Running the fridge from an inverter?

[Richard Birkett]

We have recently fitted a Victron 200 amp hour battery to replace the original gels and so we are looking at using the inverter a bit more than previously. When the inverter is on, all of the 240v sockets are live. This got me wondering if the fridge would also work on 240v and it does. The fridge is a Dometic RMT7655 and the manual says 190W with average consumption of 3.2KWh per 24 hrs.

We have 320w of solar panels on the roof and today with the inverter and fridge running for half an hour the battery stayed at 100%

So my question is really about how many amp hours the fridge will use during the hours with no/little sun?

Does anyone know?

Thanks in advance.

Richard

 

[funflair]

3.2KWh per day would be about 260amps per 24hr, so about 11amps per hour but it will use less at night as cooler and no opening of door, might be best to put it back onto gas overnight and then back on 240v during the day if the sun is shining.

Martin

 

[Ivory55]

Doesn’t VW Alan do something like that, but uses a domestic household fridge.

 

[tacr2man]

If you are going to run a fridge on batteries/ inverter probably better that its a compressor type. Come to that 12v or 230v .

 

[funflair]

Doesn’t VW Alan do something like that, but uses a domestic household fridge.

That would be a compressor though so uses a lot less power.

Martin

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[funflair]

In Spain in the winter I would run our absorption fridge on inverter 240v for the morning or until we went out and then I would put it onto the site electric that we had a limited number of KWh on, kept the usage under their maximum.

With this new van I fully intend to swap the fridge onto the main inverter backed up supply as at the moment it is on hook up only side, we have 520watts of solar so might as well use it for something rather than let it go to waste.

M

 

[Richard n Ann]

Why not configure it to run on 12v? Or is it a 2 way absorption fridge?
Anyway whatever it is, it's a compressor fridge you need for solar.

 

[Lenny HB]

I have a Votronic solar regulator that has and output which turns the fridge to 12v when the batteries are charged and there is enough solar. Does it in 30min blocks to ensure the batteries stay charged.

 

[dunnah01]

Our Dometic 150l fridge/freezer completely drained 2x110Ah batteries in one night on 12v so be careful

 

[Richard Birkett]

Thanks everyone especially Martin (Funflair). I’ll try your suggestion.
Richard

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[autorouter]

190W is about 16A at 12V. Your 320W panels will probably produce about 20A in strong sunlight. So as you say, when the sun is shining the battery stays at 100%.

I think 320W of panel is not enough to run the fridge on 12v continuously. The panels will probably yield a maximum of 1.2kWh over a whole day, compared to the average consumption of 3.2kWh in the manual.

 

[Richard Birkett]

Thanks Autorouter.
Richard

 

[PeteH]

If you are going to run a fridge on batteries/ inverter probably better that its a compressor type. Come to that 12v or 230v .

The one drawback to that, would appear to be when there is/has been low output from panels. there would be NO option to use gas, and the contents of the fridge will be at risk, unless a guaranteed EHU was available?. (or a generator?)

 

[Richard Birkett]

Thanks PeteH.
I'm only considering running it on 240v and I’m going to try Martin Funflair’s suggestion of electricity during the day & gas at night.
Richard

 

[Wissel]

Is your Victron battery their AGM deep cycle?

If so, they say they can be regularly discharged by 60-80%.

Taking the middle figure of 70%, this gives you a usable battery capacity of around 1.75KWh.

If your fridge uses 3.2KWh per 24 hours, it would empty a fully charged battery in 13 hours.

Then there's inverter inefficiency. I use a top of the range/newest Victron inverter and it's still only 92% efficient and uses another 0.2KWh itself (over 24 hours).

So on my inverter, a 3.2KWh 24 hour draw would likely be around 3.65KWh. This would drain your battery in 11.5 hours.

Solar may be okay to keep up on really sunny (UK) days, but just being overcast could reduce your charge by way over half.

I think if I were thinking of doing similar with your fridge, I'd want very good monitoring. I do run an inverter 24/7 with a 240v fridge, but it's a compressor fridge and uses way less battery power.

Thought the figures might be useful

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[Richard Birkett]

Thanks Wissel, that’s really useful information. The battery is lithium but I assume that only extends the length of time before the inevitable!
Richard

 

[autorouter]

Some fridges monitor the solar power, and when it would otherwise be wasted turn it onto 12V to make use of the extra solar power. I think they do this by simulating a D+ signal to make the control board think the engine is running.

Sounds like a relatively simple electronics exercise, but I don't know of any add-on units that will implement this.

 

[vwalan]

Doesn’t VW Alan do something like that, but uses a domestic household fridge.

yes i run an undercounter fridge /freezer. yes compressor type.
if you dont have compressor types they very often dont work in very hot climates like africa or spain specially in summer.
here in uk i run a lead into the house and run a fridge and a seperate tall fridge freezer in the house.
may till september ish it works fine.
saves a shilling on house bills and makes the expense of panels ,batteries etc worth more.
modern fridges seem to prefer pure sine wave inverters . was better twenty years ago ,then you could get an old fridge for hardly anything and they worked great. modern ones are fussy.

 

[EuroTrotters]

Inverters are fine for smaller compressor refrigeration units, not for absorption systems.

I replaced the compressor rated at 80w (220-240v) with a Swiss made 45w version on this small freezer. Now sits in TV cabinet and runs great off Victron inverter/Trojan batteries and solar.