Trailer boat - conversion of an custom ice chest to electric fridge

[walt]

edit.. I put all the details of this project here (Jan 2019)
http://analogengineering.com/sail/mac/electric_fridge.html

I have an old 1990 Mac 26S that after seeing all the fridge stuff here, Im thinking about converting to solar powered ice chest. I know a few people here have done this and I am just thinking about this at the moment so I will just describe all the plans I have and welcome any feedback (I may not follow any advice but its certainly all welcome).

My ice box is custom with 2 inches of insulation in the walls and top loading hatch and 3 inches in the bottom. I think the volume that I would cool is right at 2 cubic feet (60 qt). This will be huge vol for us as in the past this had two gallons of frozen water in it plus a 10 pnd block of ice and we can get rid of all of that.

The cooler that Im thinking about has been talked about here and its the Isotherm GE80-SX with Isec. Part of the reason for picking this one is that the cold plat is 14" by 10" which I think I have room for. I sort of like the GE150 better but I dont think I have room for the larger evap plate (14" by 15").

I have two golf cart batteries on this boat and plan to power things completely with solar so Im of the impression that the Isec control will be as easy on the batteries as possible. Im used to having a huge reserve of capacity to daily usage and adding the e fridge greatly reduces my margin which makes me a little uncomfortable. But I believe the Isec control will work the fridge hard when the sun is shining and go easy on things when its not. My batteries will still likely get more of a workout than they have in the past..

I worry about the evaporator cold plate getting banged up in the food area.. Example, a six pack of beer smacking into it while sailing (water ballast boat can be like a big dingy in windy conditions).

I dont think I will need to worry about the heat generated by the compressor and trying to exhaust this from the boat. This setup uses a max of 2.5 amps and that is a max of a little over 30 watts and it should not run at that power all the time. It would seem that the heat from the compressor would be easy to manage and no problem to just vent the heat into the boat.

I know I can very comfy live on 30 watts of solar without the fridge. I am thinking 100 watts of solar will run the fridge fine. The panel size Im thinking of will be 140 watts. I would use a single panel about 60 inches by 26 inches (about 11 square feet.. YIKES) mounted above the boat stern. This size panel weighs about 26 pounds and if I keep all the mounting light weight.. I think I can live with this. FYI, a buddy gave me a bunch of carbon fiber cloth.. thinking about trying to do this with carbon fiber and epoxy plus some AL.. I somewhat worry about all that panel area back there as when the boat heals, that panel generates both lift and drag and the rudder has to work a little harder to balance that out which is both additional stress and drag.

Based on my past experience, 100 watts of solar will supply anywhere from 15 to 35 amp hours per day (MPPT controller) but I will assume that I might get 20 on average. The spec on the Isotherm say it only uses .3 amps average in economy mode (7 amp hours per day) but at the full 2.5 amp it can run at, that would be 60 amp hours per day. If I used a 24 volt panel, I could run 14 gauge wire for the long run to the controller. A 12 volt panel would require 10 gauge. I will have to buy a new controller regardless so have not decided on this yet.

I do not plan to have any sort of gas power generation over what my outboard provides. So I may have to put in a low voltage disconnect later and my backup would be if I ever had a time period of not enough sunlight, just shut the power off and buy some ice.

 

[walt]

Where and how I would use this probably also matters for panel size. Im thinking 140 watt at the moment and think the boat is maybe too small to go much above that.

The boat would be in a slip on the shortest day of the year in December with the fridge running (Arizona). The panel would be pointed straight up and the sun stays to the south and the days are short. This might be where a low voltage disconnect is needed. Ice chest wont see huge loading.

During the summer, my wife and I may live on the boat for up to two weeks. We did one ten day trip last summer using the ice chest but.. the fridge sure would have been more comfy. Ice chest would see a few openings a day and maybe we would want to chill 3 cans a day. Most trips would be to sunny places but maybe I would be buying ice in the PNW.

 

[walt]

One other thing.. I have not looked at the Isec controller but it has a method to measure battery voltage and also a method to control the output. So it likely already has the main hardware for a low voltage disconnect or some sort of low voltage power management. Maybe there is something in that controller already so that you dont drain the batteries when the power input isnt enough?

