Thermoelectric fridge

[mikeschn]

Can someone help me out? It's late and I'm tired, and these numbers don't look right...

I just bought a thermoelectric fridge for the Escape Hatch. It's a 65 Watt Fridge, running at 110 volts.

I want to know how much of a drain that is on my battery.

So I divide 65 by 110 and I get .591 amps per hour. Does that sound right?

(Watts=AmpsxVolts)

or Watts/Volts = Amps


Oh wait, I see the problem... I want to run this at 12 volts on an inverter...

so I divide 65 by 12 and I get 5.4 amps. That sounds right.

So I can drain an 80 amp battery to halfway in about 7.4 hours.

Good thing my first campout is going to have access to electric!

Mike...

[PaulC]

Mike, Is this one of those units that only drops to about 20 degrees below ambient temp? If so, I think you will find that and icebox will be a better proposition. JMHO
Have a look here:
http://www.exploroz.com/vehicle/accessories/fridges.asp#WhatType


Cheers
Paul

[bdosborn]

so I divide 65 by 12 and I get 5.4 amps. That sounds right.

So I can drain an 80 amp battery to halfway in about 7.4 hours.

Good thing my first campout is going to have access to electric!

Mike...

BUT, the inverter isn't 100% efficient, more like about 80% for a cheaper one (assuming you're using an inverter). Figure your amp draw will be more like 5.4/0.8=6.75A. So closer to about 6 hours of usage.

BUT, the fridge isn't running all the time. I think I read somewhere that a typical refrigerator duty cycle is about 50%. That puts you back in the 12 hour range.

BUT, its a thermoelectric fridge and I don't know what the duty cycle is for those.

BUT, you're going to plug it in so its all a moot point.

Boy thats a lot of buts.
Bruce

[Denny Unfried]

Mike, all of the one's I've found have a duty cycle of 100%. I never use mine except when traveling. It's a 110/12v combo but draws a constant 3 amps.

[ARKPAT]

Mike I have one of those also 12V D.C. / 120 V A.C. Compressor-less Thermo-electric refrigerators.
The duty cycle on mine is 100% constant 3 amp. at 12V D.C. current draw and thats not counting the losses thru the 12V D.C. to 120V A.C. power brick.

I went with a 120V A.C. and inverter less effecent but has a duty cycle and a lot less battery draw from the inverter of the same time ( 24 hrs. ) span.
Also the refrig is cheaper to replace when on sale.


Pat

[mikeschn]

This is the fridge
http://www.shopdirect.com/Avanti/EC15W- ... ESSID=d51b

It can go as low as 40* below ambient.

And yes, there will be times when an icebox is a better proposition.

I don't know what the duty cycle is.

And I knew the inverter sucked out some juice for itself, but I didn't know how much. Thanks for the 80% tip Bruce.

I still have in mind that I want to build one of those old fashioned ice boxes complete with the brass hardware, but that'll come later.

Mike...

[Mary K]

For my "research" for building a Tear, I was just talking to my boss (an E.E.) about ac/dc conversions and calculating amps....

He pulled out a note pad and started calculating and I ended up with that deer in the head lamp look.

Mk

[bdosborn]

And I knew the inverter sucked out some juice for itself, but I didn't know how much. Thanks for the 80% tip Bruce.

Mike...

That's just a rough rule of thumb. The actual efficiency of an inverter is dependant on a couple of factors; the overall efficiency of the device - some inverters are better than others - and how heavily it is loaded. Inverters typically are most efficient when they are heavily loaded. Thats why I would shy away from using a 2,000W inverter unless you have a big load that requires it. For TVs and smaller loads the inverter should only be around 20% or so larger than the load for maximum efficiency. Savy RVers will use a big inverter for house loads and a little 400W for the TV or stereo to maximize battery life. (which is probably more than you wanted to know but here ya go)
Bruce

[PaulC]

I don't know what the duty cycle is.
Mike...

Mike, To the best of my knowledge, thermoelectrics work on a 100% duty cycle. That is, they always run.

Cheers
Paul