Solid state relay wiring question
henrytj
Posts: 90
I'm switching to a different forum for this question. My previous questions have been more Basic Stamp and ulc2003 related.
So here it goes.
I'm making a outlet box where the outlets can be controled by a micro controller via a ulc2003. So I'm going to use battery powered SSR's (already have several) to control the VAC outlet. One SSR per outlet. But, I also want this, a wall style switch that will bypass both SSRs and power the outlets ON. Right now I'm just making a simple 2 outlet box in a 3-gang/device metal junction box. So one section for the (2) outlets, one switch, and one place for the (2) SSRs to be inside.
My first thoughts were to buy a double-pole, double-through wall switch. HAH! Not only I haven't seen such in any hardware stores, but they are like $100 online. One pole for powering the outlet through the SSR(s) and the other pole to bypass the SSR and power the outlet directly. Doubt throw, one throw per each SSR/outlet set. But $100 is out of the question.
Now, I can find switches, (2) ganged one above the other, on the same switch plate, but they are only single-pole.
So here is the question. Is it harmful (to the SSR) to have a SPST switch bypass the contacts of the SSR? In other words when the switch is in the bypass mode, it would end up applying power to both VAC contacts of the SSR. Is that bad for the SSR? If not, it seems the simplist way to do it. If it's harmful then I have to keep searching for other double-pole switch solutions.
Hope this makes sense an I sometimes have difficulty wording my questions.
Henry
So here it goes.
I'm making a outlet box where the outlets can be controled by a micro controller via a ulc2003. So I'm going to use battery powered SSR's (already have several) to control the VAC outlet. One SSR per outlet. But, I also want this, a wall style switch that will bypass both SSRs and power the outlets ON. Right now I'm just making a simple 2 outlet box in a 3-gang/device metal junction box. So one section for the (2) outlets, one switch, and one place for the (2) SSRs to be inside.
My first thoughts were to buy a double-pole, double-through wall switch. HAH! Not only I haven't seen such in any hardware stores, but they are like $100 online. One pole for powering the outlet through the SSR(s) and the other pole to bypass the SSR and power the outlet directly. Doubt throw, one throw per each SSR/outlet set. But $100 is out of the question.
Now, I can find switches, (2) ganged one above the other, on the same switch plate, but they are only single-pole.
So here is the question. Is it harmful (to the SSR) to have a SPST switch bypass the contacts of the SSR? In other words when the switch is in the bypass mode, it would end up applying power to both VAC contacts of the SSR. Is that bad for the SSR? If not, it seems the simplist way to do it. If it's harmful then I have to keep searching for other double-pole switch solutions.
Hope this makes sense an I sometimes have difficulty wording my questions.
Henry
Comments
Like Mike said, no issues. Heck, even if the switch fails open dumping the full line voltage across the SSR output pins, you will still have no more across them than you would in normal operation with the SSR in the off mode. Consider if you have not already, appropriate snubber ckts to protect the SSRs if feeding inductive loads.
On the safety side of things though, make sure you are very careful of the clearances in your box and also ground anything that can be grounded that you or anyone else could come into contact with. Sure you don't want to go with a plastic or insulated box for this one?
FF
Thanks. Yes, I intend to ground everything. The outlet box is being made to experiment with movie lighting effects. I want to be able to plug in (2) movie lights (max 1KW) per outlet. The switches are to test, and "warm up" the lights before the take. Then the SSRs, controlled by a Basic Stamp, will flicker to see if I can get a "Lightning" (or other, like welding, etc) effects. I was thinking that the SSRs (bottom metal plate) would be attached to the bottom of the metal outlet box to act as a heat sink. Maybe I'm wrong about that idea. The current shouldn't be flowing through the SSRs for more than a minute at a time. But, through the bypass switch, the lights might be on for a while.
That's an idea. So is the indicators. But for this first test (to see if the idea to simulate Lightning, ect with movie lights) even works. If it works, a better featured outlet box can be constructed. I figure (2) outlets with a light on each, would allow to see if the effect works. Lightning often has multiple cloud to cloud discharges associated with the primary bright lightning strike.
I'm even wondering if a final box should also have it's own circuit breaker in case someone plugs in too high wattage of a light.
Thanks again.
Henry
Regarding your switching scheme. ...
The two choices are to have the 120VAC mains switched with a by-pass switch. Or to switch on the low volage side of the relay.
The advantage of switching the 120VAC mains side is that you can completely bypass any failure of the unit and verify the rest of the circuit is operating correctly.
The advantage of switching on the low voltage side is if you want to have your over-ride switches in a bank at the end of a cable that is some distance away from the SSRs and the mains wiring. It is always safer to run extension cords and cables as low voltage devices.
I'd be more concerned about a good set of fuses or circuit breakers before I got into metal boxes and grounding. With the tiny SSRs that are available these days, you won't have any heat sinks, you might build in an all plastic box, and skip grounding the box entirely.
Okay, rethinking the metal box idea. I had sent all this to my EE relative, but they have yet to get back to me. I expect that his comment might be the same. It's just that he's a busy person with job (travel) and family. I, on the other hand, am unemployed, and have what some might consider too much time. Though I do have 7 short stories currently out, two screenplays up on a review site, and planning a video for a Kickstarter project. So, I'm actually more busy than when I'm working.
Thanks. All the advice is being absorbed and processed.
Henry
I do admit that a lot of plastic boxes available still can burn with toxic fumes. But if the connections are good and the devices are reasonable, they do work well.
Theatrical wiring is especially aware of fire hazards as you have hundreds of people attending an event and any fire can create a panic far beyond the realities of the fire hazard.
Thanks,
Henry
However, adding heat stress to the outlet box might be another cause for concern. Is there ventilation inside the wall?
PS: Regarding the earth wire being a fire hazard, that would only be true if not wired correctly. In normal use the current in an earth wire will be below a few milliamps of leakage. In a fault condition the earth wire can carry the fault for the few milliseconds it takes for the circuit-breaker or fuse to trip. Modern homes are additionally wired with an earth leakage breaker so that the leakage can't be above 30 mA I think it is.