 

[walt]

Low voltage disconnect already discussed in this thread https://forums.sailboatowners.com/i...-smart-energy-controller-sec-question.185757/

Looks like this was recommended in that thread https://www.bluesea.com/products/7635/m-LVD_Low_Voltage_Disconnect

The one thing I dont like about the m-LVD (rated for 65 amps pass current) is that it burns 95 ma when its "on" (ie, connecting the load to the battery). That is 2.28 amp hour over 24 hours.

That is nearly 1/3 the current the Isotherm unit uses when it reaches economy mode (300 ma).. Its a significant load for a smaller boat setup but something I could live with.

edit.. this one http://shop.pkys.com/Victron-BP100-BatteryProtect-1224V-100A_p_6421.html can be programmed to shut off at 12 volt and restart at 13 volt. Its solid state and only uses 1.5 ma

 

[RussC]

I was just recently looking at low voltage cutoffs myself, and saw this one. Only .26Ma drain looked good to me.
https://www.amazon.com/Voltage-Battery-Disconnect-Auto-Detect/dp/B0147DYUN8

 

[walt]

• Ultra low pass-through impedance 4.5mΩ
• Ultra low standby current 0.26mA in 12V mode and 0.65mA in 24V mode
• Low normal operating current 3.5mA in 12V mode and 5.8mA in 24V mode

that does look good on first inspection. I see it can be set to shut off at 12.1. I couldnt find the voltage that it turns back on at but it says it does when the battery is recharged (or something like that). Edit - data sheet says it turns back on at 13 volts for the 12.1 volt setting.

It would drop about 11 mv (small) when passing 2.5 amps from the pass through impedance.

Hmmm.. my 9.8 hp outboard has electric start and when the electric start is used, may cause a false LVD trip... fridge would shut off until the battery voltage reached 13 volts. I will have to watch the battery voltage next time I start the outboard (not until Nov 1).

 

[walt]

I mentioned that I like the Isotherm 150 SX better than the 80 SX for my solar only (generally never powered by slip AC) application and the reason is below. These are close in price but unfortunately I dont think I can use the 150 because the evap cold plate is too large.. I think I could also somewhat have chronic undercharging of the batteries with the 80SX powered in the slip by solar only for the four months the boat would be in the slip.

The numbers...

How many amp hours per day a fridge this size needs.. You can find all sort of numbers up to 50 amp hours per day, 35 amp hours per day, 20 amp hours per day (allowing the temp to vary a little bit with Isec or ASU). Depends on size, use and insulation but I will assume 25 amp hours per day here. If someone thinks this is incorrect, it would be interesting to hear why hopefully with details. Anyhow.. assume the fridge needs 25 amp hours.

The 140 watt panel at full 12V current out of an MPPT controller is capable of 10 amps or more.

The Isotherm 80S has a max input current of 2.5 amps and the 150SX is 3.5 amps.

During the day when the solar is cranking, I might only get 6 hours of good sunlight (especially true for my winter application). So during the six hours, the 80 SX only consumed 15 AH and the 150 SX consumed 21 AH.

I like that the 150 SX can consume more power as it can better "make hay when the sun shines". The 80SX at its lower current would need to keep running during the night for the extra 10 amp hours it needs to maintain temp and of course draw from the batteries to do this. The solar panel /MPPT controller of course has excess current to recharge that 10 amp hours plus supply 2.5 amps to the fridge the next day. However, I know with my batteries that I need to be more in the bulk stage to accept much current. I would a little concerned that the system running this way would need to stay closer to the battery bulk region and might stay "chronically undercharged". At least in theory for what its worth.

The 150 SX being able to draw 21 amp hours while the sun is shining would mean most of the energy required to keep the fridge cold would be supplied directly from the panel and the batteries probably would not need to do much at night.

I am liking what Sesmith did with 160 watt of solar and the Isotherm 3701 as it likely (at least in theory) is easy on the batteries for the solar only application. The 3701 has ASU which increases power use when its available (like solar output) and also stores energy in some sort of holding plates. The 3701 can draw up to 6 amps. So in 6 hours, it could draw 36 amp hours and with more than 10 amps available from the solar controller, no problem. With the ASU and the cold holding plates, it could in theory be very easy on the batteries at night. This seems like a nice solution if you want the batteries to last as long as possible. But.. its also a larger unit and more $$$.

 

[LeeandRick]

Walt this won't be much help but move closer to a power outlet on K dock or get a slip on B dock. I was going to suggest drinking warm beer but.... at least this kicked your post back to the top. I'm sticking with my Engel and another battery. If you get this sorted you can bring the ice cream to the meteor shower outing, instead of us. Oh, the dolor of a trailer-able boat.

