Electrical Tip from Wayne...

[Wayne 962]

Hey folks. In my youth, it took me a little while and several destroyed toys to figure this one out, and many people don't realize it today, so I thought I would share.

When working with electrical devices (let's for example say, a walkman) and you lose the electrical adapter. You want to hear some tunes, so you figure that you'd start looking at your big box of adapters from devices that have long ago broken to see if you can use one with the walkman.

The important thing to remember here is to match the voltage with the requirements of the walkman. I.E. if the device needs 9 volts, make sure you give it 9 volts. Not 12, not 15 and even not 7. 12 and 15 volts will probably cause the device to "fry" and break completely. At 7 volts, you may get erratic performance.

Match the voltage - all the time. This is what you need to be concerned about.

What about current? Well, that shouldn't make a difference, usually. In general, the device will draw as much current as it needs from the adapter, assuming that the maximum current output of the adapter is greater than the current draw of the device. If your walkman draws 400 milliamps, and the adapter is rated at 1 amp, then you're perfectly fine. Using an adapter with higher amperage output is fine too - the device will only draw as much current as it needs. The exception is when you have a device that uses a high current draw (like a laptop), and you have an adapter that is rated too small. Then, the adapter might overheat or fry and result in a potentially dangerous situation.

Along the same lines, this is the reason why you can use a small adapter to light a 12V light bulb, or you can hook it up to a car battery (high current flow device) and it will work fine too. The light bulb will only draw as much current as it needs.

A good analogy is your faucet. Think of voltage as temperature of the water - too hot at any flow rate will burn you. Think of current as the flow rate out of the faucet. To fill a small glass, you can use a big faucet, but you will only turn it on as much as you need.

I was just sizing adapters for an old laptop that I have here, and I was reminded that many people may not know this info...

Hope this helps someone.

-Wayne

[slodave]

Here's one to add.... If you happen to need to McGyver a supply, say you don't need the transformer (going battery power), you cut it away and assume that the broken white line on the wire is negative.... Well, TEST first!!! I *almost* fried an expensive piece of hardware.

[equality72521]

I've got one as well, as tested by a moron I used to work with. When testing a 9 volt transformer do NOT plug it into the receptacle and then touch the tip to your tongue like a 9 volt battery.

[Bill Douglas]

Mark, I can't stop laughing.

[rusnak]

Hmmm...here's a helpful tip that's pertinent to this thread.

If you're trying to hardwire a radar detector, cell phone charger, satellite radio, GPS nav system, or anything else that normally plugs into the cigarette lighter, you will have to find a resistor with the correct voltage output and amperage right? A big headache in most cases. Take the cigarette adaptor, knock the chrome off with a grinding wheel, and solder a wire directly to the tip of the adaptor and do the same with the side contact. Now you can crip on a bullet or spade connector to the other end of the wire, and you are now good to go. 12v to 9v with 1000ma? no problem!

And, your dash will look cleaner, and you can free up the cigarette lighter for emergency use only.

[Early_S_Man]

Another thing to double-check is whether the 'new' adapter supplies AC or DC, and if DC, what the polarity of the input jack is! There are still plenty of 9 VAC Hayes modem wall warts aound ...

[rusnak]

Early S, I'm not sure if you're referring to my post about the adaptors, but I was talking about the cigarette (car) adaptor that so many auto accessories come with these days (not the 911 heavens no - the truck, the Benz, etc etc all have these infernal devices).

Anyway, yes you do want to check polarity on your cigarette lighter before completing the wiring in the dash. And the final step to the soldered adaptor thing is to wrap it with electrical tape, or do what I did and buy some huge heat shrink tubing and seal it all up. It provides support for the solder, and keeps water out. Then you just tuck in in the knee pad out of sight.

[Early_S_Man]

rusnak,

No, actually I was referring to Wayne's original post and AC adapters for laptops, etc.

One other note ... there are a TON of wall transformers and desktop [middle of the cord style] power supplies out there at the surplus electronic stores and mail order suppliers. Generally, the ratings for both Voltage and current are given, so it is entirely possible to shop around and find a cheap power supply with proper ratings for $10 to $15, or less.

