On 11/29/2014 10:04 AM, John S wrote:> On 11/29/2014 8:30 AM, rickman wrote: >> On 11/29/2014 9:04 AM, meow2222@care2.com wrote: >>> On Saturday, November 29, 2014 7:41:59 AM UTC, John Fields wrote: >>>> On Fri, 28 Nov 2014 03:00:12 -0800 (PST), meow2222@care2.com wrote: >>>>> On Friday, November 28, 2014 9:26:13 AM UTC, John Fields wrote: >>>>>> On Thu, 27 Nov 2014 20:57:10 -0800 (PST), dakupoto@gmail.com wrote: >>>>>>> On Thursday, November 27, 2014 12:45:53 PM UTC-5, John Fields wrote: >>>>>>>> On Wed, 26 Nov 2014 21:21:58 -0800 (PST), dakupoto@gmail.com wrote: >>> >>> >>>>>> For example, consider 120 volt 60Hz mains being used to drive a >>>>>> 12V/12mA load through two capacitors for "perfect" isolation from >>>>>> both sides of the mains: >>>>>> >>>>>> C1 >>>>>> 120L>-----[CAP]----+ >>>>>> |R1 >>>>>> [1000R] >>>>>> C2 | >>>>>> 120N>-----[CAP]----+ >>>>>> >>>>>> FIG 1. >>>>>> >>>>>> In order to make life easier, though, we can combine C1 and C2 -for >>>>>> now - and have our circuit look like this: >>>>>> >>>>>> E1 E2 >>>>>> / C1 / >>>>>> 120L>-----[CAP]----+ >>>>>> |R1 >>>>>> [1000R] >>>>>> <--I1--> | >>>>>> 120N>--------------+ >>>>>> >>>>>> FIG 2. >>> >>>>>> Finally, to return to the configuration in figure 1, the capacitors >>>>>> are equal-valued and in series, so the value of each must be twice >>>>>> the value of the single cap shown in figure 2, or 534nF each. >>>>>> >>>>>> That's about half a microfarad each for a 12mA load, so if the load >>>>>> goes to 120mA the caps go to about 5.5�F each, and to about 55�F >>>>>> each for a 1200mA load. >>>>>> >>>>>> Because of that and because of the safety issues surrounding using >>>>>> caps for off-line voltage droppers, transformers start looking >>>>>> better than caps somewhere between three and ten VA, I'd guess, with >>>>>> anything notmuch higher than that being no contest. >>> >>>>> The C in your circuit acts like a dropper or ballast, it doesn't >>>>> give full isolation. Touch the load and you can still get a shock. >>>>> Cs on both L&N give a load floating at half mains V, ground the load >>>>> and i doubles. >>> >>>> I disagree in that the shock can only occur if the toucher isn't >>>> floating, and since the capacitors' dielectric provides the >>>> insulation to prevent ohmic contact between the load and either side >>>> of the mains, the load is, by definition, isolated. >>> >>> Lets be clear here. Capacitors pass current at 110/230v ac. How much >>> current depends on the capacitance. A cap that passed 1A to a load >>> would also pass about 1A to a human, frying them. Its only safe when, >>> among other things, the cap is small enough to limit current to a >>> touch-safe value. >>> >>> >>>> In addition, the OP's: >>>> >>>> "Indeed, it is very much possible to provide galvanic isolation with >>>> capacitors for AC, and in fact, capacitive reactance may be used to >>>> reduce high mains side current(5A) on manageable isolated load side, >>>> as well." >>>> >>>> seems to indicate interest in situations where the load will be >>>> floating, so even a single-capacitor solution should work for him. >>> >>> Single caps work ok for the load, but leave a potential toucher >>> touching the mains directly. >>> >>> >>>>> I've long thought that CR droppers would make the basis of good >>>>> power supplies for sub-mA [touchable] loads, and could be allowed >>>>> quite safely. >>> >>>> I'd only ever advocate the use of a reactively controlled supply if >>>> it was used in a double-insulated device. >>> >>> If the caps are suitably rated and sized, and you have sufficient >>> current control for safety from either C or R in the psu, you get >>> something needing multiple failures for any risk to occur, which is >>> perfectly satisfactory safety-wise. At that point there is no need for >>> any insulation from the user. >> >> I've always wondered about the wisdom of the "multiple" failure method >> to minimize risk. Like "double insulated" hand tools, vs. grounded >> devices. If one layer of the insulation fails you are not exposed to a >> shock. But at that point the tool is only "single insulated" and the >> low risk has just become much higher. If there is no way to determine >> that one of the two protections has failed, there can potentially be >> many devices running around that are just one failure away from an >> accident. >> >> Potentially, again if there is no way to verify the proper functioning >> of each layer of protection, such a device could have been manufactured >> with one layer of protection defective. >> > > And your solution is? Quadruple insulation, or more? Little built-in > detectors? How much are you willing to pay for your safety?What are you talking about??? -- Rick
Galvanic isolation without transformers ??