 

[walt]

Another option that looks interesting to me for this mainly solar power fridge. This was sort of suggested in Jackdaws thread I linked to above (by the way, thanks for posting all that Jackdaw - very interesting and useful)

The idea here is that the fridge is only powered when the solar panel is putting out power. I think the Isotherm VE 150 air cooled system would work fine as I think I can fit the evap cooling assy (10.8 by 8.4 by 2.3 inch) and it uses up to 3.5 amps which I also like - make as much cold as you can while the sun is shining.. (link to the VE 150 below). The VE 150 does not have Isec.. but I dont think I care since it would only run when the solar is putting out power. No solar, no power to the fridge.

Where I like this setup is in the slip because it will only have a very minimal draw ever on the batteries. Fridge only runs when the sun is shining. There is no need for a low voltage disconnect. Battery is hardly involved since the fridge takes a max of 3.5 amps and a 140 watt panel will almost always exceed 3.5 amps (full sun and MPPT, the solar output can exceed 10 amps). I can be away from the slip and pretty much never worry about the batteries. Batteries would always stay fully charged.

This of course relies on the fridge insulation to hold the temp when the sun is not shining.. You would set the fridge thermostat to just above freezing and let it run all it wants when the solar is powering it. At night the solar shuts off and the fridge temp would drift up.. but since it was set near freezing, it hopefully does not get too high. This is somewhat similar to what the Isec does.. lets the temp drift up when the power input is not there.

I threw together a block diagram of what this might look like. I have a bypass switch on the solid state relay for when I was using the boat for up to two week trips and may want to manually connect the fridge up the battery. Or if I was connected to slip AC, use the bypass and the fridge would be powered from the AC battery charger through the battery.

A solid state relay that might work for this is here. Unfortunately I cant find a good spec for this part but its cheap. It will draw a little current on the input control (25 ma) but this comes directly off the solar panel and it only draws this current when the panel is running https://www.amazon.com/TOOGOO-SSR-100-Solid-Module-Solid-state/dp/B073XKF5BN/ref=sr_1_1?ie=UTF8&qid=1507645198&sr=8-1&keywords=SSR-100+DD+Solid+State+Module+Solid-state+Relay+DC-DC+100A+3-32V+DC/5-60V+DC

Links to the VE 150 fridge.. (one of the cheapest options..)
http://www.isotherm-parts.com/index...d=2118&zenid=f621ad08dfd27fa5368fcf51bf43a140

http://www.defender.com/product.jsp...em&path=-1|2276204|2276226|2530801&id=2383951

 

[walt]

woops.. need to correct something. Some solar controllers have the negative lead of the panel at some voltage other than ground. Example.. my 5 amp Genasun biases the panel negative lead at the battery voltage. Most of the solid state relays have inputs that are isolated from the output so the solution is to simply bring both leads of the panel voltage over to the ss relay input.

 

[walt]

Another post on my apparent waffling on this electric fridge.. The marina that Rick mentioned a few posts back is about a 15 minute bicycle ride from home so I go down there fairly often during the week. This is a great thing to do for retired guy. There is one 110VAC 15 amp GFCI power outlet per maybe 15 slips. So keeping AC plugged in is iffy and even if you do manage to keep plugged in, there is always the risk that someone blows the GFCI by for example unplugging a space heater at the end of a long extension cord and not resetting the socket. Anyhow.. I dont like relying on that setup and it would need at the minimum a low voltage disconnect.. But I do like the idea of having a somewhat stocked electric fridge on the boat.

I also have been trying to figure out how much current those cooling systems use and see all sorts of inconsistent info. Some manual I saw for the VE 150 said these use on average 500 watt hours over a typical 24 hour period. That is around 40 amp hours!!! Needing that much power is a deal killer for me as it needs a lot of solar (past what I could live with for my trailer boat) and also is going to work the batteries hard. The VE 150 has a fan that goes inside the cool area and while that does distribute cold better inside the chest, Im fairly sure it also causes more heat loss in the ice chest based on some testing I did with my custom chest that has an internal fan. So.. VE 150 is no longer on the short list.

Im back to thinking if I did this, I would use the Isotherm GE80 SX air cooled with Isec as this is probably best for when we use the boat on a week or two trips. Im pretty sure the GE80 SX with Isec would use considerably less power than the VE150 during camping trips where we had the fridge powered all the time.

