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PWM cap and power supply questions

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  • #16
    For those who are electrically or electronically challenged, the best way to do this might just be the battery and charger route. I would still add a can type capacitor and a film or ceramic type, as Paul suggested, near to the regulator. I would be looking for a charger that can go into trickle mode and be left on and connected to the battery. The battery solves some of the thorniest problems that come up with various power supplies. One big advantage is that high surge currents can be drawn, whereas a power supply can do any number of unwanted things if a large current surge is asked for. It can shut down, go into oscillations, pass high ripple currents, overheat in a couple of differest areas, and in the case of a switching power supply, such as found in a computer, it can end up frying it's own capacitors. This leads to noisy operation and poorer regulation, and intermittent operation, amongst other things. A motor controller might go berserk under some of these conditions, and you may have no way of knowing if something is wrong, except that 'it isn't working right'. A non electronical type person could have a difficult time with this.
    A 'smart' battery charger won't have to supply the high peak currents that may be required to start motors, etc, and with the battery connected, the regulation is pretty good already without electronics. This is of course assuming that the voltage you need to start with is in the area of 12 to 14 volts. Another bonus of the battery system is that you have the option of an emergency light in case of power failure. My basement shop gets very dark since there are no outside windows into that room. I for one would actually be getting triple duty from the battery, since I am soon to be powering two cordless drills from a battery in the shop. Their battery packs are shot and not worth the cost to replace, but the drills are still fine. Hmm, I see another application of those cordless-cum-corded drills- driving a leadscrew-
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


    • #17
      Wow! Lots of good info guys!
      Paul...I phoned as soon as I saw your post. Radio Shack doesn't carry ANY books anymore. Too bad...that sounds like it would have been something I should read. But then again I now have plenty to read right here! I just don't want to get into this thing for anymore money until I find out if it will work. My mill has a low speed of 120 rpm spindle speed and the quill feeds at .100" per revolution of the worm drive. This setup is hopefully going to be used for boring and some drilling. I've done some boring with it and it worked pretty good but trying to turn the handwheel at a constant speed is really tiring after awhile. If the thing works then I'll spend some loot on it on the right stuff. It's tempting to just buy it all from the US but it all costs me double by the time it lands here. Right now I'm into this for a couple hundred bucks....I don't really want to add a $500 power supply if the whole thing flops. Oh ya...and I blame this all on doctors and scientests...they have pills for you if your riggin doesn't work, they have pills to speed up or slow down your heart...why don't they have pills to counter "Electrical Dummassedness"
      Thanks again guys.
      I have tools I don't even know I own...


      • #18
        darryl: "cordless-cum-corded drills"

        That sounds personal.
        Super Dave


        • #19

          What voltage and current do you need - I probably have something you can have for the taking AND I can supply you with nearly anything you need in a capacitor for free - I just need to dig it out of storage.

          Don't use a battery charger! You can damage the PWM cicuits with a ****ty battery charger - they are NOT 12V power supplies! You are better off using a computer power supply. They are already highly regulated and quite clean, and relatively effecient. But like I said, just email me I have all kinds of linears and switchers - all you need to do is grab it - honest.

          Tantalums are traditionally used for the HF supression duties due to their high performance but are being replaced by the new rare earth units which are smaller and higher capacity (cheaper too and surface mount as well)

          [This message has been edited by Thrud (edited 01-05-2005).]