12v solar and chest freezer to fridge conversion - what went wrong?

[paulgareau]

On the freezer operation alone, that is, getting the load figured out before talking about batteries: On the energy draw, that 80W is "steady state", that is, after compressor startup transients have calmed down. Startup will be more. How much will vary some.

Once running and the cooling demand is met, the unit will draw a few Watts or so when the compressor is not running. The unit will cycle on/off to maintain the thermostat set point. If the unit is self defrosting, depending on method, it'll probably also draw some power during defrost cycle.

As for the daily power consumption required to keep things cool, or make ice (the two are slightly different duties), that will depend on the load the unit needs to meet. If you fill the freezer with H2O and the thermostat set point is 0 < C., the unit will run on a fairly regular cycle, and probably a large part of the time, maybe constantly, until the H2O is frozen. After that, the freezer will cool the ice further, down to the thermostat set point.

After that, with no other additions/withdrawls, the unit will simply run to maintain the freezer temp., removing any heat gain.

If ice is withdrawn and replaced with water, as sounds like what the application is, the freezer thermostat will sense the warmer temps. and the compressor will run and make ice.

If you use more ice than, say, 300 W-h per day of input will produce and still meet the heat gain demand of the unit, the compressor will run longer to meet the increased demand for more ice and energy use will be > 300 W-h/day.

FWIW, it takes about 80 as much energy to create 1 kg. of ice as it does to reduce the temp. of 1 kg. of water by 1 deg. C.

OK, I'm fairly new here so maybe I didn't ask my question the right way. BUT. This is about a chest freezer to refrigerator conversion using a johnson controls thermostat (see orig question and follow ups). I'm not making ice. This is probably good info for someone but has nothing to do with my situation or question.

Also have provided the startup and running wattage....

[max2k]

OK, I'm fairly new here so maybe I didn't ask my question the right way. BUT. This is about a chest freezer to refrigerator conversion using a johnson controls thermostat (see orig question and follow ups). I'm not making ice. This is probably good info for someone but has nothing to do with my situation or question.

Also have provided the startup and running wattage....

JPM brings a good point- your freezer energy demands will greatly depend where you set your thermostat - the colder you set the more energy it will require to maintain that temp. If you set it below freezing point on top of just cooling things inside you'll be making ice as well and that sharply takes way more energy. Running wattage makes sense only for a given temperature and freezer load. Say you put it below freezing and then placed some watery drink inside- freezer will be forced to freeze it and that process will take a lot of extra energy.

[AzRoute66]

Also surprising was that the batteries could be floating by noon, which should be impossible too.

You battery is junk. A sulphated boat anchor. You probably cannot be convinced of that until you use the Kill-A-Watt meter some more. You should be watching for battery sales while you re-measure your load.

[paulgareau]

JPM brings a good point- your freezer energy demands will greatly depend where you set your thermostat - the colder you set the more energy it will require to maintain that temp. If you set it below freezing point on top of just cooling things inside you'll be making ice as well and that sharply takes way more energy. Running wattage makes sense only for a given temperature and freezer load. Say you put it below freezing and then placed some watery drink inside- freezer will be forced to freeze it and that process will take a lot of extra energy.

Seriously? It's a refrigerator (converted). I'm not making ice. See my original post, or subsequent posts, or even the post that you replied to that said "I'm not making ice."

[paulgareau]

You battery is junk. A sulphated boat anchor. You probably cannot be convinced of that until you use the Kill-A-Watt meter some more. You should be watching for battery sales while you re-measure your load.

Really, brand new from the store? And the other batteries that had been working successfully? I'm done with the project now, it was for 6 weeks as I've said a few times.

[max2k]

Seriously? It's a refrigerator (converted). I'm not making ice. See my original post, or subsequent posts, or even the post that you replied to that said "I'm not making ice."

Calm down- it depends where you set your thermostat and we have no idea where. Cooling 1 gal of water just by 1 deg F takes about 2 Wh. Cooling it by 40 deg F will take 80Wh. If you set your thermostat too low that gal will freeze in there taking with it 80Wh to cool + 160Wh to freeze so as you can see these things add up. Maintaining low temperatures after things settled takes way less energy so if you measured your numbers on empty freezer and then loaded it with stuff at room temperature there's no wonder it depleted your battery.

