Installing an Electric Fridge

[Irish rambler]

Weyalan and Belizesailor, thanks for the heads up, The Isotherm uses a DB35 Danfoss and was insulated by Isotherm when built. You are absolutely correct that refrigeration is power hungry and our temps here at most reach around 40 C. My aim, as in all things on the boat is to keep things simple,effective and highly efficient rather than simply fit more panels, batteries and unnecessary geegaws.

[belizesailor]

Originally Posted by Irish rambler

Weyalan and Belizesailor, thanks for the heads up, The Isotherm uses a DB35 Danfoss and was insulated by Isotherm when built. ....

The BD35 (I assume "DB..." was a typo), is a very efficient little compressor. I have small fridge using one aboard my boat. It draws only about 3A @ 12V DC (36watts) when running (after the fridge has initially cooled down -- more for initial cool down). My installation, here in the tropics, has about a 30% duty cycle (rough guess) so that should be only about about 22AH per day. And the installation of this little fridge is certainly not thermally perfect -- it is front loading and could use more insulation.

If yours is drawing more than this then I expect there is a problem somewhere.

[belizesailor]

Ran across a good diagram in Danfoss literature re BD35F power consumption (attached). It shows average power consumption for a BD35F across box sizes at 25C ambient. There are of course many factors not accounted for which could effect power consumption, but this gives a good general estimate.

The document this came from is also pretty well done regarding refrigeration installations using solar for power.

http://www.ra.danfoss.com/TechnicalI..._pn100b202.pdf

[galleyslave]

I am just finishing rebuilding my fridge and freezer and have gone for the option of separate Danfoss compressors for each. This gives me the option of using both as freezers, fridges or one of each, admittedly at a price in terms of battery consumption.
Both compressors are in the same compartment with plenty of inward ventilation and I have installed an extractor fan to help keep the compartment cool.
So far so good - it works and, thanks to good insulation, is using less battery than the old installation using only one compressor.
However, I don't want the extractor fan to be switched on when neither compressor is working and, to do this, I presume that I must take the power for it from the positive feed to each compressor so that power will only be supplied to the fan when one or both compressors are running.
Question: Do I need to take any precautions (diodes or whatever?) to prevent the second compressor from running off the power of the other via the fan when, the thermostatic controls would only have one running?

[Sumner]

Not sure which unit you are using, but the one we are using has a terminal to run a fan off of. I'm just not sure if it is switched reading the documentation and only comes on when the compressor is running??

http://www.ra.danfoss.com/TechnicalI...cei100b602.pdf

It can handle up to .5 amp. If it is over that run the fan off of a relay.

I think for what you are doing I'd try coming off of that terminal on both units with diodes between them and the fan or the relay.

First I'd try and contact the company though either by phone or e-mail and see what they say.

I like your two different systems for what you are doing and if we were full time cruisers would probably do the same. Also if one goes down you still have the other while repairs are made. It takes so much energy to cool and I don't see where you should use more with the two compressors as each won't work so hard, in fact it might be more efficient overall vs. making one do both.

There is more documentation here also....

Documentation - Danfoss

Sum

[sailorchic34]

As with anything electrical its not just the amps drawn but duty cycle. My 110V fridge does draw about 14 amps @~12.6V when running. But it only runs about 2.5 minutes out of 14 minutes at 85-90 degree cabin temp. Which works out to about 2.5 amps per hour uses (including inverter losses.

As the basis compressor design is the same between the 12V and 110V units the over all power used would be near the same. The difference is run time/duty cycle. Generally the 12V units being a smaller compressor run longer.
Generally box insulation makes more of a difference.

On sunny days my two solar panels (230 watts total) carry the daily boat load, which includes the 120V fridge.

[Cheechako]

Originally Posted by sailorchic34

As with anything electrical its not just the amps drawn but duty cycle. My 110V fridge does draw about 14 amps @~12.6V when running. But it only runs about 2.5 minutes out of 14 minutes at 85-90 degree cabin temp. Which works out to about 2.5 amps per hour uses (including inverter losses.

As the basis compressor design is the same between the 12V and 110V units the over all power used would be near the same. The difference is run time/duty cycle. Generally the 12V units being a smaller compressor run longer.
Generally box insulation makes more of a difference.

On sunny days my two solar panels (230 watts total) carry the daily boat load, which includes the 120V fridge.

I've enjoyed your posts regarding the 120V fridge. I've often thought there was something wrong with all the so called facts and figures the naysayers present regarding the use of these. As is often the case, the science is complicated to the point of often being incorrect. If you miss one variable, you've got it wrong. My ex Boss/CEO used to have a saying: "figures dont lie, liars figure..."

[Sumner]

Originally Posted by sailorchic34

....Generally box insulation makes more of a difference..

As you said it is primarily the insulation. Have you tried to add insulation in some way? I still haven't seen this done with an upright (front opening door) and when I try and imagine it being done it doesn't seem to be an easy obstacle to overcome.

The main thing is does whatever a person is doing/using work for them? If it does then nothing needs to be changed.

Nice to have different options out there for different people/situations,

Sum

[Cheechako]

It would be interesting to know what they are using for insulation in modern fridges. My new 5 Star Energy Star fridge walls are 1.5 inches thick at the most, the exterior surface is not cold at all, so not much is "leaking thru".

[sailorchic34]

On my little magic chef the side walls have the condenser tubing bonded to the metal sides. (Got to be careful where one attached hold downs to it too.) So with this design, insulation could not be added. Mine has 1-1/2" insulation and is not too bad. Would love to add 2" more but maybe on the next fridge...