light sensitive switch

Light sensitive switches turn on at night and off in the morning.

Can I get a switch that does the opposite? I run a freezer from solar panels. It only draws about an amp and a half at 120 volts, but that is enough to draw down the batteries at night. If the freezer is shut off at night and turned back on in the morning, everything is still frozen solid. This has become standard operating procedure.

I want it to happen automatically.

There are outlet plug-ins with timers that you can set to go off during certain hours. I am not aware of specifically light-sensitive ones but you can definitely set them to go off/come on with multiple permutations. I have used one for a window air con to have it come on/off at a certain time before I got home. Search "outlet timer" and see if that device would work for you.

I would imagine they make switches that do that, but in any case you could reverse the action of a switch by adding a double throw relay in the circuit.

Thanks for the replies.

Yeah, a timer would do the job. I'd only have to adjust the times with the seasons. Not a problem.

I considered using a relay, but the added complexity of the circuit wouldn't be worth the expense and trouble.

For less than $10 at Lowes, I think I'll go with the timer.

Thanks again.


By the way, the freezer works great. It's a 5 cu ft and satisfies my needs. Frozen food from a few (5) solar panels.

(needs PURE SINE WAVE--modified WILL NOT work

Robert Harsell wrote:

By the way, the freezer works great. It's a 5 cu ft and satisfies my needs. Frozen food from a few (5) solar panels.

(needs PURE SINE WAVE--modified WILL NOT work

If you have the time and inclination, a separate dedicated post with more info about your experience with your freezer/solar set-up sounds like it would be really helpful for people here!

Get a standard light switch that turns on at night,  then plug an  power supply into this outlet.        Then feed this power supply to a relay who's default state is always on, when power applied it shuts off.      Then have the device you want powered controlled by this relay.


That should get the job done.

Mart Hale wrote:Get a standard light switch that turns on at night,  then plug an  power supply into this outlet.        Then feed this power supply to a relay who's default state is always on, when power applied it shuts off.      Then have the device you want powered controlled by this relay.


That should get the job done.

Yes, when I first realized that the hardware store did not sell the reversed version of the typical light-sensitive switch, my first thought was a relay system, because the most desirable design is the one that responds to ambient light. But being on a limited fixed income adds another factor to the decision-making. I wouldn't mind changing time settings a few times a year if a timed outlet can be acquired at Walmart for the price of a bag of potatoes.

Mercy Pergande wrote:

Robert Harsell wrote:

By the way, the freezer works great. It's a 5 cu ft and satisfies my needs. Frozen food from a few (5) solar panels.

(needs PURE SINE WAVE--modified WILL NOT work

If you have the time and inclination, a separate dedicated post with more info about your experience with your freezer/solar set-up sounds like it would be really helpful for people here!

I'd be pleased to put something together that might be helpful, but I'll have to give it some more thought. Alternative energy can be a slippery concept depending upon who desires what, in light of feasibility, practicability, reliability, and availability. I have a lot of experience relying solely upon the wind but less relying solely upon sunlight.

I'll try to come up with something helpful.

https://us.rs-online.com/product/phoenix-contact/2987888/70170862/

Power Relay, SPDT, 24VDC/250VAC, 250VDC, 16A, $9.44

How many potatoes sir?

If you have a smart phone I'd recommend a bluetooth/wifi smart plug. Then you can have timer control from your phone.

James Alun wrote:https://us.rs-online.com/product/phoenix-contact/2987888/70170862/

Power Relay, SPDT, 24VDC/250VAC, 250VDC, 16A, $9.44

How many potatoes sir?

shucks five pounds

Nicolas Keeton wrote:If you have a smart phone I'd recommend a bluetooth/wifi smart plug. Then you can have timer control from your phone.

flip phone

What voltage are your battery bank and inverter?
I'm wondering why you can't put a diode between the battery bank and inverter so when the voltage from the panels is higher than the battery,
it will charge the battery and run the inverter.
When the voltage from the panels drops lower than the battery the diode stops it from flowing back from the batteries to the inverter.

Of course if other things are running off this inverter, then it's probably just the AC to the freezer you want to control.
Instead of DC to the inverter.

Ah I had assumed this was to stop the freezer drawing from the battery.

Use the thermal inertia to get through the periods of no power and then use the panels to drive the freezer. Although the batteries are connected they aren't actually used.

craig howard wrote:What voltage are your battery bank and inverter?
I'm wondering why you can't put a diode between the battery bank and inverter so when the voltage from the panels is higher than the battery,
it will charge the battery and run the inverter.
When the voltage from the panels drops lower than the battery the diode stops it from flowing back from the batteries to the inverter.

