Refer power

[Copacabana]

Originally Posted by sailorboy1

I doubt overall there is much "saved" except for the batteries being higher SOC in the morning. It will still take the same energy to cool the box back down during the day (less various efficiency losses that are hardly any). Assuming everything equal over a 24 hour period it's pretty much the same energy either way. People can argue about it, but in the practical boat operation world it is meaningless really.

Personally IMO turning off the refrigerator at night to save battery power at night on a system that the batteries are still going to be 12.5V in morning if you let the refrigerator run is just a waste of time.

It all falls into whether on your boat Batteries = something that you serve, or Batteries = something that serves you.

I think you're right in that no power is actually "saved" by turning the fridge down (or off) at night. It's more a question of managing the energy that comes from the solar panels. In the afternoon I can't use the power I make from solar. I'll see 1.5 ah going into the batteries, but if I start turning on fans and stuff, I'll see 10 ah coming from the panels (to run these things). So I'm throwing away 8.5 ah during the afternoon hours. It just seems a waste to not use the excess power when the batteries can't accept it. In addition to turning the fridge setting to freezing, I also use the afternoon surplus to charge things like phones and laptops. It's really about energy management. The plus is I can keep my batteries in an almost 100% SoC almost all the time, increasing their life.

[Zzmeyer]

Interesting forum. Strong educated feelings on both sides of this. A number of posts talk about battery voltage. I was always under the impression that a simple volt meter was a poor way to measure the remaining capacity of a battery due to the impact on load on the battery. To get a proper reading you had to have a battery with no load for a fairly long period of time. Correct? I was also under the impression that the number of cycles a battery had during its lifetime was a function of how much it was discharged during each cycle. For example, the 11.8 volts in the last post might indicate a 70% discharge rate which is much greater than I would ever do. Correct, also?

[sailorboy1]

Originally Posted by Copacabana

I think you're right in that no power is actually "saved" by turning the fridge down (or off) at night. It's more a question of managing the energy that comes from the solar panels. In the afternoon I can't use the power I make from solar. I'll see 1.5 ah going into the batteries, but if I start turning on fans and stuff, I'll see 10 ah coming from the panels (to run these things). So I'm throwing away 8.5 ah during the afternoon hours. It just seems a waste to not use the excess power when the batteries can't accept it. In addition to turning the fridge setting to freezing, I also use the afternoon surplus to charge things like phones and laptops. It's really about energy management. The plus is I can keep my batteries in an almost 100% SoC almost all the time, increasing their life.

I understand. But I don't feel it matters to the solar if you turned the refrigerator off at night of not. It's still the pretty same AHs in 24 hour period. The solar should get the batteries to the same SOC at the same time of day either way all other things the same. Even if you do the turn the tmeo down thing in day and then off that only changes the daily AH load once if keep doing it the same each day.

Assuming that solaris sized enough to begin with.

[thomm225]

Originally Posted by Zzmeyer

Interesting forum. Strong educated feelings on both sides of this. A number of posts talk about battery voltage. I was always under the impression that a simple volt meter was a poor way to measure the remaining capacity of a battery due to the impact on load on the battery. To get a proper reading you had to have a battery with no load for a fairly long period of time. Correct? I was also under the impression that the number of cycles a battery had during its lifetime was a function of how much it was discharged during each cycle. For example, the 11.8 volts in the last post might indicate a 70% discharge rate which is much greater than I would ever do. Correct, also?

I don't especially like that the voltage gets that low (11.8/11.9 volts) but then again I'm still experimenting and usually within a 2 day sail of home

So far I've done that maybe 10 - 15 times on these batteries which are the so called deep cycle group 24 batteries which I have two of in parallel. They are maybe 3 years old now and were $89.00 each.

They are usually close to float going into evening which is either 13.6 volts or 14 volts depending on which solar panels I have deployed and which controller they are on

Also I don't liveaboard except when sailing over the weekend or on vacations so the batteries are usually close to fully charged most of the time as there is nothing on when at the marina until I stop by after work

[Copacabana]

Originally Posted by sailorboy1

I understand. But I don't feel it matters to the solar if you turned the refrigerator off at night of not. It's still the pretty same AHs in 24 hour period. The solar should get the batteries to the same SOC at the same time of day either way all other things the same. Even if you do the turn the tmeo down thing in day and then off that only changes the daily AH load once if keep doing it the same each day.

Assuming that solaris sized enough to begin with.

These are good points. I should do a test to see the results. I have 220 ah of batteries and 355w of solar. I think you're probably right that my batteries will get up to float at the same time in the afternoon, whether or not I turn the fridge down. Perhaps the only benefit to my system is keeping the battery SoC constantly higher, so if I wake up to a cloudy day, at least I'm starting the day with close to 100% SoC.

[Q Xopa]

Originally Posted by john61ct

It is definitely using more power per 24hrs that way. But so long as the temp doesn't risk food safety. . .

Next time you overhaul / replace the reefer, consider putting in a holding plate setup.

