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Old 19-07-2014, 12:31   #1
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Power management

Hope this is the right place for this question.

In hot climates is it worthwhile to turn up the temperature setting in the fridge at night to save power and then lower it in daylight when the solar kicks in and I am dumping power.

Have 430 amps in house batteries and 440 watts of solar and after 9:30AM batteries are always above 13.0 volts.
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Old 19-07-2014, 13:17   #2
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Re: Power management

I don't think that you would see much change in daily amperage use because at night you aren't opening and closing the fridge door which is where a lot of your energy goes.

But that is what you have batteries for- to cover the night time and cloudy day loads and build the batteries back up on the sunny days.

How many amphours do you use in an average day. That will tell whether you have enough solar and battery capacity to cover the night and cloudy days.

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Old 19-07-2014, 14:15   #3
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Re: Power management

If you want to bank some of the power you are dumping now in the daytime, an extra battery would do nicely.

If you want to "thermal bank" it in the fridge, either make more ice (if you can) or load up bottles of water during the day and chill them down. Then the water bottles or ice can help keep the temperature in the box down at night.

I'd vote for the battery and less messing around.
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Old 19-07-2014, 14:36   #4
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Re: Power management

I know of a couple of Seawind owners that turn the refer of at night. If you're over 13 volts by 9:30am it sounds like you have no trouble keeping up so why worry?
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Old 19-07-2014, 14:52   #5
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Re: Power management

It probably doesn't help much. Though it may increase the likelihood of spoiled food.

As soon as you turn down the temprature the refer then has to cool the entire thermal mass of the fridge that has warmed up overnight. Which means whatever time it didn't run at night it will have to run first thing in the morning. Net usage is probably identacle.

If the issue is lack of battery storage, then first thing in the morning add a lot of mass in the form of drinks. The fridge will have to work to cool these down, which means you are using all the excess power. Then at night the thermal mass will help to keep things cool.


On the other hand I am with hellosailor. Just add more batteries. Messing around like this is just one additional thing you have to mess with every day. Better to eliminate these headaches when possible.
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Old 19-07-2014, 16:02   #6
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Re: Power management

Quote:
Originally Posted by tomfl View Post
...Have 430 amps in house batteries and 440 watts of solar and after 9:30AM batteries are always above 13.0 volts.
Your batteries may not be charged even with the 13v reading. The surface voltage rises quickly with solar connected.

Ive been wondering about the same idea, only using the portable engle over the day to freeze coolers for my eskie. Its too loud to have running overnight anyway. And the insulation is crap. I dont mind the extra work. When the wind changes I adjust my sails. When the sun shifts I adjust my panels and if my batteries are low I manage my power. All part of the fun...
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Old 19-07-2014, 18:03   #7
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Re: Power management

I don't see the efficacy of performing any tricks here. If the temp rises over night you just have to cool it again the next morning.

Better insulation, door sealing etc - I wonder if an eletronic themometer would be an aid in identifying reefer leaks - kind of like IR for engine temps - hmmm.

More high density contents in the fridge - i.i cooling plates that will hold their temp for a long time.

I'd add battery only after breaking your noodle over minimizing cooling losses first. Any amp you use, you gotta pay back.
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Old 19-07-2014, 18:37   #8
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Re: Power management

Quote:
Originally Posted by tomfl View Post

Have 430 amps in house batteries and 440 watts of solar and after 9:30AM batteries are always above 13.0 volts.
Off charge, no battery will have a resting voltage above 13V unless:
1. your meter is wrong, or
2. Something is still charging them.


If the panels are charging, all the V reading can tell you is the state of charge rate, not battery condition.

In either case, a voltage reading in the absence of any other info can be very misleading so don't make decisions based solely on that dubious reading.
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Old 19-07-2014, 18:44   #9
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Re: Power management

Oh. joy - another battery thread...

Can we stick to fridge efficiencies on this one - LOL...
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Old 19-07-2014, 18:58   #10
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Re: Power management

Quote:
Originally Posted by Ex-Calif View Post
I don't see the efficacy of performing any tricks here. If the temp rises over night you just have to cool it again the next morning.

Better insulation, door sealing etc - I wonder if an eletronic themometer would be an aid in identifying reefer leaks - kind of like IR for engine temps - hmmm.

