I searched but couldn't find anything on:

Using 2 transformers
running the primary of one right off the mains
running the other transformer primary in series
with a large motor run capacitor to phase shift
the primary 90 degrees.
Rectify and filter both secondaries
Diode "OR" the rectified filtered outputs.
This would give me better than double the frequency
As the phase shift would overlap the
120 cycle pulsating DC.

Basicly I have 2 Eico 751 power supplies.
I like to beef up the supply to my Eico 753.

73
N8ZU

On Jul 10, 6:09 pm, raypsi wrote:
I searched but couldn't find anything on:

Using 2 transformers
running the primary of one right off the mains
running the other transformer primary in series
with a large motor run capacitor to phase shift
the primary 90 degrees.
Rectify and filter both secondaries
Diode "OR" the rectified filtered outputs.
This would give me better than double the frequency
As the phase shift would overlap the
120 cycle pulsating DC.

Basicly I have 2 Eico 751 power supplies.
I like to beef up the supply to my Eico 753.

73
N8ZU

Suggest you run a simulation of your circuit in something like
LTSpice. It probably does not behave like you are thinking it will.
Transformers are wound with enough inductance that they look like a
moderately high impedance in parallel with the reflected secondary
load. But if the secondary is loaded with a full-wave or bridge
rectifier into a big capacitance, then current flows only when the
secondary voltage is greater than the capacitor voltage (by a diode
drop or two). So you end up drawing very little current on the
primary side, except when the voltage is near the peak. As a result,
you don't get a nice phase-shifted sine on the primary side.

Even if the load looks resistive, the current in the load is not 90
degrees out of phase with the mains voltage; it's just 90 degrees out
of phase with whatever voltage drops across the capacitor.

Try some simulations with various loads and series capacitor values,
and you'll get a feel for what's going on. If you want, I could send
you the simulation file I just hacked together as a starting point.

Cheers,
Tom

On Jul 10, 9:09�pm, raypsi wrote:
I searched but couldn't find anything on:

There's a reason...

Using 2 transformers
�running the primary of one right off the mains
running the other transformer primary in series
�with a large motor run capacitor to phase shift
the primary 90 degrees.

You won't get 90 degrees phase shift because there's a resistive
component involved. And as the resistive component changes, the phase
shift will change,

Rectify and filter both secondaries

OK

Diode "OR" the rectified filtered outputs.

You don't need to do that, the rectifier circuits do it for you.

This would give me better than double the frequency

No, it wouldn't. At best it would give you double the ripple
frequency.

As the phase shift would overlap the
120 cycle pulsating DC.

At best, the pulses of the phase-shifted rectifier would be in the
valleys between the pulses of the non-phase-shifted rectifier. So
you'd get twice as many pulses - no more.

What you propose doesn't offer any real advantage over a conventional
single-phase supply. But it offers a lot of disadvantages such as
requiring more than twice as many parts. The phase-shifted supply will
have poor regulation and won't carry its share of the load.

Basicly I have 2 Eico 751 power supplies.
I like to beef up the supply to my Eico 753.

The best way to do that is to replace the old diodes and filter caps
with modern ones. The 751 power supply is more than adequate to power
the 753 if it's in good shape.

If your Eico 753 drifts, it's not the power supply. They all drift, so
much so that they became known as the "Seven-Drifty-Three" in their
time.

Another option if you can't leave well enough alone is to interconnect
the power supplies so that one supply runs the low B+, bias and
heaters, while the other one provides just the high B+

As K7ITM says, run some simulations and you'll see the reality.

73 de Jim, N2EY.

On Jul 12, 10:26Â*pm, wrote:
On Jul 10, 9:09�pm, raypsi wrote:

I searched but couldn't find anything on:

There's a reason...



Using 2 transformers
�running the primary of one right off the mains
running the other transformer primary in series
�with a large motor run capacitor to phase shift
the primary 90 degrees.

You won't get 90 degrees phase shift because there's a resistive
component involved. And as the resistive component changes, the phase
shift will change,

Rectify and filter both secondaries

OK

Diode "OR" the rectified filtered outputs.

You don't need to do that, the rectifier circuits do it for you.

This would give me better than double the frequency

No, it wouldn't. At best it would give you double the ripple
frequency.

As the phase shift would overlap the
120 cycle pulsating DC.

At best, the pulses of the phase-shifted rectifier would be in the
valleys between the pulses of the non-phase-shifted rectifier. So
you'd get twice as many pulses - no more.

What you propose doesn't offer any real advantage over a conventional
single-phase supply. But it offers a lot of disadvantages such as
requiring more than twice as many parts. The phase-shifted supply will
have poor regulation and won't carry its share of the load.

Basicly I have 2 Eico 751 power supplies.
I like to beef up the supply to my Eico 753.

The best way to do that is to replace the old diodes and filter caps
with modern ones. The 751 power supply is more than adequate to power
the 753 if it's in good shape.

If your Eico 753 drifts, it's not the power supply. They all drift, so
much so that they became known as the "Seven-Drifty-Three" in their
time.

Another option if you can't leave well enough alone is to interconnect
the power supplies so that one supply runs the low B+, bias and
heaters, while the other one provides just the high B+

As K7ITM says, run some simulations and you'll see the reality.

