Refrigeration and Power Management

[MDO]

I am interested in advice and best practices for balancing refrigerator use and power consumption while at anchor.

I have a Beneteau 331 with an Adler Barbour refrigeration unit that runs off the house battery bank (two 4D AGM batteries). The refrigeration unit runs fine and the chill box appears reasonably insulated. The boat is in the Puget Sound, so ambient temperatures are not excessively hot. The day prior to getting underway I usually run the refrigertor at the dock with shore power to get the temperatures down. I'll leave the refrigeration on while motoring out of the slip. But once I secure the engine I also secure power to the refrigeration unit.

- If I left the refigeration running, how much risk is their in running down the batteries?
- If I left the refrigeration running, Should I plan on running the engine at anchor, for an hour or so, to ensure a solid charge on the house bank?
- Is it better to just put a block of ice in the chill box and not run the refrigeration at anchor?
- Any other suggested schemes?

Thanks.

 

[Ross]

The more completely you keep the box full, the longer it will take for it to change temperature. I would freeze drinking water in bottles or jugs at home and load them in to fill any space after you put all the food in.

 

[Winkfish]

On our recent bareboat charter in Greece, where it was HOT, we'd motor out, leave the motor on for about an hour, in neutral, to charge the batteries. We'd leave the fridge on from the morining until we went to bed that night. Other than the initial morning run, we'd only run the motor to moore up or anchor. It was fine, kept things at least cool until the next morning, and even longer most days. We did have a battery monitor, so we could see how the batteries were doing and power up if we needed to.

The tip about frozen water bottles is a great idea. In fact, some stores would sell their bottled water frozen, just for the yachties.

Running the fridge will, of course, drain the batteries. You just have to experiment to see how long yours last. Keep your starting bank seperated from the house bank.

Also, just in case, one of those jumper packs is a great thing to have handy in case your batteries, esp your starting ones, do ever run down. Best $100 I've ever spent. (Well, maybe not the BEST...)

 

[druid]

It took me years to get my NovaKool setup working right on my Catalina 36. I ended up with 2 Golf-cart batteries (about 250 A-h) for the house, a high-capacity alternator, charge controller, and 45W solar panel. The converted icebox was NOT that well insulated.

The fridge used about 100 A-h a day, so I was good for overnight, two days if I really watched the consumption, or if it was sunny and I get some charge from the solar panel.

Now, I have a Waeco that is very well insulated and uses about 25 A-h a day, so I'm good for at least 2 days with my 95 A-h Group 27. Now that I've traded my 45W panel with a more efficient 80W panel, I can run the fridge indefinitely in the summer.

druid

 

[Old Skool Neil]

I have a similar setup (NovaKool refrigeration but it uses the same Danfoss compressor) and here's my top 10 list:

1. Does your drain have a trap? If not, put a rubber stopper in there.
2. Are your lids well insulated and gasketed? (I've got 3" insulation and an airtight gasket).
3. As stated by others, fill the box.
4. Keep all drinks iced in a separate cooler. This greatly reduces the number of times the fridge lid is opened.
5. Also as stated by others, an isolated engine starting battery is more important now than ever.
6. An old rule of thumb is add a battery when adding refrigeration. The point is increase your battery storage capacity as much as space and budget allow.
7. Size your alternator to 25% of battery amperage (another rule of thumb).
8. Separate your house batteries into (at least) 2 banks. When one runs low, switch to the other while you charge the first.
9. Do you have an amp meter on your house loads? With it you can measure the refrigeration amp loads and time the duty cycle. With this information you can calculate how many amp-hours your refrigeration consumes daily and adjust your alternator run time to replenish.
10. If possible, moor or anchor the boat so the galley side is shaded from the sun.

​

A note on alternators - their output lessens as the battery state of charge comes up. As a place to start, figure running twice the time your calculation indicates.
As an example, my box has very poor insulation except for the lid, the drain is plugged and with the box less than half full it the refrigeration system draws 4 amps at a 50% duty cycle. That calculates to 48 amp-hours daily and means I have to produce 48 amp-hours daily to break even.

My alternator is 100 amp so if it put out its full rating I'd need to run 1/2 hour. But it doesn't run at full output, the battery state of charge determines the alternator's output. Using my 2X fudge factor (again, as a place to start), I'd be recharging for 1 hour minimum just to keep up with the refrigeration. That doesn't account for cabin lighting, anchor light, water pressure pump, stereo, etc.

Refrigeration makes a strong case for alternate charging sources like solar and wind.

 

[lehua768]

A note on alternators - their output lessens as the battery state of charge comes up. As a place to start, figure running twice the time your calculation indicates.
As an example, my box has very poor insulation except for the lid, the drain is plugged and with the box less than half full it the refrigeration system draws 4 amps at a 50% duty cycle. That calculates to 48 amp-hours daily and means I have to produce 48 amp-hours daily to break even.My alternator is 100 amp so if it put out its full rating I'd need to run 1/2 hour. But it doesn't run at full output, the battery state of charge determines the alternator's output. Using my 2X fudge factor (again, as a place to start), I'd be recharging for 1 hour minimum just to keep up with the refrigeration. That doesn't account for cabin lighting, anchor light, water pressure pump, stereo, etc.On our recent bareboat charter in Greece, where it was HOT, we'd motor out, leave the motor on for about an hour, in neutral, to charge the batteries. We'd leave the fridge on from the morining until we went to bed that night. Other than the initial morning run, we'd only run the motor to moore up or anchor. It was fine, kept things at least cool until the next morning, and even longer most days. We did have a battery monitor, so we could see how the batteries were doing and power up if we needed to.

