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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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#1
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fusible resistor substitute
I just worked on a set that had a shorted diode that took out the 1.5
ohm 7 watt fusible resistor. I have a 10watt resistor in stock but I really don't want to use it in place of a 7. In general it seems that I never seem to have the correct size of these things around when I need them. I was wondering if there is any reason that I couldn't substitute an appropriate size fuse for this application? The current in theory to open the resistor would have to exceed 3.24 amps. So I was thinking perhaps a 4 amp fuse would do. Anyone have any thoughts on this? Thanks. Lenny Stein, Barlen Electronics. |
#2
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fusible resistor substitute
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#3
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fusible resistor substitute
Franc Zabkar wrote in
: I'm conFUSEd ... Use a SLOW BLOW fuse. They have the same characteristic you're describing, blowing faster for bigger currents. |
#4
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fusible resistor substitute
Lenny:
If it were me and I was able to pinpoint the exact fault that caused the 7 watt resistor (like a shorted semiconductor or capacitor,etc.) to burn out I would without hesistation use a 10 watt replacement (forget the fuse substitute) and let the set run for an hour or so and test for overheated components and excessive current through the resistor. Usually this type and value of low ohm resistor is used for current limiting and/or inrush current control and in light of another drastic fault condition, the 10 watt resistor would perform it's task and open up just as the original value did. electricitym - - - - - - - snipped: wrote: I just worked on a set that had a shorted diode that took out the 1.5 ohm 7 watt fusible resistor. I have a 10watt resistor in stock but I really don't want to use it in place of a 7. In general it seems that I |
#5
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fusible resistor substitute
On Mon, 26 Jun 2006 08:03:00 +1000, Franc Zabkar
put finger to keyboard and composed: On 25 Jun 2006 09:41:06 -0700, " put finger to keyboard and composed: I just worked on a set that had a shorted diode that took out the 1.5 ohm 7 watt fusible resistor. I have a 10watt resistor in stock but I really don't want to use it in place of a 7. In general it seems that I never seem to have the correct size of these things around when I need them. I was wondering if there is any reason that I couldn't substitute an appropriate size fuse for this application? The current in theory to open the resistor would have to exceed 3.24 amps. So I was thinking perhaps a 4 amp fuse would do. Anyone have any thoughts on this? Thanks. Lenny Stein, Barlen Electronics. I've always wondered about how fusible resistors were rated. Here is the datasheet for Vishay's CMF fusible 0.25W/0.5W metal film flameproof fusible resistors: http://www.vishay.com/docs/31031/cmffuse.pdf The average fusing time for the 0.25W versions is 1 sec at 15W, 16s at 5W, and 24s at ~4W. That's a lot slower than a typical glass fuse. The fusing specs also state that lower resistance parts take longer to fuse than higher resistances. Here is the datasheet for the LCA...SI carbon fusible resistor series: http://www.vishay.com/docs/20137/lcasi.pdf The LCA0207SI has a power rating of 0.25W but requires a 4A overload Oops, that should be 4W, not 4A, so the fusing current is 4x rated current. before it will fuse. At this current the maximum time to fuse is 15 secs. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#6
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fusible resistor substitute
On Mon, 26 Jun 2006 02:30:58 -0000, Jim Land
put finger to keyboard and composed: Franc Zabkar wrote in : I'm conFUSEd ... Use a SLOW BLOW fuse. They have the same characteristic you're describing, blowing faster for bigger currents. True, but it would have to be a *very* slow fuse. For instance, these slo-blo fuses require only 0.6 sec before they rupture at 4x rated current: http://www.littelfuse.com/data/en/Ti...pletccurve.pdf OTOH, the fusible carbon resistors require 15s to rupture at 4x rated current. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#7
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fusible resistor substitute
wrote in message oups.com... I just worked on a set that had a shorted diode that took out the 1.5 ohm 7 watt fusible resistor. I have a 10watt resistor in stock but I really don't want to use it in place of a 7. In general it seems that I never seem to have the correct size of these things around when I need them. I was wondering if there is any reason that I couldn't substitute an appropriate size fuse for this application? The current in theory to open the resistor would have to exceed 3.24 amps. So I was thinking perhaps a 4 amp fuse would do. Anyone have any thoughts on this? Thanks. Lenny Stein, Barlen Electronics. I think I'd look for a 1 ohm 5 watt fusible resistor. The lower resistance will roughly accout for the lower wattage rating - yet still give the protection. Mark Z. |
#8
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fusible resistor substitute
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