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Smps fuse and transistor blown up

Can you show ALL of the wiring including three phase input, DOL starter and motor. Is the comm PCB that connects to header 4 totaly floating or does it connect to anything else ? Also you have made an error in the pin numbering of the ACS756 in your schematic. (I think this is just a drawing error.)
When you say "common ground" do you really mean ground or do you mean neutral ?
Les.
Comm pcb just connected with header 4 and a Tac switch to turn on device manually. Acs756 pinout is a drawing mistake.
 

Attachments

Please post a schematic of your system. Particularly how it connects to the load. What are the details of the relay?

Also be aware that there is a very big difference between the two different loads you mention. The heater is entirely resistive, so it is very easy to turn on and off. A 3 phase motor is inductive, so it will generate voltage waveforms different that what's applied.
RELAY 33A 277VAC
ALF121
 

Attachments

Comm pcb just connected with header 4 and a Tac switch to turn on device manually. Acs756 pinout is a drawing mistake.
We have tested our device on four different motor and all of them work fine we uses tac switch to operate them. But next day when they were turned ON through our server two of them burned and two worked fine. This confuses us.
 

Les Jones

Well-Known Member
I can't see any problem with the way that it is wired. I was concerned with the the way that you described the wiring in your first post that described having two phases connected to the motor until your relay connected the third phase. I would suggest adding some filtering to the input of your switch mode power supply. Your MOV on the input is trying to shunt spikes from a very low impedance source. Putting some inductance and some resistance before the MOV would mean it would suppress spikes better. I would also move the fuse to before the MOV so that hopefully it would blow before the power supply was destroyed. As it's for use on farms I imagine it will be at the end of long cable runs so there will be a higher probability of spikes when switching large loads. The fact that the problem seems worse when they are switched remotley makes me think that switching noise is getting into the receiver so it does not give a clean output but switches on and off a few times in rapid succession.

Les.
 
Last edited:
I can't see any problem with the way that it is wired. I was concerned with the the way that you described the wiring in your first post that described having two phases connected to the motor until your relay connected the third phase. I would suggest adding some filtering to the input of your switch mode power supply. Your MOV on the input is trying to shunt spikes from a very low impedance source. Putting some inductance and some resistance before the MOV would mean it would suppress spikes better. I would also move the fuse to before the MOV so that hopefully it would blow before the power supply was destroyed. As it's for use on farms I imagine it will be at the end of long cable runs so there will be a higher probability of spikes when switching large loads. The fact that the problem seems worse when they are switched remotley makes me think that switching noise is getting into the receiver so it does not give a clean output but switches on and off a few times in rapid succession.

Les.
Our device only failing when switched ON via server. I have corrected the way our device is connected in field. See attachment.Also Placement of MOV before fuse is correct or not.
 

Attachments

rjenkinsgb

Active Member
Do you have snubbers across both the motor and the starter contactor coil?

A contactor coil can produce a massive voltage spike when switched off, which may have arced between your relay contacts and other components.

Most control gear makers have snubbers that fit to their contactors, or you can buy generic wire leaded ones - eg. 100 ohms and 0.1uF in series are a common type.

eg. a Telemechanique / Schneider one that clips on one series of contactors:
https://uk.rs-online.com/web/p/products/3950043/

A range of generic types for such as contactor or solenoid coils
https://uk.rs-online.com/web/c/passive-components/capacitors/rc-network-capacitors/

An example for three phase motor suppression:
https://uk.rs-online.com/web/p/surge-suppressor-units/0240400/
 
Do you have snubbers across both the motor and the starter contactor coil?

A contactor coil can produce a massive voltage spike when switched off, which may have arced between your relay contacts and other components.

Most control gear makers have snubbers that fit to their contactors, or you can buy generic wire leaded ones - eg. 100 ohms and 0.1uF in series are a common type.

eg. a Telemechanique / Schneider one that clips on one series of contactors:
https://uk.rs-online.com/web/p/products/3950043/

A range of generic types for such as contactor or solenoid coils
https://uk.rs-online.com/web/c/passive-components/capacitors/rc-network-capacitors/

An example for three phase motor suppression:
https://uk.rs-online.com/web/p/surge-suppressor-units/0240400/
Yes snubbers are there. Our device only blowing on power resume from mains. They are not blowing on first time run.
 
I refer you back to post #10 - you have no mains filtering on the input to the PSU - you're using it in a very harsh environment, good filtering is essential.
Thanks for ur input i have already designed a pie section LC filter as advsied by Les Jones #24. I will share the field test report as soon we deploy our product to farmer.
 
I can't see any problem with the way that it is wired. I was concerned with the the way that you described the wiring in your first post that described having two phases connected to the motor until your relay connected the third phase. I would suggest adding some filtering to the input of your switch mode power supply. Your MOV on the input is trying to shunt spikes from a very low impedance source. Putting some inductance and some resistance before the MOV would mean it would suppress spikes better. I would also move the fuse to before the MOV so that hopefully it would blow before the power supply was destroyed. As it's for use on farms I imagine it will be at the end of long cable runs so there will be a higher probability of spikes when switching large loads. The fact that the problem seems worse when they are switched remotley makes me think that switching noise is getting into the receiver so it does not give a clean output but switches on and off a few times in rapid succession.

Les.
Thanks for ur input. I have designed a pie section LC filter. With L=1H and C1=C2=6.8mF
 

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