill any battery quickly in any event. It has primarily been used in motorhomes where there is an engine driven alternator system to keep power to the refrigerator coming, without relying on the batteries. The system in my 1983 AS 310 had a 3 way refrigerator system, but had about #10 or #12 wires to the refrigerator, not the little ones typically found on trailer installations.
But, as noted in posts above it could be a poor connection, however, I think you are just overloading the wires that are already in place.
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04-16-2016, 06:12 PM
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#9
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4 Rivet Member
1979 31' Excella 500
Charlevoix
, Michigan
Join Date: Aug 2014
Posts: 350
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Quote:
Originally Posted by Al and Missy
Measure the voltage between the plus and minus battery terminals. Sounds like you are getting too much drop across the shunt, or the shunt is wired wrong.
I think there should be two wires connected to the shunt, one on each side. The monitor should be measuring voltage between the positive and negative posts and calculating current from the shunt resistance and the voltage across it.
Al
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Voltage at the positive and negative terminals of the battery bank read the same as they do from the battery monitor.
Yes, there are two wires connected to the shunt (Victron Energy Battery Monitor system by the way), well technically 3:
1. Incoming negative bus wire
2. Outgoing negative bus wire (to negative terminal on battery bank)
3. Comm wire (to battery monitor display)
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04-16-2016, 06:17 PM
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#10
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4 Rivet Member
1979 31' Excella 500
Charlevoix
, Michigan
Join Date: Aug 2014
Posts: 350
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Quote:
Originally Posted by idroba
Was the original refrigerator a 3 way one, that is could it operate on 120 volts, 12 volts, or propane? 12 volt operation of absorption refrigerators takes a lot of power, 15 or more amps as you have noted.
I suspect your original refrigerator only used 12 volts for powering the electronics or even just the light in the refrigerator, and thus has only very small wires running to it, and they are not designed for the 15 + amp load you have put on them.
12 volt operation of the cooling portion of a refrigerator is a huge load on the trailer system, and will kill any battery quickly in any event. It has primarily been used in motorhomes where there is an engine driven alternator system to keep power to the refrigerator coming, without relying on the batteries. The system in my 1983 AS 310 had a 3 way refrigerator system, but had about #10 or #12 wires to the refrigerator, not the little ones typically found on trailer installations.
But, as noted in posts above it could be a poor connection, however, I think you are just overloading the wires that are already in place.
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The original fridge was also a 3 way unit, yes.
My AS is a complete renovation; I ran 6 gauge wire from the 12v panel to the fridge knowing that it'd suck a lot of juice.
I'm wondering if it's not something with one of batteries in the 4 x 6v bank... Even with just one fantastic fan on and 1 phone plugged in to charger, the voltage drops from 12.8 to 12.26 at full charge... Seems like the bank should be able to sustain these small things without that much drop, right?
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04-16-2016, 06:36 PM
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#11
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Rivet Master
1974 Argosy 20
2014 20' Flying Cloud
Kooskia
, Idaho
Join Date: Jul 2009
Posts: 4,591
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Quote:
Originally Posted by trekerboy
The original fridge was also a 3 way unit, yes.
My AS is a complete renovation; I ran 6 gauge wire from the 12v panel to the fridge knowing that it'd suck a lot of juice.
I'm wondering if it's not something with one of batteries in the 4 x 6v bank... Even with just one fantastic fan on and 1 phone plugged in to charger, the voltage drops from 12.8 to 12.26 at full charge... Seems like the bank should be able to sustain these small things without that much drop, right?
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OK, you do understand the power requirements of the 12 volt part of the refrigerator, and had one in the original installation.
So, it does now sound like the batteries are not doing what they should. I would measure each 6 volt battery under a load, and see how close they are to each other. Most likely you will find one of the batteries in each pair to have a lower voltage across it, compared to the other. Possibly you will only find one of the four with a lower voltage, and it is dragging on the other set. Measure the voltage at the battery terminals, not someplace else in the system.
How old are the batteries, and what charging system have you been using to keep them up during the renovations?
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04-16-2016, 07:26 PM
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#12
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4 Rivet Member
2006 25' Safari
Signal Mountain
, Tennessee
Join Date: Jan 2016
Posts: 450
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Quote:
Originally Posted by trekerboy
Voltage at the positive and negative terminals of the battery bank read the same as they do from the battery monitor.
Yes, there are two wires connected to the shunt (Victron Energy Battery Monitor system by the way), well technically 3:
1. Incoming negative bus wire
2. Outgoing negative bus wire (to negative terminal on battery bank)
3. Comm wire (to battery monitor display)
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I think there should be another small gauge red wire connected to the positive battery terminal to power the monitor. At least mine has it.
