AC Fridge In Campervan -.Power Consumption Test

[hairydog]

Why is that you assume malice? The title of the thread is clear. You have done loads of measurement. Can you clarify what power the fridge is using in hot weather, or is this all just a pointless exhibition of complex measurements that have no meaning?

 

[wildebus]

In the post, I clearly state that ".... These charts are for the entire day yesterday - midnight to midnight - and show what power is being consumed - not just for the fridge, but in total. However, as per previous discussions and graphs, the fridge has a very distinctive tell-tale when it comes to power use, so it is very easy to spot Fridge Power and non-Fridge power"

So if anyone takes the total figure give, and then says in a reply that my conclusion was all the power used was for the Fridge is clearly either not bothering to read the posts properly - in which case PLEASE REREAD! ; is following their own agenda - in which case go Troll elesewhere; or Just doesn't understand simple maths - in which case ask for help, don't make daft and incorrect conclusions.


Now the purpose of the post? As the quotes from the beginning imply .... What difference does a higher ambient temp make? That is what I was answering rather than how much power is being consumed by the fridge. It is a comparison to how often the compressor comes on compared to cooker temps (as I had already established in previous posts the compressor on time and power used for each cycle and the variation was with the frequency of the on cycle).
If anyone wants to work out the power used specifically by the fridge on the specific day in question, all the info is there in this thread. I am not intending to do so as I have no need to do so as I have worked this out in general terms and have (and posted) enough data to make my conclusions.


Back to adding some members to the ignore list I guess :ninja:

 

[fifthwheel]

Thank you for such a detailed analysis, I have followed every page with interest. I did a very similar test a couple of years ago and posted my results on another self build forum.
My test was not as detailed as yours it was more redneck based as I dont have your level of knowledge when it comes to electronics. My results were convincing enough for me to buy a £75 ac fridge from Currys and use my existing 1000w inverter. I just wish I had at that time a report like yours to refer to, I would have bought a more energy efficient fridge and a psw inverter as my inverter runs the compressor motor too hot. I cant believe any one could post such negativity re your hard work and time spent compiling all this information for the benefit of others, I thought you handled it very well. The cost of 12v fridges I think are just ridiculous compared to 240v this is why I did my testing. I can afford a 12v fridge but hate being ripped off, I shall be going down this route with my van conversion and would like to thank you for your time and trouble making this available to us. regards John.

 

[hairydog]

OK, I'll try again.

Please would you measure how much power your fridge uses in 24 hours during hot weather? Clearly you do have the ability to measure the power used, so it would be useful information to share.

Ideally, the figures would be of the DC power into the inverter but if that also drives other significant loads, the AC power into the fridge would still be useful info.

 

[hairydog]

Over the past three or four days, we have mostly parked in the shade. Certainly for the last two days, the solar panel output has been more or less nil. As a result, the battery bank is down to 90.2% full.

The reason I would like to know how much power an efficient compressor fridge setup uses is to determine how big a battery bank it would need, in addition to domestic loads, in such circumstances.

This is something I can't discover for myself, because my fridge runs on gas.

 

[wildebus]

AC Fridge in a Campervan - The Conclusion.

Over the past three or four days, we have mostly parked in the shade. Certainly for the last two days, the solar panel output has been more or less nil. As a result, the battery bank is down to 90.2% full.

The reason I would like to know how much power an efficient compressor fridge setup uses is to determine how big a battery bank it would need, in addition to domestic loads, in such circumstances.

This is something I can't discover for myself, because my fridge runs on gas.

This may be of interest to you?
First the disclaimer - My Camper is not a lab, I do not check for a "control" to ensure only one thing varies, so while the information I believe is useful and interesting to those so inclined to read and review it, it should be taken for what it is - a snapshot of a single campervan at specific times.

So what an I going to show?
I decided to defrost the fridge after being away at the weekend as the icebox at the top was getting a bit 'furry'. I then later thought this would give me an idea to compare power with fridge on and fridge off with the stats I gather

• At all times the Victron 12/500 Inverter was left on, and in "On" mode (rather than "Eco")
• I chose the time range to monitor the power use to be from 9PM to 5AM as that eliminates external factors such as solar power input, courtesy lights coming on if I enter van (these are wired to leisure battery on my camper), etc.

Note that the Power, Current and Voltage ranges vary slightly between the two days as they are auto-generated (I am using screenshots of Victron VRM charts, not my own generated Excel ones here), so to compare the days for absolute values, please read across to see the values.


