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How to Figure out What Power Supply to Use (Battery Conversion)

Discussion in 'Power Electronics' started by scl789, Jul 2, 2017.

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  1. scl789

    scl789

    6
    0
    Jul 2, 2017
    Hey guys,

    I have some motorized blinds that came with battery packs. Its 8 AA batteries in series giving me 12V to the motor. I want to do away with the batteries and hard wire them.

    Taking the thing apart a little... It shows the power requirement is .7Amp and 12v. This does not seem to be too common of a power supply. Any issue using a 12v 1Amp power supply? Or will it give the unit too much wattage and over work the motor?

    Next I have a little more complicated one... Its three blinds all on one window. I would have to run the wires all together. Do I need individual power supplies for something like this? Or can I splice all the wires together and get a 2.1Amp power supply? What would happen if I only moved one blind? Would that one bind get all 2.1 Amps?

    Should I be doing this another way?

    Thanks!
     
  2. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    Get a PSU that will deliver AT LEAST the sum total of the required current(s). The blinds will only 'take' what they need, no more, no less, so providing your power supply can deliver the MAXIMUM required (all three blinds running at once) then anything of that rating or larger will work.

    And yes, wire all blinds in parallel for the single supply connection.

    Check the power packs you have at home - many electronic items use a 12V DC supply these days and you may have a spare PSU lying around that you can use.
     
  3. scl789

    scl789

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    0
    Jul 2, 2017
    Great just what i wanted to know! Any issue splicing all three together and having one lead going into the power supply?
     
  4. scl789

    scl789

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    0
    Jul 2, 2017
    Another thought popped into my head... How far can I run the wiring for this? It's all 24awg wiring. The side with the three blinds coming together I might need to go 50 feet.
     
  5. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    It's recommended to keep the volt drop under 10%.

    In your situation you may (maybe?) never use all three blinds at once but assuming worst case.....

    The 2.1A total requirement would result in a 44% volt drop using 24AWG !!!!

    18 AWG gets this down to (near enough) the 10% mark so aim for that as a minimum requirement for a 50ft run.
     
  6. scl789

    scl789

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    Jul 2, 2017
    hmmm ok. I know this is for outdoor landscaping wire but would something like this work?
    https://www.amazon.com/dp/B00FASSTFA/ref=twister_B00LI1LAJU?_encoding=UTF8&psc=1

    Run 18 or even 16AWG from this to a busbar thats closer to the shades. Go 16AWG into the busbar and then 24AWG out to each shade? The shades have 24AWG going into them. I don't really have an option to switch that. If I do it that way... I would be about 15feet for the 24AWG. Or i could splice a lower gauge wire into the 24AWG wire closer to the motor. So come off motor at 24AWG run AWG for a foot and splice in 18AWG and go to the busbar.

    Thoughts?
     
  7. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    The original wire from the blinds can stay - anything over (say) 12-15ft and you should change to 18AWG.
    Don't forget that the current flow 'splits' at a certain point to enter the individual blinds. It's only the run from the power supply to the point at which you split it off in three directions that needs to be 18AWG.
     
  8. scl789

    scl789

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    Jul 2, 2017
    Any recommendation on a power supply to use?
     
  9. Audioguru

    Audioguru

    3,087
    692
    Sep 24, 2016
    I have a couple of wall-warts that are 12VDC at 1A and they are pretty big. If the current is higher than 1A then the size and weight will be too big for a wall-wart, its weight might keep unplugging it. A switched-mode wall-wart is very small and lightweight and if you find one it can easily be rated for 12VDC at 2.1A or more.
     
  10. dave9

    dave9

    1,003
    264
    Mar 5, 2017
    It should be kept in mind that although it looks like it's a 12V circuit, this is just the peak expected voltage.

    1) Losses aren't going to matter much for short intermittent duty.

    2) Voltage can drop quite a bit and it'll still work, remembering that it probably works down to 9V or lower, depending on the drag (friction), obstacles or how well it's lubricated or pullied. Assuming a typical budget grade brushed DC motor, current drops with voltage.

    However it seems rather crazy that there is no power within 50 ft. That would be a major inconvenience in a habitable area and I'd suggest that you (or an electrician if you are not confident in it or need it because of electrical codes) run a circuit to create a nearby AC outlet. Granted, substituting 18ga wire for a DC run would be cheaper and faster.

    As for a power supply recommendation, look on Amazon or eBay for a 12V, 3A PSU to run 3 in parallel. They're around $10, but you're better off picking one that's a major brand OEM for a laptop or tablet rather than a crudely made, low quality aftermarket one for those devices or LEDs.
     
  11. scl789

    scl789

    6
    0
    Jul 2, 2017

    I want to run all the low voltage to a central area in the basement. I could come down from the window and there is a plug right there, but if I don't want to see something plugged in all the time. There is nothing covering it.
     
  12. dave9

    dave9

    1,003
    264
    Mar 5, 2017
    FuZZ1L0G1C likes this.
  13. FuZZ1L0G1C

    FuZZ1L0G1C

    368
    117
    Mar 25, 2014
    Here you go.
    Some examples....
     

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