Protecting Super-Caps

[Flyguy]

On Sunday, March 29, 2020 at 12:20:29 PM UTC-7, Winfield Hill wrote:

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

Nope, just found it online.

 

[Flyguy]

On Sunday, March 29, 2020 at 3:08:33 PM UTC-7, Winfield Hill wrote:

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

What is the rep rate of the pulses?

 

[Mikko OH2HVJ]

Winfield Hill <winfieldhill@yahoo.com> writes:

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,

Check out the terminal voltage with a scope and trigger at 70% of the
battery voltage to see if it has a sudden voltage drop for few us.

In you case that does not matter, but if the battery is used to power
some control circuit, that may cause problems.

--
mikko

 

[Winfield Hill]

Mikko OH2HVJ wrote...

Winfield Hill <winfieldhill@yahoo.com> writes:

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,

Check out the terminal voltage with a scope and trigger
at 70% of the battery voltage to see if it has a sudden
voltage drop for few us.

In your case that does not matter, but if the battery is
used to power some control circuit, that may cause problems.

The PCB has 6mF of onboard low-esr capacitance that can
supply 500A for 25us. The control power, typically 24V,
is separate from the high-current rails, 8 to 35 volts.

https://www.dropbox.com/s/2dcfzkrvf5cw9f8/RIS-796A_a2.3.pdf?dl=1
https://www.dropbox.com/s/dq381ji2so7cm7u/RIS-796A_pcb_top.JPG?dl=0

The sense resistor needs 1.25 volts, and the MOSFET, changed
to an IXFH400N075T2 for 500A operation, needs a few volts,
the rest is available for the D.U.T.

The battery voltage is almost too high, because beyond
delivering 500A for a few half-sine cycles at 60Hz, it
the power MOSFET may overheat. See Figure 19 in the
datasheet, which shows the thermal mass is used up by
15ms, and heat then flows to the heatsink. I'll need a
new version of the PCB, with two or three power MOSFETs.

https://www.dropbox.com/s/m9e07zjjyepl9y2/IXFH400N075T2.pdf?dl=1

Hey, Mikko OH2HVJ, you wanna play with one of these PCBs?


--
Thanks,
- Win

 

[Flyguy]

On Monday, March 30, 2020 at 2:52:53 AM UTC-7, Winfield Hill wrote:

Mikko OH2HVJ wrote...

Winfield Hill <winfieldhill@yahoo.com> writes:

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,

Check out the terminal voltage with a scope and trigger
at 70% of the battery voltage to see if it has a sudden
voltage drop for few us.

In your case that does not matter, but if the battery is
used to power some control circuit, that may cause problems.

The PCB has 6mF of onboard low-esr capacitance that can
supply 500A for 25us. The control power, typically 24V,
is separate from the high-current rails, 8 to 35 volts.

https://www.dropbox.com/s/2dcfzkrvf5cw9f8/RIS-796A_a2.3.pdf?dl=1
https://www.dropbox.com/s/dq381ji2so7cm7u/RIS-796A_pcb_top.JPG?dl=0

The sense resistor needs 1.25 volts, and the MOSFET, changed
to an IXFH400N075T2 for 500A operation, needs a few volts,
the rest is available for the D.U.T.

The battery voltage is almost too high, because beyond
delivering 500A for a few half-sine cycles at 60Hz, it
the power MOSFET may overheat. See Figure 19 in the
datasheet, which shows the thermal mass is used up by
15ms, and heat then flows to the heatsink. I'll need a
new version of the PCB, with two or three power MOSFETs.

https://www.dropbox.com/s/m9e07zjjyepl9y2/IXFH400N075T2.pdf?dl=1

Hey, Mikko OH2HVJ, you wanna play with one of these PCBs?


--
Thanks,
- Win

You could reduce the power dissipated by the MOSFET with a power resistor (of appropriate R and W) in series with the battery.

 

Flyguy <soar2morrow@yahoo.com> wrote in
news:28eab271-6b00-4e43-9347-712983845a6f@googlegroups.com:

On Monday, March 30, 2020 at 2:52:53 AM UTC-7, Winfield Hill
wrote:
Mikko OH2HVJ wrote...

Winfield Hill <winfieldhill@yahoo.com> writes:

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,

Check out the terminal voltage with a scope and trigger
at 70% of the battery voltage to see if it has a sudden
voltage drop for few us.

In your case that does not matter, but if the battery is
used to power some control circuit, that may cause problems.

The PCB has 6mF of onboard low-esr capacitance that can
supply 500A for 25us. The control power, typically 24V,
is separate from the high-current rails, 8 to 35 volts.

https://www.dropbox.com/s/2dcfzkrvf5cw9f8/RIS-796A_a2.3.pdf?dl=1
https://www.dropbox.com/s/dq381ji2so7cm7u/RIS-796A_pcb_top.JPG?dl=
0

The sense resistor needs 1.25 volts, and the MOSFET, changed
to an IXFH400N075T2 for 500A operation, needs a few volts,
the rest is available for the D.U.T.

The battery voltage is almost too high, because beyond
delivering 500A for a few half-sine cycles at 60Hz, it
the power MOSFET may overheat. See Figure 19 in the
datasheet, which shows the thermal mass is used up by
15ms, and heat then flows to the heatsink. I'll need a
new version of the PCB, with two or three power MOSFETs.

https://www.dropbox.com/s/m9e07zjjyepl9y2/IXFH400N075T2.pdf?dl=1

Hey, Mikko OH2HVJ, you wanna play with one of these PCBs?


--
Thanks,
- Win

You could reduce the power dissipated by the MOSFET with a power
resistor (of appropriate R and W) in series with the battery.

They called you a wastoid back in school too, eh?

 

[amdx]

On 3/29/2020 2:20 PM, Winfield Hill wrote:

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?

After a short search nothing showed up, But it does reference two
different papers written in 2016, so it's not real old.
Mikek

 

[Jasen Betts]

On 2020-03-26, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

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?

As Win says, "that's a lot of heft, for only 8ms."

low ESR prismatic Lipo can probabkly do it, that's
those pocket sized jump starters.

--
Jasen.