Protecting Super-Caps

[Winfield Hill]

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.


--
Thanks,
- Win

 

[Phil Hobbs]

On 2020-03-26 15:54, Winfield Hill wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.


How about a truck battery?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Adrian Tuddenham]

Winfield Hill <winfieldhill@yahoo.com> wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.

Lorry batteries?

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

 

[Buzz McCool]

On 3/26/20 12:54 PM, Winfield Hill wrote:
..
..
..

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max.

A colleague of mine used an LTC3780 which has output overvoltage
protection.

https://www.analog.com/en/products/ltc3780.html#product-overview

 

[Lasse Langwadt Christense]

torsdag den 26. marts 2020 kl. 20.54.45 UTC+1 skrev Winfield Hill:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.

there's plenty of ICs that in combination with a fet
with cut off the supply when exceeding a set voltage.
that would fix the fat finger on the knob problem

but I think you would also need balancing, and at those
current you probably don't want to clamp each capacitor,
maybe something like this?
http://www.etasolution.com/upload/201905/09/201905091810050738.pdf

https://de.aliexpress.com/item/33016204911.html

 

[piglet]

On 26/03/2020 7:54 pm, Winfield Hill wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.

Isn't the whole point of half sine 8.33/10ms to represent mains power
line so why not use the mains power line via appropriate transformation?

piglet

 

[Winfield Hill]

piglet wrote...

On 26/03/2020 7:54 pm, Winfield Hill wrote:
After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.
[ snip story ]

Isn't the whole point of half sine 8.33 / 10ms
to represent mains power line, so why not use the
mains power line via appropriate transformation?

They setup a simple system, I suppose. A Variac
and maybe step-down transformer, an SCR or Triac,
with a half-cycle trigger controller, and a big
old power resistor to the diode. Yawn.

We can impose a shaped, controlled, up-to-500A
current pulse to a diode under test. And more
important, we can interrupt the current at any
point during a 8.3ms pulse, and quickly measure
the diode's forward voltage at 10mA, and thereby
determine its Tj. Repeated tests with varying
time delays can let us map the junction temp vs
time. This is better than simply determining a
diode failure point. Many manufacturers claim
their spec is for 175C Tmax. How do they know?


--
Thanks,
- Win

 

[Winfield Hill]

Lasse Langwadt Christensen wrote...

but I think you would also need balancing, and at those
current you probably don't want to clamp each capacitor,
maybe something like this?
http://www.etasolution.com/upload/201905/09/201905091810050738.pdf

Yes

> https://de.aliexpress.com/item/33016204911.html

I've purchased some of these, but they never give a
schematic, and I have no idea what they do, or how
good (or bad) it might be.


--
Thanks,
- Win

 

On 26 Mar 2020 12:54:32 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

Do you have three phase mains available ?

A simple six pulse rectifier will have only 4.2 % (RMS) ripple without
any storage capacitors.

If this is still too much, use 12 or 18 pulse rectifiers, which
requires additional transformers (or at least multiple secondary
windings), so that various wye/delta configurations can be used to
generate the required phase shifts.

Since the required DC voltage is quite low (and hence the
primary/secondary turn ratio is quite large) and the pulse width is
small, the mains fuses should handle the situation easily.

 

[Winfield Hill]

upsidedown@downunder.com wrote...

Winfield Hill <winfieldhill@yahoo.com> wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

Do you have three phase mains available ?

A simple six pulse rectifier will have only 4.2 %
(RMS) ripple without any storage capacitors.

Yes, its in the building, good idea. Ripple is
no problem, because the active op-amp-controlled
MOSFET current source will simple insure that the
current remains constant. And high CMMR and PSRR
difference amplifiers provide the output signals.

https://www.dropbox.com/s/2dcfzkrvf5cw9f8/RIS-796A_a2.3.pdf?dl=1

It's only necessary to keep a minimum say 5 volts
across the MOSFET. For long-pulse, low-voltage
500A operation, I'm thinking of a IXFH400N075T2
MOSFET, which can have under 2V Vds drop at 500A.
A 2.5mR sense resistor takes up 1.25 volts. So
it's really a matter of the maximum D.U.T. drop.

