On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison <pallison49@gmail.com> wrote:>John Larkin wrote: >------------------------------ >> >> >> >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. >> >> >> > I will be driving it from both sides, but not at the same time. >> >> >> >> >> >> Sure, a transformer works either way. >> >> >> >> >> > >> >> >** But makers nominate the primary and secondary for good reasons. >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. >> >> > >> >> >> >> Any winding can magnetize the core. The primary is the one you decide >> >> to put power into and the secondary is the one you elect to take power >> >> out of. >> > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. >> > >> >> 2-winding power transformers are usually designed for equal copper >> >> loss on both windings. So are thermally symmetric. > >> >> Sometimes some windings are insulated better than others. >> >> >> >> What other catches might there be? >> > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. >> > >> That's easy to think through. Power transformer models are simple and >> easy to reverse. > > ** But real transformers are not so simple.The Spice model of a transformer is simple: each winding has ESR, there's magnetizing inductance, and there's leakage inductance. Ignore capacitances at line frequencies. Given a Spice model, you can run it in either direction, with resistive or diode loads or whatever, and Spice will tell you everything you need to know. The only gotcha it misses is core saturation. I had to take TWO semisters of Electrical Machinery at Tulane, which was a huge nuisance, but I did learn about the circuit equivalent of a transformer, which was almost worth the hassle.> >> >You may have to seriously de-rate the transformer in order to use it that way, >>> mains frequency transformers under 100VA are the most affected. > >> A 100 VA transformer is happy moving 100 VA in either direction. > > ** JL has such simple faith in overly simple models. > > I wonder why ?I design things that work, and verify by experiment if there's any doubt. And the transformer model IS simple. One thing that's often worth verifying is temperature rise, with actual mounting and air flow. Transformer vendors are vague and the thermals are hard to math out. [1] If you are concerned about reversing a transformer, just try it. [1] the affect of air flow and duty cycle on parts is rarely mentioned.
Swapping transformer I/O
Started by ●July 1, 2023
Reply by ●July 2, 20232023-07-02
Reply by ●July 2, 20232023-07-02
On a sunny day (Sun, 2 Jul 2023 04:19:47 -0700 (PDT)) it happened Phil Allison <pallison49@gmail.com> wrote in <5f09e2f5-5376-44bd-8d95-f299090aad04n@googlegroups.com>:>John Larkin wrote: >------------------------------ >> >> >> >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. >> >> >> > I will be driving it from both sides, but not at the same time. >> >> >> >> >> >> Sure, a transformer works either way. >> >> >> >> >> > >> >> >** But makers nominate the primary and secondary for good reasons. >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the >> >> >secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. >> >> > >> >> >> >> Any winding can magnetize the core. The primary is the one you decide >> >> to put power into and the secondary is the one you elect to take power >> >> out of. >> > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. >> > >> > >> >> 2-winding power transformers are usually designed for equal copper >> >> loss on both windings. So are thermally symmetric. > >> >> Sometimes some windings are insulated better than others. >> >> >> >> What other catches might there be? >> > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the >> >full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. >> > >> That's easy to think through. Power transformer models are simple and >> easy to reverse. > > ** But real transformers are not so simple. > >> >You may have to seriously de-rate the transformer in order to use it that way, >>> mains frequency transformers under 100VA are the most affected. > >> A 100 VA transformer is happy moving 100 VA in either direction. > > ** JL has such simple faith in overly simple models. > > I wonder why ?Because it works, did something for the county here like that to replaces a very complex design.. Used existing transformer models in reverse.> ...... Phil >
Reply by ●July 2, 20232023-07-02
