17' Series Electrical - 12v fridge bypass???

[Erictheexpanda]

Hi all,
I am seeking some advice, and while there were similar threads I have a very specific question.
My model: 2015 17.56-2 expanda with RM2553 150ltr fridge, and 120w solar panel fitted.

I have installed a 2nd 100Ah battery with breaker, and add a second 120w solar panel through front and rear mounted Anderson plugs as required.

While it is rare to run out of gas for the fridge when travelling, this does occur. With the current electrical set up I do not have an option to switch to 12v for a short period, as the 12v will only be used by the fridge when connected to the vehicle and the vehicle is powered on (ie high enough voltage).
I accept this is a great feature to prevent battery damage, and 3-way fridges chew through the power quickly (ie less than 5h at 15Amps). However if required, I should have the option to switch to 12v for a short period, knowing the risks, current weather, and other items drawing from the battery. The risk of battery damage can be further minimised by installing a low voltage cut off.

Has anyone actually done this? And if so how?

Any advice would be much appreciated.
Regards, and happy camping

 

[Bellbirdweb]

Hi there @Erictheexpanda, and welcome to the forum.

Whilst I haven't done exactly what you are wanting to do, I do have dual batteries in the tug with an Anderson plug going to the fridge, so when we are stopped, the fridge is still powered.

Watching the battery voltage when the engine isn't running, it drops very quickly.

If we are parked for 30 minutes or more the voltage quickly drops down to 11.5v or lower, so a low voltage cutout would probably only give you an hour at most from 2 x 100AH batteries before it dropped the power to protect them.

With solar you might get a bit more time but it's hard to know how much.

It's certainly possible to do, just not sure how much benefit you're going to get.

Do you have 2 gas cylinders ? We have never completely run out of gas, as we are religious about getting the empty filled as soon as we switch them over.

I also invested in a truma gas level tester which takes a lot of the guess work out of knowing how much gas you have left.

 

[Drover]

How long would you want it for ???? As above it wouldn't last very long, an hour at most, I regularly travel for 5 hours or so with my fridge not running as the 12v has a fault and it has no great temp drop, one day I may repair it. Even if it was running on 12v, if you are opening and closing the door often it won't do anything to keep it colder, the 12v will just, maybe, maintain the temp it was at when you switched to 12v, it won't draw the temp down anymore....
The most important thing is to have it running on 240 or gas for 2 days before you hit the road so the whole thing is chilled down and load it with chilled stuff not warm/hot, you need to get the whole cabinet chilled then all is good.

I think my fridge is the same as yours actually but I only have a 100ah and 120w panel, may increase them one day but have never run out of gas completely but soon as one runs out I refill it promptly.......I know running my fridge, Weber and HWS a bottle will give me at least 2.5 weeks at the worst.

 

[WHHEMI]

Don't do it, as said you will only get a short amount of time from your battery's anyway and the fridge realy isn't very efficient on 12 v, if you run out of gas just leave it switched off and don't open the door it will stay cold for hours.

 

[Dobbie]

Totally agree with @Drover and others re fridge efficiency.

We've never run out of gas over weeks of constant use ...I can't see if you have two gas bottles but if not, it doesn't take much to keep an eye on gas levels and top up if close to empty. If you have two, it's a good practise to refill one as soon as possible when empty.

and the fridge runs far more efficiently on 240 and gas....we've always found gas even more efficient than on 240 but that could be just luck.

12v on these fridges is far far less efficient and only recommended to keep it as close to the temp as possible. It won't cool it down and would chew up any battery capacity unless it's designed to run primarily on 12v.

Some are ...the usual discussion about compressor versus absorption fridges will give that info.

As said, always supercool the fridge for at least 24 hours before travel, add stuff to it that is already cold or frozen, only select DC when travelling and if your plug is wired to get 12v from the car, ensure your car battery is protected by some sort of switch / isolator, keep the door closed as much is possible and, if off grid, get the gas running asap.