Obtaining 500A transformers might be an issue.


--
Thanks,
- Win

 

On 27 Mar 2020 02:27:06 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

upsidedown@downunder.com wrote...

Winfield Hill <winfieldhill@yahoo.com> wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

Do you have three phase mains available ?

A simple six pulse rectifier will have only 4.2 %
(RMS) ripple without any storage capacitors.

Yes, its in the building, good idea.

Does the building have 120/208 V or industrial 277/480 V ?

Ripple is
no problem, because the active op-amp-controlled
MOSFET current source will simple insure that the
current remains constant. And high CMMR and PSRR
difference amplifiers provide the output signals.

In a six pulse rectifier, the voltage drops to 87 % before the next
phase takes over (more than 12 % pp) Even a small storage capacitor
will help ride trough the dip, i.e. keep the voltage at least say 90
% of peak voltage for less than 1 ms.

https://www.dropbox.com/s/2dcfzkrvf5cw9f8/RIS-796A_a2.3.pdf?dl=1

It's only necessary to keep a minimum say 5 volts
across the MOSFET. For long-pulse, low-voltage
500A operation, I'm thinking of a IXFH400N075T2
MOSFET, which can have under 2V Vds drop at 500A.
A 2.5mR sense resistor takes up 1.25 volts. So
it's really a matter of the maximum D.U.T. drop.

Obtaining 500A transformers might be an issue.

A single three phase transformer with 200 A secondaries should suffice
for continuous duty.

If you can't find a there phase transformer with 200 A secondaries,
look for single phase transformers with 200 A secondaries.

If you use single phase transformers, each transformer will need to
handle only 1/3 of the power (or 1/6 if 12 pulse rectifier with six
single phase transformers) is used.

With single phase transformers, look also for transformers with 208 V
primary voltage (or 277 or 480 V if available at your site).

 

[piglet]

On 27/03/2020 12:37 am, Winfield Hill wrote:

piglet wrote...

On 26/03/2020 7:54 pm, Winfield Hill wrote:
After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.
[ snip story ]

Isn't the whole point of half sine 8.33 / 10ms
to represent mains power line, so why not use the
mains power line via appropriate transformation?

They setup a simple system, I suppose. A Variac
and maybe step-down transformer, an SCR or Triac,
with a half-cycle trigger controller, and a big
old power resistor to the diode. Yawn.

We can impose a shaped, controlled, up-to-500A
current pulse to a diode under test. And more
important, we can interrupt the current at any
point during a 8.3ms pulse, and quickly measure
the diode's forward voltage at 10mA, and thereby
determine its Tj. Repeated tests with varying
time delays can let us map the junction temp vs
time. This is better than simply determining a
diode failure point. Many manufacturers claim
their spec is for 175C Tmax. How do they know?

Thanks Win, I wasn't advocating going back to an SCR, you can use your
MOSFETs to switch but meant to suggest using stepped down mains as the
high current supply.

piglet

 

[Lasse Langwadt Christense]

fredag den 27. marts 2020 kl. 10.27.19 UTC+1 skrev Winfield Hill:

upsidedown@downunder.com wrote...

Winfield Hill <winfieldhill@yahoo.com> wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

Do you have three phase mains available ?

A simple six pulse rectifier will have only 4.2 %
(RMS) ripple without any storage capacitors.

Yes, its in the building, good idea. Ripple is
no problem, because the active op-amp-controlled
MOSFET current source will simple insure that the
current remains constant. And high CMMR and PSRR
difference amplifiers provide the output signals.

https://www.dropbox.com/s/2dcfzkrvf5cw9f8/RIS-796A_a2.3.pdf?dl=1

It's only necessary to keep a minimum say 5 volts
across the MOSFET. For long-pulse, low-voltage
500A operation, I'm thinking of a IXFH400N075T2
MOSFET, which can have under 2V Vds drop at 500A.
A 2.5mR sense resistor takes up 1.25 volts. So
it's really a matter of the maximum D.U.T. drop.

