On Sun, 2004-01-25 at 13:31, Andrew Prince wrote: Make sure you get one with an AC adapter... The first two EX 3's I looked at didn't seem to have have AC adapters... TTFN Andrew

Doc... this is a BAD idea... I've fried numerous devices by using the wrong power rating... even if it was only 1mA off. The voltage almost never matters... as long as the power is correct. Hope this gets to u before you fry your machine. Lyos Gemini Norezel Doc Shipley <doc(a)mdrconsult.com> wrote: Funny coincidence, there. I just hacked a Sprint CAD-1000 AC adapter onto a JetDirect Ex+ last night. The receptacle of the JD is odd, so I had to pull the board and solder the adapter direct. Other than that, it's the right voltage, and a little over-amped (1A vs the JD's rated 800mA). --------------------------------- Do you Yahoo!? Yahoo! SiteBuilder - Free web site building tool. Try it!

This is true only of well-regulated supplies. Wall-warts (which is the form of power supply I thought we were talking about here) often are not well-regulated. A wall-wart rated at 6V 750mA is reasonably likely to supply well over 6V if used to power a device that draws only 150mA. Sometimes this doesn't matter. But sometimes it does. Of course, if we're not talking about wall-warts, but instead talking about properly regulated supplyes, never mind. /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

Lyos Norezel wrote: Ack! I typed a 20 line response about punchthrough and electrolitics and slew rates, But then I realised that it was like trying to teach my houseplant calculus. Career tip: If you want a job with electricity, become a electrician. Jim Davis.

Andy Holt wrote: Engineers that design such crap as in the later example should have their arms and legs broken and thrown into a cold, fast moving river. Regulators are pennies and what about over/under line voltage? Jim Davis. I smell a wampus!

Perhaps people need a DMM so they can check polarity, or maybe get glasses to read the markings? OMG, this is the funniest thread I've read in a while. True story: My sister last year was trying to plug in a computer modem after moving some things around. I think the input is 9V DC, well she grabbed the cord from the HP inkjet that happened to be the same size, but pumps out *24V*! All of a sudden we hear screaming and she comes running down the stairs screaming "THE MODEM IS SMOKING!!!!!!!!!!!!!!!!!!!" Now THAT is funny. Don't ask me how, but she didn't fry the modem(not totally anyhow, it still powers up OK). -- ------------ John Rollins | KD7BCY | http://www.kd7bcy.com DALnet #Apollo_Domain | Ham-Mac mailing list http://mailman.qth.net ------------

Well, not quite; voltage is one of the factors determining current. Impedance is not just a fancy word for resistance, except possibly when you're working with pure DC. A more accurate way of putting this is that the design relied on the voltage sagging under load; speaking of the power supply's internal impedance amounts to modeling it as a perfect supply (one which sustains its output voltage under any load) in series with a resistance, or more generally impedance, which "explains" (more accurately, "describes") the voltage drop under load. This is of course not a perfect model, but it's good enough for many purposes - especially since many of the mechanisms that produce the effect are due to internal resistances. This is, strictly speaking, nonsensical, though there is a grain of truth lurking in it. First, I should note that this discussion plays a bit fast and loose with terminology. Strictly speaking, what I'm saying here is true only when either the current flow is pure DC, with no AC component, or when the load is purely resistive, with no inductive or capacitive component. But for most purposes it's a close enough approximation to be workable. If the voltage *at the device*, *under load*, was the same, then there would be no difference. When you say "allowed more current to flow even though the voltage was the same", the truth there is more like "allowed more current to flow *under load* even though the voltage *without load* was the same". This is the "grain of truth" I referred to above. The reason I say it's nonsensical is that if your statement is taken as applying entirely to things under load, it simply won't work that way. Here again - the design was expecting the voltage to sag under load, "because of" (more accurately, "as can be described by") the internal impedance of the batteries. That is, the voltage was _not_ the same when it mattered - under full load - even though it may have been close enough to the same under no, or light, load. /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

