Home |
Search |
Today's Posts |
|
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. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
I want to replace the original capacitor which is located across the AC
power line in a Zenith Trans Oceanic (tube radio). The original cap is a ..047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the ..1uf offering more protection against power line spikes? Thanks |
#2
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
Across the line use a type X cap, and 250V is fine. You could (should) add a fuse in between the cap and the line for an extra margin of safety.
|
#3
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
John-Del wrote on 8/24/2017 1:38 PM:
Across the line use a type X cap, and 250V is fine. You could (should) add a fuse in between the cap and the line for an extra margin of safety. I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? -- Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998 |
#4
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, 24 August 2017 18:20:22 UTC+1, wrote:
I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks 275v ac X-rated is safer than a vanilla 600v DC type. NT |
#5
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, 24 August 2017 18:53:09 UTC+1, rickman wrote:
John-Del wrote on 8/24/2017 1:38 PM: Across the line use a type X cap, and 250V is fine. You could (should) add a fuse in between the cap and the line for an extra margin of safety. I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? Y is for shock risk, X is for fire risk only. NT |
#6
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, August 24, 2017 at 1:53:09 PM UTC-4, rickman wrote:
John-Del wrote on 8/24/2017 1:38 PM: Across the line use a type X cap, and 250V is fine. You could (should) add a fuse in between the cap and the line for an extra margin of safety. I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? -- Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998 I agree with you, but the company line says to use X caps across the line.. These vintage radios rarely were equipped with fuses and generally used standard caps across the line. In all my years in consumer electronics I only saw a few of them short (spectacularly) and they were in RCA tube TVs in the 60s. They all made a bloody mess under the chassis but none caused fires.. RCA issued a recall that included new ceramic tubular caps and we changed them whenever we serviced these chassis. I've replaced some in my own radios with mylar caps but always fused them. Nowadays I've got tons of late model power supplies that are donors for all kinds of parts, X and Y caps included. |
#7
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
In article , rickman wrote:
I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? You can't count on a fuse to eliminate all of the risk of a fire. Some types of cap can fail with a "near short circuit" - they get leaky enough to start drawing a good fraction of an ampere, but aren't a dead-short. Imagine what happens if such a cap is "protected" by a 1-ampere fuse, but is drawing 100 mA at 120 volts... that's more than 10 watts, heating up the capacitor. If the cap doesn't either short itself well enough to blow the fuse, or go "open", it can definitely heat up enough to smoke and burn. I've seen this happen... a non-X/Y-rated film cap was used "across the line", and it overheated and nearly started a fire. "X" and "Y" caps are intended to be at least somewhat self-healing... if they develop a pinhole and start to short, the localized heating burns away the metallized film in the area of the short, and it opens. If I recall correctly they're also required to use an insulating resin which is at least somewhat flame-resistant. If you're going to the trouble of replacing an across-the-line cap in some equipment you're refurbishing, I'd suggest going right to a suitable "Y" cap. The additional cost is modest and the labor to install is the same. |
#8
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
|
#9
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
Dave Platt wrote on 8/24/2017 2:32 PM:
In article , rickman wrote: I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? You can't count on a fuse to eliminate all of the risk of a fire. Some types of cap can fail with a "near short circuit" - they get leaky enough to start drawing a good fraction of an ampere, but aren't a dead-short. Imagine what happens if such a cap is "protected" by a 1-ampere fuse, but is drawing 100 mA at 120 volts... that's more than 10 watts, heating up the capacitor. If the cap doesn't either short itself well enough to blow the fuse, or go "open", it can definitely heat up enough to smoke and burn. I've seen this happen... a non-X/Y-rated film cap was used "across the line", and it overheated and nearly started a fire. "X" and "Y" caps are intended to be at least somewhat self-healing... if they develop a pinhole and start to short, the localized heating burns away the metallized film in the area of the short, and it opens. If I recall correctly they're also required to use an insulating resin which is at least somewhat flame-resistant. If you're going to the trouble of replacing an across-the-line cap in some equipment you're refurbishing, I'd suggest going right to a suitable "Y" cap. The additional cost is modest and the labor to install is the same. Ok, so there is a failure mode where the cap won't draw enough current to blow the fuse, but can locally heat up enough to smoke and burn. Isn't that true for other parts in the device? What is the purpose of this cap anyway? I assume noise filtering. Wouldn't that be just as effective on the secondary of the transformer? -- Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998 |
#10
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, August 24, 2017 at 3:46:15 PM UTC-4, rickman wrote:
Dave Platt wrote on 8/24/2017 2:32 PM: In article , rickman wrote: I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? You can't count on a fuse to eliminate all of the risk of a fire. Some types of cap can fail with a "near short circuit" - they get leaky enough to start drawing a good fraction of an ampere, but aren't a dead-short. Imagine what happens if such a cap is "protected" by a 1-ampere fuse, but is drawing 100 mA at 120 volts... that's more than 10 watts, heating up the capacitor. If the cap doesn't either short itself well enough to blow the fuse, or go "open", it can definitely heat up enough to smoke and burn. I've seen this happen... a non-X/Y-rated film cap was used "across the line", and it overheated and nearly started a fire. "X" and "Y" caps are intended to be at least somewhat self-healing... if they develop a pinhole and start to short, the localized heating burns away the metallized film in the area of the short, and it opens. If I recall correctly they're also required to use an insulating resin which is at least somewhat flame-resistant. If you're going to the trouble of replacing an across-the-line cap in some equipment you're refurbishing, I'd suggest going right to a suitable "Y" cap. The additional cost is modest and the labor to install is the same. Ok, so there is a failure mode where the cap won't draw enough current to blow the fuse, but can locally heat up enough to smoke and burn. Isn't that true for other parts in the device? It's a possibility, but in my opinion it's highly unlikely for that to happen. A line capacitor that becomes leaky *and* with at least 20 amps of source current available to it will avalanche as it builds heat and short hard - in any case pulling more current than the small fuse installed in front of it. |
#11
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, August 24, 2017 at 1:20:22 PM UTC-4, wrote:
I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks |
#12
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
X & Y caps are designed to reduce the risk of shock in one case, and fire in another. Eschewing needless complexity, let them do their jobs and install a fuse - if desired - to cover then entire appliance, designed specifically for the load involved, starting surge and so forth.