73 de Jim, N2EY.


Hey Jim:

I was getting my transformers and motors mixed up you can trick
a 3 phase motor into running from single phase. But a transformer
is a passive device. Just another pipe dream.

Yes when it was a new built kit: the Ham I bought it from wrote down
all the voltages in the manual, which I still have.
For the 6DQ6 plate supply he wrote down 790VDC in transmitt.
Maybe that's an errot on his part, I get 750VDC in transmitt and
that's with 125VAC input on the mains, With 110VAC on the mains
the plate voltage goes to 650VDC. I put in new caps and high speed
high surge current 3 amp 1000piv diodes in the supply.

73

N8ZU

On Jul 11, 1:43*am, K7ITM wrote:
On Jul 10, 6:09 pm, raypsi wrote:





I searched but couldn't find anything on:

Using 2 transformers
*running the primary of one right off the mains
running the other transformer primary in series
*with a large motor run capacitor to phase shift
the primary 90 degrees.
Rectify and filter both secondaries
Diode "OR" the rectified filtered outputs.
This would give me better than double the frequency
As the phase shift would overlap the
120 cycle pulsating DC.

Basicly I have 2 Eico 751 power supplies.
I like to beef up the supply to my Eico 753.

73
N8ZU

Suggest you run a simulation of your circuit in something like
LTSpice. *It probably does not behave like you are thinking it will.
Transformers are wound with enough inductance that they look like a
moderately high impedance in parallel with the reflected secondary
load. *But if the secondary is loaded with a full-wave or bridge
rectifier into a big capacitance, then current flows only when the
secondary voltage is greater than the capacitor voltage (by a diode
drop or two). *So you end up drawing very little current on the
primary side, except when the voltage is near the peak. *As a result,
you don't get a nice phase-shifted sine on the primary side.

Even if the load looks resistive, the current in the load is not 90
degrees out of phase with the mains voltage; it's just 90 degrees out
of phase with whatever voltage drops across the capacitor.

Try some simulations with various loads and series capacitor values,
and you'll get a feel for what's going on. *If you want, I could send
you the simulation file I just hacked together as a starting point.

Cheers,
Tom- Hide quoted text -

- Show quoted text -


Thanks Tom,

Looks like I been just chasing my tail.

I'll have to go with a 3 phase rotory converter.
That's like a 3hp 3 phase motor with phase shift
capacitor plus a run capacitor,
to run a 3 phase 3hp motor from a
single phase.
I then pull 2 phases off the motor
to run my supplys
. They use 3 phase rotory converters
to deliver 3 phase power to equipment that has to
have 3 phase power to run properly.
I seen one running on youtube.

On Sun, 13 Jul 2008 03:18:42 -0700 (PDT), raypsi
wrote:

On Jul 11, 1:43*am, K7ITM wrote:
On Jul 10, 6:09 pm, raypsi wrote:





I searched but couldn't find anything on:

Using 2 transformers
*running the primary of one right off the mains
running the other transformer primary in series
*with a large motor run capacitor to phase shift
the primary 90 degrees.
Rectify and filter both secondaries
Diode "OR" the rectified filtered outputs.
This would give me better than double the frequency
As the phase shift would overlap the
120 cycle pulsating DC.

Basicly I have 2 Eico 751 power supplies.
I like to beef up the supply to my Eico 753.

73
N8ZU

Suggest you run a simulation of your circuit in something like
LTSpice. *It probably does not behave like you are thinking it will.
Transformers are wound with enough inductance that they look like a
moderately high impedance in parallel with the reflected secondary
load. *But if the secondary is loaded with a full-wave or bridge
rectifier into a big capacitance, then current flows only when the
secondary voltage is greater than the capacitor voltage (by a diode
drop or two). *So you end up drawing very little current on the
primary side, except when the voltage is near the peak. *As a result,
you don't get a nice phase-shifted sine on the primary side.

Even if the load looks resistive, the current in the load is not 90
degrees out of phase with the mains voltage; it's just 90 degrees out
of phase with whatever voltage drops across the capacitor.

Try some simulations with various loads and series capacitor values,
and you'll get a feel for what's going on. *If you want, I could send
you the simulation file I just hacked together as a starting point.

Cheers,
Tom- Hide quoted text -

- Show quoted text -


Thanks Tom,

Looks like I been just chasing my tail.

I'll have to go with a 3 phase rotory converter.
That's like a 3hp 3 phase motor with phase shift
capacitor plus a run capacitor,
to run a 3 phase 3hp motor from a
single phase.
I then pull 2 phases off the motor
to run my supplys
. They use 3 phase rotory converters
to deliver 3 phase power to equipment that has to
have 3 phase power to run properly.
I seen one running on youtube.

Rotary converters in 2008 ????

There are quite a few solid state converters for driving 3 phase
bidirectional motors even from as single phase supply at such low
power levels.

If the original requirement was to generate sufficient power into a
tube transmitter anode supply, I would look into a switching power
supply.

There are of course problems finding high voltage rectifiers for
higher frequencies than 50/60 Hz and the RF noise might be an issue,
but if you can kill the power supply during receive, the RF noise
should not be an issue.

Paul OH3LWR