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Triac PCB Trace Width & Current

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ehabzaky

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Dear All,

I'm creating a PCB for a digital switch circuit using Triac as a solid state relay. The circuit is attached below:

Trace Question.png

The circuit is using BTA24-600B Triac and MOC3021 Optocoupler. The circuit will drive high loads as the Triac can drive up to 24 Amp current. I'm on the PCB design phase I need some expert person to help me on the following please:

1- I have used online Trace calculators to know the suitable trace width that can carry 24 amperes. I need to know does this current will pass only through the Triac Terminals 1 and 2 to the load? i.e. the red wires in the above drawing only? Should any other black wire carry high current other than the red ones? I have read the datasheet for the Triac but couldn't understand this info.

2- Is there any distance requirement between high current traces on PCB? I have seen trace width calculators but do not know is there any minimum trace spacing requirement?

Any support will be highly appreciated.

Regards,
Ehab Zaky
 

SunnySkyguy

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2 0z copper traces will not be suitable without bus bar , braid or reinforcement. for 10'C rise at 24A

Distance should be no less than triac pins with soldermask to protect from creepage surge failure. Safety requirements dictate clearance gaps depending on line voltage and if filtering is used for breakdown voltage rating.

EMI depends on area of loop.
 

ehabzaky

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Thank you SunnySkyguy for your support.

I am planning to use 4 oz with T80 track width for the traces that will carry 24 amp with acceptable temperature rise up to 50 degree that is because the line will not carry the 24 amp all time and in most of the time it will be lower. Also there will be cooling mechanism for the circuit.

The load voltage will be 240V AC.

This is my planned PCB for this circuit. I have used the T80 trace width for the Triac terminals 1 and 2 to the load only. Am I correct? Or any other traces should be T80 too?

Also the trace clearance as shown is OK? I have split each terminal in separate layer too.

Regards,
Ehab Zaky
 

ehabzaky

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Sorry forget to attach the PCB. It is included here

pcb.png
 

FvM

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Worst design detail is lack of spacing between control and power circuit. As simple rule, you shouldn't fall short of the about 6 mm spacing prescribed by the optocoupler package. Means the 1k resistor must not be placed in the control circuit region.

I don't know how you arrived at the 24 A trace width, but it seems too small. I also wonder if the connector is rated for 24 A?

Violations marked in red.

pcb.png
 

ehabzaky

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Thanks a lot FvM for your comments,

This is my first PCB try. I will have some mistakes for sure. I have updated the PCB taking your comments in account.

pcb.png

I have used multiple online trace calculators copper thickness 4 oz, trace width T80 temperature rise 50 degree as I descried earlier as the load will not be always at 24 ampere and there is some cooling mechanism too.

Still in doubt about any other traces should be same T80 thickness?

Regards,
Ehab Zaky
 

FvM

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24 A should be O.K. with 4 oz (140 µm) copper plating. But more than 2 oz is rather unusual for general pupose PCB.
 

SunnySkyguy

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copper is the expensive part of any pcb and since 99% is etched away, you are wasting mat'l.

It is cheaper to add busbars or AWG 16 jumper. and eliminate all narrow tracks to use wider track than length to connector.

Max temp rise should be chosen as 10'C.
 

FvM

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Looking at the layout in post #6, it seems easy enough to use wide copper pours for the power connections and implement the board with standard 1 oz technology.
 

ehabzaky

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Looking at the layout in post #6, it seems easy enough to use wide copper pours for the power connections and implement the board with standard 1 oz technology.

Thanks for the info. I have searched about copper pours and could understand that it is a technique used to fill the empty areas with copper on PCB. Could you guide me how to calculate or decide the shape and area of the copper pours as per the required current as the shape of the copper suppose to be irregular?
 

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