strange feedback

[bryan]

I have a counter that shuts off a relay . Whenever I send 110vac
through the relay the counter malfunctions. There are 2 transistors
and 2 schmitt triggers between the counter and the relay. I have a
diode across the coil of the relay so I don't understand why it does
this. If there is no 110vac going through the relay the counter works
perfectly.Why does the 110 affect the counter and how do I fix it?

 

[Robert Baer]

I have a counter that shuts off a relay . Whenever I send 110vac
through the relay the counter malfunctions. There are 2 transistors
and 2 schmitt triggers between the counter and the relay. I have a
diode across the coil of the relay so I don't understand why it does
this. If there is no 110vac going through the relay the counter works
perfectly.Why does the 110 affect the counter and how do I fix it?

Insufficent and contradictory info.

 

[bryan]

[email protected] (bryan) wrote in message
Why would 110v going through the contacts of a relay affect the
circuit that drives the coil of the relay?

 

[Robert Baer]

[email protected] (bryan) wrote in message
Why would 110v going through the contacts of a relay affect the
circuit that drives the coil of the relay?

As long as the two circuits (the coil circuitry and the contact
circuitry) are completely different, then there would be no effect as
you describe.
Now if the coil is driven by the same 110V supply that is switched,
there still would be no interaction as you intimate, but one could see
some correlation.
For example, the contacts are controlling a capacitive or inductive
load, so the "make" or the "break" spike would be seen on the supply to
the coil - because it is the *same* supply to the non-resistive load.
If the supply has some (relatively) appreciable internal impedance,
the switching of the load by the contacts then would reduce the
measurable supply voltage (the loss would be "inside" the supply), which
is also supplying the coil.
BUT in either case, the current thru the contacts are actually *not*
affecting the coil circuitry.
What you see are the results of the loading of the (coil) supply.

 

[bryan]

Thanks , I decided to change my circuit. Rather than use the 74161
counter I am using a 7474 to make a counter . The problem went away.