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janetnkansah1@gmail.com: Jan 20 09:13PM -0800 l wish to know the difference between negative 48 volts and the normal 48 volts. Also l will be glad if a could have a circuit for a regulated -ve 48 volts power supply at 3A. thanks

Kaz Kylheku <609-576-4089@kylheku.com>: Jan 21 05:26AM > l wish to know the difference between negative 48 volts and the normal > 48 volts.   The difference is 96 volts. Is this a trick question?

Jeff Liebermann <jeffl@cruzio.com>: Jan 20 09:35PM -0800 On Wed, 20 Jan 2016 21:13:48 -0800 (PST), janetnkansah1@gmail.com wrote:   >l wish to know the difference between negative 48 volts and the normal 48 volts.   Telecom power is postive ground or -48VDC. A "normal" 48V power supply has both the - and + terminals floating from ground. You can ground the + terminal and it will possibly make a suitable -48V telecom power supply: <http://www.sinrace.com.cn/en/knowledge-base/636-why-telecom-power-supply-has-48vdc-power-supply.html> <http://www.erlang.com/forum/erlang/thread.htx?thread=927>   >Also l will be glad if a could have a circuit for a regulated -ve 48 volts power supply at 3A. thanks   I can't help you there. If you're only making one, Small 48V power supplies are very common and cheap: <http://www.mpja.com/48-Volt-Power-Supply/products/544/>   -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

Sjouke Burry <burrynulnulfour@ppllaanneett.nnll>: Jan 21 09:12AM +0100 > l wish to know the difference between negative 48 volts and the normal 48 volts. > Also l will be glad if a could have a circuit for a regulated -ve 48 volts power supply at 3A. thanks   Study electronics for a year or two, an the answer will come to you.

Phil Allison <pallison49@gmail.com>: Jan 21 04:33AM -0800 > normal 48 volts. > Also l will be glad if a could have a circuit for a regulated > -ve 48 volts power supply at 3A. thanks   ** Those two requests ought not be in the same post from the same person.       .... Phil

Cursitor Doom <curd@notformail.com>: Jan 21 02:29PM On Thu, 21 Jan 2016 04:33:29 -0800, Phil Allison wrote:   >> volts power supply at 3A. thanks   > ** Those two requests ought not be in the same post from the same > person.   Well spotted. Does seem a bit odd.

John Heath <heathjohn2@gmail.com>: Jan 21 08:04AM -0800 > l wish to know the difference between negative 48 volts and the normal 48 volts. > Also l will be glad if a could have a circuit for a regulated -ve 48 volts power supply at 3A. thanks   Think of voltage as pressure. 5 pounds of pressure pushing electrons or 5 pounds of vacuum pulling electrons is the difference between 5 volts negative and 5 volts positive. This is not a perfect analogy but it will get you there. Current , amps , is the number of electrons moving. Wattage is amps times voltage so a voltage of 48 at 3 amps , full throttle , is 48 V times 3 A for 144 watts. Write this down and memorize it and Bob's your uncle. Also there is no such thing as a dumb question.

Cursitor Doom <curd@notformail.com>: Jan 21 02:26PM Hi all,   I'm returning to the scope smps I was working on some time ago before fitting a new bathroom intervened. I've removed the smps board from the scope for testing purposes. On cranking up the supply voltage (230V here) I get to about 150V on my variac whereupon I can hear a capacitor venting; a clear hissing sound like air being let out of a tyre. Trouble is, I can't see which cap it is out of about the dozen or so electrolytics on the board. There's no visible steam or smoke whatsoever. I've tried using a piece of thin hollow plastic pipe as a stethoscope and moving around between caps, but it's nowhere near precise enough to differentiate the cap responsible. (I'm guessing it's an electrolytic; can't think what else could make that sound). Anyway, should I just crank up the voltage to 230 in the hope that it'll blow altogether and thus be obvious, or is that going to cause collateral damage (electrical damage I mean not actual physical damage)? I've tested all the caps in circuit for ESR and capacitance and they read fine, so this must be something that only materialises at close to working voltage. I'm all out of ideas. Any suggestions?

MJC <gravity@mjcoon.plus.com>: Jan 21 03:10PM In article <n7qppp$b1t$1@dont-email.me>, curd@notformail.com says...   > On cranking up the supply voltage (230V here) I get to about 150V on my > it's nowhere near precise enough to differentiate the cap responsible. > (I'm guessing it's an electrolytic; can't think what else could make that > sound).   Could it be an electrical discharge? Try viewing in the dark (with precautions against contact!)...   Mike.

"Ralph Mowery" <rmowery28146@earthlink.net>: Jan 21 10:30AM -0500 "Cursitor Doom" <curd@notformail.com> wrote in message news:n7qppp$b1t$1@dont-email.me... > all the caps in circuit for ESR and capacitance and they read fine, so > this must be something that only materialises at close to working voltage. > I'm all out of ideas. Any suggestions?   Feel the capacitors and find which one is getting hot. An IR heat gun may be better to keep the shock hazzard down.

Phil Allison <pallison49@gmail.com>: Jan 20 08:16PM -0800 Cursitor Doom wrote:   > http://www.ebay.co.uk/itm/10x-Mullard-Tropical-Fish- > Capacitors-47nF-0-047uF-250v-/360338287201?hash=item53e5d5ea61:m:mcN- > DqTXnkkcyUmSf_Gylog   ** I've always known them as " liquorice block" caps - aka "liquorice allsorts".   http://previews.123rf.com/images/robynmac/robynmac1402/robynmac140200024/25782815-Liquorice-allsorts-over-a-white-background--Stock-Photo-allsorts.jpg   Made by Philips as the "2222 352" series PETP film in values from 1nF to 6.8uF.   Colour codes on caps never did catch on, these ones vanished in the early 1980s along with colour coded tantalums - remember them ?   PCBs used to look much prettier in those days when transistors and most op-amps had gold plated leads and shiny metal packs.     .... Phil

Tim R <timothy42b@aol.com>: Jan 20 01:16PM -0800 On Tuesday, January 19, 2016 at 1:59:21 PM UTC-5, Ian Field wrote:   > the thermostat.   > Not as bad heating half a tank from cold, but I'm guessing it would still > cost slightly more.   Except the rate of heat loss is dependent on the delta T between inside and outside. Colder tanks lose less heat, if they haven't already reached minimum, than warm tanks being kept warm, so it takes less energy.

Jeroni Paul <JERONI.PAUL@terra.es>: Jan 20 12:24PM -0800 There should be an easy way to swap capitals in this case, like hitting shift or caps lock with the text highlighted. It happens to me all the time.

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