500A power source

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 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,
 in 38120 and 66160 sizes.  All types of
 suppliers, plus completed battery systems,
 with charge balancing electronics.  Sheesh,
 it's enough to make one's head spin.  BTW,
 a simple "12V" battery has a bit too much
 voltage, an extra burden on power MOSFET(s),
 so cell-by-cell connectivity would be nice.
 Probably gonna be at least $500, no matter.
 Gotta ask Rob Legg what he thinks.


--  
 Thanks,
    - Win

Re: 500A power source
wrote:

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Polyphase buck switcher?

--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: 500A power source
John Larkin wrote...
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 Good idea, but it'd be a 5kW switcher, and
 with enough bulk capacitance to last through
 the 8ms troughs.  Each of six phases running
 at almost 100A.  Sounds like more work than
 putting together a battery.


--  
 Thanks,
    - Win

Re: 500A power source
Winfield Hill wrote...
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 18650 Li-Ion cells, while they look impressive,
 are actually really wimpy.  38120 LiFePO4 cells
 look even more impressive, but still have rather
 disappointingly-high internal resistance.  Stack
 four in series, esr is 4x higher yet, so you need
 lots of parallel stacks.  66160 cells, of either
 LiFePO4 or TLO chemistry have attractive low esr.  
 A two or three-volt drop at 500A isn't too bad.
 Whoa, they're huge.  I like TLO's safe operation.


--  
 Thanks,
    - Win

Re: 500A power source
wrote:

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MeanWell has a 5 volt 150 amp power supply for $180. Parallel two of
them.

The MeanWells can put out a bit more than rated current for a while.  

--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: 500A power source
John Larkin wrote...
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 I'd need four of them to get to 8 to 10V.  And I have
 a pile of surplus half-rack 5V 200A supplies, could
 wire up four of them.  Also a few years back I made a
 6V 400V rack-mount supply, that could probably do 500A
 for a few seconds.  Some parts I'd like to characterize
 could get by with the lower D.U.T. voltage.


--  
 Thanks,
    - Win

Re: 500A power source
On Wednesday, April 1, 2020 at 2:35:51 PM UTC-7, Winfield Hill wrote:
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Now you've changed it to 8 to 10V, before it was just 10V. LFP cell voltage
 is 3.2V, so you only need 3, given cells with low enough internal resistan
ce to keep the voltage from dropping below 8V. What you won't get is an int
egrated BMS, so you will have to take appropriate precautions. I suggested  
an external resistor to take part of the load off of the MOSFET.

Re: 500A power source
Flyguy wrote...
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 But which of the five or six battery-configuration
 choices do you recommend?


--  
 Thanks,
    - Win

Re: 500A power source
On Wednesday, April 1, 2020 at 6:47:00 PM UTC-7, Winfield Hill wrote:
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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.

Re: 500A power source
On Thursday, April 2, 2020 at 9:01:41 AM UTC-7, Flyguy wrote:
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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.

Re: 500A power source
Flyguy wrote...
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 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

Re: 500A power source
On Wed, 01 Apr 2020 18:46:46 -0700, Winfield Hill wrote:

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   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.

Re: 500A power source
Wond wrote...
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 Yes, I agree they would work.


--  
 Thanks,
    - Win

Re: 500A power source
On Fri, 03 Apr 2020 10:33:39 -0700, Winfield Hill wrote:

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

Re: 500A power source
wrote:

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The simpler the requirement, the simpler the  
solution.

If all you needed was to duplicate the 8mS half-sine  
forward surge current rating ( a non-repetitive  
test ) for rectifiers, a pulse-forming circuit  
could do it - but this is not really a linearly  
controlled method, it's just a resonant hammer  
that gets adjusted to suit pulse losses in the  
DUT.  

The period is set by the non-adjustible PFN.  
The standard specifies a peak value of the half-sine.
At 1Hz, you might lose 40W in the circuit and DUT.

A PWM buck would reduce the current stress on the  
source - so you'd not really be looking for a 500A  
source, you'd be looking for something that can  
supply the energy delivered to the DUT, and losses.

How this could be integrated into a linear test  
circuit like the RS-796A, is a puzzler. Perhaps  
PWMing the switch driver, outside of the linear  
control loop, with a choke and rated freewheeling  
diode might do it; but you'd have to sense the  
current in the DUT, not the switch current. This  
would defeats the RS-796A test modality, which  
assumes Idut = Iswitch.

Sorry if slow on the draw here. Figured it was  
a good time to catch up on paperwork, taxes etc.

RL

Re: 500A power source
onsdag den 1. april 2020 kl. 23.35.51 UTC+2 skrev Winfield Hill:
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something like this? https://hobbyking.com/en_us/turnigy-graphene-6000mah-3s-75c-lipo-pack-w-xt90.html



Re: 500A power source
Lasse Langwadt Christensen wrote...
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https://hobbyking.com/en_us/turnigy-graphene-6000mah-3s-75c-lipo-pack-w-xt90.html

 Whoa, cotta check that out.


--  
 Thanks,
    - Win

Re: 500A power source
On 01/04/2020 22:35, Winfield Hill wrote:
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Supercaps?

--  
Cheers
Clive

Re: 500A power source
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Something like 10 kF will be needed for 500 A, 2 sec and 0.1 Volt drop
--  
Uwe Bonnes                 snipped-for-privacy@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
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Re: 500A power source
On 02/04/2020 20:28, Uwe Bonnes wrote:
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Why would you want or need only 0.1V drop? 1V or even 2V drop would  
surely do. 3kF capacitors are fairly inexpensive from digi-key. The ones  
I have are rated for about 1.9kA and if I recall correctly about 0.3  
milliohms series resistance. You'd need at least 3 in series, meaning at  
most 1kF total capacitance from a single string but that should be fine.

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