[chbot] Opto isolated triacs - Digikey account anyone?

[Robin Gilks]

> 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.

Here is the schematic

https://github.com/g8ecj/irrigate/blob/master/hardware/Irrigate4.sch

> 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 ?

The triacs are 2N6073A 4A 400V devices, the triggering is by pulling the
gate down to (an effective) -12v via the 470ohm. Quadrants 1-3 trigger on
5mA, Q4 is 10mA (at normal temperatures).The loads (solenoids) pull about
190mA at 24VAC

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

There is another issue - with 24VAC, peaking at 34V plus the 12V driver
voltage, the common round the garden and paddocks is up at 46V on occasion
which is enough to tingle when kneeling in wet grass and working on wiring
with with soggy fingers!!

Using the opto isolation would allow me to ground the centre tap of the
24VAC transformer which would make the whole system safer.


> 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