Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Lapsy Senior Member Joined: 28/01/2012 Location: AustraliaPosts: 103
Posted: 11:17pm 13 Nov 2012
Copy link to clipboard
Print this post
I want to play around with a bar fridge I have.
I am interested in knowing how to select the correct inverter for the fridge.
I am trying to find out the startup power of the fridge as well as its running power.
Have read up a little online about it but still not fully understanding.
Certain there is a caculation for this, and I am also not 100% all the stickers are on the fridge for specs. I may need to hunt more info on the fridge if I can't find all the lable specs.
I understand you E.G buy an inverter rated at say 500w, but it would have peak rating also (I gather this is the startup rating of the inverter for appliances such as fridges and appliances with motors like circular saws and the like).
So matching this up to my fridge is the current deal to see if it is worth while.
Have been considering buying a waeco fridge but for a decent size one with a freezer, your looking around a grand. So you could call this topic Waeco Fridger Freezer Vs. Bar Fridge Inverted.
All help/discussion appreciated, AND, if this has been discussed in another thread (most likely!) please inform me if it will assist.
Cheers!This is my signature ---> Scribble, scrawl, a bit of light pencil shading, some indelable ink and a bit of caligraphy.
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 04:15am 14 Nov 2012
Copy link to clipboard
Print this post
Lapsy, you must also consider the capacity of the battery bank feeding the inverter .
I think a 500W inverter might be struggling to start up an inefficient bar fridge - most of them rate poorly. In my case I use a 1200W inverter and it has no trouble starting up a normal household fridge/ freezer. While its running Amps are only 1 at the 240V side I have seen 10+ amps briefly when starting up.
Why not get a decent second hand household fridge and play with that one? Just stay away from the frost free types, they chew far too much power to run off batteries.
Have a good read about inverters and how to assess their capacity in the inverter section of an electronic retailer catalog, Altronics might be a good start. Klaus
Lapsy Senior Member Joined: 28/01/2012 Location: AustraliaPosts: 103
Posted: 06:06pm 14 Nov 2012
Copy link to clipboard
Print this post
O.K
For the record so far from the model numner all I know is it's a Westinghouse Bar fridge/Freezer, about 10 years old (Don't know what you mean about frost free, but this thing ices over like the north pole, forever having to defrost it, it works too well to be honest!).
Rated at 2.5 Stars in the energy rating department. Energy consumption is 376W. Fridge is in good condition, well looked after. Been in storage for approx 5 of the 10 years I have had it. Recently been used on mains and running as it should.
The battery to run this is being taken into consideration also. I am happy to run it on it's own battery bank with it's own panels.
I am basically attempting to learn about solar, 1 appliance at a time, rather than just getting a whole system for a house. Been thinking about fridges lately as I have Radio, TV, Aquarium, lighting, phone/battery/laptop chargers going at the moment. just trying to step up to the heavier appliances.
I think the fridge energy consumption at 376w is decent compared to some and do-able. Surely others are running heavier units.
Just wondering about the startup power on someting like this. I hear it can be from 3-10 times the running consumption. Wondering how to work this out?
That said, a 3000w inverter is still probably a fair bit cheaper than a waeco fridge/freezer, but like you have stated, it is then the battery to back it all up.
Edited by Lapsy 2012-11-16This is my signature ---> Scribble, scrawl, a bit of light pencil shading, some indelable ink and a bit of caligraphy.
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 08:33pm 14 Nov 2012
Copy link to clipboard
Print this post
Think you will find that it is 376 Kwh/annum. The same as my full sized 430 Litre Westinghouse fridge. You need to know the running watts.
Power companies love beer fridges. $100 a year per beer fridge...easy money Edited by yahoo2 2012-11-16 I'm confused, no wait... maybe I'm not...
davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499
Posted: 11:42pm 14 Nov 2012
Copy link to clipboard
Print this post
Looking at running a small fridge off solar as well. The running current is 0.65 Amps, ie 150Watts. Next, I will put a datalogger on it to determine the duty cycle versus ambient temperature. I can afford about 1Kwh/day for refrigeration or about 33% of my daily energy generation.
