Hi, I am setting up an Aluminum anodizing line and I have three 20 amp heaters and one 20 amp circuit available. I tested the on time vs off time for one of the tanks and it only needs 12 sec ON and 30 sec OFF so I built a sequencer to enable all three to be plugged in at one time. I am using 3 20 amp relays and one SSR (18 amp) and a tiny 45. I also have a sense transformer so that I know if they are on. Each heater has it's own thermostat. The plan is to switch SSR off, switch a relay on and then turn the SSR on, test for current flow, wait 10 seconds if on, wait 1 sec if off and then go to the next relay. My thinking is the 0 crossover SSR will give much more life to the relays and have a smooth turn on and off.
I tested the voltage output of the sense transformer and I only see 1.8mV. I calculated the resistor to be 20 Ohms to give me a peak 2.7VDC.
3. To calculate value of terminating resistor (Rt) use the following formula:
Rt (Î©) =VREF * N / (Ipeak_primary)
Using N = 100 and Ipeak_primary as 20Amps I get:
20 ohms = 4VDC * 100 / 20Amps
At 16.6 amps for a 2000 watt heater I should see 3.32 V (minus 0.6V for the diode = 2.72V)
The circuit is connected like this. D4 is a bat85 diode. R2 is 20 ohms and the transformer is a PA1005 ( digikey link http://search.digikey.com/script... )
Where am I going wrong?