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What automatic cutoff switch to use for no battery water pumping.

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Larry12

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Joined
Sep 26, 2022
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Costa Rica
I need to make a water tank (1100 litres) with solar panels on top, and a solar powered Shurflo 12 volt water pump mounted on the bottom to send water uphill to home or livestock watering trough. This has to have an automatic shut off when solar is insufficient to run the pump.
The pump has an internal automatic shut-off when the pressure reaches 55 psi in the 1/2" output plumbing. It operates the pump again when the pressure falls below 35 psi. I want to send water up hill to another tank with a toilet type float to shut off the water when the tank gets full.
It is important on a battery-less off grid system that the pump not try to cycle when the sun is not sufficient to run it efficiently. To prevent pump overheating/failure I need something that will sense power levels and cut off all power to the pump when power is less that the required 12 volts and 6 amps DC.
I live in mountainous Costa Rica and this battery-less system will be a great boon to us. I have heard of something called "contractors" and saw these recommended for a different application. Might these work for me too? I saw some of them on Amazon ( https://a.co/d/8fQIQok ) but many reviews complained about a noisy hum and malfunctioning. I would prefer to use a reliable brand. I don't know how to hook them up either. Any knowledgeable recommendations/advice would be appreciated.
 
I believe you're looking for a 12 volt DC voltage monitoring relay.
It would sense voltage and the contacts would cut off power.
 
Voltage relays alone do not work due to panel going open circuit voltage when disconnected. You need to place an approximate load on th panel. When the voltage gets high enough, that load disconnects and the pump is then connected. You can also use a small 3-5W panel with a load on it to look like a linear power meter. The voltage relay looks at that and when it sees enough sunlight, it then turns on the pump.
 
efficientPV said:
Voltage relays alone do not work due to panel going open circuit voltage when disconnected. You need to place an approximate load on th panel. When the voltage gets high enough, that load disconnects and the pump is then connected. You can also use a small 3-5W panel with a load on it to look like a linear power meter. The voltage relay looks at that and when it sees enough sunlight, it then turns on the pump.
Click to expand...
I'm fairly new to solar. What happens when panels go 'open circuit' ? Also how do I connect a little panel with a bigger one as you describe and what would that do? What kind of load do I need and again, how to hook it up, to one small panel or the big and the small?
 
We have a 12v pump hooked up to solar panels directly. It comes on when there is enough sun and shuts off when there isn't. Not sure why you need a control for that? We have used the same pump for 4 years now. no problems with it. It always has water in it.
 
efficientPV said:
Voltage relays alone do not work due to panel going open circuit voltage when disconnected. You need to place an approximate load on th panel. When the voltage gets high enough, that load disconnects and the pump is then connected. You can also use a small 3-5W panel with a load on it to look like a linear power meter. The voltage relay looks at that and when it sees enough sunlight, it then turns on the pump.
Click to expand...
If open circuit panels are a problem, can I just attach a tiny LED light to the large panel?
I have disconnected panels from the system (in a lightning storm for instance) with no visible harm.
 
My beginner's brain is thinking that if current gets too high in that open circuit it could fry something like my pump motor. I ordered a controller like Grampa recommended above. I was hoping that would be sufficient.
 
Repeat.... You need to place an approximate load on the panel. That means applying a load which will be the minimum current to run the motor. That relay is a start for a system. It won't solve all your problems. Typically, the panels should be oversized to the load for better running time. A buck converter will provide slightly more power and prevent over voltage. You will just have to fail a couple times before you believe me.
 
It is not that I don't believe you. I just don't understand what you are saying I should do. I am not experienced in using panels without a battery but I read a little bit of people doing it. What is a buck converter? And what kind of load is being recommended specifically, a second motor when I only want one? Maybe my idea won't work but I need to know why if that is the case. That controller has a over voltage cut off and an undervoltage cut off.
 
There are pre-made devices called a Linear Current Booster (LCB) that are designed for running pumps directly from a solar panel. They allow for a float switch to be wired to them as well in order to shut down the pump when the water container is full.

There are units from several different manufacturers. Below is just one of them.

