Smps fuse and transistor blown up

Les Jones said:

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.

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ChrisP58 said:

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.

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ejazbeyond said:

Comm pcb just connected with header 4 and a Tac switch to turn on device manually. Acs756 pinout is a drawing mistake.

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Les Jones said:

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.

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rjenkinsgb said:

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:
**broken link removed**

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/

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ejazbeyond said:

Yes snubbers are there. Our device only blowing on power resume from mains. They are not blowing on first time run.

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Nigel Goodwin said:

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.

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Les Jones said:

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.

Click to expand...