Electronics > Projects, Designs, and Technical Stuff
Over-temperature circuit for water pump controller
beanflying:
If you have a flow switch planned then drop the loss of prime switch (assuming you were planning to fit a diaphragm type) the LOP will be redundant - no flow no prime. Also these generally had a separate mechanical lever to hold in while pressure was established making them a huge PITA.
Generally the KISS principle when it comes to pump and motor controls was the most reliable. Motors providing the pump was within operating parameters and not for example open pipe (maximum motor load condition) was near a zero failure condition. The only other exception to this was SWER (single wire earth return) fed rural supplies when brown outs could be an issue.
floobydust:
It would help to know what type of pump - progressive cavity, centrifugal, piston etc. because they fail in different ways.
tautech:
--- Quote from: beanflying on March 18, 2020, 06:20:52 am ---If you have a flow switch planned then drop the loss of prime switch (assuming you were planning to fit a diaphragm type) the LOP will be redundant - no flow no prime. Also these generally had a separate mechanical lever to hold in while pressure was established making them a huge PITA.
Generally the KISS principle when it comes to pump and motor controls was the most reliable. Motors providing the pump was within operating parameters and not for example open pipe (maximum motor load condition) was near a zero failure condition. The only other exception to this was SWER (single wire earth return) fed rural supplies when brown outs could be an issue.
--- End quote ---
Yep this ^
With beans help I installed a flow switch and 2s 555 timer board to a new installation last year. Installed on the suction side it detects loss of prime (my primary concern) and when used in conjunction with the 555 set to 2 secs prevents any damage to the pump from being run dry.
Phase failure and overload relays do the rest providing adequate insurance for a long trouble free life.
For this installation that's wirelessly controlled we have a halogen spotlight for ON high on the power pole that we can see for some distance that also serves as an indicator if the pump was to lose its prime, Pump ON = light ON but if light goes OFF after 2s we know pump prime is lost.
All the LV stuff is 12V cascading through cheap and cheerful relays to then switch the 440VAC mains.
calzap:
Again thanks for the replies.
Motors heat-up for reasons other than overload. For example, failure of the cooling fan. And pump-heads can heat-up for lots of reasons too ... bearing failure for one. So in addition to electrical load monitoring, heat sensors directly on the motor and pump-head provide additional insurance.
The old tech is robust. The relays will get activated only if there is a problem ... hopefully, not very many cycles for them. Further, the plan is drawn-up, and the relays are on the shelf. I use computers and MCUs when needed ... not here.
There is very little suction head. The water is drawn from a pond, the surface of which is less than a meter lower than the pump. Pump is two stage centrifugal.
And both loss of prime and the flow switch are needed. I won't go into all the reasons. But one is that because the pump is pushing water into pressurized tanks. Flow goes down as output pressure increases. So the flow switch opens before cut-out pressure is reached. In addition, before the pump starts, the flow is obviously zero, but it's important that the pump have prime before it is started.
I'm still struggling with the circuit for the flow switch. At very high flows, such as when a fire hose is being used, the output pressure drops so low that the pressure switch safety shuts-off the pump. At this point, the flow switch needs to substitute for the pressure switch. On the other hand the pressure switch needs to rule at the beginning and end of ordinary pump cycles. The circuit itself will be easy once I get the logic right.
Mike in California
tautech:
Drop your control circuitry to LV and many doors open.
Series and NO and NC wiring and then many options are possible.
I used a flow switch just like Bean linked https://www.ebay.com/itm/261846873840?ViewItem=&item=261846873840 wired NO that if it goes closed means the pump is flowing water but of course the NC 2s timer ensures the pump gets to start at power ON but if the flow switch doesn't immediately close the timer relay goes open and the pump turns OFF before any damage occurs. I could have easily set for 1s but didn't want it hiccuping.
This is the timer I used:
https://www.aliexpress.com/item/32954793505.html?spm=a2g0s.9042311.0.0.3da24c4dchjEzg
FYI this is a 12 stage vertical centrifugal shifting 6+m3/hr from a 2m suction to 60m head.
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