I thought I could remove the secondary and the shunts, then install a
new secondary and have a low voltage transformer, maybe not.
I removed the HV secondary, Then wound 10 turns and got 8 volts.
I loaded it with 2 ohms, all is well except the PF is 0.15.
I will need to have about 25 turns to get my 20 Volts, but, do I need to
do something about the PF? Why is it so low?
I expect Phil will set me straight on this.
Thanks, Mikek
Rewiinding a MOT
Started by ●June 27, 2020
Reply by ●June 27, 20202020-06-27
On Sat, 27 Jun 2020 09:31:08 -0500, amdx <nojunk@knology.net> wrote:>I thought I could remove the secondary and the shunts, then install a >new secondary and have a low voltage transformer, maybe not. > I removed the HV secondary, Then wound 10 turns and got 8 volts. > I loaded it with 2 ohms, all is well except the PF is 0.15. >I will need to have about 25 turns to get my 20 Volts, but, do I need to >do something about the PF? Why is it so low? > I expect Phil will set me straight on this. > > Thanks, MikekMicrowave transformer? I think they are designed to have a lot of leakage inductance. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●June 27, 20202020-06-27
On 6/27/2020 9:36 AM, jlarkin@highlandsniptechnology.com wrote:> On Sat, 27 Jun 2020 09:31:08 -0500, amdx <nojunk@knology.net> wrote: > >> I thought I could remove the secondary and the shunts, then install a >> new secondary and have a low voltage transformer, maybe not. >> I removed the HV secondary, Then wound 10 turns and got 8 volts. >> I loaded it with 2 ohms, all is well except the PF is 0.15. >> I will need to have about 25 turns to get my 20 Volts, but, do I need to >> do something about the PF? Why is it so low? >> I expect Phil will set me straight on this. >> >> Thanks, Mikek > > Microwave transformer? > > I think they are designed to have a lot of leakage inductance. > > >I thought the shunts had something to do with that? That's why I removed them. Mikek
Reply by ●June 27, 20202020-06-27
On Sat, 27 Jun 2020 09:58:52 -0500, amdx <nojunk@knology.net> wrote:>On 6/27/2020 9:36 AM, jlarkin@highlandsniptechnology.com wrote: >> On Sat, 27 Jun 2020 09:31:08 -0500, amdx <nojunk@knology.net> wrote: >> >>> I thought I could remove the secondary and the shunts, then install a >>> new secondary and have a low voltage transformer, maybe not. >>> I removed the HV secondary, Then wound 10 turns and got 8 volts. >>> I loaded it with 2 ohms, all is well except the PF is 0.15. >>> I will need to have about 25 turns to get my 20 Volts, but, do I need to >>> do something about the PF? Why is it so low? >>> I expect Phil will set me straight on this. >>> >>> Thanks, Mikek >> >> Microwave transformer? >> >> I think they are designed to have a lot of leakage inductance. >> >> >> > I thought the shunts had something to do with that? > That's why I removed them. > > MikekCoupling may still be loose. Measure the coil inductance and leakage inductance. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●June 27, 20202020-06-27
On 6/27/2020 10:54 AM, jlarkin@highlandsniptechnology.com wrote:> On Sat, 27 Jun 2020 09:58:52 -0500, amdx <nojunk@knology.net> wrote: > >> On 6/27/2020 9:36 AM, jlarkin@highlandsniptechnology.com wrote: >>> On Sat, 27 Jun 2020 09:31:08 -0500, amdx <nojunk@knology.net> wrote: >>> >>>> I thought I could remove the secondary and the shunts, then install a >>>> new secondary and have a low voltage transformer, maybe not. >>>> I removed the HV secondary, Then wound 10 turns and got 8 volts. >>>> I loaded it with 2 ohms, all is well except the PF is 0.15. >>>> I will need to have about 25 turns to get my 20 Volts, but, do I need to >>>> do something about the PF? Why is it so low? >>>> I expect Phil will set me straight on this. >>>> >>>> Thanks, Mikek >>> >>> Microwave transformer? >>> >>> I think they are designed to have a lot of leakage inductance. >>> >>> >>> >> I thought the shunts had something to do with that? >> That's why I removed them. >> >> Mikek > > Coupling may still be loose. Measure the coil inductance and leakage > inductance. > >This goes back to the 20 month old post that was resurrected about the transformerless power supply for the leaf blower. I decided to try a transformer supply. I need 20V at 8 amps. I think I should try to find how to decrease the leakage inductance and wind for final use before I make the coil inductance and leakage inductance measurement. I posted a picture of the transformer with 10 turns that I used to get a volt/turn measurement. I will insulate, wind properly and probably varnish dip if I get a working unit.> https://www.dropbox.com/s/bwu6aij4zwdff9g/MOT.jpg?dl=0How would I get better coupling, in the same configuration. Mikek