On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:> On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison > <palli...@gmail.com> wrote: > > >John Larkin wrote: > >------------------------------ > >> >> >> > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. > >> >> >> > I will be driving it from both sides, but not at the same time. > >> >> >> > >> >> >> Sure, a transformer works either way. > >> >> >> > >> >> > > >> >> >** But makers nominate the primary and secondary for good reasons. > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. > >> >> > > >> >> > >> >> Any winding can magnetize the core. The primary is the one you decide > >> >> to put power into and the secondary is the one you elect to take power > >> >> out of. > >> > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > >> > > >> >> 2-winding power transformers are usually designed for equal copper > >> >> loss on both windings. So are thermally symmetric. > > >> >> Sometimes some windings are insulated better than others. > >> >> > >> >> What other catches might there be? > >> > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > >> > > >> That's easy to think through. Power transformer models are simple and > >> easy to reverse. > > > > ** But real transformers are not so simple. > The Spice model of a transformer is simple: each winding has ESR, > there's magnetizing inductance, and there's leakage inductance. Ignore > capacitances at line frequencies. > > Given a Spice model, you can run it in either direction, with > resistive or diode loads or whatever, and Spice will tell you > everything you need to know. The only gotcha it misses is core > saturation. > > I had to take TWO semisters of Electrical Machinery at Tulane, which > was a huge nuisance, but I did learn about the circuit equivalent of a > transformer, which was almost worth the hassle. > > > >> >You may have to seriously de-rate the transformer in order to use it that way, > >>> mains frequency transformers under 100VA are the most affected. > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > ** JL has such simple faith in overly simple models. > > > > I wonder why ? > I design things that work, and verify by experiment if there's any > doubt. And the transformer model IS simple. > > One thing that's often worth verifying is temperature rise, with > actual mounting and air flow. Transformer vendors are vague and the > thermals are hard to math out. [1] > > If you are concerned about reversing a transformer, just try it. > > [1] the affect of air flow and duty cycle on parts is rarely > mentioned.There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect. A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.
Reply by ●July 2, 20232023-07-02
On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote:> On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote: > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison > > <palli...@gmail.com> wrote: > > > > >John Larkin wrote: > > >------------------------------ > > >> >> >> > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. > > >> >> >> > I will be driving it from both sides, but not at the same time. > > >> >> >> > > >> >> >> Sure, a transformer works either way. > > >> >> >> > > >> >> > > > >> >> >** But makers nominate the primary and secondary for good reasons. > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. > > >> >> > > > >> >> > > >> >> Any winding can magnetize the core. The primary is the one you decide > > >> >> to put power into and the secondary is the one you elect to take power > > >> >> out of. > > >> > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > > >> > > > >> >> 2-winding power transformers are usually designed for equal copper > > >> >> loss on both windings. So are thermally symmetric. > > > >> >> Sometimes some windings are insulated better than others. > > >> >> > > >> >> What other catches might there be? > > >> > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > > >> > > > >> That's easy to think through. Power transformer models are simple and > > >> easy to reverse. > > > > > > ** But real transformers are not so simple. > > The Spice model of a transformer is simple: each winding has ESR, > > there's magnetizing inductance, and there's leakage inductance. Ignore > > capacitances at line frequencies. > > > > Given a Spice model, you can run it in either direction, with > > resistive or diode loads or whatever, and Spice will tell you > > everything you need to know. The only gotcha it misses is core > > saturation. > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which > > was a huge nuisance, but I did learn about the circuit equivalent of a > > transformer, which was almost worth the hassle. > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way, > > >>> mains frequency transformers under 100VA are the most affected. > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > > > ** JL has such simple faith in overly simple models. > > > > > > I wonder why ? > > I design things that work, and verify by experiment if there's any > > doubt. And the transformer model IS simple. > > > > One thing that's often worth verifying is temperature rise, with > > actual mounting and air flow. Transformer vendors are vague and the > > thermals are hard to math out. [1] > > > > If you are concerned about reversing a transformer, just try it. > > > > [1] the affect of air flow and duty cycle on parts is rarely > > mentioned. > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect. > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.From my measurement of 250V DC (around 12% higher) out of 220V DC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better. Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V.