Peter Wieck Melrose Park, PA |
#13
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, 24 August 2017 19:37:11 UTC+1, rickman wrote:
tabbypurr wrote on 8/24/2017 2:22 PM: On Thursday, 24 August 2017 18:53:09 UTC+1, rickman wrote: John-Del wrote on 8/24/2017 1:38 PM: Across the line use a type X cap, and 250V is fine. You could (should) add a fuse in between the cap and the line for an extra margin of safety. I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? Y is for shock risk, X is for fire risk only. Ok, I stand corrected. But the question remains. Fuse and X cap is like wearing a belt and suspenders. You need belt & suspenders since both fail. Just don't put the pics online. NT |
#14
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, 24 August 2017 20:08:08 UTC+1, Dave Platt wrote:
In article , rickman wrote: I thought the X and Y capacitors were used when a short would be a safety problem as in a shock hazard. Why would there be a shock hazard if a cap across the power line shorts? If you use a fuse any concern about a fire is eliminated. Then why would you need the X cap? You can't count on a fuse to eliminate all of the risk of a fire. Some types of cap can fail with a "near short circuit" - they get leaky enough to start drawing a good fraction of an ampere, but aren't a dead-short. Imagine what happens if such a cap is "protected" by a 1-ampere fuse, but is drawing 100 mA at 120 volts... that's more than 10 watts, heating up the capacitor. If the cap doesn't either short itself well enough to blow the fuse, or go "open", it can definitely heat up enough to smoke and burn. I've seen this happen... a non-X/Y-rated film cap was used "across the line", and it overheated and nearly started a fire. "X" and "Y" caps are intended to be at least somewhat self-healing... if they develop a pinhole and start to short, the localized heating burns away the metallized film in the area of the short, and it opens. If I recall correctly they're also required to use an insulating resin which is at least somewhat flame-resistant. If you're going to the trouble of replacing an across-the-line cap in some equipment you're refurbishing, I'd suggest going right to a suitable "Y" cap. The additional cost is modest and the labor to install is the same. All my Y caps are of far lower values than the Xs. Ys are intended to be for line to chassis use, hence far lower values than used for X caps. NT |
#15
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Thursday, 24 August 2017 21:33:57 UTC+1, wrote:
X & Y caps are designed to reduce the risk of shock in one case, and fire in another. Eschewing needless complexity, let them do their jobs and install a fuse - if desired - to cover then entire appliance, designed specifically for the load involved, starting surge and so forth. Peter Wieck Melrose Park, PA Fires & shocks used to happen due to dc rated cap failure. Hence X&Y were developed. Old radios lacking any fusing don't meet modern safety standards. The mains plug or distribution unit fuse can't be relied on to always provide satisfactory cover. You can repair them as is or can add a fuse, the latter is safer of course. NT |
#16
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
|
#17
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
wrote:
---------------------------- I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. ** The use of 600V DC rated caps across a 120VAC supply line is time honoured and normally perfectly OK - long as you are not in a high lightning area.. The issue that arose was in 240VA counties when wax impregnated paper caps were replaced with plastic film types. Some of these would last only weeks before developing internal shorts and exploding. The problem was soon found to be due to tiny pockets of air trapped inside the cap when being wound - corona discharge developed across these pockets and destroyed the cap. However, such corona currents did not normally occur with 120VAC so US makers kept using plastic film types. The fix for 240VAC places was to use two 600V film caps is series, thereby limiting the effective voltage to 120VA for each. Cap makers in the UK and elsewhere developed a method of winding "two in series" film caps as a single part and these became standard for class X caps. ..... Phil |
#19
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Tuesday, 29 August 2017 11:02:29 UTC+1, Michael Terrell wrote:
wrote: I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks People, learn to do the math. 600VDC/2.828=212VAC, so the 275 volt rated capacitor would be equaL to a 777VDC capacitor. 2.828 is the peak to peak factor on a RMS sine wave. That is 1.414 volts peak, on each side of zero Erm... no. Firstly 275v ac is 389v dc peak, so a 389v dc rating. Secondly the 2 ratings are not comparable, even after conversion to dc. The 600v cap has no fusing and most likely no double layer safety feature, the 275v ac one has both. NT |
#20
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
wrote:
