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Smps fuse and transistor blown up

Thread starter #1
We are using a smps for our comm pcb , a relay and a current sensor, which uses 4.2v, 12v and 5v respectively. We are controling one phase of a three phase 5hp water motor. Also smps circuit and relay output are in parallel so output load doesnt effecting our smps. Problem is when we tested our complete device in lab on a room heater of 2kw its working fine however when tested in field on dol starter type 5hp motor our device fuse(3A) and transistor s9014 and s8550 blown up.
 

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ChrisP58

Well-Known Member
#3
We are using a smps for our comm pcb , a relay and a current sensor, which uses 4.2v, 12v and 5v respectively. We are controling one phase of a three phase 5hp water motor. Also smps circuit and relay output are in parallel so output load doesnt effecting our smps. Problem is when we tested our complete device in lab on a room heater of 2kw its working fine however when tested in field on dol starter type 5hp motor our device fuse(3A) and transistor s9014 and s8550 blown up.
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.
 
Thread starter #4
We are using a Dol starter which is connected to motor. Two phase out of three DOL starter get from main supply and one phase via our device(gsm based controller). We have also protected our circuit from back emf by using flyback diode.
 

Les Jones

Well-Known Member
#5
Can yo post a SCHEMATIC as chris requested ? What prevents the motor from burning out if two phases of it are connected but the starter but the third phase is not connected ? On the schematic you need to show the input supply to the smps. I am thinking that its's input voltage may be the problem with the strange way you are switching two of the three phases.

Les.
 
Thread starter #6
Our device is connected between main supply and DOL starter. One phase of dol starter connected via our device. I have drawn rough schematic which help u understand.
Can yo post a SCHEMATIC as chris requested ? What prevents the motor from burning out if two phases of it are connected but the starter but the third phase is not connected ? On the schematic you need to show the input supply to the smps. I am thinking that its's input voltage may be the problem with the strange way you are switching two of the three phases.

Les.
 

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Thread starter #7
As u can see in schematic output of our device is in parallel with input circuit. So no load on our internal circuit except a comm pcb( gsm module) which hardly draw 300mA . I m unable to understand how its transistor s9014 and s8550 connected in collector base config blowing with 3A fuse at input, fuse glass blown and stucked in holder. This thing only happening when we connect our device to motor and not with any other appliances.
 

rjenkinsgb

Active Member
#9
My first thought is back EMF from the motor if it does not have proper suppression.
Also be aware that the surge current starting a motor direct-on-line can be up to six times it's rated load current.

Glass fuses are not appropriate for high voltage circuits, you _must_ use "HRC" types, eg. sand-filled ceramic ones that are rated for at least the circuit voltage.
When a glass fuse blows while connected to high voltage, the metal fusewire arcs as it separates and simply vaporises, remaining conductive as plasma for some time and allowing extremely high surge currents through the circuit. It's not unusual for them to explode.

HRC fuses with proper voltage ratings quench the arc as it forms so prevent that surge. Glass ones are only suitable for low voltage circuits.

If you are trying to protect semiconductors the fuse should also have an FF or UR speed rating; normal fuses usually will not fail until after any semiconductor device in circuit has blown.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#10
Glass fuses are not appropriate for high voltage circuits, you _must_ use "HRC" types, eg. sand-filled ceramic ones that are rated for at least the circuit voltage.
When a glass fuse blows while connected to high voltage, the metal fusewire arcs as it separates and simply vaporises, remaining conductive as plasma for some time and allowing extremely high surge currents through the circuit. It's not unusual for them to explode.

HRC fuses with proper voltage ratings quench the arc as it forms so prevent that surge. Glass ones are only suitable for low voltage circuits.
Sorry, but I would completely disagree with that - in my experience the vast majority of mains fuses in domestic electronics are just glass ones, and in the few cases where they have fitted sand-filled ceramic ones they commonly fail for no reason, and also commonly explode in the case of a fault, where glass ones rarely do.

I do agree though that fuses don't protect semiconductors, but that's not the function of a fuse.

I would suggest that his problem might be down to a complete lack of mains filtering to the PSU, and that the noise and spikes introduced by the motor is destroying the PSU. This would be consistant with it having worked fine with resistive loads.
 
#11
in my experience the vast majority of mains fuses in domestic electronics are just glass ones
My experience is mainly with industrial electronics.
I've seen quite a few cracked or exploded glass fuses, with the inside metallised by the vaporized metal.
I have never had a problem with ceramic types, other than those in 13A plugs running electric heaters...
(Any fuse that explodes is being used beyond its ratings and is most likely not an HRC type, ceramic or not).

Suitability also depends on the current capacity of the circuit, which again is rather different on industrial / three phase supplies to in domestic appliances.
Any UK domestic item will have at least one HRC fuse providing short circuit protection, eg. in the plug.
 

unclejed613

Well-Known Member
Most Helpful Member
#13
it looks like you also launched an electrolytic cap in the process...
smps-2.jpg
 
Thread starter #14
Hello guys thanx for your input. Here i m providing a circuit diagram of our device for your analysis. I forget mention that our device blowing mostly when it was switched on by sending msg to gsm module by server and not when manually on by switch provided in our device.
 

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Thread starter #17
Plz wat
Can yo post a SCHEMATIC as chris requested ? What prevents the motor from burning out if two phases of it are connected but the starter but the third phase is not connected ? On the schematic you need to show the input supply to the smps. I am thinking that its's input voltage may be the problem with the strange way you are switching two of the three phases.

Les.
Plz watch attachment i have provided. Your help will save my job.
 

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#18
Your proposal DOES NOT work. It violates the principles of motor control.

To start or stop a 3 phase motor, at least 2 lines must be switched. For safety, all three must be switched.

If all you want to do is start a motor, then all you have to do is have your GSM controller drive a the motor starter.
 
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Thread starter #19
It is impossible to control a 3-phase motor by adjusting only one phase.

To control a 3 phase motor one requires to adjust all 3 phases, varying the applied voltage AND frequency while maintaining the proper angular relationships between all the phases under all the speed and load conditions.

That is what a VFD drive does.
We have tested our device in agriculture field. They worked when we have tested but blown up next day when started from server. We are controling DOL starter supply not motor directely.
 

Les Jones

Well-Known Member
#20
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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