inductive loads and diodes

[svtiss]

Hi,

we need to use a diode with inductive loads , right ?
but is it important where the diode is located , can i put the diode on my PCB and connect the load with long cable , lets 120 feet?

Thanks

 

[ericgibbs]

Hi,

we need to use a diode with inductive loads , right ?
but is it important where the diode is located , can i put the diode on my PCB and connect the load with long cable , lets 120 feet?

Thanks

hi,
No, thats not the way to do it.
It should be as close to the inductive load as possible.

 

[svtiss]

ok , can you explain why ?

thanks

 

[ericgibbs]

ok , can you explain why ?

thanks

hi,
You have to consider the EMR electromagnetic radiation cause by the back emf when the current is suddenly switched off in the inductor as well as the voltage 'spike' that would be present on the driving device mounted on the PCB.
That 120' of cable will act as an aerial and radiate electrical noise which could cause interference on your equipment and other users.

 

[tvtech]

hi,
You have to consider the EMR electromagnetic radiation cause by the back emf when the current is suddenly switched off in the inductor as well as the voltage 'spike' that would be present on the driving device mounted on the PCB.
That 120' of cable will act as an aerial and radiate electrical noise which could cause interference on your equipment and other users.

You beat me to it eric.

Rep for you.

 

[svtiss]

I thought the diodes protect the outputs ( transistors , PLC ) not the coils

 

[ericgibbs]

I thought the diodes protect the outputs ( transistors , PLC ) not the coils

Their main function is to protect the inductor drive from the high back emf at current switch off.
Is there a problem with connecting a diode at the inductor.

 

[svtiss]

well , if you have to connect to solenoid , you have find place for the diode ,for now I put the diode inside the solenoid connector with screws , and I thought would be it easy to have the diode on the PCB , and cables run from that pcb to solenoids

 

[tvtech]

Their main function is to protect the inductor drive from the high back emf at current switch off.
Is there a problem with connecting a diode at the inductor.

Interesting thought.

What is the OP up to ??

 

[svtiss]

op what?
what do you mean ?

 

[tvtech]

op what?
what do you mean ?

You need to explain yourself better. That's all. What are you building lad ???

 

[nsaspook]

well , if you have to connect to solenoid , you have find place for the diode ,for now I put the diode inside the solenoid connector with screws , and I thought would be it easy to have the diode on the PCB , and cables run from that pcb to solenoids

I've put the diodes up to a foot away (at the relay contact driving a coil) in existing circuits to cure emf problems but have always also added a .1 uf cap at the + supply lead to the coils to shunt the spike to ground. Installing the diode at the coil is the best location but sometime it's just not possible when things are potted.