17' Series Travelling with fridge on 12v

mikerezny

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Sep 11, 2016
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Mount Waverley, VIC
#61

Boots in Action

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Mar 13, 2017
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#62
Hi @MarkAW,
here is a picture taken from the bottom fridge vent showing the fridge12 V terminal block and the voltmeter I fitted.

You can get the voltmeter on eBay from China for $1.55 including postage. I mounted it in a small plastic case
https://www.ebay.com.au/itm/DC-0-30...hash=item3af9ed6d97:m:mE9kFIUxTbOrYhZ7rx68pJA

cheers
Mike
View attachment 59385
Hi @mikerezny , what a great idea to have a volt meter across the terminals for the fridge. I have just ordered same. What did you use for the neat case and mounting?? Good to have it protected a bit from dust and water spray that might enter. As my tug has a VSR, I usually have to wait a few minutes until voltage comes up, and have been relying on led lights in cigarette lighter connector for fridge in back of tug coming on to let me know battery voltage is available.
 
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mikerezny

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Sep 11, 2016
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#63
Hi @mikerezny , what a great idea to have a volt meter across the terminals for the fridge. I have just ordered same. What did you use for the neat case and mounting?? Good to have it protected a bit from dust and water spray that might enter. As my tug has a VSR, I usually have to wait a few minutes until voltage comes up, and have been relying on led lights in cigarette lighter connector for fridge in back of tug coming on to let me know battery voltage is available.
Hi @Boots in Action,
I got the case on eBay from China for $1.15 including postage from here:

https://www.ebay.com.au/itm/Black-P...osure-Box-/261979602220?var&hash=item0&_uhb=1

From memory, the size was: 65x38x22mm.

cheers
Mike
 

Boots in Action

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Mar 13, 2017
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Ferny Grove, Queensland
#66
@mikerezny @Drover @bigcol
Thanks again guys, got some great info again. Few things to try and hopefully tackle this issue - glad to know im not the only one and its likely not a dud fridge with big $$ attached.
Doing the fan install I planned to have the thermostat and an overriding switch just to be sure
Hi @Geoff83, you already have most of the good info on how to assist absorption fridges work more efficiently in very hot weather. I originally had only an in-line switch for the two 120mm fans I have installed in my van to help cool back of fridge. The bottom one attached to the vent draws in air and the top one sucks the air out. Both are controlled by a thermo switch, but can be over-ridden with an in-line switch - see pictures. I found that a 45C thermo was satisfactory for most occasions so that the fans were only on intermittently and kept the back cool. @Drover gave me the idea was to use broom holder clips from Bunnings 13mm I think and attach thermo to same with a rivet. I decided to use machine screws to hold thermo to clip as it allows me to do thermo changes in the field as was necessary on my last trip. See post " Hare and tortoise Compressor fridge verses 3 way gas absorption fridge". Other ways to imp[rove cooling and have more even temp inside fridge is to install small computer fan to move cool air around. More even temperature distribution and no more frozen lettuce, tomatoes etc. See pictures for some ideas you may want to think about.
Another very important point is to make sure there are no "dead areas" at the back and on top of fridge where hot air will be trapped. These pockets of hot air will not be removed even with fans if they are not blocked off in some way. Also, make sure that hot air coming up from the bottom is directed to go towards and out through the top vent. Plenty of other ideas on this forum. Hope they help you achieve what you want - a cooler running fridge.
 

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Jan 25, 2017
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Point Cook
#67

Boots in Action

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Mar 13, 2017
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Ferny Grove, Queensland
#68
For those that have monitored battery voltage, what is the voltage when under load of the fridge?
I checked mine today and went from 12.85 unloaded to 10.7v loaded
The battery is a new 92ah wet cell deep cycle
Cheers
Hello @MarkAW , it is normal for a battery to drop in voltage when a big load (15A plus??) is placed upon it. But it should still stay above 12 volts if battery has been properly charged - ie has been able to store the charge put into it as in the "absorption" stage. Suggest put battery on charger (preferably "smart charger") and wait until fully charged light has been on for a while (maintain stage, or float), then test again. If voltage quickly drops away to 12 volts or below in just a few minutes, then the battery is faulty. Did you fully charge battery with a charger before this test?? The charging from the alternator on car is unsatisfactory and will never be able to get battery to full storage potential. Just as a motor may start and idle okay, it is when you put it in gear and see if it will pull off without stalling that the real test of what it is capable of becomes evident. Remember, voltage is not a sign of battery strength. Only if the voltage remains high whilst doing work is that an indication of satisfactory operation. Hope this helps. The only other issue is that there is too much draw from battery - high load, short circuit etCc. other tests needed to check this.
 

