Computer Power +ve & -ve requirements of AT & ATX plugs

Do you have ANY understanding of electronics???????

Current flows from the negative terminal, via the circuitry, back to the positive terminal. In theory, whatever current leaves the negative terminal should reach the positive (some slight loss due to heat, etc). The battery you use to supply the +ve should also supply the -ve rail (in fact, usually the -ve is common and the +ve goes via the regulator to provide the desired voltage)..

Perhaps, given your question, you should leave this to someone with some basic understanding of how it all works?

Then what is the ground terminal for? {:-)

Do you have any understanding of multiple output power supplies with a single common return? AT and ATX supplies have four or more separate output voltages produced from different windings on the switching transformer.

A common AT/ATX power supply has: + 12 Volt output + 5 Volt output - 12 Volt output - 5 Volt output

ATX power supplies also have a small, separate 5 volt supply for standby mode. Each of these is connected to the common rail, which is grounded to the power supply case and computer chassis. Some supplies have a 3.3 volt supply for the CPU as well.

Learn what you're talking about before you criticize the skills of others.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

in a typical modern PC - the -12 and -5 draw bugger all, and I would be surprised if they are even needed on modern motherboards. (except of course for the serial port needing the -12 v to swing from +12 to

-12, if you are using the serial port that is). you would probably get away with a 1-2 AH battery in proportion to the 100ah battery on these other rails.

The other exception being if you had an optional device attatched to the machine that specifically needed one or both of these voltages. Older motherboards may need these voltages too as in the late 70's processors like the 8080, 2708 Eproms etc did need these supplies, but again I doubt that they drew any significant current.

And, pray tell, what has that got to do with the fact that the current flows from -ve to +ve? All you are stating here is that there is more than just a

5V and 12V supply rail, with all connected back to the -ve common ( "single common return")..

That changes nothing about my reply, or the original question of "what capacity battery to connect to the -ve rail if (x) value is connected to the

+ve rail".

Bloody yanks...

Ground, which is NOT the same as the negative or common, although sometimes the negative is connected to the chassis of the equipment to provide a 'common' connection. Ground is used on the AC side, not the DC side, and strangely enough connects to the GROUND! (i.e. bloody big copper rod driven into the ground outside with hefty green wire running to supply the electrical ground connection). In case of a fault it provides a path for the AC to ground, which helps the residual current device type circuit breakers to trip.. (they sense that the current in the active and neutral are equal - if some current is leaked to ground then the current in the active and neutral will be different and the breaker will trip, disconnecting the supply. If there is no path to ground then that doesn't happen!)

Yes folks, that IS a very, very, very basic, simplified (and from the professional angle, ridiculous) explanation so don't start - but given the obvious level of OP knowledge (or lack thereof) I'm not entering into a full on theory lesson with pretty drawings and connect the dot type lessons........... If someone else wishes to do so, please go ahead!!

Sigh, as they say "you can lead a horse to water but you can not make him drink".

2nd try. If I have two 12v batteries in series and I connect a GROUND to the common lead, then I have +12V and -12V with respect to the common ground.

Thanks. It was what I suspected, but was looking for someone with practical knowledge to give some feedback.

I will probably end up having the second battery as I am planning to use the serial inputs for sensors and keyboard inputs. It could also be used to run lighting, etc anyway.

You're obviously an engineer. [aps to REAL engineers].

I would use a DC to DC converter to supply the negative voltages at the very least. Some ICs use multiple supply voltages and can be damaged by a missing supply. Two batteries will not discharge at the same rate. There are 12 DC in PC power supplies on the market, but a small inverter and a standard power supply is a cheap and easy way to go. Its cheaper than designing the separate switch regulators, and regulates the 12 volt supplies as well.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

Explaining anything to you is like trying to teach a pig to sing. I now know what "Q!" means. :-(

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

I will keep your points in mind if it becomes something permanent.

True, and 24v between the + of batt A and - of batt B!! Commonly used with Op-Amps, etc, which need a + and - supply...

Did I really want to enter this debate???????????

Nope, I have no interest in debating whether the "computer motherboard manufacturers" are correctly using the term "ground" or not. Lets face it, with the dabble it could just as easily leak magic smoke before the debate warms up.

That is the correct definition of GROUND. But I have noticed a lot of cheap stuff getting about calling negative/neutral the ground.

In Aus though, the ground is neutral, the earth (ground) is hooked into the neutral bridge in the fuseboard, thus why f%$king up homemade GPO/etc installation jobs can cause interesting results. The powerpoles at 11kva have 3 active phases and then in many towns comes to 3 240v (3phase) lines plus a neutral return to the usually fairly large transformer.

But since we are talking about 12vDC, ground would be a poor interpretation of negative.

Q!, you are obviously aware of this as many others in the group are, but just a reminder to some why seem not to know.

--
*******************************
Glen O'Riley
Penrith, NSW, 2750
********************************
ACREM - NSW Operations Coordinator
NSW Rural Fire Service - Firefighter
NSW State Emergency Services - Member
Angel Flight - Earth Angel
Storm Chaser
********************************

It appears to me that he only wanted to know the average power drain of a computer system to establish if he needs a 6ah or 18ah battery, the figures stated are just an example.

I would be interested myself to find the average power drain/usage for such similar projects for use in country areas where the power is unreliable (up and down like a yoyo).

--
*******************************
Glen O'Riley
Penrith, NSW, 2750
********************************
ACREM - NSW Operations Coordinator
NSW Rural Fire Service - Firefighter
NSW State Emergency Services - Member
Angel Flight - Earth Angel
Storm Chaser
********************************

On Thu, 05 May 2005 10:55:54 +1000, Terry Collins put finger to keyboard and composed:

The -5V rail is most likely not used. In any case, it is not bussed to the PCI slots.

If you are lucky, the motherboard's serial ports may not require the

-12V rail. I've seen several that use an RS232 IC (eg ADM213EARS) that generates the -12V rail from the +5V supply via an internal charge pump.

Be aware that some motherboards have a BIOS or jumper option to generate an on-board "Power Good" signal. Make sure this is disabled, ie rely on the PSU's own PG pin instead.

- Franc Zabkar

--
Please remove one 's' from my address when replying by email.