I'd be asking what kind of inverter do you need for a normal fridge compressor. Will a modified sine wave inverter run the little induction motor properly?
To measure the peak current you would need a bit of test gear to measure the start-up pulse of current. Then will this information really be of much help . . . because then you need to know the peak current your inverter could supply for a similar period of time to get that motor turning over. How much is the voltage allowed to drop during the start-up phase?
I would hope the fridge manufacturer would have a better idea of what is needed in the way of a reliable starting current. They are the ones will all the fancy test gear.
> forever having to defrost it
Is the door seal shot?
As Tinker suggested you might get some surge information from the inverter manufacturer.
Good luck,
Dave
Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462
Posted: 11:48pm 14 Nov 2012
Copy link to clipboard
Print this post
Recently I saw advertisement for device that gave ‘Soft start’ for power tools, to eliminate kick-back.
Not sure if this can be used for the fridge, but I am quite sure that some AC’s have some kind of soft start arrangement too, so lights don’t dim when Air Conditioner starts.
Worth investigating to reduce need for 10 fold safety margin on inverter.George
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 03:08am 15 Nov 2012
Copy link to clipboard
Print this post
OK, some of my experience on running a fridge off batteries via a 240V inverter.
I too started off small with just one inverter but was wise enough to read up about them.
To start up a fridge compressor forget about the modified sinewave type inverters. These are OK for some stuff but none of the manufacturers recommends them for fridges. If you are anything like me you sooner or later also want to connect other AC equipment to it so you might just as well invest in an sine inverter that lets you do that.
Next, even sine wave inverters come in two flavors, high & low frequency to be exact.
The high frequency type is like the one used in computer power supplies with a puny transformer running at many Kilo Hetz to get efficiency - these do not cut it for fridges.
What you need is the low frequency type, often with an 'L' after the type #.
These have a big toroid transformer inside and therefore are quite heavy. But they pack the punch to start up a fridge compressor with ease.
They are not as cheap as the hi frequency types but well worth the investment.
My first inverter was imported from Taiwan for far less than a local electronic parts retailer sold the very same model. However, warranty wise I was lucky and it still runs today. To claim warranty one needs to ship it back for repair or exchange at my expense, making it no longer a cheap solution. Its a risk one has to choose. There are some very good Australian made low frequency sine wave inverters on the market and my second one is of that variety.
So, my ever expanding system is now running two inverters. Since these cannot be synchronised each has to power a separate part of my house, the active wire electrically isolated from one another. I use one (1200W) to power a few power points in the shed and the drinks fridge in there.
The newer inverter (1800W) powers the house lights and most power points in there, including the kitchen fridge.
With hindsight it would have been much better to go for a 3Kw inverter up front and be done with for my standalone power supply but often such lessons are learned the hard way.
So, choose carefully....
Klaus
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 01:01pm 15 Nov 2012
Copy link to clipboard
Print this post
All these small refrigerators run a sealed motor/compressor unit with an ac induction motor, and a capillary tube to create the high side/low side pressure differential.
The interesting thing about this, is that the pressure differential across the compressor will gradually leak down, and fall to zero over time when the motor is not running.
When the motor power is first applied, the piston compressor will (for an instant) have very little initial back pressure to start up against. The inrush current into the motor will still be very high, MANY times the full load running current for a second or two.
This works fine if you are connected to the mains, or have a very powerful inverter that can supply the massive inrush surge.
There is one very basic and huge potential problem here.
If you try to limit this surge current and try any soft start technique, it is not going to work.
What will happen is the motor will just stall, because as the compressor tries to start, but cannot, the pressure it has to pump against will rise very steeply, and the compressor will never reach full final running speed. It will just lock solid and stop.
It is either going to start up instantly with a massive hit of current and starting torque, or not start at all.
With the motor stalled, it will very rapidly burn out, because in these sealed units the flow of refrigerant gas back into the sealed unit is used to directly cool the motor windings. No motor revs, no flow, no motor winding cooling.
