Hey, This is my first post on this forum so please be patient with me. I was wondering if anyone knew that the mA or A that are required to run a computers 3,5, and 12V lines??? If you have no clue what im talking about please tell me so i might be able to clear it up. thnx
Welcome to the boards. I think I understand what you are asking but I'm not sure so I'll just go with my inference. The power requirements for each voltage rail (3.3,5,12, and so on) differ based on what a computer has installed, how fast it is, as well as others. The amperage required on each rail will vary since there are power suplies that put out various amounts of amperage per rail based on total wattage and effeciency. There are ATX power supply resources that might dictate the guidline to the minimum amount of amperage required per rail (in ATX ver 2.03 the 5vsb has to be at least 2Amps). Those documents will have to be Googled for since I don't have any readily available. Several websites offer minimum guidelines that are good to look into: Websites Be aware that since the start of ATX several modifications have been made to that formfactor to adjust the amperage per rail for new technology. Hope that helps.
Welcome to the forums! What you need depends on what's in the box - processor, how many drives, etc. The ATX PSU spec will give you some typical figures for various total wattages, but the spec doesn't lay down a strict mix of how the 3.3v, 5v and 12v lines are divvied up, which is one reason why some psus behave better than others of the same rating with some of the power-mad AMD processors. edit: beaten to the tape
It depends on the computer, but on average an AMD xp system draws about 12-15A on the 12 line, 15-30 on the 5V and 15-30 on the 3.3v but it all really depends on the motherboard and the drives, The motherboard can either have dc-dc convertes that are powered off of 12, or 5v so depending how they are powered, the more power used on that line. For drives, I've seen CD-roms that take 1A on each line, and conversely I've seen hard drives that take 250mA on the 12V and 300mA on the 5V. Video cards use a lot of power, so it can vary widely from a mini-ITX with a laptop hdd and CD, to a dual athlon 64 sytem with a 9800 XT and 15 15000k SCSI drives, 2 IDE 10000k drives, 2 DVD burners and 8 SATA drives, and cooling for all of that. edit:beaten to post (twice!!)
Hey, Thnx for your posts. They helped quite a bit. Just to let you know why I need to know this, I'm planning on building a computer into my car. I just get sick and tired of changing cd's. So I was just trying to figure out what kind of resistors and transformers I'm going to have to use to be able to get the right voltages and amps coming out. But thank you for your posts and if you happen to find out any more information on this subject please let me know by e-mail. thnx.
I think they make car power supplies. YOu will need to make sure the PSU gets the right amount of voltage, because the car voltage fluctuates between 7v and 14v.
A good quality high voltage inverter will do the trick although they tend to run your wallet dry. I wouldn't recommend powering off the car battery for a piece of digital sensitive equipment such as a computer.
Cars provide plenty of oomph from which to generate the requisite voltages and currents for a PC - bear in mind that starting a car draws something like 50A - 70A from the battery (albeit for a very short time). The trick is making sure that your PSU doesn't mind a fluctuating input voltage, and has excellent filtering. If you're up to it, I'd suggest a switching PSU, since they can generate all the levels you need fairly easily, and aren't picky about input levels (if properly designed). That said, they're not the kind of thing one just throws together (unless you're wierd, like cpemma ), so a simpler solution would be an inverter as suggested by Xiachunyi, which will give you mains levels. The noise issues are not from powering off a battery (which is less noisy than, say, the mains supply), but the charging circuit that cars use to recharge their batteries. If you have the available cash or bits, you might consider using a laptop with some form of (LCD based?) remote display. That way, your space and heat issues are already dealt with, as are your battery cross-overs, and most laptops run off around 18V - something easily acheivable with a simple step-up transformer. Depending on what you're planning to do, you might get away with an old(ish) laptop, which can be picked up fairly cheap. I actually thought of doing something like this, years and years ago (when I still had a car), but never got around to it, so I'd be interested to see how it turns out
You could do a setup with two batteries and some relays. You could make it so that the PC charges off the secondary battery, and the second battery is only connected to the alternator when the PC is off. This might be a problem if the PC is on whenever the alternator is, but you could set the #2 battery to charge from the #1 battery, although that'd decrease the battery life of the #1 battery, although the PC probably won't drain the second battery enough so that the #1 battery dies chargeing it... You could mount a second battery, with the required voltage regulators, and a 12v battery charger in the trunk. Make a retractable plug for the charger that comes out near the lisence plate. When you get home, you plug in the charger and it charges the batteries. You could even integrate a switching circuit so that the charger charges battery #1, so you'll never have to worry about leaving the lights on in the car, also letting you run the radio and PC while the car is off. Then when the alternator switches on it disconencts the charger from #1 so that the alternator won't go into #2.
Hey, I think I've decided to get a inverter but im not sure what Wattage I need. Im running a old 900mHz AMD, CD-ROM, Old Video Card (like a geforce 4 MX or so...), and probably a 7200 RPM 40GB hard drive. Do you happen to know the wattage to run that?
With an inverter you'll need a regular PSU. It's very wasteful, you're taking 12v, inverting it into 120v, then transforming it into 12v again.
Hey, I know it's a little pointless but I think its the easiest way to get a constant flow of voltages. Unless you have some outline of a circuit I could build to do this???
You will need the effeciency rating of your PSU and the wattage of your PSU to determine how high of an inverter you will need. You can do something like this: PSU wattage * 1+effeciency = wattage needed * 1.05 = wattage of inverter. The extra 5% is there for safety since you don't want to over draw your inverter, small spikes?. Augment percentage if you want to be much more safe.