Close, but although both are measuered in Ohms, impedence includes another factor: Phase. Resistance is non reactive. That is, it does not change with the frequency of the source voltage. Impedence is a combination of resistance and reactance (capacitive and/or inductive), and along with phase, can change with the frequency of the applied voltage. -Bryan

At 01:22 PM 1/26/04 -0700, you wrote: I take exception with your reply! While technically true, in this case we were clearly talking about a battery powered telephone therefore we're talking about pure DC with no AC. Therefore phase, frequency and impedence are irrelevent. Throwing in the talk of impedence just to show off is only confusing the issue. The orginal poster that thought voltage didn't matter clearly doesn't clearly understand electricity and I didn't won't to confuse him further by introducing AC and it's effects. Joe

At 05:21 PM 1/26/04 -0800, you wrote: Actually it's not all that complicated. You just have to know something about what you're doing and use some common sense. The one serious gottcha that will get you is when the load expects to have a significant resistance (or impedence) in the power source. Most (99%) loads don't care and 12VDC is 12VDc no matter what the source but if you connect a low impedence source (like a lead acid battery) to something that expects a high impedence source (like the photo flash that I mentioned) then the device will draw too much current and fry itself. However I've found very few things that operate that way. I keep a BIG box of wall warts and plenty of batteries around and I've made up hundreds of power supplies using non-original wall warts and/or batteries. As far as I can remember, the photo flash was the only one that gave me trouble. You definitely need to know if the device needs AC or DC and what polarity. But that's frequently marked on the chassis or the old wall wart. in fact, in the US it's required to be marked by law. If it's not marked then you have to open up the device and look at the power input circuits. Does it go to a rectifier circuit or transformer? If so then it uses an AC input. If it connects **directly** to rechargeable batteries, logic circuits or to three terminal regulator or across a capcitor then it uses DC input. You can look at the input device and get the polarity. Count the number of cells in a battery pack and multiply by their voltage (~1.3V/cell for NiCads) and that will tell you the minimum input requirement for that circuit. Raise that by about 20% to force the batteries to charge and it should work fine. Capacitors are almost always marked for polarity and voltage. Derate the voltage about 2/3 and it will almost certainly work. Logic circuits have well known voltage input levels. Look up their specs if you don't know what it is. I shouldn't have to explain that. You can get the model number from the three terminal regulators and look at the specs and get the absolute maximum input voltage and output voltage. Feed it a voltage at least 1 1/2 volts higher than the output voltage but less than the absolute max and it will work. But be aware that anything over Vout plus ~1 1/2 will be converted to heat so you may need to stay under the maximum just to prevent excess heat dissapation. The 1 1/2 volts is a typical number, if you really want to be precise, look up the exact value in the specs. They do make regulators that drop as little at .1 volts. But in most cases the regulator will be a common 780x and 1 1/2 volt drop will work fine. Or if you like, connect a variable DC supply to the input and monitor the output while you slowly vary the input voltage. You'll quickly find the point at which the regulator output starts to drop. That input voltage will be the minimum input voltage. Again, you can get the Vin Max it you stay within a reasonable amount (+50%) of the minimum you won't have any trouble. This procedure will take care of 95% of the cases. Joe When you voltage.

