Inverters - MSW or PSW?

[Neil2]

Having dithered about it most of this year I'm finally coming round to the idea that it makes more sense to run a 240v fridge from an inverter than shell out for a 12v fridge.

 

I don't have either a fridge or an inverter at the moment, the issue is primarily whether I get pure sine wave or modified sine wave.

 

Given that I don't intend to use the inverter for much else other than running the fridge, a MSW inverter would seem to be the way to go. However, I have a slight concern from reading comments about how MSW devices are less efficient when used to power induction motors, that the motors tend to run hotter and therefore have a lower life expectancy than if used with a PSW inverter.

 

Is this something to be concerned about and/or are there any other factors I should take into account?

 

 

[nicknorman]

I would use PSW for a fridge on 24/7 whereby power consumption is an important issue. I'm not even totally sure the fridge motor would start on MSW. Is there that much difference in price these days?

[Alf27]

I run our 240v fridge with a MSW inverter, the fridge runs fine. You can get good 240v fridges for under £100 where as 12v fridges are considerably more expensive.

[Detling]

I have a victron PSW which has a fairly high idle current about 1.5 amps, when the fridge is running the current goes up to 6 amps for a few minutes and then back to 1.5 amps etc. I thought I would be clever and got myself a small MSW which had an idle current of less than 1/2 an amp. so I wired it in and fridge ran fine, but the current to the inverter was 10 amps fridge on not 6 as the PSW used. As the big PSW uses about the same amp hour total in a day as the little MSW it is easier to leave the big one on and only have one thing to fail and not two. Also the small MSW had a cooling fan that was permanently running and seemed noisy at night, it may have been possible to fit a thermo switch but it would still need to run when on load whereas the big victron can run the fridge without using it's fan so it is silent. .

[Neil2]

I have a victron PSW which has a fairly high idle current about 1.5 amps, when the fridge is running the current goes up to 6 amps for a few minutes and then back to 1.5 amps etc. I thought I would be clever and got myself a small MSW which had an idle current of less than 1/2 an amp. so I wired it in and fridge ran fine, but the current to the inverter was 10 amps fridge on not 6 as the PSW used. As the big PSW uses about the same amp hour total in a day as the little MSW it is easier to leave the big one on and only have one thing to fail and not two. Also the small MSW had a cooling fan that was permanently running and seemed noisy at night, it may have been possible to fit a thermo switch but it would still need to run when on load whereas the big victron can run the fridge without using it's fan so it is silent. .

That's interesting - having read a bit about the differences I also thought the lower quiescent or "idle" current of a typical MSW might offset the drop in efficiency compared to a PSW but it seems not.

 

I read somewhere that MSW inverters are typically about 20% less efficient at powering induction motors but your experience suggests it's worse than that. Must admit I'm still concerned about the effect of using a "dirty" current which a domestic fridge isn't designed for.

[Tony Brooks]

The other thing to consider is that a PSW inverter will run just about everything within its power range where as we have heard about MSW inverters destroying expensive electrical items like toothbrushes and hair "tongs". They may also induce interference of one sort or another on mains audio-visual equipment.

[Guest]

Just a thought...

Has anyone ever considered using a dedicated inverter for a 240V fridge, and modifying so the thermostat switches the 12V feed to the inverter?

Would remove idle current, but not sure how inverters behave when first switched on - with a load!

[Neil2]

Just a thought...

Has anyone ever considered using a dedicated inverter for a 240V fridge, and modifying so the thermostat switches the 12V feed to the inverter?

Would remove idle current, but not sure how inverters behave when first switched on - with a load!

It's an interesting possibility, I must admit I feel a little back at square one with this as the PSW inverters I've looked at idle at up to 6A which is ridiculous when all I intend to run is a fridge. That was part of the appeal of the MSW units which have much lower idle currents.

 

It must be possible to rig up a separate thermostat control to switch the inverter supply on and off but I too am not sure what effect this would have on an inverter connected to a motor already under load, which is what a fridge compressor is.

[jelunga]

It's an interesting possibility, I must admit I feel a little back at square one with this as the PSW inverters I've looked at idle at up to 6A which is ridiculous when all I intend to run is a fridge. That was part of the appeal of the MSW units which have much lower idle currents.

 

It must be possible to rig up a separate thermostat control to switch the inverter supply on and off but I too am not sure what effect this would have on an inverter connected to a motor already under load, which is what a fridge compressor is.

My Victron (12/3000/16) has a no load drain in inverter mode of 15/19/5 watts dependjng which mode you select. 15 W being always on, 10 being AES mode and 5 w being search mode. Doesnt seem a lot ?

[tommytelford]

I have a Sterling MSW inverter and have yet to find anything that doesn't work perfectly well, including my laptop and tv.

 

I understand that items with digital controllers are not happy with MSW so my new Tesco special microwave is dead basic and works fine.

 

Really can't be bothered with small differences in idle speed and consumshin mine works fine and I have plenty of spare capacity and can run for 48 hours without need for a recharge.

[smileypete]

It's an interesting possibility, I must admit I feel a little back at square one with this as the PSW inverters I've looked at idle at up to 6A which is ridiculous when all I intend to run is a fridge. That was part of the appeal of the MSW units which have much lower idle currents.

 

It must be possible to rig up a separate thermostat control to switch the inverter supply on and off but I too am not sure what effect this would have on an inverter connected to a motor already under load, which is what a fridge compressor is.

 

Could use a delay relay to switch the fridge if it's a problem, would need to be rated to cope with the startup surge, eg:

 

http://www.ebay.co.uk/itm/H3Y-2-DPDT-Power-on-Time-Delay-Relay-with-base-AC-110V-AC-220V-DC-12V-DC-24V-/350882384485

 

 

My Victron (12/3000/16) has a no load drain in inverter mode of 15/19/5 watts dependjng which mode you select. 15 W being always on, 10 being AES mode and 5 w being search mode. Doesnt seem a lot ?

 

Yeah but how much is/was the Victron 12/3000/16?

 

Would be a bit expensive if just for the fridge, would be better off buying 12V.

 

cheers, Pete.

~smpt~

Edited June 30, 2014 by smileypete

[jelunga]

 

Could use a delay relay to switch the fridge if it's a problem, would need to be rated to cope with the startup surge, eg:

 

http://www.ebay.co.uk/itm/H3Y-2-DPDT-Power-on-Time-Delay-Relay-with-base-AC-110V-AC-220V-DC-12V-DC-24V-/350882384485

 

 

 

Yeah but how much is/was the Victron 12/3000/16?

 

Would be a bit expensive if just for the fridge, would be better off buying 12V.

 

cheers, Pete.

~smpt~

Quite true. That is why we have a 12v Inlander fridge. Only need the inverter when out cruising fir microwave and vacuum cleaner. Edited June 30, 2014 by jelunga