10Hp Motor Traic controller

[sribangaram]

Dear Friends I am doing 3 Phase 10 Hp motor starter through BTA 41 Traic's But my problem is getting very hot in only 15 Amp's lode and some voltage also coming after switching off Actually BTA 41 supported up to 40 Amp but why it's getting very hot only 15 Amp lode ware I am mistake please give me the suggestion Opto cupler is Moc 3021

 

[srizbf]

post your motor starter circuit for identifying the problem.

 

[FvM]

You can expect nearly 15 W losses per triac, I guess you just forgot to provide sufficient heatsinks?

A three phase solid state relays should use opto triacs with 600V rather than 400V rating because you can't be sure about symmetrical voltage sharing in all situations.

RC snubbers are generating a certain leakage current which can't be avoided.

Finally, PCB spacing is far-off from any requirements for a mains connected circuit. Just scary!

 

[KlausST]

Hi,

what´s the voltage rating of the 680R?

Klaus

 

[betwixt]

I use something similar to control slightly smaller motors but use a timing circuit so the triac is used at motor start and finish but bypassed by a relay during the remaining operation time. The triac takes the load off the relay contacts and does zero crossing switching to reduce EMC. The relay, when closed carries virtually all the running current so the triacs run cold.

Brian.

 

[sribangaram]

You can expect nearly 15 W losses per triac, I guess you just forgot to provide sufficient heatsinks?

A three phase solid state relays should use opto triacs with 600V rather than 400V rating because you can't be sure about symmetrical voltage sharing in all situations.

RC snubbers are generating a certain leakage current which can't be avoided.

Finally, PCB spacing is far-off from any requirements for a mains connected circuit. Just scary!

Friend I didn't understand how 15 W losses per triac Please explain me i have to fix the heat sink

- - - Updated - - -

Hi,

what´s the voltage rating of the 680R?

Klaus

Friend what is voltage rating i think you are asking wattage rating 1/4watt

- - - Updated - - -

post your motor starter circuit for identifying the problem.

Friend I am already posted

 

[FvM]

Triac voltage drop of 1V * 15 A = 15W, there's also a diagram in the datasheet.

A standard 0805 resistor has typically a voltage rating of 200 V which would be exceeded during voltage transients absorbed by the snubber. In case of asymmetrical switching, you'll have phase-to-phase voltage of 400 Vrms / 560 Vpk across the snubber.

I guess, srizbf is asking for a a schematic diagram.

 

[sribangaram]

Friend thanks to your reply friend I am poor in English sorry to ask please explain me again
and one more thing I don't have a schematic that is my own design

 

[FvM]

Forget about the schematic now. The circuit is quite clear from the PCB drawing.

I don't know what's your problem with understanding. To repeat the problems that have been identified so far:

- A triac needs a heatsink when carrying 15A

- Snubber 680R resistors and also 180R resistors are loaded with high pulse voltages. You should chose resistor types that are rated for respective voltage levels

- Safe isolation of mains voltage demands larger copper-to-copper distance than presently realized in your design

 

[sribangaram]

Friend I have to Attached heat sink but I don't know that is suitable to enough
680 R and 180 R resister's are size of 1206
Actually I am connect the lode but not a MOTOR I have to connect industrial heaters each one 15 Amp rating
INPUT : 3 Phase (R Y B).......................OUT PUT : 3 HEATERS 250 v 15 Amp rating

But I am getting too much heating from TRAIC'S and one traic also damaged after 3 or 4 mint's
My dought is this traic will be supported up to 40 amp but why it's damage the only 15 Amp and why it's getting too much heat with out fully lode I am sending the Photos of heat shrink please see this and one more thing sorry to forget the mention 1/4 watt 10 k resister's connected to traic from A1 to G Please see the picture

 

[KlausST]

Hi,

680 R and 180 R resister's are size of 1206

Each electronic device has a datasheet. Find the datasheet for your resistors and look for "voltage rating"

Read the datasheet for each single device in your design. Even the heatsink.

You should be able to calculate the heatsink on your own.

My dought is this traic will be supported up to 40 amp but why it's damage the only 15 Amp and why it's getting too much heat with out fully lode

You can find all the necessary information in the datasheet.
For example:
* Datasheet says 40A current rating is only true as long as Tc is below 95°. Additionally there is Figure2 with SOA diagram. To ensure this you need a heat sink.
* Disspated power is given in Figure1.
With the information of 50°C/W thermal resistance (junction to ambient) we can calculate that you must not dissipate more than 2W of power without heat sink. This is at about 2A. No wonder the triac blows.
There are a lot of application notes on how to calculate heatsink. Look at the internet sites of heatsink manufacturers.
A picture of a heatsink gives no technical data so we can´t calculate it for you. Also we don´t know what max ambient temperature we have to calculate with and how the air flow will be.

We all have to read datasheets. And we all have to learn how to calculate the different values.

Klaus

 

[FvM]

Do you have a K/W specification of the heatsink? I guess it can't be better than 10 K/W, in other words simply too small for 12 or 15 W power dissipation.

1206 resistor has slightly higher voltage rating than 0805, still too small pulse voltage margin.

 

[KlausST]

Hi,

in other words simply too small for 12 or 15 W power dissipation.

Isn´t it about 15W per triac? --> about 40W in total?

Klaus

 

[FvM]

Yes, there are three heatsinks.