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Discussion Starter #1
I have an engine driven refrigerator but I was wondering whether it might not be more efficient to replace the compressor with a high output alternator and redo the refrigeration to run off one of those off the shelf units.

Probably also safer in the long run, i.e. the temp in the refer is automatically kept in the right range?

At present I have a condensing unit that uses the raw water from the engine.

For an electric compressor the choice is (i) air cooled, (ii) water cooled with (iii) additional pump or I think some sort of external heat exchanger on the outside of the hull.

I don't like (ii) (iii) because they will not work on the hard and (iii) is a bit bulky anyway.

What about the efficiency of air cooled in the tropics?

Would a combo condensing system make any sense?
 

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To make my reply easier, most of this reply is from my posting on Anything-Sailing.

Dump the engine driven system!!

When I bought my Freedom 32 it had a Seafrost engine driven holding block system, it was an R12 system and had lost it's refrigerant charge due to lack of use. The holding block had 2 circuits so I had considered a 110v compressor on the spare circuit while at dock and repairing and upgrading the engine driven system to an R134a system.

Well, speaking with Cleave at Seafrost he proposed replacing the engine driven system with one of their 12volt BD systems. I was nervous about this as Freedom 32's only have space for 3 group 24 batteries and so I only have about 160 to 170 amps of house capacity and to increase it required loosing storage space and the starting another project, neither of which I wanted at the time. As the boat was only used to day sails and weekends away, I decided to go with the advice and give it a try, it was going to work out cheaper than my original plan anyway!!

So I ordered a 12volt pre-charged BD system along with a evaporator plate style freezer bin that was sized to fit my reefer.

Installation was complete within a couple of hours, the hardest part was removing the old holding block, damn that thing was awkward and heavy, installing the new freezer bin also took as much time again. The installation, plumbing and wiring of the compressor unit was easy and took probably 30 to 35 mins.

I installed this system in September/October last year and to date I am very pleased with the performance. The boat is now being used as a live aboard during the week and I have really cold beers and can can store frozen meals for the week. The system runs 24/7 off the batteries which also have sufficient capacity for day sails so far and I think may also be ok for weekends based on how the unit has performed so far. However, the heat of summer may have me reviewing my battery capacity, but I have a well insulated reefer and remain hopeful based on current performance plus I have eliminated several items from my engine room and adjacent lockers with the removal of the engine driven, sea water cooled system.

During the winter months while maintaining cabin temperature at 68 degrees the unit is operating about 40% of the time, I am expecting this to 70% / 75% during the summer. Maybe the addition of the variable speed controller for the Danfoss BD compressor could reduce the runtime!

Disclosure, I do not work for or have any commercial interest in Seafrost, I do however work for a company that does on occasions supply Seafrost equipment, when requested, for customer use with our products.

Bob
 

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If you have a seafrost system, call Cleve at seafrost. He'll talk you through all the variations and help you out. Excellent technical support.
 

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Discussion Starter #4
Did you go for air-cooled or water-cooled?

Thanks for that info.

I guess most off the shelf units are air cooled, but in the tropics this could actually heat up the cabin and decrease the effectiveness of the refer.

So ideally some way to have the condenser air cooled sometimes and water cooled at other times might be best. But does this exist, is it worth it?
 

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matt
seafrost has done work with various types of systems, have you looked at their site?

Have you considered keeping the engine drive system and add a dc system?

since you already have the engine system, it becomes 'free' to operate when you do run the engine, and it adds redundancy
 

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Discussion Starter #6
seafrost has done work with various types of systems, have you looked at their site?
Looked at them all at one time and another, but will look again.

Have you considered keeping the engine drive system and add a dc system?
Yes, but there is not a lot of room. If I was to have an electric version I would need more alternator output to charge the batteries quickly. Any high output alternator would go on the bracket where the engine driven compressor is. Wish I could fit both but not possible.

since you already have the engine system, it becomes 'free' to operate when you do run the engine, and it adds redundancy
Yes it would. It all actually works now but I need the run the engine for about three hours to cool it down then one hour a day. It seems a shame to break down a working system. I'll think about it, but then where will I put the hi output alternator?
Thanks for your thoughts.
 

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What is the current alternator?

You can get up to about 100 amps on a small frame alternator. That could replace the current alternator, if it's too low powered.

Do you have alternate sources of power?

If you are going to run the engine to charge batteries and power the refer, it would be more efficient to run an engine driven refer directly.

With a high power alternator, how log will you need to run the engine to charge the batteries?

I'm thinking you could run the engine with the 100 amp alternator that charges the batteries AND the engine driven compressor chills the cold plates. The cold plates should be able to stay cold for 24 hours on one hour of engine time. After that, the 12 volt system kicks in to extend the refer chill time. depending on the battery bank, you could get another 24 hours. Add solar and win and get another 24 hours before running the engine.

