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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#41
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
Ecnerwal wrote: In article , "N Cook" wrote: Anyone know the term for laying double traces of solder along copper traces to increase current carrying , so I can research it ? No, but it's a dumb idea. It's fairly easy to dump solder "accurately" on a trace (if not covered by soldermask, hopefully that's obvious) - just heat and feed solder, it will follow the trace, and you can build it up quite a ways simply from surface tension. If you need more current capacity on the trace, bend up a chunk of copper wire that actually conducts well and solder that on. Solder is a lousy conductor, compared to copper. The copper will hold more solder on there, but most of the current will be carried by the copper. I've seen something similar done intentionally and neatly inside a couple of amplifiers. The power trace has a number of tinned copper wire 'links' in parallel with it on the 'top' of the pcb. Quite clever since it can be done with auto-insert machinery. Personally I prefer to use equipment cable to deliver power to where it's needed rather than string it out along pcb traces. Graham |
#42
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
Eeyore wrote:
"Ron(UK)" wrote: Eeyore wrote: "Ron(UK)" wrote: You're never going to be able to protect against stray metal object clattering around inside, Quite ! and I`m sure the original designers never gave it a thought. In which case it shouldn't have a CE sticker. I would imagine that the stray object originated inside the amp, probably a panel screw or captive nut never secured in the first place. I thought the OP said something did actually fall inside ? Maybe How often you you pick up an item of gear and hear something loose rolling around inside Thankfully not too often. I do recall one time about 30 yrs ago when I withdrew a Bulgin mains lead and the earth prong of the equipment connector came out with it though ! They were just held in place with screws ! They were held in by the same screw that held the cable iirc I once found the entire tip and centre core of a jackplug neatly welded twixt power transistor and heatsink. Presumably some clown snapped off the plug, so pushed it right through with another. The one thing most designers fail to allow for is the stupidity of the end user. Ron(UK) |
#43
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
"Nutcase ****ing ****" So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added fuses of what rating ? ** Be very wary of adding +/- DC rail fues to any power amp designed without them. Very likely if one or other DC fuse blows or is removed, the amp's output will swing fully to the rail with its fuse still intact. Recipe for fried speakers. You have been warned. I'm just trying to engineer a more respectable equivalent of fuses for trace rupture. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Eventually one DC rail ruptured as a fuse. ** BULL**** !!!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! I've now decided to do some calculation to determine what the rupture current for that trace was. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Then as the common return almost fused and is the same dimension but in the even worse case then carries twice the current , halving this trace rupture current to use as the fuse rupture current and reduce that for current carying capacity , by half again ? ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! If all output trannies fused short circuit all round so loading both DC rails the combined common return would have ruptured at whatever that rupture current is for the trace that did burn up. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Anyone know the term for laying double traces of solder along copper traces to increase current carrying , so I can research it ? ** That term is : ******** !!!!!!!!!!! I'm intrigued how you lay quite accurate molten solder runs and parallel over and with existing traces. ** YOU are intrigued with eating your own putrid faeces. Anyway measurements: Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major axes of .15mm and .8mm. ** Where are the guys in white suits ??? Hope they have those tranquillisers jabs handy ... From tables of fusing currents for copper, also tin and lead (NB in the form of circular wires ) for different diameters. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Copper fusing current of the trace = 12 amps Lead+Tin elipse then 6 amps (not as much as I would have intuitively thought) ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Total 18 amps so 18/4 = 4.5 amps conventional fuse rating. Presumably the circular to sheet allowance would up this 4.5 amp figure , but by how much ? ** BULL**** !!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Diverse Devices, Southampton, England ** Straight from the local schizophrenia ward to YOU !!!!!!!! Usenet is the GREATEST lunatic magnet in the known universe. Boy oh boy ............. - have we got ourselves a ****ing LIVE ONE !! ......... Phil |
#44
