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| Thread ID: 54689 | 2005-02-19 09:48:00 | Build a DC-DC converter | george12 (7) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 326471 | 2005-02-19 09:48:00 | Hi, I want to build a power supply that will allow me to run an ATX motherboard from 12V DC. Efficiency is not THAT important, but would be nice obviously. 12V rail is easy, but I need a fair bit of current for 3.3 and 5V. I can handle the control logic OK. Just the power itself is all I need. I think it will have to be switching, as a normal voltage regulator will just end up making a lot of heat and not much power. And only go up to around ~3A at DSE. I can easily get access to power supplies to get parts from to use, that's not a problem. It only needs to power a Cel 366. If someone can just dump me with a circuit diagram I will be very pleased indeed. Cheers George |
george12 (7) | ||
| 326472 | 2005-02-19 20:29:00 | That is major electronic design and construction exercise george. Run it off a standard PSU instead and use a 12-230 volt convertor. You will only need about 250 watts if you are not going to load it up too much. Perhaps you could explain more about the project? Cheers Billy 8-{) |
Billy T (70) | ||
| 326473 | 2005-02-19 20:38:00 | it could get a tasd dangerous or not? wouldnt you need a sparky to do this sort of stuff? | Prescott (11) | ||
| 326474 | 2005-02-19 23:17:00 | Course not, I never need sparkies. I am pretty OK at wiring up things - I just made a Jacob's ladder (www.geocities.com) using an ignition coil power supply (www.geocities.com). They're really cool. Additionally, (my room used to be a shed, it's separate from the house) the only thing a sparky wired to my room is the power - I did phone, network, intercom... Prescott, it wouldn't be dangerous as the highest voltage is 12v, which doesn't shock. You can put your fingers across a car battery, won't feel a thing. OK, it's not going to be easy I gather. I guess I should give up on that one. The purpose is for the massive RC car I built, I had the (over?)ambitious thought of shoving a motherboard in there and controlling it by Wifi, coz I want a camera on it, and am having trouble thinking of a good way to send the image back. I thought it could be a way, seeing as I have loads and loads of old ATX motherboards, and webcams etc. But thinking more its rather impractical. Very impractical. But nonetheless, if I could make the converter it would be really useful in other things. But I think this might be above my skill. Just buy a $60 inverter if I really really need to do it ever. What would be a way to send data from a camera over about a KM? |
george12 (7) | ||
| 326475 | 2005-02-20 00:54:00 | Prescott, it wouldn't be dangerous as the highest voltage is 12v, which doesn't shock. You can put your fingers across a car battery, won't feel a thing. Its not the voltage you have to worry about, its the current. 12V can easily cause you damage if the current is high enough. |
craigb (4884) | ||
| 326476 | 2005-02-20 01:09:00 | Under no circumstances is 12v dangerous, danger starts round 48v. If however the 12 volt source was used to make a high voltage switching regulater/inverter and the 12v is low impedance enough then it could sustain the generated 240 v or whatever for a long enough time to kill you. To do what you want to do, which is to make a mother board run off 12v, there should be no danger at all. |
zqwerty (97) | ||
| 326477 | 2005-02-20 02:38:00 | It's not too difficult, nor is it dangerous (except that you could burn yourself with a soldering iron) to make a single voltage SM supply. There are some very nice chips around. One I use is the MC34063A, because I acquired a lot of cellphone chargers which include them. The data sheet gives example circuits, and the calculations aren't difficult. The problem comes in when you need lots of amps. You need a reasonable amount of inductance, and you must have a non-saturating core. This becomes a problem above a couple of amps. I have thought of using air cored inductors, but of course they are a bit bigger than an irondust toroid. If you want tens of amps, or even "fives" of amps, and multiple voltages, you really need to go to the style of ordinary computer power supplies, which rectify the mains to about 340V DC, then make that into high frequency AC to drive a transformer. The transformer input circuit is contriolled by feedback from the 5V supply. All the others are related to that by their tuirns ratios. A ferrite cored transformer can handle the watts at high frequencies. You might be able to rip out the high voltage stuff, and rewind the primary of the existing transformer with 1/20th of the turns. (That's likely to be not very many turns, but it would have to be quite heavy wire or several windings in parallel). I'd even consider making a HF inverter to replace the existing high voltage section. But. It's likely to be more difficult than it appears to be at first, and take a lot longer. Without proper test gear (including an oscilloscope) it might be veryu frustrating. (And popping MOSfets can get expensive.) What I would strongly recommend is that you buy a cheap inverter from Dick Smith or Jaycar (they both have specials frequently), and feed a computer power supply from 230V. ;) |
Graham L (2) | ||
| 326478 | 2005-02-20 02:51:00 | The big problem here is that george wants it to go mobile in a (large) model car . By the time he installs a battery big enough to supply the necessary current for any reasonable period of time, the whole assembly will be too heavy to do anything useful . I'd go for an old notebook george (maybe with a broken screen to get the cost down) You don't need a lot of computing power for what you want to do so start with the mobile aspect presorted . . Maybe you could even find an old Toshiba Libretto . I have a 50CT and it is the size of a video casstte . It is a P75 with 32MB ram (not for sale sorry, I still use it regularly for instrument downloads) . Cheers Billy 8-{) |
Billy T (70) | ||
| 326479 | 2005-02-20 02:55:00 | And of course, for a laptop, you can buy a DC-DC converter (Silicon Chip) kit from DSE or Jaycar which will handle it. Works well. | Graham L (2) | ||
| 326480 | 2005-02-20 03:06:00 | And of course, for a laptop, you can buy a DC-DC converter (Silicon Chip) kit from DSE or Jaycar which will handle it . Works well . May not even need that Graham, most laptops have an external converter which means you can plug in an external DC supply . The only problem is that they usually want 15 volts, not 12 so george would have to stack another 3-4 volts on top of the motor supply, assuming it is 12 volts . An extra 6 volts would be even better as it would allow for reducing voltage as the main battery goes flat . Cheers Billy 8-{) |
Billy T (70) | ||
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