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Thread: TECH 7 AMPAC 780 DUAL ACTION controller

  1. #21
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    HS3014
    500 +/-3.5 (not sure if that's +/- or =)
    60 LED

  2. #22
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    duplicated - deleted

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    So those are 30 mA each with 3.1 forward volts needed. And each threesome is wired in parallel with nominally 90mA going into each node -- 30mA per LED.

    I'm coming up with 155 ohms, so rounding up to 180 ohms of resistance, for 17 VDC source voltage.

    But if you just get a regulated 12 volt DC power supply, you should be able to do what @kingmeow suggested by cutting the strip where marked.

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    May I ask what numbers you used? I'm finding this very informative. I took a DC course this summer, but was largely theoretical, and have not done much measuring actual circuits.

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    I just ran a search for HS 3014 LED. Then I plugged the current value (30mA per LED) and forward voltage 3.1 volts (LED voltage drop) into the calculator along with the 17 VDC source.

    But since there are three LEDs in parallel, you can use 90mA, because the current will branch three ways almost equally through each of the three LEDs in each mini-strip.

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    Paul's calculation seems correct to me given the spec. But I'm not sure what the question is West Coast. Are you trying to source the correct power source?

    Just count how many gang of 3 will be in your cut strip and multiply by 0.09A and you will get the total current draw. Then source a 17VDC (12V is close enough) supply that can produce at least that much current plus 10% as a safety overhead.

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  10. #27
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    No, I have a power source outputting anywhere from 14 to 18 Vdc depending on where you read. Controller has 14Vdc embossed on the terminals. The PDF instructions state 18Vdc. So either way I'm a few volts heavy of the 12Vdc needed for my LED. I suppose measuring it correctly would give me the exact number.

    Here's the controller: https://www.fleischmann.de/en/produc.../products.html

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    I'm more confused. And that's probably due to us getting off track a little discussing dropping resistors.

    Let's get the power source correct. Are you going to use the Tech 7 or the Fleischmann above? Your subject line says Tech 7 but then you're talking Fleischmann above.

    If Tech 7
    You will need to get some kind of bridge rectifier to convert the 14.8V AC to DC so you can power the LEDs. Once you do that, measure the DC output. The rectifier will drop the AC voltage slightly in the conversion process. This is good for you as it gets you closer to 12VDC from 14.8VAC. Check the specs on how many amps the accessory terminal put out. Just make sure the number of triplet LEDs, at 90 mA per triplet, don't exceed the rated amps or go beyond 90% of it.

    If Fleischmann
    From the PDF above, it doesn't say what voltage is the accessory terminal. Are you using the controller only and using your own wall wart? I don't see the 18VDC anywhere on the PDF. It just says 850 mA for the accessory terminal. If you are using your power source that eventually gets you 14-18 VDC at the output, I would be very cautious on the 18VDC. I think that's too much for your 12VDC LED strip. That's 50% more votlage! 14VDC will probably work fine. You can test it by cutting off a triplet, if you can spare one set, and put the 14VDC to it and see what happens. My guess is that it will be extremely bright. Maybe too bright for your needs.
    Last edited by kingmeow; 25th Dec 2018 at 12:17 PM.

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    Hi, and apologies for the confusion in the title of my thread. I will see if I can edit it. For now I will go with the Fleischmann 18VDC in the PDF under the technical specs:

    Technical data (valid exclusively for controller 6720 in conjunction with mains transformer 671001)

    • Control area of the power output: 0 14 volts, continuous power up to 600 mA.
    • Separate DC power output 18 volts for lighting and electrically operated accessories.
    • Maximum power rating: 1000mA (18VA).


    Again, I am suspect of this claim, since on the controller itself it has 14VDC embossed by the terminals. But even at 14VDC it is too bright. I will try to get a persice measurement from these terminals.

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    Ah, much clearer now. . It might be 18V no load and once you connect a load it drops to 14V. This is just a guess on my part as the cheaper power packs are not very well regulated.

    But either way it looks like you tried it and it's too bright. I would get one of those cheapy wall wart and try that. Try to get one where it's multi voltage switchable, like 6, 9, 12 volts. I suspect 9V might be enough to get you the brightness you need. If not, you can switch to 12V.

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  16. #31
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    Can I still try the resistor method? The separate wall wart is an option, but I want to minimize the amount of cords I'm running - this is to be a coffee table layout after all That DC dimmer may also do the trick. Otherwise this is not a bad little controller. I was able to find Circuit-Test switching power supply to go from 110VAC to 18VDC. The Fleischmann starter sets usually come with a 220V plug.

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    Well, you can but it gets a little tricky is you are trying to use a dropping resistor for the entire strip. Here's how you would do it. Correct me Paul and any others out there!

    Say you have a true 18VDC source. Your light strip uses 12VDC. So you need to drop 4 volts. BUT(!) you need to figure out how many sets of those triplets you are using at 90ma per set. Let's just say 10 sets, so the strip is drawing 900 mA.

    R = V / I, solving for R, R = 4 / 0.9 = 4.44 Ohm or roughly 5 Ohms.

    BUT(!) most of the resistor you see are typically 1/8 to 1/4 watt. 0.9A will fry them. So now you need to get a power resistor with the possibility of needing a heat sink depending on how hot it gets.

    (W)att = V x I, solving for W, W = 4 x 0.9 = 3.6 watt.

    Something like this. They are big at almost 2" long.

    https://www.amazon.com/Uxcell-a11111600ux0197-Wirewound-Ceramic-Resistor/dp/B0087YHZC2/ref=sr_1_16?ie=UTF8&qid=1545766675&sr=8-16&keywords=5+ohm+power+resistor#feature-bullets-btf

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