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Forum Index : Electronics : 240v Freezer through Inverter Experiment
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norcold Guru  Joined: 06/02/2011 Location: AustraliaPosts: 670 |
I have a Morningstar Pro 20 that is in its 2nd vehicle, would be getting near 25 years old. Still performing as if it were when new. With 400 watt of solar and 225amp battery and that charge controller see little problems running say a Danfoss, Engel or similar. If you wire the fridge from the load side of the controller, rather then direct from battery, it should cut it out before the batteries are down, plus some portable fridges have a switchable cut-out that allow you to vary the cut-out voltage. Would consider say a Honda 10i, to charge those batteries on cloudy days. Runs for 8-9 hours on 2l of petrol have been told the small inverter Kawasaki generator does even better. But with monitoring of battery with a hydrometer and good sun don`t see a problem. Monitoring a fridge is a pleasant duty 
We come from the land downunder. Vic |
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Jaffasoft Senior Member  Joined: 03/11/2010 Location: AustraliaPosts: 102 |
That's good to read.. I was worried it might have been to small. What would be the best way to go as a dedicated Freezer only nothing else? I've got two cows running around (this is not for the RV but home base possibly) that keep telling me they want to be frozen. Would be 1/4 to half one after others get a share! 148Ltr would be enough I guess! I have been welling over the idea of maybe building one with an R Value of close to 30. It would be a hack type arrangement just in a shed with motor away from the box a little, a condenser through external wall in the windy spot under tree shade. Though I may be opening a tin of worms since evaporater plates and condenser sizes etc is a bit of a science?? |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Depending on what sort of sun conditions you experience, with care your 400 watts solar-225ah battery combination, and of course the capabilities of your proposed fridge, you will have ample power to run keeping food frozen ie. buy frozen food and keep frozen. The missus and I (and 2 dogs) travelled OZ for 2 years 99-2000 (gold fossicking)with 260 watts solar, 110ah Trojan, and a 60l 12v Danfoss powered fridge/freezer (Norcold of course) combination. Only 50mm insulation. We had a backup generator(for charging) which we hardly used(mainly whilst in Victoria) Always had a cold beer and frozen food. Got 3 years out of that Trojan , it had a rough life. My experience here, Insulation gains are small once you reach 75mm. The purists will argue with this I know but this is my experience. For portable applications where bulkiness is a hindrance, 50mm insulation is adequate. I`m talking polyurethane not polystyrene. To freeze your cows, forget 12v. 12v will take too long to freeze that amount of meat, the quality of the frozen meat will be lousy. The quicker food is frozen the better it`s quality. This has very little to do with insulation, all about heat removal. You can have a 12v 50watt unit with say 300mm of top insulation, and it`ll be licked by a 200watt 240v domestic unit with 50mm say so insulation. Now for the disclaimer. This is all from my experience, get a brand name 12v fridge/freezer. one that's been around awhile. Names like Trailblazer, Bushman, Evacool, Waeco, Engel etc. and while my experience is not up to date, I`d put the Danfoss compressor on the top. Old saying- "only the rich can afford to buy cheaply" For a more up to date reference to fridge brands try the 4WD and RV forums. We come from the land downunder. Vic |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I used to mess around with this type of thing a lot many years ago. The way I would go about this would be to find a fairly large window air conditioner and use the compressor and condenser in that, leaving it all mounted inside the original air conditioner box. It will be cheap (free?) and single phase, and the condenser and the condenser fan will be sized suitably for the compressor. You will then need to make up your own evaporator, realising that in a freezer it will need to be fairly large, the bigger the better ! The problem then becomes matching the evaporator capacity to the condensing unit and knowing how much refrigerant to initially charge the system with. there is a simple way around both these problems that then make the whole thing fairly non critical. The first thing you will need will be to get a thermostatic expansion valve to suit the type of refrigerant gas you plan to use. Some types of refrigerant gas are now illegal, or difficult to obtain, or horrendously expensive, so a suitable expansion valve needs to be sourced. This expansion valve is plumbed into the liquid line going to the evaporator, and it has a temperature sensing bulb (filled with the exact same refrigerant gas) that needs to be placed in intimate thermal contact with the suction line going back to the compressor. This will throttle the liquid going to the evaporator and ensure that only fully boiled off