Night of July 18/19
The Fridge is running after being defrosted. It has drinks in the door pocket but apart from that is mostly empty.


FridgeON - PIV by David, on Flickr
You see this kind of sawtooth pattern here - each 'tooth' is the fridge coming on for a set time.
When the fridge is on, total power draw is around 52W; When the fridge is off, the total power draw is 18W.
This 18W constant use will be: Inverter O/H, Raspberry Pi computer, Network Router & Wi-Fi Radio Booster, and finally the roof fan (left set to Auto so I cannot be sure if it is actively running or not).

There seems to be two different patterns of Fridge activity which I will guess is a factor of the amount of cooling required. The chart above shows short - 5 minute - bursts of Compressor on-time, but quite frequent. The other (more common pattern looking at historical data) is the Compressor being on less frequently but for a longer time (around 15 mins).

This shows what I am referring to:
Fridge Power Use Pattern last Night

CompPattern-18-19 by David, on Flickr

Fridge Power Use Pattern - same time period a couple of weeks ago

CompPattern-5-6 by David, on Flickr

As can be seen, the power draw when on and when off is identical, and the only difference is the on-duration and its frequency (here is a chart with the two graphs overlaid)

CompPattern-Overlay by David, on Flickr

I suspect the short bursts happen when the fridge is needing more cooling - At the time of the first chart, it was still in the process of bring down the internal temp from the Ambient (defrosted with door open)
As far as numbers go, with the short bursts, it uses 4Wh each time it kicks on (I have added 0.6Wh for the big on-rush that happens each time but lasts just a few seconds).
And the longer but less frequent runs it uses 10Wh each time.
To extrpolate the data for a full day, multiply the number of on-times by the power to get a ballpark figure (remembering not to use the longer on-time duration power use with the more frequent events of course!)


Night of July 16/17
The Fridge was turned off and door left open, but was NOT unplugged (this is relevant!)

FridgeDEFROST - PIV by David, on Flickr
An interesting pattern here - I don't know for sure but I think this is down to the data graphing granularity being limited plus maybe the roof fan motor (I really don't know!). Bear in mind here that each line mark is just a single Watt difference so step changes can appear exaggerated.
The difference here is that the minimum power draw has gone up to 22W from 18W, and starts off a little higher at 27W. I am going to guess that the step-down drop every couple of hours is the Roof Fan slowing down slightly as the ambient temp drops (as mentioned it is automatic and varies the speed depending on difference between ambient temp and target temp set)

Why is the minimum higher now than when the fridge was running? actually very simple to answer that ... The fridge door was open which meant the light was on! that is (I think) a nominal 6W bulb.
If I knew I would be doing some comparisions like this, I would have actually unplugged the fridge (maybe next time I will do so?)



Anyways, that is the minute by minute graphing of the two nights - what is the conclusion?

Here we are with the same times blocked
BLOCKED TIMES ARE RIGHT SO IGNORE FOLLOWING SENTENCE IN BRACKETS (I actually included between 21:00 and 22:00 so ignore first hour in blocked section)
Fridge ON

FridgeON - Consumption by David, on Flickr

Fridge OFF

FridgeDEFROST - Consumption by David, on Flickr

So the Fridge being ON meant over the 8 hours examined, the Fridge drew approx 30Wh more power on the graphs.
Add on the Fridge Light use that shouldn't really have been in the OFF chart (so 6W x 8 Hours) and you will get a total of 78Wh usage over a 8 Hour Period specific to the Fridge being on.
Extrapolate again for a 24 Hour period, and we will get 234Wh in a day (the official specs quote 84kWh/Annum which is 230Wh/Day)

If you want to add in an Inverter overhead, that might be relevant if the Inverter serves just the Fridge (in my Camper, the Inverter has other uses 24/7 so I leave it on regardless of Fridge. The overhead of the Victron is mean to be something like 4W IIRC)

What I can say is that despite the very high temps we have had in the UK recently, the Fridge has worked without a hiccup and food and drink has been kept cold and it has had to work at the same temperature extremes that a Weaco 12V Compressor would (i.e. above the Weaco/Dometic official upper operating limit).
The power usage once at the set temp oddly seems to vary very little no matter whatever the ambient temp is (which will be due to the insulation I guess?). I would have expected it to go up (but at the same time, the solar would harvest more and more than compensate so wouldn't matter)


This may or may not have answered some questions, but that is probably it from me in terms of providing power usage for the fridge installation.

