power supply design question

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.)

Norelco electric shavers. Two are rechargeable types with built in charger s, and each having two 1.20 volt nicads. I've replaced the batteries in bot h of these portable units several times over the years and now it seems lik e neither one will charge it's batteries anymore.

ne has a bad power supply as well. I have tried to repair these shavers but I think the problem on each one is in the hybrid circuit and/or other prop rietory parts. And since these are quite old I'm pretty certain that no par ts would be available.

source using an LM317T, (please refer to the link below). I set the charg e 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 re quire 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, i nstalling two batteries, a small switch, and building a small breadboard ve rsion of this 50ma. constant current charger to use with each shaver. I hav e been charging my AA nicad's and NMIH's off my adjustable current bench po wer supplies like this for years without ever having any problems. I can re member to take them off charge after 14 hours or so.

ctly from an automobile cigarette lighter jack would work fine. And I can e asily make that an option, however I would prefer to have the shaver work w ith 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.

perating 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 wi thout power line isolation, I would not feel comfortable with that arrangem ent.

me up with a simple miniature isolated primary supply that will provide aro und 12.0 volts of filtered DC. and one that I can build into the shavers. I 'm hoping that the old guts that I stripped out of each shaver will afford me that room. A 12 volt transformer would be the most simple way to accompl ish what I'm trying to do, but I don't think I've ever seen one small enoug h to fit inside one of these shavers. I have enough room for something that would measure about a one inch cube.

a 120V 60HZ transformer this small even exist? This primary supply would no t 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 a ny assistance. Lenny

William I was just joking man. It's not confrontational or anything like that. We b oth respect each others feelings. It was really nothing more than good natu red ragging. But tell me more about this breast binding. That sounds like s omething I might be interested in. Lenny

-- snip --

So don't design a switcher; use one out of a wall-wart cell phone charger. 5 volt 0.5 amp ones are common. There's generally a resistor or Zener you can tweak to adjust the voltage, but how much higher you could go, I don't know (depends on the specific SMPS, too).

Isaac

Norelco electric shavers. Two are rechargeable types with built in charger s, and each having two 1.20 volt nicads. I've replaced the batteries in bot h of these portable units several times over the years and now it seems lik e neither one will charge it's batteries anymore.

ne has a bad power supply as well. I have tried to repair these shavers but I think the problem on each one is in the hybrid circuit and/or other prop rietory parts. And since these are quite old I'm pretty certain that no par ts would be available.

source using an LM317T, (please refer to the link below). I set the charg e 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 re quire 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, i nstalling two batteries, a small switch, and building a small breadboard ve rsion of this 50ma. constant current charger to use with each shaver. I hav e been charging my AA nicad's and NMIH's off my adjustable current bench po wer supplies like this for years without ever having any problems. I can re member to take them off charge after 14 hours or so.

ctly from an automobile cigarette lighter jack would work fine. And I can e asily make that an option, however I would prefer to have the shaver work w ith 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.

perating 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 wi thout power line isolation, I would not feel comfortable with that arrangem ent.

me up with a simple miniature isolated primary supply that will provide aro und 12.0 volts of filtered DC. and one that I can build into the shavers. I 'm hoping that the old guts that I stripped out of each shaver will afford me that room. A 12 volt transformer would be the most simple way to accompl ish what I'm trying to do, but I don't think I've ever seen one small enoug h to fit inside one of these shavers. I have enough room for something that would measure about a one inch cube.

a 120V 60HZ transformer this small even exist? This primary supply would no t 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 a ny assistance. Lenny

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

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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.

I never considered the thrift store. While that would take the sense of acc omplishment out of the equation, it would resolve the problem. But I wasn't really looking for an easy way out, (that's probably become fairly obvious by 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 the shaver with it's batteries as well. Do you think that one would handle 50m a? Lenny