LCB 20A 12/24v Solar Pump Controller

LCB 20A 12/24v Solar Pump Controller Linear Current boosters used in solar direct pumping applications, Compatible with 12 or 24 VDC Solar Direct PUMPS; The controller has terminals for float switc...
thesolarstore.com thesolarstore.com
 
kayakingphotos said:
There are pre-made devices called a Linear Current Booster (LCB) that are designed for running pumps directly from a solar panel. They allow for a float switch to be wired to them as well in order to shut down the pump when the water container is full.

There are units from several different manufacturers. Below is just one of them.

LCB 20A 12/24v Solar Pump Controller

LCB 20A 12/24v Solar Pump Controller Linear Current boosters used in solar direct pumping applications, Compatible with 12 or 24 VDC Solar Direct PUMPS; The controller has terminals for float switc...
thesolarstore.com thesolarstore.com
Click to expand...
Shutflo pumps shut off at 45-55 psi according to the particular pump model specs when water in the output plumbing reached that psi. Fill a tank that has a floating toilet tank type shut off and when the tank is full the pump is automatically shut off. So I don't have to be there to monitor it. I use this system with batteries at home. I want to do it without a battery. Thanks much for your help. I check out that link!
 
I seem to remember a older Mppt controller that had a function to turn on lights at night via the load output.
No idea if the newer ones will do this.
 
You asked a 15 second question giving very few details as to what panels are intended for use and the pump. You got a 15 second answer.
Here is how you connect a voltage relay and a load to prevent extreme cycling of on/off. A boost converter can be inserted at A.
no battery control.jpg
 
efficientPV said:
Repeat.... You need to place an approximate load on the panel. That means applying a load which will be the minimum current to run the motor. That relay is a start for a system. It won't solve all your problems. Typically, the panels should be oversized to the load for better running time. A buck converter will provide slightly more power and prevent over voltage. You will just have to fail a couple times before you believe me.
Click to expand...
"Typically, the panels should be oversized to the load for better running time." Please recommend me a panel output to shoot for. The pump is a Shutflo 2088 series, 12 volt DC and it calls for a 6amp slow-blo fuse.
 
I'm not doing any of this, but it's an interesting thread. If I'm following it correctly, when under-voltage is detected, the monitoring relay opens and stops the pump. However, this creates an open circuit to the panel and the panel voltage increases (nowhere for the sunlight energy to go). When the panel voltage increases, the monitoring relay is satisfied, closes the pump circuit, and starts the pump again. When the pump starts, the panel is no longer open circuit, so the panel voltage drops. The very fast on-off cycle sounds like a bad thing.

To break the cycle, you add something that prevents the panels from going open circuit. It looks like the buck converter is attached to the input of the monitoring relay? Do you attach the 2 ohm load to the output of the buck converter? Would something like this work, or...did I get this all wrong?

 
You have all the answers, I know little of your situation. Surflow is a good company and has charts for flow rate for head and current. I have no idea of your sun conditions, what panels you have easy access to and how much water has to be pumped each day. Pump current is probably closer to 4A. Panel voltage varies with current and temperature. Oversizing panels will raise voltage to the motor and may limit life. 12V panels are usually more expensive than grid tie and lower wattage making a buck converter cost effective in increasing current and limiting voltage. You need to do some calculations or wing it like everyone else does and hop for the best. I can provide advice, but I don't design for people.
 
donb108 said:
I'm not doing any of this, but it's an interesting thread. If I'm following it correctly, when under-voltage is detected, the monitoring relay opens and stops the pump. However, this creates an open circuit to the panel and the panel voltage increases (nowhere for the sunlight energy to go). When the panel voltage increases, the monitoring relay is satisfied, closes the pump circuit, and starts the pump again. When the pump starts, the panel is no longer open circuit, so the panel voltage drops. The very fast on-off cycle sounds like a bad thing.

To break the cycle, you add something that prevents the panels from going open circuit. It looks like the buck converter is attached to the input of the monitoring relay? Do you attach the 2 ohm load to the output of the buck converter? Would something like this work, or...did I get this all wrong?

Click to expand...
Just like the schematic. Those buck converters are pretty small for almost anything. A buck converter works well until it is asked to provide more wattage than the panel can supply. Then panel voltage goes into a death spiral. Any buck converter can be modified with just a couple components to make a linear current booster. That modification keeps the panel voltage from dropping below a set panel voltage.
 
This is why you buy a solar pump so you don't have to reinvent the electronics to make it work.

I mean if the electronics is your hobby, great, but this is a solved problem. They make pumps that do all this out of the box.
 
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