 

[Don12364]

In simple terms a typical refrigerator consumes about one battery full of power a day (assumes only using 50% of available power to prolong battery life as recommended). So a long weekend can do for most boat's systems.

As a comparison I used to go to the fish dock and bribe the attendant to fill two supermarket trolley bags with crushed ice. We put about 20lb in each. It was real heavy to carry (and cold on the legs too!)
We then tipped a bag into the bottom of each of our refer compartments below the lower tray. It lasted four days with the refer not switching on at all.
Many compartments were originally designed for ice anyway.

If your marina has an ice machine its a no brainer really to use ice to help out the ship's batteries. You can even deep freeze a couple of large plastic drinks bottles and use these.
Alternatively double up your house batteries, use up your locker space, they are heavy and the boat has to carry them all the time, then replace them every few years and think of how much ice that would buy!
I did just that and now realise I was wrong.

 

[Stu Jackson]

Good advice here

and in addition, do an energy budget. You'll find links to many of them if you do a search on this forum's engine.

As Donalex says, a fridge is 60 ah a day. That's pretty much the consensus after 20 to 30 years of them being around.

Size your house bank to match, based on how often you want to recharge or partially recharge, and go from there. Sizing banks has to do with how you sail, 'cuz if you're a marina hopper you need less than an anchor out or an overnight ocean sailor.

Your boat is big enough to warrant buying Nigel Calder's Boatowner's Manual for Mechanical and Electrical Systems.

 

[Maine Sail]

and in addition, do an energy budget. You'll find links to many of them if you do a search on this forum's engine.

As Donalex says, a fridge is 60 ah a day. That's pretty much the consensus after 20 to 30 years of them being around.

Size your house bank to match, based on how often you want to recharge or partially recharge, and go from there. Sizing banks has to do with how you sail, 'cuz if you're a marina hopper you need less than an anchor out or an overnight ocean sailor.

Your boat is big enough to warrant buying Nigel Calder's Boatowner's Manual for Mechanical and Electrical Systems.

To add on to all the other excellent advice:

The life of batteries is directly proportional to the number of discharges as well as the DOD or depth of discharge.

Cycling the batteries to a 50% DOD is the generally accepted low you want to regularly discharge to. If you can keep your state of charge to 60% or 70% you're doing even better and your batteries will last longer and give a longer cycle life.

One other thing that is often overlooked, is that when away from shore power, and charging off an alternator, you will rarely get back to any more than 80-85% of capacity so your real usable Ah's from a 200 amp bank quickly become 80-85 amp hours of usable battery life before you hit 50% DOD..


Here's some math:

The suggested max discharge depth for deep cycle batts is 50% of rated Ah capacity.

The average group 4D has only 160Ah's. With two @ 160 Ah you will get a max of 160 Ah of usable capacity for two batteries in parallel before hitting the 50% threshold.

Two Group 4D's

160Ah + 160 Ah = 320 Ah's (Based on Exide Nautilus 4D)

160 Ah's use @ a 50% DOD = 160 Ah's left

160 Ah - This is your usable capacity if you can guarantee a 100% charge every day.

If recharging while away from the dock, with an alternator, the best you can usually get back to is about 80% SOC.

80% SOC of a 320 Ah bank = 256 Ah's of usable capacity

256 Ah's (80%) - 160 Ah's (to a 50% SOC) = 96 usable Ah's while out cruising!

96 Ah's - This is your usable Ah capacity while away from the dock and only using the alternator to re-charge.

An AB fridge can draw 5+/- amps. If you figure it runs for 50% of the 24 hour day, you've burned about 60 Ah's with just the fridge or 62.5% of your total usable bank capacity while away from the dock using the 80% rule.

Ideally you should do an energy budget to know what your other draws total. It seems that you can do one night without charging at this point if you want to follow the 50% - 80% rule..

You might also consider a battery monitor as it will tell you how efficient your fridge really is. Some fridges cycle as low as 25% and some as high as 80% of the time. That can be a big difference and could be a costly mistake if it is a high cycler vs. a low cycler.

A Victron BMV-600 Battery Monitor (LINK) will be the best $175.10 you've spent..

So to answer your question you certainly can run your fridge over night depending upon your other consumption needs. Other needs might include anchor light, cabin lights, plotter, radar, stereo, VHF, depth, wind speed, water pressure etc. etc. etc...

 

[Winkfish]

As for putting ice in the ice box, remember that block ice lasts longer than cubed or crushed ice.

