500A power source

On 2 Apr 2020 05:35:36 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

upsidedown@downunder.com wrote...

On 1 Apr 2020 14:35:43 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

In my search for a 8 to 10V, 500A source,
needed for 2 seconds,

Since you need 2 seconds and you have three phase
available on site, why not use a three phase
transformer and a six pulse rectifier ?

Yes, we already agreed that's a viable solution.
But looking around for suitable transformer(s),
I wasn't able to find much. Yes, looking in
the wrong place, no doubt.

Did you also look for transformers with 208 V primary intended to be
used in delta ? Did you calculate the secondary voltages, when
primaries are fed from 120 V in wye configuration ?

Did you check the rectified DC voltage, when the secondaries are
connected in wye vs. delta ?

 

[Flyguy]

On Thursday, April 2, 2020 at 9:01:41 AM UTC-7, Flyguy wrote:

On Wednesday, April 1, 2020 at 6:47:00 PM UTC-7, Winfield Hill wrote:
Flyguy wrote...

I suggested an external resistor to take part of
the load off of the MOSFET.

But which of the five or six battery-configuration
choices do you recommend?


--
Thanks,
- Win

The Bioenno I originally recommended. You have to either:
1. Increase your MOSFET heat sink.
2. Use a larger MOSFET.
3. Use more MOSFETs.
4. Add a dropping resistor.
5. A combination of 1-4.
Add a series resistor is the easiest.

I looked at your PCB layout - what kind of heat sink are you using now? What is your average power dissipation for normal, continuous operation? Improving that heat sink is probably the easiest solution.

 

[Flyguy]

On Wednesday, April 1, 2020 at 6:47:00 PM UTC-7, Winfield Hill wrote:

Flyguy wrote...

I suggested an external resistor to take part of
the load off of the MOSFET.

But which of the five or six battery-configuration
choices do you recommend?


--
Thanks,
- Win

The Bioenno I originally recommended. You have to either:
1. Increase your MOSFET heat sink.
2. Use a larger MOSFET.
3. Use more MOSFETs.
4. Add a dropping resistor.
5. A combination of 1-4.
Add a series resistor is the easiest.

 

On Thu, 2 Apr 2020 05:50:58 -0700 (PDT), Michael Terrell
<terrell.michael.a@gmail.com> wrote:

On Thursday, April 2, 2020 at 8:35:47 AM UTC-4, Winfield Hill wrote:
upsidedown wrote...

On 1 Apr 2020 14:35:43 -0700, Winfield Hill wrote:

In my search for a 8 to 10V, 500A source,
needed for 2 seconds,

Since you need 2 seconds and you have three phase
available on site, why not use a three phase
transformer and a six pulse rectifier ?

Yes, we already agreed that's a viable solution.
But looking around for suitable transformer(s),
I wasn't able to find much. Yes, looking in
the wrong place, no doubt.


The main power transformer from one piece of broadcast NTSC video equipment I maintained in the late '80s had a 1000A, regulated 5VDC power supply that was over a half ton. It ran on 208, three phase. It was in a Vital Industries 'SqueezeZoom. It was the first electronic special effects system of its kind, and it sold for US $250,000. One was used at the studio that produced the Sonny and Cher show, where they came back on stage in all the costumes they wore throughout the show, with no loss of video quality. Sadly most or all were scraped when TV went digital. Some industrial surplus stores might turn up similar transformers. Mendelson's, in Dayton Ohio used to have tons of large, low voltage transformers from early mainframes.

Early high power low voltage (+5 V or -5.2 V) computers power supplies
used sometimes a center tapped transformers and two diodes instead of
a 4 diode bridge, thus suffering only a single diode voltage drop. If
you can find such a transformer, run the full secondary into 4 diode
bridge, it might be suitable for 10 Vdc,

To find suitable three phase transformers, look also for 277/480 V
primary and run them at 120 V or 208 V and you might find a suitable
transformer.

 

[Winfield Hill]

Flyguy wrote...

On Thursday, April 2, 2020 at 9:01:41 AM UTC-7, Flyguy wrote:
On Wednesday, April 1, 2020 at 6:47:00 PM UTC-7, Winfield Hill wrote:
Flyguy wrote...

I suggested an external resistor to take part of
the load off of the MOSFET.

But which of the five or six battery-configuration
choices do you recommend?