 

[Full Member]

This may be of interest to you?
First the disclaimer - My Camper is not a lab, I do not check for a "control" to ensure only one thing varies, so while the information I believe is useful and interesting to those so inclined to read and review it, it should be taken for what it is - a snapshot of a single campervan at specific times.

So what an I going to show?
I decided to defrost the fridge after being away at the weekend as the icebox at the top was getting a bit 'furry'. I then later thought this would give me an idea to compare power with fridge on and fridge off with the stats I gather

• At all times the Victron 12/500 Inverter was left on, and in "On" mode (rather than "Eco")
• I chose the time range to monitor the power usde to be from 10PM to 5AM as that eliminates external factors such as solar power input, courtesy lights coming on if I enter van (these are wired to leisure battery on my camper), etc.

Note that the Power, Current and Voltage ranges vary slightly between the two days as they are auto-generated (I am using screenshots of Victron VRM charts, not my own generated Excel ones here), so to compare the days for absolute values, please read across to see the values.


Night of July 18/19
The Fridge is running after being defrosted. It has drinks in the door pocket but apart from that is mostly empty.


FridgeON - PIV by David, on Flickr
You see this kind of sawtooth pattern here - each 'tooth' is the fridge coming on for a set time.
When the fridge is on, total power draw is around 52W; When the fridge is off, the total power draw is 18W.
This 18W constant use will be: Inverter O/H, Raspberry Pi computer, Network Router & Wi-Fi Radio Booster, and finally the roof fan (left set to Auto so I cannot be sure if it is actively running or not).

There seems to be two different patterns of Fridge activity which I will guess is a factor of the amount of cooling required. The chart above shows short - 5 minute - bursts of Compressor on-time, but quite frequent. The other (more common pattern looking at historical data) is the Compressor being on less frequently but for a longer time (around 15 mins).

This shows what I am referring to:
Fridge Power Use Pattern last Night

CompPattern-18-19 by David, on Flickr

Fridge Power Use Pattern - same time period a couple of weeks ago

CompPattern-5-6 by David, on Flickr

As can be seen, the power draw when on and when off is identical, and the only difference is the on-duration and its frequency (here is a chart with the two graphs overlaid)

CompPattern-Overlay by David, on Flickr

I suspect the short bursts happen when the fridge is needing more cooling - At the time of the first chart, it was still in the process of bring down the internal temp from the Ambient (defrosted with door open)
As far as numbers go, with the short bursts, it uses 4Wh each time it kicks on (I have added 0.6Wh for the big on-rush that happens each time but lasts just a few seconds).
And the longer but less frequent runs it uses 10Wh each time.
To extrpolate the data for a full day, multiply the number of on-times by the power to get a ballpark figure (remembering not to use the longer on-time duration power use with the more frequent events of course!)


Night of July 16/17
The Fridge was turned off and door left open, but was NOT unplugged (this is relevant!)

FridgeDEFROST - PIV by David, on Flickr
An interesting pattern here - I don't know for sure but I think this is down to the data graphing granularity being limited plus maybe the roof fan motor (I really don't know!). Bear in mind here that each line mark is just a single Watt difference so step changes can appear exaggerated.
The difference here is that the minimum power draw has gone up to 22W from 18W, and starts off a little higher at 27W. I am going to guess that the step-down drop every couple of hours is the Roof Fan slowing down slightly as the ambient temp drops (as mentioned it is automatic and varies the speed depending on difference between ambient temp and target temp set)

Why is the minimum higher now than when the fridge was running? actually very simple to answer that ... The fridge door was open which meant the light was on! that is (I think) a nominal 6W bulb.
If I knew I would be doing some comparisions like this, I would have actually unplugged the fridge (maybe next time I will do so?)



Anyways, that is the minute by minute graphing of the two nights - what is the conclusion?

