A stand alone fridge system on a pocket cruiser...

THECUSCUS · Jun 17, 2020

This is my experience with a similar scenario. My boat has an Adler-Barbour fridge, 300ah house bank, 100amp Alt. For the previous 3 years we would run the fridge only on our weekend trips (2-3 days), with 1 100w Solbian panel. We had a deficit in ah's each day, but weren't out long enough to go below 50%. During the week, the panel had no troubles bringing the bank back to 100%. We are on a mooring ball, so no shore power charging. This year I added a 170w Sunpower panel, everything else is the same. I have had the fridge on for the last 3weeks (to keep the beer cold) and the batteries have been at or near 100% every evening that I have checked (no more than 2 days between checking).

dlochner · Jun 17, 2020

The first step is to develop an energy budget. What is the current draw for each electrical device and how many hours a day will each be used. Total the daily current draw and base the battery size on that number. It is best to not go under a 50% State of Charge, so a 200 ah battery has about 100 ah available if starting from a fully charged battery in good health. In practice, there is only about 30% really available due to charging inefficiencies. It takes much longer to go from 80% SOC to 100% SOC than it does to go from 50% to 80%.

Because of the inefficiencies, calculating charging is more complex than simply adding back the amp hours that were taken out. If 20 amp hours are taken out, then it may require 25 amp hours to bring the battery back to where it started. (There is a formula for calculating some of this, search for Peukert Equation.)

In a recent article, Nigel Calder estimated the daily output of a solar panel at 3 times the nominal rating. In your case, with a 100 watt panel you would have about 300 watts or 25 ah output for a good quality panel.

Two 6v Golf Cart batteries will provide about 210 ah for about about $120 each, or maybe less if you shop around. See this article about marine deep cycle batteries.

What is a Deep Cycle Battery? - Marine How To

Light Cycle vs. Deeper Cycle NOTE: This article deals with FLOODED marine batteries, not AGM or GEL batteries. The Problem: The problem, as I see it, is one of dishonest marketing where multiple battery types wear the same clothes (sticker) and will perform differently when

marinehowto.com

If you go with a larger battery you will need a new 3 stage charger. A 20-30 amp charger will be needed. The solar panel alone will not provide enough power to keep the expensive batteries charged. Partial State of Charge (PSOC) is a battery killer as are the quick automotive style chargers.

You might also want to consider one of these solar powered refrigerators:

Solar Coolers

Keep your food cold or frozen without ice - powered by solar energy and lithium ion. Free US shipping + free returns on all products.

gosun.co

Full Disclosure: I do have a very small financial interest in Go Sun.

srimes · Jun 17, 2020

If only it was as simple as the published specs! You won't get 200AH out of a typical 200AH battery, you won't even get the as much energy out as was put in, and 10A solar panel won't produce 10A under real conditions.

Batteries "leak" energy, and the larger the battery bank the more it loses. If upgrading a "bar minimum" system I would lean towards added solar capacity.

Will Gilmore · Jun 17, 2020

What are the advantages to keeping the house system separate from the reefer system?
I like the idea, but then, when I start thinking about having extra capacity to share across, in case one goes low, etc. I start thinking, "why separate them, just add capacity to one central system?" For sure, add charging capacity, but what is the advantage of keeping the two systems separate?

srimes said:
Batteries "leak" energy, and the larger the battery bank the more it loses.

Can you specify what this means? Are you talking about larger batteries vs smaller batteries or more batteries vs less batteries?
If you have a 100AH 12v battery that leaks charge at a rate of x, two 100AH batteries should leak charge at a rate of 2x. So, are you saying that one 200AH 12v battery leaks charge at a rate greater than 2x? Or is this what you mean by the increased leakage rate of bigger banks? In the first scenario, the proportional leakage of total system capacity is the same. y hours to 50% depletion, regardless of the size of the bank.

-Will (Dragonfly)

dlochner · Jun 17, 2020

The other advantage to a stand alone/portable refrigerator is portability. Works well at tail gate parties, summer picnics and on the boat.

srimes · Jun 17, 2020

Will Gilmore said:
What are the advantages to keeping the house system separate from the reefer system?
I like the idea, but then, when I start thinking about having extra capacity to share across, in case one goes low, etc. I start thinking, "why separate them, just add capacity to one central system?" For sure, add charging capacity, but what is the advantage of keeping the two systems separate?

Can you specify what this means? Are you talking about larger batteries vs smaller batteries or more batteries vs less batteries?
If you have a 100AH 12v battery that leaks charge at a rate of x, two 100AH batteries should leak charge at a rate of 2x. So, are you saying that one 200AH 12v battery leaks charge at a rate greater than 2x? Or is this what you mean by the increased leakage rate of bigger banks? In the first scenario, the proportional leakage of total system capacity is the same. y hours to 50% depletion, regardless of the size of the bank.

-Will (Dragonfly)

Yup, they self discharge as a function of total capacity, quick search brings up 4%/week at 80F. So a 100AH will lose 4ah/wk 200ah (as 1 bat or 2, doesn't matter) will lose 8. At this scale it doesn't look like much of a significant factor, but it can be for houses.