Of course if other things are running off this inverter, then it's probably just the AC to the freezer you want to control.
Instead of DC to the inverter.

It's a 12 volt system.

I don't understand the part of your comment regarding a diode between the battery bank and the inverter. The batteries are connected through a heavy cable directly to the inverter. Presently, the pure sine wave inverter runs only the freezer. It's dedicated to the freezer. I have an old Cobra modified wave inverter for all other uses. Modified sine wave is usable for most purposes, but it's no good for the freezer compressor.

The problem is much simpler than you imagine. I only want to turn off the freezer when the sun goes down, and turn it back on when the sun rises. Relying on alternative energy can become a complicated matter. In the interest of keeping things as simple as possible, I'll use the fact that frozen food remains well frozen from dusk to dawn even if the freezer is turned off. This simple fact allows that there is no need to draw from the battery bank when the panels are not producing electricity.

I'll simply use a timed outlet that shut's off at 8 PM and turns back on at 8 AM. As the seasons change, I'll adjust the timer accordingly.

Thanks for the reply.

James Alun wrote:Ah I had assumed this was to stop the freezer drawing from the battery.

Use the thermal inertia to get through the periods of no power and then use the panels to drive the freezer. Although the batteries are connected they aren't actually used.

You had assumed correctly. The freezer runs off the inverter which gets its power from the battery bank via thick cables.

The panels cannot drive the freezer. The batteries are essential. The starting current for a refrigeration compressor is high. The panels could not possibly supply such a high current.

As I'm writing this, I'm looking out my window and realize that dawn is approaching. Soon I'll go outside and turn on the freezer. Last night, I turned off the freezer.

Do you run your freezer from the grid? Imagine if every day you needed to remember to turn your freezer off at night and back on in the morning for the rest of your life. Wouldn't it become kind of a pita? I want it to happen automatically.

Yeah, I'll get a simple timer. Too bad reverse light-sensitive switches aren't available, but that's alright. A timer will suffice.

I came to permies seeking an answer to my dilemma and found it.

Thanks for all the replies.

That is what we are saying: you can.

You use a relay so that it reverses. Kind of how you can use a cheap electric heat thermostat and reverse it for cooling mode by using a 10 dollar relay.

It just swaps the normally open and normally closed terminals.

It does not matter if it senses daylight or temperature: sensors are stupid and relays turn it into Opposite Day to put it in non electrical terms.

The diode idea was to have the panels run the fridge and charge the batteries.
But if the panels can't power the freezer by itself, that won't work.

There are also some folks on utube that have panels dedicated to just their freezer.
Because there is so much loss when you start including batteries.

He's right.
You can hook a relay to the normal, turns-on-at-night type switch.
So when the switch turns on, it turns off power to the inverter.
Or turns off power from the inverter.

Same problem with temp switches.
They commonly turn on when it's cold and off when the heater is warmed up.
Hard to get the common adjustable temperature switches to turn on the fan to a solar heat box
if they turn off when it gets hot.
So I rigged a relay to invert the output.

James Alun wrote:Ah I had assumed this was to stop the freezer drawing from the battery.

Use the thermal inertia to get through the periods of no power and then use the panels to drive the freezer. Although the batteries are connected they aren't actually used.

The panels do drive the freezer as they are the only source of power. So in that sense they do drive the freezer. The problem is that the starting current of the freezer is high. The batteries can provide the high starting current. Also, the inverter needs the batteries. It can't run off the solar panels by themselves. I only wanted the freezer to shut off at night when there is no sunlight. If the freezer runs at night it is using only the batteries and they run down to the point where their voltage is too low and it's not good for batteries to be discharged too low. I figured it was better to turn the freezer off and rely on the fact that the food will stay frozen well enough until morning when the sun rises, saving the batteries. I'm trying to protect the batteries from too much discharge. During the day battery voltage remains high. As long as the freezer is off at night, battery voltage remains high at night also.

I found a thread here on permies from which I learned a lot: https://permies.com/t/142346/Quick-Dirty-cheap-Grid-Freezer

I hadn't thought of brine. After reading this thread I decided to use brine. Presently I keep about a half dozen gallon jugs of water in the freezer. I'm going to replace the water with brine.

I bought a timer from Walmart. (my mistake--two bags of potatoes) It does the trick--turned off last night and turned on this morning.

A word on how good the freezer works. Into the freezer I placed, after it had shut down for the night, two ribeye steaks, two pigs feet, and three one-pound containers of strawberries (everything unfrozen). This morning, before the freezer turned on, everything was frozen solid.