Hmm, that is an interesting assesment. Care to elaborate? I would say it depends on many unkown factors, but generally would not be the case.

[Q Xopa]

Originally Posted by john61ct

I don't care to belabor the argument, so just noting you are wrong, particularly the last bit, and leave it at that for now.

Wot? I have no idea who or what this referring to?

[john61ct]

Originally Posted by Q Xopa

Wot? I have no idea who or what this referring to?

The post immediately preceding addressed to me.

Originally Posted by Q Xopa

Hmm, that is an interesting assesment. Care to elaborate?

I don't at this time.

Easy enough to A/B test for anyone with two identical fridges.

But also just widespread "common knowledge" in refrigeration and aircon generally.

[sailorboy1]

Originally Posted by john61ct

But also just widespread "common knowledge" in refrigeration and aircon generally.

common maybe in the myth non science based world

it's probably in the chapter right before putting empty water bottles in the frig to "take up space" to magically change heat transfer rates across the insulation

[a64pilot]

Originally Posted by Copacabana

I think you're right in that no power is actually "saved" by turning the fridge down (or off) at night. It's more a question of managing the energy that comes from the solar panels. In the afternoon I can't use the power I make from solar. I'll see 1.5 ah going into the batteries, but if I start turning on fans and stuff, I'll see 10 ah coming from the panels (to run these things). So I'm throwing away 8.5 ah during the afternoon hours. It just seems a waste to not use the excess power when the batteries can't accept it. In addition to turning the fridge setting to freezing, I also use the afternoon surplus to charge things like phones and laptops. It's really about energy management. The plus is I can keep my batteries in an almost 100% SoC almost all the time, increasing their life.

No, you will save power and not just batteries, one reason is your raising the average temperature. Say your set point is 35f, and of course if you leave the fridge in 24/7 the temp remains close to set point, but if you turn it off, then of course it gets warmer over the night and now you average temp is 40f. That 5 degrees higher average temp will reduce power consumption.
Of course increasing the fridge set point to 40f will also reduce power consumption, even more actually as you never get colder.
Then as I said earlier every time a system cycles on, there is some time before the system really begins to cool, and during that time, your essentially wasting power, the more frequent those cycles, the more power that is wasted.
If a system is in stasis, that is equilibrium with nothing changing, just the heat load from insulation, which is the way almost all systems are tested, a system that runs 100% of the time is the most efficient, then you have the smallest possible system doing the job.

However of course that’s not going to work in real life, in real life you need a system with quite a lot of excess capacity so that it can cool down that case of beer or the watermelon or whatever you tossed in in a timely manner.
Enter a variable speed compressor, now you can have your cake and eat it too, it will slow down and save lots of power, but can speed up whenever the cooling load demands.
Generally the slower a compressor runs, the higher the COP, which is coefficient of performance, meaning how efficient it is, not just how much cooling it can provide, but a measurement of efficiency, so a compressor that can slow down and extend its cycle times is more efficient than one that cycles on and off regularly.

Danfoss now has an AEO module, AEO stands for Automatic Energy optimization, this module will slow down or speed up the compressor to optimize cycle times and will prevent rapid cycling and decrease power consumption, yet can speed up the compressor to cool down that case of beer when needed.

Then the Solar question, assuming you have a decent sized solar array and have lead acid batteries, there is a point during the day that due to battery acceptance, your Solar can make more power than the bank can accept.
May as well use that excess power cooling down the fridge.
That is one way that a true eutetic system can be used efficiently, you use the excess Solar power to phase change a liquid so that overnight that large mass of ice can absorb quite a lot of heat melting the frozen liquid.
But you don’t have one, so that’s sort of mute.

[sailorboy1]

Endless debate over a small unpractical amount of theory energy

[model 10]

I learned some stuff. I need a bigger boat so I can't hear the compressor and what I'm doing ain't so bad.
What I really need is a better controller and better door gaskets. I have a plan for creating a door gasket using modeling clay and I have a controller that 3rd day may have suggested. I need to install that too.
A friend gave me 2 fire prone 100 w solar flex panels, they should really help out this season.

[john61ct]

LOL, fire prone panels and modeling clay?

[Simi 60]

Living at anchor for 4 years and still haven't quite figured ours out.
All our refrigeration (2 x 100L & 1 x 500L) is 240v household stuff running off inverter and for 6 mths of the year, 100% sun powered.

If I turn off the big fridge, which I do every second night due to an icing thermostat, at 4am the batteries show 24.3v and a 90% SOC.

If I leave everything on overnight, we get a 23.5v alarm triggered around 4am and the batteries show 85% SOC.

One side of this discussion says that if the batts are down to 23.5v/11.25v that things are getting dire.
The other side of the argument is at 85% SOC all is well
I daresay if I turned EVERYTHING off the batts would bounce back to over 24.5v/12.25v indicating they are fine.

[flyingfin]

get a wind generator so you can run it all night,the noise of the wind gen will overwhelm the fridge noise!