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| Thread ID: 56063 | 2005-03-26 06:19:00 | 13.8v regulated power supply from AT PSU? | george12 (7) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 338192 | 2005-03-26 06:19:00 | Hi For my battery-powered PC, I am after a regulated 13.8v supply at around 8 amps. The actual power supply can be switching, and the regulation linear. Now I have an 8 amp 12v AT PSU I use for this sort of stuff, but it's 12v not 13.8v. Will it be easy to modify? Can I do this: Switch the switch to 120V, and go between 5V and 12V for 14 volts? Will it work, or will it kill the PSU? If not, what is the best way. I'd like to avoid rewinding the transformer. |
george12 (7) | ||
| 338193 | 2005-03-26 06:26:00 | Or could I go between 12V and -5V for 17v, and regulate down? If I use a negative rail (rate only 0.5A), do I get the full 8A of +12V, or only 0.5A? Or some kind of combination? Sorry for double-posting. Cheers |
george12 (7) | ||
| 338194 | 2005-03-26 06:56:00 | If you used the 120v switch, the PSU will last for 1.0012 seconds before the smoke escapes from the capacitors and the PSU stops. The -ve rails are very low current capable. You cannot get 17v at a reasonable output that way. You need to source the circuit diagram for the power supply to determine how to alter the output voltage, but I think it will require rewinding the switchmode transformer. |
godfather (25) | ||
| 338195 | 2005-03-26 06:57:00 | I seem to remember there was an article in Silicon Chip magazine about doing just that. I will try to find it tonight and see if the essentials can be posted. Cheers |
Terry Porritt (14) | ||
| 338196 | 2005-03-26 06:58:00 | www.qrp4u.de As always george, Google holds the answers as well. |
godfather (25) | ||
| 338197 | 2005-03-26 07:55:00 | Yeah, I did come across that, but it was a little difficult to grasp. I'd probably just break it. I was just wondering if there was a simpler way. Seems there isn't. Oh well... I've got a non-switchmode one that will do I suppose. It's rated 5A, so 7A is pushing it, but it should be OK. |
george12 (7) | ||
| 338198 | 2005-03-26 08:01:00 | The reference Godfather posted looks quite similar to the Silicon Chip article. The biggest job is rewinding the transformer. This involves removing the existing varnish insulation, SiChip say dunk in a bucket of paint stripper overnight. There are detailed instructions and photos, and details of the insulation methods required between windings and terminations to give double insulation. The article was in the October 2003 issue, pages 25 to 33. Back issues can be obtained from SiChip. http://www.siliconchip.com.au |
Terry Porritt (14) | ||
| 338199 | 2005-03-26 08:06:00 | You could think of using a motor driven car alternator with rectification and regulation :dogeye: | Terry Porritt (14) | ||
| 338200 | 2005-03-26 16:02:00 | You can make great mains voltage AC generators out of them, only problem is it's 300-400Hz not 50Hz, so things like clocks don't like it, and some wall warts overheat. Back on topic, I guess I will use the good old-fashioned 5 amp transformer and regulate it to 13.8v with the help of a 7805 and 3 diodes to bump it up to 13.8v. And a big, heatsinked transistor. Only problem, the transformer is MASSIVE (won't fit in the case, or barely) and still only rated 5a. Gawd I hate linear power supplies when you get into the high currents :(. |
george12 (7) | ||
| 338201 | 2005-03-26 22:28:00 | A 7805 + 3 diodes will give 6.8 volts Try a 7812.... And remember the maximum current for a 78xx is 1.5 amps, so you need a series pass 2N3055 or two. |
godfather (25) | ||
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