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
"Nutcase ****ing ****"
So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added fuses of what rating ? ** Be very wary of adding +/- DC rail fues to any power amp designed without them. Very likely if one or other DC fuse blows or is removed, the amp's output will swing fully to the rail with its fuse still intact. Recipe for fried speakers. You have been warned. I'm just trying to engineer a more respectable equivalent of fuses for trace rupture. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Eventually one DC rail ruptured as a fuse. ** BULL**** !!!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! I've now decided to do some calculation to determine what the rupture current for that trace was. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Then as the common return almost fused and is the same dimension but in the even worse case then carries twice the current , halving this trace rupture current to use as the fuse rupture current and reduce that for current carying capacity , by half again ? ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! If all output trannies fused short circuit all round so loading both DC rails the combined common return would have ruptured at whatever that rupture current is for the trace that did burn up. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Anyone know the term for laying double traces of solder along copper traces to increase current carrying , so I can research it ? ** That term is : ******** !!!!!!!!!!! I'm intrigued how you lay quite accurate molten solder runs and parallel over and with existing traces. ** YOU are intrigued with eating your own putrid faeces. Anyway measurements: Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major axes of .15mm and .8mm. ** Where are the guys in white suits ??? Hope they have those tranquillisers jabs handy ... From tables of fusing currents for copper, also tin and lead (NB in the form of circular wires ) for different diameters. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Copper fusing current of the trace = 12 amps Lead+Tin elipse then 6 amps (not as much as I would have intuitively thought) ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Total 18 amps so 18/4 = 4.5 amps conventional fuse rating. Presumably the circular to sheet allowance would up this 4.5 amp figure , but by how much ? ** BULL**** !!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Diverse Devices, Southampton, England ** Straight from the local schizophrenia ward to YOU !!!!!!!! Usenet is the GREATEST lunatic magnet in the known universe. Boy oh boy ............. - have we got ourselves a ****ing LIVE ONE !! ......... Phil |
#45
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
"Nutcase ****ing ****"
So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added fuses of what rating ? ** Be very wary of adding +/- DC rail fues to any power amp designed without them. Very likely if one or other DC fuse blows or is removed, the amp's output will swing fully to the rail with its fuse still intact. Recipe for fried speakers. You have been warned. I'm just trying to engineer a more respectable equivalent of fuses for trace rupture. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Eventually one DC rail ruptured as a fuse. ** BULL**** !!!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! I've now decided to do some calculation to determine what the rupture current for that trace was. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Then as the common return almost fused and is the same dimension but in the even worse case then carries twice the current , halving this trace rupture current to use as the fuse rupture current and reduce that for current carying capacity , by half again ? ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! If all output trannies fused short circuit all round so loading both DC rails the combined common return would have ruptured at whatever that rupture current is for the trace that did burn up. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Anyone know the term for laying double traces of solder along copper traces to increase current carrying , so I can research it ? ** That term is : ******** !!!!!!!!!!! I'm intrigued how you lay quite accurate molten solder runs and parallel over and with existing traces. ** YOU are intrigued with eating your own putrid faeces. Anyway measurements: Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major axes of .15mm and .8mm. ** Where are the guys in white suits ??? Hope they have those tranquillisers jabs handy ... From tables of fusing currents for copper, also tin and lead (NB in the form of circular wires ) for different diameters. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Copper fusing current of the trace = 12 amps Lead+Tin elipse then 6 amps (not as much as I would have intuitively thought) ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Total 18 amps so 18/4 = 4.5 amps conventional fuse rating. Presumably the circular to sheet allowance would up this 4.5 amp figure , but by how much ? ** BULL**** !!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Diverse Devices, Southampton, England ** Straight from the local schizophrenia ward to YOU !!!!!!!! Usenet is the GREATEST lunatic magnet in the known universe. Boy oh boy ............. - have we got ourselves a ****ing LIVE ONE !! ......... Phil |
