Inverter sizing

Trotter

Trotter

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The idea of fitting a domestic fridge to Demi is still going around my head.
One I’ve looked at has a Annual consumption of 106kwh.

Using this:- kWh x 1000 divided by 8700 ( rounded up hours in a year ) = watts

If I’ve got this right, 106 annual kWh is a little over 12wh.
But that figure would be @ 240v. So 12wh x 12 volts = 20watt minimum inverter.

There’s a 3000w inverter in Demi. Because of the 2w drain it has, a smaller inverter would be an better alternative.
 
Have a look here

12v Dometic fridge uses less power. You need an inverter that can power the motor in the fridge anything from 300w to 800w depending on fridge. There will be an inrush of power as the motor starts up that your inverter will have to cope with. I took my Dometic CFX3 25 to bits the other day. It has a neat 12v compressor and a 240v to 12v power supply which auto switches depending if we are on EHU or not. You may also have to find someway of keeping the door shut when travelling. Our small freezer uses about 2A per hour from the battery so 48A in every 24H period. The 360w solar and driving keep it all working using a 120Ah lithium.
 
I went with a Victron phoenix 12/800w when I pulled our 3 way out and swapped it for a 240v undercounter ...

Works great and doesn't appear to consume any more power than our 40l waeco 12v compressor cool box .

Runs in eco mode so only actually runs fully when power is required ...rest of the time it just sits in stand by .

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jeffmossy said:
Somebody was telling me that there is a company that converts 240v fridges to 12v Derek, would that not be a better option for you?
Click to expand...
I talked to someone a couple of years ago about doing that. Tbh, it seems more trouble than it’s worth. Maybe I would have found a use for the Bluetti 🫣
QFour said:
Have a look here

12v Dometic fridge uses less power. You need an inverter that can power the motor in the fridge anything from 300w to 800w depending on fridge. There will be an inrush of power as the motor starts up that your inverter will have to cope with. I took my Dometic CFX3 25 to bits the other day. It has a neat 12v compressor and a 240v to 12v power supply which auto switches depending if we are on EHU or not. You may also have to find someway of keeping the door shut when travelling. Our small freezer uses about 2A per hour from the battery so 48A in every 24H period. The 360w solar and driving keep it all working using a 120Ah lithium.
Click to expand...

I’ve got a couple of the cheaper chest fridges. The Vevor is brilliant. Holds its temperature very well. The other one, a Alpicool knock off. Not so good.
Not sure I want to go to the expense of the Dometic.
But thanks both for your interest.
 
Trotter said:
The idea of fitting a domestic fridge to Demi is still going around my head.
One I’ve looked at has a Annual consumption of 106kwh.

Using this:- kWh x 1000 divided by 8700 ( rounded up hours in a year ) = watts

If I’ve got this right, 106 annual kWh is a little over 12wh.
But that figure would be @ 240v. So 12wh x 12 volts = 20watt minimum inverter.

There’s a 3000w inverter in Demi. Because of the 2w drain it has, a smaller inverter would be an better alternative.
Click to expand...
The compressor fridge has an on/off duty cycle. the actual cycle varies depending on ambient temp and usage, but that 106kWh number is the total for the year including the off time. When running, the power demand will be around 60W or so
However, due to the in-rush surge of the compressor each time it kicks on, it could be demanding over 600W, so you need an inverter that can cope with at least 600W and possibly more.
This video shows the current demand for the start cycle (if you watch on Youtube you will see more info in the video description)


If you are looking for a fridge to fit, depending on the gap you have, this is an excellent unit
I fitted one of these in my last conversion and it was superb and more economical than the "proper" Waeco CRX50 12V compressor fridge I had in the previous van.
The 12V fridges are usually less economical than a 240V fridge in fact, but the inverter overhead often swings the advantage slightly back in the 12V favour - but the fact the 12V fridge is often 4 or 5 times more expensive totally wipes out that avantage.

And if that is of interest, I happen to have one of those Inventor for sale ;) bought as a spare a few years ago and never used, so just looking to cover my costs to clear it out the way :) . It is very much a Fridge. the icebox is just a chiller, not a freezer section, but I think you may have mentioned you just wanted a fridge anyway?
 
wildebus said:
The compressor fridge has an on/off duty cycle. the actual cycle varies depending on ambient temp and usage, but that 106kWh number is the total for the year including the off time. When running, the power demand will be around 60W or so
However, due to the in-rush surge of the compressor each time it kicks on, it could be demanding over 600W, so you need an inverter that can cope with at least 600W and possibly more.
This video shows the current demand for the start cycle (if you watch on Youtube you will see more info in the video description)


If you are looking for a fridge to fit, depending on the gap you have, this is an excellent unit
I fitted one of these in my last conversion and it was superb and more economical than the "proper" Waeco CRX50 12V compressor fridge I had in the previous van.
The 12V fridges are usually less economical than a 240V fridge in fact, but the inverter overhead often swings the advantage slightly back in the 12V favour - but the fact the 12V fridge is often 4 or 5 times more expensive totally wipes out that avantage.