vapour goes back to the compressor. You could possibly re use a thermostatic expansion valve from a car air conditioner. It will say on it what type of refrigerant gas it is to be used with, and that is very important. This would also be about the right size for a window air conditioner condensing unit. The second thing you will need to do is fit a liquid "receiver" to the system. This is just a storage tank to store surplus liquid refrigerant placed between the condenser outlet and the liquid line going to the expansion valve. The condenser drains into the top, and solid liquid recovered from the lowest part of the tank. This receiver tank may be fairly full or fairly empty, but it ensures only bubble free liquid goes to the expansion valve, and that liquid refrigerant cannot back up into the condenser. It compensates for how much the evaporator is flooded, and how much gas has been originally charged into the system. If you are working on the cheap, a small tall skinny propane tank should do the job. It just needs a siphon tube extending right to the bottom for the liquid, the condenser drains into the top. A special custom Mickey Mouse home made brass fitting screwed and into the top of a propane tank should do it. I am sure that with a bit of improvisation, a decent capacity refrigeration system could be put together for virtually the cost of the gas, and the hiring of a refrigeration guy to properly evacuate, charge, and leak test your system. There are a few other embellishments to make the system much nicer, such as a filter drier, high and low side pressure gauges, and a sight glass in the liquid line. Cheers, Tony. |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
I like this idea of the "swing compressor" very much. Brilliant! Piston compressors may start-up against back pressure from the capillary pipe on the pressure (hot) side and at top dead centre. Also, just a little movement at the first stroke is also a "stroke" of genius. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
I had a 24 volt Danfos compressor fitted to a 325 liter conventional freezer, doubled the cost of the freezer but lasted for years, and only draws around 4 amps, I believe you can get them for 12 volts as well, eventually developed an internal leak somewhere in the casing but the unit still worked well, re gassing every few weeks drove my mate mad so he condemned it, he was going to fit a independent evaporator inside but never got around to doing it. Then I got a 240 volt unit the same size and run it off an inverter, but it used a lot more watts, one more panel and a extra battery solved that. All the best Bob Foolin Around |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
But the swing compressor in my old Engel fridge also has a big drawback. Perhaps the later Engel fridges have overcome this but the one I have has the compressor run at 20V AC. This, when connected via a transformer to 230V mains works very well. Connect it to 12V DC and the 20VAC was made by a transistor flip flop, driving a transformer winding. Now, if the battery ran down a little there was less 'swing stroke' generated, making the unit work ever harder and accelerating battery run down. That put me off the 'swing compressor' idea for good, give me a constant displacement stroke from a rotary compressor any time. Klaus |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Jaffasoft, What intrigues me is your mention of $2 ex Telstra batteries from the tip? Have been told by scrap dealers with pallets full of them they are not allowed to sell them to me and you reckon they were tipped? By Telstra?? This is a sales policy by Telstra and not a general federal env. policy of not selling lead containing things back to the public. Also, it has been suggested that Telstra batteries were found dumped in the bush and that led to this rule so Telstra cannot be accused of harming the env. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
I heard about this! I don't know how they got to the tip they were just there, I asked if I could buy them and they said yes. Think possibly a once off as haven't seen any again. I think its a crap rule that Telstra has made anyway and probably has an alternative motive behind it. But it's not the only poor management that company does. It's more then probably the battery manufacturer that does not want them reused to increase there sales. It could be from to many thefts from Telstra Exchange boxes. Who knows?? So are Telstra just as worried about people reselling millions of mobile phone batteries and ppl dumbing them out the car window when there no good! Opening a tin of worms!! You can buy the exact same Telstra brand new from the manufacturer so what's the difference. They are just not branded with the Telstra logo. Here you can see em here , in the photo second from the left. I spoke to this companies battery rep in person on the phone about charging these batteries. While I'm here.. fridge/freezer is going great... been going straight well over a month. It froze a rabbit, a Cray fish, fishing bate and a few other things. Suns good here though so far. |
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