Started by ●November 27, 2014
Reply by ●November 29, 20142014-11-29
Reply by ●November 29, 20142014-11-29
On 11/29/2014 10:11 AM, meow2222@care2.com wrote:> On Saturday, November 29, 2014 2:31:07 PM UTC, rickman wrote: >> On 11/29/2014 9:04 AM, meow2222@care2.com wrote: >>> On Saturday, November 29, 2014 7:41:59 AM UTC, John Fields wrote: >>>> On Fri, 28 Nov 2014 03:00:12 -0800 (PST), meow2222@care2.com wrote: >>>>> On Friday, November 28, 2014 9:26:13 AM UTC, John Fields wrote: >>>>>> On Thu, 27 Nov 2014 20:57:10 -0800 (PST), dakupoto@gmail.com wrote: >>>>>>> On Thursday, November 27, 2014 12:45:53 PM UTC-5, John Fields wrote: >>>>>>>> On Wed, 26 Nov 2014 21:21:58 -0800 (PST), dakupoto@gmail.com wrote: >>> >>> >>>>>> For example, consider 120 volt 60Hz mains being used to drive a >>>>>> 12V/12mA load through two capacitors for "perfect" isolation from >>>>>> both sides of the mains: >>>>>> >>>>>> C1 >>>>>> 120L>-----[CAP]----+ >>>>>> |R1 >>>>>> [1000R] >>>>>> C2 | >>>>>> 120N>-----[CAP]----+ >>>>>> >>>>>> FIG 1. >>>>>> >>>>>> In order to make life easier, though, we can combine C1 and C2 -for >>>>>> now - and have our circuit look like this: >>>>>> >>>>>> E1 E2 >>>>>> / C1 / >>>>>> 120L>-----[CAP]----+ >>>>>> |R1 >>>>>> [1000R] >>>>>> <--I1--> | >>>>>> 120N>--------------+ >>>>>> >>>>>> FIG 2. >>> >>>>>> Finally, to return to the configuration in figure 1, the capacitors >>>>>> are equal-valued and in series, so the value of each must be twice >>>>>> the value of the single cap shown in figure 2, or 534nF each. >>>>>> >>>>>> That's about half a microfarad each for a 12mA load, so if the load >>>>>> goes to 120mA the caps go to about 5.5湩 each, and to about 55湩 >>>>>> each for a 1200mA load. >>>>>> >>>>>> Because of that and because of the safety issues surrounding using >>>>>> caps for off-line voltage droppers, transformers start looking >>>>>> better than caps somewhere between three and ten VA, I'd guess, with >>>>>> anything notmuch higher than that being no contest. >>> >>>>> The C in your circuit acts like a dropper or ballast, it doesn't give full isolation. Touch the load and you can still get a shock. Cs on both L&N give a load floating at half mains V, ground the load and i doubles. >>> >>>> I disagree in that the shock can only occur if the toucher isn't >>>> floating, and since the capacitors' dielectric provides the >>>> insulation to prevent ohmic contact between the load and either side >>>> of the mains, the load is, by definition, isolated. >>> >>> Lets be clear here. Capacitors pass current at 110/230v ac. How much current depends on the capacitance. A cap that passed 1A to a load would also pass about 1A to a human, frying them. Its only safe when, among other things, the cap is small enough to limit current to a touch-safe value. >>> >>> >>>> In addition, the OP's: >>>> >>>> "Indeed, it is very much possible to provide galvanic isolation with >>>> capacitors for AC, and in fact, capacitive reactance may be used to >>>> reduce high mains side current(5A) on manageable isolated load side, >>>> as well." >>>> >>>> seems to indicate interest in situations where the load will be >>>> floating, so even a single-capacitor solution should work for him. >>> >>> Single caps work ok for the load, but leave a potential toucher touching the mains directly. >>> >>> >>>>> I've long thought that CR droppers would make the basis of good power supplies for sub-mA [touchable] loads, and could be allowed quite safely. >>> >>>> I'd only ever advocate the use of a reactively controlled supply if >>>> it was used in a double-insulated device. >>> >>> If the caps are suitably rated and sized, and you have sufficient current control for safety from either C or R in the psu, you get something needing multiple failures for any risk to occur, which is perfectly satisfactory safety-wise. At that point there is no need for any insulation from the user. >> >> I've always wondered about the wisdom of the "multiple" failure method >> to minimize risk. Like "double insulated" hand tools, vs. grounded >> devices. If one layer of the insulation fails you are not exposed to a >> shock. But at that point the tool is only "single insulated" and the >> low risk has just become much higher. If there is no way to determine >> that one of the two protections has failed, there can potentially be >> many devices running around that are just one failure away from an >> accident. > > There are. Its a big improvement.There are what? What is a big improvement?>> Potentially, again if there is no way to verify the proper functioning >> of each layer of protection, such a device could have been manufactured >> with one layer of protection defective. > > Plenty of those about.I'm not convinced we weren't a lot better with mandatory grounds on all hand held power tools.... other than the battery powered ones of course, lol. -- Rick
