Potentiometer Input Proportioanl Controller for DC...

Hi guys,

One of my customers builds small machines that have a small 24V/60W heater in them. The heater is powered by a 240/24V step-down transformer. The output to the heater is controlled by a potentiometer connected to a Crydom proportional controller SSR (LINK). The SSR is controlling the primary to the transformer. This current setup works fine.

Since the machine also has a 24VDC power supply for the control circuit, he is wondering if we could simply increase the size of this DC supply, and use it to power the heater. This would eliminate the need for the transformer.

My question is if anyone makes a similar potentiometer input SSR, but with a DC output? Alternatively, maybe a just a potentiometer with an on-board circuit to provide a PWM output? This could then control a standard DC output SSR to vary the heater output.

Ideally, the cost for the DC conversion needs to be less than or equal to the cost of the current AC setup. The current components consist of the transformer, SSR, and potentiometer. The DC version would include the additional cost of the larger DC supply, plus whatever is needed to control 24VDC to the heater (pot and controller).

Any thoughts?



-Eric

P.S. I'm not looking for a 'homebrew' solution (i.e. Arduino, etc.)...

Bump for a fresh set of views...



-Eric

Connect the heater to the output of exisiting SSR but use a fixed resistor in series with the pot to limit the maximum output. Saves the transformer.

What's included in the control circuit? Could you more easily convert it to 24 VAC?

Would something like this work?

Good idea Steve, but I can't use AC for the control circuit, because he uses a special guard switch that is only available in a 24VDC version...

I'm not sure I understand your answer, L D[AR2,P#0.0]...

To clarify, attached is a picture of the heater portion of the schematic. This is how it's currently wired. This system works fine as it stands now.



-Eric

burnerman said:

Would something like this work?

Click to expand...

That is exactly the type of item I had in mind. I may buy one to try.

Thanks!...

-Eric

Eric Nelson said:

I'm not sure I understand your answer, L D[AR2,P#0.0]...
-Eric

Click to expand...

The data sheet for the SSR shows that the on time is a function of the resistance. By inserting a fixed resistor in series with your variable resistor you could set a maximum on time with the pot at zero resistance. The characteristics show a sudden cut off at about 10% on time which is what you would need for the 24v heater - my suggestion is thus not a runner.
The characteristic for the 240V version of the SSR combined with the resistance values you have shown indicates control over the 100%-90% on range.