Even with current limited to full load amps it will burn out in minutes.
Your best bet will be to find a digital ac amp meter with a peak hold feature.
Let the refrigerator cycle on and off normally, and measure the peak startup current surge. You are going to be very surprised at what you see.
Unfortunately the inverter is going to have to provide that, and there is no way around it.
Edited by Warpspeed 2012-11-16Cheers, Tony.
Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462
Posted: 03:48pm 15 Nov 2012
Copy link to clipboard
Print this post
Would capacitor on A/C side be any good to accumulate some power and assist with kick required in first couple of seconds?George
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:55pm 15 Nov 2012
Copy link to clipboard
Print this post
A capacitor across the ac supply is just going to load the inverter even more.
Most inverters don't like pure capacitive loads anyway.
Cheers, Tony.
Lapsy Senior Member Joined: 28/01/2012 Location: AustraliaPosts: 103
Posted: 05:32pm 15 Nov 2012
Copy link to clipboard
Print this post
This has been sitting unused for about 6 months...
Door seals fine! The freezer just ices over the shelf wildly sometimes! Cant complain really. Takes over a month or so to build. I can run the thing on the lowest setting and it is sufficient for my needs. Holds a weeks meat and veg for me so....
Edited by Lapsy 2012-11-17This is my signature ---> Scribble, scrawl, a bit of light pencil shading, some indelable ink and a bit of caligraphy.
Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462
Posted: 05:54pm 15 Nov 2012
Copy link to clipboard
Print this post
It says 0.6A full load.
If starting load is 10 times that, inverter needs to allow for 1500W surge.
Interesting if 1,000W/2,000W pure sine inverter would be enough?George
Lapsy Senior Member Joined: 28/01/2012 Location: AustraliaPosts: 103
Posted: 10:50pm 15 Nov 2012
Copy link to clipboard
Print this post
So for arguments sake we say this would work on a 1000/2000w.
Whats the battery drain like on something like this?
Would we need a couple of batteries to keep this thing running for about 18-20 hrs a day..? I don't mind shutting it off for an hour here or there during the day to save the electric pull.. E.G every 5-6 hours on turn it off for an hour? Should not drastically affect the temperature or food much if you throw in a few cooler bricks to compensate.
I understand a 24/7 power supply to something like this may be a big ask. Or a big cost!
Waeco DC fridge Freezer Vs. Bar fridge inverted.
Who's winning and whats the score so far?
Suppose you could call this quarter time! Haha This is my signature ---> Scribble, scrawl, a bit of light pencil shading, some indelable ink and a bit of caligraphy.
Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462
Posted: 12:28am 16 Nov 2012
Copy link to clipboard
Print this post
From what is said about deep cycle batteries, looks that less discharged before being 100% charged up again the better.
Even if in theory they can be 50%, or maybe even 80% (?) discharged, event like that shortens service life dramatically.
Making 20% discharge best option.
Another BIG problem is clement weather.
It is not uncommon to have more than 3 or 5 cloudy days.
1 or 2 weeks of bad weather might not happen that often, but we have to have plan ‘B’ should it happen.
Suppose petrol generator.
(Or big feast to get rid of food from the fridge before it spoils)
Not sure exactly, but 1000/2000 pure sine inverter uses 1A by itself by just being connected
Efficiency is usually 80% rarely 90%
I am pretty sure resident Gurus can calculate it for you.
Read about Li-Fe-Po batteries, that can be safely discharged 80%, but right now they are very expensive.
Apparently with long life expectancy they right now provide cheaper 1kWh than Deep Cycle lead acid batteries, but initial cost is huge.
Worst bit is, that most probably I should not make posts on the matter as I don’t know enough.
George
Lapsy Senior Member Joined: 28/01/2012 Location: AustraliaPosts: 103
Posted: 04:33am 16 Nov 2012
Copy link to clipboard
Print this post
Even if you can run a fridge for 3-6 months of the year during summer, it's probably worth it. Or is it now?
