| Forum Home | ||||
| Press F1 | ||||
| Thread ID: 47692 | 2004-08-02 22:00:00 | Replacement PSU fan - what precautions? | Greg S (201) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 257656 | 2004-08-02 23:51:00 | > why not just get another psu they're cheap enuf .. PSU $60 - $100 Fan $6 - $20 Doesn't take a lot of mathematics to work out what's the better option. As it happens I'm gonna finish a few jobs then try the fan from an older PSU I have lying around |
Greg S (201) | ||
| 257657 | 2004-08-02 23:54:00 | > to quote from Mark Minasi (haven't got book in front > of me, so may not be dead accurate)-"these things > can kill you". they hold residual electric current > for long periods after being switched off-he quotes > the example of a TV(holds similar components to the > dangerous ones in PSU's) which he had in his attic > for years, and still got a nasty shock off it. Any > electrical guys on forum who can supply more details > of the nature of the threat ? The PSU has capacitors charged to a few hundred volts. These should have "bleeder" resistors on them, and would discharge over a few minutes. The resistors could be faulty (or missing, to save cost) and the capacitors would hold a charge for a few hours. A TV picture tube has about 25,000 volts on the internal coating on the picture tume, and its a very low-loss capacitor in nature. It can hold a charge for a very long time. Doubt that is years though. Power supplies in computers do not have picture tubes in them. |
godfather (25) | ||
| 257658 | 2004-08-02 23:55:00 | > to quote from Mark Minasi (haven't got book in front > of me, so may not be dead accurate)-"these things > can kill you". they hold residual electric current > for long periods after being switched off-he quotes > the example of a TV(holds similar components to the > dangerous ones in PSU's) which he had in his attic > for years, and still got a nasty shock off it. What I really need then is some way to discharge the current it's holding - anybody got a little brother I can borrow? :D All my little brothers are all too growed up to fall for such a test :( |
Greg S (201) | ||
| 257659 | 2004-08-03 00:03:00 | > The PSU has capacitors charged to a few hundred > volts. These should have "bleeder" resistors on them, > and would discharge over a few minutes. The resistors > could be faulty (or missing, to save cost) and the > capacitors would hold a charge for a few hours. > A TV picture tube has about 25,000 volts on the > internal coating on the picture tume, and its a very > low-loss capacitor in nature. It can hold a charge > for a very long time. Doubt that is years though. capacitors were what I was talking about, throwing in a quote from something I read as an attempt to minimise the danger for a fellow forum member. My apologies for being so ignorant as to not know the full in-depth nature of the issue-next time I'll study the textbooks before I dare to post, if that will please you sir > Power supplies in computers do not have picture tubes > in them. you don't say !!!!!! here was I wondering how they fitted a tube into such a tiny box icy |
icyred (5795) | ||
| 257660 | 2004-08-03 00:09:00 | Thanks GF. Icy - it's all good - cheers |
Greg S (201) | ||
| 257661 | 2004-08-03 00:34:00 | Just don't give it the tongue test Greg . Using little brothers for experimental (& experiential) purposes reminds me of the time when my older brother and one of his mates wanted to know what a 12 gauge shotgun cartridge outside a of a shotgun would do if discharged . To this end they clamped a cartrifge in an engineers vice (pointing down) and put together the following ingredients: Dads good pair of Sydcrome adjustable pliers, a centre punch, a ball peen hammer, some fast talk and one guilible little brother (who never noticed the garage empty when he raised the hammer) . Mum got to the garage as quick as it took my sibling and his mate to evacuate the property, I was still holding the hammer and pliers the punch was somewhere else . God knows what mum was saying but I got the idea she wasn't very happy with me and I couldn't make much out of what dad was saying when he got home from work but, actions speak volumes don't they . My parents still disbelieve that I was merely the victim on the odd accassion when the subject is raised . The one piece of forethought the lads had had, was to take the shot out of the cartridge although they packed in some wadding to replace it . They obviously had my wellfare at heart . Cheers Murray ;P |
Murray P (44) | ||
| 257662 | 2004-08-03 01:05:00 | > Using little brothers for experimental..... They obviously > had my wellfare at heart. > > Cheers Murray ;P Great story Murray! :^O The worst that happened to me was my older brother poured a packet of catterpilla killer powder over me to see what'd happen! |
Greg S (201) | ||
| 257663 | 2004-08-03 01:57:00 | One day I'll tell you the story of the time my brother left a heap of what he thought were dud firecrackers on the front porch oh, and a box of matches, think I was four or five at the time and it was only my second look at the inside of an A&E department or the time soon after he took up Karate and felt the need to test out his newly acquired prowess as an action man (boy) or the time he needed to test the brakes on the new trolley he had made (using rollers from my sister's roller skates), we lived at the top of a long hill at the time. Then there is the one about the flamethrower he, and the same mate, made out of dad's garden sprayer or...... This all happened before I was 8 or 9. Needless to say, in adult life, I do not gamble :D Cheers Murray P |
Murray P (44) | ||
| 257664 | 2004-08-03 05:30:00 | >> Power supplies in computers do not have picture tubes >> in them. >you don't say !!!!!! >here was I wondering how they fitted a tube into such a tiny box > Actually, they DO have crt's in them. To make them fit in such a small box, the manufacturer takes all the vacuum out of the tube, thus allowing it to be de-hydrated and shrunk 'till it is all wrinkly and small. For laptop psu's they zip them as well, just ask Ripley. R2 |
R2x1 (4628) | ||
| 257665 | 2004-08-03 05:43:00 | A CRT might be a few hundred picafarads, at 20KV or so . The energy stored is ½CV^2, so say ½(200x10^-12 X 400 x 10^6) --> . 04 joule . You would feel that . A PSU capacitor might be a few hundred microfarads at 330V . This amounts to about . 1 joule . You would really feel that . I used to work with supplies with several microfarads at 10kV . I treated them with great respect . Hundreds of joules can be harmful . |
Graham L (2) | ||
| 1 2 3 | |||||