I wouldn't do all this from scratch but since you already have the engine system, perhaps it works to have a dual system. I love the redundancy too.
 

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Don't you currently have an alternator in addition to the engine-driven compressor? You could swap out the existing alternator for a high output one.

I plan on adding an electric compressor and keeping (recharging) the existing Sea Frost engine-driven system. Not sure how many amp hours it will use per day. I'm adding a wind generator to keep the fridge going so we don't ever have to run the engine for cooling.

Helpful thread. Thanks.
 

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Remove the old system, regardless of which replacement system you choose. I understand that the current system has been fully amortized, but to retain it implies 2x the weight, complexity,and upkeep.

Glacier Bay makes a DC driven unit that will charge the plates when it senses excess capacity available from the alternator. I'm sure the sea frost alternatives are as good too.
 

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I think a good DC-based system is a much better idea. If you plan the size and have proper electrical setup, you can often use it without having to run the engine to charge the batteries, especially if you have a decent passive charging setup.
 

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You could always fit a 2nd high output large frame alternator in the position the refrigeration compressor is now, that may be a cheaper, you have a back-up system then.
 

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Discussion Starter #12
What is the current alternator?
You can get up to about 100 amps on a small frame alternator. That could replace the current alternator, if it's too low powered.
Yes it is a small frame 85amp alternator on a sole mini 35hp engine.
I tried finding a more powerful alternator, by talking to the manufacturer and
the distributor and then various auto electricians - even took the alternator to them and tried to get something more powerful in that configuration but ended up that there was nothing with the same frame. So I just had it rewound and put it back on. I still think there must be a high powered alternator that matches what I have, but that will have to wait.
Do you have alternate sources of power?
Yes, I have an Airex wind gen which puts out a few amps but less than I would have expected. Also a few small solar panels for trickle charging. May get some larger panels later.


If you are going to run the engine to charge batteries and power the refer, it would be more efficient to run an engine driven refer directly.
Yes I would have thought so to, but I found that running the engine for an hour every day a bit of an annoyance. Also despite the engine driven compressor being quite powerful it just takes time to get the temperature down. In the tropics it will take even longer. I read something about this in Nigel Calder's book also.

With a high power alternator, how log will you need to run the engine to charge the batteries?
I have a 3 stage Next Step Ample Power regulator and have some additional batteries installed but not yet connected, that will take the house bank to 500ah all Absorbed Mat. The most the alternator has put out is I think around around 50 amps, but for most charging it is way below that more like 20-30amps then dropping off fairly quickly.

So how long will it take to charge, I am not sure. Maybe later I will get bigger solar panels and maybe a more programmable 3 stage reg. I don't want a external generator and no room for a genset.

I'm thinking you could run the engine with the 100 amp alternator that charges the batteries AND the engine driven compressor chills the cold plates. The cold plates should be able to stay cold for 24 hours on one hour of engine time. After that, the 12 volt system kicks in to extend the refer chill time. depending on the battery bank, you could get another 24 hours. Add solar and win and get another 24 hours before running the engine.

I wouldn't do all this from scratch but since you already have the engine system, perhaps it works to have a dual system. I love the redundancy too.
Yes it could work. I guess the demand on electric system would be less if used in conjunction with the working engine system and so the existing alternator might be enough at least in the short term. I could put the cold plate on the inside of the ice box and that would be it.

Yeh not bad, it could work.

Then for other stuff like running computers, water maker, etc I will have to get more solar panels and modify the mounting brackets to take a 100 amp alternator.
 

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couple of things come to mind. A 100 amp alternator isn't all that much more than the 85 amp you have. Not sure why it's not putting out rated or near rated output.

Do you know the generally accepted real life capacity of your house bank?
You should not run it down beyond 50%, it is then time consuming to get it back to 100% as the charge drops off after reaching 80%. So that means you get 30% of the rated capacity in practical real life use!!!! That is 150 amps of ususable capacity. Probably one days supply of DC power if you include the refer. So you will have to run the engine every day anyway to recharge the batteries.

If it were me, I'd leave the engine drive system in. Your one hour engine runtime will chill the cold plates down AND charge the batteries. Your 150 amps might get you a second day without running the engine so you'd run the engine every other day. With DC only you will run the engine every day. With engine driven cold plates you will run the engine every day. Combining the two could get you every other day running of the engine.
Not sure where that leaves your watermaker but that is more power consumed. Perhaps the one hour engine run time can be the watermaker run time and not have to draw from your batteries? Of course that pulls from the alternator capacity!
Which BTW, the 85 amps means you only put that much into the batteries in an hour, max. So my concept of running the engine one hour to charge the batteries isn't actually enough. To get the 150 amps back in, you'd need to run 2 hours. So it might be 2 hours every other day.

