3-way fridges, fooling the 12v.

[tonyidle]

It depends on the specific model. I just looked at one Dometic fridge and the 12 volt element was 60W the other one 175W.

If that's correct I doubt it would work at all on 60W. I can't find one under 120W.

 

[pappajohn]

I have done it by running an EHU cable from the inverter, out the window to the external EHU socket. (obviously running on 240v not 12)

I assume you turned off the onboard charge.
Your inverter wiill be trying to charge the battery but drawing more current than the charger can provide.

 

[IRHP]

I've

My Thetford 3 way apparently will only maintain the cold when using 12v and doesn't actually cool anything. So in my case I no longer use it on auto rather I manually set it to only use gas.

I've seen this written a few times. Mine will get colder when driving, there's not much difference between the 12v and 240v elements

 

[Barriesimpson]

I've


I've seen this written a few times. Mine will get colder when driving, there's not much difference between the 12v and 240v elements



View attachment 944005

Well that's 15% which is quite a lot and I do notice the difference.

 

[StillGoing]

My Dometic 3-way, before it died, was 250W on 230V and 170W on 12V.

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[the1andonly]

For most vans, isn't the fridge 12v supply wired to the cab battery/alternator? Telling it to switch to 12v mode with an S+ wire when you're parked up will drain just the cab battery won't it?

For most vans not all. My Rapido is not connected to SB at all just LB which is charged by alternator(split charge now B2B) A simple connection from S+on Votronics to fridge is all that is needed. Mine is abit more conveluted in that i Mimiced the D+ to fridge with a relay. There is a thread here doing the same with a 8 series fridge with no S+.

 

[Lenny HB]

It can be done. I assume you're aware how hideously inefficient 3 way fridges are on electric? Roughly 200w of draw, which adds up very quickly! And yet they sip gas.

I wouldn't call one 1 Lt a day sipping that's £1 a day if you are using LPG or £2 plus a day on calor.

 

[Lenny HB]

Our current series 10 Dometic fridge both mains and 12v elements are 190 watt.

Last van I had a Votronic solar controller with an AES output that gave a 12v signal when the batteries were charged and solar was coming in, it did it in ½ hour blocks to give the batteries a chance to recover.
You connect the AES output to the fridge S+.
I found with the stupid firmware on the Dometic fridge the list of power priority solar is at the top, so when on mains the batteries were charged so the solar controller was giving out the AES signal so the fridge switched to 12v. I fitted a relay to disable the AES from the controller, you can use a switch.

The new van I've fitted all Victron (no AES on solar) so I'm goining to use the programable relay in my the BMV 712 Shunt to give me a 12v signal to turn on say at 90% and off at say 50% (I have nearly 500ah of Lithium) and feed this signal via a timer to the fridge so it will switch in one blocks, I will also be able to set start and finish times to suit time of year.

 

[Barriesimpson]

I wouldn't call one 1 Lt a day sipping that's £1 a day if you are using LPG or £2 plus a day on calor.

Mine uses 400g in 24 hours.

 

[Richard n Ann]

Mine uses 400g in 24 hours.

That's about 800ml of liquid then, so similar

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[Lenny HB]

Mine uses 400g in 24 hours.

That's nearly a litre is that actual use or quoting from the spec.
My litre a day was actual use the spec was about 450g.

 

[Barriesimpson]

That's nearly a litre is that actual use or quoting from the spec.
My litre a day was actual use the spec was about 450g.

Spec, but 11kg bottle lasts around 16 days including hot water usage, which is minimal.

 

[denisejoe]

To actually do it is guide simple just find the 12v signal wire at the back of the fridge and replace it with a 12v + switched so you can turn it off if needed. It doesn’t need a heavy wire as it’s not the wire that powers the fridge

 

[Widge]

My fridge on mains performs about the same as on 12v... Not great. We'll often plug the van in on the drive the day before we go away. It will take a full day for the fridge to get down to 5C. It's much faster on gas.

I do the same, but also fill the freezer compartment with pre frozen cool blocks, this seems to help.

 

[VXman]

I assume you turned off the onboard charge.
Your inverter wiill be trying to charge the battery but drawing more current than the charger can provide.

Yes.

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[VXman]

Just looking at the specs for my Fridge - Thetford N4142. It states 'max input' so not sure if that is the actual rating of the element?

Anyway -

on mains - 240watts
on 12 volt - 205 watts (so pretty similar to mains power) It seems to keep nice and cool when on 12 volt
on gas - 22,9 g/h (not sure what that means)

Interestingly, the gas on these fridges is on (as in burning) pretty much constantly. I reckon on for 50mins every hour, For us 20 litres of gas lasts 2 weeks ish. in the summer. That's fridge, showers for 2 daily and cooking.

 

[Richard n Ann]

Our freezer worked well on 12v (120w). From ambient to minus 12 with a 2 hour drive.

 

[Lenny HB]

on gas - 22,9 g/h (not sure what that means)

549 grams per 24 hours or 1.1 Lt.

 

[VXman]

549 grams per 24 hours or 1.1 Lt.

Could you kindly extrapolate on that - what does g/h mean - what is 22,9 - how did you work it out?

 

[Lenny HB]

Could you kindly extrapolate on that - what does g/h mean - what is 22,9 - how did you work it out?

Grams per hour so 22.9 x 24 =549.6 grams, 0.549kg a day or 0.549 x1. 96 to convert to litres = 1.08 Lt.

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[autorouter]

what is 22,9

Europeans use a comma instead of a dot for the decimal point, so 22,9 just means 22.9