#46
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
"Nutcase ****ing ****"
So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added fuses of what rating ? ** Be very wary of adding +/- DC rail fues to any power amp designed without them. Very likely if one or other DC fuse blows or is removed, the amp's output will swing fully to the rail with its fuse still intact. Recipe for fried speakers. You have been warned. I'm just trying to engineer a more respectable equivalent of fuses for trace rupture. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Eventually one DC rail ruptured as a fuse. ** BULL**** !!!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! I've now decided to do some calculation to determine what the rupture current for that trace was. ** BULL**** !!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Then as the common return almost fused and is the same dimension but in the even worse case then carries twice the current , halving this trace rupture current to use as the fuse rupture current and reduce that for current carying capacity , by half again ? ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! If all output trannies fused short circuit all round so loading both DC rails the combined common return would have ruptured at whatever that rupture current is for the trace that did burn up. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Anyone know the term for laying double traces of solder along copper traces to increase current carrying , so I can research it ? ** That term is : ******** !!!!!!!!!!! I'm intrigued how you lay quite accurate molten solder runs and parallel over and with existing traces. ** YOU are intrigued with eating your own putrid faeces. Anyway measurements: Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major axes of .15mm and .8mm. ** Where are the guys in white suits ??? Hope they have those tranquillisers jabs handy ... From tables of fusing currents for copper, also tin and lead (NB in the form of circular wires ) for different diameters. ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Copper fusing current of the trace = 12 amps Lead+Tin elipse then 6 amps (not as much as I would have intuitively thought) ** BULL**** !!!!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Total 18 amps so 18/4 = 4.5 amps conventional fuse rating. Presumably the circular to sheet allowance would up this 4.5 amp figure , but by how much ? ** BULL**** !!!!!!!!!! You are a total ****ing nut case ASSHOLE !!!!!!! Diverse Devices, Southampton, England ** Straight from the local schizophrenia ward to YOU !!!!!!!! Usenet is the GREATEST lunatic magnet in the known universe. Boy oh boy ............. - have we got ourselves a ****ing LIVE ONE !! ......... Phil |
#47
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
" Diverse Devices, Southampton, England" http://home.graffiti.net/diverse:graffiti.net/ ** Straight from the local schizophrenia ward to YOU !!!!!! Usenet is the GREATEST lunatic magnet in the known universe. Boy oh boy ........ - have we got ourselves a ****ing LIVE ONE !! ....... Phil |
#48
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
" Diverse Devices, Southampton, England" http://home.graffiti.net/diverse:graffiti.net/ ** Straight from the local schizophrenia ward to YOU !!!!!! Usenet is the GREATEST lunatic magnet in the known universe. Boy oh boy ........ - have we got ourselves a ****ing LIVE ONE !! ....... Phil |
#49
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
Ecnerwal wrote in message
... In article , "N Cook" wrote: Anyone know the term for laying double traces of solder along copper traces to increase current carrying , so I can research it ? No, but it's a dumb idea. It's fairly easy to dump solder "accurately" on a trace (if not covered by soldermask, hopefully that's obvious) - just heat and feed solder, it will follow the trace, and you can build it up quite a ways simply from surface tension. If you need more current capacity on the trace, bend up a chunk of copper wire that actually conducts well and solder that on. Solder is a lousy conductor, compared to copper. The copper will hold more solder on there, but most of the current will be carried by the copper. -- Cats, coffee, chocolate...vices to live by I get the impression board layout designers just use what has worked before as far as track dimensions etc and don't actually consider in great detail catastrophic failure modes. Yes this kit does support the CE mark. I've not been able to find design data/tables for such traces. I may dig out a low voltage 60 amp transformer fed via a variac and sacrifice some otherwise unaffected tracks on this board to determine what sort of amperage to cause excessive heating and then another bit of track to find the rupture current. Having to avoid localised failure at my test join-points with a lot of distributed solder. |
#50
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
