[chbot] Opto isolated triacs - Digikey account anyone?

[Mark Atherton]

R,

Might be worth a bit more effort to understand the failure mechanism 
before going much further.

Do you have an accurate schematic of exactly how they are wired, 
including return paths. Also the trigger mechanism.

I seem to remember that you were using four-quadrant TRIACS and were 
using a (continuous) DC current to fire the device in two of it's quadrants (?)

This will be fine, provided that the sensitivity of the chosen 
quadrants are identical.

If not, you might get (say) 170 degrees of conduction in one 
quadrant, and 150 degrees in the other - which will give the 
appearance of a DC component.

There is also the uncertainty introduced by the nature if the 
inductive loads...

Can you put a 1 ohm resistor inline with one leg of one of the 
solenoids and look at the current waveform - that may answer your question.

Also, what is the TRIAC part number ?

Finally, if there is a significant load current inbalance, it may be 
possible to resolve it by just cranking up drive current.

Interesting issue.

-mark

At 11:22 a.m. 28/12/2014, you wrote:
>Greetings all
>
>I'm going to have to change the way I drive the triacs on my irrigation
>controller as I think the asymmetric switching I'm currently using is
>causing a DC component to get to the solenoids and blowing them up (8-9 of
>them so far this year at over $40 a pop!)
>
>The simplest mod I can come up with is to put zero switching opto triacs
>between the existing drivers and triacs - that only requires a 4 pin DIL
>and 1 or 2 resistors (times 32 for the number of channels on the
>controller)
>
>The Toshiba part TLP361J(F) available from Digikey looks like it will do
>the job but I'm pretty sure you need an account to get stuff from them.
>Can anyone assist in this area?
>
>Cheers
>
>--
>Robin Gilks
>Internet: robin at gilks.org    http://www.gilks.org
>Tel:      (+64) (3) 347 4370