For the marina solar only case where I want to power the fridge ONLY when I have solar power input, I have modified the setup I am thinking about. I would still have the fridge only turn on when the sun was shining but I have added a zener diode so that the threshold where the solid state relay turns on would be around 13 volts solar panel voltage rather than 3. 13 volt would ensure that the panel was actually starting to put out some power. The diagram is just a concept and has not been tested and of course there usually are some details to work out.

http://www.defender.com/product.jsp?path=-1|2276179|2276204|2276226|2530801&id=3103519

Amazon seems to have everything.. even zener diodes https://www.amazon.com/Frentaly®-300Pcs-2V-Assorted-Assortment/dp/B015D0B3B6/ref=sr_1_1?ie=UTF8&qid=1507733751&sr=8-1&keywords=zener

 

[jeepbluetj]

Some solar controllers have load terminals that energize when there's solar input - If your controller has that you may just need to hook it to the relay.

 

[walt]

I had a controller in the past that had a "light control" output and could have been used to power a fridge without the need for a relay.. But it would only turn light on when there was no sun since you only need lights at night. Ie, its the wrong "polarity". You could electrical invert this signal but then it gets more complex than what I have shown. Im hoping to keep this as much off the shelf as possible.

I did not know about a terminal that comes on when the controller senses power from the panel.. will look out for that. What I have shown works best with MPPT and I can pick the controller based only on its primary function.

Edit.. I found this MPPT controller with a programmable load output. The load control looks to me more of a low voltage disconnect so it does not do what Im looking for - and that is something that tells when the solar panel is producing power. What I have in the last figure still looks like a way to know when the solar is outputting power and its very few parts.

:Link to the solar controller where with the programmable load output https://www.solar-electric.com/sb1524ix.html

 

[walt]

Update..

Turns out that the solar panels I have been looking at are all very close in size and weight for 140, 150 and 160 watts. So I may as well go with 160 watts. The size of these panels are all close to 59 inch by 26.5 inch and I have done a mock-up to see if this was just too big for this boat or if I would have to rename the boat "water world".

Im planning on two slats that will attach to both the coaming and the rail and have somewhat of a minimal cantilever attachment to the panel. Those slats are pine and I plan to wrap them with a couple layers of carbon fiber/ epoxy. The panel will weigh just under 27 pounds and the I weighed a pile of wood and AL that I plan to use for the mount and that was about 15 pounds. So Im hoping for a total added weight of around 42 pounds.

I also checked my ice chest and the height inside the chest is 10.3 inch. The evaporator cooling plate is 10 by 14 inch so should barely fit.

Still planning on the setup with the solid state relay so that I can have a mode (set by a switch) where the panel is only turned on when the solar panel is putting out power. Im going to add some "hysteresis" so that the power to the fridge will never oscillate under any condition in the mode where power is only applied when the sun is shining. When the switch is flipped, the fridge will be powered from the batteries all the time. The hysteresis will add a few parts (3 resistors and a E cap).

So. Im still thinking about this but likely the "floating RV" project is a go and will start ordering parts.

 

[RussC]

With the proper angle that should also keep the stern firmly planted in the water at high speed for better cornering.

 

[walt]

hmmm is that a vote that this might be a little too large for that size boat ?? LOL.. We have been climbing the ladder this morning and it had to be that high to easily get in from the ladder. As I have to remind my wife, what 60 YO folks are NOT climbing from a little rubber inflatable kayak up a ladder and doing some limbo over the rail and under the panel to get on their boat?

FYI, I brought the panel down just under four inches from whats in this pic

 

[LeeandRick]

Does N know you posted this picture?

 

[walt]

Who??

Of course NOT..

 

[Meriachee]

You might consider the crutch being above the panel, and at the same time consider not having to read the bridge clearance sign quickly....

 

[walt]

Regarding the crutch, I would have to remove the panel for lowering the mast and trailering. However I think I can make the mount so that the panel is easy to remove and just keep it in the cockpit. The two side supports would stay on the boat. On the positive side of this, I thought I was going to have to mess with the crutch because if I do this, I want to make sure the only thing that might shade the panel is the sail. There is also a VHF antenna there that will have to go because of shading. With the panel where it is, I wont have to mess with the crutch, it will always be there just below the panel. Even if I need to drop the mast out on the water (an overall easy thing to do and something I need to keep as an option for one particular bridge I know about), I would just have to temporarily remove the panel.