SCR Build Problem

[JCBrew1]

Hello, I have built a SCR 240V for my boil keg to control my 5500 W heating element. I followed George’s design on Barley & Hops on YouTube. I ran a test run and my Volt/Amp meter states that when I have the Potentiometer set at 0% I am running at 214V. When I set the Potentiometer at 100% I run at 241V. Why do I not have control of the voltage at zero on the Potentiometer? It should run from zero Volt to 240 Volt. My SSR-40VA is the 2W model as George explained, but my Potentiometer is the RV24YN 20S B303. I wonder if I have the wrong Potentiometer possibly. Can anybody offer any help?

 

[doug293cz]

Is your element connected (or some other 240V load) to the SSVR when you are checking the voltage? Solid state switches are not perfect switches - they leak when they are off. If you have a load connected, the leakage current (a few milliamps) flows thru the load, and the voltage across the load is approximately 0. If you have no load connected, then the leakage current tries to flow thru your high impedance voltmeter, and you get almost full line voltage across your meter. The result being you cannot test the output voltage from a solid state switch without a load connected to the switch.

Brew on

 

[doug293cz]

I looked up the RV24YN 20S B303 potentiometer, and its range goes from 0 ohms to 30k (30,000) ohms (that's what the "B303" suffix tells us.) The specs for the SSVR call for a potentiometer that has a max resistance from 470k ohms to 560k ohms. The potentiometer that you currently have will not work.

Brew on

 

[JCBrew1]

Is your element connected (or some other 240V load) to the SSVR when you are checking the voltage? Solid state switches are not perfect switches - they leak when they are off. If you have a load connected, the leakage current (a few milliamps) flows thru the load, and the voltage across the load is approximately 0. If you have no load connected, then the leakage current tries to flow thru your high impedance voltmeter, and you get almost full line voltage across your meter. The result being you cannot test the output voltage from a solid state switch without a load connected to the switch.

Brew on

Thanks Doug293cz, I did have a 5500 w element on my boiler submerged in water while testing. I did get another potentiometer and tested it and it works better, it may not be the perfect match to my SSR but at about half rotation from zero, it shows up at around 27 volt and increases up to the 240 V I expected. I will see if I can find another potentiometer more closely matched to my SSR possibly so the potentiometer starts at zero to 240v hopefully.

 

[JCBrew1]

I looked up the RV24YN 20S B303 potentiometer, and its range goes from 0 ohms to 30k (30,000) ohms (that's what the "B303" suffix tells us.) The specs for the SSVR call for a potentiometer that has a max resistance from 470k ohms to 560k ohms. The potentiometer that you currently have will not work.

Brew on

Doug, I will try to find the correct Potentiometer for this SSVR. Thanks for your help. I am new to the electrical stuff and trying to learn. Thanks again.

 

[JCBrew1]

Doug, I will try to find the correct Potentiometer for this SSVR. Thanks for your help. I am new to the electrical stuff and trying to learn. Thanks again.

Do you happen to know how to buy the correct Potentiometer? Do you buy one rated at 470k Ohm or do you buy one based upon the max range at 560k Ohm?

 

[doug293cz]

Do you happen to know how to buy the correct Potentiometer? Do you buy one rated at 470k Ohm or do you buy one based upon the max range at 560k Ohm?

I think a resistance near the high end of the spec (560K ohm) will get you closer to 0 volts at the low end. Although, I don't know how much difference it will make in practice.

Since power = V^2 / R, the power to the element drops very rapidly with decreasing voltage. Your element has a resistance of about 10.47 ohms, so even at 10V output the power will be about 9.5W or 0.17% of full power.

Brew on

 

[JCBrew1]

I think a resistance near the high end of the spec (560K ohm) will get you closer to 0 volts at the low end. Although, I don't know how much difference it will make in practice.

Since power = V^2 / R, the power to the element drops very rapidly with decreasing voltage. Your element has a resistance of about 10.47 ohms, so even at 10V output the power will be about 9.5W or 0.17% of full power.

Brew on

Thanks for the info. I will try the new Potentiometer at the 570k rating.

 

[RufusBrewer]

There are linear taper potentiometers and log taper potentiometers. If you use one type when the other is required, you will most likely have unsatisfactory results. Verify which type your device needs, verify what you have.

There are SCR, SSR SSVR . They can look alike and seem to be the same, but they are different and not interchangeable. It is worth the time to confirm what you have and what it takes to control it. I.e. potentiometer will not control an SSR.

 

[doug293cz]

There are linear taper potentiometers and log taper potentiometers. If you use one type when the other is required, you will most likely have unsatisfactory results. Verify which type your device needs, verify what you have.

There are SCR, SSR SSVR . They can look alike and seem to be the same, but they are different and not interchangeable. It is worth the time to confirm what you have and what it takes to control it. I.e. potentiometer will not control an SSR.

SSVRs require linear taper potentiometers. Log(arithmic) taper potentiometers are used primarily in audio volume control applications.

Brew on