Now that I've got this working: The SSRs I'm using are Teledyne 641-1.
They are working, but in testing I noticed that they bleed through
about 8VAC from the 120VAC when they are 'off'. Is this normal?
---
I don't know if 8V is normal, but some voltgage there is inevitable
because of the relay's leakage current.
When you measure the output voltage of the relay, you'll have a
circuit that looks like this:
120V>-----+----E1
|
[RELAY]
|
+----E2
|
[METER]
|
120VAC>---+----0V
And simplifying it:
120V>-----+----E1
|
[R1]
|
+----E2
|
[R2]
|
120VAC>---+----0V
Assuming that the impedance of your voltmeter is 10 megohms, we can
solve for the OFF resistance of the relay like this:
R2 (E1-E2) 1E7R (120V - 8V)
R1 = ----------- = ----------------- = 1.4E8R = 140 megohms
E2 8V
Now, assuming that your pumps draw 100mA from the mains means that
they have an impedance of:
E 120V
R = --- = ------ = 1200 ohms.
I 0.1A
Then with the motor connected to the relay instead of the meter, we
have:
120V>-----+----E1
|
[140M] R1
|
+----E2
|
[1200R] R2
|
120VAC>---+----0V
Solving for the voltage across the motor yields:
E1 R2 120V * 1200R
E2 = --------- = ----------------- = 1.029E-3V ~ 1mV
R1 + R2 1.4E8R + 1200R
and the current through it will be:
E 0.001V
I = --- = -------- ~ 8.3E-7A = 0.83 microamp,
R 1200R
so not to worry!-)
Is there something that I can do to stop that.
---
Get relays with lower leakage, but there's no problem with what you
have now.
According to their data sheet, the leakage at 100C is only 1mA, so
you should be fine with what you've got.
