PDA

View Full Version : Controlling wiring test of 4awg wire with 635amps going through it.



liveforphysics
07 July 2012, 1248
This is a little test to show what happens to a foot of 4awg wire with 635amps going through it.


It's also important to realize that your controllers output (brushed or brushless alike) can be outputting 500-600amps to the motor while your battery current may be only 30-40amps (going slowly up a hill in traffic or whatever), and you don't even realize how much burden your cabling is under.


Enjoy!


http://www.youtube.com/watch?v=zJ3U76ulKLM

Hugues
07 July 2012, 1349
Thanks for the experiment, interesting.

One question: here you tested 650 amps DC continuous. But 650 amps in a motor with 3 phases, is the equivalent current in each phases a bit less ? Like divided by 3 or something like this ? Each phase is not ON all the time right ?

liveforphysics
07 July 2012, 1840
On a controller, phase current rating is typically RMS phase amps. Meaning, the 550RMS current is the same as 550amps DC .

EVcycle
07 July 2012, 1841
Someone is Craaaaaaaaaaaaaaazy!

Hugues
07 July 2012, 2320
On a controller, phase current rating is typically RMS phase amps. Meaning, the 550RMS current is the same as 550amps DC .

This is something i would like to learn more about, especially the relation between battery amps and phase RMS amps.

For example, when i look at this graph from my motor, on page 2:
http://www.electricmotorsport.com/store/pdf-downloads/AC_Drives/AC20.pdf

This is probably battery amps , right ? So how does one get RMS amps from this ? is there a rule of thumb to define peak RMS amps for a particular motor ? and under which conditions it happens ?

I think RMS means "Root Mean Square" and refers to the mathematical formula to derive amps from an AC sin wave, am I right ?

thanks for your science

podolefsky
08 July 2012, 0010
This is something i would like to learn more about, especially the relation between battery amps and phase RMS amps.

For example, when i look at this graph from my motor, on page 2:
http://www.electricmotorsport.com/store/pdf-downloads/AC_Drives/AC20.pdf

This is probably battery amps , right ? So how does one get RMS amps from this ? is there a rule of thumb to define peak RMS amps for a particular motor ? and under which conditions it happens ?

I think RMS means "Root Mean Square" and refers to the mathematical formula to derive amps from an AC sin wave, am I right ?

thanks for your science


Yes, that's battery current in that chart. If you could see motor current, it would be constant 700A up until about 2000 RPM. Above 2000 RPM, battery and motor currents are equal. (at 48V)

You're right, RMS is root mean square. For a sinewave, RMS current is peak current / sqrt(2). A DC motor controller also has an RMS current value, but it's calculated differently.

More here:

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

podolefsky
08 July 2012, 0040
Interesting test. Pretty much what you'd expect if you keep 635A going for 2 minutes. And technically, the Curtis 650A AC controllers are rated for 650A RMS for 2 min...but the AC motors aren't. Neither are 60Ah LiFePO4 cells. Typically, you only see current that high for a few sec at a time, so another thing you showed is that 4 AWG will probably be OK in normal operation of a non-race bike. I'd still use 00 though.

I'd be interested in seeing the same test with 00. It'll heat up too - I'm going to estimate it takes about 8x the time to hit the same temperature as 4 AWG (heat generated goes as 1/r^2, heat dissipated goes roughly as r. Since 4 AWG is about 1/2 the radius of 00, it generates heat 4 times as fast and dissipates it 1/2 as fast, so it heats up at 8x the rate).

[edit] Forgot another factor - energy goes up at 8x, but temperature is proportional 1/volume, which for a given length goes up as 1/r^2, so there should be another factor of 4.

In other words, the insulation of 00 should be steaming after about an hour at 635A.

Hugues
08 July 2012, 0140
Yes, that's battery current in that chart. If you could see motor current, it would be constant 700A up until about 2000 RPM. Above 2000 RPM, battery and motor currents are equal. (at 48V)

...

thanks. just to be sure, when you say 700A motor side in your example, you mean 700 RMS amps ?

Hugues
08 July 2012, 0141
deleted - double post

podolefsky
08 July 2012, 0900
thanks. just to be sure, when you say 700A motor side in your example, you mean 700 RMS amps ?

yup, 700A RMS.

it's always RMS. It's just that you don't usually refer to the RMS value of a DC signal. Since an AC signal varies, you use the RMS value.

CliC
08 July 2012, 1658
Dude! I love your destructive-in-the-name-of-science bent (I watched some of your "battery robustness" videos :)).


It's also important to realize that your controllers output (brushed or brushless alike) can be outputting 500-600amps to the motor while your battery current may be only 30-40amps (going slowly up a hill in traffic or whatever), and you don't even realize how much burden your cabling is under.


Is that 500-600A peak? I don't see how it could be RMS if the battery is only supplying 40A, and the controller is not bucking the battery voltage.

podolefsky
08 July 2012, 1758
Is that 500-600A peak? I don't see how it could be RMS if the battery is only supplying 40A, and the controller is not bucking the battery voltage.

RMS because it *is* bucking

Hugues
08 July 2012, 2150
I googled "bucking" but I can't find anything related to our topic ,

Does it mean "amplifying" in this context ?

podolefsky
08 July 2012, 2210
I googled "bucking" but I can't find anything related to our topic ,

Does it mean "amplifying" in this context ?

It means reducing. A buck converter reduces voltage (and generally boosts current).

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

Allen_okc
09 July 2012, 0720
:cool: awesome testing video - i just one question Liveforphysics - where do you get your awesome testing equipment???

CliC
09 July 2012, 2235
RMS because it *is* bucking
Yes, I suppose it is. I gotta think about the entire system.


where do you get your awesome testing equipment???
I was wondering the same thing :) I sure don't have 6 or 7 100+ -amp power supplies lying around.

liveforphysics
09 July 2012, 2313
I have spent about $20k in the last 3 years on power supplies. That video has like a 10th of my power supplies.

Some of those supplies new are over $20k alone, but I buy them broken for $500 or whatever, and repair them.

__Tango
10 July 2012, 0520
Hughes: thanks for asking these questions. I would have if you didn't beat me to it. :)

LFP: just another example of why I call you :)