Here we are with the same times blocked (I actually included between 21:00 and 22:00 so ignore first hour in blocked section)
Fridge ON

FridgeON - Consumption by David, on Flickr

Fridge OFF

FridgeDEFROST - Consumption by David, on Flickr

So the Fridge being ON meant over the 7 hours examined, the Fridge drew approx 30Wh more power on the graphs.
Add on the Fridge Light use that shouldn't really have been in the OFF chart (so 6W x 7 Hours) and you will get a total of 72Wh over a 7 Hour Period specific to the Fridge being on.
Extrapolate again for a 24 Hour period, and we will get 245Wh in a day (the official specs quote 84kWh/Annum which is 230Wh/Day)

If you want to add in an Inverter overhead, that might be relevant if the Inverter serves just the Fridge (in my Camper, the Inverter has other uses 24/7 so I leave it on regardless of Fridge. The overhead of the Victron is mean to be something like 4W IIRC)

What I can say is that despite the very high temps we have had in the UK recently, the Fridge has worked without a hiccup and food and drink has been kept cold and it has had to work at the same temperature extremes that a Weaco 12V Compressor would (i.e. above the Weaco/Dometic official upper operating limit).
The power usage once at the set temp oddly seems to vary very little no matter whatever the ambient temp is (which will be due to the insulation I guess?). I would have expected it to go up (but at the same time, the solar would harvest more and more than compensate so wouldn't matter)


This may or may not have answered some questions, but that is probably it from me in terms of providing power usage for the fridge installation.

That's a very good piece of work, very well presented.
We often have opinions. It's great to have facts.
We'll done and thank you, wildebus. You've set the bar high throughout this thread.

Colin ???

 

[Nabsim]

Great stuff Dave. My Waeco has been working brilliantly through the hot weather with everything chilled nicely so at the moment I have no need to change. If/when the day comes though I will be looking up your (hopefully old by then) threads and looking at AC fridge

 

[hairydog]

This may be of interest to you?
This may or may not have answered some questions, but that is probably it from me in terms of providing power usage for the fridge installation.

It's very interesting, but couldn't you pick one fairly warm day, disconnect the solar panel and see how much power the fridge uses in a 24 hour period including a typical summer's day? That would seem to give a clear indication without taking all that much effort.

Do the fans run on mains voltage? If the only thing using mains is the fridge, fitting a standalone power meter on the inverter input would give the figures more easily, though you'd not get the fancy graphs.

[later]This is the sort of thing I mean: In fact I think this is the model I have, and it seems to work very well. Digital LCD Watt Meter Voltmeter Ammeter Battery Balance 60V100A DC RC Amp Analy Voltage Current Energy Power Tester- US$10.08 online shopping | NewFrog.com or Digital Monitor LCD Watt Meter 60V/100A DC Ammeter RC Battery Power Amp Analyzer 6666964554023 | eBay

 

[hairydog]

So the Fridge being ON meant over the 8 hours examined, the Fridge drew approx 30Wh more power on the graphs.
Add on the Fridge Light use that shouldn't really have been in the OFF chart (so 6W x 8 Hours) and you will get a total of 78Wh usage over a 8 Hour Period specific to the Fridge being on.
Extrapolate again for a 24 Hour period, and we will get 234Wh in a day (the official specs quote 84kWh/Annum which is 230Wh/Day)

If you want to add in an Inverter overhead, that might be relevant if the Inverter serves just the Fridge (in my Camper, the Inverter has other uses 24/7 so I leave it on regardless of Fridge. The overhead of the Victron is mean to be something like 4W IIRC)

So with the inverter overhead, you are looking at about 234 + 96 = 330Wh per day to run the fridge.

 

[wildebus]

Probably about the 330Wh mark - more than a 12V fridge when you include the inverter, but less than a 12V fridge without the Inverter.
As said, I use the inverter for other things anyway - primarily the network router and WiFi booster, but also laptop charging and power tool battery charging.
I know people say "get a 12 version of [insert device here]" but I don't go along with that idea TBH. Yes. It is more energy efficient but very inefficient financially - if you have a 240V charger why spend more money on a 12V charger, and then repeat multiple times? The amount spent doing that would likely buy an extra battery
Fan is 12V (it is a MaxxAir 7500k fan )

I could repeat the tests in hundreds of different combinations but I have reached the conclusions I need to and the various information items I have posted over time on this thread (including in weather at the other extreme) can be used by people to draw their own conclusions about this option.

 

[wildebus]

It's very interesting, but couldn't you pick one fairly warm day, disconnect the solar panel and see how much power the fridge uses in a 24 hour period including a typical summer's day? That would seem to give a clear indication without taking all that much effort.

Do the fans run on mains voltage? If the only thing using mains is the fridge, fitting a standalone power meter on the inverter input would give the figures more easily, though you'd not get the fancy graphs.

