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Thread: cob led + mini transformer that can operate on 380/400/415v

  1. #11
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    Quote Originally Posted by MrFluffy View Post
    Given how generic and wooly the spec's are on these things are, It may even be possible to feed 380v to something rated at 280v max on its print label and it cope, but ignoring spec's seems like a bad thing in general to get into, even with chinese spec's...

    Holy grail would have been someone who's had the same issue chiming in saying "hey, this brand from xyz can cope with higher input voltages" and it be silk-screened or printed onto the label of them.
    100% guarantee that it is going to blow up if connected to 400v instead of 240v.

    Easiest way is to add small transformer(s) to supply lower voltage at xx volts.
    If you have stash of 230v transformers you can connect two of those in series for 400v operation.
    2pcs 230v-->110v transformers with primaries in series and secondaries in parallel would give you 95vac on secondary. Lots of switch mode power supplies and led drivers available with input voltage range starting at 90vac.

  2. #12
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    There are switching supplies rated for 480 VAC input, but they are usually three-phase and rated in kW, with cost over $1000.

    You may find DC-DC converters rated for EVs which may have input as high as 800 VDC, but they are also several hundred watts and dollars to match, although some may be available as salvage.

    There are also DC-DC converters rated for 100-1000 VDC input, with outputs of 5,12, and 24 VDC, and power of 5, 10, 15, and up to 40 watts, for about $60-$120:
    https://www.mouser.com/Power/DC-DC-C...e&Ns=Pricing|0

    Most control and machine tool transformers are available with 240/480 primaries, and power of 50-1000 watts, but tend to be heavy, bulky, and expensive for new units. Used ones might be pretty cheap and usable.

    It is possible to use two similar transformers with 240 VAC primaries wired in series, and secondaries in parallel, to divide the primary voltages equally.

    Two identical 85-265 VAC switching supplies might be wired with inputs in series, but you may need to add external balancing resistors or power zeners on their input capacitors to assure balance at start-up. The outputs in parallel on the load will usually cause equal current draw on the inputs to balance voltages.

    Here is a 60 watt power supply with 24 VDC output rated for 480 VAC input (three phase), for $59:
    https://www.automationdirect.com/adc...t/PSB24-060S-3

    They also have a 50 VA 240/480 primary 120/240 secondary control transformer for $40:
    https://www.automationdirect.com/adc...0_VAC/PH50MQMJ

    Another idea would be using a transformer with a high voltage secondary in reverse. Old TVs and radios often had plate voltages of 400-600 VDC produced by transformers, so you might find one with 300-0-300 VAC or 600V, so at 480 VAC on secondary it would provide about 95 VAC on the primary.

    Miscellaneous ideas:

    https://www.ebay.com/itm/AS-2T230-20...r/371663807251

    https://www.ebay.com/itm/AS-1T250-10...r/372195217634

    https://www.ebay.com/itm/120-208-240...t/122827679666

    https://www.ebay.com/itm/ZETTLER-AHR...6/360757587554

    https://www.ebay.com/itm/General-Sig...r/332622434099

    https://www.ebay.com/itm/CUTLER-HAMM...Y/222727978947

  3. #13
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    Quote Originally Posted by PStechPaul View Post

    Two identical 85-265 VAC switching supplies might be wired with inputs in series, but you may need to add external balancing resistors or power zeners on their input capacitors to assure balance at start-up. The outputs in parallel on the load will usually cause equal current draw on the inputs to balance voltages.
    Imbossibru.
    This sounds like disaster. This is a unstable combination that is doomed to fail because of imbalance in input side. This would work with unregulated power supplies like transformer but not with your typical SMPS.
    Because of the internal regulation in the power supplies they output roughly constant output power but the one with even a fraction smaller input voltage is going to (attempt to) draw larger input current. Larger input current leads to further voltage imbalance and that causes again increased current demand from primary. Unregulated SMPS would work but those are not too common.

  4. #14
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    Yes, I see what you mean. For a fixed load, a PSU will draw more primary current as the voltage is reduced, so its impedance will drop. A resistive voltage divider or zeners would be inefficient. Also, regulated supplies with outputs in parallel may "fight" each other, where the one with slightly higher output voltage will tend to supply all the load current, perhaps until it reaches an overcurrent limit shut-down. Isolating the outputs from each other with diodes will help some, but still not a good solution.

    If you have a transformer with two 240 VAC windings, you might be able to connect them in series as an autotransformer to provide a center tap on a 480 VAC source, and then two 240 VAC supplies could be used, one on each winding. There is still the problem of outputs in parallel, but you could use two 12V outputs in series to get 24 VDC.

  5. #15
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    Cost over $1000? I guess you did not check out the link to DigiKey that I posted above. Here is a 5 Amp supply that runs on single phase or on one of the three phases in a three phase supply.

    https://www.digikey.com/product-deta...088-ND/7707216

    DigiKey's price is $65.

    There were over 100 supplies in that link. When I narrowed the search down to 5A supplies I was still at about 25 to choose from, many of which were under $100.

    The building of ever better and ever less expensive power supplies (AC to DC) is one of the hot areas of electronics today. Prices for switching supplies are really reasonable. BTW, that $65 price from a top line supplier like DigiKey tells me that you can probably find similar items on the web for half that amount or even less. I guess the military and GM will pay $1000 or more, but certainly not I.



    Quote Originally Posted by PStechPaul View Post
    There are switching supplies rated for 480 VAC input, but they are usually three-phase and rated in kW, with cost over $1000.

    You may find DC-DC converters rated for EVs which may have input as high as 800 VDC, but they are also several hundred watts and dollars to match, although some may be available as salvage.

    ...<snip>...
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  6. #16
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    Quote Originally Posted by Paul Alciatore View Post
    If an LED ASSEMBLY is designed to run on a specific Voltage, then a Voltage regulated supply is just fine. We are not talking about naked LEDs here which would operate in current mode and somewhere between 1.5 and 3 Volts. A 24 Volt LED assembly, such as a COB, will have it's own current regulation and be just fine with that Voltage.
    ALL of the COB led's YOU linked from digikey need to be used with constant current supply.
    As an example the datasheet from Bridgelux COB:
    https://www.bridgelux.com/sites/defa...%20Rev%20J.pdf

    BXRC-xxx400x-D-7x model worst-case drive voltage at 1amp: hot 25,8v and cold 32v
    Driving one at constant voltage would result very dim led or burnt led depending on temperatures and product variation.

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