Running 3 way fridge via inverter

[linkshouse]

I have an Electrolux RM270 fridge fitted to my van.

I suspect the 12v section is faulty (I will investigate more fully in due course) as it cools fine on mains hook up and on gas, but even if it is cold already does not stay cold when 12v whilst driving.

Looking at the specs and wiring diagram I see that 240v element is 105 watts and the 12v element is 100 watts. Also, the 240v element is controlled by a thermostat whereas the 12V element is on all the time the 12V is present (engine running).

It seems to me that a reasonable solution might be to, take the 12v supply to the fridge and use this via an inverter to feed the 240V fridge circuit. I realise that I would not then be able to use the fridge on mains hookup.

Any thoughts?

 

[hairydog]

I don't recommend it! But if you really want to go to all that trouble instead of replacing a cheap 12v element or finding the faulty relay/blown fuse that is causing the problem, do it with a relay, so that when there is mains power, the fridge runs on it.
If you can't do that yourself, find somene who can.

 

[SimonM]

I don’t know. But, here goes nothing, could you put a ehu style socket for the fridge and run fr9m the inverter into same socket. Then, when on hookup, and your fridge isn’t now connected, have a lead from an internal socket to go to the fridge socket. Does that make sense?

 

[oppy]

Just a thunk, ours stopped working on 12v (whilst driving) and I, like you, put a shout out and one suggestion was that the relay may have died. So for the princely sum of £4 the problem was solved. In our 'van the relay is in a block of 2 just by the starter battery and because I didn't know which was which, I replaced them both. It's a standard 5 blade 30 amp jobbie.

 

[linkshouse]

I don't recommend it! But if you really want to go to all that trouble instead of replacing a cheap 12v element or finding the faulty relay/blown fuse that is causing the problem, do it with a relay, so that when there is mains power, the fridge runs on it.
If you can't do that yourself, find somene who can.

Ah well, I had just assumed that as the fridge was so old spares would be non existent.

I do intend to investigate the fault properly as I am a retired electrician.

I was just exploring options from the armchair so to speak.

I read the post a while back about using a domestic mains fridge via inverter and have considered this but since the existing fridge works on gas and mains I just thought I ask if anyone else had used or considered this approach.

 

[wildebus]

If you have something like a Kill-a-watt meter, I would plug the fridge into the meter and then into the mains supply and run it for say a day to see just how much power it is drawing. That will tell you if it is feasible to run off your battery bank via an inverter.
A Compressor Fridge is very efficient and will run on average only around 20%-25% of the time. I think the 3-way fridges tend to run near constantly when on mains? If that is the case and it is pulling around 100W, then you would be out of power pretty quickly

 

[linkshouse]

If you have something like a Kill-a-watt meter, I would plug the fridge into the meter and then into the mains supply and run it for say a day to see just how much power it is drawing. That will tell you if it is feasible to run off your battery bank via an inverter.
A Compressor Fridge is very efficient and will run on average only around 20%-25% of the time. I think the 3-way fridges tend to run near constantly when on mains? If that is the case and it is pulling around 100W, then you would be out of power pretty quickly

I only intended to run it via the inverter when on the move, essentially just replicating the way the normal 12v system works. I realise that there would be the inverter overhead but again, whilst on the move considered that covered.

All that said, I had discounted the option of a simple repair on the grounds of obsolescence but hairy dogs post prompted me to look and replacement elements are available on eBay for around £12.

The only rub then is that it would mean taking the fridge out and if I did that I could be sorely tempted to go down your route of fitting a domestic compressor fridge.

 

[wildebus]

I only intended to run it via the inverter when on the move, essentially just replicating the way the normal 12v system works. I realise that there would be the inverter overhead but again, whilst on the move considered that covered.

All that said, I had discounted the option of a simple repair on the grounds of obsolescence but hairy dogs post prompted me to look and replacement elements are available on eBay for around £12.

The only rub then is that it would mean taking the fridge out and if I did that I could be sorely tempted to go down your route of fitting a domestic compressor fridge.

I missed that point In which case sounds like a perfectly reasonable option if the 12V side cannot be fixed.

 

[mistericeman]

I only intended to run it via the inverter when on the move, essentially just replicating the way the normal 12v system works. I realise that there would be the inverter overhead but again, whilst on the move considered that covered.

All that said, I had discounted the option of a simple repair on the grounds of obsolescence but hairy dogs post prompted me to look and replacement elements are available on eBay for around £12.

The only rub then is that it would mean taking the fridge out and if I did that I could be sorely tempted to go down your route of fitting a domestic compressor fridge.

