constant current power supply

On a sunny day (Thu, 1 Aug 2013 06:48:21 -0700 (PDT)) it happened snipped-for-privacy@gmail.com wrote in :

No no, keep the beard, say goodbye to the wife.

>

There are many possible ways. I favor the brute force and simplicity of using an LM317 adjustable voltage regulator in constant current mode. It's probably not cheap enough for Jeorg...

Rather than try to ASCII sketch it here, I'll suggest you search for that - it in the data sheet, and it's available multiple other places on the web. You will need some sort of basic DC supply (roughly between 7 and 40 volts - 12 is often easy to find) to feed it - some sort of wall-wart or computer supply that's disused is usually the cost-effective approach rather than building one from scratch.

You could even get fancy and put a shut-off timer on it; or not.

--
Cats, coffee, chocolate...vices to live by 
Please don't feed the trolls. Killfile and ignore them so they will go away.

A 5-volt wall wart and a 50 ohm resistor should do it. The cheap USB power supply things are 5 volts.

I've found that the best shaving concept is to use cheap Bic or Walgreens disposable razors in the shower. I get my best ideas in the shower, so all that hot water is a business expense.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

Use a 6V wall wart and a series incandescent lamp to set the current. EASY! Gives indication of charging. Fails open circuit == safe.

Just get a new Norelco with a lithium battery. I'm using the "James Bond Spectra" edition and still get about 140 minutes per charge. Over the decade, blades probably add up to the cost of the razor.

Back in the day I also replaced the nicads, but only once per device. I think you would get about 5 years on the nicads, but after a decade you might as well get improved technology.

Norelco has great price fixing on those blades. Close to $30, while their top of the line razors are about $160 on sale, sometimes packages with a spare set of blades.

Norelco electric shavers. Two are rechargeable types with built in charger s, and two 1.2volt nicads. I've replaced the batteries in both of these por table units several times over the years and now it seems like 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 rietor y parts and since these are quite old I'm pretty certain that no par ts would be available.

and build a 50ma. constant current charger to use with each. I have been c harging my AA nicad's and NMIH's like this for years without ever having an y problems. I can remember to take them off charge after 14 hours or so.

aps point me in the right direction? Although I rather like it, my wife is getting tired of the beard. Thanks, Lenny

I found a circuit. Thanks everyone for the tips. I figure a 56 ohm resistor on the LM317 circuit should do it. Lenny

I have had phillips shavers for years, since we go away camping for long periods I just hook it up to 12v (vehicle, no current limit) and it charges ok. When the led flashes you are done. I would think a 12vdc wallwart would see you through ??

That's not a bad idea, those USB 5VDC are pretty cheap. But why even bother when you can buy something like this for $7 at WalMart or $9 at any drug store chain:

The resistor should be ~ 25 ohms, not 56 ohms, if you want

50 mA charge current. R = 1.25/I

Ed

Norelco electric shavers. Two are rechargeable types with built in charger s, and two 1.2volt nicads. I've replaced the batteries in both of these por table units several times over the years and now it seems like 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 rietor y parts and since these are quite old I'm pretty certain that no par ts would be available.

and build a 50ma. constant current charger to use with each. I have been c harging my AA nicad's and NMIH's like this for years without ever having an y problems. I can remember to take them off charge after 14 hours or so.

aps point me in the right direction? Although I rather like it, my wife is getting tired of the beard. Thanks, Lenny

You're correct about the 25 ohm resistor Ed. I built my charger circuit usi ng an LM317T. I set the current for .05A with a 22 ohm resistor, and it wor ks quite well with a supply of 12V +/- 50 %. So charging the shaver's batteries directly from a 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 tha t is from 120VAC.

I'm sure that I can figure a way to drop the AC line down to a safe operati ng level and then (hot), rectify and filter the DC to run the IC. And altho ugh Norelco was doing this, and as far as I can tell without power line iso lation, I would not feel comfortable with that arrangment.

A 12 volt transformer would be the most simple way to accomplish what I'm t rying to do, but I don't think I've ever seen one small enough to fit insid e the shaver. I have enough room for something that would measure about a o ne 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. I'm not experienced enough to try to design a sw itcher 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 any further assistance. Lenny