Jud - s/v Sputnik

Marine refrigeration qn - “magnetic compressor?”

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Anyone know what brand/type of fridge this might be that’s mentioned in this article?  The article is entitled, “An Unusual High-Latitude Vessel”, about a 1980s-era cold-moulded wood hull 40’er that’s been sailed to some challenging destinations.  They talk about their low-amp draw electrical system, and highly rate their low-amp drawing fridge: “Our refrigerator (which we did use, especially at anchor when the boat was well heated) employs an ingenious magnetic compressor that uses at most four amps when running.”

(They also highly rate their very low-amp Katadyn water maker - but at US$4000... :-) )

https://www.oceannavigator.com/an-unusual-high-latitude-vessel/

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29 minutes ago, Jud - s/v Sputnik said:

Our refrigerator (which we did use, especially at anchor when the boat was well heated) employs an ingenious magnetic compressor that uses at most four amps when running.”

Not sure what they're describing but many Danfoss based 12 volt setups draw about four amps when the compressor is running.

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vaguely recall something in the late 90's being 2 opposed pistons with so much electronic gear attached and exposed it wasnt worth going into, low amps sure but the danfoss BD has em licked for reliable, leastways that was my take then and maybe something was done to improve them

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20 minutes ago, weightless said:

Not sure what they're describing but many Danfoss based 12 volt setups draw about four amps when the compressor is running.

Thanks.  (I must admit I’ve no idea what my NovaKool brand fridge [no idea what compressor make it is] I installed over 10 yrs ago draws.  Time to check.)

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33 minutes ago, Jud - s/v Sputnik said:

Thanks.  (I must admit I’ve no idea what my NovaKool brand fridge [no idea what compressor make it is] I installed over 10 yrs ago draws.  Time to check.)

Our Nova Kool draws ± 6A.

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4 minutes ago, Max Rockatansky said:

Sounds like a poor description of a Sawafuji swing motor

Used in the Engels, I have one in my camper, works great, draws little.

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6 minutes ago, bmiller said:

Used in the Engels, I have one in my camper, works great, draws little.

Right - I thought “Sawafuji swing motor” rang a bell.  They’re in the well-regarded Engel fridge/freezers.  Maybe that’s what she’s referring to in the original article.  (Seems like a decent idea - I almost got one years back, but for some reason, now fortunately long since forgotten, I opted for the undoubtedly more complicated and more expensive installation of a fixed fridge and custom vacuum panel-lined box...but I really like the idea of the Engel.)

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I can't tell you my tiny Engel fridge amp draw as my boat is in Panama, but it is a very effective and quiet unit i'm glad to have on the boat I bought. 

Troy of Free Range Sailing, despite needing to work on his Katadyne Survivor 40 after only 200 hours, seems to like the unit a lot. 

 

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Viewing the issue from a high level...there are several ways to pump refrigerant without allowing it to leak out. Depends where one places the seal. Nearly all small refrigeration pumps choose to seal the incoming wires. A simple and nearly ideal solution. I would guess a "magnetic" solution leaves the motor windings outside to couple the energy across the seal with magnetism. Seems foolish given the complexity. (However Danfoss could well work on the reliability of their electronic drive box.)

Doubtful a crude device like the Katadyn can compete on energy consumption with pressure recovery systems such as the Spectra. Simple and inexpensive to build, however, so has a market.

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My Engel 35, circa 10 years aboard w/non-stop usage and still going strong, is advertised as drawing between 0.8 and 2.3 amps/hour. The temperature setting knob goes from 0-5, and I don't think I have ever run it over 2.25 or so, otherwise everything freezes solid.

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Theres no free lunch on refrigeration, most of the low draw gimics are just that.  It's all about efficiency in keeping the heat out.  The simple hermetic Danfoss is a standard for a reason.  There are tons of simple ways to add insulation etc and make the system more efficient. I would guess any system is going to draw very little in high latitudes.  

In several years I would guess CO2 transcritical units  will become available and then you will see a decent bump in efficiency based on its improved properties.  I think Aus Germany Brazil etc are making headway in small vending machine size units which is a decent crossover to a vessels requirements.

