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Forum Index : Electronics : 240v Freezer through Inverter Experiment
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Jaffasoft Senior Member  Joined: 03/11/2010 Location: AustraliaPosts: 102 |
I had a small not very old freezer and a 12v/240v 2500 watt 5000 watt surge inverter so my thinking was to try avoid the huge cost of an Engel 12v DC fridge. With 400 watts of Solar Panel and two very old 12v ex Telstra 6v 70 amp hour batteries in series they only seem to hold 12.2 volts at best. It fired up and ran well I had ice after a while. I tried to switch it on at night when the panels were not getting any energy and the batteries didn't have enough grunt to start. The fridge motor was drawing big amps and tripped the 50amp breaker in the inverter positive line once. A couple of other occasions it just repetitively kept surging trying to start. Anyway first thing I did was take an old mechanical thermostat out of an old fridge, since the idea of this whole thing was to use the freezer as a fridge. I didn't have much success with the thermostats and eventually got better results with a timer connected to a regular 30amp car relay to switch the inverter on through the positive line from the battery to the inverter. The timer used 2.4 wat 24/7 and the freezer we're now calling a fridge was set to come on five minutes every half hour from 10am till 5pm so off all night. It worked well in the experiment and the temperature inside was between zero and 4 degrees. It would not have worried me if it was 4 to 9 degrees but I didn't refine it much more. Since ive lived without a fridge for the last few years anything was going to be better! Then tragedy struck! In the last week or so its been very cloudy and one time the inverter surged to try and start the motor and could not, then I heard a fizzing noise and a puff of smoke came out of the inverter. By by inverter the idea is all over. One fried inverter. Im back to the drawing board now wandering how I am goingto go about this? Folk out the money for a 12DC fridge or buy another inverter and get back on the horse and try the freezer inverter again. One thing that has changed since this happened is it spurred me to finally get new batteries. So two brand new T105 225 amp hr Trojan Batteries arrived this week. For the technologicaly minded the freezers single phase compressor motors label is rated at .86 amps at 220-240v, 50Hz, 103 watts. I pulled the inverter apart and found a MOFET was burnt brand have ordered a part to maybe repair the inverter but I do not know if this will be successful. Any opinions or insight would be interesting. |
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| Gordz Regular Member  Joined: 10/08/2013 Location: AustraliaPosts: 55 |
IMHO it is unlikely to be just one FET that is blown, there should be a bank of them along with drivers. Also from what I have seen in mains fridges is that the startup current is often way more than the run current. It all depends on the type of compressor motor. Engels use the Danfoss compressor range which use brushless DC motors so they are pretty 'green' in energy terms. |
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| davef Guru  Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I have seen it suggested that these motors can drawn up to 10 times their running current. Still that should be about 1/5th of the (advertised) surge capability of your inverter. I wonder if the battery voltage was being pulled so low that the inverter was doing a "low-voltage disconnect" and it couldn't stand the repeated stop/start conditions. Your new batteries at 450amp/hr will probably be more than 10 times better at handling the starting current. Another thing to consider: if the motor doesn't start "real fast" then it will keep on drawing heavy current. Is it a heavy unit with a real big transformer in it or is it a "switcher"? |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
I don't like my chances of fixing the inverter but at $2.90 or so for two FETs l'l give it a go. Yes, there is six FETs, three each side fixed to a heatsink via some sort of sticky double sided tape, everything is bolted onto the heat sink. I am assuming one FET because I could smell my way to the area and found the collector pin or emmitor pin burnt right through the wire. It's the only FET that doesn't seem to have a 40amp blade fuse next to the big wire coils next to the five others. I will be prepared that possibly its more damage in there I cant see? The current draw is much higher on start up then run current. I looking into adding a start capacitor in parallel untill the math got a bit complicated for me. It was bizarre the watch the current draw as on initial startup I could momentarily see the amp meter go up to 30-40amps but could not tell because it was so quick. It would settle to 14 amps or so and as the motor warmed up would slowly drop to as far down as 2.5 amps then give it eight minutes or more an it would gradually rising up to 10-14 amps. Batteries have a 97 date printed into a led post and only 70amp hr. I think it sucked the last life out of them. Needing the higher amps the volts dropped down as low as 11.6v. The inverter is rated to shutoff low volts of 10 and beep. I heard no beep. In the manual it says surge current of 550 watts and 660wat in surge. So it might have been that or high amps that caused the heat burn-out. If I bought another inverter and tried it again these two 6 v 225 amp batteries in series for a total of 225 amp hrs might run well but I wouldn't buy an inverter that big again but take a punt with 1000 wat pure sin wave maybe. If it worked im fairly sure it would easiely only need to run five minutes an hr only during the day to keep food stuffs cold enough for me. |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I don't understand this comment. Initially it was a 2500W continuous, 5000W surge rated inverter. 5KW (surge rating) at 13V is about 380Amps. |
