dumb question volts/amps - how much is too much?

Typically, a device "pulls" what it needs for a lack of a better way of describing it. For instance, a battery capable of powering the space shuttle at 12V could also start my motorcycle, but not the other way around.

"Joe AutoDrill" on Tue, 26 Apr 2011 14:28:03

-0400 typed in rec.crafts.metalworking the following:

Ah, so "one way of thinking about it"is that - yes, the wall wart can supply up to 1 amp at 12 VDC, but the router is only going to use half an Amp.

Thanks.

Now to see if I let the magic smoke out. (I've been told by Electrical Engineers, that electrical items run on smoke, and letting the smoke out is what causes them to fail.)

tschus pyotr

pyotr filipivich fired this volley in news: snipped-for-privacy@4ax.com:

But the other way of thinking about it is that some Wal Warts are not regulated. If not, and you do not draw something near to their ratings, they may damage the powered equipment by supplying too high a voltage.

The little lightweight switching supplies are almost always regulated, but the heavier transformer-based units are often just a transformer, bridge rectifier, and filter capacitor; Their outputs can vary 50% from the rating at full load.

LLoyd

Yes, more than likely. Make sure that the supply is regulated (just stick a voltmeter across it without a load and read the voltage if you're not sure- it should read 12V within a fraction of a volt). If it weighs only a few ounces, it's a switching supply and they're virtually always regulated.

It's instructive to see what happens to a wall-wart when you abuse it. If you short the output of one, most of them will fry themselves in an instant from the current overload.

I've done that for entertainment when I no longer have use for them. I have too many in my junk box as it is. I have two of them that did not. The transformers in them must be so pathetically underbuilt that they just buzzed. Most of them are somewhat self-limiting by virtue of extreme transformer inefficiency, but most in my limited experience will not tolerate a direct short.

Regarding the motor, if you supply too much voltage, you probably will get a surprise regarding that 1/2 Amp.

That's because they are almost always with Underwriters Labs as being a "current limiting device" and as such they are actually designed to fry in an overcurrent situation--and the main reason they are so prevalent these days is exactly because this...IE, in many situations it allows manufacturers to circumvent agency certification so long as the device is sold along with a "listed power supply"....essentially making it faster, easier and less costly for manufacturers to bring new electronic items to the marketplace..

That said, beware of "counterfiet UL stickers", items imported from Communist China being notorious for this particular consumer fraud.

:Xns9ED399F9754E7lloydspmindspringcom@216.168.3.70...

Boy, Ed, you sure are easily entertained.

Many of these things have fusible links under the first layer of tape in the transformer, others have "polyfuse" type circuit interruptors. Would you prefer, perhaps, that they supply unlimited current and just catch fire when you short them?

BTW, regarding the original question: Yes, a properly working device will draw only what current it needs from your 12V supply (assuming it's putting out something near 12V), but the designers sometimes rely on the overcurrent protection built into the supply rather than spending the extra $0.25 to put a fuse in the router. So, if you had a fault situation in the device and it was connected to a larger than expected supply, you *could* have a fire. In reality, it's unlikely; at the currents your talking about (0.5A vs 1.0A) it's virtually impossible, but I've seen installations which have large numbers of consumer-grade devices connected to a single large supply, and that sort of thing could be a problem.

I used to tear the wings off of flies, until I discovered RCM.

It would be fun to watch. d8-)

More or less correct. However I'm betting that the router doesn't even need 12 volts. Probably that has a LOT of overhead in it. Most electronics out there use around 5-6 volts. The extra allows for voltage sags, spikes due to other items starting up. If you opened the router the first items in the power feed will likely be a couple of capacitors and a couple of regulators. Likely a 7805 type with maybe a 7905 if it also has a negative rail.

Most routers that I've seen use a switching power supply to knock down an input voltage (5 or 12VDC) to 3.3VDC and lower for most of the juice.

Here's a typical one-chip switch (not router)

138 has the current requirements..

up to 22mA typical at 3.3V = 73mW up to 330 or so mA typical at 2.5V = 825mW up to 150mA typical at 1.5V = 225mW

plus more for power supply losses, LEDs etc.

Best regards, Spehro Pefhany

Most wall warts are not regulated and are meant to produce proper voltage at the operating current. They may supply higher voltage at lower current.

i

Ignoramus7326 fired this volley in news:08OdnVkhQOc60SrQnZ2dnUVZ snipped-for-privacy@giganews.com:

That may have been true in the past, but more and more we're seeing the switching variety, now that they've included the switching transistors on the control chips.

Usually, now, you'll see electronics powered by switchers, and DC motor- driven appliances by the dumb type. But with the cost and manual labor associated with assembling a transformer, I expect more will become switchers, even for the motor devices.

LLoyd

"Probably" - but all I know is what I can decipher off the sticker. B-)

No motor in a router - not in the computer type anyway - and a 12 volt 1/2 amp Motor type router is only 6 watts, or roughly 1/100 hp.

The 12V 1A rating is the maximum it's rated for. For example, it's common for a 120V circuit breaker to be rated for 15A, that doesn't mean your clock will draw 15A, it just the most you can draw from that circuit. So, a 12V

1A supply can supply 12V at UP TO 1A, 0.001A should be fine as long as there isn't a minimum rating on the wall wart. Your wall wart should be good for supplying 12V from 0 to 1A. Using 0.5A, no problem, trying to use 2A will give you problems.

RogerN

Supply verses demand.

The wart can supply an amp. The router only draws 1/2 amp. Live is good.

If the draw approaches the supply's capability things get if-ier. At some point the draw will pull the voltage down below spec. At some other point that will really suck.

Letting the magic smpke out causes the house to smell bad!

Think of voltage as the Pressure.

Current is the flow based on the pressure and the resistance to that pressure.

In other words - the voltage sets the current flow on a load. The router uses 12v and has a resistance (simple terms here) that draws 1/2 an amp - so the wall wort runs in idle.

you might have a faster starting speed - that might not be good. It might not matter. Start current is higher than run current.

The wart can handle the higher currents when starting and when loaded.

Mart> I've a wall wart which is rated 12 V DC at 1 amp output

Yes, that's correct.