Obtaining 500A transformers might be an issue.

a stack of toroid transformers, ignore the secondaries and add
a new with some welding wire?

next issue is the six 500A diodes

 

[Joe Gwinn]

On Fri, 27 Mar 2020 06:23:22 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

fredag den 27. marts 2020 kl. 10.27.19 UTC+1 skrev Winfield Hill:
upsidedown@downunder.com wrote...

Winfield Hill <winfieldhill@yahoo.com> wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

Do you have three phase mains available ?

A simple six pulse rectifier will have only 4.2 %
(RMS) ripple without any storage capacitors.

Yes, its in the building, good idea. Ripple is
no problem, because the active op-amp-controlled
MOSFET current source will simple insure that the
current remains constant. And high CMMR and PSRR
difference amplifiers provide the output signals.

https://www.dropbox.com/s/2dcfzkrvf5cw9f8/RIS-796A_a2.3.pdf?dl=1

It's only necessary to keep a minimum say 5 volts
across the MOSFET. For long-pulse, low-voltage
500A operation, I'm thinking of a IXFH400N075T2
MOSFET, which can have under 2V Vds drop at 500A.
A 2.5mR sense resistor takes up 1.25 volts. So
it's really a matter of the maximum D.U.T. drop.

Obtaining 500A transformers might be an issue.


a stack of toroid transformers, ignore the secondaries and add
a new with some welding wire?

Also sold are toroid power transformers with only the primary winding,
the user to provide the secondary. Of welding cable.


>next issue is the six 500A diodes

Actually, widely available albeit expensive. Probably is hockey-pick
diode range. One possibility is Infineon's "High Power Thyristors and
Diodes" line. Get the "Selection Guide 2019/2020" from the Infineon
website. Vishay, IXYS, et al, also have candidates.

These high-power diodes have considerable thermal capacity, and so can
be pulsed pretty aggressively. Schottkey diodes may also be
available, but I have not checked.

Joe Gwinn

 

[George Herold]

On Thursday, March 26, 2020 at 5:34:29 PM UTC-4, piglet wrote:

On 26/03/2020 7:54 pm, Winfield Hill wrote:
After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.



Isn't the whole point of half sine 8.33/10ms to represent mains power
line so why not use the mains power line via appropriate transformation?

piglet

Youch! sounds like a buzz box ac/ dc arc welder... those things
scare me some.

George H.

 

[Flyguy]

On Thursday, March 26, 2020 at 12:54:45 PM UTC-7, Winfield Hill wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.


--
Thanks,
- Win

A LiFePo4 starter battery could do it. They have internal resistance in the neighborhood of 10 mohm. This one has 500 CCA, so it should deliver at least 10 V at 500 amp at room temp.
https://www.bioennopower.com/collections/12v-series-lfp-lifepo4-batteries-high-discharge-rate/products/12v-500-cca-lfp-starter-battery-abs-blp-20500m-1

 

[M Philbrook]

In article <cce0edb2-c818-4501-8ecd-9add8d09dd7b@googlegroups.com>,
ggherold@gmail.com says...

On Thursday, March 26, 2020 at 5:34:29 PM UTC-4, piglet wrote:
On 26/03/2020 7:54 pm, Winfield Hill wrote:
After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.



Isn't the whole point of half sine 8.33/10ms to represent mains power
line so why not use the mains power line via appropriate transformation?

piglet

Youch! sounds like a buzz box ac/ dc arc welder... those things
scare me some.

George H.

They make welding caps that type of job.

They are noramlly much larger in termina lugs and some of them.

A low ESR and low value cap for a welder is about 10 x the size of a
normal cap and mount with screws to the steel for heat sinking ...

I've seen ring type oscillators for induction heating use these caps
due to the required low ESR. Btw, ringing induction heater supplies are
very interesting in design, simple but works.

