AVR-Chat

Off-topic slightly, but does anyone know what the current carrying
capacity of #16 magnet wire is, for T<= 200uS?

DC I know, but I'm not finding any refs about short time periods.


-- 

"The very powerful and the very stupid have one thing in common. Instead of
altering their views to fit the facts, they alter the facts to fit their
views... which can be very uncomfortable if you happen to be one of the
facts that needs altering." Doctor Who, Face of Evil

Slightly less than when it goes open circuit ;)

Regards,

Kat.

David VanHorn wrote:

>
> Off-topic slightly, but does anyone know what the current carrying
> capacity of #16 magnet wire is, for T<= 200uS?
>
> DC I know, but I'm not finding any refs about short time periods.
>
> -- 
>
> "The very powerful and the very stupid have one thing in common. 
> Instead of
> altering their views to fit the facts, they alter the facts to fit their
> views... which can be very uncomfortable if you happen to be one of the
> facts that needs altering." Doctor Who, Face of Evil
>
>

On Thu, Feb 19, 2009 at 7:35 PM, Kathy Quinlan <kaqdialup@iinet.net.au> wrote:
> Slightly less than when it goes open circuit ;)

BTDT, and got some cool sort of aerogelish thingys hanging in the air
for a while.

Look at "Ampacity" in the wire tables. I think that rating has to do more
like what you are looking for. The problem with industrial wire tables is
that there is one rating for wire in a conduit and another based on free
air, insulation melting, and so forth. National Electrical Code just does
not envision short pulse operation.

I would guess that for short pulses like that, it would be at least 2X DC
but that is just a guess.

Jim Wagner
Oregon Research Electronics

> Off-topic slightly, but does anyone know what the current carrying
> capacity of #16 magnet wire is, for T<= 200uS?
>
> DC I know, but I'm not finding any refs about short time periods.
>
>
> --
>
> "The very powerful and the very stupid have one thing in common. Instead
> of
> altering their views to fit the facts, they alter the facts to fit their
> views... which can be very uncomfortable if you happen to be one of the
> facts that needs altering." Doctor Who, Face of Evil
>

> I would guess that for short pulses like that, it would be at least 2X DC
> but that is just a guess.


I'm operating at roughly 1kA

The shunt is rated at 50mV/25A, and my last test shot read 5.5Vp with
a risetime of about 200uS and hold time of 750-ish uS.

The shunt is suggesting 2750A, but I think it's too inductive.

400V into 100uH is what's going on.

On Feb 19, 2009, at 5:28 PM, David VanHorn wrote:

> > I would guess that for short pulses like that, it would be at  
> least 2X DC
> > but that is just a guess.
>
> I'm operating at roughly 1kA
>
> The shunt is rated at 50mV/25A, and my last test shot read 5.5Vp with
> a risetime of about 200uS and hold time of 750-ish uS.
>
> The shunt is suggesting 2750A, but I think it's too inductive.
>
> 
Hope you are using Kelvin contacts!

Jim Wagner

[Non-text portions of this message have been removed]

In this mode, the current capacity depends on a whole bunch of things.  
Thermal mass, length, heat sinking capability of the end-terminals,  
melting point of the alloy are just a few. You might be able to model  
it with some sort of finite-element simulator but you would spend a  
lot of hours doing that and what you got would be hard to validate.

Jim Wagner

On Feb 19, 2009, at 5:28 PM, David VanHorn wrote:

> > I would guess that for short pulses like that, it would be at  
> least 2X DC
> > but that is just a guess.
>
> I'm operating at roughly 1kA
>
> The shunt is rated at 50mV/25A, and my last test shot read 5.5Vp with
> a risetime of about 200uS and hold time of 750-ish uS.
>
> The shunt is suggesting 2750A, but I think it's too inductive.
>
> 



[Non-text portions of this message have been removed]

> Hope you are using Kelvin contacts!

I am.  The results are still >3X too high to be believed.

