Heat sink calculation

[tedstruk]

I have to rework a 409046 leslie control for a gulbransen/CBS organ into a 409347 because of a lack of a 409347, so it will require a resistor, and maybe a jumper or two. The board has SC146M thyristors on it now, and one is blown. The circuit requires SC141D's which I have ordered. It also requires 3 - 330 ohm resistors of which there are only 2 on the 409096 board. With this extra resistance, the new thyristors will require a heat sink, and they are fitted with a pin for mounting.
I remember there was a formula for calculating the size of heatsink when they are required, but I can't remember it. I have some scrap heat sink material, but I don't know if it would be a good idea to just cut some pieces so there is lots of dissipation. can anyone help me here? The thyristors are 6a/400 v, the resistors Rtot is 760 ohms, and the caps are .1 uf, reed relay is -12v, diode 1N4148.

 

[kellys_eye]

Schematic? What you described makes no sense whatsoever.

 

[tedstruk]

Sorry!! made perfect sense to me!!!
I got 2 different builds to use as guides in the repair manual.
One is a 409347, the other is 870241
BUT...
The board I have is a 409046, so I got a Triple threat!!!!
The board had SC146M transistors on it.

The diagram for the 409347 calls for SC141D's thyristors which I ordered.

This diagram has 4 resistors 3 - 330ohm 1 - 100ohm

The 409046 board I have, has 3 resistors and they are 3 - 100ohm

The third diagram is for a 870241 controller, and it has 3-100ohm and 1-330ohm

They are all close to the same thing ...

I was wondering if maybe the thyristors blew because of not having a heat sink on them...

I found the formula in You tube
TempJunction - TempAmbient / PowerDissipated = JuncAmbient

So where
Pd(PowerDissipation) = Vdrop x I(Amps)

JunctionCase + CaseSink + SinkAmbient = device dissipation eg. 25degrees centigrade to see if you need a sink or not.

 

[(*steve*)]

Most of your formulae seem incorrect.

There is a resource on heatsinking that may help you.

 

[kellys_eye]

One is a 409347

meaningless to 99.9% of people - what IS that????

the other is 870241

meaningless to 99.9% of people - what IS that????

The board I have is a 409046

meaningless to 99.9% of people - what IS that????

This diagram has

what diagram? Show it.....

I was wondering if maybe the thyristors blew because of not having a heat sink on them...

If they needed heatsinks they'd have been fitted with them.

So where
Pd(PowerDissipation) = Vdrop x I(Amps)

JunctionCase + CaseSink + SinkAmbient = device dissipation eg. 25degrees centigrade to see if you need a sink or not.

but WHAT'S THE LOAD?

Without schematics this is all guess work.

 

[(*steve*)]

If they needed heatsinks they'd have been fitted with them.

What you described makes no sense whatsoever.

double

 

[brevor]

I worked on those organs years ago, The triacs dont require heatsinks.