# Solar powered Swimming pool filtration pump controller

#### insidethebox

Joined May 21, 2014
7
I am trying to come up with a circuit to control a swimming pool filtration pump and heat pump, using a small solar panel (say 0.5W) to power a 12V/240V relay.
To give some background, I have an array of residential solar PV panels powering the house and swimming pool and I want the pool pumps to switch on automatically when there is a reasonable amount of sun. I don't particularly want to have to connect the main house PV panels to the pumps but I thought if I have a mini panel powering the circuit that it will act as a power source and light sensor. The capacitor is included to even out the input current from the mini panel.

I would be grateful if someone could advise whether this circuit would work and what improvements could be made?

I am a complete amateur/novice so please be gentle!

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#### alfacliff

Joined Dec 13, 2013
2,458
the diode is not needed. why the variable resistor? a .5 watt panel might not be large enough for the relay, have you checked specs on power relays with enough current capability for the pump?

#### wayneh

Joined Sep 9, 2010
17,153
I think that circuit will cause a lot of trouble by not hard switching the relay, even if the panel has enough power. Under some conditions it won't. You don't want it to "chatter", as that would be hard on the pump.

Look up basic solar cell relay circuits and you'll find they use a transistor or comparator to make the switch of the relay coil current. On or off, not in between. Personally, I'd use a comparator such as LM339 (a quad comparator on one IC) and switch the coil current with a small transistor. I think I'd establish a reference voltage with a zener diode, so that when the panel voltage exceeds some voltage set by the zener, the comparator triggers the transistor which in turn activates the relay. Your cap will help deliver a good surge to the coil.

#### Bernard

Joined Aug 7, 2008
5,788
Do you have the 12 V relay & specs? If not a solid state relay might be pratical @ about $US 45. OPTO 22, mod 380D45, 1 k @ 3 V input. Thread Starter #### insidethebox Joined May 21, 2014 7 Thank you for your collective comments. I shall investigate comparators and establish a spec for the relay. I assume I spec the relay based on the power and current of the pump? With regard to the transistor and comparator I will do some more research and sketch a modified circuit up, hopefully for further comment. Thread Starter #### insidethebox Joined May 21, 2014 7 the diode is not needed. why the variable resistor? a .5 watt panel might not be large enough for the relay, have you checked specs on power relays with enough current capability for the pump? I thought I needed the diode to make sure the current out of the solar panel always went one way? I thought I could use the variable resistor to fine tune the current? Thread Starter #### insidethebox Joined May 21, 2014 7 Do you have the 12 V relay & specs? If not a solid state relay might be pratical @ about$ US 45. OPTO 22, mod 380D45, 1 k @ 3 V input.
No I don't have the relay spec yet, what are the advantages of using solid state relays?
I assume I spec the relay based on the power and current of the pump? The pump is 0.8kW max 3.8A 230v @50Hz.

#### wayneh

Joined Sep 9, 2010
17,153
I believe that panel will be able to activate - but not overpower - that relay in full sun, if that's what you mean. What is a question mark is what happens when a cloud goes over, or at dawn and dusk. I think you will have a problem with chatter when the light changes gradually.

But it's fine to hook it up to experiment. Maybe you'll prove me wrong. If not, there are fixes. Just be sure to stay aware of the potential for a problem - listen to the relay and see how your load reacts. You might even use a bright lamp to simulate sunlight, to see how it goes.

#### insidethebox

Joined May 21, 2014
7
I believe that panel will be able to activate - but not overpower - that relay in full sun, if that's what you mean. What is a question mark is what happens when a cloud goes over, or at dawn and dusk. I think you will have a problem with chatter when the light changes gradually.

But it's fine to hook it up to experiment. Maybe you'll prove me wrong. If not, there are fixes. Just be sure to stay aware of the potential for a problem - listen to the relay and see how your load reacts. You might even use a bright lamp to simulate sunlight, to see how it goes.
I was hoping the capacitor would smooth out the "chatter" caused by the variation in the load?

Also I still intend to follow your suggestion of zener diode, LM339 and transistor to control the voltage, but I haven't a clue what I'm doing with any of that so I need to do a lot more reading before I can upload a new circuit. But I thought if I started with the panel and relay specs and worked backwards it would be a reasonable approach.

#### Alec_t

Joined Sep 17, 2013
12,163
I was hoping the capacitor would smooth out the "chatter" caused by the variation in the load?
Any practical size capacitor would only be able to bridge drop-out periods of a fraction of a second, whereas a pump won't take kindly to drop-outs of even several seconds. At the least I think you will need a comparator with hysteresis. You may also need the comparator to trigger a timer to keep the pump running for a minimum of several minutes at a time regardless of light level changes.
But I thought if I started with the panel and relay specs and worked backwards it would be a reasonable approach.
Good thinking. Circuit design is all about knowing the input conditions and output requirements then interfacing the two.

#### wayneh

Joined Sep 9, 2010
17,153
Glad to hear you're still thinking of using the comparator and transistor.

To help get you started I've attached a portion of a schematic that I used in another project. It contains the essential elements you need, and your relay will replace the TEC load.

Starting from the top, the lines coming from the left are:
Solar panel V+
same, perhaps divided down with resistors
Solar panel V-
Reference voltage, Vref. This is where you adjust the set point.

R3 sets the level of hysteresis, and I'd start with maybe 1M or 470K ohms, to see how it goes. Also, you'll want a logic level MOSFET. The one shown needs ~10V to switch fully on. You need one that comes fully on at <5V.

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#### insidethebox

Joined May 21, 2014
7
Hi Wayneh,

Firstly, thank you for all your guidance.

If I go for a LM339 comparator and Transistor (MOSFET), do I still need the Zener diode?
When you say "needs ~10V to switch fully on" what is the name of that voltage parameter, to assist me in locating a 5V version when reviewing specs?

#### wayneh

Joined Sep 9, 2010
17,153
You need a reference voltage on one of the comparator pins. A zener is a handy way to create a reference voltage. There are other ways, but I think a zener is fine for this application. Note that you can still adjust the reference voltage at the comparator down from whatever the zener voltage is, using resistors as shown in my schematic. I do think you will want the ability to adjust while you are experimenting. You MIGHT be able to use fixed resistors once you get everything set the way you like.

The gate voltage is often called Vgs (∆V from gate to source). Don't be misled by the so-called threshold voltage - that's where the MOSFET starts to conduct and you don't really care about that. This one is overkill for your application, but is a good example. Read here also.

One problem: When the voltage reaches a high enough level and the power to the relay turns on, the panel voltage will be drawn down by that load. It will be well below whatever the set point was where it turned on. Your comparator will need enough hysteresis that it will still hold its "on" state under those conditions. For instance if the relay comes on at 6V, it might not need to be turned off until voltage falls to 3V. I think you'll need to experiment a bit with your components and determine the right on and off voltages to ensure solid switching. Then we can verify the design you need to achieve that. I recall some clever solutions I've learned in this forum for a "voltage-controlled switch with hysteresis".

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#### Alec_t

Joined Sep 17, 2013
12,163
Don't be misled by the so-called threshold voltage - that's where the MOSFET starts to conduct and you don't really care about that.
Well, it's an indication of whether or not logic-level voltages are likely to be usable to turn the device on. Normally the Vgs should be several times Vthreshold in order to turn it fully on. Unless a FET is rated as 'logic level' in its spec, a Vgs of around 10V is often used.