On Thu, Feb 19, 2009 at 9:37 PM, Jim Wagner <wagnerj@proaxis.com> wrote:
> In this mode, the current capacity depends on a whole bunch of things.
> Thermal mass, length, heat sinking capability of the end-terminals,
> melting point of the alloy are just a few. You might be able to model
> it with some sort of finite-element simulator but you would spend a
> lot of hours doing that and what you got would be hard to validate.

It's in the form of a 44mm ID two-layer coil, with 64 turns.

I was hoping someone here had done "exploding wire" experiments and
could offer guidance.

My risetime looks great, and the flyback diode is damping the ringing
fine, but I am nervous that at 1kA I'm pushing the wire too hard.
Still, it hardly has time to get hot.

Done the exploding wire deal Dave, both intentionally and non.

1.  How are you measuring your shunt voltage and waveform?  A scope I 
presume.

2.  Your shunt will be somewhat inductive at these frequencies and currents.

3.  Your frequency components will appear because of the pulsed 
waveform, so you'll need to be aware of that.

4.  Have you tried to cancel fields by running the cable into and out of 
your shunt in opposite directions?  At these kinds of currents, physical 
placement of the wires will have an affect.  For example; we built a 
multi-station circuit breaker calibration system for distribution 
transformers, substation types up to 2500 amps, some years ago and the 
way we had to match station impedances was to change the routing of the 
350 MCM cables.  To achieve 0.25% system accuracy this was no minor 
accomplishment and the station impedances had to be matched even better 
than this.

5.  Could the difference be caused by an induced field in your probes?  
1KA at ~1mSec is a huge field to contend with.  200uSec rise time makes 
things even more interesting.  Physical routing of your wires might 
reduce any problems of this nature as well.

6.  Have you thought about "skin effect?"  That makes life even more 
interesting at high currents and itsy bitsy rise times.  If you 
calculate this for 60 HZ you'll be amazed at the difference it will make 
in the resistance of a wire with frequency.  If you can do an FFT 
analysis of your wave?  Then take the highest significant harmonic 
component and calculate the skin effect you might be in for a little 
surprise.

          http://en.wikipedia.org/wiki/Skin_effect

7.  16 AWG copper wire has a DC resistance of 4.02 milli-ohms per foot.  
Can you measure or estimate the length of your wire?

8.  Can you take a comparable length of copper wire, stretched out 
straight, and get the same or similar readings?

9.  You're right about the timing of your pulse not being great enough 
to cause serious heating.  How about your duty cycle?

10.  The TCR of copper is +0.39% per degree C at 20C.  Not significant, 
but still a factor.

11.  Don't forget about your magnetic pulse and it's affect on item 5 
above.  We built a small transformer impulse test system once that went 
on a pilot line in the lab.  They were supposed to build a steel 
shielded room, but it wound up being copper as any normal RF screen room 
would be.  Impulse testing is basically generating about a million volts 
then jumping an arc to the transformer to simulate a lightening strike.  
We struck that baby off the first time ... and blew up every instrument 
in the lab with the magnetic pulse.  Did I mention that we only did that 
one time?

I'm going to be gone for a couple of days but this ought to give you a 
couple of days worth of experimentation.  Let's see what results you get 
from the above and then look deeper if it's still a problem.


REB



David VanHorn wrote:
> On Thu, Feb 19, 2009 at 9:37 PM, Jim Wagner <wagnerj@proaxis.com> wrote:
>   
>> In this mode, the current capacity depends on a whole bunch of things.
>> Thermal mass, length, heat sinking capability of the end-terminals,
>> melting point of the alloy are just a few. You might be able to model
>> it with some sort of finite-element simulator but you would spend a
>> lot of hours doing that and what you got would be hard to validate.
>>     
>
> It's in the form of a 44mm ID two-layer coil, with 64 turns.
>
> I was hoping someone here had done "exploding wire" experiments and
> could offer guidance.
>
> My risetime looks great, and the flyback diode is damping the ringing
> fine, but I am nervous that at 1kA I'm pushing the wire too hard.
> Still, it hardly has time to get hot.
>


[Non-text portions of this message have been removed]

Roy makes a good point about skin effect. Forgot about that. Could be  
part of your excessive impedance.