Reply by ●July 2, 20232023-07-02
On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote:> On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote: > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote: > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison > > > <palli...@gmail.com> wrote: > > > > > > >John Larkin wrote: > > > >------------------------------ > > > >> >> >> > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. > > > >> >> >> > I will be driving it from both sides, but not at the same time. > > > >> >> >> > > > >> >> >> Sure, a transformer works either way. > > > >> >> >> > > > >> >> > > > > >> >> >** But makers nominate the primary and secondary for good reasons. > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. > > > >> >> > > > > >> >> > > > >> >> Any winding can magnetize the core. The primary is the one you decide > > > >> >> to put power into and the secondary is the one you elect to take power > > > >> >> out of. > > > >> > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > > > >> > > > > >> >> 2-winding power transformers are usually designed for equal copper > > > >> >> loss on both windings. So are thermally symmetric. > > > > >> >> Sometimes some windings are insulated better than others. > > > >> >> > > > >> >> What other catches might there be? > > > >> > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > > > >> > > > > >> That's easy to think through. Power transformer models are simple and > > > >> easy to reverse. > > > > > > > > ** But real transformers are not so simple. > > > The Spice model of a transformer is simple: each winding has ESR, > > > there's magnetizing inductance, and there's leakage inductance. Ignore > > > capacitances at line frequencies. > > > > > > Given a Spice model, you can run it in either direction, with > > > resistive or diode loads or whatever, and Spice will tell you > > > everything you need to know. The only gotcha it misses is core > > > saturation. > > > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which > > > was a huge nuisance, but I did learn about the circuit equivalent of a > > > transformer, which was almost worth the hassle. > > > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way, > > > >>> mains frequency transformers under 100VA are the most affected. > > > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > > > > > ** JL has such simple faith in overly simple models. > > > > > > > > I wonder why ? > > > I design things that work, and verify by experiment if there's any > > > doubt. And the transformer model IS simple. > > > > > > One thing that's often worth verifying is temperature rise, with > > > actual mounting and air flow. Transformer vendors are vague and the > > > thermals are hard to math out. [1] > > > > > > If you are concerned about reversing a transformer, just try it. > > > > > > [1] the affect of air flow and duty cycle on parts is rarely > > > mentioned. > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect. > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher. > From my measurement of 250V DC (around 12% higher) out of 220V DC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better.You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.> > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V.If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection.
Reply by ●July 2, 20232023-07-02
On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote:> On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote: > > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote: > > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote: > > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison > > > > <palli...@gmail.com> wrote: > > > > > > > > >John Larkin wrote: > > > > >------------------------------ > > > > >> >> >> > > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. > > > > >> >> >> > I will be driving it from both sides, but not at the same time. > > > > >> >> >> > > > > >> >> >> Sure, a transformer works either way. > > > > >> >> >> > > > > >> >> > > > > > >> >> >** But makers nominate the primary and secondary for good reasons. > > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. > > > > >> >> > > > > > >> >> > > > > >> >> Any winding can magnetize the core. The primary is the one you decide > > > > >> >> to put power into and the secondary is the one you elect to take power > > > > >> >> out of. > > > > >> > > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > > > > >> > > > > > >> >> 2-winding power transformers are usually designed for equal copper > > > > >> >> loss on both windings. So are thermally symmetric. > > > > > >> >> Sometimes some windings are insulated better than others. > > > > >> >> > > > > >> >> What other catches might there be? > > > > >> > > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > > > > >> > > > > > >> That's easy to think through. Power transformer models are simple and > > > > >> easy to reverse. > > > > > > > > > > ** But real transformers are not so simple. > > > > The Spice model of a transformer is simple: each winding has ESR, > > > > there's magnetizing inductance, and there's leakage inductance. Ignore > > > > capacitances at line frequencies. > > > > > > > > Given a Spice model, you can run it in either direction, with > > > > resistive or diode loads or whatever, and Spice will tell you > > > > everything you need to know. The only gotcha it misses is core > > > > saturation. > > > > > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which > > > > was a huge nuisance, but I did learn about the circuit equivalent of a > > > > transformer, which was almost worth the hassle. > > > > > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way, > > > > >>> mains frequency transformers under 100VA are the most affected. > > > > > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > > > > > > > ** JL has such simple faith in overly simple models. > > > > > > > > > > I wonder why ? > > > > I design things that work, and verify by experiment if there's any > > > > doubt. And the transformer model IS simple. > > > > > > > > One thing that's often worth verifying is temperature rise, with > > > > actual mounting and air flow. Transformer vendors are vague and the > > > > thermals are hard to math out. [1] > > > > > > > > If you are concerned about reversing a transformer, just try it. > > > > > > > > [1] the affect of air flow and duty cycle on parts is rarely > > > > mentioned. > > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect. > > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher. > > From my measurement of 250V DC (around 12% higher) out of 220V AC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better. > You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.Full bridge rectifier and 82uF 450V capacitor. Steady reading of 450V DC. I can try out a different inverter. I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine.> > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be e.asier to adjust input between 20V to 24V.> If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection.Ordered a 10W version to test. Will get the 100W version if it works.
