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Variable High Current Power Supply

Discussion in 'DIY' started by Pipes, Nov 29, 2012.

  1. Pipes

    Pipes The guy with the Afterthoughts Accessory Maker

    Messages:
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    Location:
    Up there... some where...
    Finding a hard time finding that power supply that has the output you need?
    This little device can solve that for you. It has so many applications that I thought I'd throw the main idea out there and let imaginations run a muck.
    I was using ecigs in LV or 3.7 volt mode for some time when I started vaping and switched over to 6 volt when I bought my ThermoVape T1. Switching my inventory over to standardise seemed like a good idea. Now however, I have found the 3.7 volt system was better in many regards. Switching back was a pita and finding a 3.7 volt high current supply seems next to impossible.
    Found out about the OKR technology (Buck step down regulator) and went with it. What makes it so special is the efficiency is over 90% which means no heat sink needed. At least for our current levels anyway. The output is variable via a trim potentiometer and the size is sooo small. Really blows me away it can handle 10 amps.

    OK, so we have a variable regulator which can handle the current without a heat sink. I already posted about modding a car adapter and this is pretty much the same except using a standard step down CCTV type supply. In this case a 12 VAC 4.5 amp cube.

    Here are the specs of the OKR.

    [​IMG]

    And the block diagram.

    [​IMG]

    This is the schematic of the unit I put together. Note the resister is 150 ohm, not 1 ohm. (typo) The pots are 470 ohm.

    [​IMG]

    Basically, I wanted 2 presets which can be changed via a switch which is not easily accessible. Don't want to be burning up my stuff by mistake. Trust me, I do that too often as it is.
    I set it for 3.7 and 6, but could be anything you want. The capacitor in the picture below is
    220 mF capacitor but found it was too low. I ended up putting in a 2200 mF cap as the first one would cause the OKR to screw up under load. (too much ripple)
    Here is the power cube I used before modification:

    [​IMG]

    It is pretty strait forward with just a little circuit board with the wires attached and a fuse. I changed the fuse to a 6 amp in the mod.
    Got the rectifier mounted and the resistive board part made up here.

    [​IMG]

    A closer look at the resistive board. I re-used the board that was already in there. Also drilled some pilot holes for the access ports.

    [​IMG]

    Here the board is mounted. I used the JB putty weld to hold in place. That stuff is so cool.

    [​IMG]

    Getting close here. Only two wires from the resistive pack and wiring in the OKR. Once all wired up the OKR easily fit in the open gap in front of the transformer.

    All closed up and ready to rock.

    [​IMG]

    Adjusted for 3.7 volt, checked under load and had to tweak up to 4.5 volt without load to get 3.7 volt under load. This is a normal effect and was expected do to voltage drop along the output wire.
    Yeah, works great and let those manufacturers change their device voltages, I'm ready...

    Now as I said, there are many ways to use this puppy. Rechargeable 12 volt devices are common place and now you can mod those devices. Flashlights, boast assist batteries, camping stuff etc, etc,. Can even just make a box with an input that will take almost anything (within limits) in and give you an adjusted output. This would save having to open up an existing supply and finding realistate for the mod.

    The OKR can be found here for $10 a pop.

    Happy Modding,
    Pipes
     
    hektik8625 and charliedontsurf like this.
  2. Fully Melted

    Fully Melted It's OK to enjoy your medicine.

    Very nice way to build an inexpensive multi-voltage supply Pipes. Bravo! :clap:
    I like the switch idea! My supplies are fully VV but use a pot "lock" knob on the adjustment. That leaves mine open to inquisitive little fingers to play... I dig the 2 pole switch better. 10 amps with 90% efficiency in a Dc step down is pretty amazing.
    Is that 3N246 bridge rated at 1.5 amps?

    I just shot off a company email to muRata Power Solutions asking for 10 engineering samples. This will save me a ton as I'm using Delta VV supplies that cost $100 a shot to do the job of a $10 DC-DC converter! (but it's an item we stock at my business for a video device we build, so it was convenient but not cheap.)

    My hat is off to you Sir, good find.
     
    charliedontsurf and Pipes like this.
  3. Pipes

    Pipes The guy with the Afterthoughts Accessory Maker

    Messages:
    1,272
    Location:
    Up there... some where...
    Thanks FM.
    It is a nice unit in deed. The 3N246 in picture was just in the program I used, missed that. The rectifier I used was a KBU403G 4 Amp 300 V rating. Clipped it to a piece of aluminium and the enclosure presses it against the transformer core for a heat sink.

    I was thinking another easy power source could be a laptop power supply. They are typically 16 - 19 volts 3-4 amp. Should do fine for our needs here. Just need a small box containing the OKR and resistive bridge pack. To be fancy you could add a little LED volt meter. If intending to use under high current for prolonged time I would likely heat sink it somewhat. Another good use for that JB putty weld...? Gotta love that stuff.

    And for sure keep us posted how the unit works out for you. :nod:
    New territory is always nice having confirmed.

    Pipes
     
    charliedontsurf likes this.

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