Offroad Trailblazers and Envoys

Thermoelectric Cooler

Discussion on how to enjoy the outdoors.

by bartonmd » Fri May 10, 2013 2:39 pm

JamesDowning wrote: but even then, you probably wouldn't be able to recharge your second battery enough during the day's driving cycle to be sustainable.


Most, cars even, will recharge a battery from dead in an hour or 2 of driving.

Most car batteries are around ~60Ah, so it only has to put in 15A to be fully charged up in 4 hours of driving.

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by Trail X » Fri May 10, 2013 3:35 pm

But the charging curve isn't linear, the charging current is relative to the charging voltage differential, which makes the charging curve somewhat asymptotic in its effectiveness (especially when you add more wire between the alternator and battery).

I do know that with driving roughly 50 minutes a day, my little 43qt fridge will draw down my deep cycle rear battery in about 8 days. I'm contemplating making one of those reflective insulating bags for the fridge.
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by bartonmd » Fri May 10, 2013 4:05 pm

Yeah, I know it's not linear,(EE, remember) which makes it hard to get FULLY charged, but easy to get 90% charged pretty quickly.

IIRC, don't you have a time delay on your secondary battery setup? Like 5 minutes or something? So if it's 5 minutes, and you drive 25 minutes per trip, you're only charging 40 minutes/day. That's a long shot from the ~6-7 hours of engine-on time that we have on an average wheeling trip. I think part of your issue is that since your battery is back with your frig, not up near the engine, the most it can charge is ~30A or something, so it would need at least 2 full hours of charging to get nearly fully charged. Whereas, if your battery was up by the engine, it could really dump current into it from the alternator, and get it ~80% charged every trip, and it would be fine all the time, though not "fully" charged.

What I normally do with the thermoelectric frig/cooler is, it runs when we're driving, then I unplug it at camp, and it stays cold over night. Plug it back in, in the morning, and it's on most of the day while we're wheeling. Seems to work out pretty well, especially for an $80 frig.

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by dvanbramer88 » Fri May 10, 2013 4:34 pm

What did i start? lol

Anyway, I would probably use it for something similar like mike uses his, run it while driving and unplug at night. For over-landing/expeditions this would work fine. For actual camping at a stationary location, Ice and a normal cooler works fine for me, especially when there is a place to buy ice. And I only go on those type trips once or twice a year. To break down my camping

State park/established camp ground:has a place to buy Ice: 1-2 times a year (fishing trips)
TECORE: 1-2 times a year; no place to buy Ice but plenty of driving to run a fridge.
Overnight kayak trips: No power, complete isolation. No room or weight capacity for Ice/cooler anyway.

And than there are those day trips and tailgating where the fridge would get used while driving to maintain temp without having to mess with water/ice.

On the kayak trips I freeze half my water and refridge the rest and keep that in a small soft sided cooler on the deck of my kayak. Everything else I bring doesn't require refrigeration.

So the cooler and ice has a place, and the fridge has a place too.
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by dvanbramer88 » Fri May 10, 2013 4:37 pm

Also; what you be the best way to measure the draw of this fridge? I have a few full function multimeters like the one in my picture.
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by The Roadie » Fri May 10, 2013 7:57 pm

Most meters have a suitable 10A DC current function, but you have to plug in one lead to a different banana jack on the front. Then splice into either one of the wires going to the unit from your accessory receptacle.

Added because I don't know your experience level: Current has to be measured in SERIES with the wiring going to the load, which means cutting into the wiring. Voltage is measured in parallel, which means just touching the meter leads to the high and low side of the load.
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by Trail X » Sat May 11, 2013 8:54 am

bartonmd wrote:Yeah, I know it's not linear,(EE, remember) which makes it hard to get FULLY charged, but easy to get 90% charged pretty quickly.

Sorry, its been a long week. I concur with everything you said. This thread has got me thinking that I should evaluate my setup again. Thinking maybe I should upgrade my wite gauge yet again to get rid of any extra voltage drop...
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by The Roadie » Sat May 11, 2013 12:40 pm

I have this nifty clamp-on ammeter that uses a Hall Effect sensor to measure DC current without disconnecting the wire. I hooked up my rear battery through a switch to the rear fuse block feed. To see if I needed to upgrade the wire when I first put it in, I measured the current going into a totally dead, discharged Optima (my former starting battery) that I put behind the driver's seat for the fridge. It was 75 A peak, tapering down to 30 A within a minute or two. If you have thicker wire, the potential current will be higher, which could put the Megafuse at risk. Actually, with thicker wire, you'd bypass the megafuse and go right to the alternator (150A rating), but I think 75A peak recharge current is plenty enough for anything but a lithium ion battery. And with LiIon, you run the risk of a Boeing 787 Dreamliner incident onboard.

The rear fuseblock wiring gauge has the desirable effect of limiting the current.
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