Reply by ●November 29, 20142014-11-29
Den l=C3=B8rdag den 29. november 2014 16.29.25 UTC+1 skrev rickman:> On 11/29/2014 10:11 AM, meow2222@care2.com wrote: > > On Saturday, November 29, 2014 2:31:07 PM UTC, rickman wrote: > >> On 11/29/2014 9:04 AM, meow2222@care2.com wrote: > >>> On Saturday, November 29, 2014 7:41:59 AM UTC, John Fields wrote: > >>>> On Fri, 28 Nov 2014 03:00:12 -0800 (PST), meow2222@care2.com wrote: > >>>>> On Friday, November 28, 2014 9:26:13 AM UTC, John Fields wrote: > >>>>>> On Thu, 27 Nov 2014 20:57:10 -0800 (PST), dakupoto@gmail.com wrote=:> >>>>>>> On Thursday, November 27, 2014 12:45:53 PM UTC-5, John Fields wro=te:> >>>>>>>> On Wed, 26 Nov 2014 21:21:58 -0800 (PST), dakupoto@gmail.com wro=te:> >>> > >>> > >>>>>> For example, consider 120 volt 60Hz mains being used to drive a > >>>>>> 12V/12mA load through two capacitors for "perfect" isolation from > >>>>>> both sides of the mains: > >>>>>> > >>>>>> C1 > >>>>>> 120L>-----[CAP]----+ > >>>>>> |R1 > >>>>>> [1000R] > >>>>>> C2 | > >>>>>> 120N>-----[CAP]----+ > >>>>>> > >>>>>> FIG 1. > >>>>>> > >>>>>> In order to make life easier, though, we can combine C1 and C2 -fo=r> >>>>>> now - and have our circuit look like this: > >>>>>> > >>>>>> E1 E2 > >>>>>> / C1 / > >>>>>> 120L>-----[CAP]----+ > >>>>>> |R1 > >>>>>> [1000R] > >>>>>> <--I1--> | > >>>>>> 120N>--------------+ > >>>>>> > >>>>>> FIG 2. > >>> > >>>>>> Finally, to return to the configuration in figure 1, the capacitor=s> >>>>>> are equal-valued and in series, so the value of each must be twice > >>>>>> the value of the single cap shown in figure 2, or 534nF each. > >>>>>> > >>>>>> That's about half a microfarad each for a 12mA load, so if the loa=d> >>>>>> goes to 120mA the caps go to about 5.5=E6=B9=A9 each, and to about=55=E6=B9=A9> >>>>>> each for a 1200mA load. > >>>>>> > >>>>>> Because of that and because of the safety issues surrounding using > >>>>>> caps for off-line voltage droppers, transformers start looking > >>>>>> better than caps somewhere between three and ten VA, I'd guess, wi=th> >>>>>> anything notmuch higher than that being no contest. > >>> > >>>>> The C in your circuit acts like a dropper or ballast, it doesn't gi=ve full isolation. Touch the load and you can still get a shock. Cs on both= L&N give a load floating at half mains V, ground the load and i doubles.> >>> > >>>> I disagree in that the shock can only occur if the toucher isn't > >>>> floating, and since the capacitors' dielectric provides the > >>>> insulation to prevent ohmic contact between the load and either side > >>>> of the mains, the load is, by definition, isolated. > >>> > >>> Lets be clear here. Capacitors pass current at 110/230v ac. How much =current depends on the capacitance. A cap that passed 1A to a load would al= so pass about 1A to a human, frying them. Its only safe when, among other t= hings, the cap is small enough to limit current to a touch-safe value.> >>> > >>> > >>>> In addition, the OP's: > >>>> > >>>> "Indeed, it is very much possible to provide galvanic isolation with > >>>> capacitors for AC, and in fact, capacitive reactance may be used to > >>>> reduce high mains side current(5A) on manageable isolated load side, > >>>> as well." > >>>> > >>>> seems to indicate interest in situations where the load will be > >>>> floating, so even a single-capacitor solution should work for him. > >>> > >>> Single caps work ok for the load, but leave a potential toucher touch=ing the mains directly.> >>> > >>> > >>>>> I've long thought that CR droppers would make the basis of good pow=er supplies for sub-mA [touchable] loads, and could be allowed quite safely= .