Photocell switch to preserve batteries

[mnakkach]

The title sounds strange but i couldn't find any better summary for a title.

In an off-grid system, using lithium batteries, PV and inverters, during winter, non critical devices such as water heaters, water pumps, heating system, consume high power, I have installed timers so they operate during the day light between 10am to 3pm to avoid draining the batteries, but it is happening frequently and mainly during cloudy days they drain the batteries leaving no power for night time.

I need to automate powering off such devices when there is no direct sunlight and resuming them when sunlight comes back.

I thought about installing a photocell automatic switch and connect it to a relay to work in an opposite way, the relay should close (to operate the non critical appliances) when photocell switch open (during sunlight) and visa versa. Also I thought about the sensitivity, I need to tune it to open during strong sunlight only, it should close in foggy/cloudy light, i thought about adding some layers of plastic or cloths to tune it. All the photocells I found in the market are non adjustable and they are very sensitive to light while i need a photocell with dark sunglasses to do the job .

Maybe I am trying to reinvent the wheel in difficult way while such a solution could be already available out of the box in the market, or maybe someone has done this setup?

I couldn't find such details while searching in this forum, your feedbacks please...

Thanks

 

[MisterSandals]

I would likely disable those appliances based on battery voltage (and possibly in combination with timers as you described).

 

[mnakkach]

I would likely disable those appliances based on battery voltage (and possibly in combination with timers as you described).

There are some inverters having such feature called TWIN, they have a second output for non critical appliances, but my experience was bad since they are not well built and having design defects.

But if i manage to automate testing and controlling on/off based on battery voltage or SOC then i won't be having the circuit closed till battery is 100% full, bringing the battery to 100% may take till noon time or more, even if i set it to lower % then the non critical will utilize the battery, the point which i want to avoid.

I need the non critical to operate between 10am and 3pm (this is already set) when there is direct sunlight regarding of battery SOC %

 

[MisterSandals]

Look for a battery protection device with a settable voltage.

 

[Supervstech]

I use photocells all the time, they come with a metal shield to diminish sensitivity... you could put them in a shaded area, or put black tape over part of the cell too.

 

[mnakkach]

Look for a battery protection device with a settable voltage.

But this will disconnect the battery and causes the inverters to shutdown. This is how my inverter works, it doesn't work without battery, moreover, if i suppose the inverter will keep working without battery only on solar, i have other appliances in the house that are critical and should utilize the battery.

I only need to create a new output line that is non critical that disconnects when there is no direct sunlight, no one is bothered about having such appliances switching off/on many times during the day, at the end if there is extra sunlight then i need them to operate, that's how i thought about the photocell switch

 

[mnakkach]

I use photocells all the time, they come with a metal shield to diminish sensitivity... you could put them in a shaded area, or put black tape over part of the cell too.

This is good, have you ever used them for the same explained purpose ?

 

[Supervstech]

Fairly easy.
I would use a DIN rail box and some din contactors triggered by the photocell.

 

[Supervstech]

This is good, have you ever used them for the same explained purpose ?

No, I use them for landscape lighting or other lighting controls, so opposite of your intention, but most have NO/NC leads, or a relay can be used

 

[meetyg]

First, you need to think about HOW you will turn those appliances on/off and what their amperage rating is.
I say this because the photocell will probably control a relay. You will need an AC relay that will handle those loads.

Some solutions come to mind:

1. Photocell Controls a relay. You might need to use some resistors with the photocell to get the required voltage for the relay signal pin.
2. Same as above, but maybe use a microcontroller like an Arduino.
3. You could also use a small solar panel next to your solar panels, which will power the relay.

 

[timselectric]

Yup, it will work great. I've done it many times before.
Since you already have timers, it's a simple addition.

 

[mnakkach]

Not sure about wiring, I have the below contactor, I have the line power coming from the photocell I call it L1, and i have another power feed from the inverter I call it L2, I call output from the contactor as L3.

I should connect L1 and L2 to the contactor and it should work in a way to provide output to L3 from L2 source when L1 is off, it should disconnect L3 when L1 is on.

I hope someone can assist with the wiring diagram

Thanks

 

[Supervstech]

Not sure about wiring, I have the below contactor, I have the line power coming from the photocell I call it L1, and i have another power feed from the inverter I call it L2, I call output from the contactor as L3.

I should connect L1 and L2 to the contactor and it should work in a way to provide output to L3 from L2 source when L1 is off, it should disconnect L3 when L1 is on.

I hope someone can assist with the wiring diagram

Thanks

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