AC Fridge In Campervan -.Power Consumption Test

Nabsim said:

If that was pained red Dave I would say it was my Bestek 300w unit. I did post what mine used when plugged in but no load a bit back. Got stuff on at the moment so cant check but I think it was either 0.1 or 0.2 amp

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The Bestek Red one on Amazon looks identical.
100% sure it is just a rebadged Bestek for what is likely to be the first of a range of Amazon OEM Inverters (which to me bodes well as Amazon have the resources to do much more extensive testing and QA then just about anyone else)

xsilvergs said:

What current draw is there when it has no load on the output?

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I checked this but forgot to post ... looks like 0.4A

wildebus said:

I checked this but forgot to post ... looks like 0.4A

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Thanks for info, so approximately 4.8 Watts.
Victron quote for the 12/500 Phoenix in ECO mode 1 Watt! I haven't checked it myself.

So to power a thermostatically controlled fridge which may only run for 12 minutes in an hour the next 48 minutes are spent consuming/wasting, in this example 3.8 Watts over a Victron inverter.

I only use this case as an example of how power can be saved or wasted!

Thanks again for answering my question as I had no idea of the difference.

Yup. seems right. this little inverter has just an on-off switch, nothing fancy. Running a compressor fridge which may have a duty cycle of say 20% (so on 12 minutes in every hour) with an inverter that is always on will certainly eat more power than one with an power saving mode.
And what makes it worse is that because you need an inverter that will cope with the inrush, you have to 'oversize' it compared to what the fridge needs 99% of the time - and a bigger inverter will also have a bigger overhead.

The Multiplus's have quite a neat setup - it is called AES in their case (think it stands for "Advanced Energy Saving"?) - See the lower part of the screenshot below

And Victrons short explanation

AES type
The inverter supports two methods of power reduction (not available on all models) when there is no or low load connected.
Both of them change the output of the inverter.


The first method is called "modified sine wave".
This waveshape reduces the RMS value of the output while it maintains the peak voltage. This will result in a lower power consumption.


The second method is called "search mode" and it will reduce the power consumption even further than the "modified sine wave" method. The output is switched off during most of the time and approximate once per 2 seconds the output is switched on as shown below. When a load is detected the output will remain on.
Disadvantage of this option is that it can take some time (at most about 1 second) before the inverter detects that a load is connected.
If this is unacceptable one should choose the "modified sine wave" option.

I use the AES in my setup and find it is very effective, but you do need to set the start and stop wattages up right for best effect.
I found 'search mode' works well - there is a pulse of power every few seconds when the inverter wakes up to check for demand. The effect is that the mains tester (tend to leave it plugged in) flashes on (makes it look like a car alarm which is handy actually ) and if I open the fridge door, the light flashes on in the same way.
I also tried the first 'modified sine wave' method that worked but did use more power. In this case the fridge light would be dimmer than normal when the fridge wasn't running but would stay on and not flash on and off - handier really, but the better power consumpion of 'search mode' won the day.
Downside of 'search mode' in my setup was the Induction Hob beeps everytime it gets power - so every few seconds .. Beep! Adding a spur switch fixed that
Search mode is meant to use something like 1-2W off-load I think. Modified sine wave method is a fair bit higher (14W off-load from memory?)

High end Samsung fridges have variable speed compressors. Hopefully when that technology filters down we'll be able to use small inverters as the inrush current will be comparatively small too.

Just finalising control of my 3-Way Thetford fridge freezer. The idea is, when the AGM battery is charging from solar and the Victron MPPT goes into Absorption or Float mode the inverter can be enabled. The fridge then switches from gas to inverter thus saving me gas. Should the MPPT switch to either Bulk or Off (at night) the inverter is disabled and the fridge returns to gas.



The controls are simple, Auto uses the above method to control the inverter, ON allows manual use of the inverter at any time, OFF disables the inverter.



There may be a need to use % SOC as a switch point, luckily the BMV gives that.

Let the testing begin.

Looks good. I will have a proper look at the diagram when on the computer (tablet screen too small to really view it).

As an aside, using the BMV relay for power control when controlled by the SOC adds a slight annoyance to the info it gives I found
The monitor has a "Time Remaining" indication, which is based on how much time is left at the current power draw to hit your minimum SOC.
But ... That SOC seems to be set by the value you use to control the Relay - so if you use the relay as a way to utilize high battery levels rather than warn of low ones, the SOC will be set a lot higher (mine is set to 96% to control the water heater, for example) and the Time Remaining indication is therefore way too low, and any alarms linked to it would be misleading.

I guess if you used it this way, you could regard the "Time Remaining" number as not being the actual battery bank remaining, but for how much longer the fridge might be running off the battery for?

wildebus said:

Looks good. I will have a proper look at the diagram when on the computer (tablet screen too small to really view it).

