[chbot] Opto isolated triacs - Digikey account anyone?

[Robin Gilks]

> Robin,
>
> Any chance of a PDF schematic ?

Attached

> If you are happy moving to optos, then that has the possibility of
> fixing all manner of issues in one-fell-swoop.

Very true - one of the reasons I feel its a good idea to bite the bullet!

> Still might be worth taking a look at coil current before and after
> just to be sure that a) the DC offset is actually causing the issue,
> and ii) the new solution resolves the issue.
>
> I am still having a hard time understanding how even a 20% DC content
> can physically burn out solenoid windings (if this is the correct
> failure mechanism) - sounds more like a high current impulse problem
> - again, measuring coil current with a scope + resistor may be useful.

No real idea of the mechanism but all but one have failed at switch on as
far as I can tell. I monitor the valve current and if its out of spec the
controller flags the problem - if it fails during operation when there may
be several active there is no way to know which one failed so the
controller does an emergency restart of everything and carries on with the
scheduled activity which will show up an individual valve failure as it
(tries to) starts up.

> Have you measured AC current of the energized solenoid using a DMM
> (try the same test on DC amps) ?

Just using a current transformer.

> Also, any chance of unwinding a busted solenoid, and measuring how
> much current is actually required to fuse the single-strand conductor ?

The solenoid is totally encapsulated - I've tried to get into one before
but its just a mass of plastic and wire :(

http://www.bidgeepumps.com.au/store/index.php?main_page=popup_image&pID=1467&zenid=3b43c19a3413aca0a505c7e28d5adbd8



>
> -mark
>
>>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.
>
>


-- 
Robin Gilks
Internet: robin at gilks.org    http://www.gilks.org
Tel:      (+64) (3) 347 4370
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Irrigate4.pdf
Type: application/download
Size: 15314 bytes
Desc: not available
URL: <http://lists.ourshack.com/pipermail/chchrobotics/attachments/20141228/9ae58a08/attachment-0001.bin>