The Bioenno I originally recommended. You have to either:
1. Increase your MOSFET heat sink.
2. Use a larger MOSFET.
3. Use more MOSFETs.
4. Add a dropping resistor.
5. A combination of 1-4.
Add a series resistor is the easiest.

I looked at your PCB layout - what kind of heat sink
are you using now? What is your average power dissipation
for normal, continuous operation? Improving that heat sink
is probably the easiest solution.

The PCB can either take a 10W heatsink with the MOSFET
mounted vertically, or a 100W heatsink with the MOSFET
mounted underneath. The power limitation comes from
the TO-247 MOSFET, a IXFH400N075T2, and I don't think
a bigger heatsink will help much, as its 8ms Transient
Thermal Impedance is right at the limit. But simply
expanding the PCB to spread the work across two FETs
would not be difficult, and perhaps much easier than
futzing around with making lower supply voltages (a
bigger heatsink, to handle an added bolt-on power
resistor, is another possibility).

That would be yet another new RIS-976 version, maybe
RIS-796B, but it's probably inevitable anyway. Diode
half-sine testing wants a microcontroller interface.


--
Thanks,
- Win

 

[Winfield Hill]

Chris Jones wrote...

On 02/04/2020 23:46, Winfield Hill wrote:
Chris Jones wrote...

On 02/04/2020 20:28, Uwe Bonnes wrote:
Clive Arthur <cliveta@nowaytoday.co.uk> wrote:
On 01/04/2020 22:35, Winfield Hill wrote:
In my search for a 8 to 10V, 500A source,
needed for 2 seconds, I've been looking at
LiFePO4, and LTO (Lithium Titanate) cells

Something like 10 kF will be needed for 500 A,
2 sec and 0.1 Volt drop

Why would you want or need only 0.1V drop?
1V or even 2V drop would surely do.

I can handle 2V drop, and while the peak current
will be 500A, the RMS current will only be 177A.
About $112 worth of capacitors would do for a
33ms 2-cycle budget - simple and very useful.
But a full 100-cycle capability looks like it
would be much more expensive than batteries.

So if you had 4x Maxwell BCAP3000P270, total price
$256, that would give you 750F at 10.8V initial
voltage. After 2 seconds of 500A DC, it would
discharge by 1.33V to about 9.46V. The internal
resistance would drop another 580mV, so it would
be down to 8.88V at the capacitor terminals whilst
the current is still on.

Those are awesome parts, yes that would work well.


--
Thanks,
- Win

 

[Flyguy]

On Thursday, April 2, 2020 at 11:21:41 AM UTC-7, Winfield Hill wrote:

Chris Jones wrote...

On 02/04/2020 23:46, Winfield Hill wrote:
Chris Jones wrote...

On 02/04/2020 20:28, Uwe Bonnes wrote:
Clive Arthur <cliveta@nowaytoday.co.uk> wrote:
On 01/04/2020 22:35, Winfield Hill wrote:
In my search for a 8 to 10V, 500A source,
needed for 2 seconds, I've been looking at
LiFePO4, and LTO (Lithium Titanate) cells

Something like 10 kF will be needed for 500 A,
2 sec and 0.1 Volt drop

Why would you want or need only 0.1V drop?
1V or even 2V drop would surely do.

I can handle 2V drop, and while the peak current
will be 500A, the RMS current will only be 177A.
About $112 worth of capacitors would do for a
33ms 2-cycle budget - simple and very useful.
But a full 100-cycle capability looks like it
would be much more expensive than batteries.

So if you had 4x Maxwell BCAP3000P270, total price
$256, that would give you 750F at 10.8V initial
voltage. After 2 seconds of 500A DC, it would
discharge by 1.33V to about 9.46V. The internal
resistance would drop another 580mV, so it would
be down to 8.88V at the capacitor terminals whilst
the current is still on.

Those are awesome parts, yes that would work well.


--
Thanks,
- Win

Ok, then you need to chose door #2 and get a bigger hammer:

https://ixapps.ixys.com/DataSheet/VMO650-01F.pdf

 

[Flyguy]

On Thursday, April 2, 2020 at 6:16:31 PM UTC-7, Flyguy wrote:

On Thursday, April 2, 2020 at 11:21:41 AM UTC-7, Winfield Hill wrote:
Chris Jones wrote...

On 02/04/2020 23:46, Winfield Hill wrote:
Chris Jones wrote...