Reply by ●July 2, 20232023-07-02
On Sunday, July 2, 2023 at 12:46:04 PM UTC-7, Eddy Lee wrote:> On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote: > > On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote: > > > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote: > > > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote: > > > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison > > > > > <palli...@gmail.com> wrote: > > > > > > > > > > >John Larkin wrote: > > > > > >------------------------------ > > > > > >> >> >> > > > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. > > > > > >> >> >> > I will be driving it from both sides, but not at the same time. > > > > > >> >> >> > > > > > >> >> >> Sure, a transformer works either way. > > > > > >> >> >> > > > > > >> >> > > > > > > >> >> >** But makers nominate the primary and secondary for good reasons. > > > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. > > > > > >> >> > > > > > > >> >> > > > > > >> >> Any winding can magnetize the core. The primary is the one you decide > > > > > >> >> to put power into and the secondary is the one you elect to take power > > > > > >> >> out of. > > > > > >> > > > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > > > > > >> > > > > > > >> >> 2-winding power transformers are usually designed for equal copper > > > > > >> >> loss on both windings. So are thermally symmetric. > > > > > > >> >> Sometimes some windings are insulated better than others. > > > > > >> >> > > > > > >> >> What other catches might there be? > > > > > >> > > > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > > > > > >> > > > > > > >> That's easy to think through. Power transformer models are simple and > > > > > >> easy to reverse. > > > > > > > > > > > > ** But real transformers are not so simple. > > > > > The Spice model of a transformer is simple: each winding has ESR, > > > > > there's magnetizing inductance, and there's leakage inductance. Ignore > > > > > capacitances at line frequencies. > > > > > > > > > > Given a Spice model, you can run it in either direction, with > > > > > resistive or diode loads or whatever, and Spice will tell you > > > > > everything you need to know. The only gotcha it misses is core > > > > > saturation. > > > > > > > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which > > > > > was a huge nuisance, but I did learn about the circuit equivalent of a > > > > > transformer, which was almost worth the hassle. > > > > > > > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way, > > > > > >>> mains frequency transformers under 100VA are the most affected. > > > > > > > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > > > > > > > > > ** JL has such simple faith in overly simple models. > > > > > > > > > > > > I wonder why ? > > > > > I design things that work, and verify by experiment if there's any > > > > > doubt. And the transformer model IS simple. > > > > > > > > > > One thing that's often worth verifying is temperature rise, with > > > > > actual mounting and air flow. Transformer vendors are vague and the > > > > > thermals are hard to math out. [1] > > > > > > > > > > If you are concerned about reversing a transformer, just try it. > > > > > > > > > > [1] the affect of air flow and duty cycle on parts is rarely > > > > > mentioned. > > > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect. > > > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher. > > > From my measurement of 250V DC (around 12% higher) out of 220V AC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better. > > You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC. > Full bridge rectifier and 82uF 450V capacitor. Steady reading of 350V DC. I can try out a different inverter. > > I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine. > > > > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be e. > asier to adjust input between 20V to 24V. > > If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection. > Ordered a 10W version to test. Will get the 100W version if it works.Correction: 450V DC to 350V DC.
