Triacs in // to drive a bigger load ?

[ze_dib]

Triacs in //

Hi guys,

Can I put triac in // to drice a bigger load ?

What sould be take into account before such a thing ?


Regards,


Ze_DiB

 

[IanP]

Re: Triacs in //

It is not THE BEST practice, but you can connect triacs in parallel ..
Use this table as a guide:

Total AC current / point                  triac to use

.1 to 7 Amps                                  one 10 Amp triac
>7 Amps to 16 Amps                  one 20 Amp triac
>16 Amps to 32 Amps               two 20 Amp triacs in parallel
>32 Amps to 48 Amps               three 20 Amp triacs in parallel
>48 Amps to 64 Amps               four 20 Amp triacs in parallel
>64 Amps to 80 Amps               five 20 Amp triacs in parallel
>80 Amps to 96 Amps               six 20 Amp triacs in parallel

Some manufacturers supply the inrush current rating (initial on current) for their products and you can use this value as the AC current for calculating the total load ..

Regards,
IanP

 

[the_edge]

Re: Triacs in //

I tried that once, and the triacs worked but the rest of the circuit suffered from an unforeseen consequences... It just started smoking... And then I realised why smoking is bad
My opinion? Not recomended, unless you are not totaly sure of what are you doing...

 

[ze_dib]

Re: Triacs in //

Hi, The edge,

What went wrong ? your control system was not (opto-) isolated from the AC ?

What I forecast is on 220V rms :
- 500 to 1250W : a 12A triac
- 1500 to 2000W : a 25A triac

On 110V rms :
- 500 to 1250W : a 25A triac
- 1500 to 2000W : 2x 25A triac in //

it should be OK

Shall the // mount have a particular design to limit the unbalanced turn on delay ?

regards

 

[Sal]

Triacs in //

Hi

I guess you are talking of using 2 or more triacs in parallel, with the same gating control and the same load. From the design viewpoint I think the following points should be taked care of

- Triacs and other devices are not ideal, which means that although ideally they will behave synchronized, in practice it may not occur because of the physical differents from one device to the other. Unless they are built in the same semiconducor buffer the assumption is that they have different characteristics, even though they are infinitesimal.

- These differences will be present at the triggering times, and at some point fewer than expected triacs may be working, These abrupt changes in current may distort the sine wave which the triacs are feeding to the load. In fact, it will be very interesting if you can see this phenomena with an oscilloscope once the circuit is settled.

- In order to make the cirduit to work you may need to compensate the triggering differences by using coils and capacitors. it seems a bit complex, It would be good to know what your load is. I mean if it is a motor, I rather use relays to get the work done, if you are controlling light cicuits, there should be no problem at all

good luck

Sal

 

[the_edge]

Re: Triacs in //

What went wrong ? your control system was not (opto-) isolated from the AC ?

Thanks for your concern, but that was long time ago... I just gave an example...

Sal gave you good explication...

 

[ze_dib]

Re: Triacs in //

HI,

First of all, thank for such an answer.

The load is resistive, the Ac frequency is low (50Hz), in regard to the triac switch time, and the driver I forecast is a Zero volt switching.

Taking all those information into accouint, I think there shall not have too many troubles in use :
Even if the switch dealy change from one triac to another, the switching will not happen in the High voltage of the sine.

thank for your advice,

regards

Ze_Dib