# SSR with PWM



## dave_h (7/1/16)

Hey everyone,

Im in the process of putting elements in my pots and have a question about SSRs and PWMs.

Do you have to match up the PWMs output to the SSRs input voltages exaclty?

Im looking at getting these two 

http://www.aliexpress.com/item/DC-to-AC-Solid-State-Relay-SSR-40A-3-32VDC-90-480VAC-w-Aluminum-Heat-Sink/2019948013.html?spm=2114.01020208.3.10.jSu6Sc&ws_ab_test=searchweb201556_3,searchweb201644_0_10001_10002_10005_10006_10003_10004_62,searchweb201560_2,searchweb1451318400_6150

http://www.aliexpress.com/item/Free-Shipping-6V-12-24V-10A-Pulse-Width-Modulator-PWM-DC-Motor-Speed-Control-Switch-Controller/1814315755.html?spm=2114.01020208.3.136.374fsr&ws_ab_test=searchweb201556_3,searchweb201644_0_10001_10002_10005_10006_10003_10004_62,searchweb201560_2,searchweb1451318400_6150

My understanding is that SSRs are always on and when the get a voltage they cycle the power off, so would I need to feed 32V DC in to get the element to go off, and say 16V to be at 50%.

Thanks

Dave


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## SBOB (7/1/16)

You have a few things wrong... 
They simply operate as an on/off relay, so there is no % output. 

Might be easier to google
'how does an ssr work'
And
'how does pwm work'

The first few results of both will explain it in more detail than I could write here


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## QldKev (7/1/16)

What are you trying to achieve? Do you simply want to turn down the power to the element? 

If so, then you can achieve it using a specific type of SSR. 
SSR
http://www.ebay.com.au/itm/Solid-State-Relay-SSR-Voltage-Resistance-Regulator-25A-24-380V-AC-470-560K-Ohm-/291558388701?hash=item43e23bf3dd:g:Eu4AAOSwDNdV7Z2Y

then you need a variable resistance to control it, so a potentiometer matched resistance and current potential.
POT
http://www.ebay.com.au/itm/Replacement-6mm-Shaft-Dia-470K-Ohm-2W-Pots-Potentiometer-w-Knob-W6-/201402807813?hash=item2ee48af605:g:xrYAAOSwMmBVxIvu


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## TheWiggman (7/1/16)

dave_h said:


> My understanding is that SSRs are always on and when the get a voltage they cycle the power off, so would I need to feed 32V DC in to get the element to go off, and say 16V to be at 50%.


Other way around. They are an open circuit until a voltage is applied across the control terminals. In the SSR you've quoted that voltage is can be anywhere between 3 - 32V DC.

Pulse width modulation is an entirely different concept. It is a power source that will maintain a voltage but turn off at a set frequency (21kHz in for this one). The 'pulse width' is the amount of time they remain on for per cycle. These are typically used to control DC motor speed and maintain torque (thus power), as simply lowering the voltage will reduce both speed and torque.


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## dave_h (7/1/16)

Many thanks for the replies, I didnt know there were more than one type of SSR.

Spent ages Googling and had first seen people using potentiometers then all I came across seemed to be SSRs with PWMs, happy I asked here 

Thanks for the links QldKev, I will go with something similar. Yes they are for controlling the intensity of the elements.

Cheers Dave


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## TheWiggman (7/1/16)

For the price I reckon these kits are hard to beat: http://www.stilldragon.com.au/diy-controller-kit/


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## dave_h (9/1/16)

Kit looks great Wingman, if I was in Oz I would buy two!


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## TheWiggman (9/1/16)

Unless you like going home alone, you don't want me as your wingman


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