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DC 17V from PC power supply?

Started by Mr. Man-wai Chang June 25, 2013
1. If I shorted the +5V and +12V in the molex connector,
    would I get +17V? What's the max. current?

2. Could I use 17V to charge a notebook battery rated 16V and 3.8A?
    Would it hurt the battery?

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Mr. Man-wai Chang submitted this idea :
> 1. If I shorted the +5V and +12V in the molex connector, > would I get +17V? What's the max. current? > > 2. Could I use 17V to charge a notebook battery rated 16V and 3.8A? > Would it hurt the battery?
NO! Shorted is the correct description. They are both referenced to ground so MAGIC SMOKE will result. :-? -- John G
On 25/06/2013 8:01 PM, John G wrote:
> Mr. Man-wai Chang submitted this idea : >> 1. If I shorted the +5V and +12V in the molex connector, >> would I get +17V? What's the max. current? > NO! > Shorted is the correct description. > They are both referenced to ground so MAGIC SMOKE will result. :-? >
Thanks! Expected answer! :) -- @~@ Remain silent. Nothing from soldiers and magicians is real! / v \ Simplicity is Beauty! May the Force and farces be with you! /( _ )\ (Fedora 18 i686) Linux 3.9.6-200.fc18.i686 ^ ^ 21:12:01 up 6:41 0 users load average: 0.00 0.01 0.05 不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA): http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
On 25/06/2013 8:01 PM, John G wrote:
> NO! > Shorted is the correct description. > They are both referenced to ground so MAGIC SMOKE will result. :-?
OTOH, should I attempt -5V and +12V pins at the power connector? Or should I try +5V and -12V? Which one is safer and could supplies 4A? -- @~@ Remain silent. Nothing from soldiers and magicians is real! / v \ Simplicity is Beauty! May the Force and farces be with you! /( _ )\ (Fedora 18 i686) Linux 3.9.6-200.fc18.i686 ^ ^ 21:18:01 up 6:47 0 users load average: 0.00 0.01 0.05 不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA): http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
On 6/25/2013 9:19 AM, Mr. Man-wai Chang wrote:
> On 25/06/2013 8:01 PM, John G wrote: >> NO! >> Shorted is the correct description. >> They are both referenced to ground so MAGIC SMOKE will result. :-? > > OTOH, should I attempt -5V and +12V pins at the power connector? Or > should I try +5V and -12V? > > Which one is safer and could supplies 4A? >
If you manage to find 17 volts the current rating will that of the lower rated source.Look at the supply label. It will say what the current rating of each supply is. The 5 volt supply can supply much more than the 12 volts but you will need to use the lesser rating. Tom
"Tom Biasi"  wrote in message news:51c9aef1$0$25604$607ed4bc@cv.net...

> If you manage to find 17 volts the current rating will that of the =
lower=20
> rated source.Look at the supply label. It will say what the current =
rating=20
> of each supply is. The 5 volt supply can supply much more than the 12=20 > volts but you will need to use the lesser rating.
Usually the +5V and +12V supplies are fairly high current. And in many = cases=20 only the +5V supply is directly regulated. It might be possible to = reverse=20 the diodes and output capacitor on the +12V supply to make it -12V, and = then=20 you should get 17V between them. The outputs are referenced to ground = and=20 may be tied to chassis, so you may have to float it. You can probably = find a=20 nominal 16-20 VDC laptop supply capable of 4 amps for about $10 and it = would=20 be much safer, smaller, and more convenient. But if you want to play = with an=20 ATX or similar power supply, there are schematics available that give a=20 general idea of how they are made. http://www.pavouk.org/hw/en_atxps.html Another possibility is to change the feedback resistors so that you get = 17V=20 from the 12V supply (while the 5V output will go up to about 7 volts). = Just=20 make sure the PSU doesn't have a crowbar on the 5V supply. There are other web pages showing ways to hack these PSUs to make = battery=20 chargers and get various voltages and even make DC-DC converters out of=20 them. Paul=20
On 6/25/13 4:38 AM, Mr. Man-wai Chang wrote:
> > 1. If I shorted the +5V and +12V in the molex connector, > would I get +17V? What's the max. current?
No.
> > 2. Could I use 17V to charge a notebook battery rated 16V and 3.8A? > Would it hurt the battery?
Potentially. Also, battery charging circuits aren't just applying the rated voltage. There is a lot more to it than that. Based on your recent posts here, I suggest finding a good book about DC electricity. Maybe taking a class or two. Or three. I just finished the third (DC, then AC, then Linear Circuits). There are a lot of things that are just intuitive with electronics, but a lot that isn't. Just guessing and trying will end up in a lot of magic smoke, and potentially loud bangs and fires. I'm a huge fan of HyperPhysics, though that isn't where I learned electronics from. It might be a good starting place though... <http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/cktetrcon.html#c1>
"Mr. Man-wai Chang"  wrote in message news:kqbv6h$tms$1@dont-email.me...

> 2. Could I use 17V to charge a notebook battery rated 16V and 3.8A?=20 > Would it hurt the battery?
You can probably use a surplus or used notebook supply of similar specs. = Here's one with 19V and 2.65A for just $4: http://www.mpja.com/19-Volt-Desktop-Power-Supply-265A-EIAJ-Plug/productin= fo/19078%20PS/ And if you need 4.74A and can spare $15: http://www.mpja.com/19V-474A-Desktop-Supply-Delta/productinfo/30336%20PS/= You can always add one or more diodes in series with the output to lower = the=20 voltage. And these units may also have built-in current limiters and = battery=20 charging profile circuits (although those would more likely be built = into=20 the laptop computer - at least that's how I would design it - I wouldn't = trust an external device that could be swapped with something else). Paul=20
On Tue, 25 Jun 2013, Mr. Man-wai Chang wrote:

> > 1. If I shorted the +5V and +12V in the molex connector, > would I get +17V? What's the max. current? >
No, because probably one side of each is already grounded inside the pwoer supply.
> 2. Could I use 17V to charge a notebook battery rated 16V and 3.8A? > Would it hurt the battery? >
NO, because these likely are fancy batteries and you don't just push current through them, it has to be controlled based on the state of the battery. Leave the batteries in the notebook, and charge it that way. The charger already came with the notebook, it also powers the notebook. If the charger/power supply is missing, then find one that will do the job. I see them endlessly no longer big because they are switching supplies. I pulled an XBOX 360 supply out of a pile of junk when the students moved out at the end of April. Then a few weeks ago, I found another one, except the actual XBOX 360 was with it. Michael
On Tue, 25 Jun 2013, Mr. Man-wai Chang wrote:

> On 25/06/2013 8:01 PM, John G wrote: >> NO! >> Shorted is the correct description. >> They are both referenced to ground so MAGIC SMOKE will result. :-? > > OTOH, should I attempt -5V and +12V pins at the power connector? Or should I > try +5V and -12V? >
The minus supplies, if they are even still there, have minimal current, were way in the beginning because RAM might have needed some negative voltage (I can't remember if those RAM were still in existence in 1981 whtn the IBM PC came out, but they were lower density RAM), and of course, RS232 interfaces need -12. FOr much of the time, those neagative supplies have eitehr been underused or not used at all. Plus, the negative supplies will also have one side ground, just like the positive supplies. And even worse, -5 plus +12 is 7volts, the minus subtracts from the positive. Michael