Can you not get to the element via the lower external vent?

 

[linkshouse]

Can you not get to the element via the lower external vent?

If the blumming wind and rain ever stop for more than a couple hours I’ll have a poke through the vents.

 

[hairydog]

I would VERY strongly advise you against getting a compressor fridge, unless you want endless power problems.
If your fridge is OK on mains and gas, I would try leaving it on gas when driving until you get a chance to fix it. I'm sure lots of people will think this dangerous, but I have a different opinion.
However, there is nothing difficult or complex about a 12v heating element, a relay and a fuse. You could replace the lot if needed (which it won't be: only one bit will have failed). The fuse is 20p, the relay £1 to £5, depending where you buy it, the element £25 to £30, depending where you buy it. But it is just as likely to be one poor connection: loose and/or corroded.

 

[mistericeman]

I would VERY strongly advise you against getting a compressor fridge, unless you want endless power problems.
If your fridge is OK on mains and gas, I would try leaving it on gas when driving until you get a chance to fix it. I'm sure lots of people will think this dangerous, but I have a different opinion.
However, there is nothing difficult or complex about a 12v heating element, a relay and a fuse. You could replace the lot if needed (which it won't be: only one bit will have failed). The fuse is 20p, the relay £1 to £5, depending where you buy it, the element £25 to £30, depending where you buy it. But it is just as likely to be one poor connection: loose and/or corroded.

What endless power problems???

I'm interested to hear what power problems you've suffered before I junk the 3 way in the Swift and replace it with a compressor one.

 

[2cv]

What endless power problems???

I'm interested to hear what power problems you've suffered before I junk the 3 way in the Swift and replace it with a compressor one.

I’m no expert, but it seems clear to me that a compressor fridge will use more battery power than a 3 way, simply because no gas is being used. Whether this causes a problem depends on battery capacity, solar set up and time of year.

 

[oppy]

You don't say how old your van / fridge is, ours is 22 years old, had a new 240 element in 2014, but as I said, the 12v only needed a relay. Seeing as you are a sparks, do check out the cheaper option first

 

[linkshouse]

You don't say how old your van / fridge is, ours is 22 years old, had a new 240 element in 2014, but as I said, the 12v only needed a relay. Seeing as you are a sparks, do check out the cheaper option first

It is a 1991 Hymer.

I will definitely check out the repair of the 12V system before doing anything else.

I must confess to starting this thread more out of interest than need. I had assumed that getting replacement elements, if indeed that turns out to be the problem, would be nigh on impossible. I now find that they are readily available on eBay for around £12 - £15 so I suspect that will be the route I will take in the end.

As I alluded in my last reply, the weather up here is awful at the moment (and showing no signs of changing any time soon) so it will have to wait for a change in that before I can go any further.

 

[linkshouse]

It occurs to me that it might look as though I am just swinging my leg asking a rhetorical question if I intend to just do the repair anyway.

I think perhaps there is an aspect that I was querying that has not been noticed.

What seems strange to me is that the 240V element is fed through a thermostat to control the temperature of the fridge so it will switch on and off as required once the fridge reaches temp, whereas the 12V circuit feeds the 12V element continuously (whilst driving).

So, once the fridge is down to temperature it would seem that the 240V circuit should cycle on and off and therefore use less power overall.

 

[hairydog]

What endless power problems???

I'm interested to hear what power problems you've suffered before I junk the 3 way in the Swift and replace it with a compressor one.

For this calculation, I assume that a compressor fridge will use about 45Ah per day. Add another 20Ah for habitation use. (In summer, more for the fridge, less for habitation, in winter the other way round). So that's 65Ah. You may want to increase or decrease these figures a bit, but they're about right.

Batteries are around 80% efficient, so you need to put about 76Ah (or a bit over 1000 watt hours) into the batteries each day to get 65Ah out.
Where will you get that power from?

Solar?
In winter in the UK you can expect an average of about 0.6 hours of sun each day. So you will need to have enough solar panels to give 76Ah of power in 36 minutes of sun: That's 1700 watts of panels. How big is your roof?

Split charge relay?
People see a 40A relay and 100A alternator and think their batteries will charge at 40A. Not so. Start the engine and you'll get 20 to 25A for a few minutes, then it will drop to the teens of amps and fade away, as soon as the alternator is happy with the starter battery voltage.

Battery to Battery Charger?
Way better than a SCR, you can expect to see 35A to 45A (at least for the first couple of hours), so as long as you have a good B2B charger and drive for two or three hours EVERY day, you'll be OK.
But even at a typical 30mph average, you'll do the equivalent of John O Groats to Lands End every nine days.