Reply by ●July 2, 20232023-07-02
On Sunday, July 2, 2023 at 12:51:41 PM UTC-7, Eddy Lee wrote:> On Sunday, July 2, 2023 at 12:46:04 PM UTC-7, Eddy Lee wrote: > > On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote: > > > On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote: > > > > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote: > > > > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote: > > > > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison > > > > > > <palli...@gmail.com> wrote: > > > > > > > > > > > > >John Larkin wrote: > > > > > > >------------------------------ > > > > > > >> >> >> > > > > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. > > > > > > >> >> >> > I will be driving it from both sides, but not at the same time. > > > > > > >> >> >> > > > > > > >> >> >> Sure, a transformer works either way. > > > > > > >> >> >> > > > > > > >> >> > > > > > > > >> >> >** But makers nominate the primary and secondary for good reasons. > > > > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. > > > > > > >> >> > > > > > > > >> >> > > > > > > >> >> Any winding can magnetize the core. The primary is the one you decide > > > > > > >> >> to put power into and the secondary is the one you elect to take power > > > > > > >> >> out of. > > > > > > >> > > > > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > > > > > > >> > > > > > > > >> >> 2-winding power transformers are usually designed for equal copper > > > > > > >> >> loss on both windings. So are thermally symmetric. > > > > > > > >> >> Sometimes some windings are insulated better than others. > > > > > > >> >> > > > > > > >> >> What other catches might there be? > > > > > > >> > > > > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > > > > > > >> > > > > > > > >> That's easy to think through. Power transformer models are simple and > > > > > > >> easy to reverse. > > > > > > > > > > > > > > ** But real transformers are not so simple. > > > > > > The Spice model of a transformer is simple: each winding has ESR, > > > > > > there's magnetizing inductance, and there's leakage inductance. Ignore > > > > > > capacitances at line frequencies. > > > > > > > > > > > > Given a Spice model, you can run it in either direction, with > > > > > > resistive or diode loads or whatever, and Spice will tell you > > > > > > everything you need to know. The only gotcha it misses is core > > > > > > saturation. > > > > > > > > > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which > > > > > > was a huge nuisance, but I did learn about the circuit equivalent of a > > > > > > transformer, which was almost worth the hassle. > > > > > > > > > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way, > > > > > > >>> mains frequency transformers under 100VA are the most affected. > > > > > > > > > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > > > > > > > > > > > ** JL has such simple faith in overly simple models. > > > > > > > > > > > > > > I wonder why ? > > > > > > I design things that work, and verify by experiment if there's any > > > > > > doubt. And the transformer model IS simple. > > > > > > > > > > > > One thing that's often worth verifying is temperature rise, with > > > > > > actual mounting and air flow. Transformer vendors are vague and the > > > > > > thermals are hard to math out. [1] > > > > > > > > > > > > If you are concerned about reversing a transformer, just try it. > > > > > > > > > > > > [1] the affect of air flow and duty cycle on parts is rarely > > > > > > mentioned. > > > > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect. > > > > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher. > > > > From my measurement of 250V DC (around 12% higher) out of 220V AC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better. > > > You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.> > Full bridge rectifier and 82uF 450V capacitor. Steady reading of 250V DC. I can try out a different inverter. > > > > I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine. > > > > > > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V. > > > If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection. > > Ordered a 10W version to test. Will get the 100W version if it works. > Correction: 450V DC to 350V DC.Correction again: measured 250V DC out of 220V AC inverter. 250V DC (from inverter) + 170V (from wall) would be perfect. But the wall is not always available.
