For years I have trying various different manufacturers for a suitable pump for a particular application. Each one I tried had a problem (reliability, size, noise, etc). Eventually I found the prefect pump, it´s silent, reliable (not had a single breakdown yet) and small. Then the bastards went and changed the design. The new pumps look identical, but the electronics are different. Before there were two versions, one that detected a temperature differential and one that had an extra wire that detects mains. They´ve ditched the mains detection one (which is the one I was using) and replaced it with a plug that shorts out the socket for the temperature sensor (so it runs all the time it has power). This is where the problem is. When they detected the mains, they would run on for a few minutes after the signal was lost. Obviously, this is not possible when the only way to control the pump is actually cut the power to it. I need the run-on, its the most important part.
So, I though I would just redesign the pcb to include a timer circuit and ditch their temperature circuit. Pretty easy to do and had it working on the breadboard. When it came to laying out the PCB I couldn´t physically fit all the components on the PCB, and there are not hardly any parts. I re-used some of the original parts (transformer, bridge rectifier, triac, opto-triac and caps) and added a couple of transistors, a HCF4060 and a voltage divider for the mains detection. All the parts I tried are in the smallest SMD packages I could find. So I either need to think of a better way to do it with less components, or make my original design and put it in a box. The thing is, if I do that, then I need to buy all the parts(I wont be able to re-use the parts on the PCB because I´ll have to leave that in place), and a box. This is now getting expensive and the pumps are already expensive to start with (about 150% more than what I used last).
So is it worth spending any more time on this trying to figure out a solution, or do I just cut my losses and buy delay timer relays? What would you do? It must be possible somehow as they used to do it in the same case in the old pumps.
Some specs;
Pumps consumes 0.07amps 230Vac
The PCB is 45 x 45mm, and available space after the transformer, connector for the motor and cap for the motor is 10x33mm (double sided). In that space I would need, the timer circuit and mains voltage detection. In that space now is an op-amp and some resistors.
The transformer output is 9V 0.35VA and has a bridge rectifier(MB2S) immediately after it.