On Tuesday, 29 August 2017 11:02:29 UTC+1, Michael Terrell wrote: wrote: I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks People, learn to do the math. 600VDC/2.828=212VAC, so the 275 volt rated capacitor would be equaL to a 777VDC capacitor. 2.828 is the peak to peak factor on a RMS sine wave. That is 1.414 volts peak, on each side of zero Erm... no. Firstly 275v ac is 389v dc peak, so a 389v dc rating. Secondly the 2 ratings are not comparable, even after conversion to dc. The 600v cap has no fusing and most likely no double layer safety feature, the 275v ac one has both. Think again. You have a negative and a positive peak, not just a single peak. You have to add them together. That is why the original DC cap was 600V, not 300V. -- Never **** off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-) |
#21
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
|
#22
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Wednesday, 30 August 2017 00:12:17 UTC+1, Michael Terrell wrote:
tabbypurr wrote: On Tuesday, 29 August 2017 11:02:29 UTC+1, Michael Terrell wrote: wrote: I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks People, learn to do the math. 600VDC/2.828=212VAC, so the 275 volt rated capacitor would be equaL to a 777VDC capacitor. 2.828 is the peak to peak factor on a RMS sine wave. That is 1.414 volts peak, on each side of zero Erm... no. Firstly 275v ac is 389v dc peak, so a 389v dc rating. Secondly the 2 ratings are not comparable, even after conversion to dc. The 600v cap has no fusing and most likely no double layer safety feature, the 275v ac one has both. Think again. You have a negative and a positive peak, not just a single peak. You have to add them together. That is why the original DC cap was 600V, not 300V. 275v ac = 389v peak, which can be withstood by a 389v rated capacitor. The reason they used 600v was to improve safety & reliability. However time showed that it wasn't good enough. X & Y caps are much better attempts to address the failure/safety issues. NT |
#23
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
Michael A. Terrell wrote on 8/29/2017 7:12 PM:
wrote: On Tuesday, 29 August 2017 11:02:29 UTC+1, Michael Terrell wrote: wrote: I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks People, learn to do the math. 600VDC/2.828=212VAC, so the 275 volt rated capacitor would be equaL to a 777VDC capacitor. 2.828 is the peak to peak factor on a RMS sine wave. That is 1.414 volts peak, on each side of zero Erm... no. Firstly 275v ac is 389v dc peak, so a 389v dc rating. Secondly the 2 ratings are not comparable, even after conversion to dc. The 600v cap has no fusing and most likely no double layer safety feature, the 275v ac one has both. Think again. You have a negative and a positive peak, not just a single peak. You have to add them together. That is why the original DC cap was 600V, not 300V. You are very good at math, but not so good at electronics. You don't need to consider the peak to peak voltage because the cap doesn't see them both at the same time. It sees one peak, then it sees the other peak. The fact that they are opposite polarity doesn't mean you need to add them to consider the capacitor voltage rating. -- Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998 |
#24
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
On Wednesday, 30 August 2017 00:12:17 UTC+1, Michael Terrell wrote:
tabbypurr wrote: On Tuesday, 29 August 2017 11:02:29 UTC+1, Michael Terrell wrote: wrote: I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors http://www.tuberadios.com/capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks People, learn to do the math. 600VDC/2.828=212VAC, so the 275 volt rated capacitor would be equaL to a 777VDC capacitor. 2.828 is the peak to peak factor on a RMS sine wave. That is 1.414 volts peak, on each side of zero Erm... no. Firstly 275v ac is 389v dc peak, so a 389v dc rating. Secondly the 2 ratings are not comparable, even after conversion to dc. The 600v cap has no fusing and most likely no double layer safety feature, the 275v ac one has both. Think again. You have a negative and a positive peak, not just a single peak. You have to add them together. That is why the original DC cap was 600V, not 300V. Sorry but that ain't so. NT |
#25
Posted to sci.electronics.repair
|
|||
|
|||
Radial X2-AC Safety Capacitors (Question)
Michael Terrell wrote:
------------------------ Think again. You have a negative and a positive peak, not just a single peak. You have to add them together. ** Nonsense, the DC rating is not exceeded by a reversing voltage. That is why the original DC cap was 600V, not 300V. ** False. It's simply that 600V rated caps survive much better. AC supply and load bridging involves spike voltages that can break down the insulation. ...... Phil |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Replacing Cans/Radial Capacitors w/ Axial Type | Electronics Repair | |||
Consumer Product Safety Comm. to discuss proposed SawStop technology safety rule | Woodworking | |||
Question about start capacitors | Metalworking | |||
Question about identifying SMT capacitors | Electronics Repair | |||
Computer power supply capacitors - generic question | Electronics Repair |