On 02/04/2020 20:28, Uwe Bonnes wrote:
Clive Arthur <cliveta@nowaytoday.co.uk> wrote:
On 01/04/2020 22:35, Winfield Hill wrote:
In my search for a 8 to 10V, 500A source,
needed for 2 seconds, I've been looking at
LiFePO4, and LTO (Lithium Titanate) cells

Something like 10 kF will be needed for 500 A,
2 sec and 0.1 Volt drop

Why would you want or need only 0.1V drop?
1V or even 2V drop would surely do.

I can handle 2V drop, and while the peak current
will be 500A, the RMS current will only be 177A.
About $112 worth of capacitors would do for a
33ms 2-cycle budget - simple and very useful.
But a full 100-cycle capability looks like it
would be much more expensive than batteries.

So if you had 4x Maxwell BCAP3000P270, total price
$256, that would give you 750F at 10.8V initial
voltage. After 2 seconds of 500A DC, it would
discharge by 1.33V to about 9.46V. The internal
resistance would drop another 580mV, so it would
be down to 8.88V at the capacitor terminals whilst
the current is still on.

Those are awesome parts, yes that would work well.


--
Thanks,
- Win

Ok, then you need to chose door #2 and get a bigger hammer:

https://ixapps.ixys.com/DataSheet/VMO650-01F.pdf

....and here is a smaller, and much cheaper, hammer:

https://www.digikey.com/product-detail/en/ixys/IXTN600N04T2/IXTN600N04T2-ND/2354478

 

[Winfield Hill]

Flyguy wrote...

On Thursday, April 2, 2020 at 6:16:31 PM UTC-7, Flyguy wrote:

Ok, then you need to chose door #2 and get a bigger hammer:

https://ixapps.ixys.com/DataSheet/VMO650-01F.pdf

...and here is a smaller, and much cheaper, hammer:

https://www.digikey.com/product-detail/en/ixys/IXTN600N04T2/IXTN600N04T2-
ND/2354478

Yep. They would do the job.


--
Thanks,
- Win

 

[Wond]

On Wed, 01 Apr 2020 18:46:46 -0700, Winfield Hill wrote:

Flyguy wrote...

I suggested an external resistor to take part of
the load off of the MOSFET.

But which of the five or six battery-configuration choices do you
recommend?

My knowlege is not current, I used to do a lot of marine work. Large
working vessels like salmon seiners and towboats used 32VDC systems,
obtained by series connecting four large 8V lead-acid batteries. I'm sure
the starting load on those big diesel engines could approach 500A. I
believe GM made the batteries, could be worth a look.

 

[Winfield Hill]

Wond wrote...

Winfield Hill wrote:
Flyguy wrote...

I suggested an external resistor to take part of
the load off of the MOSFET.

But which of the five or six battery-configuration
choices do you recommend?

My knowlege is not current, I used to do a lot of marine work. Large
working vessels like salmon seiners and towboats used 32VDC systems,
obtained by series connecting four large 8V lead-acid batteries. I'm sure
the starting load on those big diesel engines could approach 500A. I
believe GM made the batteries, could be worth a look.

Yes, I agree they would work.


--
Thanks,
- Win

 

[Wond]

On Fri, 03 Apr 2020 10:33:39 -0700, Winfield Hill wrote:

Wond wrote...

Winfield Hill wrote:
Flyguy wrote...

I suggested an external resistor to take part of
the load off of the MOSFET.

But which of the five or six battery-configuration
choices do you recommend?

My knowlege is not current, I used to do a lot of marine work. Large
working vessels like salmon seiners and towboats used 32VDC systems,
obtained by series connecting four large 8V lead-acid batteries. I'm
sure the starting load on those big diesel engines could approach 500A.
I believe GM made the batteries, could be worth a look.

Yes, I agree they would work.

found this-
<http://www.powerstridebattery.com/marine-batteries/8-volt-marine-
batteries/13-4-1-8-volt-marine-battery>

 

[Tim Williams]

"Winfield Hill" <winfieldhill@yahoo.com> wrote in message
news:r64mri018am@drn.newsguy.com...

I can handle 2V drop, and while the peak current
will be 500A, the RMS current will only be 177A.
About $112 worth of capacitors would do for a
33ms 2-cycle budget - simple and very useful.
But a full 100-cycle capability looks like it
would be much more expensive than batteries.

You didn't mention there would be reps. What PRF?

