Start stop circuit with contactor and push buttons - Page 1
Forum section: electronics / beginners

author: mike buba
author_rank: Contributor
timestamp: July 12, 2022, 08:51:56 am
content: I am trying to implement standard start stop (or e-stop) circuit with contactor and push buttons.As I understand push buttons should be push-pull (latched) to keep the coil energized to close the contacts; but pretty much everywhere I looked (online and on site) they use momentary (spring return) to close or open contactors.I am thinking of using this contactorhttps://www.se.com/uk/en/product/A9C22712/ict-16a-2no-230-240v-50hz-contactor/. Even technical support advises to sue momentary switch for start, but then gives only pulse signal to coil, and doe snot keep it energized.It is possible I am missing something there.Are push buttons latched or momentary in this case.There are also impulse relays, but this is different. I am interested in contactors.

author: themadhippy
author_rank: Super Contributor
timestamp: July 12, 2022, 09:22:44 am
content: the thing marked as CR aint a capacitor,its one of the contactors switches,so a brief press of the push button closes the contacts CR, that keeps the contactor powered

author: mike buba
author_rank: Contributor
timestamp: July 12, 2022, 09:42:35 am
content: Is this some separate component I should get apart from contactor and push button? Or is it already "build in" in the contactor; and noted in the datasheets?

author: Zero999
author_rank: Super Contributor
timestamp: July 12, 2022, 10:00:47 am
content: Quote from: mike buba on July 12, 2022, 09:42:35 amPresumably this is safety critical, so a safety relay is required?What's the emergency stop circuit connected to? This is important because it determines the performance level of the safety circuit.

author: mike buba
author_rank: Contributor
timestamp: July 12, 2022, 10:18:13 am
content: It is not safety critical; a least I wasn't considering it. It is to power up the converter cubicle and motor drive.Another set of push buttons for digital I/O shall be used for run and stop functionalities.Now I am trying to understand how to control the main contactor and if CR option is in A9C22712, i.e., do I need to use latched or momentary push button (https://www.se.com/uk/en/product/A9C22712/ict-16a-2no-230-240v-50hz-contactor/).

author: themadhippy
author_rank: Super Contributor
timestamp: July 12, 2022, 10:57:13 am
content: QuoteYesIt depends on the contactor,some will have an "auxiliary " set of contacts for the self hold circuit,others require you to add a separate module .The model you linked to is a double pole device so you could use one pole for the self hold circuit and the other pole to switch your load,but here in the uk at least ,that wont meet the requirements for an isolator

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 12, 2022, 11:35:40 am
content: You can use one of the pole for latching but it's best to get the auxilarry contact listed on the same page.

author: eblc1388
author_rank: Frequent Contributor
timestamp: July 12, 2022, 01:15:23 pm
content: Quote from: BeBuLamar on July 12, 2022, 11:35:40 amIt does listed on the same page under in the Accessories section. However, they want 30 GBP for one set of aux NO+NC contact, which bring the total of the contactor to some 90 GBP.@mike buba:Shop around before you buy that contactor + a pair of aux contact in the link. I found on Ebay a new 4NO main contacts one(on which you can use 1 main contact as the auxiliary contact at less than 20 GBP

author: eblc1388
author_rank: Frequent Contributor
timestamp: July 12, 2022, 01:41:53 pm
content: Quote from: mike buba on July 12, 2022, 08:51:56 amExcept for the "Emergency STOP" push button, which latches in the operated position once operated by user, most push buttons for start/stop action will be momentary.The push buttons you are going to use for start/stop function, besides being of different color in the button fasia, usually will contain both "Normal Close" and "Normal Open" type contacts on the same push button. You would need to wire them up yourself using the correct set of contact. I enclose a diagram below to show how one should wire up the contactor. Ask here if you have any slight doubts regarding the actual wiring.

author: mike buba
author_rank: Contributor
timestamp: July 12, 2022, 05:10:57 pm
content: So, for contactors to close, the coil has to be energised (all the time).What confuses me about using a momentary button to Start is that the coil is energised only when the button is pressed; and contacts are closed. When it is released, there is no current thought the could and contacts are open.For example, if I takethis contactorandAuxiliary contact, 1NO+1NC, the auxiliary contactor only gives status to control or HMI. I am not sure that this combination with the typical NO and NC momentary push button will work. Even that Schneider auxiliary device for 30 GBP is for remote indication auxiliary, 1 NO + 1 NC.This is the schmatics I have for now. The schematics must be wrong because I do not how this can work with momentary push buttons for start and stop.[ Specified attachment is not available ]themadhippy mentioned that some contactors will have self hold circuit,others require you to add a separate module. How to know which one I am looking at?

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 12, 2022, 07:19:50 pm
content: Sorry I don't know how to post a schematic but you would wire one of those NO aux contact to bypass the start button. When the contactor pulled in the aux contact will close any bypass the start button so you don't need to hold the start button down.

author: themadhippy
author_rank: Super Contributor
timestamp: July 12, 2022, 07:39:36 pm
content: Quotenope,i saidQuoteThe auxiliary contacts are wire in parallel with the start button ,when you push the start button the coil is energised causing the auxiliary contacts to make ,that maintains the supply to the coil even if you release the start button.the second circuit you posted isnt a self hold,push the button contactor operates,let the button go contactor drops outInstead of getting hung up on extra modules and contacts use a bog standard 4 pole contactor,for examplehttps://www.tlc-direct.co.uk/Products/WYMESB24.html2 poles for your load switching,1 pole as the self hold contact and a spare wayedit to addheres the circuit you posted modified to self hold with the contactor i linked to

author: mike buba
author_rank: Contributor
timestamp: July 12, 2022, 08:17:49 pm
content: Quote from: themadhippy on July 12, 2022, 07:39:36 pmApologies for misquotingQuote from: themadhippy on July 12, 2022, 07:39:36 pmThank you very much... Now it all makes senseEven if I decide to use auxiliary contact 1NO+1NC, I would know how to wire it all.