Funny... I powered a very old typewriter with more than 50V over the stated rating. The rating for the Amps matched EXACTLY and it ran like a dream until recently when some water got into the PSU, BTW this is a WELL regulated unit... refusing to be off by more than half a volt. I did the same with a more recent device (a digital thermostat used to control certain devices in my bedroom)... and recently that device fried when I had to get a new PSU. The power rating was still 50V over rating and I got one that was just a little over the rated amps (I forgot to check) and plugged it in... when I turned it on all hell broke loose. What do you have to say to that? *mumbles* buncha smartass know-it-alls... why in my day... *continues inane rambling* Lyos Gemini Norezel John Rollins <kd7bcy(a)teleport.com> wrote: Perhaps people need a DMM so they can check polarity, or maybe get glasses to read the markings? OMG, this is the funniest thread I've read in a while. True story: My sister last year was trying to plug in a computer modem after moving some things around. I think the input is 9V DC, well she grabbed the cord from the HP inkjet that happened to be the same size, but pumps out *24V*! All of a sudden we hear screaming and she comes running down the stairs screaming "THE MODEM IS SMOKING!!!!!!!!!!!!!!!!!!!" Now THAT is funny. Don't ask me how, but she didn't fry the modem(not totally anyhow, it still powers up OK). -- ------------ John Rollins | KD7BCY | http://www.kd7bcy.com DALnet #Apollo_Domain | Ham-Mac mailing list http://mailman.qth.net ------------ --------------------------------- Do you Yahoo!? Yahoo! SiteBuilder - Free web site building tool. Try it!

On Monday 26 January 2004 23:22, Lyos Norezel wrote: AAAAHHH!!! And just when I thought this thread was over. :( Pat -- Purdue University ITAP/RCS Information Technology at Purdue Research Computing and Storage http://www.itap.purdue.edu/rcs/

You are using WALL WARTS that are over 50V????? Hardly any wall warts are rated for submersible use! In the future, don't put water into them.

Upon the date 01:49 AM 1/26/04 -0800, Lyos Norezel said something like: Exactly. No! Please!! :-/ I respectfully request you yourself visit your local electrical technology teacher or an electrical engineer you know well and present your interpretation of the effects of current supplied by a power supply upon a device which you had presented to us in this thread. Stand back and watch how s/he responds. Christian Fandt, Electronic/Electrical Historian Jamestown, NY USA cfandt(a)netsync.net Member of Antique Wireless Association URL: http://www.antiquewireless.org/

First fundamental error : 'volts' do no run through anything. A voltage is measured across something. Currents run through things. OK, IIRC, the short circuit current of an alkaline (Duracell-like) D cell is about 6A. Care to explain to me why you are not instantly killed by this current if you touch the ends of such a cell (To the rest of you, _I_ know the answer, OK...) Similarlly I would be _very_ wary of touching the output of a power supply that could continuously supply 1kV at 0.4mA. I would guess it would quite happily supply 0.5mA for long enough to kill me! You know, I have a PSU on my bench that will supply up to 8A continously. I have _never_ fried anything by using it, unless I cranked the voltage up too high. The fact that it _can_ supply 8A doesn't mean it's going to do so if given a single 7400 as a load. Similarly, I just said that the short-circuit current of a D cell was about 6A. A typical torch (flashlight to you) might have a bulb that draws 300mA in it. Why doesn't this burn out instantly at switch-on? OK. Did you check if the adapter needed was AC or DC? If the latter, was the polarity correct. There are many reasons why the wrong adapter may do damageg, but having it capable of safely supplying 1A rather than 0.8A is not one of them! At least in the UK, schoolteachers are not a reliable source of information. People who have been doing electrical and electronic engineering for 30 years or more tend to be. And there are plenty of such people on this list. -tony

Jim Battle <frustum(a)pacbell.net> wrote: Lyos -- Power supplies are almost always supply constant voltage, not constant current. The current rating is the maximum amount of current they can supply while still nominally achieving their specified voltage rating. If you hooked up a "5V 1000A" power supply to something that normally required "5V 350 mA", nothing bad would happen. Your high school electricity teacher is groaning in shame right now... please go consult him/her. Lyos Norezel P.S.-see other post --------------------------------- Do you Yahoo!? Yahoo! SiteBuilder - Free web site building tool. Try it!

Er... what? The voltage rating is the value you need to worry about. If you put a 16V supply on a device that needs 5V, you're gonna smoke the device. As for the current rating, the device will not draw more current from the PS than it requires, so as long as the supply is rated at or above your requirements, you're okay. It won't smoke your device if the current is exactly the same. --------------------------------- Do you Yahoo!? Yahoo! SiteBuilder - Free web site building tool. Try it!

