Plasma blows relay..........!!!!WHY

[japes]

Hi Guys,

Me and my dad is building a Milling and Plasma Table.

The milling Part works fine.

I am running Mach3. I have connected up the relay as in photo attached but as soon as we turn on our 3 phase plasma cutter the relay blows( I test the relay by removing the signal wire and touching the ground, before the plasma blows it it clicks when touching ground, after it is blown I do the same but only the light goes on. if I power of the 5v and back up it clicks then only).

It blows the relay and Mach3 says limit switch triggered. (I'm guessing the faulty relay causes that).

Can you guys please help as this is our only issue left. I hope before the machine is complete.

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[Al_The_Man]

Is it the contact side that blows?
If so it is most likely that you are overloading the contact rating or a short circuit/high load develops to blow it.
What load are you switching?
Max.

[japes]

Is there a way to check what side is bowed? I will have to check the load tommorow. We are using a 3-phase plasma machine

[Al_The_Man]

You could energize the relay but disconnect the load side, and if you have a meter, see if there is continuity across the output.
Al.

[japes]

Thanks, I will test. Is my wiring correct as on photo? And is the limit switch triggered error from relay blowing

[japes]

You could energize the relay but disconnect the load side, and if you have a meter, see if there is continuity across the output.
Al.

Load is to much yes, is there a bigger relay we can use on mach3 to activate the plasma

[Al_The_Man]

Find out the actual load and size a relay accordingly, you may find it hard to find one rated for 5vdc coil.
If so you could use a 2n7000 Fet and a 12v -24v relay.
See PDF.
Al.

[japes]

We spoke to the people where we are purchasing the plasma. they said the relay will be fine. I think it is another issue. I am getting 24v out of all my output ports on mach3.....is this normal? so my signal pin to turn relay on and of has 24v on. I have my V+ (on Mach3 board) running to the V+ on my power supply. Then I have V- (on mach3 board) running GND (where my wall plug runs to on power supply) because there is no V- on the power supply only a COM connection.

When I connect up my relay with a 5 v power supply I test it by touching the int 1 pin to a GND wire then it opens. Must it not touch a V+ to open?

[Al_The_Man]

The output from the PC port should be 5vdc maximum, not sure where the 24v would be coming from?
Unless you have some external wiring mistake!
Al.

[japes]

Yes we have a extra 24v power supply for limit switches and estop

[japes]

This is my wiring diagram

[Al_The_Man]

That would be 24v supply common, not earth ground.
There should be a separate earth ground terminal on the input of the P.S. for the service GND.
Al.

[japes]

or can I ground it on the body where all the other grounds are? It is currently on the the earth on the power supply. Any idea why my relay switches on when i touch my signal wire to the ground. As I understand it must open when i touch the 5v......but it shorts out when i touch the 5v

[john-100]

is this how your machine is wired?



your diagram of the arduino relay does not have the "snubber " across the relay contacts (100 ohm resistor in series with 0.1uF)
the "snubber" helps to reduce the arc as the relay opens

assuming all of your power supplies have no connection between the output and the supply ground

the connection shown between the work piece and the 24V negative can explain why touching a wire from the relay boards input to ground switches on the relay

it will also explain why connecting the +5v to ground short circuits it

John

PS
wiring diagram V2
a possible alternative relay board connection
with opto-isolator input circuit powered by USB motion card +5V



PPS

part of photo of relay board posted

when the jumper is fitted
JD-VCC & VCC are connected together

relay boards circuit diagram adapted from diagram found on line