I seen a Waeco Fridge the other day second hand for about $160 I think. Smaller one no freezer so...
Might be cheaper to get lumps of dry ice delivered to your door a few times a week or something.
Im open to all options....
Maybe this thread could be changed to - Cheapest way to constantly freeze something (E.G Meat) in a food grade manner.
Maybe some form of cold enclosed/trapped gas maybe a better solution? I've no idea. Bury the meat as far underground as you can but not too close to the core of the earth as thats hot too. Dammit, see.... there is no end to the variables... Just cook and eat everything immediatly! That solves the problem haha!
Forgot to also mention, I have been talking about 12v inverters.
If I put the fridge on it's own circuit, would starting at 24v or higher be of more advantage? The panels running it could match the voltage also. I would say this may increases costs a bit? Unsure (as usual haha)...Edited by Lapsy 2012-11-17This is my signature ---> Scribble, scrawl, a bit of light pencil shading, some indelable ink and a bit of caligraphy.
Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462
Posted: 11:06am 16 Nov 2012
Copy link to clipboard
Print this post
Read about blocks of ice cut in winter and stored in special basements for use in summer.
Making this option maybe a goer.
Famous South Australian in abandoned opal mines that give thermal protection from winter cold and summer heat are good examples of earth's insulating properties.
If you want to keep something frozen, the best option is chest freezer, actually anything with lid lifted up is way better then ordinary door type one.
But I am yet to see chest type fridge for sale and definitely ordinary fridge cannot be put on its back as for normal operation fridge is designed to be upright.
Come to think about it, we could rip the fridge guts out, even put it further away for better isolation from the heat produced by compressor and then play with shell.
Even doing that I think it would not be enough as internal tubes need to be in vertical position.
As to higher voltage, resident Gurus are of the same opinion running their systems at 48V DC for lowering Amperage in wires.
George
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:14pm 16 Nov 2012
Copy link to clipboard
Print this post
I suppose a lot depends on the insulation, how often you open the door, and the temperature of the stuff when you put it in there.
There is also the problem of short cycling the compressor.
If the "off" time is fairly long, the refrigerant gas pressure across the compressor drops to zero. But if the compressor keeps starting up, it may be forced to start against a fairly high residual pressure which is going to significantly increase the start up current surge.
This can often happen during cooking a main family meal, the fridge door is open, shut, open, shut, open, shut.
The compressor starts short cycling, and the inverter may have a VERY difficult time.
Another interesting thing to be aware of.
Most if not all, frost free refrigerators have a heating element(!) located behind the evaporator plate.
When the compressor turns off, the heating element comes on.
The idea here is to heat the evaporator plate up to just above freezing, to prevent ice buildup.
A terrific idea, and an absolute energy killer.
You can disconnect this, it is usually connected directly across the motor contacts located within the thermostat. But then the evaporator plate will very quickly ice up and require frequent manual defrosting.
No simple easy solutions to all this.
I suppose you could always build your own refrigerator with massive insulation and two quite independent refrigeration systems.
The idea here would be to run one system for a certain period maybe a day or two, and let it ice up. Then switch over to the second system for a day or two.
This would allow regular full defrosting to keep the evaporator plate efficiency high, without having to deliberately apply any extra heat.
It would also offer some redundancy, and open up a few other possibilities.Cheers, Tony.
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 02:57pm 16 Nov 2012
Copy link to clipboard
Print this post
Off the shelf in Australia the best I have seen for a large chest freezer is the vestfrost SE325 which averages about 700 watts per day. I have spoken to bonzabuy and they sell 40 to 50 a month. I don't remember what the starting current is, but I have got an idea that it is pretty good.
If you go to the vestfrost website (Denmark)it is not listed in their models because it has been superseded by a new model....about 4 years ago! The new one (model SW321C) runs an inverter style motor on the compressor, so it has a very soft start and chews 500 to 550 watts per day. I quizzed them about this, the story is that the market here is too small to make it economical to get the rubber stamp needed to sell them here.