Not sure why you aren't getting any juice out of the wind gen...
 

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My engine driven system (old R12 unit) finally packed it in and we had to make the same decisions.

We finally decided to do the following;
We're rebuilding the engine driven system to run on new environmentally appropriate coolant. This means a new compressor and some other parts but much of the old can be retained.
We're also adding a 12 V system.

Our engine has a power take-off shaft coming off the front of the engine. This shaft powers the high output alternator for the house bank and the compressor. When running the engine at anchor for charging batteries, the compressor helps to put some load on the engine.
The 12 V will allow us to have cool beer and fresh food in marinas and when on the hard, as well as when our solar panels (we're adding) and KISS wind generator keeps up. It allso gives redundancy.

So, I'm in the camp of those who argue it doesn't make sense to remove something that's worked well. If its' broken fix it. We're adding the 12V for reasons mentioned. We went with air cooled for simplicity and cost. The heat will be nothing compared to that from having to run the engine for the compressor only.
 

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Discussion Starter #15 (Edited)
Wavering.

I think a good DC-based system is a much better idea. If you plan the size and have proper electrical setup, you can often use it without having to run the engine to charge the batteries, especially if you have a decent passive charging setup.
You are probably right, I have spent a lot of time and effort on the engine driven compressor refer, and although it works, I am not 100% happy with it.
It is in fact fairly complicated and for some of the controls there is no manual. The insulation is old (20yrs), so maybe its is not that efficient. Also it is impossible to set a temperature you want exactly, it just swings up and down. I got it down to I think -23 deg C (my memory of the exact temp is a bit hazy) but it comes up pretty quickly even with a fairly cool ambient temp. Definitely has to be run every day and maybe sometimes twice a day to be sure. In the tropics it could be a health hazard. I read somewhere about placing some refer insulation over the hatch so maybe I will try that.

Though I wonder if it is worth to replace it and get a large ~150amp 2nd
alternator, since the current draw on recharge is generally pretty low at present?

Perhaps this is a decision I will make as I go along, depending on long term power usage. I was thinking of adding a hot water heater that works off an engine heat exchanger and power, so presumably It could absorb any surplus power.

I could install an electric refer system and if the engine driven system fails, I might rip it out and redo the entire box thing using modern insulation and maybe even make the box bigger at the same time.

Any thoughts on the efficiency of air cooled in the tropics?

Are there any other air/water cooled combination refers?
 

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Discussion Starter #16
My engine driven system (old R12 unit) finally packed it in and we had to make the same decisions.

We finally decided to do the following;
We're rebuilding the engine driven system to run on new environmentally appropriate coolant. This means a new compressor and some other parts but much of the old can be retained.
We're also adding a 12 V system.
Yes that is what I did, i.e. new compressor new gas R134A for default but the initial charge was some sort of hybrid gas the refer man had.

Our engine has a power take-off shaft coming off the front of the engine. This shaft powers the high output alternator for the house bank and the compressor. When running the engine at anchor for charging batteries, the compressor helps to put some load on the engine.
The 12 V will allow us to have cool beer and fresh food in marinas and when on the hard, as well as when our solar panels (we're adding) and KISS wind generator keeps up. It allso gives redundancy.

So, I'm in the camp of those who argue it doesn't make sense to remove something that's worked well. If its' broken fix it. We're adding the 12V for reasons mentioned. We went with air cooled for simplicity and cost. The heat will be nothing compared to that from having to run the engine for the compressor only.
Ok, that also sounds good. I don't understand how you have a compressor and an alternator off the front of the engine though?

Are they both mounted on the engine or are they mounted on the boat?

Do they both run off belts?

Also what temp can you get the refer down to and how quickly would the temp come up in say a 25 deg C day? Maybe I am expecting too much of my refer.
 

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Discussion Starter #17 (Edited)
Power Usage

couple of things come to mind. A 100 amp alternator isn't all that much more than the 85 amp you have. Not sure why it's not putting out rated or near rated output.
I am not sure either, could be the settings on the Reg, I will have play around with it. It is a bit user unfriendly compared to modern regs, there are tiny quick blow in line fuses and the readout is in flashing leds.

Do you know the generally accepted real life capacity of your house bank?
You should not run it down beyond 50%, it is then time consuming to get it back to 100% as the charge drops off after reaching 80%. So that means you get 30% of the rated capacity in practical real life use!!!! That is 150 amps of ususable capacity. Probably one days supply of DC power if you include the refer. So you will have to run the engine every day anyway to recharge the batteries.
I think the docs said they can be taken down to 50% charge, they are good quality and were bought as house batteries. I got a lot batteries for autopilot usage.

