Cheap Fridge <$400 shipped

[trasko]

I'll add a data-point to all the other good info I've found in this thread (which, by the way, is the reason I went with this fridge).

Went camping for 3 days, 2 nights. Total of 56 hours run time took a pair of 6V 220ah batteries down to 12.31V which is approximately 33% of "full." That makes 145ah used which works out to an average of ~2.6ah per hour.

All that was connected was the fridge. I'd say outside temps were between 55F at night to 80F during the day. I had maybe 20 drinks + food pre-chilled for the previous 24 hours on AC power. Temp. was set to 37F the whole time. Check the picture to see the ghetto-rig. It worked great. :coffeedrink:

In the past week I've started copying the rest of the folks here with the reflectix. We'll see how that goes.

Can I say X amp-hours per hour? Ha. Please correct me because I struggle with how to use amp-hour in a sentence sometimes. It makes sense when I use it as a capacity ("this 6v battery has 220ah capacity") but doesn't sound right when referring to a rate of consumption.

 

[JamesDowning]

I'm a bit rusty at this stuff, but amp-hours per hour is really the same as amps. If you want to know the amount of energy actually used, multiply the amps x voltage x time, and based on your numbers you will get 6,048 kilojoules. To put that in perspective, a gallon of gasoline has approx 130,000 kj.

However, I'm not entirely sure you can make the conjecture of how many amp hours were used based solely on the voltage drop. It may prove to be a rather rough estimate though. Also, if each battery was 220ah, wouldn't 66% used be a total of 440ah? I'm not sure if the battery capacities are additive or not, since you're using them in series and not parallel.

 

[trasko]

I'm a bit rusty at this stuff, but amp-hours per hour is really the same as amps. If you want to know the amount of energy actually used, multiply the amps x voltage x time, and based on your numbers you will get 6,048 kilojoules. To put that in perspective, a gallon of gasoline has approx 130,000 kj.

However, I'm not entirely sure you can make the conjecture of how many amp hours were used based solely on the voltage drop. It may prove to be a rather rough estimate though. Also, if each battery was 220ah, wouldn't 66% used be a total of 440ah? I'm not sure if the battery capacities are additive or not, since you're using them in series and not parallel.

In series you do not add ah capacity. Also, I meant to say I *used* 66% with only 33% remaining. I think determining the state of the batteries by voltage isn't ideal but in this case all the circumstances were in my favor. I always tested after or while a load was on the batts, I tested numerous times over the course of 2 days and saw a very steady change, the temperature plays a part in accuracy but 80F is almost exactly what all the charts are designed for, etc... To top it off, that number seems very reasonable.

Based upon other people's numbers I was expecting to get an overall average of 2 amps being pulled (given the duty cycle I expected) so that was a bit low. I am glad I went with the bigger golf-cart batteries. 24 hrs * 2.7amps = 64.8ah. That seems high but it is what I'm getting with the limited measuring tools I have available. I'll borrow an ammeter for my next trip.

 

[CRJeepin]

Glad I found this thread, been looking for a freezer for a while and this looks like it is a good way to go. Anybody have a recent discount code for Compact Appliance?

Also curious if anyone has advice on whether the 43q is big enough for a family of 4? Or maybe better off with the 60q....

Thanks to all that contributed to this!

 

[Strizzo]

batteries rated amp-hours is always a bit misleading, because that will actually change depending on the load put on the batteries. if you were to put a 220 amp load on one of those batteries it probably wouldn't last an hour. similarly, if you put a significantly lower load on it than was used to determine the amp-hour rating it would likely last longer than you would think.

that said, amps per hour = amp-hours, so your load of 2.6A for one hour would be 2.6Ah. this is obviously averaged over the hour since the fridge isn't running all the time, and most tests seem to put it at around 4amps draw when the compressor is running. at 2.6Ah load, for 56 hours = 145.6 Ah total draw. is this where you got your 66% figure, or did you figure the 66% from the voltage and then back out to 2.6Ah? i guess i'm trying to figure out where you came up with 2.6A average consumption per hour.

 

[JamesDowning]

that said, amps per hour = amp-hours

I hate to be a stickler, but Amp-Hour does not mean amps per hour. Per implies division, and that is not the case. Amp-hour means Amps times Hours. An amp-hour is equal to 3600 coulombs. A coulomb is a measure of electrical charge and is defined as the amount of charge transported by 1 amp in 1 sec.

Units are tough to keep straight sometimes.

 

[Herbie]

Refer back to my data from post 713, which is, as far as I know, the most accurate sample done to date on these fridges:

Model: FP430
Peak Amps: 4.782
Compressor-On Duty Cycle: 16.67% (holding 36F at 72F ambient)
Total Amp-Hours (24H elapsed): 14.1151
Avg. "Amp-Hours per Hour": 0.58823

I will be running another test in a hot car soon, so more data to come - but I will say that after a half-dozen trips with the fridge, my "real world" consumption is pretty close to this data since the car is warmer during the day (fridge works harder) but much cooler at night (fridge works hardly at all).

Hope that helps.

 

[trasko]

batteries rated amp-hours is always a bit misleading, because that will actually change depending on the load put on the batteries. if you were to put a 220 amp load on one of those batteries it probably wouldn't last an hour. similarly, if you put a significantly lower load on it than was used to determine the amp-hour rating it would likely last longer than you would think.

