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Thread: Dirk Cheap SSR Issues

  1. #11
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    Default Re: Dirk Cheap SSR Issues

    Looking at the datasheets a few things stick out that may explain the behavior.

    The VO2223 lists a max LED trigger current of 10ma. Assuming the DirkCheap Module has a 680 Ohm resistor as Dirk mentioned, only 5ma will be delivered to the VO2223 LED after the forward LED voltage drop is accounted for. This does not mean that the VO2223 will not trigger, however it does mean that it COULD trigger more slowly. This is shown in the Figures 9 and 11 on page 4 of the VO2223 datasheet. This phenomena will get worse if the transformer on the Ren64 is heavily loaded and additional voltage drop occurs.

    Assuming the AC/SSR you have uses the MOC3023, it's datasheet lists 5ma as the max trigger current. This explains why it works as expected.

    Using 330 Ohm resistors on the DirkCheap module instead of a 680 Ohms should correct the issue.
    Last edited by ebrady; 11-22-2012 at 01:50 AM. Reason: Hillbilly Grammar

  2. #12
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    Default

    BTW if the resistors are changed you may also need a higher current transformer on the REN 64.

  3. #13
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    Default Re: Dirk Cheap SSR Issues

    Another consideration is the total current the PIC chip can handle. The reason we went with 680's was to make the DirkCheap compatible with the Simple32's current draw capacity. So with a 24, you might be okay with the 330 -- just do the math.

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  4. #14
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    Default Re: Dirk Cheap SSR Issues

    Hmm - - add in longer cabling (i.e. voltage drop) and the fact that the VO2223 has a Vf of 1.3v vs the Vf of 1.15v on the MOC3023 there would be even less current across it. Perhaps some value between the 330 and 680 and still meet the SR32 power output budget would be good - not sure if that's possible.
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  5. #15
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    Default Re: Dirk Cheap SSR Issues

    Quote Originally Posted by budude View Post
    Hmm - - add in longer cabling (i.e. voltage drop) and the fact that the VO2223 has a Vf of 1.3v vs the Vf of 1.15v on the MOC3023 there would be even less current across it. Perhaps some value between the 330 and 680 and still meet the SR32 power output budget would be good - not sure if that's possible.
    Yah, Mactayl worked the numbers pretty hard and the 680 provided just a little bit of headroom -- don't remember how much but I seem to recall it was only in the 10-12ma range, so it's pretty tight. That's one of the problems with a single chip that incorporates so many channels. It'd be fine if the chip designers could provide 4x the capacity that an 8-bit chip might, but that's generally not the case. <sigh>

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  6. #16
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    Default Re: Dirk Cheap SSR Issues

    Quote Originally Posted by dirknerkle View Post
    Yah, Mactayl worked the numbers pretty hard and the 680 provided just a little bit of headroom -- don't remember how much but I seem to recall it was only in the 10-12ma range, so it's pretty tight. That's one of the problems with a single chip that incorporates so many channels. It'd be fine if the chip designers could provide 4x the capacity that an 8-bit chip might, but that's generally not the case. <sigh>
    A while back I was running the Dirk Cheap SSR with a 510 ohm resistor with the SR 32 during testing but it was getting close to the current limit specs that the PIC could handle with all the 32 outputs turned on. So we decided to go with the standard 680 ohms that were in most of the designs for SSR's and never thought that a Ren64 would have an issue with the 680 ohm resistor.

  7. #17
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    Default Re: Dirk Cheap SSR Issues

    So, this is not what I wanted to read. I have just converted a good number of my SSRs to dirks. I have sold most of my SSRozs and SSRezs. If I have this trouble, I will be screwed. Should I take the time to change something now or do I just set them up and pray? I have 24 dirk cheapies and was not nervous until now
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  8. #18
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    Well I'm going to be testing this topic this upcoming week! As this is my first year and I went "all in" with the renard 64 and 16 dirk cheap ssrs. To further stress it I have the 1A transformer and all the LEDs installed on it (wlc ventures kit)

    99% of what I'm powering is LED strings not sure that matters though.

    I was going to add some Incan 100ct strings from the 200$ lowes sale to max it out.

    Currently only have 44 channels populated in my sequences though.

    I'll be sure to report back my findings ;)
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  9. #19
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    Default Re: Dirk Cheap SSR Issues

    My 2 cents...

    For the PIC16F688 used on Renard64, (but not on SR) the maximum current through the ground pin is 95 mA. So one thing that you do is change the resistors on the Dirk-Cheap-SSR to 330 Ω. This should be close enough to meeting the specs for both the PIC and the VO2223. With this change, though, you would be right at the limits of the power supply on the Renard64 if you have the on-board channel LEDs in place and have all 64 channels at 100% (you never do this, right)? In this situation the current draw would be 1.1 or 1.2A, just over the design limits of 1A. As a designer, I don't like it. As a user who has already built the board I would go with it, especially if I set the maximum brightness to 99% (or 254), which significantly reduces the load on the regulator and power supply (because the opto duty cycle is 100% with 100% brightness, below 90% with 99% brightness).

    And I haven't been following the SR designs closely enough lately to be able to comment on those...
    Phil

  10. #20
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    Default Re: Dirk Cheap SSR Issues

    Incidentally, the graphs for the VO2223 shows the situation getting worse at low temperatures, as the forward voltage of the LED increases at low temps. So I don't think that I'd ignore this potential problem if I'm in a place likely to see freezing or sub-freezing temperatures.
    Phil

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