Reply by ●June 27, 20202020-06-27
Well yeah, you loaded it to a teensy fraction of its load capacity. Protip: put +20% turns on the primary to reduce saturation. All your PF is going into harmonics. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/ "amdx" <nojunk@knology.net> wrote in message news:rd7l7q$ki6$1@dont-email.me...>I thought I could remove the secondary and the shunts, then install a new >secondary and have a low voltage transformer, maybe not. > I removed the HV secondary, Then wound 10 turns and got 8 volts. > I loaded it with 2 ohms, all is well except the PF is 0.15. > I will need to have about 25 turns to get my 20 Volts, but, do I need to > do something about the PF? Why is it so low? > I expect Phil will set me straight on this. > > Thanks, Mikek
Reply by ●June 27, 20202020-06-27
"amdx" wrote in message news:rd7smj$sr4$1@dont-email.me...> >On 6/27/2020 10:54 AM, jlarkin@highlandsniptechnology.com wrote: >> On Sat, 27 Jun 2020 09:58:52 -0500, amdx <nojunk@knology.net> wrote: >> >>> On 6/27/2020 9:36 AM, jlarkin@highlandsniptechnology.com wrote: >>>> On Sat, 27 Jun 2020 09:31:08 -0500, amdx <nojunk@knology.net> wrote: >>>> >>>>> I thought I could remove the secondary and the shunts, then install a >>>>> new secondary and have a low voltage transformer, maybe not. >>>>> I removed the HV secondary, Then wound 10 turns and got 8 volts. >>>>> I loaded it with 2 ohms, all is well except the PF is 0.15. >>>>> I will need to have about 25 turns to get my 20 Volts, but, do I need >>>>> to >>>>> do something about the PF? Why is it so low? >>>>> I expect Phil will set me straight on this. >>>>> >>>>> Thanks, Mikek >>>> >>>> Microwave transformer? >>>> >>>> I think they are designed to have a lot of leakage inductance. >>>> >>>> >>>> >>> I thought the shunts had something to do with that? >>> That's why I removed them. >>> >>> Mikek >> >> Coupling may still be loose. Measure the coil inductance and leakage >> inductance. >> >> > This goes back to the 20 month old post that was resurrected about the > transformerless power supply for the leaf blower. I decided to try a > transformer supply. I need 20V at 8 amps. > I think I should try to find how to decrease the leakage inductance and > wind for final use before I make the coil inductance and leakage > inductance measurement. >I posted a picture of the transformer with 10 turns that I used to get a >volt/turn measurement. I will insulate, wind properly and probably varnish >dip if I get a working unit. >> https://www.dropbox.com/s/bwu6aij4zwdff9g/MOT.jpg?dl=0 > >How would I get better coupling, in the same configuration. > > MikekMy favorite surplus outlet has a 24V 10A transformer that may work for you depending on duty cycle and actual load: https://www.mpja.com/24V-10A-Center-Tapped-12-0-12-Transformer/productinfo/27846+TR/ -- Regards, Carl Ijames
Reply by ●June 27, 20202020-06-27
On 2020-06-27, amdx <nojunk@knology.net> wrote:> I thought I could remove the secondary and the shunts, then install a > new secondary and have a low voltage transformer, maybe not.> I removed the HV secondary, Then wound 10 turns and got 8 volts. > I loaded it with 2 ohms, all is well except the PF is 0.15.You've increased the magnetic resistance by removing the shunts so now it's running further into partial saturation, you can maybe fix that by adding some primary turns, the core is built with E and I stacked instead of interleaved this makes for more gap which probably isn't helping either. At low loads magnetising current will dominate the current draw, giving low power factor.> I will need to have about 25 turns to get my 20 Volts, but, do I need to > do something about the PF? Why is it so low? > I expect Phil will set me straight on this.If you're running a rectifier into a capacitor PF will be low because conduction angle, This can be improved by putting a choke between the rectifier and the capacitor. -- Jasen.
