Non-MR2 pumps: How To
Once Dave B has his up and running and is happy, I'll start to ship them.
Ref the FETs (transistor) for other pumps:
these should work, $3.85 from Digikey (I'd buy a couple):
http://www.fairchildsemi.com/ds/FD/FDP025N06.pdf
http://www.fairchildsemi.com/ds/FD/FDP025N06.pdf
You need to screw it to a heatsink/chassis using the hole on the metal tab.
It needs Bare metal contact to conduct the heat away from the transisitor (actually you should use heatsink grease).
Note, I can't see if the metal tab is connected to any of the three pins on the FET. You need to be careful of this. If it is connected to the DRAIN (D) you're ok. If it's any of the other two, you need to use a special insulating mica washer under the transistor, which will still conduct the heat away, but electrically isolate the tab, such as:
http://www.mcmelectronics.com/product/21-1175
digikey probably has them, also.
and there is also a plastic spacer that stops the screw making electric contact.
You can just use a multimeter to see if the metal tab is connected to any of the 3 pins.
To hook up the transistor:
Connect the DRAIN (D) to ground
connect the SOURCE (S) to one side of the motor
connect the other side of the motor to 12v
connect the GATE (G) to 12v to start the pump and 0v to stop the pump.
Keep the wires to the motor short to reduce RF emmision.
Later you may have to add a ferrite bead around the wire to stop radio interference, but just get the basic stuff working 1st ;-).
If can get this working, I can send you a specially programmed controller that will connect to the GATE of tge FET transistor and will then speed control the pump.
Eventually, you need to water proof the circuit. You could buy a metal project box that is at least splash proof and screw the transistor to the inside of that to act as a heat sink. Then mount the box close to the pump on the frame to help pull the heat away.
I don't have acces to a stand alone pump, so I can't test this myself, but is someone else could pioneer this and share the details, that would be good.
oh, I just found the FET insulator kits from Jameco (insulator, washer, bolt and nut) from Jameco:
http://www.jameco.com/Jameco/catalogs/c291/P17.pdf
bottom left of the page, part number 34121, $3.95 for 5 sets
on the same page are nice heatlinks and one transistor may work, IRF3205
but the digikey one is better, as it has less ON resistance (RdsOn) which means that it won't get as hot.
I would buy two FETs and wire them in parallel, then connect the gate to 12v and run the pump for 2mins under load to make sure they don't overheat. BTW, don't run them w/o the heatrsink or they will burn up very quickly.
As a side note, I once had a PC that was flakey and kept crashing, I goit more and more frustrqated with it until one time it crashed I kicked the PC case (not very hard). But hard enough to knock off the heatsink/fan crom the CPU. Those CPU's generate huge amont of heat, the cpu burned up in <5secs .. it just went up in smoke!! Once you let the "magic smoke" out of electronics, they don't work anymore. The magic smoke is what makes them work.
BTW, the MR2 spyder pumps have the FETs built in and use the aluminum motor pump body as the heatsink.
That's all for now ;-)
Ian