As an aside, using the BMV relay for power control when controlled by the SOC adds a slight annoyance to the info it gives I found
The monitor has a "Time Remaining" indication, which is based on how much time is left at the current power draw to hit your minimum SOC.
But ... That SOC seems to be set by the value you use to control the Relay - so if you use the relay as a way to utilize high battery levels rather than warn of low ones, the SOC will be set a lot higher (mine is set to 96% to control the water heater, for example) and the Time Remaining indication is therefore way too low, and any alarms linked to it would be misleading.

I guess if you used it this way, you could regard the "Time Remaining" number as not being the actual battery bank remaining, but for how much longer the fridge might be running off the battery for?

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I use the RPi which is doing all logging and gives the GUI, the Pi talks to an Arduino which happens to be sat near the Inverter. The Pi does the logic and send instructions to the Arduino which has a relay attached and operates the inverters remote. The Arduino has only been measuring Leisure battery temp so far.

ah yes, when you said "....There may be a need to use % SOC as a switch point, luckily the BMV gives that ", I was thinking BMV relay as opposed to BMV information.

Have you had to add any hardware to control the inverter on-off or is there an "remote input" on the inverter controller that lets you add external switching when in Auto mode? (not sure what inverter you have?)

There was only one inverter, had to be Victron.
Arduino clone and a relay board, control of Arduino is two way over MQTT from RPi.

Has anyone figured out where the evaporator coils are in this inventor fridge? I think they're in the sides as that's the area that seems to get hot when faced with 30c in the van. I've rigged up a fan to cool the compressor as that just runs constantly, but can't help thinking one of those fridges with evaporator coils at the back would be more efficient in the heat, as I could get a fan on them too, also they'd be outside the body of the fridge, rather than inside.
Most websites don't show the back of fridges in their numerous photos, but something like this might work better in the summer.

My fridge has the radiator on the back. I can’t remember the make until I look at it. I have two fans to pull out the hot air.

Found the inventor fridge on ebay for 89.99 as a rebranded cookology. It has slight differences, such as a T rating which is better, but it's clearly the same brand. Here's the 2 for comparison.

It does look very similar. The Temp setting dial is fitted a little differently (and better placed than the inventor - that dial is probably the only thing that annoys me with the Inventor).

However .... one comment - this is quoted as an A+ Energy Rating rather than an A++ rating that the Inventor has.
This is the info from the Inverter listing on Amazon

• Energy Class A++ (20% Lower Power Consumption than any A+ Mini Fridge)
• Low Noise Level 42dB(A), Ideal for office, bedrooms, kitchen

I'd ask for the info on the Energy Sticker that I think all white goods have to have nowadays? This is the Inventors one.

As an update to my Thetford 3-way Fridge Freezer running from a Victron 12/500 Phoenix pure sine inverter powered from a Varta 95Ah AGM battery. With the fridge in auto mode it favours 230v AC over LPG. There is 400 watts of solar panel (2 x 150W and 1 x 100W) and the peak over the 5 days was 303 Watts.

The inverter is in ECO mode, I have adjusted the search interval to 2 seconds and search time is 0.2 seconds. With these settings the inverter will power the fridge without the gas kicking in first.

This weekend we have been at the Motorhomer Rally in the New Forest near Lymington where the weather has been hot and sunny with some cloud's.

The inverter is controlled by a Raspberry Pi which obtains the SOC of the battery from the BMV-712. When the SOC is greater than 92% the inverter is switched on and stays on until the SOC drops 89%. Once the SOC drops below 89% the inverter is disabled, the RPi then waits for the solar to raise the SOC back to 92% before enabling the inverter. This hysteresis stops the inverter kicking in and out close to the switching points.

I am very happy and surprised how well this setup has worked and how little LPG has been required to run the fridge. Although LPG is cheap, solar energy is free, and should the gas run out I would have to drive to refill it.

In the periods were the battery is above 92% SOC and the fridge is not demanding power the available energy could be used to heat the water in the Truma.

The two 150W panels are manually tiltable to about 45 degrees. One thing I noticed: All panels were laying horizontal and at around 8 am there was 115 Watts measured by the MPPT as it charged the battery after the previous evenings TV and YouTube viewing. Raising the East facing 150W panel from 0* to 45* increased the collected Watts by 60 taking the total to approx 175W! If I could have raised the second panel without casting shadows the sooner the battery would have been charged quicker further reducing gas consumption.

We had a great weekend, thanks Sue, Martin (aka Moonshadow) and Geeky Phillip.

xsilvergs said:

As an update to my Thetford 3-way Fridge Freezer running from a Victron 12/500 Phoenix pure sine inverter powered from a Varta 95Ah AGM battery. With the fridge in auto mode it favours 230v AC over LPG. There is 400 watts of solar panel (2 x 150W and 1 x 100W) and the peak over the 5 days was 303 Watts.

The inverter is in ECO mode, I have adjusted the search interval to 2 seconds and search time is 0.2 seconds. With these settings the inverter will power the fridge without the gas kicking in first.

This weekend we have been at the Motorhomer Rally in the New Forest near Lymington where the weather has been hot and sunny with some cloud's.