__________________
Don
'06 Safari 25 LS
'18 GMC 2500HD Duramax/Allison
TN,”Greenest State in the Land of the Free”.Davy Crocket
" America is not a place;it's a road." Mark Twain
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04-16-2016, 07:34 PM
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#13
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4 Rivet Member
1979 31' Excella 500
Charlevoix
, Michigan
Join Date: Aug 2014
Posts: 350
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Quote:
Originally Posted by Tn Traveler
I think there should be another small gauge red wire connected to the positive battery terminal to power the monitor. At least mine has it.
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Doh! You're right, there is. So 4 wires total connected to the shunt.
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04-16-2016, 07:38 PM
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#14
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4 Rivet Member
1979 31' Excella 500
Charlevoix
, Michigan
Join Date: Aug 2014
Posts: 350
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Quote:
Originally Posted by idroba
OK, you do understand the power requirements of the 12 volt part of the refrigerator, and had one in the original installation.
So, it does now sound like the batteries are not doing what they should. I would measure each 6 volt battery under a load, and see how close they are to each other. Most likely you will find one of the batteries in each pair to have a lower voltage across it, compared to the other. Possibly you will only find one of the four with a lower voltage, and it is dragging on the other set. Measure the voltage at the battery terminals, not someplace else in the system.
How old are the batteries, and what charging system have you been using to keep them up during the renovations?
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Batteries are almost 2 years old. Been using the integrated charger/inverter/transfer-switch combo unit (AIMS Power PICOGLF20W12V120VR 2000W Pure Sine Inverter Charger) to keep batteries topped up.
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04-17-2016, 09:44 PM
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#15
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Rivet Master
1966 24' Tradewind
1995 34' Excella
Lynchburg
, Virginia
Join Date: Jun 2006
Posts: 4,225
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If you are using 175 watts when operating your fridge on 12v, this sounds like the power requirement of operating the fridge heating element. When on 12v the heating should be by propane and not electricity. 12v should only be used for fridge control electronics. Heating of the chimney should be electrical when plugged into 120v or by propane when 120v is not available.
Dan
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04-17-2016, 10:04 PM
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#16
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Rivet Master
1974 Argosy 26
Morrill
, Nebraska
Join Date: Nov 2009
Posts: 6,014
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Voltage Drop when Fridge on DC
I believe they call it a 3 way because it can cool with propane, 120 volt AC or 12 volt DC.
175 watts on 12 volts is almost 15 amps. Probably more when you figure in the losses. If the element were powered continuously it would reduce a battery's capacity in short order.
It would be relatively easy to duplicate the load of the refer by turning the refer off or putting it in another mode.
The start the furnace, the water pump ceiling fan; stove exhaust fan and every 12 volt light in the coach. Furnace= 6-8 amps; water pump 3-4 amps; fans combined 4-6 amps.
Try this to see if you get a similar voltage drop.
I still say it is a bad connection or battery or something is not wired correctly. The #6 wire you are using should be more than adequate to power the refer.
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04-20-2016, 09:23 PM
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#17
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4 Rivet Member
1979 31' Excella 500
Charlevoix
, Michigan
Join Date: Aug 2014
Posts: 350
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The results are in
Quote:
Originally Posted by TG Twinkie
I believe they call it a 3 way because it can cool with propane, 120 volt AC or 12 volt DC.
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That's correct, this fridge can cool using either 120v, propane or 12v as a power source.
Quote:
Originally Posted by TG Twinkie
It would be relatively easy to duplicate the load of the refer by turning the refer off or putting it in another mode. Start the furnace, the water pump, ceiling fan, stove exhaust fan and every 12 volt light in the coach. Furnace= 6-8 amps; water pump 3-4 amps; fans combined 4-6 amps. Try this to see if you get a similar voltage drop.
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Ok, started with 12.9 volts then had 3 ceiling fans, 1 hood vent exhaust, 1 bathroom ceiling exhaust, 14 LED lights, 2 USB wall chargers all going at the same time: 194 watts, 17 amps (fridge only was 175 watts, 15 amps). Voltage dropped to 11.5v (lights dimmed a little, you could hear the pitch of the fans change).
So, in summary, to answer your question, I think this qualifies as a similar voltage drop to the fridge. Does this point to culprit? I guess this means it's not a problem specific to the fridge or its' wiring per se...
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04-21-2016, 07:36 AM
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#18
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Rivet Master
1974 Argosy 26
Morrill
, Nebraska
Join Date: Nov 2009
Posts: 6,014
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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.
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04-21-2016, 09:10 AM
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#19
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3 Rivet Member
1979 31' Excella 500
Florida
, Florida
Join Date: Jul 2014
Posts: 119
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Do the lights ever dim or flicker?
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04-21-2016, 09:26 AM
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#20
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Rivet Master
1966 24' Tradewind
1995 34' Excella
Lynchburg
, Virginia
Join Date: Jun 2006
Posts: 4,225
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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
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