That's a difference of only .6ah/day so probably just ignore it.

jssailem · Jul 8, 2020

In January, I was looking at one of these units by Dometic.
DOMETIC CFX3 95DZ

Dometic CFX3 95DZ - Dual Zone Powered 12 Volt Cooler, 94L

Dometic CFX3 95DZ - Dometic’s largest dual zone car fridge option. Set independent temperatures for each side for a car fridge freezer that fits perfectly in the back of your pickup truck or trailer slide out. Reaching temperatures as low as -7°F, while using less power than a 60W light bulb...

www.dometic.com

I have seen them installed on a roll out platform into a cupboard. All the benefits of a portable refrigerator, looking like a built in.

Then I found the NovaKool Line and opted for the actual built in.

As far as powering, you can opt for what ever you install. The unit is not picky. AC/DC/Inverter/Solar. I would choose a sine wave inverter just to reduce the wear on the electronics.

cb32863 · Jul 8, 2020

Could you re-purpose your icebox and use something like this? Isotherm GE80-SX Compact Air Cooled Refrigeration Component System with ISEC* Or are you also looking for more space?

TomY · Jul 8, 2020

rgranger said:
I guess I was trying to recreate the "solar cooler" idea that @dlochner cited in post #3. I don't want the fridge to ever run down critical safety systems and I don't want to worry that a well meaning guest (worried that the beer might get warm) might flip the battery switch and run down my aux. bank

I like the solar cooler idea but the dimensions were not listed on the website and from the look I don't think the dimensions will fit in the space I have in mind. But I did click the customer service button and request the dimensions of the solar cooler. If that will fit... it might be the best way to go. I might need to splice the power cord and add length...

I get what you're trying to do and I think we'll see more of it in the future. For most here, systems on the forum to run refrigeration consist of beefy generation and large battery storage. Some have space to mount large solar panels as well. It works great for most but it's expensive and means often running a diesel to charge. The goal is 24/7 refrigeration.

On a 26' boat with an outboard and simple systems, I like the idea of a big solar generator.

You might have to live with partial refrigeration (over night, cloudy days) but that could mean small storage and a large panel that you can set up during the day and cool your stand alone reefer. You can stow the large panel to sail. Use it when you need it.

My son has been doing something similar with his boat. One group 27 deep cycle battery and a 100 amp panel and controller. With that he easily runs a large lap top and can work remotely. I thought he was crazy at first but the idea makes more sense to me now.

Bob J. · Jul 8, 2020

dlochner said:
The other advantage to a stand alone/portable refrigerator is portability. Works well at tail gate parties, summer picnics and on the boat.

Until you need to transport it in a dinghy & lift into your boat

Bob J. · Jul 8, 2020

I converted my ice box with an Isotherm conversion unit. I insulated the lid with 3 layers of 1" blue styrofoam. I also use the silver bubble wrap to help reduce the size of the box based upon what's being stored. Because I have a 4 hour haul to my boat I transfer the 2 frozen 1 gallon water bottles from my cooler to the ice box. I don't think my refer system uses more than 15 AH in a 24 hour period. Last week after 5 days on the boat the water bottles still had ice in them.
My mooring neighbor installed a 100 watt 24 volt panel on his boat last year. He has had no issues in keeping his battery bank charged & his beer cold.

I felt a clarification was in order, hence the edit. I boat up in Maine so unlike many here, I'm not dealing with the unrelenting heat as many of you do during the summer months.

LeeandRick · Jul 9, 2020

We highly recommend the portable. I bought an Engel MT 45 in 2006 for extra refrigeration space when we lived in an RV. It is 12/24 volt or 120 volt. It goes in the car for Costco runs (150 miles each way), in the backseat of the truck for camping trips, underneath the camper when we are parked for a long period (120 volt mode), on the back porch for parties, and of course it has a mount in the boat. This is the third boat it's been on. These units can also be freezers. People from HPCC 2012 are still wondering how we brought out 2 gallons of hard frozen ice cream, out of a San Juan 21, on the third day of camping at Steam Boat Cove.

We have only one group 31 house battery. The Engle and other usage would drop the resting battery voltage to 11.9 volts after 2 nights 3 days in ambient temps around 75 degrees and box temp of 35 degrees. We added 100 watts of solar I never give it a second thought now. If we are going to be out several days in the car I will put a group 24 in next to the refrigerator so we don't run the Kia battery down.

Other than a few dings on the outside, this 15 year old unit works like new and probably has close to 8 years (70,000 hours) of run time.

If you want to read a lot about refrigeration electrical consumption search Walt (an electrical engineer) here on SBO.

AaronD · Jul 9, 2020

I'd been thinking about. adding a very small portable (20-30qt size) as a freezer on our C-22.

We'd keep a bit of ice cream for the crew and re-freeze the ice packs for the main coolers (cycling ice packs back and forth). If the batteries run low when we're not close to shore power, well, we'd just have to eat up the ice cream

(and wait a few days to re-freeze the ice packs). Since it will be accessed infrequently, I'll mount it in otherwise unused space in the coffin

At least that's my current theory. To be tested next season, unless someone here gives me reason to rethink that plan.

dlochner · Jul 9, 2020

Misfits said:
Until you need to transport it in a dinghy & lift into your boat

The one I suggested only weighs 28 pounds. Obviously if you load it up with beer and food, it will weigh more, however, it is easy enough to empty and refill on the boat.