"Ron(UK)" wrote: Eeyore wrote: "Ron(UK)" wrote: Eeyore wrote: "Ron(UK)" wrote: You're never going to be able to protect against stray metal object clattering around inside, Quite ! and I`m sure the original designers never gave it a thought. In which case it shouldn't have a CE sticker. I would imagine that the stray object originated inside the amp, probably a panel screw or captive nut never secured in the first place. I thought the OP said something did actually fall inside ? Maybe How often you you pick up an item of gear and hear something loose rolling around inside Thankfully not too often. I do recall one time about 30 yrs ago when I withdrew a Bulgin mains lead and the earth prong of the equipment connector came out with it though ! They were just held in place with screws ! They were held in by the same screw that held the cable iirc There was another one - oh actually I think that terminal section did actually have a male thread on it. I once found the entire tip and centre core of a jackplug neatly welded twixt power transistor and heatsink. Presumably some clown snapped off the plug, so pushed it right through with another LOL ! The one thing most designers fail to allow for is the stupidity of the end user. 'Tis often true. Graham |
#51
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
N Cook wrote: I get the impression board layout designers just use what has worked before as far as track dimensions etc There are published guidelines for temp rise vs current, copper thickness and track width. You'll find a chart of same in IEC60065 (electrical safety) in fact. The board layout guy will only use the data supplied by the design engineer. They're not psychic. Some 'design engineers' have a clue however. and don't actually consider in great detail catastrophic failure modes. Good designers will design for that. Yes this kit does support the CE mark. So what's the damn make and model FFS ! Why are you refusing to tell us one of the most important pieces of information ? Graham |
#52
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
N Cook wrote:
I get the impression board layout designers just use what has worked before as far as track dimensions etc and don't actually consider in great detail catastrophic failure modes. On a well designed circuit board, you can often see which traces are involved with each part of the circuit. Broad traces carry the heavy current, spidery ones are the signal path. I remember a time when some quality gear actually had the signal path screened onto the component side of the board, together with typical voltages etc. That was when they actually wanted us to repair the stuff. I dont think any designer worries too much about 'catastrophic failure'! .. Yes this kit does support the CE mark. You still havent shared with us the make and model Ron(UK) |
#53
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
Eeyore wrote:
I do recall one time about 30 yrs ago when I withdrew a Bulgin mains lead and the earth prong of the equipment connector came out with it though ! They were just held in place with screws ! They were held in by the same screw that held the cable iirc There was another one - oh actually I think that terminal section did actually have a male thread on it. Aye that`s right, and when they came loose, Johnny guitar would try to tighten it by sticking a screwdriver (table knife) in the slot in the pin and twist, neatly snapping half the pin off! Ron(UK) |
#54
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
"N Cook" wrote in message ... Ecnerwal wrote in message ... In article , "N Cook" wrote: Anyone know the term for laying double traces of solder along copper traces to increase current carrying , so I can research it ? No, but it's a dumb idea. It's fairly easy to dump solder "accurately" on a trace (if not covered by soldermask, hopefully that's obvious) - just heat and feed solder, it will follow the trace, and you can build it up quite a ways simply from surface tension. If you need more current capacity on the trace, bend up a chunk of copper wire that actually conducts well and solder that on. Solder is a lousy conductor, compared to copper. The copper will hold more solder on there, but most of the current will be carried by the copper. -- Cats, coffee, chocolate...vices to live by I get the impression board layout designers just use what has worked before as far as track dimensions etc and don't actually consider in great detail catastrophic failure modes. Yes this kit does support the CE mark. I've not been able to find design data/tables for such traces. I may dig out a low voltage 60 amp transformer fed via a variac and sacrifice some otherwise unaffected tracks on this board to determine what sort of amperage to cause excessive heating and then another bit of track to find the rupture current. Having to avoid localised failure at my test join-points with a lot of distributed solder. Just interested ... Do you actually make a living out of repairing this stuff ? If I spent as much time as you seem to, worrying about esoteric things like how much current a track will take before it vapourises, I would long since have ceased to earn enough money to get by on. These days, I find that it has to be 'wheel it in, fix it, wheel it out , invoice it, next please'. If the bit called 'fix it' takes longer than an hour, and the value of the kit is less than 150 quid, that bit changes to 'bin it' ... Arfa |