Jim Wagner

On Feb 19, 2009, at 10:25 PM, Roy E. Burrage wrote:

> Done the exploding wire deal Dave, both intentionally and non.
>
> 1. How are you measuring your shunt voltage and waveform? A scope I
> presume.
>
> 2. Your shunt will be somewhat inductive at these frequencies and  
> currents.
>
> 3. Your frequency components will appear because of the pulsed
> waveform, so you'll need to be aware of that.
>
> 4. Have you tried to cancel fields by running the cable into and out  
> of
> your shunt in opposite directions? At these kinds of currents,  
> physical
> placement of the wires will have an affect. For example; we built a
> multi-station circuit breaker calibration system for distribution
> transformers, substation types up to 2500 amps, some years ago and the
> way we had to match station impedances was to change the routing of  
> the
> 350 MCM cables. To achieve 0.25% system accuracy this was no minor
> accomplishment and the station impedances had to be matched even  
> better
> than this.
>
> 5. Could the difference be caused by an induced field in your probes?
> 1KA at ~1mSec is a huge field to contend with. 200uSec rise time makes
> things even more interesting. Physical routing of your wires might
> reduce any problems of this nature as well.
>
> 6. Have you thought about "skin effect?" That makes life even more
> interesting at high currents and itsy bitsy rise times. If you
> calculate this for 60 HZ you'll be amazed at the difference it will  
> make
> in the resistance of a wire with frequency. If you can do an FFT
> analysis of your wave? Then take the highest significant harmonic
> component and calculate the skin effect you might be in for a little
> surprise.
>
> http://en.wikipedia.org/wiki/Skin_effect
>
> 7. 16 AWG copper wire has a DC resistance of 4.02 milli-ohms per foot.
> Can you measure or estimate the length of your wire?
>
> 8. Can you take a comparable length of copper wire, stretched out
> straight, and get the same or similar readings?
>
> 9. You're right about the timing of your pulse not being great enough
> to cause serious heating. How about your duty cycle?
>
> 10. The TCR of copper is +0.39% per degree C at 20C. Not significant,
> but still a factor.
>
> 11. Don't forget about your magnetic pulse and it's affect on item 5
> above. We built a small transformer impulse test system once that went
> on a pilot line in the lab. They were supposed to build a steel
> shielded room, but it wound up being copper as any normal RF screen  
> room
> would be. Impulse testing is basically generating about a million  
> volts
> then jumping an arc to the transformer to simulate a lightening  
> strike.
> We struck that baby off the first time ... and blew up every  
> instrument
> in the lab with the magnetic pulse. Did I mention that we only did  
> that
> one time?
>
> I'm going to be gone for a couple of days but this ought to give you a
> couple of days worth of experimentation. Let's see what results you  
> get
> from the above and then look deeper if it's still a problem.
>
> REB
>



[Non-text portions of this message have been removed]

> 1.  How are you measuring your shunt voltage and waveform?  A scope I presume.

Yes

> 2.  Your shunt will be somewhat inductive at these frequencies and currents.

Yes

> 3.  Your frequency components will appear because of the pulsed
> waveform, so you'll need to be aware of that.

Right

> 4.  Have you tried to cancel fields by running the cable into and out of
> your shunt in opposite directions?

I haven't looked at this yet, it's a bit mechanically difficult at this point.

> 5.  Could the difference be caused by an induced field in your probes?
> 1KA at ~1mSec is a huge field to contend with.  200uSec rise time makes
> things even more interesting.  Physical routing of your wires might
> reduce any problems of this nature as well.

Could be.

> 6.  Have you thought about "skin effect?"  That makes life even more
> interesting at high currents and itsy bitsy rise times.  If you
> calculate this for 60 HZ you'll be amazed at the difference it will make
> in the resistance of a wire with frequency.  If you can do an FFT
> analysis of your wave?  Then take the highest significant harmonic
> component and calculate the skin effect you might be in for a little
> surprise.

The part that would be interesting is the 100uS risetime, Anything
else isn't all that relevant for me.



