Hi have built two home made solar panels to heat my swimming pool in the summer. At the moment the 12v pump runs cont. and thus the output temp is not much higher than the input. I want a cheap 12v repeat timer, that runs the pump for say a minute then off for a minute in a continuous cycle. Any ideas please
Hi there Mark, I know nothing about repeat timers (sure someone else here does though) but there may be other solutions to your problem:
 use a 12v pwm motor speed controller to reduce your pump speed. these can be had for i think £12-15
 use a proper 12v differential temperature controller. The REUK one is the cheapest at £30 but has a preset temperature difference setting which is not variable. the modified vellemann thermostat diff controller that norm has developed (see his posts) can be built for under £10
 use a small pv panel and a 12v pump designed specifically for pv with a mppt tracker. these are typically available for around £50 upwards. that way the pump speed is only greater when the panel is receiving more sunlight.
Note that having only a slight difference between input & output temperatures, provided the input is less than the output, is the most efficient way of capturing energy from a panel. it may however be that your panel is sometimes cooling the pool which is clearly negative efficiency?
Hi These are the two panels, 1 glazed and the othe unglazed (the crazy ceter and other joint had to be used with T connecters cause thats all i had ) The glazed one builds up a good amount of heat if left for a minute and this is why i thought of the timer, but if you say it will be more efficient if it runs cont. and is only a few degrees hot than the input i won't need to bother???
if your pipework is well insulated then too high a flow rate is not necessarily a bad thing provided the panel is radiating less heat than it's gaining. otherwise the panel will simply cool your pool.
if you don't want to splash out on a differential temp controller, which is the most efficient way to control the pump, and if you had a target temperature for your pool in mind, say 30 degrees, you could maybe use a £5 stat on your panel, set to say 35 degrees C, so the pump only comes on when the panel is above 35. this would provide a simple but crude form of control and whilst not as good as a differential temperature controller, at least it would generally prevent the panel from cooling your pool.
keep your pics below 1024kb in size and you can upload one pic per post, provided you are logged in.
Panels look good - Well done and thanks for posting pics.
If you're not going for a differential temp controller, but want to provide some limited control to stop your pumps coming on when your panel is below X degrees, then you could use a cheap thermostat on your panel(s).
For a mechanical (bimetallic) themostat, here's one at £5 - ebay item 120748056398.