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Topic Title: Pump control circuit.
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Created On: 24 August 2013 12:46 PM
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 24 August 2013 12:46 PM
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AMN

Posts: 644
Joined: 29 June 2007

I have a job to do which is a bit out of my usual scope but struggling a bit at the moment with the design.

I have two water pumps each controlled by a float switch and in separate sumps. The switching of these pumps is causing me a bit of a headache. Both pumps cannot be allowed to start simultaneously so was contemplating a time delay relay from pump one and a couple of contactors to stall the starting of pump two if it should start at the same time. Pump two also needs to be able to operate independently of pump one. The problem I have is that pump two must not stop if it is already running when pump one starts.
Both pumps are supplied from the same final circuit. Can anyone suggest what I need to do to get this to work properly.

Many thanks in advance.

AMN
 24 August 2013 01:17 PM
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paulskyrme

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One of these:
https://www.automation.siemens.com/mcms/programmable-logic-controller/en/logic-module-logo/Pages/Default.aspx
would do it with just 2 contactors & overloads for the power side, plus what ever other circuit protection you need.
Remember do it to 60204 though.
 24 August 2013 06:05 PM
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slittle

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Got to be programmable logic as Paul has said otherwise you're going to be into a shed load of contacts to interlock the two.

The schneider ones aren't bad either, they had some nice simple to drive software. I think the 4 input/output one is around £80 last time I brought one.

Bear in mind the floats and control circuits should ideally be 24v. Shouldn't be a problem as most logic controllers are available with 24v psu's.



Stu
 24 August 2013 06:12 PM
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paulskyrme

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Stu,
IF, you have long control cable runs IMHO 110V is better, less volt drop to think about.
No reason for it to be 24V, 110 still meets all requirements, as long as the source is suitably designed, and TBH, the same design requirements, apply no matter what your control voltage.
 24 August 2013 06:37 PM
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slittle

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Paul,

True.

I probably should have said "try and avoid 230 or worst still 400 volts on the float switches.

I had a sewage pumping station a couple of weeks ago with 230volt floats than nearly gave the sewage man a nasty surprise... One float was damaged and as he lifted it up to tilt it (for test purposes) it went "pop" in style.

I've seen all sorts recently where someone has cobbled a starter and float together with no thought for what they are doing or leaving behind.

Mind you, just had a similar experience with a 20 year old grainstore panel MCB feeding a contactor had operated causing a conveyor motor to stop (or the motor stopped causing the MCB to operate ) but because there are no aux contacts the contactor stayed in and the panel was happily chucking grain into a stopped conveyor..... Caused a bit of a pile up !


Stu
 24 August 2013 07:13 PM
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paulskyrme

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Stu,
Under 60204 you can't use 400V on control these days except in very limited circumstances.
You an use 230V, but, NOT direct from the mains, it must be transformer derived in the control panel so no real advantage over 110V really.
 24 August 2013 07:14 PM
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slittle

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I know.....trouble is people still do it


Stu
 24 August 2013 07:14 PM
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paulskyrme

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Just read the rest of your post, sorry.
Very bad design!

(shocked smiley) <(I don't know how to do a shocked smiley!)
 24 August 2013 08:06 PM
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AMN

Posts: 644
Joined: 29 June 2007

Thanks for that very useful advice. I have not used that bit of kit before so just a bit worried about how to install it, is it straight forward enough or is there a bit of a learning curve involved?
As far as I am aware the float switches are 230V but will look into that.

Cheers

AMN
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