[PNPmacnab]

Really light on the panels. Why does everyone go cheap on panels? They cost far less than batteries. I've been using a chest fridge for years ( five months at a time), first with a 5CF and then with a 7CF when that outgassed. I use only a single car battery and a little more than a KW of panels. Fridge only operates during the day and will only start when battery is at least 13.7V. Cold is stored in mass liquids and electronically controlled to 33F. A mechanical thermostat is asking for disaster.

[AzRoute66]

Really, brand new from the store? And the other batteries that had been working successfully? I'm done with the project now, it was for 6 weeks as I've said a few times.

I don't know when you bought them, I only know you've been charging them with a 250W panel. You said, "...so I used Walmart 24DC marine, deep cycle batteries." Tell us more about which batteries, when you got them, how you wired them, what changed when you put them in, and what changed from then to now... I'm pretty much on board with max2k in post #15. Those "other batteries that had been working successfully", weren't them the ones floating by noon?

[J.P.M.]

OK, I'm fairly new here so maybe I didn't ask my question the right way. BUT. This is about a chest freezer to refrigerator conversion using a johnson controls thermostat (see orig question and follow ups). I'm not making ice. This is probably good info for someone but has nothing to do with my situation or question.

Also have provided the startup and running wattage....

I thought I read in your 1st post that you got tired of buying ice ?

In any case, the way I learned it, it's perhaps a good idea to identify the loads and the duty before designing a system to meet those loads and duties.

You obviously have that all well in hand

If you consider such information as I provided as having nothing to do with your situation, forget I wrote anything. Sorry to have bothered you.

[max2k]

I thought I read in your 1st post that you got tired of buying ice ?

In any case, the way I learned it, it's perhaps a good idea to identify the loads and the duty before designing a system to meet those loads and duties.

You obviously have that all well in hand

If you consider such information as I provided as having nothing to do with your situation, forget I wrote anything. Sorry to have bothered you.

you don't believe in miracles that OP realizes his ignorance and amount of details involved in reliable design and comes around? I don't- I bet he's now searching Net up and down for quick-n-dirty shortcut. Trouble is there's none and with just little patience and attention to details he could accomplish what he is after. Oh well.

[J.P.M.]

you don't believe in miracles that OP realizes his ignorance and amount of details involved in reliable design and comes around? I don't- I bet he's now searching Net up and down for quick-n-dirty shortcut. Trouble is there's none and with just little patience and attention to details he could accomplish what he is after. Oh well.

NOMB. Besides, some folks you just can't reach. All the best to the OP and A.M.F.

[Logan5]

Cognitive dissonance

[sdold]

To be fair, it sounded (to me at least) like he was buying ice to keep his food cold.

[jflorey2]

Sorry man, but I told you what batteries I was using. I also said I got them because I needed a quick and dirty system. You're still not answering the question. And are you saying it's OK to buy junk after I've done math?

In some cases, yes. If you have an application where you need short-duration high power discharges (i.e. periodic opening of a garage door or something) with no steady loads then "junk" (in this case a starter battery) might just work. How do you know if you can use a battery like this instead of a better deep cycle battery? You do the math; figure out the loads, how many watts and watt-hours you are going to need and go from there.

[J.P.M.]

To be fair, it sounded (to me at least) like he was buying ice to keep his food cold.

Maybe, but it sounded to me that the duty was about making ice in a recycled or some such freezer, and then using the ice to keep food (or more importantly beer ???) cold.

Either, or any way, it takes as much energy to melt ice as it does to make ice. Just reverse the direction of the heat flow.

As for keeping any box and its contents cold, at any given (steady) temp. diff., ambient to cold box, once cooled down, the heat loss/gain will most entirely only be f(cold box heat loss rate), with some additional consideration for cooling added warm contents, opening/closing door(s) or, indeed, making ice or freezing things in a possible freezer section. That is the cooling duty that the application needs to be designed to meet.

Startup transients in compression equipment are an important issue, but confined mostly to the battery/PV system design particulars and are in addition to and different from considerations of making and keeping stuff cold to prevent spoilage.