[later]This is the sort of thing I mean: In fact I think this is the model I have, and it seems to work very well. Digital LCD Watt Meter Voltmeter Ammeter Battery Balance 60V100A DC RC Amp Analy Voltage Current Energy Power Tester- US$10.08 online shopping | NewFrog.com or Digital Monitor LCD Watt Meter 60V/100A DC Ammeter RC Battery Power Amp Analyzer 6666964554023 | eBay

Ref your first point, I really don't need to do that as I know precisely how much power is consumed and precisely how much the solar array is providing with the data provided by the MPPT controller and the BMV-712 monitor feeding into a Victron Venus GX system which does the minute by minute collation. (I can download the spreadsheets as well if I want to).
You will have noticed in the last charts it is showing consumption and where the power is from - Battery or Solar. I can alsos select "Solar" and see how the solar is being used; or just see the two side by side.
I chose the time range I did as it shows the current and voltage changes which is of passing interest (at least to myself) without the effect of solar.

Oh. The items I listed using power generally ... I should have also included an add-on fridge fan (set to come on at 30C so probably on very little overnight) and a 4G Nokia Mobile on permanent charge (used as a dedicated MiFi)

 

[hairydog]

It seems to me that for many people (athough not in your setup) it could make sense to use a dedicated inverter to power the fridge, using the fridge's thermostat to turn power to the inverter on and off.

That way you'd get lower inverter losses. Perhaps saving about 50 watt hours a day.

I'm not sure whether you could use a cheap MSW inverter. An electic motor might not be as power efficient with a lumpy waveform.

 

[wildebus]

It seems to me that for many people (athough not in your setup) it could make sense to use a dedicated inverter to power the fridge, using the fridge's thermostat to turn power to the inverter on and off.

That way you'd get lower inverter losses. Perhaps saving about 50 watt hours a day.

I'm not sure whether you could use a cheap MSW inverter. An electic motor might not be as power efficient with a lumpy waveform.

Your suggestion would work quite well I think, but would need some additional gizmo between thermostat and inverter (as the thermostat would not supply any power to switch on the inverter as the inverter is off and so the fridge will have no power). The controller I am using to activate the extra fan for the compressor would work maybe but that has an on-off range of 3 degrees and maybe needs to be tighter?

The Victron Inverter I am using has an eco mode, and turns on when it detects a demand - but I found that a fridge does not activate it. (I didn't investigate this much as , as said, I want the inverter on generally anyway).

 

[Fletch6]

.

 

[wildebus]

I think Hairydog means run the 12v power supply wiring through the stat for the inverter, the original 230v wires on the stat would need to be shorted together.

probably - not something that I need to think about it

What could well be possible is using the remote wired feature on the Victron Inverters where instead of having the remote link shorted, you just run that link to the 'stat and back, so no addtional power supply required and also when the inverter has power removed (as opposed to being just off), there is no power going to the fridge - either 230V or 12V.
This is probably what I would do if I had a need to. But as I don't, I won't

 

[hairydog]

I think Hairydog means run the 12v power supply wiring through the stat for the inverter, the original 230v wires on the stat would need to be shorted together.

What I had in mind was using the 230v thermostat contacts to switch on and off power to the inverter (though a relay), which I'd do by cutting into the wiring between the thermostat and the fridge, and yes, the fridge side of the cut wires would need to be shorted together.

The only issue I can see is that the interior light wouldn't work unless the compressor was running.

 

[wildebus]

Could you just put the thermostat on full (or as cold as you would ever want), and not change any wiring anywhere within the Fridge - then use a separate temp probe which goes to a controller (such as the one I am using for my fan control) to turn the inverter on and off when it hits the required threshold?
This might simplify mucking around with dismantling bits and pieces of the actual fridge which could be awkward?


This is something I might have a play with actually out of curiosity and also could be of some worth over the winter where I generally won't be using the camper as a camper but might want to keep the fridge going in readiness? The Solar Array might have issues keeping up if extended non-use, especially if we have snow again, so this would extend the time if I can't be bothered to hookup at home.
(It doesn't matter in that scenario if the network router and Booster has no power as the Raspberry Pi will revert to using a WiFi connection direct to the mobile phone rather than its normal route of the router)

PS - the light is a good clue when I tried the Victron in ECO mode when first playing around, when I opened the door the light would come on every 10 seconds momentarily as the Inverter was checking for a load - and the light was not a great enough load (needed >15W to activate)

 

[Derekoak]

Victron inverter

@wildebus can you tell me what exact model inverter you used and a cheap place to get it?

 

[hairydog]

If getting into the fridge wiring is difficult, you could do that, but then you lose the option of using the fridge's temperature control.