What happens if i connect a relay 'inverted'

delta_soft

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Oct 2014
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Hi,

I have a relay and i connected by accident a relay with the wires inverted to the PLC (DELTA). By this i mean the the wire from the PLC (OUT) was connected to "+" on the relay instead of "-" and the "-" from the relay to "+" on the power source. o_Oo_Oo_O

I need to say that the PLC powered off until i disconnected the relay. After connecting it as I should do it from the begin it works.

Apparently everything works but I want ask you if there is any possibility that something "burned out" inside of the PLC?

Also guys, i have an other question regarding firmware update. Is there any way to update it for DELTA?

Thanks!
 
Nothing should happen....
1. There should be optocoupler, inside PLC. On most PLC there is.
2. If there is not optocoupler, most components are at least 30VDC proof.
3. Most PLC can be connected either sink or source, so it means + can be connected to OUT.
 
Some DC coil relays have a 'protection diode' wired inverted, especially if they have an LED indicator. The PLC output may have protected itself from a higher than normal current load. I hope your PLC output was not harmed.
 
Some DC coil relays have a 'protection diode' wired inverted, especially if they have an LED indicator. The PLC output may have protected itself from a higher than normal current load. I hope your PLC output was not harmed.
So if that output (Y1) is still working everything is ok?

Thanks!
 
I don't know anything about the Delta PLC or its output structure. Obviously it is a good sign that it appears to be working but beyond that I can't say.
 
I don't know anything about the Delta PLC or its output structure. Obviously it is a good sign that it appears to be working but beyond that I can't say.

I can attach you an image with the electric circuit of OUT :)
(the blue selection)
I am a beginner and that why I'm asking you to help if you wish.

Thank You Sir!

ddd.jpg
 
Apparently everything works but I want ask you if there is any possibility that something "burned out" inside of the PLC?
If your wiring diagram is correct, then your PLC has relay outputs. That means the relay output contact is isolated from the internal parts of the PLC. At worst, if you caused a short circuit, the relay output contact may be slightly burned or charred. If it still works, then most likely it is undamaged, or not damaged enough to stop working.

I don't understand why wiring a relay contact backwards would cause the PLC to stop. Did you have external 24 VDC power, or were you using the PLC internal 24 VDC power supply? If using internal 24 VDC power, then you may have overloaded the power supply, and that could cause the PLC to shut down due to lack of 24 volts.
 
If your wiring diagram is correct, then your PLC has relay outputs. That means the relay output contact is isolated from the internal parts of the PLC. At worst, if you caused a short circuit, the relay output contact may be slightly burned or charred. If it still works, then most likely it is undamaged, or not damaged enough to stop working.

I don't understand why wiring a relay contact backwards would cause the PLC to stop. Did you have external 24 VDC power, or were you using the PLC internal 24 VDC power supply? If using internal 24 VDC power, then you may have overloaded the power supply, and that could cause the PLC to shut down due to lack of 24 volts.

Yes, you are 100% right (i used PLC external power source for PLC and the Relay), this is what happened. So it is no problem with the PLC, simply it didn't had enough power to power on.
 
Doesn't matter that it's a Delta. Diode on coil is probably 1N4007 or similar. 1 Amp rating, peak for 1ms is 45 Amps. Cut those ratings in half for PLC output.
When the output turned on, the diode shorted the output as Bernie said in post #3. The short caused the 24 DC supply to go into overcurrent shutdown. With a power supply of 150 Watts or less, the transistor and diode should have been able to tolerate the surge.
I would expect fuses on a larger supply, and devices should be able to handle surge until fuse blows.
The worst case would be pinhole damage internal to the diode or transistor. This would happen with a spike when the fuse blows. Devices with pinhole damage usually fail within a day or two. (#1 cause is lightening hits on home electronics.)
If Y1 is working and you didn't blow a fuse, you're fine. If you did blow a fuse, continue testing for a couple of days.
 
Doesn't matter that it's a Delta. Diode on coil is probably 1N4007 or similar. 1 Amp rating, peak for 1ms is 45 Amps. Cut those ratings in half for PLC output.
When the output turned on, the diode shorted the output as Bernie said in post #3. The short caused the 24 DC supply to go into overcurrent shutdown. With a power supply of 150 Watts or less, the transistor and diode should have been able to tolerate the surge.
I would expect fuses on a larger supply, and devices should be able to handle surge until fuse blows.
The worst case would be pinhole damage internal to the diode or transistor. This would happen with a spike when the fuse blows. Devices with pinhole damage usually fail within a day or two. (#1 cause is lightening hits on home electronics.)
If Y1 is working and you didn't blow a fuse, you're fine. If you did blow a fuse, continue testing for a couple of days.

No smoke, no sparks :) and Y1 is working :)
 
the problem is with the relay coil, a contact is never a problem, but as bernie asks it is the diode in the coil, please check the relais or give us the typenumber.
when Y1 is still working the coil has no diode, or the power supply is not big nough to destroy the output.
 
the problem is with the relay coil, a contact is never a problem, but as bernie asks it is the diode in the coil, please check the relais or give us the typenumber.
when Y1 is still working the coil has no diode, or the power supply is not big nough to destroy the output.

PLC DETAILS

MODEL: DVP10SX11R
OUTPUT MODEUL: 1.5A 250Vac 50/60HZ RES LOAD

RELAY INFO (24V):
JW2SN
 
Last edited:

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