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Topic Title: help with panel build
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Created On: 12 March 2013 12:40 AM
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 12 March 2013 12:40 AM
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peterspark

Posts: 3
Joined: 12 March 2013

hi hope some one can point me in the right direction i have just build a control panel with led indection lamps on the door of the panel ,completed the build and testing my motor ciruits ,ect while i start my motor ciruits the runing led green lamp lights up and i get a back feed to the other leds lamps they light up?for a split second and also when i stop the ciruit .tested for loose connections all ok . the circuit this 24v dc
thanks for any help
 12 March 2013 09:26 AM
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oneye

Posts: 158
Joined: 25 February 2008

It is assumed you are using 24vdc type led's which are effective lamp replacements.

You need to give a clue as to the design....

Some illuminate door panel lights direct from PLC outputs in which case you could detect transient conditions on other lamps.
If switching the LED direct from the contactor (contactor auxilary contact) then you appear to be looking for a fairly large transient current.

Do you get the same effect by manually pushing the contactor into it's energised position ?
 12 March 2013 11:22 AM
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Dave69

Posts: 428
Joined: 16 July 2011

What are the other lamps for? Is the panel PLC or relay logic and do you have back emf diodes fitted to coills of cantactors and relays?
As already said "You need to give a clue as to the design.... " or a circuit diagram
 12 March 2013 10:17 PM
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peterspark

Posts: 3
Joined: 12 March 2013

hi thanks for your help with the panel ,it has no plc controller outputs the LED are for running and stopped lamps for motor circuits (clip on aux) on the contactors and high level alarms from a vega level switches. i have wired o volts to each LEDS LAMPS (dasiy chained) i do not have any emf diodes fitted to the panel could this be the problem?
thanks for any help
 12 March 2013 10:35 PM
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Dave69

Posts: 428
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when de-energising a DC coil you get back emf that can cause baiscally a spike in the control voltage, it is always good practice to fit diodes across the coils of relays, contactors etc.

Are you using a seperate contact for run and stop lights or just a change over contact with the N/C doing stopped and N/O running?

Do all the lamps come on only when you energise a contactor or also when you de-energise it? Also as Oneye has already asked do you get the same thing if you just push the contactor in by hand?

Also can I ask why you decided on a 24V DC control circuit?
 13 March 2013 06:07 PM
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peterspark

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Joined: 12 March 2013

thanks for your help , i think it might be emf as you said. Do i need to fit the diodes to every contactors? and relays ect and what type of diode would i need i do i wire it across a1 and a2 of the contactors .ect .the running and stop lamp are wired via a n/c n/o aux contactor which clips on the contactor.all the light do come on when i energise and de energise the contactors.
i have not tested ,if i push in the contactor by hand as i have not been in the workshop i will be next week, as for the 24volt dc control they asked for that type ,as i would have done it 110volt control cicruit
many thanks for your help

Edited: 13 March 2013 at 06:22 PM by peterspark
 14 March 2013 01:35 PM
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Dave69

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I always bung bog standard 1N4001 diodes across the coils. The diodes should be wired across the coils so that they do not cause a short circuit, ie they oppose the current flow

Its basic Lenz's Law (i Think) Induced EMFs and their resultant currents are in such a direction as to oppose the motion that produced them
 14 March 2013 01:38 PM
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Dave69

Posts: 428
Joined: 16 July 2011

But by the way I am not sure that fitting diodes will cure your problem if you say the lights come on when you energise the contactor, without seeing a circuit diagram it is hard to tell. Do you have a lamp test circuit wired in the panel?
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