Reply by ●July 2, 20232023-07-02
On Sunday, July 2, 2023 at 4:19:08 PM UTC-4, Eddy Lee wrote:> On Sunday, July 2, 2023 at 12:51:41 PM UTC-7, Eddy Lee wrote: > > On Sunday, July 2, 2023 at 12:46:04 PM UTC-7, Eddy Lee wrote: > > > On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote: > > > > On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote: > > > > > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote: > > > > > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote: > > > > > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison > > > > > > > <palli...@gmail.com> wrote: > > > > > > > > > > > > > > >John Larkin wrote: > > > > > > > >------------------------------ > > > > > > > >> >> >> > > > > > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity. > > > > > > > >> >> >> > I will be driving it from both sides, but not at the same time. > > > > > > > >> >> >> > > > > > > > >> >> >> Sure, a transformer works either way. > > > > > > > >> >> >> > > > > > > > >> >> > > > > > > > > >> >> >** But makers nominate the primary and secondary for good reasons. > > > > > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary. > > > > > > > >> >> > > > > > > > > >> >> > > > > > > > >> >> Any winding can magnetize the core. The primary is the one you decide > > > > > > > >> >> to put power into and the secondary is the one you elect to take power > > > > > > > >> >> out of. > > > > > > > >> > > > > > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > > > > > > > >> > > > > > > > > >> >> 2-winding power transformers are usually designed for equal copper > > > > > > > >> >> loss on both windings. So are thermally symmetric. > > > > > > > > >> >> Sometimes some windings are insulated better than others. > > > > > > > >> >> > > > > > > > >> >> What other catches might there be? > > > > > > > >> > > > > > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > > > > > > > >> > > > > > > > > >> That's easy to think through. Power transformer models are simple and > > > > > > > >> easy to reverse. > > > > > > > > > > > > > > > > ** But real transformers are not so simple. > > > > > > > The Spice model of a transformer is simple: each winding has ESR, > > > > > > > there's magnetizing inductance, and there's leakage inductance. Ignore > > > > > > > capacitances at line frequencies. > > > > > > > > > > > > > > Given a Spice model, you can run it in either direction, with > > > > > > > resistive or diode loads or whatever, and Spice will tell you > > > > > > > everything you need to know. The only gotcha it misses is core > > > > > > > saturation. > > > > > > > > > > > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which > > > > > > > was a huge nuisance, but I did learn about the circuit equivalent of a > > > > > > > transformer, which was almost worth the hassle. > > > > > > > > > > > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way, > > > > > > > >>> mains frequency transformers under 100VA are the most affected. > > > > > > > > > > > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > > > > > > > > > > > > > ** JL has such simple faith in overly simple models. > > > > > > > > > > > > > > > > I wonder why ? > > > > > > > I design things that work, and verify by experiment if there's any > > > > > > > doubt. And the transformer model IS simple. > > > > > > > > > > > > > > One thing that's often worth verifying is temperature rise, with > > > > > > > actual mounting and air flow. Transformer vendors are vague and the > > > > > > > thermals are hard to math out. [1] > > > > > > > > > > > > > > If you are concerned about reversing a transformer, just try it. > > > > > > > > > > > > > > [1] the affect of air flow and duty cycle on parts is rarely > > > > > > > mentioned. > > > > > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect. > > > > > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher. > > > > > From my measurement of 250V DC (around 12% higher) out of 220V AC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better. > > > > You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC. > > > Full bridge rectifier and 82uF 450V capacitor. Steady reading of 250V DC. I can try out a different inverter. > > > > > > I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine. > > > > > > > > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V. > > > > If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection. > > > Ordered a 10W version to test. Will get the 100W version if it works. > > Correction: 450V DC to 350V DC. > Correction again: measured 250V DC out of 220V AC inverter. > > 250V DC (from inverter) + 170V (from wall) would be perfect. But the wall is not always available.Some of these inverters put out square waves. The RMS of a square wave of amplitude V is V. So if the nameplate says 220V,RMS, its peak is only 220V, which is down 30% from a transformer output. Others put out some kind of stepped waveform, but you'll have the same effect. That would explain the discrepancies you're seeing with them.
Reply by ●July 2, 20232023-07-02
John Larkin wrote: ---------------------------> >> > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly. > >> > > >> >> 2-winding power transformers are usually designed for equal copper > >> >> loss on both windings. So are thermally symmetric. > > >> >> Sometimes some windings are insulated better than others. > >> >> > >> >> What other catches might there be? > >> > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions. > >> > > >> That's easy to think through. Power transformer models are simple and > >> easy to reverse. > > > > ** But real transformers are not so simple. > > Given a Spice model, you can run it in either direction, with > resistive or diode loads or whatever, and Spice will tell you > everything you need to know. The only gotcha it misses is core > saturation.** That "gotcha" is the biggie here.> >> >You may have to seriously de-rate the transformer in order to use it that way, > >>> mains frequency transformers under 100VA are the most affected. > > > >> A 100 VA transformer is happy moving 100 VA in either direction. > > > > ** JL has such simple faith in overly simple models. > > > > I wonder why ? > > If you are concerned about reversing a transformer, just try it. >** LOL - of *course* I have and that is why I know about the pitfalls. ....... Phil