Yes, I didn't get in to this but at 5amps max draw you're looking at "20 hour" amp-hour rating or better so I didn't bother mentioning it. This is still 220ah. This is another factor in my feeling that conditions were in my favor for measurement.

that said, amps per hour = amp-hours, so your load of 2.6A for one hour would be 2.6Ah. this is obviously averaged over the hour since the fridge isn't running all the time, and most tests seem to put it at around 4amps draw when the compressor is running. at 2.6Ah load, for 56 hours = 145.6 Ah total draw. is this where you got your 66% figure, or did you figure the 66% from the voltage and then back out to 2.6Ah? i guess i'm trying to figure out where you came up with 2.6A average consumption per hour.

I got my estimates like this: After the trip batteries were at 12.30V - 12.31V. That (on charts of deep-cycle, wet-cell, 70-80F) comes out to about 33% of "capacity" remaining measuring ONLY by the voltage. That means I USED 66% of 220ah whic is about 145ah. Then divide that by 56 hours and you get ~2.6ah.

I hate to be a stickler, but Amp-Hour does not mean amps per hour. Per implies division, and that is not the case. Amp-hour means Amps times Hours. An amp-hour is equal to 3600 coulombs. A coulomb is a measure of electrical charge and is defined as the amount of charge transported by 1 amp in 1 sec.

Thanks, it helps to think of an amp-hour as a convenient way to refer to 3600 coulombs.

Refer back to my data from post 713, which is, as far as I know, the most accurate sample done to date on these fridges:

I will be running another test in a hot car soon, so more data to come - but I will say that after a half-dozen trips with the fridge, my "real world" consumption is pretty close to this data since the car is warmer during the day (fridge works harder) but much cooler at night (fridge works hardly at all).

I tend to agree that your setup should be the most accurate, but frankly I have to say it doesn't agree with my research on other people's experience (nor mine). Why do you think this is? There are a few factors in the favor of the fridge in your test: 1) no direct sunlight; 2) no moving air; 3) no opening/closing of lid. Hmmph!

 

[pods8]

I got my estimates like this: After the trip batteries were at 12.30V - 12.31V. That (on charts of deep-cycle, wet-cell, 70-80F) comes out to about 33% of "capacity" remaining measuring ONLY by the voltage. That means I USED 66% of 220ah whic is about 145ah. Then divide that by 56 hours and you get ~2.6ah.

Just wandering through but I think you're reading the charts wrong, 12.3V is ~70% charged/ ~30% depleted, not the other way around. You used half of what you think you did.

 

[trasko]

Whoa maybe you are right. 1.3ah average would be a really great value for me as I was lamenting not being able to go more than 2 days without a recharge. Being able to double that would be a really awesome improvement. Ha, well I guess that shows the pitfall of using voltage to measure your capacity. I've got an EE friend who I might can get to help me setup a way to measure this properly on the next trip...

 

[teotwaki]

These are really great toys for measuring these sorts of experiments: Watt's Up

http://www.rc-electronics-usa.com/ammeters/dc-amp-meter.html

 

[CaliMobber]

Another update:

Just went on a 4 day trip to the desert and southern sierras this last weekend. I started the car everyday so no long term battery use was in this trip but the fridge worked perfect. I had the fridge set at 35deg the whole trip so everything was nice and cold. super cold by the coors light cans At one point, with the truck all sealed up and the 100 deg desert weather The whole outside of the fridge was getting super hot and I was a little worried the heat exchanges would have trouble working so I open the back hatch for a little and let the hot air out. I did use my sun shade on the fridge most of the time. So another successful camping trip with my fridge

 

[evldave]

Here's an update on a recent trip I took w/my Edgestar on the outside of the trailer (fully exposed to the elements).

First portion of the trip was following the Washington Backcountry Discovery Route (WABDR) for 5 days...went about 500 miles offroad, through mud pits (yes, it got muddy, but not too bad), lots of dust, a massive thunderstorm (tons and tons of rain), lots more dust, got smashed by my hitch bike rack on a deep dip (truck going up hill, trailer going downhill), and lots more dust. Also at one point in very thick trees, had the handle ripped off and had to replace w/a tie-strap to hold it down to the trailer.

2nd portion of trip was stationary at the PNW Overland Rally...highs in the mid-upper 80s, in direct sunlight, mostly holding beer, and opened a lot on a regular basis (there was a lot of beer drinking).

For the travel portion, the fridge held up amazingly well. I can't describe the amount of dust/dirt I cleaned out from the vents after I got home. Only glitch was at one point the fridge spiked up to like 40-42 degrees for no reason (truck was running) for a little bit, then went back down.

Biggest issue was the stationary portion of the trip. Lots of hot direct sun + lots of beer = drained battery fast (I was using a cheapo WW deep cycle battery)...ended up having to charge it via the truck almost every day. At one point, it went into low voltage mode and I lost 2 kabobs because it warmed up too much That was my fault for not putting it under shade.

For my next trip (5 days travel to the California Overland Rally + 4 days sitting), I'm going to move the fridge into the trailer and put a cooler outside full of ice, dry ice & beer (separated of course). That should protect the fridge from the elements (although I'm very impressed with it so far), but should also get some more life out of my battery before I have to charge it again (assuming I haven't hosed the battery already).

 

[Strizzo]

I hate to be a stickler, but Amp-Hour does not mean amps per hour. Per implies division, and that is not the case. Amp-hour means Amps times Hours. An amp-hour is equal to 3600 coulombs. A coulomb is a measure of electrical charge and is defined as the amount of charge transported by 1 amp in 1 sec.

Units are tough to keep straight sometimes.

you are right, i got turned sideways somewhere in the middle, what i meant to say was 1 amp for one hour = 1 amp-hour

made sense in my head, i swear!

 

[Strizzo]

These are really great toys for measuring these sorts of experiments: Watt's Up

http://www.rc-electronics-usa.com/ammeters/dc-amp-meter.html

that they are, also really good to make sure you don't smoke your motors and speed controls