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Old 10-19-2012, 07:36 AM   #21
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Here are link on compressor speed contol. Danfoss BD35 and BD 50 compressors have variable speed capability and can run at speeds between 2,000 and 3,500 RPM. The longer and slower these compressors run, the more efficient they get, so it makes good sense to exploit this feature.

Speed Controllers for Danfoss BD 35/50 Compressors
http://coastalcoolaids.com/images/Co..._with_pics.pdf
http://www.ra.danfoss.com/TechnicalI...ehc100d702.pdf
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Old 10-19-2012, 07:41 AM   #22
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<P>FF, is that 60-100 amp-hrs in a 24 hr period? My unit draws a max of 7 amps when running on 12 VDC.</P>
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Old 10-19-2012, 08:36 AM   #23
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Adding to the ventillation of the refrigerator coils will certainly help its efficiency, but you're just transferring the heat load to the cabin or galley. It's usually not much of a problem because it's a large space, but the heat removed from the inside of the refrigerator has to go someplace.

I've always thought the best plan would be to transfer the heat to seawater just like the airconditioner typically does. I believe such units are available but they are not very common, probably because of initial cost.

I suppose it would be possible to cobble something like this up by attaching copper tubing to the refrigerator coils and pumping seawater through the tubing and dumping it overboard.

Would it be worth the trouble? I don't know.
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Old 10-19-2012, 11:11 AM   #24
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Quote:
Originally Posted by FF View Post
Sea Freeze lit sez 60-100A DC consumption with no cabin temps specified.

60-100A is NORMAL for most fridges, a bit higher for inverter fed AC box store fridges.
FF, Is that 60-100 Amp Hours per day?
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Old 10-19-2012, 11:56 AM   #25
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...I've always thought the best plan would be to transfer the heat to seawater just like the airconditioner typically does. I believe such units are available but they are not very common, probably because of initial cost.

I suppose it would be possible to cobble something like this up by attaching copper tubing to the refrigerator coils and pumping seawater through the tubing and dumping it overboard.

Would it be worth the trouble? I don't know.
We had a water cooled system on our last boat. Efficient as long as the water temperature was less than 90F. When we were on the hard, we had to shut it off.

Waeco makes an affordable water cooled system. SeaFrost also does but more money.

After living with a 12 VDC water cooled refrigeration/freezer system for 10 years and now having a 12VDC air cooled refrigeration/freezer system for 5 years (BD-35F and BD-50F). We prefer the current system. It's about the same in amps/day but better temperature control, more dependable, one less thru hull, no water pump and it works great on the hard.
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Old 10-19-2012, 12:02 PM   #26
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FF, Is that 60-100 Amp Hours per day?
I would say yes. We have a Danfoss BD-35 compressor for the refrigerator and a Danfoss BD-50F for the freezer. Our total amps, for 24 hours, is ~125-140 amps.
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Old 10-19-2012, 12:43 PM   #27
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a tip I found to work on two different units.. remove the defrost tray in the fridge unit if it has one . Seem to help a bit as tray blocks almost all of the coil
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Old 10-19-2012, 01:41 PM   #28
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I've always thought the best plan would be to transfer the heat to seawater just like the airconditioner typically does.
These are actually fairly popular up here, usually in larger or newer boats.
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Old 10-19-2012, 02:57 PM   #29
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The other upgrade to the typical marine refrigerator is the cold plate design where the system freezes a plate when there is excess energy available (engine running or shore power available) and then uses the stored cold (technically incorrect language, but easier to understand) to reduce compressor run time when on battery power.
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Old 10-19-2012, 03:49 PM   #30
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Ron I just help a friend put a system in his sail boat that can use air or seawater. Its a Seafrost. It only uses .5gpm and it has the same danfoss BD 35 compressor I have. It is VERY efficient. I runs less than 2 hours a day, but the insulation package we put in between R50 and R100. We used VIPs (vacuum insulated panels). One inch gets you R40-50.The system has a smart controller that varies the speed of the compressor based on performance.