All this you obviously know but I think to look at the option of 12v over gas as a primary power source while off grid is asking for trouble.

I'm not trying to be contentious but have spent hours investigating variations of this in recent weeks.

Our new van has an electronic panel which requires constant 12v access but I was concerned about the possible drain on the battery while off grid. It draws 0.7 amps just for the panel, not for the main power source. I have now been reassured that I can comfortably run it on gas and still have the fridge electronics working. I can live with the 0.7 amps and will still use the car alternator power to keep it cool while travelling.

Good luck with it. I'd ask Santa for a gas monitor and isolator as that'd solve your dilemma efficiently.


and :welcome:

 

[Duncanblake36]

I have a really stupid assumption that I need clarity on. I always thought that the 12v DC Fridge power comes from your battery in the van and not the car. Or do I have it completely wrong.

Is it wired only to the car plug which means it bypasses the van battery?

The reason I asked is I went and plugged the van in now to 240 and the fridge was left on DC but the batteries are full?

I think I have answered my own question but confirmation would be good.

If it is vehicle only then what is the best way to hook it into the Vans Battery.

My setup has duel batteries with a Dc to Dc charger from my hilux for the whole reason of charging the batteries when the fridge is on DC.

Longest trips have been about 5 hours on DC so haven't noticed a major increase in temp as the fridge is normally pretty cold before we leave.

Any input would be great - especially re-directing the power.

 

[Bellbirdweb]

@Duncanblake36 yes you have answered your own question.

The 3 way fridges pull 15-17A when on DC and only maintain temperature they don't actually cool, so it would run your bateries flat quickly and not cool properly.

The only fridges generally wired to the house batterie are compressor fridges.

I run dual batteries in the car and have the van fridge wired to run from the aux battery. It can pull it down to 11.5v ( flat) in 30 minutes, so you would kill your house batteries very quickly.

 

[Drover]

Well yep, you have about sussed it out, a quick run down on how most vans operate nowadays....

With a 3 way fridge you will have 240v, Gas and 12v, the 12v is only used when hooked up to the tug and draws power only from it when it's running otherwise it will kill a battery in an hour or so, thats why they don't run off the van battery plus the 12v fridge will only keep the temp stable, maybe, it won't cool down a fridge except over say about a week in a cool climate with the door nailed shut, basically if you were going to spend $500 or more to set it up, then spend the money elsewhere. Do not hook it up to the van battery. You will need a unit like a Fridge Switch or some other relay to cut the 12v to van when the engine is shut down, do a search and you will find the thread covering this.

Unless as stated above by @Bellbirdweb you have a compressor fridge.

Not a stupid assumption, just one of those thought bubbles that sometimes pop up......................if you have solar panels then you shouldn't need power from the tug either to charge the batteries, mine get plenty of charge from the panels, in fact I have no circuit form the tug to do it and very rarely use the 240v charger.

 

[Brenton]

I run mine from the second battery in the tug via an anderson running direct from fridge 12v dc to van drawbar. i leave it plugged in and running on 240 until ready to leave then plug in anderson and turn onto 12v dc. if stopped for a long time i disconnect it and leave it off keeping itself cool without opening. then i turn it back onto 12v dc when moving again and run on gas at camp. I will be pulling the fridge out eventually and replacing it with a compressor fridge so it just runs on 12v all the time. they work more efficiently and i free camp all the time so will expand the battery bank and do this.

 

[Dobbie]

Here's another with fridge wired to car's second battery...though we had an Anderson plug failure last trip so nothing came through. It didn't matter and we certainly weren't concerned as the solar was more than enough.

I was more worried that the Anderson plug still gave us van brakes and lights....and it did.

Must fix it!

Personally, I'd never rely on battery power totally for the fridge ....and I know others disagree. The fridge efficiency is fine via gas, the extra batteries and solar are heavy and expensive and I'm happier relying on gas rather than the sun to keep my food cold when free camping. We've never had even a whisper of a problem.

I can't see the point in reinventing the wheel.