And if that is of interest, I happen to have one of those Inventor for sale ;) bought as a spare a few years ago and never used, so just looking to cover my costs to clear it out the way :) . It is very much a Fridge. the icebox is just a chiller, not a freezer section, but I think you may have mentioned you just wanted a fridge anyway?
Click to expand...
Still trying to weigh up the advantage of swapping out the 3way. I've already got a spare 1500w psw. The little Bluetti may have a use after all
 
Everything has its price Dave
 
nabsim said:
I wouldn’t swap a working 3 way out Del
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Good point Neil, but It has let me down a couple of times. Now that I’m spending a longer in the van, I need to know that I can depend on it..
Fortunately, I do have an alternative, to use temporary in case of a failure.
But that brings us back to the amount of stuff l can carry in the van, “ just in case”. And the amount of failed projects are mounting up in the shed.😬
 
To be,honest the only possible time I can see a absorbtion fridge winning over a compressor type is IF you don't move around in the winter where the lack of solar would be an issue without using hook up ...
BUT when we use,the van,in winter we tend to move every few days AND the demand in the fridge is less with the weather being cooler .

For our uses I'd never go back to a absorbtion fridge after having a compressor type .
 
mistericeman said:
To be,honest the only possible time I can see a absorbtion fridge winning over a compressor type is IF you don't move around in the winter where the lack of solar would be an issue without using hook up ...
BUT when we use,the van,in winter we tend to move every few days AND the demand in the fridge is less with the weather being cooler .

For our uses I'd never go back to a absorbtion fridge after having a compressor type .
Click to expand...
Yes same, I wouldn’t replace a compressor with a 3 way, I don’t use EHU unless it’s a real emergency either but I do use my generator every few days. I was meaning if I had a working 3 way I wouldn’t take it out to fit something else.
 
hi,
reading this with interest.
I few thoughts from my own experience.
over the winter I removed gas completely from the motorhome and put in a bigger (460Ah) battery and a 3KW inverter.
This allowed me to upgrade to combi oven, induction hotplate, large fridge/freezer, domestic water heater, etc. and just back from 4 weeks in the alps with no issues.
I have a few solar panels on the roof and it all seemed to cope rather well.
but, with only 3KW, had to be careful about the hotplate and the oven and only use one at the time or the inverter would shut down momentarely.
but the Fridge/Freezer is the best thing we did. like being in a normal kitchen, lots of room for beer and ice cream :)
if anything, I would go up to 24V by adding another battery, I have seen that I can get different inverters for 24v that can go higher KW and allow for cooker and hotplate to be on at the same time.
all hte best and happy camping
 
nabsim said:
Yes same, I wouldn’t replace a compressor with a 3 way, I don’t use EHU unless it’s a real emergency either but I do use my generator every few days. I was meaning if I had a working 3 way I wouldn’t take it out to fit something else.
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Nikki (very) often says, I'm spending money for the sake of it. TBH, this van bears little resemblance to the one I bought 5years ago. My hobby, and more importantly perhaps, my home 6 or 7 months a year, for the present anyway. At 75, I've no idea how much longer I can continue. Thankfully, the much maligned NHS, replaces any worn out bits for me.
The plan was 10 years, so I'm halfway through. Time to enjoy it, and stop "improving" it ? Easier to say than do, dunno.
Much as it pains me, I'll stick with the 3way, until it fails.
Maybe :unsure:
 
Trotter said:
Nikki (very) often says, I'm spending money for the sake of it. TBH, this van bears little resemblance to the one I bought 5years ago. My hobby, and more importantly perhaps, my home 6 or 7 months a year, for the present anyway. At 75, I've no idea how much longer I can continue. Thankfully, the much maligned NHS, replaces any worn out bits for me.
The plan was 10 years, so I'm halfway through. Time to enjoy it, and stop "improving" it ? Easier to say than do, dunno.
Much as it pains me, I'll stick with the 3way, until it fails.
Maybe :unsure:
Click to expand...
I thought getting a Motorhome (very kindly sold to us at a bargain can't say no price by my late Aunty)
Would mean no more of the electric pfaffing after building our transit ....

Couple of years later and I've replaced the 1 flooded lead acid battery
With 3 x AGMs ...
400w of solar
Victron MPPT controller
Victron battery monitoring
Victron inverter to power domestic 240v fridge
Victron mains charger
Ring rscdc30 B2B (was combined solar but that bit failed )
Teltonika rut 950 mobile router with external antenna
Lift up amplified tv antenna
TV etc
Fitted a Eberspacher in place of the gas fire
Swapped the calor bottles for 2 x gaslow bottles

Seems I'm also an inveterate modifier ...

That said we now have a Motorhome that is actually capable of not needing introvenus electric hook up .
 
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