Drover

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#69
At first until everything is heated up it will draw heaps then will rise up a small bit but the fridge should always be on a 12v source that is generated constantly not just drawing from a battery, doesn't do the battery much good in the long run and won't keep the thing cold anyway as it will go flat, so checking what happens when no power to battery is usefull for info but not a true indication of whats happening when being used, like an air compressor it should always be used when engine running to keep a constant supply of 12v to them.
Check when engine running and you will see what your voltage drop is from vehicle to fridge, it shouldn't be a great deal.
 
Jan 25, 2017
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Point Cook
#70
I will hook up the battery to the charger to ensure fully charged and try again

Will also see what the voltage drop when the car is running

As the fridge wasn't turned on prior as you said Drover "until everything is heated up it will draw heaps' i will also run the fridge on 240v over night and then check the voltage off the battery
 

mikerezny

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Sep 11, 2016
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#71
As the fridge wasn't turned on prior as you said Drover "until everything is heated up it will draw heaps' i will also run the fridge on 240v over night and then check the voltage off the battery
Hi @MarkAW,

most threw-way fridges do NOT have a thermostat controlling the 12V element. My Dometic 90l RM2350 has a 175 W element for 12V operation and is definitely not controlled by a thermostat.

Consequently it draws about 15A constantly regardless of the temperature of the fridge.

It would be worth having a good read of the manual for your particular fridge to determine the wattage of your 12V element and whether it is controlled by a thermostat or not.

cheers
Mike
 

Boots in Action

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Mar 13, 2017
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Ferny Grove, Queensland
#72
At first until everything is heated up it will draw heaps then will rise up a small bit but the fridge should always be on a 12v source that is generated constantly not just drawing from a battery, doesn't do the battery much good in the long run and won't keep the thing cold anyway as it will go flat, so checking what happens when no power to battery is usefull for info but not a true indication of whats happening when being used, like an air compressor it should always be used when engine running to keep a constant supply of 12v to them.
Check when engine running and you will see what your voltage drop is from vehicle to fridge, it shouldn't be a great deal.
Hi @Drover , just a technical point. The heating element for the fridge is a fixed resistor and will not change on start up or when hot. Unlike a compressor fridge, when more power is drawn on startup of compressor motor and then current draw drops back. There normally would not be any change whether hot or cold on a heating element. For the real Tech Heads, the resistance gets higher as element heats up and this reduces the current flowing in circuit. The colder the element, the more current flow.
 
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Boots in Action

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Mar 13, 2017
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Ferny Grove, Queensland
#73
Hi @MarkAW,

most threw-way fridges do NOT have a thermostat controlling the 12V element. My Dometic 90l RM2350 has a 175 W element for 12V operation and is definitely not controlled by a thermostat.

Consequently it draws about 15A constantly regardless of the temperature of the fridge.

It would be worth having a good read of the manual for your particular fridge to determine the wattage of your 12V element and whether it is controlled by a thermostat or not.

cheers
Mike
Yes @mikerezny , you Tech Head!!
 
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mikerezny

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Sep 11, 2016
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Mount Waverley, VIC
#74
Will also see what the voltage drop when the car is running
Hi @MarkAW,

WRT to measuring the voltages on 12V there are TWO separate issues you need to consider.
1: The actual voltage measured at the 12V source. Since the fridge draws at least 15A on 12V, the voltage measured at the terminals of a standalone battery will be different with no load or when a load is connected. Secondly as the battery discharges, this voltage will decrease over time.

2: Secondly, there will be a voltage drop across the cables connecting the battery to the fridge. This voltage drop will depend on the thickness of the cable. The thicker the cable, the less the voltage drop. It can be tricky to measure this voltage accurately if the voltage at the battery terminals is varying at the same time. I get around this by using the car battery with the engine running to ensure a steady voltage. My suggestion is that the voltage difference between the battery and the fridge terminals should be less than 1V. In my particular setup it is 0.8V.

cheers
Mike
 

Drover

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#75
That's what I thought I said !!??!! , when I first fire it up from cold it chews some juice, then in a short time ,a minute maybe ?, then the power draw drops by about a poofteenth once the element gets cooking . Don't have any volt figures as long as it worked all was good.........but using a stand alone battery figures is just academic as you wouldn't in real time. 12v needs power station back up.
 

Boots in Action

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Mar 13, 2017
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Ferny Grove, Queensland
#76
That's what I thought I said !!??!! , when I first fire it up from cold it chews some juice, then in a short time ,a minute maybe ?, then the power draw drops by about a poofteenth once the element gets cooking . Don't have any volt figures as long as it worked all was good.........but using a stand alone battery figures is just academic as you wouldn't in real time. 12v needs power station back up.
Sorry if I misunderstood @Drover. You are right about operating the fridge on a stand alone battery. It won't run for too long as voltage drops. That is just a test of @MarkAW 's battery. It should be able to sustain voltage ABOVE 12 volts for a short time if battery has been properly and fully charged. If no guts available for this short test, having a continuous 12 volts power station back up would not improve the situation as charger would be trying to bring battery up AS WELL as run fridge element!! Definitely do not recommend running 12 volt fridge for long on only battery power, even if battery is high capacity and in good condition of charge.
 