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Old 10-19-2012, 05:01 PM   #31
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The other upgrade to the typical marine refrigerator is the cold plate design where the system freezes a plate when there is excess energy available (engine running or shore power available) and then uses the stored cold (technically incorrect language, but easier to understand) to reduce compressor run time when on battery power.

The upgrade is expensive with 2 separate compressors plus the cold plates take a lot room the box (s). Caulder does a good discussion of refrigeration in his book "Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems. He basically says that the DC evaporative plate systems are hard to beat with the small size, efficacy and reliability.
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Old 10-19-2012, 07:59 PM   #32
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Quote:
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. Caulder does a good discussion of refrigeration in his book "Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems. He basically says that the DC evaporative plate systems are hard to beat with the small size, efficacy and reliability.
Nigel Calder has another small book devoted entirely to refrigeration, even including building one! I got my copy from Amazon, can`t give more details of it, I lent it to a friend and....
Eutectic systems work for me, anything to get that big draw off the batteries. BruceK
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Old 10-20-2012, 06:48 AM   #33
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FF, Is that 60-100 Amp Hours per day?

Yes, this is the most common power burn.

A 300A bat set would be required for just the reefer , for each day of quiet ship.

Eutetic plates work best with a huge energy source. On out 90/90 the engine runs a cast iron auto Air Cond compressor with dual belts.

This will freeze the plates (roughly 10,000BTU cap) in 2 hours and thats good for 4 days , tho we try a 3 day off between re cool.

Great insulation , so tiny loads , is the BEST !!! way to have no problems but as noted at this time it requires a special build and is not inexpen$ive.
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Old 11-06-2012, 06:06 PM   #34
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Compressor speed test

I have completed data collection on my frig at the four selectable compressor speeds. I used a temperature data logger that recorded temps every 5 minutes. I then took that information and integrated the Danfoss tech manual amperage draw at the various temperatures. The Compressor draws lower amps at lower temps. The results indicate that the highest speed comsumes the least amps in a 24 hr period even with the compressor starting twice as much.
Highest speed:3500 RPM = 59.5 amp-hrs. Lowest speed 2000 RPM = 79.7 amp-hrs.
If you are a curious data geek, send me a message and I will send the spreadsheets and graphs!
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Old 11-06-2012, 10:27 PM   #35
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Thanks for the update Dave. I haven't had time to make the adjustments to our fridge but look forward to doing it and watching the results.
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Old 11-08-2012, 07:29 AM   #36
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"The Compressor draws lower amps at lower temps."

This is because the WORK being done drops as the temp differential drops.

The most amps is usually in the cooling a warm box condition , where its doing more air cond than cooling.
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Old 11-19-2012, 05:10 PM   #37
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I have tried putting the blue cooler "ice packs" in my little Nova Cool freezer when I know I will be motoring all day. (I don't use my freezer anyhow) but they never seemed to freeze for me. Later I drilled holes in them, replaced 1/2 the fluid with water, and taped over the holes. They still didn't freeze in a 6-8 hp run. Did the same thing again (resulting in 25% original strength fluid) still didn't freeze. Only when I did it a 3rd time (12% original strength) did they freeze in a 6 hr run.
What's up with this stuff?
I thought I was making a "poor man's" removable eutetic plate...
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Old 11-19-2012, 05:30 PM   #38
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Not a Crown drinker. Knob Creek, Bulleit, and most any single scotch works for me.
what no JD?.......not my cup of tea either but i can stomach a sip or two of a good scotch once in awhile
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Old 11-20-2012, 07:21 AM   #39
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I thought I was making a "poor man's" removable eutetic plate...

In order for the eutetic fluid to freeze it must be cooled below its melt temperature.

Your setup is not getting cold enough to freeze the stock solution.

Lowering the box thermostat enough to freeze the eutetic solution may result in frozen milk and lettuce.
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