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norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
The Engels of my era used their own "swing compressor". Have they gone over to the Danfoss compressor now? I note a lot of the portables that used Danfoss now are using Italian or Chinese compressors that are Danfoss look-a-likes. A 5000 watt peak inverter should have no troubles starting a modern domestic refrigerator, providing of course the battery is up to it. We come from the land downunder. Vic |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
I don't understand it either! In the manual it has Rated Power 2500W Surge Power 5000W under this column further down it has a thing described as: Overload Protection >550W >660W Shut off output voltage, re-power on to recover Bat.Lowalarm 10VDC or 20.5VDC or 44VDC Bat.Lowshutdown 19.5VDC 19.5VDC 42VDC Over Voltage 15-16 or 30~32V 60~65V Output Short Auto. Shut-off Bat. Polarity By fuse open Over Temperature >60c/>140. What seems strange is if it has all this overload protection and fuses why didn't it do its designed job and protect it from blowing up and blow a fuse or shut down. |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
I was a bit confused about this so I went the the manufacturers official web site at engelaustralia.com.au. It describes there a Sawafuji Swing Motor where you can see the inner workings and designs of the motor in clear images. http://www.engelaustralia.com.au/about_SwingMotor.asp Unique to Engel this purpose built compressor is designed to be a portable refrigeration compressor and is one of the key reasons why ENGEL is 'A LEGEND IN RELIABILITY'. What is the first rule in engineering? Keep it simple! The Sawafuji Swing Motor is a true reciprocating compressor; it has only one moving part. It doesn't get any simpler. The piston is connected to an electro dynamic device which is powered by the use of magnetic fields. With this technology there is no need for bearings, cranks or con-rods, so less moving parts means less chance of failure. With only one moving part there is a very low friction loss which means this is a highly efficient compressor. It has no high start up current draw because when it starts up it can simply move down just a fraction then return. Then it slowly increases the distance the piston travels each stroke until it reaches a full stroke. The Sawafuji Swing Motor does not need to perform a full stroke on start up unlike many rotary type compressors that must perform a complete cycle and need much more current to start. Because this is purpose built and designed to be a portable refrigerator compressor it has to be engineered to take the harshest of Australian conditions. The Sawafuji Swing Motor is located inside the compressor casing with pins locating in rubber bushes then suspended in between shock absorbent springs. It operates at 30 degrees angles and on rough corrugated tracks without losing efficiency. The leading brand for over 40 Years, only ENGEL portable fridge-freezers guarantee to go anywhere. Their reputation speaks for itself. ENGEL's commitment to continuous improvement means that the ENGEL of today is the most reliable, the most efficient ever, quieter and full of features to ensure it is easier to use than ever before. |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Yes I didn`t think Engel had gone over to the Danfoss. Not that the Danfoss can`t compete, in fact my experience puts the Danfoss ahead especially in efficiency. But I am not exactly impartial, I built portable and solar fridges for 20 years using the Danfoss compressor. One of my sale pitches was the units would not only serve the customer well but their children also, that sometimes sadly has been proven with time. We come from the land downunder. Vic |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
Don't think anyone will go wrong with either motor they get good reviews across the board. I'm going to try kill another inverter before buying one. Just not sure if there is any particular type of inverter to use? |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Have only one experience with inverter brands, have been off-grid since 06 with a Selectronic. Only time I`ve had to reset it is when I`ve run the MIG continuous for a little too long. It just does not fail, fingers crossed. We come from the land downunder. Vic |
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| crez Senior Member Joined: 24/10/2012 Location: AustraliaPosts: 152 |
The control systems in older fridges and freezers are usually set up to be off long enuf to allow the refrigerant head pressure to dissipate before restarting. Even when running from the mains, many compressors will fail to restart and will trip a slow thermal protection device if a short power interruption happens. When experimenting, make sure you don't do rapid 'stop then restart' operations. When repairing your inverter look for a low resistance (around 22 ohm) in series with the gate of the dead FETs. They often go open circuit. David |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
