Determining inrush current on manufactured AC and DC Pumps

Thread Starter

coolro18

Joined Jul 10, 2020
17
I would set up some kind of sequencer start device, rather than place all on line at once, max 30sec between each should be ample.
Max.
And for these manufactured pumps that come with pressure switches or thermal protection, would an overload relay be necessary?
 

KMoffett

Joined Dec 19, 2007
2,918
And for these manufactured pumps that come with pressure switches or thermal protection, would an overload relay be necessary?
I don't recall anywhere that you explained what's the purpose on all these pumps. Often that can tell the why and how of problem. And can help us help you. ;)
 

Thread Starter

coolro18

Joined Jul 10, 2020
17
I don't recall anywhere that you explained what's the purpose on all these pumps. Often that can tell the why and how of problem. And can help us help you. ;)
They will be pumping fluid and switched on/off on the scale of minutes based on logic from a controller
 

KMoffett

Joined Dec 19, 2007
2,918
The multivibrator on the left produces the DC voltage that slowly goes up and down and the two transistors on the right are the voltage controlled audio oscillator that slowly causes the audio frequency to go up and down.
The oscillator makes narrow pulses causing the sound to be a like a buzzer.
They will be pumping fluid and switched on/off on the scale of minutes based on logic from a controller
Yes, that was pretty well implied. But what is the purpose of all of this? Is it a highly secret project that we would have sign an NDA to know?
 

GetDeviceInfo

Joined Jun 7, 2009
2,192
And for these manufactured pumps that come with pressure switches or thermal protection, would an overload relay be necessary?
Yes, and proper O/C, which can be found in the same device. The question begs, are you to code? Voltage droop can be a big problem in remote or under sized service. If you are to code, your plan will have specified if you have controlled start or not. If you are not to code, you need to do a backwards analysis to answer your question.
 

Thread Starter

coolro18

Joined Jul 10, 2020
17
Yes, and proper O/C, which can be found in the same device. The question begs, are you to code? Voltage droop can be a big problem in remote or under sized service. If you are to code, your plan will have specified if you have controlled start or not. If you are not to code, you need to do a backwards analysis to answer your question.
Yes, the lines will likely be running over 75 ft.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
They will be pumping fluid and switched on/off on the scale of minutes based on logic from a controller
If using a controller then it could be easy to fit a on/off valve on the load side that would be closed momentarily at switch on.
This should reduce inrush amount and time.

Many years ago I found this out the hard way after designing a parts washer for a company, using a 3.5hp 3ph pump.
All the wiring and O/L was to code, but the pump would trip the O/L after some minutes of use.
After contacting the pump manuf. they reviewed the design and pointed out that the pump discharge outlet was full bore and very short with no lift required.
This evidentally placed full load on the pump, a reduction of the output from 2" to 1 1/2" cured the issue! :cool:
Max.
 

Thread Starter

coolro18

Joined Jul 10, 2020
17
If using a controller then it could be easy to fit a on/off valve on the load side that would be closed momentarily at switch on.
This should reduce inrush amount and time.

Many years ago I found this out the hard way after designing a parts washer for a company, using a 3.5hp 3ph pump.
All the wiring and O/L was to code, but the pump would trip the O/L after some minutes of use.
After contacting the pump manuf. they reviewed the design and pointed out that the pump discharge outlet was full bore and very short with no lift required.
This evidentally placed full load on the pump, a reduction of the output from 2" to 1 1/2" cured the issue! :cool:
Max.
How would the on/off valve change the amount of inrush current? Is it just that the pump is starting with no load? And how would this change if the pump was operating with an additional pressure switch?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
All initial load on the motor is added to the inrush, which also prolongs the inrush, the solution in #27 gets the motor up to operating rpm ASAP.
A normal motor off load at start, should be up to operating rpm/current within a few hundred Milli-seconds.
Max.
 
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