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Thread: 1000 watt air cooled transformer

  1. #11
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    The OP, having described it as an "air cooled transformer" makes me believe that they are really DC power supplies. Betcha it has a heat sink with fins that suggested the air cooled description.

    This really points to a problem with some people in this trade. To some, a transformer is anything that takes a higher voltage and reduces it to a lower one and that leads to all sorts of confusion.

    A transformer only works with AC and steps up or steps down the voltage. It is not (in our work) used with DC nor can it, by itself, produce a DC voltage. So if you come across a "box" that takes an AC voltage and produces a DC voltage it is a power supply. Don't call it a transformer. And if you are not sure check it with your meter!

    -Hal

  2. #12
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    180307-1736 EST

    If the transformer output is AC, then does anyone notice flicker from the lights? If AC excitation goes to the LED strip, then the LEDs are on for slightly less than 1/2 cycle at a pulse rate of 60 times per second.

    Another question is what is the PIV (peak inverse voltage) rating of the LED strip? How does this compare with the AC peak voltage?

    .

  3. #13
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    180307-2413 EST

    hbiss:

    Your post was very good. Greg1707 never provided very useful information, and he probably won't provide any more information.

    If we extrapolate from the measurements on my LED strip, 20 W for 8 ft, and assume double brightness (120 LEDs vs the 60 in my strip), then for 32 ft of lights at 24 V current would be about 160 W/24 V = 6.7 A. One might expect moderate life from a DC pulse width modulated dimmer rated at 8 A. But this depends upon real life conditions (heat transfer) and how valid is the manufacturer's specification.

    We don't even know if the dimmer was a DC dimmer, or if it was in a DC circuit.

    Far too much information was not provided.

    .

  4. #14
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    Yes, power supply or driver not transformer

    Quote Originally Posted by gar View Post
    180307-2413 EST



    hbiss:

    Your post was very good. Greg1707 never provided very useful information, and he probably won't provide any more information.

    If we extrapolate from the measurements on my LED strip, 20 W for 8 ft, and assume double brightness (120 LEDs vs the 60 in my strip), then for 32 ft of lights at 24 V current would be about 160 W/24 V = 6.7 A. One might expect moderate life from a DC pulse width modulated dimmer rated at 8 A. But this depends upon real life conditions (heat transfer) and how valid is the manufacturer's specification.

    We don't even know if the dimmer was a DC dimmer, or if it was in a DC circuit.

    Far too much information was not provided.

    .
    I am not sure why you would think I would disappear and not provide further information?

    I showed by ignorance about this topic by referring to the power supply or driver as a transformer. I have no experience in this area and just lumped everything together that changes or reduces voltage or current. I am glad to have this pointed out.
    So, yes, the LED lights were powered by a 24 volt DC power supply. All is working well. Thanks for the support.

  5. #15
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    180308-1344 EST

    Greg1707:

    Why? Because many posters want help and then never come back with feedback.

    That we now clearly know that the "transformers" are DC power supplies that helps greatly.

    We don't know where the failing dimmers were.

    If I have a DC power supply consisting of a transformer, rectifier, and filter capacitor, with a very large capacitor so there is little output ripple, then I can change the output DC voltage by varying the magnitude of the input sine wave voltage. Easy smooth control of DC voltage, it is proportional to input voltage. Basically the sine wave peaks determine the DC voltage because of the large output capacitor. If no capacitor, then the output is probably a half wave or a full wave rectified. If the load is a resistance then average DC voltage is the average of a sine curve. Full wave this 0.636 of the sine peak, and half wave is 0.318.

    If the input to said power supply is from a Triac type phase shift dimmer, then we only get dimming control with a phase shift to turn on of 90 to 180 degrees, and it is not linear with phase angle. But there is a further problem. The + and - half cycles must have exactly the sane average current. Otherwise there is a net DC current component and this will drive the transformer core into saturation. In turn either the dimmer and/or the transformer burns up.

    If the AC to DC power supply has a voltage regulated output, then over a reasonable change in input voltage there will be little output voltage change and thus input voltage adjustment is not a workable dimming approach.

    If dimming was done on the DC side of the circuit, then the DC dimmers were almost certainly overloaded, or a bad design.

    .

  6. #16
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    Quote Originally Posted by gar View Post
    180308-1344 EST

    [COLOR=#000000]...
    ...

    If dimming was done on the DC side of the circuit, then the DC dimmers were almost certainly overloaded, or a bad design.

    .
    One other remote possibility with low voltage, high current, wiring is that there were bad terminations or screw connections at the input and/or output of the dimmer module. Voltage drop there would both produce local heating and possibly require a higher current to satisfy the needs of the load (not the case with unregulated LED strips). That local heating would combine with the normal heat dissipation in the dimmer to potentially overheat it.

  7. #17
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    180308-1553 EST

    GoldDigger:

    Good point.

    On the Armacost LED Dimmer I obtained at Home Depot it has the following characteristics:

    1. It is in a small plastic box about 1.5 H x 2 W and 2.3 long.
    2. Not designed for heat transfer.
    3. Power connections are via a small Phoenix separable terminal block.
    4. Nice looking package.

    I have not looked inside. Without testing I would probably only loaqd it to 4 A. Half of the rqting.

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