And storage...
You shouldn't discharge your batteries below 50% without damage and can't fill them above about 90% without long term charging, so assuming that you stick to that 40% range, to allow for a week of cloudy weather and no driving, you will need to have 1137Ah of battery bank to provide 455Ah of usable storage. How is your payload?

Gas fridges are about half as efficient as compressor ones, but every kilogramme of LPG has 13.7kWh of energy in it. So the fridge uses 1000Wh of power each day, instead of the 540Wh a compressor fridge would, but that's only 73g (or 0.146L) of LPG - less than 10p worth.

 

[Minisorella]

It occurs to me that it might look as though I am just swinging my leg asking a rhetorical question if I intend to just do the repair anyway.

I think perhaps there is an aspect that I was querying that has not been noticed.

What seems strange to me is that the 240V element is fed through a thermostat to control the temperature of the fridge so it will switch on and off as required once the fridge reaches temp, whereas the 12V circuit feeds the 12V element continuously (whilst driving).

So, once the fridge is down to temperature it would seem that the 240V circuit should cycle on and off and therefore use less power overall.

I'm pretty useless on power stuff but I have been told that the 12v mode when driving is a mere 'trickle' that will help maintain the current temperature in the fridge, ie it won't bring it down any further. Makes sense that it doesn't involve a thermostat or any switching on and off. I'm surprised that the 12v element is that high tbh. Mind you, I truly know nothing other than what I've been told! On the bright side, with the cold weather, you might not even need the fridge for a while!

 

[mistericeman]

For this calculation, I assume that a compressor fridge will use about 45Ah per day. Add another 20Ah for habitation use. (In summer, more for the fridge, less for habitation, in winter the other way round). So that's 65Ah. You may want to increase or decrease these figures a bit, but they're about right.

Batteries are around 80% efficient, so you need to put about 76Ah (or a bit over 1000 watt hours) into the batteries each day to get 65Ah out.
Where will you get that power from?

Solar?
In winter in the UK you can expect an average of about 0.6 hours of sun each day. So you will need to have enough solar panels to give 76Ah of power in 36 minutes of sun: That's 1700 watts of panels. How big is your roof?

Split charge relay?
People see a 40A relay and 100A alternator and think their batteries will charge at 40A. Not so. Start the engine and you'll get 20 to 25A for a few minutes, then it will drop to the teens of amps and fade away, as soon as the alternator is happy with the starter battery voltage.

Battery to Battery Charger?
Way better than a SCR, you can expect to see 35A to 45A (at least for the first couple of hours), so as long as you have a good B2B charger and drive for two or three hours EVERY day, you'll be OK.
But even at a typical 30mph average, you'll do the equivalent of John O Groats to Lands End every nine days.

And storage...
You shouldn't discharge your batteries below 50% without damage and can't fill them above about 90% without long term charging, so assuming that you stick to that 40% range, to allow for a week of cloudy weather and no driving, you will need to have 1137Ah of battery bank to provide 455Ah of usable storage. How is your payload?

Gas fridges are about half as efficient as compressor ones, but every kilogramme of LPG has 13.7kWh of energy in it. So the fridge uses 1000Wh of power each day, instead of the 540Wh a compressor fridge would, but that's only 73g (or 0.146L) of LPG - less than 10p worth.

Interesting calcs....

However after running a 40l Waeco compressor from 3 x 100ah leisure batteries for the last 3 years or so...
Charged by 2 cheap and chearful solar panels/£20 pwm controller flat on the roof and a durite VSR....
The coolbox has never been switched off....
We hammer the electric as all cooking is electric along with eberspacher heating...

I've never used hook up Barring a handful of times when we've not been away in winter and the vans not moved as the weather has been that bad.

Needless to say... As cheap as lpg is (refillable)
Ill be swapping the 3 way for a compressor type again and fitting an eberspacher along with extra batteries and solar.

All depends on your intended usage of the van BUT the pfaff of changing fuel sources on the fridge and not just being able to leave it running loaded and ready to go makes a 3 way a real backward step in my book...
And definitely don't want to be tethered to hook up and where the nearest available post is.

 

[hairydog]

All depends on your intended usage of the van BUT the pfaff of changing fuel sources on the fridge and not just being able to leave it running loaded and ready to go makes a 3 way a real backward step in my book...
And definitely don't want to be tethered to hook up and where the nearest available post is.

My fridge is AES. You switch it on the day before you plan to go away. You switch it off again when you get home. That's it.
Yes, they're not cheap, but they're far cheaper and less hassle than th 12v stuff needed for a compressor fridge.