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I have three Engel units: two drop-ins and a chest. The drop-ins are in the galley: one is used as a freezer, the other for food. The chest is in the pit: drinks and overflow. The idea here is to keep from constantly opening the food cooler, you see.

As noted above, the Engel (Sawafuji swing compressor) is quite good on power. Full tilt boogie for ALL THREE compressors is 8.7-9 amps (as per my monitor) and they probably only run 50% of the time. They have been in use full time since I moved aboard in Nov 2016. I have been moving between the northern Gulf of Mexico to the Keys and Bahamas. Hot and humid. I do not have AC, nor do I live on a dock (most of the time.)

The only thing about these Engels is the dismal lids/gaskets, and I’ve complained here about that. I am working on rectifying the issues, and when I do, I expect the consumption to drop even further.

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Recalling a local newspaper article some years ago, I dug around a little:

A guy named Dan Conry put together a team in 1994 and developed a new type of magnetic refrigeration compressor.  Conry’s concept compressor was developed in Australia, and then commercialized in Canada. Following the backing of a joint venture with Danfoss, the product that was subsequently developed has achieved global recognition

 To quote a blurb:
"Danfoss is the leading manufacturer of oil free compressors and is the pioneer of the Danfoss Turbocor® compressor - the world's first oil-free magnetic bearing compressor for the HVAC industry."

A 2010 article shows Danfoss and Conroy opening a developmental research facility to push this farther.  It's located in Tallahassee, FL, which is also (not coincidentally I'm sure) home to the National High Magnetics Laboratory at Florida State University.

One can find anything on the internet!  The question for us is, when does this all filter down to small marine refrigeration?  For that matter, is the Engel refrigeration mentioned above Australian, and maybe the first of Conry's work?

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4 hours ago, Max Rockatansky said:

I have three Engel units: two drop-ins and a chest. The drop-ins are in the galley: one is used as a freezer, the other for food. The chest is in the pit: drinks and overflow. The idea here is to keep from constantly opening the food cooler, you see.

As noted above, the Engel (Sawafuji swing compressor) is quite good on power. Full tilt boogie for ALL THREE compressors is 8.7-9 amps (as per my monitor) and they probably only run 50% of the time. They have been in use full time since I moved aboard in Nov 2016. I have been moving between the northern Gulf of Mexico to the Keys and Bahamas. Hot and humid. I do not have AC, nor do I live on a dock (most of the time.)

The only thing about these Engels is the dismal lids/gaskets, and I’ve complained here about that. I am working on rectifying the issues, and when I do, I expect the consumption to drop even further.

I am kicking myself for not getting a Engel.  We have two small fridges and were going to go with a Engel for a freezer beverage unit bit I convinced myself to get a drop in freezer with water cooled comp.  Have never quite had it on installed right and rarely use it, the Engel would have made alot more sense and been a fraction of the cost.

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If you get a swing compressor make sure to align it fore-aft on the boat. They don’t like significant heel (I think the manual says 25 degrees). 

I had one on my last boat and it was pretty good. I have a Danfoss now and efficiency is very similar. 

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So while we are on the refrigeration topic, I have an issue at the moment.

The Valiant has two adjoining freezer boxes, one with two eutectic plates in it, the other with one plate and a 12v fridge unit.

There is a biggish 3/4 hp 240v AC compressor on the eutectic plates and a small 12v one on the fridge unit.

We are replacing both compressor and condenser units, and it is difficult to find a big enough 12 V unit to run the freezer plates, so the plan is a 1/2hp AC unit for the plates and a small 12v Danfoss for the fridge.

The plan is to freeze the plates down on shore, and run the AC unit through an inverter when the engine is running, using up spare amps from the alternator.

My question is how big an inverter do we need to handle the start up surge current of the AC unit compressor. We are in Oz, so this thing is 240V, but the wattage rating would be the same as a 110v compressor.

As far as I can see the surge can be up to 10 times the running current, and a soft start is not an option as the motor has to start up against a load so it will just stall out if there are not enough amps.

