Bar Fridge + Inverter + Solar Panels

onecoolair · May 10, 2013

Piratenorm said:
Can anyone give me a compelling reason why a bar fridge (cheap at Walmart) plus a good inverter plus a large solar panel wouldn't make for an easy and efficient refrigerator arrangement? Unplug the fridge from the inverter when you want to make coffee or burn toast then plug it back in again.
A fridge conversion kit is approx. $1,000. plus the solar panel, say $1,500 total. Let's not quibble, rounding it out at $1,500 is about par.
A good bar fridge is less than $200., a good inverter another 3, solar panel 4-5, adds up to about a grand. That's a $500. saving in my book.
So, a compelling reason this isn't a good idea. I have the $1,500, but if I can save 5 it's money I can buy something else for the boat with.
Thanks.

Sound like good idea to me. Now pm me so you can deposit what's left of the savings to my pay-pal account.

Maine Sail · May 11, 2013

Lets say the bar fridge draws 1.6A at 120V but now you want to invert it from 12V to 120V

Here's a good approximation formula for inverter sizing:

AC Amperage X 10 X 1.20 = DC Current Draw

The 1.20 is the approx 20% inefficiency of the inverter:

1.6A X 10 X 1.20 = 19.2A

A 140W panel is capable of 20 - 40Ah per day. You can use approx 20Ah in just one hour of fridge run time...

Keep on mind that many toasters and coffee pots burn upwards of 12A at 115V !!!!

12 X 10 X 1.20 = 144A

If it takes you 20 minutes to make coffee you've just burned 48Ah but at such a high load you batteries don't really have the capacity you think so it is more like burning about 75Ah's....

No if we really want to get into it we should always account for the Peukert factor. The Peukert corrected load is the load the battery actually sees when you draw current at at over the 20 hour rate. The 20 hour rating for a 210Ah bank is a 10.5A load.

At 10.5A you will get 210Ah out of the battery.

At 144A, if the inverter did not shut off on low voltage first, you'd only get 103Ah's...

So figuring two group 31 batteries and a bank size of 210Ah the numbers look like this:

144A Load = 277A Peukert Corrected Amp Load (Peukert of 1.25)

Sailvayu · May 11, 2013

What mainsail is basically saying is this is not a real good idea. Coffee makers and toaster draw too much power to be practical. you could run a fridge but you might be better off with a 12 volt unit with a well insulated box. I think your cost estimates on the installation is off and a good inverter properly installed will run a bit more. Same with solar [panel although they are coming down. When it comes to boats there are few easy ways out. Also a built in unit properly done will add value to the boat.

Maine Sail · May 11, 2013

Sailvayu said:
What mainsail is basically saying is this is not a real good idea. Coffee makers and toaster draw too much power to be practical. you could run a fridge but you might be better off with a 12 volt unit with a well insulated box. I think your cost estimates on the installation is off and a good inverter properly installed will run a bit more. Same with solar [panel although they are coming down. When it comes to boats there are few easy ways out. Also a built in unit properly done will add value to the boat.

Exactly... Look into 12V DC refrigeration, a French Press and a burner top toaster..... A properly installed marine inverter, with transfer switch or auto transfer, for those loads, will run you quite a bit more money than just an el-cheapo inverter.... DC is always a lot more efficient..

Chief RA · Jun 10, 2013

I am a little late commenting on this but I have an alternative. Buy your bar refer for shore power use. Buy an Igloo DC portable cooler that will run on 5 amps DC w/ appropriate solar panels/batteries.
My Igloo (10 yrs old) will run STRAIGHT from a 75 watt solar panel (no battery) and keeps my beer cold even with night down time! Day temps around 80 to 90 degrees. Hope this helps some of you.
Chief, Electronic & Industrial Eng. (certified Radar,Comm,Sonar, FCC lic.1890)

jrowan · Jun 13, 2013

Norm,

Chief's idea isn't a bad one, since if there's not enough juice from the solar panel to power the small 12 volt cooler, then the worst case scenario is it won't cool adequately.
Although the cooler will get very inconsistent power which will fluctuate greatly, & will lessen the lifespan of the cooler. But at least it won't kill your house batteries from constantly over drawing them. I think I talked with U before about the 110 volt fridge that we have. We plug it into shore power, & it will continue to stay cool for at least half a day out, before things heat up again. I can testify that without getting too technical, that a 110 volt based fridge will utterly kill your average double group 27 type batteries in a matter of a few hours. We also have one of those 12 volt type coolers. They usually draw more then 5 amps & will also destroy a typical deep cell battery capacity overnight. The cheapest method of refrigeration for short term cruising is a block of ice. That's why sailors have relied on it for decades. As far as short term inverter requirements, consider an inverter powered by your engine's alternator. It produces far more voltage output for the short amount of high power consumption that a coffee put or toaster requires. But mainsail is right about using a French press with water boiled from a stove is a lot less of a cost expense & hassle. Most blue water crusing boats have a huge bank of many deep cell batteries to afford the power requirements, that we frankly cannot afford to buy & maintain. My advice: keep it simple & you'll be happier & not go broke. It is simply not feasible for the average sailor to attempt to recreate a home kitchen on water. That's why most of us resort to boat camping in the end. Its just simpler, easier & cheaper.

jrowan · Jun 13, 2013

ps. If you get a little creative then toasters & coffee makers are not necessary when cruising. Take a coffee filter, place your coffee grounds inside & tie it off. Pour boiling water into the cup with the filter bag: voila instant coffee. Or buy the instant single serving packets of coffee, even easier. Toast bread over a stove top with metal toasting tongs that you can buy at any camping supply. A small propane fired burner is a hell of a lot less expensive, less complicated, more reliable, useful....... Cheers.

Chief RA · Jun 15, 2013

Piratenorm:
My Igloo cooler has run for 5 yrs on a 75w solar panel. They will run well on LESS than 5 amps from a solar panel due to higher DC voltage output. (60w=5a x 12v or 60w=4a x 15v) You will not get full no load voltage of 18v from the solar panel, thus 15v loaded in this example. Hope this clarifies my original post, Chief

Maine Sail · Jun 20, 2013

Piratenorm said:
OK, I've taken all your advice and my install is almost complete. I went big, a 235 watt solar panel, 20 amp controller and all the required safety protocols have been followed. The fridge is the Isotherm 3 cf stand up, draws 3.5 amps only and although I have way more power from the panel than the fridge could ever use the cost of the large panel equaled a panel half that size so why not? I still have the 2 group 27 deep cycle house batteries. I will have the install completed shortly and never have to worry about offshore power needs again. I am off for a month cruising the North Channel in 2 weeks. Thanks for all the input.
Norm

Did you use an MPPT controller? Most of the 235W panels have a Vmp of about 30V and if using a standard controller that extra voltage gets wasted when charging a 12V bank... An MPPT controller can make use of that extra voltage by converting it into usable current..

Chief RA · Jun 20, 2013

Norm: Guys like you who learn from us makes it all seem quite special to help. It was a privilege to assist! Sounds like you really set your boat up very special and I am sure your lady will love it (and you)! Chief