Customizing the solar control electronics

With a plethora of manufacturers and models for pool solar controllers, it can be challenging to put together a system that just works, without resorting to sourcing everything from a single manufacturer and buying their overpriced controllers.

Our Equipment

Our pump is a premium variable speed model, but has no timer or even an on/off switch. When it is plugged in, it is running. It has a large dial to control the speed manually, and an RJ-45 socked to control the speed electronically.

Our salt water chlorinator has a comprehensive timer. It also has a power socket for the pump to plug into such that it can turn the pump on and off as required according to it’s configured schedule (also turning itself on and off).

This setup works well for a standard system. We can set the desired pump power using the manual dial on it, and use the chlorinator to configure a daily schedule.

The addition of solar heating complicates matters. We have a solar controller that will operate an automatic valve and send water to the roof panels when the roof temperature is higher than it’s configured temperature. As with the chlorinator, it also has an output to power the pump when it’s required.

Problems

The chlorinator needs to be able to turn on the pump, and the solar controller also needs to be able to turn on the pump (i.e. We need a a mains OR gate).
When the solar is on (with or without the chlorinator), the pump speed needs to be higher to push the water up to the second floor roof.

Part one of the solution: Mains OR switch

We want the pump to run according to the chlorinator timer, but also outside these times if the roof is hot and the solar controller wants to run. So we need an OR gate with the chlorinator and solar controller power sockets as inputs and the pump as output.

Two AC relays wired in parallel achieve this:

I’m using these power relays. The finished unit looks like this:

Part two of the solution: Speed control via 0 ➜ 10V signal

Once the pump is on, we need to set the speed depending on whether the solar is enabled. Fortunately the pump allows for external speed control via a 0-10V signal. The solar controller includes isolated relay contacts that switch when the controller turns on/off. We can therefore do the following:

Edit: As it turns out, the controller’s relay outputs are not isolated at all and are in fact the the same 24VAC outputs that control the actuators, necessitating additional circuitry. Ideally the addition of a 24VAC relay would have solved this, but I only had a 12VDC one on hand and so added this, a rectifier, and voltage regulator as follows:

Updated speed control schematic — Revised speed control schematic after unexpected solar controller output.

I used an old aluminum 5 1/4" drive bay cover to mount the potentiometers, printed out a label to stick on it, and mounted the whole thing in a box with some cable glands to feed the cables through.