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Michael Terrell]

On Thursday, April 2, 2020 at 10:04:34 AM UTC-4, Winfield Hill wrote:

Michael Terrell wrote...

On Thursday, April 2, 2020, Winfield Hill wrote:
upsidedown wrote...
Winfield Hill wrote:

In my search for a 8 to 10V, 500A source,
needed for 2 seconds ...

Since you need 2 seconds and you have three phase
available on site, why not use a three phase
transformer and a six pulse rectifier ?

Yes, we already agreed that's a viable solution.
But looking around for suitable transformer(s),
I wasn't able to find much. Yes, looking in
the wrong place, no doubt.

The main power transformer from one piece of broadcast
NTSC video equipment I maintained in the late '80s had a
1000A, regulated 5VDC power supply that was over a half ton.
It ran on 208, three phase. It was in a Vital Industries
'SqueezeZoom. It was the first electronic special effects
system of its kind, and it sold for US $250,000. One was
used at the studio that produced the Sonny and Cher show,
where they came back on stage in all the costumes they wore
throughout the show, with no loss of video quality. Sadly
most or all were scraped when TV went digital. Some
industrial surplus stores might turn up similar transformers.
Mendelson's, in Dayton Ohio used to have tons of large, low
voltage transformers from early mainframes.

Wow, impressive. But I actually may not need a
high VA rating, because I'm only drawing current
for 2 seconds. I do need low winding resistance.
350A for 8ms, 177A for 33ms, down to 20A for 2 sec.
Hopefully no more than 3V drop at 350A = 8mR max.
Probably not a low number compared to your story.

That 1000A supply was used for a Z80B based computer system, with a lot of slow, power hungry RAM. Enough to store two pages of live video, and chroma. Things ave really changed in 35 years. A used, high speed 12 bit A/D converter hybrid was $1400, and the RAM was already obsolete.

 

[Winfield Hill]

Tim Williams wrote...

Winfield Hill wrote...

I can handle 2V drop, and while the peak current
will be 500A, the RMS current will only be 177A.
About $112 worth of capacitors would do for a
33ms 2-cycle budget - simple and very useful.
But a full 100-cycle capability looks like it
would be much more expensive than batteries.

You didn't mention there would be reps. What PRF?

Half-sine test would be at 60Hz or 50Hz. When
measuring the peal operating capability of a
diode, peak current must be lowered with more
cycles. Manufacturer's plots typically show
about 1/16 peak current for 100 cycles as for 1.


--
Thanks,
- Win

 

[Winfield Hill]

Michael Terrell wrote...

The main power transformer from one piece of broadcast
NTSC video equipment I maintained in the late '80s had a
1000A, regulated 5VDC power supply that was over a half ton.
It ran on 208, three phase. It was in a Vital Industries
'SqueezeZoom. It was the first electronic special effects
system of its kind, and it sold for US $250,000.

That 1000A supply was used for a Z80B based computer system,
with a lot of slow, power hungry RAM. Enough to store two
pages of live video, and chroma.

Whoa, a 5kW Z80 system! Most of ours were under 100W.


--
Thanks,
- Win

 

[Michael Terrell]

On Saturday, April 4, 2020 at 9:59:36 AM UTC-4, Winfield Hill wrote:

Michael Terrell wrote...

The main power transformer from one piece of broadcast
NTSC video equipment I maintained in the late '80s had a
1000A, regulated 5VDC power supply that was over a half ton.
It ran on 208, three phase. It was in a Vital Industries
'SqueezeZoom. It was the first electronic special effects
system of its kind, and it sold for US $250,000.

That 1000A supply was used for a Z80B based computer system,
with a lot of slow, power hungry RAM. Enough to store two
pages of live video, and chroma.

Whoa, a 5kW Z80 system! Most of ours were under 100W.

It was a full relay rack of circuit boards and fans. 768KB of 12 bit wide 4Kx1 TI DRAM per video page. It was so slow that 16 chips per bit were addressed at once, then read in sequence to get the required data rate. There was a huge sticker inside the front door showing where each memory board appeared in a video page. That used most of the 1000A. Other voltages for the analog circuits came from another set of power supplies. The thing was on 24/7/365, along with the video switcher for master control. That filled another full rack. It was a PITA. Someone had 'recapped' it, butt hey replaced the sealed liquid tantalums with cheap imported 85C electrolytics. I would replace about $500 of them with the original style per month. It was obvious that the component costs made up a large part of the %250,00 from the SqueezeZoom, and about $50,000 for the switching system.

