DC only please no inverter

[AlanJohn]

Looking at all the diy videos...can't find one without a inverter. Don't need an inverter, just DC for fridge. Is there one that has no inverter?

 

[gnubie]

If you don't need the inverter, delete that part of the system. If you can describe your needs I'm sure someone here can give you guidance as to what you need to do.

It sounds like you need battery, panels, charge controller, a few fuses and a means to connect them all up but we'll see what the forum comes up with once you can give a little detail.

 

[John Frum]

What system voltage do you wish?
How many watt hours does your fridge use per day?
How many days do you want it to run off of battery without sun?

 

[AlanJohn]

Wow that was quick. OK for a Sylvan GO camper, need to power a thermoelectric cooler (50w), same for a 24ft sailboat. Am planning on buying
RICH SOLAR 200 Watts 12 Volts Monocrystalline Solar Kit along with
Valence U27-12XP Lithium Ion 12v 138Ah U-Charge Battery Modules
What else do I need?

 

[Hedges]

Just for day sailing, I presume?
Thermoelectric is very inefficient, and 50W power in can only compensate for about 2 or 3 watts worth of heat leaking through insulation.
I think a bag of ice in an ice ice chest would be more effective.

If you can pick up a 12V refrigerator with compressor, you'll get much more cooling out of your power.

 

[John Frum]

Here is the topology

use_case {
    power a 12 volt refridgerator with a 50 watt draw via solar power with 2 days of autonomy
    1200 watt hours per day 2400 watt hours total
}
legend {
    monitor { shunt based battery monitor }
    scc { solar charge controller }
    nnnawg|NNN| { fused connection point where nnn denotes the wire gage and NNN denotes the fuse amperage
    nnnawg|___| { un-fused connection point where nnn denotes the wire gage
    <-> { bi-directional current flow }
    -> { uni-directional current flow }
    <- { uni-directional current flow }
}
fridge {
    * thermoelectric cooler (50w)
    neg
    pos
}
battery {
    * 2x Valence U27-12XP Lithium Ion 12v 138Ah U-Charge Battery Modules
    pos
    neg
}
monitor {
    pos
    neg {
        upstream
        downstream
    }
}
panel {
    * RICH SOLAR 200 Watts 12 Volts Monocrystalline Solar Kit
    pos
    neg
}
scc {
    * 20 amp pwm solar charge controller
    upstream {
        pos
        neg
    }
    downstream {
        pos { 010awg|___|<-disconnect<-panel.pos }
        neg { 010awg|___|->panel.neg }
    }
}
dc_fuse_block {
    * 30 amp per circuit 100 amp aggregate
    upstream {
        pos { 006awg|___|<->breaker_100_amp<->battery.pos }
        neg { 010awg|___|<->monitor.neg<->battery.neg }
    }
    downstream {
        pos {
            010awg|040|<-scc.upstream.pos
            010awg|040|->refridgerator.pos
            016awg|001|->monitor.pos
        }
        neg {
            010awg|___|->scc.upstream.neg
            010awg|___|<-refridgerator.neg
        }
    }
}

 

[John Frum]

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If you have any questions just holler.

 

[GXMnow]

They don't list much about the charge controller. It does say PWM on the front which is pretty basic and not the best efficiency, but that is normal for the price range. The "Load Output" terminals should have a shut off if the battery get's too low, but it does not give any details. The Valence battery has a built in BMS, so you will still be safe there, but it would be nice to have external load cut protection. Rich solar panels get decent reviews, so they probably can put out close to their ratings. But you should realize the 200 watts will basically only happen if the panels are cool, the sky is clear with no haze, smoke, or smog, and they are perfect flat face directly at the sun at noon. Actually expect 80% and over a day, if you leave them at one angle, maybe 1 KWH on a good day.

If it is just a 50 watt fridge, you should get over 24 hours from the battery, but it will take most of it. A full day of charge will put about 50% of one battery capacity back in with good sun if the fridge is not running. With it running, it will take over 1/3 of the solar power so it might not run 50 watts constant 24 hours a day on just 200 watts of solar panel. The battery will deplete. A second battery will get you a bit more time.

All you really need is a terminal block and fuse. How nice to do you wan it to be? You can install the battery in a marine style battery box, mount the charge controller on the side, use an inline fuse holder and have an XT-60 connector hanging out to plug in your load. You can get everything you need at Amazon. Do you have a soldering iron, a crimper, drill, screws and nuts, electrical tape and/or heat shrink tubing, wire ties?

I have 2 small thermo electric cooler type "Coolers" and they do make the ice melt a bit slower in hot weather, but they are not a true refrigerator. Like Hedges said, Those TEC Peltier modules just can't move enough energy.

 

[John Frum]

simpler drawing using the load leads of the solar charge controller

use_case {
    power a 12 volt refridgerator with a 50 watt draw via solar power with 2 days of autonomy
    1200 watt hours per day 2400 watt hours total
}
legend {
    scc { solar charge controller }
    nnnawg|NNN| { fused connection point where nnn denotes the wire gage and NNN denotes the fuse amperage
    nnnawg|___| { un-fused connection point where nnn denotes the wire gage
    <-> { bi-directional current flow }
    -> { uni-directional current flow }
    <- { uni-directional current flow }
}
fridge {
    * thermoelectric cooler (50w)
    neg
    pos
}
battery {
    * 2x Valence U27-12XP Lithium Ion 12v 138Ah U-Charge Battery Modules
    pos
    neg
}
panel {
    * RICH SOLAR 200 Watts 12 Volts Monocrystalline Solar Kit
    pos
    neg
}
scc {
    * 20 amp pwm solar charge controller
    system {
        pos { 010awg|___|<->breaker_030_amp<->battery.pos }
        neg { 010awg|___|<->battery.neg }
    }
    pv {
        pos { 010awg|___|<-disconnect<-panel.pos }
        neg { 010awg|___|->panel.neg }
    }
    load {
        pos { 010awg|030|->refridgerator.pos }
        neg { 010awg|___|<-refridgerator.neg }
       
    }
}

 

[AlanJohn]

Thank you, a lot to digest.

 

[Hedges]

Here's a 12V fridge:

Norcold NR740BB (Replaces Model DE0740BB*) 2 CU FT DC Refrigerator

www.suremarineservice.com

Unfortunately, they cost on the order of a grand, because they are a specialty item.

I think you're better off buying a used cube fridge off Craigslist for $50, and getting a sine-wave inverter rated for about 5 times the label on the fridge (for starting surge.) As for the inverter, look for low standby power consumption or a sleep mode where it only powers up occasionally to check for loads. For use on a boat, one that is sealed or has conformal coated boards for environmental protection is probably necessary, unless you're only on fresh water.

 

[PHoganDive]

FYI, thermoelectric cooler are TERRIBLE for cooling vs the power they use. A normal phase-change refrigeration cooler is typically 3-600% more energy efficient. You should REALLY change the fridge away from a thermoelectric one.

 

[Zil]

There are many 12 volt dc compressor fridges on the market. Google or Amazon. They don't cost a grand.