More high density contents in the fridge - i.i cooling plates that will hold their temp for a long time.
Yes, there is no free lunch here - not even with high density contents unless they are eutectic in nature and refroze in someone else's freezer when not in yours.

An IR temp gun is very useful for finding insulation and gasket problems. I shoot around ours regularly just for fun.

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Old 19-07-2014, 19:06   #11
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Re: Power management

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Yes, there is no free lunch here - not even with high density contents unless they are eutectic in nature and refroze in someone else's freezer when not in yours.

An IR temp gun is very useful for finding insulation and gasket problems. I shoot around ours regularly just for fun.

Mark
Yup on the plates. Any energy taken out of them has to be replaced as well.

I was still thinking along the lines of cooing the plates during the day when Tom has that "extra" energy laying around and using that with the change the thermostat at night strategy - Sort of like making ice during the day and putting in the reefer at night.
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Old 19-07-2014, 19:14   #12
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Re: Power management

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Originally Posted by Ex-Calif View Post
Yup on the plates. Any energy taken out of them has to be replaced as well.

I was still thinking along the lines of cooing the plates during the day when Tom has that "extra" energy laying around and using that with the change the thermostat at night strategy - Sort of like making ice during the day and putting in the reefer at night.
I still don't see how that works out. He would put cold stuff in and turn the fridge off at night, and then……..

during the day he would cool down the warm stuff so that it would be ready for night again.

The stuff stays in the fridge. Unless it is removed to someone else's fridge for cooling and returned for night, then the energy usage (on his boat) is the same regardless.

Even if he had a special place where extra energy could be applied during the day to super cool stuff for night, this would be the same amount of energy over time as if he did nothing at all.

His solar panels don't care if they are cooling some stuff or refilling the batteries.

No?

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Old 19-07-2014, 19:24   #13
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Re: Power management

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I still don't see how that works out. He would put cold stuff in and turn the fridge off at night, and then……..

during the day he would cool down the warm stuff so that it would be ready for night again.

The stuff stays in the fridge. Unless it is removed to someone else's fridge for cooling and returned for night, then the energy usage (on his boat) is the same regardless.

Even if he had a special place where extra energy could be applied during the day to super cool stuff for night, this would be the same amount of energy over time as if he did nothing at all.

His solar panels don't care if they are cooling some stuff or refilling the batteries.

No?

Mark
Totally agree - Maybe I am solving the wrong problem.

I understood the issue was batts going down below desired at night when God turns the sun off, but but Tom has lots of extra amps during the day.

So to your point - store the daytime energy in super-cooled items, or store it in another added battery.

If the reefer can go colder - a simpler strategy is set it colder during the day and higher at night.

You are 100% correct - usage the same, not counting energy transfer losses (had to add that for the physicists waiting to pounce - LOL)
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Old 21-07-2014, 13:05   #14
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Re: Power management

I think its useful to differentiate storage (batteries), charging events or periods (engine or generator, solar during day, hydro when sailing), more-or-less steady loads (refrigeration, autopilot, navigation electronics), night time loads (lighting), and high power loads that can be done when sufficient power is available (watermakers, ice makers).

Related opinions:

I think wind generators are basically a waste of time. That is opinion.
I think shore power is a waste of time if you ever want to cruise for more than a weekend (if it works cruising, it will still work in a marina).
I think generators and engines are a horribly inefficient way to charge LA batteries, OK for high charge accepting batteries (I agree with Nigel Calder).

I think hydro maybe useful only to provide additional power for autopilot, as autopilot load and hydro generation may more or less track.

I think an engine alternator is fine for a starting battery, and, what the heck,charging other stuff when the iron genny happens to be running, but not as a consistent source of electricity. So no ned for a large alternator.

So solar seems the way to go for the source of all other electricity.

Since solar is less consistent that the loads, its necessary to have much more than "needed."

What is "needed" includes refer, nav, lighting, and autopilot (unless you also go with the hassle of hydro generator).

So the excess, when available (after charging the batteries) is used for watermaker and icemaker. And maybe Airconditioning, if you like that sort of thing.

So load management is turning on the watermaker, icemaker, and airconditioning, in that order, after the batteries reach full charge. And turning them off again, in reverse order, as current decreases in the afternoon.
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Old 21-07-2014, 13:35   #15
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Re: Power management

The best option is a high efficiency chest reefer. Cold air doesn't spill out when opened and if it's a good one, will not need to run much at all unless something new and warm is put in.


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