relay 1

[bryanpullin]

I have a preloaded counter that I use to shut off a relay . It works great until I run 110vac through the contacts of the relay.Then it makes the counter load up various numbers that it pulls out of the sky. I have tried to isolate the relay with an opto isolator and with diodes and transistors , but to no avail.Any ideas????

 

[Skogsgurra]

I think that you get EMI from the contact when it closes and when it breaks the load. Especially if the load is inductive.

Try to make the relay load less noisy by either putting an RC combination across the load. 100 nanofarads and 47 or 100 ohms is usually a good choice for small loads. You may need up to 1 microfarad and a smaller resistor for larger loads.

A varistor (MOV) across the load usually also helps. Select the MOV operating voltage higher than the load voltage and do not forget that it is the peak voltage that counts (RMS times sqrt(2)).

 

[bryanpullin]

I put a varistor across the load (110vac motor)and it improved a bit. As far as the RC network I'm not sure what you mean. I used a 1uF and a 22 ohm then a 100 ohm . They both fried.I had them across the load like you stated.

 

[Skogsgurra]

I guess that you connected them in parallel. They shall be connected in series.

Like this: ---resistor----capacitor---

 

[bryanpullin]

110 hot ---motor hot line
1
1
1uf
1
1
resistor
1
1
110 neutral---neutral motor line

 

[bryanpullin]

cap and resistor in series
the rc combo in parallel with the motor

 

[Skogsgurra]

That's correct! Did you fry capacitor and resistors? Or only the resistors? One microfarad at 60 Hz and 110 V shouldn't pass more than about 20 mA. And that shouldn't fry the 22 ohms resistor. Even if it is a 1/4 W one.

Hate to ask this question: Did you get yourself an electrolytic capacitor? They do not go well with AC.

 

[bryanpullin]

It was an electrolytic cap. However I switched to a .22 uF 250 v non electolytic cap and left out the resister and put the mov in parallel with it. It works like a charm. I was so stoked.

 

[Skogsgurra]

Me happy. What does "stoked" mean in this context?