Geoff Reed wrote: Bwahahaha, I've written 10 replies, but canceled them all, because I can't teach a house plant calculus. You Win. I need to teach my 10 yo daughter more electronics, so she doesn't get hooked up with whoever is feeding this person such balony. It sounds like scientology or orgon energy! Jim Davis.

At 04:27 AM 1/26/2004, you wrote: I kept writing responses (and deleting them), and finally decided that my last statement covered it pretty well :)

Lyos Norezel wrote: WHAT??? I can see an under current supply getting pulled down and causing the evil bug in the LM309K and other vintage regulators to start that self destructive activity. But, too much current is a GOOD THING, Unless you have a short, then, well. But No, You are wrong on multiple levels. Are you a troll? Jim Davis.

However, rememebr that the dissipation of a linear regulator (like the 7805) increases with the input voltage. IIRC, the 7805 is specified to work on a 7V to 35V input, and will supply a maximum current of 1A. The output, of course, is 5V. Now, if we give it 7V on the input, the power dissipated (neglecting the small amount used by the 7805's control circuitry) is (7-5)/1 = 2W If wie give it 35V, the power dissipated is 30W. The former may well be OK with a fairly small heat sink, the latter will almost certainly cause things to overheat. So please don't think a 35V AC adapter is safe just because there's a 7805 in there. In gneneral, such devices use AC adapters with internal regulator circuits. You _must_ use a regulated adapter with them. -tony

On Mon, 2004-01-26 at 15:26, Doc Shipley wrote: Yup. Many years of running things of bench PSUs have taught me this. That's not to say I've never fried stuff, but usually only when I've inadvertently wound it up to +/-30v and really cooked stuff. Current has never been a problem (although running my fully loaded Acorn Atom did make the bench PSU heat up quite a bit). Gordon.

On Jan 26, 2004, at 1:32 PM, Tom Jennings wrote: Thank you all, and if anybody cares, after 24 hours of fairly heavy use neither the adapter nor JetDirect proper are more than mildly warm to the touch. One very nice thing about the Sprint adapter is that it has an actual cord & plug between PSU and outlet. I guess that makes it a floor-wart. :) Half the jacks in my power strips are wasted because the wall-warts take up 3 slots. I think I'll solder cords on all of 'em. Doc

On Jan 26, 2004, at 4:36 PM, Teo Zenios wrote: Nah, I've been meaning to get down to the hardware store and build a power strip. You can get the aluminum channel and top plates with variously spaced knockouts for standard wall-mount sockets. Add the heavy-duty extension cord that got mowed last fall and a few sockets and you've got a sweet grounded PDU running along the back of your bench. Actually, I keep threatening to just inlet the desktop itself. :) Doc

On Mon, 26 Jan 2004, Doc Shipley wrote: I've got a JetDirect 300X sans power supply. It has a super funky connector and I can't find anything that'll fit the stupid thing. It says it can accept 9-35V, center positive (amps? who knows). Anyone know of an equivalent HP supply that'll fit this, or if it requires a super special expensive HP adapter? -- Sellam Ismail Vintage Computer Festival ------------------------------------------------------------------------------ International Man of Intrigue and Danger http://www.vintage.org [ Old computing resources for business || Buy/Sell/Trade Vintage Computers ] [ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]

On Mon, 2004-01-26 at 13:02, Doc Shipley wrote: That's not as much fun though as melting and bad smells.

"Doc Shipley" <doc(a)mdrconsult.com> wrote: This is a solved problem: Cyberguys sells something they call a "liberator", actually a one foot extension cord, to take care of this for $1.79. See: http://www.cyberguys.com/templates/searchdetail.asp?T1=121+2550 Paul Pennington Augusta, Georgia

FYI There is another binary file attached Spammer/Wormer out there. This traffic is large. Personally I am getting about 3x the old max. number of viral emails due to it. details: "Mydoom|Novarg", was detected nationally yesterday. jea