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I have an engine-run compressor and want to add an electric compressor for use when on a mooring. I believe the current system is a seafrost. It is fresh water cooled (using engine coolant). There are 2 holding plates, one in the freezer and one in the fridge. Electricity will not be an issue because of a fourwinds wind generator and the mooring is in a windy place (average wind speed in July is 12 knots).

Is it possible to add a second, electric compressor?

Do I have to worry about isolating the compressors (maybe with a reverse flow preventer) from each other, or can they simply be put in parallel?

Has anybody done this?
 

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Discussion Starter #2
It would be good to keep the milk cold this summer, even when we aren't on the boat.
 

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Adding a second compressor is going to complicate the setup alot, and create lots of possible points of failure. It might be simpler to have a small electric 12 VDC fridge for the stuff that has to stay aboard. A small Engel would be my suggestion. They're portable. Most are dual voltage, so can run on AC when connected to shorepower or 12 VDC when out on the mooring.
 

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It was set up that way in another boat I had. BUT, it had two plates with TWO separate feed return systems into each plate. One from the engine and one from the electric compressor. They ran into each plate but separately cooled it. They were not piped together. If one broke the other cooled. I would think you would have to replace the plates or just add a separate 12 volt system with its own plates. call sea frost. I have found them helpful.
 

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You could also have additional 12v system inside the same box.
Similar double cooling system is used on my boat:
On fridge with:
1) factory installed 12v simple system - that was left as it was
2) added 220V (over inverter) holding plate with separate compressor and everything.
Yes, it takes more space in the fridge and in the cabinets, but you have full redundancy.
 

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I don't think you want to use the same system at all. If you want full redundancy with the engine driven system, suggest you just add a complete 12V system with separate plates. If you think your wind gen is going to keep up with it at anchor....think again. It won't even keep up fully with one box. If the engine system is working...suggest you just get a small 12V system for the fridge box and run the engine whenever batteries get low or the freezer needs to be brought back down below 32.
My 52 had a SeaFrost 12V 1/2 HP system but we ran the generator when using that and had a huge battery bank and 130amp charger to keep up with two large boxes like yours.
 

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How old is your Seafrost? You might want to junk it and put in a 12v system.
Year is 2000.

She's a Beneteau 505.
 

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I don't think you want to use the same system at all. If you want full redundancy with the engine driven system, suggest you just add a complete 12V system with separate plates. If you think your wind gen is going to keep up with it at anchor....think again. It won't even keep up fully with one box. If the engine system is working...suggest you just get a small 12V system for the fridge box and run the engine whenever batteries get low or the freezer needs to be brought back down below 32.
My 52 had a SeaFrost 12V 1/2 HP system but we ran the generator when using that and had a huge battery bank and 130amp charger to keep up with two large boxes like yours.
I might have to add a couple large solar panels to keep up then. And then I would have diverse (belt-and-suspenders) methods of generating electricity.
 

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Call Seafrost, Cleve is very helpful.

I'm not sure what you mean by 'electric compressor'? 12 volt? 120 volt?

I have 2 cold plates in my freezer with a spillover to the frig. Boat came with engine driven and shore assist systems. Thinking of adding a 12 volt to the existing setup for longer term anchoring rather than have to run the engine an hour every day.
 

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Call Seafrost, Cleve is very helpful.

I'm not sure what you mean by 'electric compressor'? 12 volt? 120 volt?

I have 2 cold plates in my freezer with a spillover to the frig. Boat came with engine driven and shore assist systems. Thinking of adding a 12 volt to the existing setup for longer term anchoring rather than have to run the engine an hour every day.
I was thinking 12 volt, so I woouldn't have the inefficiencies of an inverter. (Better to have the inefficiencies the other way around, if I'm ever connected to shore power.)

I don't want to have to run the engine for an hour each day either.

What is a "shore assist" system?
 

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I haven't read all the posts so forgive me if I'm repeating.

AFAIK, the heart of a fridge system is the expansion valve and AFAIK each expansion valve is matched to the compressor. I don't believe you can have two compressors running off the same expansion valve.

There will very concievable be a boffin out there who will say this is [email protected]. if there is, he'll not get an argument from me :)
 

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The way my system is rigged, I have 2 holding plates and 2 compressors.
One compressor is engine driven and feeds into plate A and then into plate B. The other compressor is A/C powered and feeds into plate B and then into plate A with a separate set of lines. In fact, the engine system is R-12 and the A/C is R-134A so they are definately separate!
The A/C system isn't powerful enough for a quick genset chilling of the plates. It's designed to run 24/7 off shorepower. It works great that way.
I would prefer a 12 volt system but since I already have these 2...
 

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Discussion Starter #15
Go to

seafrost marine refrigeration

and you'll find it.

My boat came with the Engine Driven system. I don't use it much (maybe a week or two a year), but it seems to work OK.

Barry
Good input. I found some interesting options on their site.

As everyone knows, the costs start adding up, especially if I need a completely separate system. I'm wondering if it's better to just run the motor an hour each day or just buy ice!
 

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I just looked at the back side of my fridge, based upon a comment someone posted somewhere (looked for the thread, couldn'find it). Guess what I found? It's another cooling-line input on each of my 2 holding plates.
 

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Discussion Starter #17 (Edited)
xort - saw your post on anyting-sailing.com that it might not work like I think it will. I'll call Clive at Seafrost.
 

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Study up on their website first. It was confusing to me but gave me a basis to ask better questions. There are 2 kinds of 12 volt systems, Cleve explained better what the differences are. He and I came to the conclusion that IF the engine drive system is working, then leave it in and add the 12 volt system to compliment the engine system.

Think of this...the more you cycle your batteries down, the quicker they will need replacing. That is a given fact. So when you run the engine and get 'free' referigeration, you are lessening the need to run the 12 volt system and lessening the cycling of your house bank. Saves you money on battery replacement. Having the engine drive AND the 12 volt system gives you independant redundency. I have read of a lot of accounts of refers going on the fritz and loosing a whole load of food, especially frozen meats.

again, I'll say that if a boat does not already have an engine drive system, it's probably not cost effective to add one. But why throw out a perfectly good system that is already in place. The only issue is that they do take up space in the box. I'm willing to live with that for the benefits of redundency and free referigeration. The biggest stumbling block with engine drive is at the dock. The 12 volt steps in nicely there.
 

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What your $$$uggesting , using the same evap plates and a common piping system with 2 comps is very complicated to set up, even for people in the hvac biz (moi ? ) :D Err.. anyway you would need "reversing valves" at least 2 of them. They are used in hot gas by pass and heat pump systems. boaters call em "reverse cycle" It's really better to use separated systems as stated by others. Good luck!
 

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Thanks Xort and Denise. I'll do some more studying of the website and then call Clive. There's no real rush on this, compared with the things that have to be done before launching. So I might pause this project a month or two.
 
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