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power supply design question

Discussion in 'Electronic Repair' started by [email protected], Aug 4, 2013.

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  1. Guest

    Perhaps this isn't the forum for this but I thought I'd try. I have three Norelco electric shavers. Two are rechargeable types with built in chargers,and each having two 1.20 volt nicads. I've replaced the batteries in both of these portable units several times over the years and now it seems like neither one will charge it's batteries anymore.

    The third one uses the same 2.4 volt motor but it runs off 120VAC. That onehas a bad power supply as well. I have tried to repair these shavers but Ithink the problem on each one is in the hybrid circuit and/or other proprietory parts. And since these are quite old I'm pretty certain that no partswould be available.

    So I have built and am currently bench testing a .050 A. constant current source using an LM317T, (please refer to the link below). I set the charge current for .050A with a 22 ohm resistor, and it works quite well with a supply of 12V +/- 50 %. And as a bonus at this setting the chip does not require a heat sink.This test setup is currently charging two .600AH AA NMIH batteries. I plan on eliminating everything but the motor in each shaver, installing two batteries, a small switch, and building a small breadboard version of this 50ma. constant current charger to use with each shaver. I have been charging my AA nicad's and NMIH's off my adjustable current bench power supplies like this for years without ever having any problems. I can remember to take them off charge after 14 hours or so.

    So in theory using this arrangement, charging the shaver's batteries directly from an automobile cigarette lighter jack would work fine. And I can easily make that an option, however I would prefer to have the shaver work with the supplied coil cord as originally intended, and that is from 120VAC. One reason being (and perhaps it sounds petty) but it would be nice to be able to keep both the coil cord and shaver in their small zippered case and not have to add, (and bring) an external primary supply with me everywhere the shaver goes.

    Now I'm sure that I can figure a way to drop the AC line down to a safe operating level and then (hot), rectify and filter the DC to run the IC. And perhaps Norelco was doing this in each shaver, and as far as I can tell without power line isolation, I would not feel comfortable with that arrangement.

    So now to complete the project in a technically correct way, I need to comeup with a simple miniature isolated primary supply that will provide around 12.0 volts of filtered DC. and one that I can build into the shavers. I'mhoping that the old guts that I stripped out of each shaver will afford methat room. A 12 volt transformer would be the most simple way to accomplish what I'm trying to do, but I don't think I've ever seen one small enough to fit inside one of these shavers. I have enough room for something that would measure about a one inch cube.

    So, this probably sounds like a stupid question, but I have to ask. Does a 120V 60HZ transformer this small even exist? This primary supply would not even have to be regulated and the current requirements are miniscule.. I'm not experienced enough to try to design a switcher for this application. I would just like to keep this real simple if possible. Of course if I had a bit more real estate to work with this would be a non issue. Thanks for anyassistance. Lenny

    I 'm kind of liking the beard but the old lady is getting tired of it.
  2. wrote in message
    Your beard is part of your face. Your wife has no more right to ask you to
    shave it off than you do to ask her to bind her breasts.

    Stand up for your rights as a man. Don't let your wife emasculate you. (I'm
    not kidding.)
  3. Guest

    I was just joking man. It's not confrontational or anything like that. We both respect each others feelings. It was really nothing more than good natured ragging. But tell me more about this breast binding. That sounds like something I might be interested in. Lenny
  4. Guest

    That is really a novel idea. And it might work if I could find the right one and right size, however the board is arranged so that components are on one side and batteries are on the other. So the chance of finding a power supply from some other product that would just fit right is is probably slim.Lenny
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    Kalyan Ram Guest


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  6. mike

    mike Guest

    They make some pretty small usb chargers these days. The 5V PS that
    came with the magicjack isn't much bigger than a standard wall plug.
    No idea what's inside it.

    Surely you're aware that all this messing around is more trouble than going
    down to the thrift store and buying a shaver that's compatible with the
    heads you already have. Most have nothing more wrong than batteries.
  7. Guest

    I never considered the thrift store. While that would take the sense of accomplishment out of the equation, it would resolve the problem. But I wasn'treally looking for an easy way out, (that's probably become fairly obviousby this time), or another shaver for that matter.

    Anyway for the time being I've set up one shaver to charge at a 50ma. rate from a car cigarette lighter jack. Although this is a much lower rate than the OEM Norelco setup, It works quite well. The 12V cord with it's plug as well even fits in the leatherette case, so this too is a workable situation.. In the meantime I'll look for a small USB charger that can fit inside theshaver with it's batteries as well. Do you think that one would handle 50ma? Lenny
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