SSR's WILL NOT WORK for the DC portion of lordratner's application. It will turn ON, but he will have to pull the fuse or otherwise cut the DC power to the box to turn it off. I am betting that he will NOT be happy about that development.

Check out the datasheets for the components in question. They are MOSFET SSRs, not triac SSRs. The SSRs, at least for the one praondevou linked to and the first one that OP linked to in post #19 are rated for DC.

 

Ok, I want to start by saying that you guys have been awesome to help me out so much. I know I'm the guy with no clue, and I appreciate your patience. At least now I know what my students feel like when they ask me a question!

Ok, so looking through data sheets and what not, here is my latest choice:

http://www.digikey.com/product-detail/en/AQV252GAX/255-3375-1-ND/2810282

Handles DC or AC. I'm using DC, so it should be "B or C connection" which according to the second chart will handle a minimum of just under 2 amps at 85 degrees C (can't imagine it getting near that), perfect for my needs (1 amp).

I still don't know how to figure out what resistor I should put between the 8VDC and the input though. Is there a formula I should know (obviously there is).

I'm feeling good about this one. How far off base am I?

EDIT: Looking at http://media.digikey.com/pdf/Data Sheets/Panasonic Electric Works PDFs/PhotoMOS hookup diagram.pdf

Under AQV20 series, Connection B, there are 4 diagrams. I believe I want the top right setup... 12 VDC+ goes to the SSR, then from there to the various components. It's in brackets, so I don't know what that means, but I'm hoping it means my plan will work.

Comments?

 

here is my latest choice http://www.digikey.com/product-detail/en/AQV252GAX/255-3375-1-ND/2810282

looks good to me. just keep in mind it's SMD, meaning, it solders to the top of a board. so you might need a breakout board, or else you might have to dive into the art of PCB making.

I still don't know how to figure out what resistor I should put between the 8VDC and the input though. Is there a formula I should know (obviously there is).

The formula is out there if you google it, but I'm lazy. I use this calculator. Plugging in the numbers from your datasheet:
source voltage: 8v
diode forward voltage: 1.5V
diode forward current: 7.5mA (datasheets says between 5 & 10mA)

It gives me a resistor value of 1KΩ

there are 4 diagrams. I believe I want the top right setup... 12 VDC+ goes to the SSR, then from there to the various components.

yup, looks good to me.

 

looks good to me. just keep in mind it's SMD, meaning, it solders to the top of a board. so you might need a breakout board, or else you might have to dive into the art of PCB making.

Ack, it's always something.

My plan is to solder a wire to each (used) terminal, then bundle the wires and tape them up tight so I dont jostle the pins while making the connections. Will I be able to do that with this guy, or do I need to find a different style?

If not, then I guess this will be easier to solder to, correct?
http://www.digikey.com/product-detail/en/LCA717/CLA325-ND/2275713

 

Ack, it's always something.

My plan is to solder a wire to each (used) terminal, then bundle the wires and tape them up tight so I dont jostle the pins while making the connections. Will I be able to do that with this guy, or do I need to find a different style?

if you have time to devote to it, you could try to find a through-hole type, but I doubt you will succeed. I've already been trumped on previous non-kosher notion of crimping the legs on the MOSFET, so I won't officially "condone" soldering wires to SMD leads, but hey, it's your part, and you're free to do what you want. I've never tried it, but now I want to, just to see.

 

if you have time to devote to it, you could try to find a through-hole type, but I doubt you will succeed. I've already been trumped on previous non-kosher notion of crimping the legs on the MOSFET, so I won't officially "condone" soldering wires to SMD leads, but hey, it's your part, and you're free to do what you want. I've never tried it, but now I want to, just to see.

From above:
http://www.digikey.com/product-detai...325-ND/2275713

It's a through hole, so longer pins. If its only going to cost me a couple bucks to put it on a small board and do it right, I will, but that will open up a whole new round of questions...

 

From above:
http://www.digikey.com/product-detai...325-ND/2275713

It's a through hole, so longer pins. If its only going to cost me a couple bucks to put it on a small board and do it right, I will, but that will open up a whole new round of questions...

excellent, good hunting. I knew you could do it! (actually, I didn't)

So yeah all you need is a little radioshack board and some terminals and a resistor.

and, now for your new round of questions....?

 

excellent, good hunting. I knew you could do it! (actually, I didn't)

So yeah all you need is a little radioshack board and some terminals and a resistor.

and, now for your new round of questions....?

Nevermind, the rest was very straight forward, and amazingly, it all works!

Thanks again to everyone for their input, you guys made the project work.

 

The nightmare continues...

So I got everything wired up, and it worked perfectly, for over a week.

Now all of a sudden, it doesnt. The SSR was working as expected, allowing the 12VDC to flow when the 8VDC was applied to it, now it always allows it to pass, but in an odd way.

Using a multimeter between the two load terminals of the SSR, the resistance goes from infinity to ~0 when the SSR goes from open to closed, as expected. This is confirmed by the tone function on the multimeter, which when connected to the load terminals of the SSR, sounds when the input voltage is applied, and does not sound when the input voltage cuts out.

However, when I measure the voltage from the output load terminal, it is 12.02 VDC when the input voltage is applied and the SSR is closed, but only drops to 11.56VDC then the input voltage is cut off and the SSR is open (and I know it's open based on the infinity resistance). And when it is connected to the LED and DC/AC SSR it is supposed to control, they are permanently on.

How is this possible? I tried a replacement SSR, and the same thing is happening.I would understand if it never worked in the first place, but it worked fine, and then with no changes from me, stopped working.

 

So did you use the LCA717?

What resistor value did you use?

DC or AC/DC configuration (1st page of the datasheet)

If you short the LED pins, is the output still ON?

 

MOSFETs have parasitic (reverse biased) diodes in them, if you connect them backwards they always conduct. Try swapping your load side connections.

 

So did you use the LCA717?

What resistor value did you use?

DC or AC/DC configuration (1st page of the datasheet)

If you short the LED pins, is the output still ON?

Yes.

10K

DC

Not sure what you mean by shorting them, but if I leave them completely disconnected from anything, the load voltage still passes through, albeit at 11.56V instead of 12V.

But it didnt do this before.

 

MOSFETs have parasitic (reverse biased) diodes in them, if you connect them backwards they always conduct. Try swapping your load side connections.

Ok, I'll try that.

EDIT: That did it! Once again you guys have saved me from failure.

Though I'm still baffled as to how it worked before, then suddenly stopped without me opening it up, I'm just glad it's fixed.