Yep, ive been carefully not to do this though it has done it few times and I quickly switch the inverter off. I found a consistent 10.9 ohms across all but one resistor which was going to the dead FETs gate. Each resistor going to each FET is (Brown, black, black, gold) in series with the gate of each FET. The dead FET was measuring 1273 ohms across the resistor (huge difference) same coloured resistor. Also found a wire solder break on the negative wire to the fan, so the inverter might have got hot over the last three weeks on/off experiments causing it to fail eventually. Though it was a cold start that it finally blew! |
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| crez Senior Member Joined: 24/10/2012 Location: AustraliaPosts: 152 |
looks like you need a new 10 ohm resistor. hopefully the damage doesn't go further back into driver transistors/ICs. Check nearby transistors for cracks or burn marks. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
It would be wise to remove and check all of the components around the power stages. If even one faulty component remains, it will probably blow up again when powered up. I hate working on inverters for this very reason. Be patient and be thorough. Cheers, Tony. |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
Got that! Is an inverter always "filled up" with electricity when connected to the battery and prior to being switched on? Would wiring it to always have the leads from the battery to inverter connected and instead wire in the timer and the relay to switch it on at the inverter. I can not find any hard start kits similar to what Supco make in America, they wont export them to Australia. One is designed for 1/12 to 1HP motors, has the relay built in, bleed resistor and capacitor. Would have been good to wire One other these in. |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
With the risks associated and stuffing around with this or fixing it again or buying another inverter it could still be hard on my new Trojon Batteries. I'm planning on these lasting ten years and only 30% discharge at most hopefully. I done just go camping in this Van, I live in it for years. I was catching redies the other day and had had nowhere I could freeze them. Already probably lost a 375$ inverter that was two yr old with next to no use. I could buy something like this for under $500 even though they have not got the claims to fame Engel has: Danfoss BD35F Motor Fridge Freezer I have noticed a least four other branding names on this same designed fridge the others dont say they have a danfoss motor though. So not sure if this is a mistake. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Buying a refrigerator that is designed to work direct from 12 or 24 volts dc is definitely the best way to go IMHO. It probably has a dc motor (?) and a transformer/rectifier to run off the 240v mains. However it works, it should be more efficient and a much more reliable way to go about it IMHO. Those small inverters are great things, but you need to be a bit careful about what types of 240 volt loads they are used with. Cheers, Tony. |
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| Jaffasoft Senior Member Joined: 03/11/2010 Location: AustraliaPosts: 102 |
Could you rely on any fridge/freezer with a BD35F or BD50F compressor or is it the quality of other components as a whole package? I have been spinning with fridge research for days, there is a lot of manufacturers that use the danfoss compressors. I liked the look of the stainless steal in the one in the link as it suits the esthetics of the RV I am converting. I have since found another four very similar looking but they all have different compressors. I have listed my research notes below for anyone else's interests sack: All very similar looking design but each slightly different and all found listed in ebay PolyCool 80ltr W630 x L430 x H690. Black Insulation Cover, two compartments Ultimo 80ltr 690 x 490 x 624.5 generic compressor Glacio 80ltr 640 x 450 x 620 WANCOOL compressor, grey insulation cover EvaKool 80ltr W490 L680 H570 Domus compressor, white insulation cover, one compartment, one wire rack Easy Cool 80Ltr W690 x D490 x H630mm Danfoss BD-35F compressor(said it was BD35F in three ad but will not confirm and since ad has been editted taking compressor description out). Stedi 80Ltr Danfoss compressor L 880mm x W 550mm x H 490mm(little to wide for my application) Other brands using the danfoss compressor. It seems all of the big and best known brand names use the danfoss BD35F Compressor. Trailblazer BD35F Autofridge BD-35F compressor National Luna Danfoss BD-35F compressor Waeco Danfoss BD-35F compressor EvaKool Black 70ltr Danfoss BD-35 compressor Bushmen Danfoss BD-35F compressor Cenco 80Ltr Danfoss Westinghouse Danfoss BD-50F compressor Fisher and Paykel Danfoss BD-50F compressor Primus Secop. 790L x 465D x 615H BD50F I have emailed the above seller in the link with a simple question to confirm if it is a Danfoss BD35F compressor and after three emails over four days hasn't given any definitive answer! He replied once only saying its here in the box ready to post. Acknowledging nothing about if its a Danfoss Compressor or not. Though I have watched the ad descriptions get editted taking any reference to a Danfoss Compressor out now. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
You have probably been talking to sales people that would not know a compressor if one fell out of the sky and hit them on the head. Try and get onto the service department and ask some tech guy. Cheers, Tony. |
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