> >>> > >>>> I'd only ever advocate the use of a reactively controlled supply if > >>>> it was used in a double-insulated device. > >>> > >>> If the caps are suitably rated and sized, and you have sufficient cur=rent control for safety from either C or R in the psu, you get something ne= eding multiple failures for any risk to occur, which is perfectly satisfact= ory safety-wise. At that point there is no need for any insulation from the= user.> >> > >> I've always wondered about the wisdom of the "multiple" failure method > >> to minimize risk. Like "double insulated" hand tools, vs. grounded > >> devices. If one layer of the insulation fails you are not exposed to =a> >> shock. But at that point the tool is only "single insulated" and the > >> low risk has just become much higher. If there is no way to determine > >> that one of the two protections has failed, there can potentially be > >> many devices running around that are just one failure away from an > >> accident. > > > > There are. Its a big improvement. >=20 > There are what? What is a big improvement? >=20 >=20 > >> Potentially, again if there is no way to verify the proper functioning > >> of each layer of protection, such a device could have been manufacture=d> >> with one layer of protection defective. > > > > Plenty of those about. >=20 > I'm not convinced we weren't a lot better with mandatory grounds on all==20> hand held power tools.... other than the battery powered ones of course,==20> lol. >=20Around here very little is grounded, most sockets and plugs don't even have ground. ground fault interrupter is mandatory =20 The biggest problem is that it puts the chassis of most things with switchi= ng supplies at 120V via the Y capacitors It'll give you good jolt if you touch something grounded and a computer,=20 plenty of inputs have been killed by plugging an ungrounded computer into a= TV grounded via the antenna cable -Lasse
Reply by ●November 29, 20142014-11-29
On Sat, 29 Nov 2014 09:30:27 -0500, rickman <gnuarm@gmail.com> wrote:>> If the caps are suitably rated and sized, and you have sufficient current control for safety from either C or R in the psu, you get something needing multiple failures for any risk to occur, which is perfectly satisfactory safety-wise. At that point there is no need for any insulation from the user. > >I've always wondered about the wisdom of the "multiple" failure method >to minimize risk. Like "double insulated" hand tools, vs. grounded >devices. If one layer of the insulation fails you are not exposed to a >shock. But at that point the tool is only "single insulated" and the >low risk has just become much higher. If there is no way to determine >that one of the two protections has failed, there can potentially be >many devices running around that are just one failure away from an >accident. > >Potentially, again if there is no way to verify the proper functioning >of each layer of protection, such a device could have been manufactured >with one layer of protection defective.One method used in operation theaters is the IT earthing practice. It is a normal three phase feed but the Neutral is not connected to ground. Assuming a 230/400 V system, a ground fault from L1 phase to ground will put L1 to ground potential and L2 and L3 will be 400 V from ground and Neutral will be above 230 V ground. No big deal, the system continues to function normally and the operation can be completed. With a big (megaohms) resistor from the star point (Neutral) to ground, there is the 230 V, which will active an indication that there are somewhere a ground fault, which needs to be fixed before starting the next operation.
Reply by ●November 29, 20142014-11-29