> 7.  16 AWG copper wire has a DC resistance of 4.02 milli-ohms per foot.
> Can you measure or estimate the length of your wire?

About 6 meters.  With 400V pushing, the DCR shouldn't be interesting.

> 8.  Can you take a comparable length of copper wire, stretched out
> straight, and get the same or similar readings?

That wouldn't have enough inductance to keep the current "down" to the
kA region.


> 9.  You're right about the timing of your pulse not being great enough
> to cause serious heating.  How about your duty cycle?

WAY below .1%  :)    Minutes between pulses at this point.

> 10.  The TCR of copper is +0.39% per degree C at 20C.  Not significant,
> but still a factor.
>
> 11.  Don't forget about your magnetic pulse and it's affect on item 5
> above.  We built a small transformer impulse test system once that went
> on a pilot line in the lab.  They were supposed to build a steel
> shielded room, but it wound up being copper as any normal RF screen room
> would be.  Impulse testing is basically generating about a million volts
> then jumping an arc to the transformer to simulate a lightening strike.
> We struck that baby off the first time ... and blew up every instrument
> in the lab with the magnetic pulse.  Did I mention that we only did that
> one time?

Whoops.. :)

> I'm going to be gone for a couple of days but this ought to give you a
> couple of days worth of experimentation.  Let's see what results you get
> from the above and then look deeper if it's still a problem.


This setup was just a proof of concept.  My only sore point is that I
don't really know what currents I was getting up to.
But I know it wasn't 2.5-3X the theoretical limit.

The shunt I'm using is from All Electronics,
http://www.allelectronics.com/make-a-store/item/SNT-25/25-AMP-SHUNT-50MV-25A/-/1.html



I did notice this morning, that my ground leads to the scope were
several inches apart on the rig. I've changed that to single point,
and I'll re-test.
That may have hosed the measurements a bit.

> I was hoping someone here had done "exploding wire" experiments and
> could offer guidance.

http://www.pupman.com/hvlistarchives/
http://www.fusor.net

Zetex has Avalanche rated transistors.
http://www.zetex.com/3.0/3-3-2b.asp?rid=14

If money is no object also look up Saturable Reactors
made from Metglas.

-- 
http://www.wearablesmartsensors.com/
http://www.softwaresafety.net/
http://www.designer-iii.com/
http://www.unusualresearch.com/

On Sat, Feb 21, 2009 at 11:27 AM, Bob Paddock <bob.paddock@gmail.com> wrote:
>> I was hoping someone here had done "exploding wire" experiments and
>> could offer guidance.
>
> http://www.pupman.com/hvlistarchives/
> http://www.fusor.net
>
> Zetex has Avalanche rated transistors.
> http://www.zetex.com/3.0/3-3-2b.asp?rid=14
>
> If money is no object also look up Saturable Reactors
> made from Metglas.


I'm not trying to explode the wire, I'm just figuring that those folks
would know where the limits are.
The target here is to get up in about the 1.5T range in a small coil,
with about 100uS risetime.

David VanHorn wrote:
> On Sat, Feb 21, 2009 at 11:27 AM, Bob Paddock <bob.paddock@gmail.com> wrote:
>>> I was hoping someone here had done "exploding wire" experiments and
>>> could offer guidance.
>> http://www.pupman.com/hvlistarchives/
>> http://www.fusor.net
>>
>> Zetex has Avalanche rated transistors.
>> http://www.zetex.com/3.0/3-3-2b.asp?rid=14
>>
>> If money is no object also look up Saturable Reactors
>> made from Metglas.
> 
> 
> I'm not trying to explode the wire, I'm just figuring that those folks
> would know where the limits are.
> The target here is to get up in about the 1.5T range in a small coil,
> with about 100uS risetime.

Have you considered using  I squared t for a rough bounds?

As for measuring the current, if you are doing more than a bit of this 
you may want to invest in a Rogowski coil to get a high frequency 
measurement capability without interfering  with the circuit.

Robert

-- 
http://www.aeolusdevelopment.com/

  From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time?  37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live....
we currently have stock."