DC 17V from PC power supply?

M

Mr. Man-wai Chang

Guest
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?

--
@~@ 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
^ ^ 19:33:02 up 5:02 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
 
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?
Click to expand...
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. :-?
Click to expand...
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. :-?
Click to expand...
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
Click to expand...
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
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.
Click to expand...
Usually the +5V and +12V supplies are fairly high current. And in many cases
only the +5V supply is directly regulated. It might be possible to reverse
the diodes and output capacitor on the +12V supply to make it -12V, and then
you should get 17V between them. The outputs are referenced to ground and
may be tied to chassis, so you may have to float it. You can probably find a
nominal 16-20 VDC laptop supply capable of 4 amps for about $10 and it would
be much safer, smaller, and more convenient. But if you want to play with an
ATX or similar power supply, there are schematics available that give a
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
from the 12V supply (while the 5V output will go up to about 7 volts). Just
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
chargers and get various voltages and even make DC-DC converters out of
them.

Paul
 
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?
Click to expand...
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?
Would it hurt the battery?
Click to expand...
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/productinfo/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
voltage. And these units may also have built-in current limiters and battery
charging profile circuits (although those would more likely be built into
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
 
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
Click to expand...
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
Click to expand...
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,
Click to expand...
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
 
Michael Black wrote:
And even worse, -5 plus +12 is 7 volts, the minus
subtracts from the positive.
Click to expand...

No, it doesn't. The -5 V supply has it's positive end connected to
common, so they add. +5 V & +12 V supplies would have 7 V between the
outputs.
 
"John G" <greentest@ozemail.com.au> wrote in message
news:tdOdnWvxEqI1G1TMnZ2dnUVZ_uednZ2d@westnet.com.au...
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. :-?
Click to expand...
The correct term is: "let the magic smoke out".
 
"Mr. Man-wai Chang" <toylet.toylet@gmail.com> wrote in message
news:kqc53t$th6$2@dont-email.me...
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?
Click to expand...
On older PSUs, the -12V had a 7912 regulator (1A max).

Your best bet is an open frame 5 & 12V switcher that can be modified.

You'll probably find a TL431 programmable zener with sampling resistors
connected to the 5V rail, with suitable modification of the resistors, you
can sample the 12V rail instead - if you adjust the resistor values to get
17V, watch the voltage ratings of the electrolytics or you'll get loud bangs
and confetti (and let the magic smoke out).

If you find a surplus Aztec open frame switcher - they use a house coded
TL431, but its obvious when you see it.
 
"Michael Black" <et472@ncf.ca> wrote in message
news:alpine.LNX.2.02.1306251532390.5374@darkstar.example.org...
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
Click to expand...
The original 5150 PC had provision for 3 rail RAM, selected by the
configuration DIP switches.

I have yet to aquire a 5150 board that hadn't been fucked up by someone
messing with the DIP switches!
 
"P E Schoen" <paul@peschoen.com> wrote in message
news:kqcl62$rtn$1@dont-email.me...
"Mr. Man-wai Chang" wrote in message news:kqbv6h$tms$1@dont-email.me...

2. Could I use 17V to charge a notebook battery rated 16V and 3.8A? 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/productinfo/19078%20PS/

And if you need 4.74A and can spare $15:
http://www.mpja.com/19V-474A-Desktop-Supply-Delta/productinfo/30336%20PS/
Click to expand...
In the UK; Maplin sells a universal laptop PSU with a voltage selector
switch and an assortment of power jack attachments.

This device depends on the laptop having its own internal charging circuit,
its not intended for charging any battery directly.

Most developed countries probably have a better choice than our just Maplin.
 
"Michael Black" <et472@ncf.ca> wrote in message
news:alpine.LNX.2.02.1306251529490.5374@darkstar.example.org...
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.
Click to expand...
If its a lithium battery - charging with anything other than properly
designed circuitry can be very dangerous!
 
On Tue, 25 Jun 2013, Ian Field wrote:

"Michael Black" <et472@ncf.ca> wrote in message
news:alpine.LNX.2.02.1306251532390.5374@darkstar.example.org...
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

The original 5150 PC had provision for 3 rail RAM, selected by the
configuration DIP switches.

I have yet to aquire a 5150 board that hadn't been fucked up by someone
messing with the DIP switches!

I'd forgotten about the dip switches on those.
Click to expand...

But how many were actually shipped with low density RAM? I thought it was
the 4K RAM that needed negative voltage, and I thought by the time the
IBM came out, it would use 64K RAM, which I thought did away with the need
for negative voltage.

Michael
 
Michael Black wrote:
On Tue, 25 Jun 2013, Ian Field wrote:



"Michael Black" <et472@ncf.ca> wrote in message
news:alpine.LNX.2.02.1306251532390.5374@darkstar.example.org...
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

The original 5150 PC had provision for 3 rail RAM, selected by the
configuration DIP switches.

I have yet to aquire a 5150 board that hadn't been fucked up by someone
messing with the DIP switches!

I'd forgotten about the dip switches on those.

But how many were actually shipped with low density RAM? I thought it was
the 4K RAM that needed negative voltage, and I thought by the time the
IBM came out, it would use 64K RAM, which I thought did away with the need
for negative voltage.
Click to expand...

The early PC motherboards were shipped with four banks of 16K RAM.
 
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?

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

No
Click to expand...
Jamie
 
Guess this project is too dangerous for a beginner! Thank you all! :)

--
@~@ 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
^ ^ 12:30:01 up 21:59 0 users load average: 0.04 0.04 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
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top