Cant get a decent answer from the supplier, so my plan is to put the unit in and use a clamp meter on it on shore power to check the loads, then order the inverter after that.

Wondering if anyone has some first hand experience with this sort of thing, I think we are looking at a 2000w inverter with a 4000w surge capacity, but would appreciate some real life experience

 

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10x running current would be extreme. 5x would be more in the normal range but it really varies with the motor. The vendor should have the "locked rotor amperage" of the motor which is pretty much a peak.

Starting caps?  

https://highperformancehvac.com/start-capacitors-hvac-compressors/#:~:text=Most HVAC technicians know HVAC,get an HVAC compressor started.

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I don't think a clamp-on meter will tell you anything useful during motor startup. A really fancy one can measure instantaneous current or power factor from which the real wattage can be derived. But what does one do with those values given the sparse datasheets of inverters? Study power factor if you are interested and have coffee brewing.

The inverter is specified in power (Watts) but the meter measures average current (Amps) and the short story is that with the power factor abusing the system there is no way to convert from Watts to Amps without much more info. Cannot simply divide by average voltage.

I'd try really hard to do it with 12 V Danfoss compressors. It is all figured out already.

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Unfortunately 1/2 hp seems to be way out of the league for 12v compressors...

Thanks for that info on the start cap Zonker.

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1 hour ago, Zonker said:

10x running current would be extreme. 5x would be more in the normal range but it really varies with the motor. The vendor should have the "locked rotor amperage" of the motor which is pretty much a peak.

Starting caps?  

https://highperformancehvac.com/start-capacitors-hvac-compressors/#:~:text=Most HVAC technicians know HVAC,get an HVAC compressor started.

The Canadian Electrical Code “defines” locked rotor current as 6x rated motor current.  It can vary a bit, of course, but it’s a good rule of thumb that electricians use for various calcs.

As for power factor and reactive power (wasted power, not true power, or watts), the easy way to grasp what true power (watts) vs. reactive power (VARS) is...of course through beer :-)

A2BA6A8C-CF05-4132-A4B6-363A7743128B.png

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5 hours ago, olaf hart said:

So while we are on the refrigeration topic, I have an issue at the moment.

The Valiant has two adjoining freezer boxes, one with two eutectic plates in it, the other with one plate and a 12v fridge unit.

There is a biggish 3/4 hp 240v AC compressor on the eutectic plates and a small 12v one on the fridge unit.

We are replacing both compressor and condenser units, and it is difficult to find a big enough 12 V unit to run the freezer plates, so the plan is a 1/2hp AC unit for the plates and a small 12v Danfoss for the fridge.

The plan is to freeze the plates down on shore, and run the AC unit through an inverter when the engine is running, using up spare amps from the alternator.

My question is how big an inverter do we need to handle the start up surge current of the AC unit compressor. We are in Oz, so this thing is 240V, but the wattage rating would be the same as a 110v compressor.

As far as I can see the surge can be up to 10 times the running current, and a soft start is not an option as the motor has to start up against a load so it will just stall out if there are not enough amps.

Cant get a decent answer from the supplier, so my plan is to put the unit in and use a clamp meter on it on shore power to check the loads, then order the inverter after that.

Wondering if anyone has some first hand experience with this sort of thing, I think we are looking at a 2000w inverter with a 4000w surge capacity, but would appreciate some real life experience

 

had a lot of joy running a solenoid valve between suction and discharge at the compressor, set to about 10 seconds on a timer is all you need to drop a significant load on startup, started doing this with R12 and it;s been pretty good with 134a and 404a thus far

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11 hours ago, olaf hart said:

My question is how big an inverter do we need to handle the start up surge current of the AC unit compressor. We are in Oz, so this thing is 240V, but the wattage rating would be the same as a 110v compressor.

As far as I can see the surge can be up to 10 times the running current, and a soft start is not an option as the motor has to start up against a load so it will just stall out if there are not enough amps.

 

In reading the links other posted earlier in this thread, one of the quoted advantages of the magnetic compressors was that they didn't have the big start up load.  The piston just moves a little bit at first and gradually builds up to the full compressor stroke. 

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