On 11/29/2014 9:26 AM, rickman wrote:> On 11/29/2014 10:04 AM, John S wrote: >> On 11/29/2014 8:30 AM, rickman wrote: >>> On 11/29/2014 9:04 AM, meow2222@care2.com wrote: >>>> On Saturday, November 29, 2014 7:41:59 AM UTC, John Fields wrote: >>>>> On Fri, 28 Nov 2014 03:00:12 -0800 (PST), meow2222@care2.com wrote: >>>>>> On Friday, November 28, 2014 9:26:13 AM UTC, John Fields wrote: >>>>>>> On Thu, 27 Nov 2014 20:57:10 -0800 (PST), dakupoto@gmail.com wrote: >>>>>>>> On Thursday, November 27, 2014 12:45:53 PM UTC-5, John Fields >>>>>>>> wrote: >>>>>>>>> On Wed, 26 Nov 2014 21:21:58 -0800 (PST), dakupoto@gmail.com >>>>>>>>> wrote: >>>> >>>> >>>>>>> For example, consider 120 volt 60Hz mains being used to drive a >>>>>>> 12V/12mA load through two capacitors for "perfect" isolation from >>>>>>> both sides of the mains: >>>>>>> >>>>>>> C1 >>>>>>> 120L>-----[CAP]----+ >>>>>>> |R1 >>>>>>> [1000R] >>>>>>> C2 | >>>>>>> 120N>-----[CAP]----+ >>>>>>> >>>>>>> FIG 1. >>>>>>> >>>>>>> In order to make life easier, though, we can combine C1 and C2 -for >>>>>>> now - and have our circuit look like this: >>>>>>> >>>>>>> E1 E2 >>>>>>> / C1 / >>>>>>> 120L>-----[CAP]----+ >>>>>>> |R1 >>>>>>> [1000R] >>>>>>> <--I1--> | >>>>>>> 120N>--------------+ >>>>>>> >>>>>>> FIG 2. >>>> >>>>>>> Finally, to return to the configuration in figure 1, the capacitors >>>>>>> are equal-valued and in series, so the value of each must be twice >>>>>>> the value of the single cap shown in figure 2, or 534nF each. >>>>>>> >>>>>>> That's about half a microfarad each for a 12mA load, so if the load >>>>>>> goes to 120mA the caps go to about 5.5�F each, and to about 55�F >>>>>>> each for a 1200mA load. >>>>>>> >>>>>>> Because of that and because of the safety issues surrounding using >>>>>>> caps for off-line voltage droppers, transformers start looking >>>>>>> better than caps somewhere between three and ten VA, I'd guess, with >>>>>>> anything notmuch higher than that being no contest. >>>> >>>>>> The C in your circuit acts like a dropper or ballast, it doesn't >>>>>> give full isolation. Touch the load and you can still get a shock. >>>>>> Cs on both L&N give a load floating at half mains V, ground the load >>>>>> and i doubles. >>>> >>>>> I disagree in that the shock can only occur if the toucher isn't >>>>> floating, and since the capacitors' dielectric provides the >>>>> insulation to prevent ohmic contact between the load and either side >>>>> of the mains, the load is, by definition, isolated. >>>> >>>> Lets be clear here. Capacitors pass current at 110/230v ac. How much >>>> current depends on the capacitance. A cap that passed 1A to a load >>>> would also pass about 1A to a human, frying them. Its only safe when, >>>> among other things, the cap is small enough to limit current to a >>>> touch-safe value. >>>> >>>> >>>>> In addition, the OP's: >>>>> >>>>> "Indeed, it is very much possible to provide galvanic isolation with >>>>> capacitors for AC, and in fact, capacitive reactance may be used to >>>>> reduce high mains side current(5A) on manageable isolated load side, >>>>> as well." >>>>> >>>>> seems to indicate interest in situations where the load will be >>>>> floating, so even a single-capacitor solution should work for him. >>>> >>>> Single caps work ok for the load, but leave a potential toucher >>>> touching the mains directly. >>>> >>>> >>>>>> I've long thought that CR droppers would make the basis of good >>>>>> power supplies for sub-mA [touchable] loads, and could be allowed >>>>>> quite safely. >>>> >>>>> I'd only ever advocate the use of a reactively controlled supply if >>>>> it was used in a double-insulated device. >>>> >>>> If the caps are suitably rated and sized, and you have sufficient >>>> current control for safety from either C or R in the psu, you get >>>> something needing multiple failures for any risk to occur, which is >>>> perfectly satisfactory safety-wise. At that point there is no need for >>>> any insulation from the user. >>> >>> I've always wondered about the wisdom of the "multiple" failure method >>> to minimize risk. Like "double insulated" hand tools, vs. grounded >>> devices. If one layer of the insulation fails you are not exposed to a >>> shock. But at that point the tool is only "single insulated" and the >>> low risk has just become much higher. If there is no way to determine >>> that one of the two protections has failed, there can potentially be >>> many devices running around that are just one failure away from an >>> accident. >>> >>> Potentially, again if there is no way to verify the proper functioning >>> of each layer of protection, such a device could have been manufactured >>> with one layer of protection defective. >>> >> >> And your solution is? Quadruple insulation, or more? Little built-in >> detectors? How much are you willing to pay for your safety? > > What are you talking about???What is your solution to the problem?