The inverter is controlled by a Raspberry Pi which obtains the SOC of the battery from the BMV-712. When the SOC is greater than 92% the inverter is switched on and stays on until the SOC drops 89%. Once the SOC drops below 89% the inverter is disabled, the RPi then waits for the solar to raise the SOC back to 92% before enabling the inverter. This hysteresis stops the inverter kicking in and out close to the switching points.

I am very happy and surprised how well this setup has worked and how little LPG has been required to run the fridge. Although LPG is cheap, solar energy is free, and should the gas run out I would have to drive to refill it.

In the periods were the battery is above 92% SOC and the fridge is not demanding power the available energy could be used to heat the water in the Truma.
....

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This is very interesting
I have not possessed a 3-way fridge, or analysed their power use, but my understanding of them was their power demand did not tend to cut in and out but was much more constant. But it sounds like in your experience above, when the inverter is enabled (SOC above 92%), the Fridge will not cause the inverter to be on always as there is not a constant demand, but will cut in or out in a similar way to how a Compressor Fridge?

Do you know how much battery power the Fridge is using over a time period?
I am quite likely getting another motorhome which is, like the majority are, Gas-orientated. I am hoping to change the emphasis to electric supply, but without changing appliances - and your finding on the 3-way fridge makes me think I could run the 3-way fridge much more on 230V Inverted power than I had expected?

wildebus said:

This is very interesting
I have not possessed a 3-way fridge, or analysed their power use, but my understanding of them was their power demand did not tend to cut in and out but was much more constant. But it sounds like in your experience above, when the inverter is enabled (SOC above 92%), the Fridge will not cause the inverter to be on always as there is not a constant demand, but will cut in or out in a similar way to how a Compressor Fridge?

Do you know how much battery power the Fridge is using over a time period?
I am quite likely getting another motorhome which is, like the majority are, Gas-orientated. I am hoping to change the emphasis to electric supply, but without changing appliances - and your finding on the 3-way fridge makes me think I could run the 3-way fridge much more on 230V Inverted power than I had expected?

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I hope to be working in the van tomorrow, I'll have a look if I get time.

Our Thetford is an N3150, we usually run it on setting "1" which is the lowest (less cold), "5" being the highest (most cold) so one would assume it uses minimum power. At setting "1" our fridge is at around +6 to +7*C and the freezer is around -10*C. If the battery had depleted to 89% SOC and the fridge required more cooling it automatically reverted to gas for a short period of time.

I think (will confirm tomorrow) the DC current draw is about 17 Amps when running. There is no current shown in the Victron phone app. Looking at the VE.Direct Protocol (section 2.5) I may be able to read current using HEX through the VE.Direct port, but that's on the to-do list.

Have you got the Inverter connected to the Pi? I have not connected one of the Phoenix inverters to a Venus systems so not sure what level of data you can get (I think AC info is restricted to Multiplus type kit?)
17A DC is a fair amount of power use (~200W ish) so running on Batteries won't be a option for long I guess, but handy if good solar harvesting with nowhere else to go.

I wonder what is least efficient on Gas in terms of Motorhome Dual Fuel Gas/Electric Applicances? Fridge, Water Heater or Cooker? Just thinking that if you are using all three when off-grid and have good harvesting, which device should you use with your excess Electricity for the best return?
I suspect Cooking might be the one with the open flames heating the atmosphere rather than the food, but then that air heating could be useful if you wanted the heater on anyway of course. Summertime, cooking with spare electric could beat cooling on electric?

wildebus said:

Have you got the Inverter connected to the Pi? I have not connected one of the Phoenix inverters to a Venus systems so not sure what level of data you can get (I think AC info is restricted to Multiplus type kit?)
17A DC is a fair amount of power use (~200W ish) so running on Batteries won't be a option for long I guess, but handy with good solar harvesting with nowhere else to go.

I wonder what is least efficient on Gas in terms of Motorhome Dual Fuel Gas/Electric Applicances? Fridge, Water Heater or Cooker? Just thinking that if you are using all three when off-grid and have good harvesting, which device should you use with your excess Electricity for the best return?
I suspect Cooking might be the one with the open flames heating the atmosphere rather than the food, but then that air heating could be useful if you wanted the heater on anyway of course. Summertime, cooking with spare electric could beat cooling on electric?

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At this moment the RPi is reading data from all devices over USB or communicating with more distant devices via Arduino over WiFi.

For example, when it's time to turn the Inverter on it tells the Arduino which enables a relay. The relays contacts operate the Phoenix via its Remote connection.

In future I hope to dispense with the really and use HEX over the VE.Direct where the Bluetooth goes in.

We have a propane range style cooker at work and are still on the same 47kg cylinder for the last 8 years. When I lived in Wiltshire (no gas in village) a 47kg would last around 2 1/2 years at home. Murky was first fitted with a gas/mains caver water heater. It did seem to get through more gas than I would have liked. Hence the conversion to the calorifier. Though the down side of cooking with gas is the condensation