One interesting thing about the SqueezeZoom. Even though the video circuits were very low noise, you could zoom into infinity and generate a great moving star field like you would expect to see on the view screen of a faster than light star ship. It was much better than the paper with holes punched in it, that was common in movies and TV shows. We played a prank on the Video engineer one day. I set it up to zoom to infinity, while another engineer set the Chyron to flash 'GAME OVER' in huge letters. He freaked when he got back from lunch!

 

On Sat, 4 Apr 2020 05:28:10 -0700 (PDT), Michael Terrell
<terrell.michael.a@gmail.com> wrote:

On Thursday, April 2, 2020 at 10:04:34 AM UTC-4, Winfield Hill wrote:
Michael Terrell wrote...

On Thursday, April 2, 2020, Winfield Hill wrote:
upsidedown wrote...
Winfield Hill wrote:

In my search for a 8 to 10V, 500A source,
needed for 2 seconds ...

Since you need 2 seconds and you have three phase
available on site, why not use a three phase
transformer and a six pulse rectifier ?

Yes, we already agreed that's a viable solution.
But looking around for suitable transformer(s),
I wasn't able to find much. Yes, looking in
the wrong place, no doubt.

The main power transformer from one piece of broadcast
NTSC video equipment I maintained in the late '80s had a
1000A, regulated 5VDC power supply that was over a half ton.
It ran on 208, three phase. It was in a Vital Industries
'SqueezeZoom. It was the first electronic special effects
system of its kind, and it sold for US $250,000. One was
used at the studio that produced the Sonny and Cher show,
where they came back on stage in all the costumes they wore
throughout the show, with no loss of video quality.

Did it really go from 3 phase rectifiers directly to 5 Vdc ? The
standard practice with big computers needing several kilowatts was to
generate low ripple 8 Vdc from 3ph rectifiers and using local 7805 or
309K regulators on each PCB. This helped avoiding the DC power harness
voltage drops.

Even when using 2102 memory chips (1024 x 1 bit 50 mA static RAMs)
that 1000 A current would have been able to easily power a full
megabyte of static RAM.

That amount of memory would have store multiple NTSC frames,
especially if the composite video was sampled at 3 x Fsc (3 x 3.57
MHz) as was the practice in he 1970's.

Still wondering why they did not use core memory as large computers
did ?

Sadly
most or all were scraped when TV went digital. Some
industrial surplus stores might turn up similar transformers.
Mendelson's, in Dayton Ohio used to have tons of large, low
voltage transformers from early mainframes.

Wow, impressive. But I actually may not need a
high VA rating, because I'm only drawing current
for 2 seconds. I do need low winding resistance.
350A for 8ms, 177A for 33ms, down to 20A for 2 sec.
Hopefully no more than 3V drop at 350A = 8mR max.
Probably not a low number compared to your story.


That 1000A supply was used for a Z80B based computer system, with a lot of slow, power hungry RAM. Enough to store two pages of live video, and chroma. Things ave really changed in 35 years. A used, high speed 12 bit A/D converter hybrid was $1400, and the RAM was already obsolete.

Sounds like it after all stored component video (3 x 4 bit) or 6 bits
for luma and 6 bit chroma, not composite.

 

On Sat, 4 Apr 2020 09:36:53 -0700 (PDT), Michael Terrell
<terrell.michael.a@gmail.com> wrote:

On Saturday, April 4, 2020 at 9:59:36 AM UTC-4, Winfield Hill wrote:
Michael Terrell wrote...

The main power transformer from one piece of broadcast
NTSC video equipment I maintained in the late '80s had a
1000A, regulated 5VDC power supply that was over a half ton.
It ran on 208, three phase. It was in a Vital Industries
'SqueezeZoom. It was the first electronic special effects
system of its kind, and it sold for US $250,000.

That 1000A supply was used for a Z80B based computer system,
with a lot of slow, power hungry RAM. Enough to store two
pages of live video, and chroma.

Whoa, a 5kW Z80 system! Most of ours were under 100W.

It was a full relay rack of circuit boards and fans. 768KB of 12 bit wide 4Kx1 TI DRAM per video page.

With 768 KW x 12 bits that makes just more than 2200 chips, consuming
less than 100 W, since all chips weren't accessed all the time.

>It was so slow that 16 chips per bit were addressed at once, then read in sequence to get the required data rate.

