6 September 2016
I loved Joe Bidwell’s article in the July issue of Nuts &
Volts regarding the water pump protection system! It
opened my eyes to control devices that I never knew
existed. I have a few questions I am hoping Joe would
help me with.
There is a box called the "pump control" that is
mentioned several times. Why is it necessary and what is
In the article, Joe says the pump current can be
checked at the pump control box while the pump is
running. How do you do that?
I would like to get Joe’s opinion. Instead of purchasing
separate units for the voltage relay, time-out relay, and
time-delay relay, what would you think of building a single
device from scratch using a PIC microcontroller driving a
single relay? Other than design/construction time savings,
are there any advantages to spending the dollars to
purchase the commercially manufactured units?
Judy May W1ORO
I’m glad that you enjoyed the article, Judy. I’ll do my
best to answer your questions. Pump Control Box: Single-phase pumps in this range come in two varieties: “
two-wire” and “three-wire.” (There is also a ground wire, so
actually either three or four wires are fed down to the
pump). All of these pumps have separate Start and Run
windings. The Start winding gets a momentary voltage
through the start relay and capacitor. The two-wire pumps
have this built into the motor, so a control box is not
needed. They can run right from the pressure switch. My
pump is a three-wire that brings the Start winding up
separately from the Run winding. The Control Box just
houses the start relay and capacitor. Hope that explains it.
Measuring Current: If you look at the bottom left of
Figure 9, you’ll see a yellow wire that loops back into the
control box. This is one of the 240V lines that runs the
pump. I looped it so I could use a clamp-on ammeter to
check current. You can really do this on either of the 240V
lines anywhere on your system.
PIC Microcontroller: I don’t know why you couldn’t do
all of these functions with a PIC. I personally don’t have
much experience with them. I took the hardware approach
mainly because I started out with the voltage relay which I
found on a ‘surplus’ shelf for $10. My concern with a PIC
approach would be with the voltage spikes generated by
motor starts, and even the contactor relay energizing.
Maybe that is not an issue, just my opinion.
Thanks for your note.
Joe Bidwell KF7ODK
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