 

[Flyguy]

On Sunday, March 29, 2020 at 5:47:00 AM UTC-7, M Philbrook wrote:

In article <cce0edb2-c818-4501-8ecd-9add8d09dd7b@googlegroups.com>,
ggherold@gmail.com says...

On Thursday, March 26, 2020 at 5:34:29 PM UTC-4, piglet wrote:
On 26/03/2020 7:54 pm, Winfield Hill wrote:
After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

In fact, my 300-watt Xantrex bench supply, 15V,
20A, can't handle the task. For that duration,
I need an honest 10-volt 500-amp power source.
OK, surely stacks of hefty 18650 cells can do
the job? No way, too high internal resistance.

I can stack six surplus 1kW 5V, 200A supplies,
but whoa, that's a lot of heft, for only 8ms.

Aha, eight DGH407Q2R7 supercaps series-parallel
400F 2.7V can do it, 2.8mR each, for 5.6mR net,
2.8V esr drop at 500A, +0.1V dV/dt drop in 8.3ms.
Don't take much space! The Xantrex supply can
keep them charged.

But oops, better add some serious overvoltage
protection, to limit the 10V capacitor bank to
10.8V, absolute max. 20A shunt protection to
limit my Xantrex knob twirling to 10.2 volts,
with shutoff, to avoid making the overvoltage
protection circuit dissipate 200W.

Been there, done that? Let us know about it.



Isn't the whole point of half sine 8.33/10ms to represent mains power
line so why not use the mains power line via appropriate transformation?

piglet

Youch! sounds like a buzz box ac/ dc arc welder... those things
scare me some.

George H.

They make welding caps that type of job.

They are noramlly much larger in termina lugs and some of them.

A low ESR and low value cap for a welder is about 10 x the size of a
normal cap and mount with screws to the steel for heat sinking ...

I've seen ring type oscillators for induction heating use these caps
due to the required low ESR. Btw, ringing induction heater supplies are
very interesting in design, simple but works.

Here is an interesting solution that uses high-voltage caps coupled thru a transformer to produce low-voltage, high-current pulses:

https://ewi.org/wp-content/uploads/2016/10/Examination-of-Electrolytic-Capacitors-for-Welding-Applications.pdf

 

[Winfield Hill]

Flyguy wrote...

Here is an interesting solution that uses high-voltage
caps coupled thru a transformer to produce low-voltage,
high-current pulses:

https://ewi.org/wp-content/uploads/2016/10/Examination-of-Electrolytic-
Capacitors-for-Welding-Applications.pdf

Do you know where that was published, and its date?


--
Thanks,
- Win

 

[Winfield Hill]

Flyguy wrote...

On Thursday, March 26, 2020, Winfield Hill wrote:

After working hard to get my RIS-796A "analog"
high-current source working to 500A for 10ms,
for 8.3 ms single half sine-wave forward surge
current tests, I realized the on-board low-esr
caps, although happy delivering 500A currents,
quickly run out of charge for such long pulses.

A LiFePo4 starter battery could do it. They have
internal resistance in the neighborhood of 10 mohm.
This one has 500 CCA, so it should deliver at least
10 V at 500 amp at room temp.
https://www.bioennopower.com/collections/12v-series-lfp-lifepo4-batteries-high-
discharge-rate/products/12v-500-cca-lfp-starter-battery-abs-blp-20500m-1

That's an awesome battery, small and lightweight,
it looks like it's just the ticket. My SuperCap
scheme would only work for one or two half cycles,
whereas the diode guys want to test for up to 100
cycles. I'd like to be able to do a good fraction
of that, before the MOSFET overheats. At an RMS
average power level of say 1.4kW, a IXFH400N075T2
MOSFET can handle several cycles, and with two
FETs, the heatsink should handle continuous heat.

OK, this brings up the issue of fuse-protection,
otherwise a short could lead to an explosion.
I'm having trouble finding an appropriate fuse,
but the battery's built-in shutoff will do. The
PCB has a 30A auto fuse, but it'll blow in 10ms,
so I could short across it with the BLP-20500M.


--
Thanks,
- Win