#55
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
Meat Plow wrote:
On Sat, 14 Jul 2007 22:37:37 +0100, N Cook wrote: Eeyore wrote in message ... N Cook wrote: The 2 reservoir caps are 6800uF, 80V rating with presumably about 65V on each , when all is in working order. That's a reasonable size. They won't be causing excessive switch on current. Is the power transformer toroidal or EI ? That's where the big difference is. Toroids will take a considerable switch-on current (it's largely due to their magnetic characteristics). Graham Toroidal , not E-I lamination transformer I'm coming around to thinking 5 amp anti-surge in the mains fuse-holder and a 5 amp fuse shunted in the + and - rail traces from the DC side of the bridge rectifier before the reservoir caps, but undecided whether quick-blow or anti-surge ones there. Fix the amp, put the fuses of your choice in and put it through its paces. You'll probably want to run some music through it at high volume preferably some Hip Hop barf. See which fuses blow and which don't. There are uses for sine, square, multiple sine, and complex waveforms in testing. I suggest using each for what it will make esily visible in the performance. -- JosephKK Gegen dummheit kampfen die Gotter Selbst, vergebens.Â*Â* --Schiller |
#56
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
Tim Shoppa wrote:
CJT wrote: Tim Shoppa wrote: N Cook wrote: 400 watt RMS amp for use on 240 V mains. Destructed due to metal dropping in and shorting the amp . The only fuse is on the mains rated at 8 amp, maker's design rating, which shows no sag , discolour or anything like that, ie untouched. Shorted power trannies, burnt low power trannies and even a piece of 3mm trace from the main bridge rectifier burnt through and that had 2 runs of added solder over the track for current carrying, the other polarity trace overheated but not ruptured I'm thinking of bridging that gap with a fuse and another on the other rail after cutting it. The mains transformer is rated at 2x 47V,5 amp. So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added fuses of what rating ? The power supply to your amp probably has massively oversize filter capacitors. Average current draw at 400W out might be only two amps, but because of the rectifier-filter construction it doesn't draw that two amps continuously. It draws it in very brief gulps 120 times a second. Typical conduction angle might be 20 percent in a well designed supply; with massively oversize filter caps it could be as small as 5 percent. Massively oversized filter caps have been all the rage in consumer audio for too many decades now. The size of fuse you have to put in depends not on simple average current (2 amps) but the root-mean-square (RMS) current (which could indeed be 8 amps at full load). That shouldn't be terribly hard to calculate, assuming a conduction angle of your choice. So how about adding some support for the assertion? 10% conduction angle gives peak current of 20A, RMS current of 6.3A, not too unreasonable to choose an 8A fuse in that case. 6.25% conduction angle gives 8A RMS, but that'd blow the fuse way too often. It takes big capacitors and toroidal transformers with really stiff windings but many folks are building audio power supplies that way. I personally don't like razor-thin conduction angles like 10% but that's the style of other folks, not me! Tim. I don't feel like whipping up bulk supply simulation right now, please run yours and tell me the ripple voltages at 10% conduction and 6.25 % conduction. -- JosephKK Gegen dummheit kampfen die Gotter Selbst, vergebens.Â*Â* --Schiller |
#57
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
Eeyore wrote in message
... N Cook wrote: I get the impression board layout designers just use what has worked before as far as track dimensions etc There are published guidelines for temp rise vs current, copper thickness and track width. You'll find a chart of same in IEC60065 (electrical safety) in fact. The board layout guy will only use the data supplied by the design engineer. They're not psychic. Some 'design engineers' have a clue however. and don't actually consider in great detail catastrophic failure modes. Good designers will design for that. Yes this kit does support the CE mark. So what's the damn make and model FFS ! Why are you refusing to tell us one of the most important pieces of information ? Graham I was having a play with track width calculator http://www.pcbco.com.au/tracecalc.html and assuming it is still sort of valid at very high temps. Putting the melting point of copper of 1080 deg C then for 3.5mm strip of presumably 1 oz copper then the rupture current would be about 48 amps which seems reasonable. I knew it must be higher than 12 amps as that calculation was for round wire. By 1080 deg C we can forget about the solder run beefings. I think I'll leave my 60 amp transformer on the shelf - I'm happy with 48 amps -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#58
