[Imp]

Have just fitted a 240v Cookology fridge in my Citroen edispatch .

My original inverter, which I have had some time, is a 2000w and had no problems with it.
It's powered my induction job with no worries.

I have now connected it up to the 0.45w fridge and it keeps knocking out the inverter.
Thinking its the wiring so I have plugged it directly in to the inverter but same thing happens so tried disconnected the earth, no good.

Have had it connected to house mains with no problem?

Any one any ideas I may try.

 

[farmergiles]

Is it a compressor fridge? If so, it maybe the switch on surge as the motor starts (inductive load).

 

[Imp]

Is it a compressor fridge? If so, it maybe the switch on surge as the motor starts (inductive load).

Thanks for your quick response.
Yes it is compressor type, the problem is it starts OK then after an indeterminate time it cuts out.

 

[farmergiles]

Thanks for your quick response.
Yes it is compressor type, the problem is it starts OK then after an indeterminate time it cuts out.

That's surprising for a 2kw inverter but other than trying a different brand, I can't think of an explanation. Presumably the inverter does not heat up nor display a low battery light?

 

[Tandy0]

I think you maybe need a better inverter. I bet a heating appliance would work on any old waveform. Maybe look for a 'pure sine wave' inverter.

 

[Jeremy Harris]

As above, a pure sine wave inverter may well give better performance than a modified sine wave model, especially with a reactive load like a fridge compressor. The other thing worth noting is that inverter power ratings are often exceedingly optimistic. I've seen one rated at 4,000 W that in reality struggled to run a ~600 W load. It's almost as if some of the manufacturers just make up the numbers, so they look good.

Checking the wiring is definitely a good thing to do, as an inverter does draw a lot of current from the 12 V supply. Almost all of them have low voltage protection, so will shut down when the voltage at the internal 12 V terminals reaches a low voltage threshold, that could be around 10 V for some models. At 450 W on the 230 VAC side, and allowing for 85% efficiency, a 12 V inverter is going to draw around 44 A, so needs not just pretty hefty wiring, but also low resistance connections. It only takes a resistance of around 0.045Ω to drop a couple of volts with a load of 450 W. Even a very slightly loose connection could easily introduce that sort of resistance, and the cable needs to be pretty hefty too, at least 6mm². and ideally around 10mm², perhaps bigger if the run is more than a couple of metres.

 

[mikegs]

I've seen one rated at 4,000 W

The Chinese eBay Watt is generally accepted to be about 1/10th of an SI Watt. Common error in the unwary.

 

[farmergiles]

As above, a pure sine wave inverter may well give better performance than a modified sine wave model, especially with a reactive load like a fridge compressor. The other thing worth noting is that inverter power ratings are often exceedingly optimistic. I've seen one rated at 4,000 W that in reality struggled to run a ~600 W load. It's almost as if some of the manufacturers just make up the numbers, so they look good.

Checking the wiring is definitely a good thing to do, as an inverter does draw a lot of current from the 12 V supply. Almost all of them have low voltage protection, so will shut down when the voltage at the internal 12 V terminals reaches a low voltage threshold, that could be around 10 V for some models. At 450 W on the 230 VAC side, and allowing for 85% efficiency, a 12 V inverter is going to draw around 44 A, so needs not just pretty hefty wiring, but also low resistance connections. It only takes a resistance of around 0.045Ω to drop a couple of volts with a load of 450 W. Even a very slightly loose connection could easily introduce that sort of resistance, and the cable needs to be pretty hefty too, at least 6mm². and ideally around 10mm², perhaps bigger if the run is more than a couple of metres.

I don't think his fridge is 450w, but 45litres & 65watts otherwise it would be massive. Compressor fridges are usually well under 100watts - 45-65w commonly. Which is all the more surprising that he has a problem.

 

[Jeremy Harris]

I don't think his fridge is 450w, but 45litres & 65watts otherwise it would be massive. Compressor fridges are usually well under 100watts - 45-65w commonly. Which is all the more surprising that he has a problem.

Good point, that does seem to be on the high side for a fridge. Just did a quick reality check to see roughly what a fridge might draw on start up, by unplugging our fridge/freezer, leaving it for half an hour then plugging it in with a monitor inline. At start up it drew about 5.6 A from a 244 VAC supply for about 1.6 seconds, then settled back down to about 2.1 A as the steady state running current. Obviously this was for a much bigger unit, but the ratio of start up to run power may be about the same.

The start up power was a surprisingly high 1,366 W for about 1.6 seconds, with a run power of 512 W. The run power won't be anything like the continuous power, as it tends to run for a relatively short time, then shuts down for ages before starting up again. According to the label, the average run power works out to be about 28 W, so clearly the thing runs at a fairly low duty cycle.

Still, the relatively high starting power, perhaps together with a power factor that may be well off unity during the start up phase, might be enough to upset a modified square wave inverter. The PF, in particular, might be an issue. During start up, the PF I measured dropped to about 0.58, although when running it was up around 0.95. I do know that some inverters don't handle reactive loads that well, and with a PF of around 0.6 at start up, combined with the 2 to 3 times higher starting current, it seems possible that the inverter was being quite heavily loaded, in terms of the current (rather than true power) it was being asked to supply.

 

[farmergiles]

Still, the relatively high starting power, perhaps together with a power factor that may be well off unity during the start up phase, might be enough to upset a modified square wave inverter. The PF, in particular, might be an issue. During start up, the PF I measured dropped to about 0.58, although when running it was up around 0.95. I do know that some inverters don't handle reactive loads that well, and with a PF of around 0.6 at start up, combined with the 2 to 3 times higher starting current, it seems possible that the inverter was being quite heavily loaded, in terms of the current (rather than true power) it was being asked to supply.

Yes, could well be the PF causing the random shutting down but still strange that the fridge always started.

 

[Jeremy Harris]

Yes, could well be the PF causing the random shutting down but still strange that the fridge always started.

It may be that the inverter low voltage protection circuit has a time delay, perhaps to try and prevent it tripping out on short duration surges. Hard to do a remote diagnosis without being able to see the cables, connections etc, but I could imagine a scenario where the fridge perhaps stays in start up mode for too long, perhaps because the voltage dips, or because the inverter has a problem with the PF. I know that most fridges have a start/run relay that is either current operated or operated via a PTC element. It may be that this is a bit sluggish, perhaps, so holding the compressor in start mode for too long. It would seem to work OK like this, but the current drawn would be a lot higher. Coupled with the probable time delay on the low voltage shutdown in the inverter, and, perhaps, a higher than acceptable voltage drop on the supply to the inverter, this might be the cause.

 

[Orrery]

My whole house has a background usage of under 400W - that with 2 fridges, a freezer and and fridge/freezer and whole lot of other things going on.

 

[Imp]

My apologies to all of you about the fridge I said it was 0.45 w, that should have been amps which you guessed any way.
The next is that the inverter is pure sine wave 2000w running at 240v.

Today I plugged it in to the Nissan env 2000 which we also have, which has a 2000w inverter running at 220v not as good as the other and I have had no problem running the fridge.
I also tried out the fridge when we first got, on a 5000w inverter in the house, as we are off grid, again no problem.

I have a 1800w electric water heater so tried that on the the one giving problems, it heated up the water and the thermostat switched it off with no problems.
I have to say the 25mm cable did get warm which is to be expected.

The inverter had no problems running an induction hob which we have used for 2 yrs.

So the only thing I can think is that there is a problem with the cheap Chinese fridge and the inverter , therefore new inverter!!!

To all of you who have put forward all your great ideas, thank you, sorry if I was a bit misleading in my first letter.