If it were me, I'd leave the engine drive system in. Your one hour engine runtime will chill the cold plates down AND charge the batteries. Your 150 amps might get you a second day without running the engine so you'd run the engine every other day. With DC only you will run the engine every day. With engine driven cold plates you will run the engine every day. Combining the two could get you every other day running of the engine.
Not sure where that leaves your watermaker but that is more power consumed. Perhaps the one hour engine run time can be the watermaker run time and not have to draw from your batteries? Of course that pulls from the alternator capacity!
Which BTW, the 85 amps means you only put that much into the batteries in an hour, max. So my concept of running the engine one hour to charge the batteries isn't actually enough. To get the 150 amps back in, you'd need to run 2 hours. So it might be 2 hours every other day.
Here is a rough estimate of power used:
10ah = 40amps * .25hr Say bfast - toast+coffee
36ah = -1.5amp * 24hr Fridge elec (not purchased yet)
10ah = 2.0amp * 5hr Lights (flurescent)
2ah = 0.25amp * 8hr Anchor light
10ah = 5amp * 2hr Water Maker (not purchased yet)
30ah = 30amp * 1hr Hot water heater (not installed yet)
12ah = 0.5amp * 24hr Radios
50ah = 10amp * 5hr Entertainment DVD/CD/Computer
-------------------------------------------------------------------
160ah Total
Does this look about right? It seems high to me?

What I really need (or maybe not) are amp hour meters on the input and output side to monitor things. At present I have a single meter that monitors amps in and amps out and is supposed to monitor the battery level, but it does not really work as advertised, because so many assumptions need to be made about the batteries ability to absorb the charge and this is actually dependent on ambient temp, battery age, charge state, voltage in, other loads etc.

Not sure why you aren't getting any juice out of the wind gen...
I am not either, although I think there is a setting to adjust the voltage at which the batteries are considered fully charged, i.e. the AirX self regulates. I think this voltage may be set too low. Now that it is up it is difficult to make this adjustment. Oh well.
 

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...Any thoughts on the efficiency of air cooled in the tropics?

Are there any other air/water cooled combination refers?

There are now some DC holding plate systems which seem to offer a lot of the benefits of both engine and DC systems -- maybe worth investigating further.

Aboard a boat on which I cruised a fair bit, we installed an air-cooled unit. It managed pretty well, even in some extremely high heat conditions (49C/120F). But it definitely lost efficiency, and dumped some heat back in the cabin. Most of the time it managed very well. The big advantage being that you can use it even when the boat is on the hard.

On our current boat we have a Frigoboat DC unit with a keel-cooler. It is extremely efficient. Unlike other water-cooled systems, it has the advantage of not requiring any winterization for colder climates. But it can not be used when the boat is on the hard.

Air is less efficient for exchanging the heat than water, but it is the simplest installation, requiring no holes in the hull or pumps. If you go with an air-cooled system, try to duct the heat to a wet/hanging locker so that you can scavenge some benefit from it.
 

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Yes that is what I did, i.e. new compressor new gas R134A for default but the initial charge was some sort of hybrid gas the refer man had.
I'm not sure what you are saying here. But, If you tried to put the new hybrid referigerant into the old R-12 system, you probably wasted your money and damaged the compressor. According to Cleve at Seafrost, the old R-12 systems CANNOT use any of the newer hybrid referigerants. You must use R-12. If you got a new compressor, you should have got R-134A.

Have you called Cleve? He knows a lot more than us.

Also, what is the condition of your insulation? No matter what system you use, it will work poorly if the box insulation has broken down. When old insulation gets wet from condensation, it breaks down.
Here is another place to go for some excellent information, buy his book...
KollmannMarine Boat Refrigeration Specialist
 

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Discussion Starter #20
I'm not sure what you are saying here. But, If you tried to put the new hybrid referigerant into the old R-12 system, you probably wasted your money and damaged the compressor. According to Cleve at Seafrost, the old R-12 systems CANNOT use any of the newer hybrid referigerants. You must use R-12. If you got a new compressor, you should have got R-134A.
No I got a new compressor set up for R134A, flushed the system all ok on that front. It works, but does not seem to hold the "cold" as long as I'd hoped.

Also, what is the condition of your insulation? No matter what system you use, it will work poorly if the box insulation has broken down. When old insulation gets wet from condensation, it breaks down.
Yes you're right the insulation might be the problem here.

Here is another place to go for some excellent information, buy his book...
KollmannMarine Boat Refrigeration Specialist
Thanks, looks like good info.
 
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