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Thread: Another DC SSR Question

  1. #1
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    Default Another DC SSR Question

    I've been looking at the circuit diagram for the DC SSR at the Wiki Page and the Chrismtas in Melbourne page.

    Why is a separate power source needed for the optos? Why can't I use the 5V coming from the controller for pins 10, 12, 14, and 16 on the K847PH Optocoupler?

  2. #2
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    Default Re: Another DC SSR Question

    It's there to separate the two sides of the logic to prevent a situation where the high voltage fed into the DC side feeds back up to the controller and smoking the PICs. It's really the whole purpose of having the optos in the first place.
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  3. #3
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    Default Re: Another DC SSR Question

    Ok, thanks, makes sense. Next question:

    I was thinking about providing the power for the application at the application. What is the trade off between trying to power it over a long distance between the SSR and the application itself?

    Here are my two scenarios:


    and


  4. #4
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    Default Re: Another DC SSR Question

    I'm assuming in your first option that the power supply would be co-located with the flood (say a wall wort or something similar). You would need multiple supplies - albeit smaller/cheaper ones so cost probably washes. You would also have to an AC source at each light to power the supply whereas in the second (more typical) example, it would be fed over a Cat5 cable. Less worries about packaging the supplies and keeping them dry, etc.

    The problem with #1 is that the DCSSR is a switched ground system and you would want to have a common ground available at the DCSSR to be switched via the MOSFETs on them.

    You didn't have option #3 - - putting the DCSSR in the same enclosure as the floodlight. I'm not sure how long your "Long Distance" is though as you would have to account for drop over the cable from the controller.
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  5. #5
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    Default Re: Another DC SSR Question

    I thought about option #3 first, but then I have to have a long control cable. I don't know how long the distance is. I move every three years at the maximum... trying to maintain my flexibility. Mostly I have the SSRs close to the controller and let extension cords do the rest of the job. Just keep adding every year to the extension cord inventory. One day I might settle down and change my configuration, but for now this works.

    For options 1 & 2. I realize for #1, I have to have three power supplies and that is ok if I have to do it that way. If I did it that way, I was planning on linking the grounds via the RJ45 cable... not sure if that works or not. Option #2 takes less power supplies, but I was concerned about the power over such small wires, but I'm not planning on that much current anyway. Hopefully not over 300mA based on my calculations. But not knowing the distance I don't know what the drop in voltage would be either.

    Thanks for the feedback... will have to keep thinking about it for a while.

  6. #6
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    Default Re: Another DC SSR Question

    Quote Originally Posted by paul.milne View Post
    I thought about option #3 first, but then I have to have a long control cable. I don't know how long the distance is. I move every three years at the maximum... trying to maintain my flexibility. Mostly I have the SSRs close to the controller and let extension cords do the rest of the job. Just keep adding every year to the extension cord inventory. One day I might settle down and change my configuration, but for now this works.

    For options 1 & 2. I realize for #1, I have to have three power supplies and that is ok if I have to do it that way. If I did it that way, I was planning on linking the grounds via the RJ45 cable... not sure if that works or not. Option #2 takes less power supplies, but I was concerned about the power over such small wires, but I'm not planning on that much current anyway. Hopefully not over 300mA based on my calculations. But not knowing the distance I don't know what the drop in voltage would be either.

    Thanks for the feedback... will have to keep thinking about it for a while.
    Cat5 is OK for this - I run 4 x 360mA leads (@5v) for my SuperStrips - no problems at all. I made sure all my cables were all the same length so all would drop the same amount and then tweaked my supply just a bit to allow for the drop. There are lots of folks that run everything like this over Cat5 - especially with floods and strips.
    Brian

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  7. #7
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    Default Re: Another DC SSR Question

    Power over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling. PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable for low power levels.[1] Power can come from a power supply within a PoE-enabled networking device such as an Ethernet switch or can be injected into a cable run with a midspan power supply.

    The original IEEE 802.3af-2003[2] PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA[3][4]) to each device.[5] Only 12.95 W is assured to be available at the powered device as some power is dissipated in the cable.[6]

    The updated IEEE 802.3at-2009[7] PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power.[8] Some vendors have announced products that claim to comply with the 802.3at standard and offer up to 51 W of power over a single cable by utilizing all four pairs in the Cat.5 cable.[9] Numerous non-standard schemes had been used prior to PoE standardization to provide power over Ethernet cabling. Some are still in active use

    Also that is only using 2 pair you are going to use four pair.. What you are going to be doing it more like 802.3at but you can double that as you're using all 4 pair. I don't think you'll have much power problems.. Also I think PoE is rated upto about 150ft.. To supply power at those ratings. You more than likely need no where near that much..

  8. #8
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    Default Re: Another DC SSR Question

    LOL Budude was writing the simple version while I was trying to get all my technical data straight lol.. but basically said the same thing.. Cat5 is very robust..

  9. #9
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    Default Re: Another DC SSR Question

    Quote Originally Posted by chelmuth View Post
    LOL Budude was writing the simple version while I was trying to get all my technical data straight lol.. but basically said the same thing.. Cat5 is very robust..
    My Chuck Norrisnish has come back...
    Brian

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