Reply by ●November 29, 20142014-11-29
In article <6e3ad3e8-2540-443d-b7ff-c3a402bf27d2@googlegroups.com>, pallison49@gmail.com says...> > John Fields wrote: > > > > > I disagree in that the shock can only occur if the toucher isn't > > floating, and since the capacitors' dielectric provides the > > insulation to prevent ohmic contact between the load and either side > > of the mains, the load is, by definition, isolated. > > ** Utterly insane crap. > > > > I'd only ever advocate the use of a reactively controlled supply if > > it was used in a double-insulated device. > > > ** Even worse insane crap. > > John Fields is very seriously demented. > > You **MUST** ignore whatever this sad, sick ghost of a human being says. > > He has no control of his insanity. > > > > > .... PhilYeah, that maybe true however, every one needs to start some where! :) Jamie
Reply by ●November 29, 20142014-11-29
On 11/29/2014 11:13 AM, Lasse Langwadt Christensen wrote:> Den lørdag den 29. november 2014 16.29.25 UTC+1 skrev rickman: >> On 11/29/2014 10:11 AM, meow2222@care2.com wrote: >>> On Saturday, November 29, 2014 2:31:07 PM UTC, rickman wrote: >>>> On 11/29/2014 9:04 AM, meow2222@care2.com wrote: >>>>> On Saturday, November 29, 2014 7:41:59 AM UTC, John Fields wrote: >>>>>> On Fri, 28 Nov 2014 03:00:12 -0800 (PST), meow2222@care2.com wrote: >>>>>>> On Friday, November 28, 2014 9:26:13 AM UTC, John Fields wrote: >>>>>>>> On Thu, 27 Nov 2014 20:57:10 -0800 (PST), dakupoto@gmail.com wrote: >>>>>>>>> On Thursday, November 27, 2014 12:45:53 PM UTC-5, John Fields wrote: >>>>>>>>>> On Wed, 26 Nov 2014 21:21:58 -0800 (PST), dakupoto@gmail.com wrote: >>>>> >>>>> >>>>>>>> For example, consider 120 volt 60Hz mains being used to drive a >>>>>>>> 12V/12mA load through two capacitors for "perfect" isolation from >>>>>>>> both sides of the mains: >>>>>>>> >>>>>>>> C1 >>>>>>>> 120L>-----[CAP]----+ >>>>>>>> |R1 >>>>>>>> [1000R] >>>>>>>> C2 | >>>>>>>> 120N>-----[CAP]----+ >>>>>>>> >>>>>>>> FIG 1. >>>>>>>> >>>>>>>> In order to make life easier, though, we can combine C1 and C2 -for >>>>>>>> now - and have our circuit look like this: >>>>>>>> >>>>>>>> E1 E2 >>>>>>>> / C1 / >>>>>>>> 120L>-----[CAP]----+ >>>>>>>> |R1 >>>>>>>> [1000R] >>>>>>>> <--I1--> | >>>>>>>> 120N>--------------+ >>>>>>>> >>>>>>>> FIG 2. >>>>> >>>>>>>> Finally, to return to the configuration in figure 1, the capacitors >>>>>>>> are equal-valued and in series, so the value of each must be twice >>>>>>>> the value of the single cap shown in figure 2, or 534nF each. >>>>>>>> >>>>>>>> That's about half a microfarad each for a 12mA load, so if the load >>>>>>>> goes to 120mA the caps go to about 5.5湩 each, and to about 55湩 >>>>>>>> each for a 1200mA load. >>>>>>>> >>>>>>>> Because of that and because of the safety issues surrounding using >>>>>>>> caps for off-line voltage droppers, transformers start looking >>>>>>>> better than caps somewhere between three and ten VA, I'd guess, with >>>>>>>> anything notmuch higher than that being no contest. >>>>> >>>>>>> The C in your circuit acts like a dropper or ballast, it doesn't give full isolation. Touch the load and you can still get a shock. Cs on both L&N give a load floating at half mains V, ground the load and i doubles. >>>>> >>>>>> I disagree in that the shock can only occur if the toucher isn't >>>>>> floating, and since the capacitors' dielectric provides the >>>>>> insulation to prevent ohmic contact between the load and either side >>>>>> of the mains, the load is, by definition, isolated. >>>>> >>>>> Lets be clear here. Capacitors pass current at 110/230v ac. How much current depends on the capacitance. A cap that passed 1A to a load would also pass about 1A to a human, frying them. Its only safe when, among other things, the cap is small enough to limit current to a touch-safe value. >>>>> >>>>> >>>>>> In addition, the OP's: >>>>>> >>>>>> "Indeed, it is very much possible to provide galvanic isolation with >>>>>> capacitors for AC, and in fact, capacitive reactance may be used to >>>>>> reduce high mains side current(5A) on manageable isolated load side, >>>>>> as well." >>>>>> >>>>>> seems to indicate interest in situations where the load will be >>>>>> floating, so even a single-capacitor solution should work for him. >>>>> >>>>> Single caps work ok for the load, but leave a potential toucher touching the mains directly. >>>>> >>>>> >>>>>>> I've long thought that CR droppers would make the basis of good power supplies for sub-mA [touchable] loads, and could be allowed quite safely.. >>>>> >>>>>> I'd only ever advocate the use of a reactively controlled supply if >>>>>> it was used in a double-insulated device. >>>>> >>>>> If the caps are suitably rated and sized, and you have sufficient