Posted to sci.electronics.repair,sci.electronics.design
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Opinions on adding fuses to power amp
N Cook wrote in message
... Eeyore wrote in message ... N Cook wrote: I get the impression board layout designers just use what has worked before as far as track dimensions etc There are published guidelines for temp rise vs current, copper thickness and track width. You'll find a chart of same in IEC60065 (electrical safety) in fact. The board layout guy will only use the data supplied by the design engineer. They're not psychic. Some 'design engineers' have a clue however. and don't actually consider in great detail catastrophic failure modes. Good designers will design for that. Yes this kit does support the CE mark. So what's the damn make and model FFS ! Why are you refusing to tell us one of the most important pieces of information ? Graham I was having a play with track width calculator http://www.pcbco.com.au/tracecalc.html and assuming it is still sort of valid at very high temps. Putting the melting point of copper of 1080 deg C then for 3.5mm strip of presumably 1 oz copper then the rupture current would be about 48 amps which seems reasonable. I knew it must be higher than 12 amps as that calculation was for round wire. By 1080 deg C we can forget about the solder run beefings. I think I'll leave my 60 amp transformer on the shelf - I'm happy with 48 amps -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ I think, assuming they survive ordinary power-ups a few times, I'll settle on a mains side 4 amp anti-surge , with a 5 amp A/S ready to hand spare and 2 off 10 amp quick-blow in the DC lines. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#59
Posted to sci.electronics.repair
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Opinions on adding fuses to power amp
joseph2k wrote:
Tim Shoppa wrote: CJT wrote: Tim Shoppa wrote: N Cook wrote: 400 watt RMS amp for use on 240 V mains. Destructed due to metal dropping in and shorting the amp . The only fuse is on the mains rated at 8 amp, maker's design rating, which shows no sag , discolour or anything like that, ie untouched. Shorted power trannies, burnt low power trannies and even a piece of 3mm trace from the main bridge rectifier burnt through and that had 2 runs of added solder over the track for current carrying, the other polarity trace overheated but not ruptured I'm thinking of bridging that gap with a fuse and another on the other rail after cutting it. The mains transformer is rated at 2x 47V,5 amp. So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added fuses of what rating ? The power supply to your amp probably has massively oversize filter capacitors. Average current draw at 400W out might be only two amps, but because of the rectifier-filter construction it doesn't draw that two amps continuously. It draws it in very brief gulps 120 times a second. Typical conduction angle might be 20 percent in a well designed supply; with massively oversize filter caps it could be as small as 5 percent. Massively oversized filter caps have been all the rage in consumer audio for too many decades now. The size of fuse you have to put in depends not on simple average current (2 amps) but the root-mean-square (RMS) current (which could indeed be 8 amps at full load). That shouldn't be terribly hard to calculate, assuming a conduction angle of your choice. So how about adding some support for the assertion? 10% conduction angle gives peak current of 20A, RMS current of 6.3A, not too unreasonable to choose an 8A fuse in that case. 6.25% conduction angle gives 8A RMS, but that'd blow the fuse way too often. It takes big capacitors and toroidal transformers with really stiff windings but many folks are building audio power supplies that way. I personally don't like razor-thin conduction angles like 10% but that's the style of other folks, not me! Tim. I don't feel like whipping up bulk supply simulation right now, please run yours and tell me the ripple voltages at 10% conduction and 6.25 % conduction. I refuse to run such a simulation: this is the sort of stuff that was discussed in two pages of a 1930's-era electronics textbook in the beginning of a chapter on power supplies. Math is what a high-school student was expected to know. You might as well ask me to run a simulation to prove that 1 volt across 1kohm gives 1mA :-). I'll give you the result: at 10% conduction angle, ripple is 5%. (If you have a pocket calculator, the voltage at the bottom of the ripple is Vpeak*cos(.1*pi).) At 6.25% conduction angle, the ripple is 2%. Other handy results: 15% conduction angle, ripple is 11%. 20% conduction angle gives ripple of 19%. If you look a little later in the 70-year old electronics texts, they get into I2R and other losses in transformers and making the proper economic choice in sizing transformers and capcitors. They also get into my favorite filtering method, choke-input! (A method at least mentioned in the better of the more modern textbooks). Tim. |
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