Looking for Solid State Relay control.....

paradym · May 16, 2003

Howdy All !!!

Could someone throw up a simple circuit that will let me take a analog input signal and drive a solid state relay that will give a proportional output from the relay.

The spec’s are -

Controled load by solid state relay - 2 amps at 120 volts AC

solid state relay,
Standard 25 amp solid state relay
Input - 3-32 VDC.
Output - 120/240 VAC.

Control,
1. Operate on 12 VDC or be loop powered at 12 VDC.
2. Accept a 4 - 20 mA input signal.
3. Output a proportional pulse signal to drive the solid state relay for a 0 to 120 volt out.

Thanks in advance guys !!!!!

Ron Beaufort · May 16, 2003

unless you're dead set on building your own, take a look at this - i've used this type for several years with good success -

http://www.omega.com/ppt/pptsc.asp?ref=PCM

also - you probably already know this but - if you have a regular DC discrete output module, you can easily program a "time-proportional" output signal to pulse the solid-state relay's control circuit off and on - but i'll bet that you really want to keep that 4-20mA output signal don't you?

paradym · May 16, 2003

Thanks Ron for the feedback.

The controller is for a personal project that I'm already over budget on.

I got PLENTY of components that I can scrounge through to make something along with some time.

If you or anyone else got something, Please throw it out.

Thanks

TimothyMoulder · May 16, 2003

555?

Would a 555 timer circuit work, fed through a relay?

I'll draw up the circuit if a chip timer is an option.

TM

TimothyMoulder · May 16, 2003

Here it is

Attached is a bitmap of a Voltage Controlled Oscillator from the Radio Shack Engineer's Mini-Notebook on 555 timers

Text reads :

"The 555 oscillates at a frequency determined by R1 and C1. A voltage applied to the input changes the oscillation frequency of the 555. As voltage increases (developed across R3 -- TM) the oscillation frequency DECREASES (emphasis mine -- TM)"

This may not be the answer you are after, but I thought it might help steer you somewhere useful

Good Luck!

TM

paradym · May 16, 2003

Thanks for the circuit Tim,

From what I see, I think that should do it.

Thanks again.

(me loves this place :site: )

TimothyMoulder · May 16, 2003

TYPO!

Oops!

The second pin 3 (lower left corner, analog feed-in point) should be pin 5.

The rest are okay

Sorry for the mix-up, but whil we're on the subject, go to the Shack and get those mini-notebooks. I've had mine for ten years, and at 99 cents, they're the best value in the store.

TM

Eric Nelson · May 16, 2003

Re: TYPO!

TimothyMoulder said:
...go to the Shack and get those mini-notebooks. I've had mine for ten years, and at 99 cents, they're the best value in the store...

Radio Shack: "You've got questions, we've got blank stares"...

But yes, those books ARE very good!

beerchug

-Eric

paradym · Jun 10, 2003

Hey again,

Tried the 555 circuit, didn't give me the desired effect with the solid state relay since the relay is a zero crossover unit.

Found a Triac controller circuit that should meet my needs as it controls the firing on the phase angle.

http://www.sas.org/E-Bulletin/2001-11-02/labNotes2/labNotes.html

My only problem, I've been looking at the schematic and I don't see an easy way to insert a 4-20 mA signal from a PLC to replace the pot for controlling the output.

Any ideas guys.

Thanks in advance.

Parts List

• C1, C2, C3 0.1 µF, 600V dc Myar
• F1 6A fuse in fuse holder
• J1 2-prong male ac bulkhead connector
• J2 2-prong female ac bulkhead connector
• Q1 international rectifier IRD54C diac
• Q2 international rectifier IRT82C triac
• R1, R3, R4 1K,1W
• R2, 100K, 1/2 W potentiometer

Eric Nelson · Jun 10, 2003

You know my opinion about "home-brew" stuff, so I won't rant about that again...

Have you looked for an 'off-the-shelf' solution? IOW, check THIS LINK (or HERE for the .pdf). For ~$100 you can save yourself a lot of aggravation... :nodi:

beerchug

-Eric

paradym · Jun 11, 2003

Thanks Eric,

The controller is for a personal project and I'm tight for $$$.

The controller is for a light control for MY aquarium (Hey, sounds like I heard that in some other thread) that I'm building a PLC system from scrap and scrounged parts to make.

though also my thoughts are to carry this over to a work project if I can get the cost down (I got a possible line on some good, high current Triac's)controlling a heating table with 20 "Hot Spots"

Any help/info that someone can throw out would be appreciated.

Eric Nelson · Jun 11, 2003

You ARE building a dimmer, right?

Let's hope you're not creating a 'fish discotheque' with pulsing lights. The poor fish might have a seizure!...

If you're just trying to create a PLC controlled light dimmer, you might want to check into the home automation stuff. Places like SmartHome sell cheap interface-able dimmers that you could hack. You probably already know about the home automation section at epanorama.net, but if not, click HERE. Lotsa good info there!

Have fun!

beerchug

-Eric

Tom Jenkins · Jun 11, 2003

"I don't see an easy way to insert a 4-20 mA signal from a PLC to replace the pot for controlling the output."

I is jist a lowly mechanical whut got led astray into this electrical stuff, but it seems t'me thet if'n you put a dropping resistor in place of pot wiper to R3 connekshun (or maybe instead of R3) you'd get a voltage. Run yer 4-20 mA through the resistor t' get a voltage. You is gonna haf t' figger out the size of the resistor to make it match the input votage range needed.

panic mode · Jun 11, 2003

Check out clasic dimmer circuits and try to modify them.
For example here is simple one (not trivial but it should
be straight forward even for begginer):
https://www.onsemi.com/pub/Collateral/AND8011-D.PDF

Once you make it working try to control charging of the
2.75uF capacitor with your analog output (where the hell
do they find such values?).

Probably the simplest way is to use load resistor for your
current loop to convert the 4-20mA into say 2-10V.
Disconnect the 2.5kOhm potentiometer connection to +12V and
use voltage from your sensor to charge the timers circuit.

And be carefull with the circuit, don't get electrocuted.

panic mode

panic mode · Jun 11, 2003

And in case you are trying to simplify circuit,
you can get rid of the NPN transisitor and 1kOhm
resistor (but leave the 620 Ohm). Then connect the
cathode of the optocoupler to the pin3 of the 555 chip.
Typical 555 can provide ca 200mA out (sink or source)
so load of one LED and 620 Ohm resistor should be no
problem (some 15mA with used 12V power).

panic mode

Looking for Solid State Relay control.....

paradym

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