current control for safety from either C or R in the psu, you get something needing multiple failures for any risk to occur, which is perfectly satisfactory safety-wise. At that point there is no need for any insulation from the user. >>>> >>>> I've always wondered about the wisdom of the "multiple" failure method >>>> to minimize risk. Like "double insulated" hand tools, vs. grounded >>>> devices. If one layer of the insulation fails you are not exposed to a >>>> shock. But at that point the tool is only "single insulated" and the >>>> low risk has just become much higher. If there is no way to determine >>>> that one of the two protections has failed, there can potentially be >>>> many devices running around that are just one failure away from an >>>> accident. >>> >>> There are. Its a big improvement. >> >> There are what? What is a big improvement? >> >> >>>> Potentially, again if there is no way to verify the proper functioning >>>> of each layer of protection, such a device could have been manufactured >>>> with one layer of protection defective. >>> >>> Plenty of those about. >> >> I'm not convinced we weren't a lot better with mandatory grounds on all >> hand held power tools.... other than the battery powered ones of course, >> lol. >> > > Around here very little is grounded, most sockets and plugs don't even have > ground. ground fault interrupter is mandatory > > The biggest problem is that it puts the chassis of most things with switching supplies at 120V via the Y capacitors > It'll give you good jolt if you touch something grounded and a computer, > plenty of inputs have been killed by plugging an ungrounded computer into a TV > grounded via the antenna cableI have no idea what you are talking about. I guess you aren't in the US. Here outlets have ground by law. Hot chassis have not be used here in over 50 years! -- Rick
Reply by ●November 29, 20142014-11-29
On 29/11/14 08:23, Jasen Betts wrote:> On 2014-11-28, Phil Allison <pallison49@gmail.com> wrote: >> daku...@gmail.com wrote: >>> Recently, >>> we were discussing the general issue of >>> galvanic isolation, and one of the items >>> discussed was capacitive isolation. Indeed, >>> it is very much possible to provide galvanic >>> isolation with capacitors for AC, and in >>> fact, capacitive reactance may be used >>> to reduce high mains side current(5A) >>> on manageable isolated load side, as well. >>> May be this scheme could be used in some >>> low power power supplies. Surely this would >>> reduce the time needed to wind transformer >>> coils. >> >> >> ** You are talking complete bollocks. >> >> Capacitive *galvanic* isolation from the AC supply only works for signals - not power. > > increase the power frequency to several megahertzc and you can push > quite a bit through capacitors2nF requires 80MHz to reach 1 ohm. Are you sure you want a kilowatt of 80MHz just to save on magnetics?
Reply by ●November 30, 20142014-11-30
On Sat, 29 Nov 2014 20:22:30 -0500, rickman <gnuarm@gmail.com> wrote:>On 11/29/2014 11:13 AM, Lasse Langwadt Christensen wrote: >> Den l�rdag den 29. november 2014 16.29.25 UTC+1 skrev rickman: >>> On 11/29/2014 10:11 AM, meow2222@care2.com wrote: >>>> On Saturday, November 29, 2014 2:31:07 PM UTC, rickman wrote: >>>>> On 11/29/2014 9:04 AM, meow2222@care2.com wrote: >>>>>> On Saturday, November 29, 2014 7:41:59 AM UTC, John Fields wrote: >>>>>>> On Fri, 28 Nov 2014 03:00:12 -0800 (PST), meow2222@care2.com wrote: >>>>>>>> On Friday, November 28, 2014 9:26:13 AM UTC, John Fields wrote: >>>>>>>>> On Thu, 27 Nov 2014 20:57:10 -0800 (PST), dakupoto@gmail.com wrote: >>>>>>>>>> On Thursday, November 27, 2014 12:45:53 PM UTC-5, John Fields wrote: >>>>>>>>>>> On Wed, 26 Nov 2014 21:21:58 -0800 (PST), dakupoto@gmail.com wrote: >>>>>> >>>>>> >>>>>>>>> For example, consider 120 volt 60Hz mains being used to drive a >>>>>>>>> 12V/12mA load through two capacitors for "perfect" isolation from >>>>>>>>> both sides of the mains: >>>>>>>>> >>>>>>>>> C1 >>>>>>>>> 120L>-----[CAP]----+ >>>>>>>>> |R1 >>>>>>>>> [1000R] >>>>>>>>> C2 | >>>>>>>>> 120N>-----[CAP]----+ >>>>>>>>> >>>>>>>>> FIG 1. >>>>>>>>> >>>>>>>>> In order to make life easier, though, we can combine C1 and C2 -for >>>>>>>>> now - and have our circuit look like this: >>>>>>>>> >>>>>>>>> E1 E2 >>>>>>>>> / C1 / >>>>>>>>> 120L>-----[CAP]----+ >>>>>>>>> |R1 >>>>>>>>> [1000R] >>>>>>>>> <--I1--> | >>>>>>>>> 120N>--------------+ >>>>>>>>> >>>>>>>>> FIG 2. >>>>>> >>>>>>>>> Finally, to return to the configuration in figure 1, the capacitors >>>>>>>>> are equal-valued and in series, so the value of each must be twice >>>>>>>>> the value of the single cap shown in figure 2, or 534nF each. >>>>>>>>> >>>>>>>>> That's about half a microfarad each for