BT150 Thyristor equivalent(BT151) has just exploded !!!

[Elecbegginner]

Hello everyone after fixing a speed variation card with the help of a triac, now i got one with the same problem , but it has a thyristor , the original thyristor's code is BT150, so i bought its equivalent" BT 151" .

But when i turned on the card , after several switching the motor has turned , and the collector was making flames , then after that the thyristor exploded .

Is this due to the motor or the thyristor ??

 

[john monks]

Do you have a schematic or a make and model?

 

[Elecbegginner]

Right now nothing , but ill sure do it later .
So what do you think its the cause of this problem??

 

[john monks]

My guess is the motor but I can't tell for sure. If this is a DC motor then there is probably a bridge rectifier surrounding the motor and some of those diodes may be shorted. If this is an AC motor then you can simply disconnect the motor and see if you get line voltage where the motor was connected. The BT 151 is rated for less current than the BT 150 so that could be a factor.
So is the motor a DC or AC motor?
If it as an AC motor I suggest disconnecting the motor and measuring some voltages.

 

[Elecbegginner]

Yes its an AC 220 V motor , one fact is that the relay is energized after power up of the card , witch means that the card is fine at least .

I've just took a look at the thyristor's datasheets , and i see significant AMPS ratings difference , the BT 150 is the one with lower current at 2.5 A on state current vs 7.5A for the BT 151 ???

 

[(*steve*)]

and the collector was making flames

Just out of curiosity... What "collector"?

 

[Elecbegginner]

Its the motor's rotor collector

 

[john monks]

My mistake is noted, the BT151 has a greater current rating so I wouldn't think that is a problem. Is there a way you could safely test the motor independently.

Thinking about this further I had a lot of power tools that had flames shooting off the collector and I just threw them out. I don't know if it was a shorted turn or bad brushes but either way I didn't feel like messing with it. So I believe your motor bad.

 

[Elecbegginner]

My mistake is noted, the BT151 has a greater current rating so I wouldn't think that is a problem. Is there a way you could safely test the motor independently.

Thinking about this further I had a lot of power tools that had flames shooting off the collector and I just threw them out. I don't know if it was a shorted turn or bad brushes but either way I didn't feel like messing with it. So I believe your motor bad.

Yes that what i think too , the 151 can handle much more current , so i guess its the motor , i will check it and replay later .

Thanks .

 

[duke37]

Disconnect the motor.
Measure the resistance from one brush to the other.
Turn the motor slowly and see if the resistance changes.
Look for signs of burning on the commutator.
Check the brushes for wear.

If a winding has failed, there will be a burnt section on the commutator.
The commutator should be a smooth chocolate brown.

 

[CDRIVE]

I've never heard an armature called a collector. Is that a Euro term?

Chris

 

[Elecbegginner]

I've never heard an armature called a collector. Is that a Euro term?

Chris

Yes its European term ,

 

[Elecbegginner]

Disconnect the motor.
Measure the resistance from one brush to the other.
Turn the motor slowly and see if the resistance changes.
Look for signs of burning on the commutator.
Check the brushes for wear.

If a winding has failed, there will be a burnt section on the commutator.
The commutator should be a smooth chocolate brown.

Thanks for the tips , i have actually another motor witch is working fine , i used it to test the other similar card , should i test with and see the results ?
am just afraid ill burn the thyristor again !!!!!

 

[duke37]

To protect the thysistor, put a car headlight bulb in series to limit the current.

I have never heard of a collector in this application, I assumed commutator was intended.

 

[Elecbegginner]

To protect the thysistor, put a car headlight bulb in series to limit the current.

I have never heard of a collector in this application, I assumed commutator was intended.

Yes indeed the commutator was making flames , maybe due to lack of brush carbon
And for the bulb , should i put it in series with the thyristor's gate ??

 

[Elecbegginner]

OK guys i used another fresh thyristor with same code BT151 , but without any motor connected , i get output reading starting from 190V to 220V witch is not normal , because normally the motor should be running slow in the first speed at about 75 volts then raising till 220 volts witch is the maximum speed .

And when i connect the motor it does not turn even with 190 volts at output .

Do you guys have any idea ??

 

[CDRIVE]

I think you don't quite grasp how a Thyristor works. It does not vary the level of the output voltage.

Chris

 

[Elecbegginner]

Yes a little explanation would be really helpful , thanks in advance BTW

 

[duke37]

I made abig boob when I suggested limiting current with a car headlight bulb. I thought you were running at 12V

To check the motor, put a filament bulb (mains) in series to limit the current.
To check the thyristor, use a light bulb as a load.

It looks as if you have a dead motor. What sort is it? Does it contain brushes running on a commutator?
Is there any connection across the input terminals? If not, then turn the motor by hand and see if there is an intermittent connection.

The thyristor works by chopping the sine wave so that the average power is reduced. The output voltage measured will depend on the way the meter works.

 

[CDRIVE]

Yes a little explanation would be really helpful , thanks in advance BTW

Google is your friend.

http://www.youtube.com/watch?feature=player_detailpage&v=v58KiktJLyE

Chris