DIYbanter - View Single Post - problem with triacs with neon transformer loads

(Ken Smith) wrote:

In article ,
Winfield Hill wrote:
[.. neon sign xformer ..]

The problem with switching transformer primaries with triacs is
the high inrush current that can develop.

Yes, but not, I think for the reason you suggest.

The secondary capacitance of the transformer reflects back into
the primary. There is a primary leakage inductance that is
intentionally built into the transformer to limit the current
secondary to under (IIRC) 6mA. Between these two effects, you end
up with a funny ring when the switch closes. It could be that
something in this is getting his triac.

Also the OP didn't say anything about snubbing. The triac may be
refiring on the dv/dt when it switches off.

Here's the original post:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~
Hi,

I am designed a commercial neon lamp two channel flasher and
connected to my hotels name board. The circuit is having two
parts, one is flashing circuit and the other is the output stage,
wher the phase line is switched. In the out put stage i have used
BTA 41 triacs for switching the neon transformer, ie the phase to
the transformer is connected through the triac. The gate signal is
controlled through one MOC3083 opto triac. the output from the
flashing circuit is connected to the opto triac's(MOC3083) input
(LED).

I have installed the flasher in my hotel's neon name board. there
is two transformers connected to one flasher channel. it was
working for the last 4 months. last week one channel was not
flashing. only one channel is flashing the other channel is in ON
state, ie not blinking.

The next when i checked the flasher in my lab both of the channels
was flashing. again i connected the flasher to the same neon
board. After two weeks agin the same problem occured, ie one
channel was not flashing. Can anbody know the reason for that. Is
that problem with Opto triac(MOC3083) or BTA 41. Is there any
possibility of humidity or temparature cause the problem?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~

He has two triacs connected to one flasher channel. It worked for 4
months. Then one channel failed while the other continued working.
Both worked when he took it to the lab. Returned to service, same
problem after two weeks.

Do you think a ringing problem or dv/dt could give these symptoms?

Regards,

Mike Monett