zero switching SSR workaround??? electronics teaser...

[reverb]

I am building a simple PID controlled system for maintaining mash temp. Just like many others.

the PID controller is a mypin TA4. it takes a 240V AC input power, and it outputs 240V. Unfortunately the output maximum load is limited to 3A so i cannot use it to directly drive the heater element.

So i bought a SSR 15Amp 240vAC to 240vAC to allow me to switch the element on and off. Unfortunately it is zero switching not random, so it doesn't work at all for resistive loads. (didn't previously know there was a difference!)

Does anyone know of a way to wire/work around a zero switching SSR to make it behave like a Random switching SSR?

A friend mentioned a diode bridge rectifier, but then the input wouldn't be ac, so it wouldn't switch the ssr right?

Any help from the gifted boffins out there would be appreciated!

And if there's nothing i can do... can anyone recommend a cheap (it's not used very often!) SSR AC to AC with RANDOM SWITCHING! Ha Ha!

On a slightly more philosophical note, what would be the point of an AC to AC zero switching SSR? it basically turns on and off an ac circuit 60 times a second resulting in the circuit being complete only half the time! So what could this be used for?

Many thanks.

Many thanks.

 

[Fil]

Hi reverb.

im far from expert but have used the sestos pids for a while now..

this ebay ad http://www.ebay.co.uk/itm/TA4-SNR-Digit ... 2a32a7f5bd

suggests that you need to supply a dc powersupply to power the ssr??

External supplied SSR power: 24V/ MAX 30mA

If the same model as yours???

if you need an expensive ac/ac ssr id consider getting a different controller it cld work out cheaper as the dc driven ssrs are just a couple of squid..

 

[nicknoxx]

Disclaimer: This might not work.
Connect the output of the PID to a 12v transformer and use this to drive a cheap DC/AC SSR

Edit:
This video
http://www.youtube.com/watch?v=2NpcMycHDvk
shows how to modify a PID to power a SSR directly. You'll still need an SSR that is DC driven.

 

[rpt]

I think your problem is that the output of your PID is AC but the SSR needs DC for its switching signal. Zero or random switching makes no difference. Both types should work fine with a resistive load.

 

[Kevin Wood]

Agreed, there should be no problem with a zero switching SSR for resistive loads, so I'd say you need to look elsewhere.

Are you sure the PID doesn't output DC to drive a DC input SSR?

If you're sure it's an AC output, try driving a mains light bulb from it to check that the output is doing what's expected. If that works, connect the AC input PID in parallel with the light bulb. I'm thinking that the internal PID in the controller might need a little load to function correctly.

 

[rpt]

Are you sure it outputs 240V? There are a number of different models in the family so it isn't immediately clear, but it looks to me that the unit either has a relay or a solid state relay. The former can switch 240V AC or 30V DC upto 3A. The SSR version can switch 24V +- 2V upto 20mA.

 

[Kevin Wood]

Are you sure it outputs 240V? There are a number of different models in the family so it isn't immediately clear, but it looks to me that the unit either has a relay or a solid state relay. The former can switch 240V AC or 30V DC upto 3A. The SSR version can switch 24V +- 2V upto 20mA.

Well spotted, and if it's the mechanical relay version (which sounds plausible) you probably want to remove the relay and convert it to a DC output to switch the PID, because the mechanical relay won't survive too long being driven by a PID and the noise will get on your nerves.

Can you post the full part number on the device so we can identify it?