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Jan 25, 2017
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Point Cook
#77
Ok, checked voltage again
With the car running or turned off the 2nd battery is 12.85v at the battery terminals and at fridge terminals in the bottom vent.

When the fridge is on DC the battery at terminals is 12.4v and at the fridge terminals is 11v. Voltage stayed the same with the car running or turned off.

So i’m Losing 1.4v somewhere along the wire or through the 12 pin

I had an Anderson plug fitted to the caravan by jayco when purchased but can’t remember if it went direct to the fridge or caravan battery charger?

I have some 6 AWG cable which I will put an Anderson plug on one end and connect the other direct on battery and check for voltage drop which is either from the 12 pin or jayco wiring to the fridge

Hopefully can reduce this voltage drop
 

Boots in Action

Well-Known Member
Mar 13, 2017
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Ferny Grove, Queensland
#78
Ok, checked voltage again
With the car running or turned off the 2nd battery is 12.85v at the battery terminals and at fridge terminals in the bottom vent.

When the fridge is on DC the battery at terminals is 12.4v and at the fridge terminals is 11v. Voltage stayed the same with the car running or turned off.

So i’m Losing 1.4v somewhere along the wire or through the 12 pin

I had an Anderson plug fitted to the caravan by jayco when purchased but can’t remember if it went direct to the fridge or caravan battery charger?

I have some 6 AWG cable which I will put an Anderson plug on one end and connect the other direct on battery and check for voltage drop which is either from the 12 pin or jayco wiring to the fridge

Hopefully can reduce this voltage drop
Hi again @MarkAW , you seem to be narrowing it down a bit now. At least the battery is starting off at a good voltage WITHOUT LOAD. A drop of .4V would be reasonable for the battery voltage to drop when load (15A??) placed in circuit. However, a drop of approx 1.4V is not good on wiring. Normally, with the engine running, one can expect that the higher voltage would be maintained to a certain degree. I think that the reason for voltage loss will be confirmed when you bypass the 12 pin connector and run a heavy 6AWG cable directly from battery terminals to Anderson plug on drawbar of van. Try it with engine off and note readings at battery and fridge terminals. Then do the same with engine running. There should be a substantial increase in battery voltage (with alternator input voltage) and a similar increase in voltage at fridge terminals. Normally, the heavy wire from Anderson plug at van drawbar is connected directly to the fridge terminals and NOT through the SETEC distribution box. There maybe however a thinner wire that splits off the positive and goes to the SETEC to trickle charge the battery when connected to the car and engine is running. This line has a power diode connected in line which prevents current going back to the tug battery if the van battery is at a higher state of charge. The penalty for this diode setup is a loss of about .8V to the van battery. But this does NOT affect the voltage going to the fridge terminals, which should be nearly the same as battery voltage of tug - less a very small voltage loss in connecting wiring. Give it a go and please report your findings. It will help others on this forum if they see success in what you have done.
 

Drover

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Nov 7, 2013
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#79
Usually if they wire up an Anderson for the fridge you will see the heavier cable at the fridge terminal block and the 12pin circuit will be disconnected, I would say yours probably goes to the Setec or it could be direct to battery, the circuit from the 12pin will more than likely go thru the Birds Nest under the van, thats a big conglomeration of crappy wire connections which more than likely will be where your loss is.
Running 6 B&S from draw bar direct to fridge is the best way if you can't redo the Anderson already fitted but you need to have similar cable set up on the tug or you could end up with some hot spots if they are just using the original wiring harness in tug. If using 6 B&S on van you will need to put an Anderson on the end at fridge so you can reduce the cable size to connect to the fridge without having to pair down cable or get a bigger connector block....

When digging around in the birds nest or the 12pin, the purple and orange wires are usually for your Break Safe charging circuit and operating circuit, don't disconnect as happened to mine when they refitted a new plug to van, one of the rare times I left things to the Professionals and they stuffed it up.

By power station I was meaning alternator, engine or similar, not a battery charger because then you would need 240v or heaps of solar ........and if you had a genny why bother with 12v.....
 
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Jan 25, 2017
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Point Cook
#80
I called Jayco and was told the anderson plug on my draw bar went directly to the battery, unfortunately not to the fridge.

First thing i will do is to remove wires on both sides of the 12 pin to an anderson plug and see if that reduces voltage drop. Hopefully most of the voltage drop is at the 12 pin.

If that doesn't reduce the voltage drop i'll have to run a 6AWG gauge wire direct from fridge to draw bar anderson plug