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Auotmatic Load Control Circuit

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Sooraj_tk

New Member
Hello All,

I need your help in designing a circuit for the below mentioned scenario:

I need to connect 12V 1.5 Amp submersible water pump directly to a solar panel.

I might be using 12V 60W or 80W panel for this.

I need a circuit which can limit the Voltage/current from the panel to 12v/1.5 Amp. if the incoming voltage/current is from the panel is less than 12v/1.5 Amp
, it should cut off and the motor should be Off

The Panel output Current keeps varying with the intensity of the sunlight.

Could you please help me to design a circuit.

Thanks and Regards,
TK
 

AnalogKid

Well-Known Member
Most Helpful Member
First, you don't have to limit the current; the motor draws only as much current it needs. So you want two separate circuit functions, one to regulate the voltage to no more than 12 V; and one to monitor the voltage to see if it dips below 12 V.

When the monitor circuit disconnects the pump from the PV (photo-voltaic, or solar panel), the panel voltage will rise above 12 V. If the monitor then reconnects the pump, the voltage will drop below 12 V again and the system will cycle like this continuously until there is enough light to run the pump correctly. This oscillation is bad for the pump. Think about a minimum off time to reduce this oscillation on cloudy days. One minute, ten minutes, whatever; since we don't know what the pump is doing, we can't recommend anything.

What is the maximum output voltage of the PV on a sunny day with nothing connected to it?
Where are you located?
What is your skill set for building a small circuit with a heatsink?

ak
 

ronsimpson

Well-Known Member
Most Helpful Member
First, you don't have to limit the current; the motor draws only as much current it
Yes/no
It is true the motor will draw 1.5A when running. But at startup it will far exceed 1.5A. If there is no battery the startup current will collapse the cell voltage. I think you will need a some storage device that can supply 3 to 4 amps for 2 seconds to get up and running.
 

MichaelaJoy

Active Member
You'd need a battery, which would charge from the solar panels and deliver the necessary current to

A ) Start the motor up, because there will be a surge upon startup.

and

B ) Be able to deliver power when the output of the solar cell(s) are not producing enough current to run the motor.

Here's one place to look
http://microcontrollerslab.com/solar-nicad-battery-charger/

Here's one that's already designed and built. You'd have to evaluate it to be sure it fits your needs.
https://www.powerstream.com/solar-charge-alternate.htm
 

ronsimpson

Well-Known Member
Most Helpful Member
You'd need a battery
More to think about.
Lets say there is no start up problem.
Lets say you have the motor running at 1.5A and the cell can deliver 1.6A or more at noon. Every thing is good.
By 2:00 the cell output drops to 1.4A and the cell voltage will drop to near zero volts and the motor will stop.

By 4:00 the cell output is only .75A and there is no chance of the motor working.
With a battery of 1.5A for 10 minutes; The battery will charge up at 0.75A with the motor off. (20 minutes)
Then the motor will turn on and run at 1.5A while the cells supply 0.75A leaving the battery discharging at 0.75A. (20 minutes)
In this case the cycle time is 20+20=40 minutes. It is better to have the motor running 1/2 the time then not running at all.
 

Sooraj_tk

New Member
First, you don't have to limit the current; the motor draws only as much current it needs. So you want two separate circuit functions, one to regulate the voltage to no more than 12 V; and one to monitor the voltage to see if it dips below 12 V.

When the monitor circuit disconnects the pump from the PV (photo-voltaic, or solar panel), the panel voltage will rise above 12 V. If the monitor then reconnects the pump, the voltage will drop below 12 V again and the system will cycle like this continuously until there is enough light to run the pump correctly. This oscillation is bad for the pump. Think about a minimum off time to reduce this oscillation on cloudy days. One minute, ten minutes, whatever; since we don't know what the pump is doing, we can't recommend anything.

What is the maximum output voltage of the PV on a sunny day with nothing connected to it?
Where are you located?
What is your skill set for building a small circuit with a heatsink?

ak
@ Present I am using a solar charge controller + 12v 7AH battery + 12v 20W solar Panel. Day time it charges and evening the motor work for 2 hour approx. I am using a submersible micro motor for filtering purpose. Theoretically 20W panel can supply 12V to 18V/ 1.6 amp.

Apart from operating with battery, I want to utilize the daylight and run it during day as well without battery support.

I tried connecting motor directly to panel (used a 12v Regulator LM317). But the panel was not giving enough power. It was suppling max of 800 ma but voltage is always above 12v. The motor was not Pumping.

So thinking of using a 80W panle (or higher). My idea is to utilize the motor to max possible hours.

If am using a 12V 80W panel theoretically it is supposed to deliver 6 amp (Hope I am correct).

Say I am using the voltage monitor or Regulator circuit, if the voltage is normal and current is less, motor is not pumping water, doesn't it heat-up the motor and reduce the life of the motor?
 

MikeMl

Well-Known Member
Most Helpful Member
I would connect the panel directly to the battery, assuming a ~20Voc panel connected to a 12V SLA battery. That way, the panel is being operated near its MPPT.

To prevent the battery from being overcharged, I would use a shunt regulator that bypasses current around the battery when the battery voltage exceeds ~14V.

To prevent the motor from over discharging the battery, I would use a voltage sensitive switch that has hysteresis; make the cut-in voltage (motor starts running) about 12.5V. Make the cut-out voltage about 11.6V (motor stops running).

Delaying the motor start until the battery reaches 12.5V means that about 50% of the charge removed from the battery the previous night has been put back before the motor starts. As the motor starts, its current-inrush transient comes from the battery. If the panel is sized appropriately, as the sun gets higher in the sky, the panel delivers the motor running current with some left over to recharge the battery towards the voltage at which point the shunt regulator holds the battery voltage constant.

As the sun sets, the motor will continue running until the battery is depleted down to the cutoff voltage, at which point the motor stops drawing current.

The SLA battery must be rated for repeated deep charge-discharge cycling use, otherwise it will have a very short life.

I built a system like this for pumping water in my wife's greenhouse. I have the schematic somewhere. In this case, the solar panel was too small to ever run the pump directly, so effectively, the voltage sensitive switch turned the system into a pulse width modulator, so the pump ran at ~50% duty cycle while the sun angle was high, and the pump ran at a lower duty cycle morning and evening, and not at all during the night. Because the panel was too small to run the motor, no shunt regulator was needed. Only if the panel can produce more current than the motor requires is it possible to overcharge the battery.
 
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