[Wayne 962]

Plus Radio Shack sells a universal one with 6 or 7 tips on it that you can switch to different voltages. Those go for about $20. Much easier than trying to find one that matches the proper voltage, and connector plug...

-Wayne

[gduke]

So, Wayne I should be able to replace my 2.6amp batteries for my cordess drill w/ 3.0 amp batterries when they wear out and have longer use of the drill?

Gary

[drl911]

Originally posted by gduke
So, Wayne I should be able to replace my 2.6amp batteries for my cordess drill w/ 3.0 amp batterries when they wear out and have longer use of the drill?

Gary

Your cordless tool batteries are labeled in units of volts and amp hour. And yes, they will last longer given you are comparing from the same brand of power tool. Some power tool manufacturers are less ethical in their battery labeling than others.

Dan

[Early_S_Man]

Gary,

The typical cordless drill battery pack has 2.4 A-h 'sub-C' Nicads in it ... which can be replaced by identically-sized sub-C 3.3 A-h Nimh cells. They are a bit pricey, but the longer runtime should be a better investment than a replacement battery pack from the mfr!

[drl911]

Beware that power tool OEM chargers from the various manufacturers are not all designed to specifically work with NiMH batteries. Same goes for Lithium Ion batteries.

Dan

[Scooter]

And this is Porsche technical how?

[David]

I had the hardest time with my first EE course as an ME student. The prof was pure EE and couldn't relate to the few ME students in the class. Finally someone explained the water in a pipe analogy and it all made sense. Strange how mechanical guys and electrical guys think completely different.

[Jim Sims]

It is pitiful how few know something as simple and basic as Ohm's law and have a physical understanding of what it means. This is junior high or at best high school level physics. Thirty years ago it was taught and understood everywhere, even out in the darkest fields of the republic. The football players in class understood it. How many today even know what a Thevenin equivalent is? Lost and gullible souls now abound in a world built on science and technology. They do know though that "Britney" has shaved her head.

[ZOA NOM]

Norton & Thevenin. We aren't in Kansas any more...

[porsche930dude]

britney shaved her head?
Wayne thanks for the info. I was thinking of converting the charger for my rc car from battery power to ac but wasnt sure what to look for in a adapter. you info is exactly what i needed thanks

[911pcars]

An additional note on chargers/adapters. "Universal" adapters provide different levels of voltage via a built-in switch for 3, 5, 9 and 12 volts and adapter plugs for the various jacks found on electronic devices (cell phones, calculators, low-voltage lamps, MP3/CD players, self-powered speakers, etc.)

Besides confirming the adapter can output the required voltage and current for the device, make sure the polarity of the plug matches the polarity requirements of the accessory jack. The tip and ring polarities must match, otherwise you risk the chance of destroying the accessory (similar to hooking up a car battery backwards). Pay attention to the symbol next to the input jack so you can set the appropriate switch on the adapter/charger.

Here's a somewhat related thread here.

Sherwood

[Zeke]

Originally posted by Jim Sims
It is pitiful how few know something as simple and basic as Ohm's law and have a physical understanding of what it means. This is junior high or at best high school level physics. Thirty years ago it was taught and understood everywhere, even out in the darkest fields of the republic. The football players in class understood it. How many today even know what a Thevenin equivalent is? Lost and gullible souls now abound in a world built on science and technology. They do know though that "Britney" has shaved her head.

Well, since this is OT anyway.....

Jim, do you know any musicians? Can you read the grain of a piece of lumber and know which way it will warp or cup? Can you tell how much thinner to add to a bucket of paint by the feel of the brush (the first time and get it right)? Can you sketch in perspective? Do you cook w/o recipes?

There are many of us that don't excel in areas that are not all electrons, 1's and 0's, etc. I appreciate your contribution to the bbs each and every time until you say that anyone who cannot dispense on Ohm's law is sub par.

Now, without the benefit of using google (or another search), Ohm's law states something about volts and amps being divisable by current (and maybe that's way off). None of this can be observed as water in a pipe at different temps. It may be objective, but it's obscure to many.