Neil, what's your point about the drain? Are you saying better to leave the melted water in rather than drain it out? My simple mind just didn't quite understand what you were getting at. Thanks!

 

[Ross]

Contain your melt water and use it for drinking and cooking water. It comes off the ice at 32 degrees and is still storing cold. This is why I freeze water in jugs. putting a trap in the drain prevents air from entering the box. That air carrys humidity. When the water vapor in the air condences it gives up the latent heat of vaporization at the rate of 1000 btu's per pound. If you have condensate in your cooler it has a heat value equal to about 7 pounds of ice per pound(pint) of condensate.

 

[Bill Roosa]

Drain plug

I though the drain plug was to keep the cold air in. alternatly you can put a loop (under sink trap) in the drain hose to accomplish the same thing AND still drain the water out.

 

[Ross]

I know of at least one couple that catches their melt water in a bucket and cool their wine with it. Terrible waste to dump that nice cold water overboard without some use of it.

 

[Bob S]

I agree with Ross. I keep a gallon jug of water in the freezer @ home and bring it in the cooler with food when we go to the boat. I can go 2 days before I have to recharge. I took Maine's and Stu's advice and installed a battery monitor. Only once did I bring the state of charge to 49%. I have a house bank of 260ah and all LED's. On a five day mooring I managed 3 days but didn't need an anchor light and shut the frig off when going to bed and turned it back on in the morning. This is my first season using it and it is a really nice feature to have.

 

[Ross]

I don't have refrigeration just an ice box. But that Ice box has 4 inches of foam insulation all around including the lid. We drink quite a bit of cranberry juice and save the 3 liter bottles that have nice handles, these we fill and freeze and take to the boat. 8 of them gives us about 50 pounds of ice and leaves plenty of room for food. that ice will keep cold for us for at least 10 days we haven't been out longer so we don't know for certain just how long.

 

[shemandr]

If you can stand box wine, and some of it is drinkable, the plastic liner bags make an excellent container to freeze water in. They lay flat and have a drain valve on them. We used to freeze two or three and put them in the bottom of the ice box. When they were melted they provided drinking water. If they weren't completely melted its cold drinking water.
I'm not sure shutting the fridge off is a net plus. If the unit cycles on more to regain the cold its using just as much battery AH's -yes? I like to hear opinions about that from our more technical posters.

 

[PKFK]

Isotherm with ASU ROCKS !

Hi -

I have had an Isotherm with ASU fridge for about 3 years now. We installed it as a conversion to one of the ice-boxes on the boat.

This system has a smart microprocessor that runs the compressor at 175% speed when it senses the engine is runnig - "storing" cold in the holding plate.

It is possible to charge the holding plate faster than the charge acceptance rate of the house batteries (although when the engine is running you are doing both).

We cruise in Ottawa (HOT summers) and I am very impressed with the system. I do not have an amp-hour meter on the boat, but the system is rated about 24AH per 24 hour period if I recall correctly.....it is MUCH more efficenct than a standard evaporator/condenser setup.

No commercial affiliations with Isotherm - just a pleased customer passing along my opinion !

**Note that not alll Isotherm fridges have this feature - you need to select an ASU (Automatic Start Up) system**

Paul

 

[Old Skool Neil]

Neil, what's your point about the drain? Are you saying better to leave the melted water in rather than drain it out? My simple mind just didn't quite understand what you were getting at.

Bill Roosa said it for me. A drain trap with melt in it seals off the drain atmospherically. Without a trap an open drain lets the cold air spill into the bilge. A stopper prevents this. To drain any melt the stopper can be temporarily removed.

 

[Ross]

Bill Roosa said it for me. A drain trap with melt in it seals off the drain atmospherically. Without a trap an open drain lets the cold air spill into the bilge. A stopper prevents this. To drain any melt the stopper can be temporarily removed.

If you are spilling cold air, warm humid air is taking its place. Thus the need to prevent air flow.

 

[FastOlson]

Power, Batteries, and... Cold Beers

Power management --
We have arranged to used the least power we can for our reefer box, and run it continuously.
There are no "secrets" to it, as you will find from most any book or article on reefers for boats.
First you need a well-insulated box. Our boat was built by Ericson with foam sprayed all around the bottom and sides to about 3 inches. I have added another inch of foam to most of it. Our lid did not have any foam so I added an inch of foil-face rigid foam to the underside. I also sealed the lid edge with stick-on soft foam to keep moisture from migrating in.

We used to use blocks of ice until blocks dissappeared from any vendors anywhere near a waterfront. Then I installed a Frigoboat system with their 'keel cooler'.

Our house bank is a pair of flooded golf cart batts and we can easily live on the hook for over two days and still start the diesel with power to spare.

The Frigoboat SSC motor controller keeps the amp draw down to around 3.8 amps when it runs... and that's not too often.
Only "problem" is that if we forget and turn the temp dial above 5 (halfway) on the scale the box becomes a freezer and all the pop cans break!

To reiterate, I would focus first on insulation of the existing box. There are several well-regarded refrigeration vendors for the cooling part of the project.

Don't forget to plug the old drain hold in the bottom of the box that lets all the cold out!