a 12mA load, so if the load >>>>>>>>> goes to 120mA the caps go to about 5.5? each, and to about 55? >>>>>>>>> each for a 1200mA load. >>>>>>>>> >>>>>>>>> Because of that and because of the safety issues surrounding using >>>>>>>>> caps for off-line voltage droppers, transformers start looking >>>>>>>>> better than caps somewhere between three and ten VA, I'd guess, with >>>>>>>>> anything notmuch higher than that being no contest. >>>>>> >>>>>>>> The C in your circuit acts like a dropper or ballast, it doesn't give full isolation. Touch the load and you can still get a shock. Cs on both L&N give a load floating at half mains V, ground the load and i doubles. >>>>>> >>>>>>> I disagree in that the shock can only occur if the toucher isn't >>>>>>> floating, and since the capacitors' dielectric provides the >>>>>>> insulation to prevent ohmic contact between the load and either side >>>>>>> of the mains, the load is, by definition, isolated. >>>>>> >>>>>> Lets be clear here. Capacitors pass current at 110/230v ac. How much current depends on the capacitance. A cap that passed 1A to a load would also pass about 1A to a human, frying them. Its only safe when, among other things, the cap is small enough to limit current to a touch-safe value. >>>>>> >>>>>> >>>>>>> In addition, the OP's: >>>>>>> >>>>>>> "Indeed, it is very much possible to provide galvanic isolation with >>>>>>> capacitors for AC, and in fact, capacitive reactance may be used to >>>>>>> reduce high mains side current(5A) on manageable isolated load side, >>>>>>> as well." >>>>>>> >>>>>>> seems to indicate interest in situations where the load will be >>>>>>> floating, so even a single-capacitor solution should work for him. >>>>>> >>>>>> Single caps work ok for the load, but leave a potential toucher touching the mains directly. >>>>>> >>>>>> >>>>>>>> I've long thought that CR droppers would make the basis of good power supplies for sub-mA [touchable] loads, and could be allowed quite safely.. >>>>>> >>>>>>> I'd only ever advocate the use of a reactively controlled supply if >>>>>>> it was used in a double-insulated device. >>>>>> >>>>>> If the caps are suitably rated and sized, and you have sufficient current control for safety from either C or R in the psu, you get something needing multiple failures for any risk to occur, which is perfectly satisfactory safety-wise. At that point there is no need for any insulation from the user. >>>>> >>>>> I've always wondered about the wisdom of the "multiple" failure method >>>>> to minimize risk. Like "double insulated" hand tools, vs. grounded >>>>> devices. If one layer of the insulation fails you are not exposed to a >>>>> shock. But at that point the tool is only "single insulated" and the >>>>> low risk has just become much higher. If there is no way to determine >>>>> that one of the two protections has failed, there can potentially be >>>>> many devices running around that are just one failure away from an >>>>> accident. >>>> >>>> There are. Its a big improvement. >>> >>> There are what? What is a big improvement? >>> >>> >>>>> Potentially, again if there is no way to verify the proper functioning >>>>> of each layer of protection, such a device could have been manufactured >>>>> with one layer of protection defective. >>>> >>>> Plenty of those about. >>> >>> I'm not convinced we weren't a lot better with mandatory grounds on all >>> hand held power tools.... other than the battery powered ones of course, >>> lol. >>> >> >> Around here very little is grounded, most sockets and plugs don't even have >> ground. ground fault interrupter is mandatory >> >> The biggest problem is that it puts the chassis of most things with switching supplies at 120V via the Y capacitors >> It'll give you good jolt if you touch something grounded and a computer, >> plenty of inputs have been killed by plugging an ungrounded computer into a TV >> grounded via the antenna cable > >I have no idea what you are talking about. I guess you aren't in the >US.Have you noticed that 95 % of the human population live outside the US.>Here outlets have ground by law. > >Hot chassis have not be used here in over 50 years!
Reply by ●November 30, 20142014-11-30
<upsidedown@downunder.com> wrote:> On Sat, 29 Nov 2014 20:22:30 -0500, rickman <gnuarm@gmail.com> wrote: >[...]> > > >I have no idea what you are talking about. I guess you aren't in the > >US. > > Have you noticed that 95 % of the human population live outside the > US.We are often misled when we fail to see the bigger picture. SCHOOLMASTER: Is the earth round or flat? BOY: Umm... Flat! SCHOOLMASTER: No, it's round. BOY: Well it's flat where I live. (With acknowledgements to Will Hay) -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