I got a bit angry about this a couple of years ago because ALL the govt energy saving websites were recommending that we buy this new freezer, that is not available in Oz I chewed some ears and got some action...the websites have been changed.
The major sticking point in super insulating a modern fridge or freezer is that the condenser element is built into the walls of the unit so the heat will be trapped between the layers of insulation.
The DIY solution would be to pinch an external condenser from an old fridge or upright freezer, cut the pipes to the inbuilt condenser and fit the external style one in to the system with some flexible piping (modern fridges have better insulation than the old ones otherwise we would just use the old fridge and fit a new compressor).
This means that more insulation can be added to the fridge AND the condenser can be mounted in a draft cupboard, cool air from under the house flows past the condenser and into the roof.
This will get to about the 120 Watts per day mark. The Mt Best chest freezer to fridge conversion is the ultimate low energy solution. The challenge with this (as with all fridges) is dealing with the water that accumulates from the humidity. A rack needs to be fitted so nothing touches the damp floor and a drain hose is needed to remove the water every 3 weeks. I have heard that vegies last for an eternity in one of these suckers!
I hold the record for the shortest time taken to blacken a bunch of carrots in the crisper. Edited by yahoo2 2012-11-18 I'm confused, no wait... maybe I'm not...
Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462
Posted: 11:13pm 16 Nov 2012
Copy link to clipboard
Print this post
With power usage like this, with few losses for 12V side we would be looking for 10-15 Ah
(Hope my conversion is right).
Assuming that inverter uses up another 24 Ah a day, we are looking for 40Ah a day in total.
If we allow for 5 days of shocking weather, we would need system to be able to give 200Ah
And it is up to us, to have system drain down to 80% total capacity (we use only 20% of total capacity) which would require battery bank to hold 1,000Ah
or 500Ah if we allow system to drain down to 60%
(we use 40% of total capacity – slightly shortening life of Deep Cycle Battery system compared to system drained down just 20% of total capacity)
Should we have Li-Fe-Po battery bank that can be drained down to 20% then 250Ah bank would suffice.
George
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 02:55am 17 Nov 2012
Copy link to clipboard
Print this post
That is exactly what I did to keep my drinks cool in my shed.
I bought a cheap second hand working normal household fridge.
I then gutted it to get the working bits out without breaking any copper tubes & loosing the gas. That was the hard part as these days they use foamed in insulation and its one big job to extract the tubing from it.
Next I built a plywood chest type enclosure with a top opening lid. The inside was first painted & sealed, then layers of second hand polystyrene foam built up to a 75mm thickness, including the lid. The inside then received a home made box (from ABS plastic) that was sealed at the corners to stop condensed water draining into the insulation.
The fridge evaporator (flat plate bent into a box) was carefully unwrapped and bent into a L shape to fit along the side wall of my new fridge chest. The pipes entered via a small channel just under the lid. The compressor & condenser stands on a shelf along the wall next to the fridge. The copper tube is actually long enough for this to be located further away but I just bent it carefully into a inverted U to shorten it.
I bought a new thermostat to control it as the original one broke during the dismantling process. Its set to + 5 degrees but could easily set to freezing as the compressor is quite big for my set up.
The lid has a double seal, just two strips of the thin adhesive backed foam rubber available from Bunnings.
Its not pretty but very functional and comes on perhaps once per hour during the day and runs about 3 minutes, very economical indeed.
To take care of condensation I have one of those water sopping cloths on the bottom inside which gets periodically wrung out over the sink.
The original fridge had a heater wire that ran around the door opening behind the seal and was 'ON' when the compressor cycled 'OFF', using a fair bit of power. I did not re use that but still have kept it for a future project Klaus
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
.
The new one (model SW321C) runs an inverter style motor on the compressor, so it has a very soft start and chews 500 to 550 watts per day. I quizzed them about this, the story is that the market here is too small to make it economical to get the rubber stamp needed to sell them here.
I chewed some ears and got some action...the websites have been changed. 
