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Electronics Diodes for controlling fan speed.

Discussion in 'Modding' started by scoob8000, 29 Jan 2008.

  1. scoob8000

    scoob8000 Wheres my plasma cutter?

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    So I've been doing a bit of reading on using diodes to slow fans down.

    Most reference the 1n4001 which is rated for a 1 amp load.

    What about controlling heavier loads (think water pump)? Could I use several in parallel or does that do something different? :)

    Or is there a better, higher rated diode with the same voltage drop?

    I've seen some rectifier diodes good for 30 amps, but I have no idea how to understand the voltage/current specs. :(
     
  2. veryevil

    veryevil Minimodder

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    Hi, all general purpose diodes will drop 0.7v across them. The 1N4001 is rated at 1 amp as do other diodes in the 1N4xxx series but they are rated for higher voltages.

    The 1N5400 is rated at 3A but will still drop 0.7v

    Using serveral 1N4001's in parallel will also handle more current but with the same voltage drop.

    What current rating is the pump?

    There are also other ways of changing the voltage on a fan / pump
     
  3. scoob8000

    scoob8000 Wheres my plasma cutter?

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    It's rated at 18watts max, so if my math is correct thats 1.3 amp at 12 volt.

    The diode bus appealed to me because I can pick a 6 position switch. Plus ease of design is another big plus for an electronics newb like me. :)

    I plan on building two for my new waterkeg, one to control the pump, and another to control the fans.
     
  4. veryevil

    veryevil Minimodder

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    Hi, you could either use a 3A diode for that for 2 1As but withe that you aren't going to get much of a drop in speed unless you have a series string of them. also you would have to work out the lowest voltage the pump would spin at under load.

    Also you would need to know the start up current as pumps / motors require more current on starting so 2 Amps current rating (2 1A in parallel might not be enough)
     
  5. ArcSpark

    ArcSpark Did I let the magic smoke out?

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  6. scoob8000

    scoob8000 Wheres my plasma cutter?

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    I just ordered a good handful of 1n5400's for $ .19 each.

    I'm not going to go all out with the pump, maybe 2 speed settings below full speed. I'm thinking 7volt mod for low, diodes for 9ish volts, and then full power.

    For the fans, I ordered a double pole, 6 position switch to build a diodebus, sans indicator led's.
     
  7. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    Paralleling diodes doesnt always work too well, diodes may not share the current nicely without a low resistance resistor in series to force them to "play nice" I.E. a .1 ohm or so resistor. But I would avoid using a resistor when you can still get a 3A diode for pretty cheap. If anything just for a neater circuit board.
     
  8. scoob8000

    scoob8000 Wheres my plasma cutter?

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    I can't believe I never found out about using diodes to drop voltage until now.

    They seem far superior to resistors for controlling fans in every way. Even superior to fan controllers,
    providing you don't need adjustability.

    I already have some neat ideas dreamt up. Instead of a rotary switch, use several micro toggle switches. Each switch you tick on, slows the fan down even more.

    Thanks for the help guys
     

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