Reply by ●June 27, 20202020-06-27
On 6/27/2020 4:18 PM, Carl wrote:> "amdx" wrote in message news:rd7smj$sr4$1@dont-email.me... >> >> On 6/27/2020 10:54 AM, jlarkin@highlandsniptechnology.com wrote: >>> On Sat, 27 Jun 2020 09:58:52 -0500, amdx <nojunk@knology.net> wrote: >>> >>>> On 6/27/2020 9:36 AM, jlarkin@highlandsniptechnology.com wrote: >>>>> On Sat, 27 Jun 2020 09:31:08 -0500, amdx <nojunk@knology.net> wrote: >>>>> >>>>>> I thought I could remove the secondary and the shunts, then install a >>>>>> new secondary and have a low voltage transformer, maybe not. >>>>>> I removed the HV secondary, Then wound 10 turns and got 8 volts. >>>>>> I loaded it with 2 ohms, all is well except the PF is 0.15. >>>>>> I will need to have about 25 turns to get my 20 Volts, but, do I >>>>>> need to >>>>>> do something about the PF? Why is it so low? >>>>>> I expect Phil will set me straight on this. >>>>>> >>>>>> Thanks, Mikek >>>>> >>>>> Microwave transformer? >>>>> >>>>> I think they are designed to have a lot of leakage inductance. >>>>> >>>>> >>>>> >>>> I thought the shunts had something to do with that? >>>> That's why I removed them. >>>> >>>> Mikek >>> >>> Coupling may still be loose. Measure the coil inductance and leakage >>> inductance. >>> >>> >> This goes back to the 20 month old post that was resurrected about >> the transformerless power supply for the leaf blower. I decided to try >> a transformer supply. I need 20V at 8 amps. >> I think I should try to find how to decrease the leakage inductance >> and wind for final use before I make the coil inductance and leakage >> inductance measurement. >> I posted a picture of the transformer with 10 turns that I used to get >> a volt/turn measurement. I will insulate, wind properly and probably >> varnish dip if I get a working unit. >>> https://www.dropbox.com/s/bwu6aij4zwdff9g/MOT.jpg?dl=0 >> >> How would I get better coupling, in the same configuration. >> >> Mikek > > My favorite surplus outlet has a 24V 10A transformer that may work for > you depending on duty cycle and actual load: > https://www.mpja.com/24V-10A-Center-Tapped-12-0-12-Transformer/productinfo/27846+TR/ > >Ya, that's $50 by the time I get it to the door. I'd rather have a project, wind it so all I need is a Fullwave bridge. I have motor wire, insulation, the bridges, so I don't need to buy anything. Mikek -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
Reply by ●June 27, 20202020-06-27
On 6/27/2020 4:19 PM, Jasen Betts wrote:> On 2020-06-27, amdx <nojunk@knology.net> wrote: >> I thought I could remove the secondary and the shunts, then install a >> new secondary and have a low voltage transformer, maybe not. > >> I removed the HV secondary, Then wound 10 turns and got 8 volts. >> I loaded it with 2 ohms, all is well except the PF is 0.15. > > You've increased the magnetic resistance by removing the shunts so now > it's running further into partial saturation, you can maybe fix that by > adding some primary turns, the core is built with E and I stacked > instead of interleaved this makes for more gap which probably isn't > helping either. > > At low loads magnetising current will dominate the current draw, giving > low power factor. > >> I will need to have about 25 turns to get my 20 Volts, but, do I need to >> do something about the PF? Why is it so low? >> I expect Phil will set me straight on this. > > If you're running a rectifier into a capacitor PF will be low because > conduction angle, This can be improved by putting a choke between the > rectifier and the capacitor. >So I need to add more turns to the primary, 20% and also the primary is designed for about 1000 watts. I loaded it with about 35 watts, so most of the primary current was magnetizing current. The end result will be say 22 volts @ 8 amps, about 175 watts, about 18% of the primary designed capacity. Should I add more that 20% to the primary? Mikek -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