More likely 12 or 24 chips/sample.

There was a huge sticker inside the front door showing where each memory board appeared in a video page. That used most of the 1000A. Other voltages for the analog circuits came from another set of power supplies. The thing was on 24/7/365, along with the video switcher for master control. That filled another full rack. It was a PITA. Someone had 'recapped' it, butt hey replaced the sealed liquid tantalums with cheap imported 85C electrolytics. I would replace about $500 of them with the original style per month. It was obvious that the component costs made up a large part of the %250,00 from the SqueezeZoom, and about $50,000 for the switching system.

One interesting thing about the SqueezeZoom. Even though the video circuits were very low noise, you could zoom into infinity and generate a great moving star field like you would expect to see on the view screen of a faster than light star ship. It was much better than the paper with holes punched in it, that was common in movies and TV shows. We played a prank on the Video engineer one day. I set it up to zoom to infinity, while another engineer set the Chyron to flash 'GAME OVER' in huge letters. He freaked when he got back from lunch!

 

[Michael Terrell]

On Saturday, April 4, 2020 at 2:17:43 PM UTC-4, upsid...@downunder.com wrote:

On Sat, 4 Apr 2020 05:28:10 -0700 (PDT), Michael Terrell wrote:

On Thursday, April 2, 2020 at 10:04:34 AM UTC-4, Winfield Hill wrote:
Michael Terrell wrote...

On Thursday, April 2, 2020, Winfield Hill wrote:
upsidedown wrote...
Winfield Hill wrote:

In my search for a 8 to 10V, 500A source,
needed for 2 seconds ...

Since you need 2 seconds and you have three phase
available on site, why not use a three phase
transformer and a six pulse rectifier ?

Yes, we already agreed that's a viable solution.
But looking around for suitable transformer(s),
I wasn't able to find much. Yes, looking in
the wrong place, no doubt.

The main power transformer from one piece of broadcast
NTSC video equipment I maintained in the late '80s had a
1000A, regulated 5VDC power supply that was over a half ton.
It ran on 208, three phase. It was in a Vital Industries
'SqueezeZoom. It was the first electronic special effects
system of its kind, and it sold for US $250,000. One was
used at the studio that produced the Sonny and Cher show,
where they came back on stage in all the costumes they wore
throughout the show, with no loss of video quality.

Did it really go from 3 phase rectifiers directly to 5 Vdc ? The
standard practice with big computers needing several kilowatts was to
generate low ripple 8 Vdc from 3ph rectifiers and using local 7805 or
309K regulators on each PCB. This helped avoiding the DC power harness
voltage drops.

It had a pair of very heavy copper buss bars that ran most of the height of the rack. Each board would have needed multiple regulators, and the extra space for heatsinks would have split the system into two full racks. It would have required even more cooling, as well. A single lare regulated system eliminated the extra space, heat and load balancing.

Even when using 2102 memory chips (1024 x 1 bit 50 mA static RAMs)
that 1000 A current would have been able to easily power a full
megabyte of static RAM.

Static ram was too slow, even using that paging system. This was designed in the early '80s by a Professor of EE at the University in Gainesville Florida.

That amount of memory would have store multiple NTSC frames,
especially if the composite video was sampled at 3 x Fsc (3 x 3.57
MHz) as was the practice in he 1970's.

It stored two frames.

Still wondering why they did not use core memory as large computers
did ?

Core was even slower that the available SRAM.

Sadly
most or all were scraped when TV went digital. Some
industrial surplus stores might turn up similar transformers.
Mendelson's, in Dayton Ohio used to have tons of large, low
voltage transformers from early mainframes.

Wow, impressive. But I actually may not need a
high VA rating, because I'm only drawing current
for 2 seconds. I do need low winding resistance.
350A for 8ms, 177A for 33ms, down to 20A for 2 sec.
Hopefully no more than 3V drop at 350A = 8mR max.
Probably not a low number compared to your story.


That 1000A supply was used for a Z80B based computer system, with a lot of slow, power hungry RAM. Enough to store two pages of live video, and chroma. Things ave really changed in 35 years. A used, high speed 12 bit A/D converter hybrid was $1400, and the RAM was already obsolete.

Sounds like it after all stored component video (3 x 4 bit) or 6 bits
for luma and 6 bit chroma, not composite.

It stored 12 bits of video, and six more of Chroma.