Using Off-the-Shelf Motion/Daylight Sensors to Drive Multiple, Diverse Loads

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Atom54

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I have seen older posts on this and other forum discussing this issue but I haven't been able to find a definitive answer (this forum suggested an answer, but it has not been confirmed). When using an Off-the-Shelf Motion/Daylight Sensors (like you might find in a big box store) that may have either a mechanical or triac switch, can I use a solid state relay like an Opto-22 120A10 (see link below) as a complete solution for driving multiple diverse loads (e.g., incandescent light, LED light and a small motor or transformer for 12v lights) off the same circuit? Will that take care of the feedback, chatter, flicker and other issues? For example, can I run the 120v output (up to 250W) coming out of the Off-the-Shelf Motion/Daylight Sensor switch (that usually runs incandescent lights) to the control of the Opto-22 and then run power (from the same circuit that is running the motion sensor) through the Opto-22 switch contacts to various loads (e.g., incandescent light, LED light and a transformer for 12v lights) without problems?

here's the link to the Opto-22 http://www.opto22.com/site/pr_details.aspx?cid=3&item=120A10

Thanks in advance for your thoughts on this,
George
 

dfmischler

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Facilities Manager
I don't see any obvious problems if your expectations are realistic, but it takes more information than you can get out of the data sheet alone to fully answer your question. For example, will the control input of the 120A10 SSR draw enough current to keep the motion detector switch working properly (i.e. wetting current for a relay and turn-on/holding current for a triac)? What is the maximum inrush current of your load? For how long (see page 5 of the data sheet)? Can you maintain a low enough ambient temperature at the SSR surface to avoid needing an external heatsink (again, see page 5)? And so on. Sorry if this seems like weasling, but you need to compare everything in the data sheet against your application to see if it is a match.

EDIT: The data sheet says the SSR will switch at 400 Hz but with increased leakage current. This suggests to me that it will not control chatter well at some frequencies.

I also might have some safety concerns if consumer grade equipment was leaking 7mA at 120VAC when apparently off
 
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dfmischler

Senior Member
Location
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Facilities Manager
Oops. I think the data sheet is referring to 400Hz power, not switching frequency. The switching speed is controlled by the time constant of the 1uF cap, the 4.7K resistor and the LED.
 

gar

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Location
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EE
141227-1607 EST

Atom54:

Some experimental results using an older (20 years possibly) Crydom D2410 10 A SSR:

1. Leakage current at 120 V measured ewith a 1 k resistor is 2.5 mA. Approximately equal to a 48,000 ohm resistor. This is mostly from the built in capacitor-resistor snubber network.

2. Voltage across a Cree 9.5 W from this leakage current is about 4 V. Thus, Cree is approximately equivalent to a 1.6 k resistor. No flashing of the Cree. The leakage current voltage across the Cree is a constant.

3. With only a 100 k load the load voltage from leakage current is about 74 V. This is in the ballpark of 80 V calculated from 120*100/150. With the SSR energized the load voltage is about 119 V from a source of 121 V. Thus, no holding current problem from a very light load.

4. With a CFL and the SSR off there is a short flash every 1 to 2 seconds from the leakage current. The load voltage varies from 14 to 28 V. A 10 k 5 W shunt resistor across the CFL eliminates the flash and the load voltage is a constant 16 V.

You can try other experiments.

.
 

iwire

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Maybe it is just my own fault for not understanding the question or the issue but we just use simply pilot relays and lighting contractors.
 

gar

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Location
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Occupation
EE
141228-0913 EST

iwire:

Can you buy a control relay plus lighting contactor for about $ 30? The SSR will probably require a 1 to 5 k shunt resistor across its input to bleed leakage current. The particular referenced SSR is rated 10 A and at that current level may require a heat sink.

There is a 120A25 rated at 25 A at essentially the same price. It dissipates about 1.3 W per anpere. Run at full rating and you need to get rid of 33 W.

The SSR may be advantageous for use with a motion sensor, or other high cycle application even with its high power dissipation.

.
 

dfmischler

Senior Member
Location
Western NY
Occupation
Facilities Manager
Maybe it is just my own fault for not understanding the question or the issue but we just use simply pilot relays and lighting contactors.

And that seems to (still) be a better general purpose solution than SSRs. I love SSRs, especially for logic control of low voltage AC circuits (e.g. no back-EMF when shutting off as compared to a relay coil), but at line voltage relays are a lot simpler to design with, and there are fewer pitfalls. It's a switch, not a "leaky valve".

I think the OP probably prefers an SSR solution because he thinks it is preferable to have no moving parts, no contacts to wear out, etc. I don't think he has really looked at the leakage current and power dissipation issues (yet), but those can lead to serious problems. He wants a 1 component design that will handle a wide range of applications and I'm just not sure it can be done with the present technology (yet).
 
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iwire

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Location
Massachusetts
141228-0913 EST

iwire:

Can you buy a control relay plus lighting contactor for about $ 30?

Nope.

Can I get an inspector to pass a semi-conductor relay for use as a lighting contactor when I see nothing indicating it is suitable for that use?

Is it still $30 once I buy and install it in an enclosure?

When I 're-invent the wheel' for a customer am I really doing them a favor or am I making it difficult and more costly to service in the future?

There is a lot to be said for the kiss principle when labor rates are high. :)
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
141228-1633 EST

iwire:

I probably would not use an an SSR in most residential power applications, too much power dissipation. I would use a GE RR relay, and appropriate control circuits.

However, for a better understanding of the application of Opto-22 SSRs see http://www.opto22.com/documents/0859_Solid_State_Relays_data_sheet.pdf . They do have an advantage for switching incandescent bulbs. That is somewhat increased bulb life by turning on at a voltage zero crossing, and reducing filament shock.

Another useful reference is http://www.farnell.com/datasheets/1572354.pdf for P&B electromechanical relays.

I have applied the KUP relay to very severe service by switching a DC circuit of about 1 A at 108 V to a very inductive load, a 1000 #-ft clutch, at about 5 to 20 cycles per minute. Generally this was over a period of 2 shifts per day, call it 16 hours. Possibly a million cycles per year. These relays would last from 6 to 12 months. The failure mode was from unidirectional current flow and a conical build up of material on one contact with a conical hole in the opposite contact. I should have designed a polarity switching means and life would have been much greater, but this gave electricians something to do.

.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
141230-1109 EST

Atom54:

Rereading your first post I have to question what problem you want to solve?

I have a big box store motion sensor that clearly has an electromechanical relay output. Two ways to verify this without opening the unit. I can hear the relay click, and the output is full line voltage. Rated 600 W, but I don't really know what that means. Is it incandescent, resistive, or motor. See the datasheet for the various ratings.

Consulting a Cooper data sheet for the VS306U,
http://www.cooperindustries.com/con...ocuments/spec_sheets/OccSensor Spec Sheet.pdf ,
I find at least one discrepancy. My unit has a neutral, and probably requires it. The data sheet shows no neutral to the unit in any schematic, and verbally specifies no neutral.

By the description of the workable loads there is further verification of this as a mechanical relay output.

If your loads do not exceed the rating of the device, then there is no need for an external relay.

Again what problem do you want to solve?

.
 
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