Ok, some info for people considering how to power their solar pump...
I bought a variable voltage power supply home from the office and had a play. Here are my (rough and ready) results...
12V : The pump shifted 8l/min of water in my test setup. Amps used was roughly in line with pump wattage.
7V : A rough mid-point between 12V and 3.4V. 5l/min shifted, so it appears roughly linear.
3.4V : This was the lowest voltage that the pump still operated at. It shifted 2.5l/min.
3.3-0V : pump is dead, no water shifted.
So the pump gives a (roughly) linear response of 2.5-8l/min between 3.4V and 12V (if I had more timed I'd take more sample points).
For me, the key result is that the minimum flow of the pump when using voltage control is 2.5l/min. I had hoped to go down to 1l/min when sparging, but clearly this isn't going to happen. Bummer.
I went back to my (possibly dodgy) PWM controller, Results are...
On : 8l/min.
Min : 6l/min (!!!)
Below "min" the pump wouldn't shift anything. So the range supported by my PWM is 6-8l/min, which is not worth the bother of fiddling with the PWM. I'm going to take the PWM controller into the office and monitor the output with a scope to see if it really is duff. Will post back with the results...
Mark1964's bypass valve is starting to look like a good solution...
I bought a variable voltage power supply home from the office and had a play. Here are my (rough and ready) results...
12V : The pump shifted 8l/min of water in my test setup. Amps used was roughly in line with pump wattage.
7V : A rough mid-point between 12V and 3.4V. 5l/min shifted, so it appears roughly linear.
3.4V : This was the lowest voltage that the pump still operated at. It shifted 2.5l/min.
3.3-0V : pump is dead, no water shifted.
So the pump gives a (roughly) linear response of 2.5-8l/min between 3.4V and 12V (if I had more timed I'd take more sample points).
For me, the key result is that the minimum flow of the pump when using voltage control is 2.5l/min. I had hoped to go down to 1l/min when sparging, but clearly this isn't going to happen. Bummer.
I went back to my (possibly dodgy) PWM controller, Results are...
On : 8l/min.
Min : 6l/min (!!!)
Below "min" the pump wouldn't shift anything. So the range supported by my PWM is 6-8l/min, which is not worth the bother of fiddling with the PWM. I'm going to take the PWM controller into the office and monitor the output with a scope to see if it really is duff. Will post back with the results...
Mark1964's bypass valve is starting to look like a good solution...