# Cable size



## Ziggythewiz (May 16, 2010)

Many people run 2/0 for everything, but 1/0 should be fine and will be cheaper and possibly easier to source.


----------



## Sunking (Aug 10, 2009)

Although I do not care for the idea but the golf cart guys using 650 amp controllers all use 4 and 2 AWG between the batteries and controller.


----------



## major (Apr 4, 2008)

greif said:


> need help sizing cable, will be running 72 volts, 500 amp canotroller. max lentgh of cable will be 5 ft. what size should I use


This question comes up all the time. Here it is from a few months ago. http://www.diyelectriccar.com/forums/showthread.php?p=245897#post245897


----------



## Sunking (Aug 10, 2009)

Major I deal with cable ampacity issues everyday in my profession with Dc battery plants.

Have you ever tossed around the idea designing based on percentage of voltage drop, rather than the current on its own.

For example let's say no more then 1% between batteries and controller, and controller to motor.?

It can get you into trouble with very short distances, but is easy kept in check to make sure it does not exceed the cable insulation thermal ratings. Once you get beyond 5 feet in most cases it is a bit of overkill, especially when you get to low voltages of say 100 or less.

It certainly conserves power by not wasting it on IR heat losses.


----------



## Ziggythewiz (May 16, 2010)

Sunking said:


> Major I deal with cable ampacity issues everyday in my profession with Dc battery plants.
> 
> For example let's say no more then 1% between batteries and controller, and controller to motor.?
> 
> It certainly conserves power by not wasting it on IR heat losses.


Do your DC battery plants carry their cabling with them? Also, they probably have a duty cycle much higher than a car used for 1-2 hrs/day.

I don't feel like running the numbers now, but I'd guess if you went with 4/0 vs 1/0 to cut down the voltage drop, you'd likely lose more power carrying the extra weight than the difference in cable would save.


----------



## Sunking (Aug 10, 2009)

Ziggythewiz said:


> I don't feel like running the numbers now, but I'd guess if you went with 4/0 vs 1/0 to cut down the voltage drop, you'd likely lose more power carrying the extra weight than the difference in cable would save.


I don't think it would work out that way, and you might be surprised. 

I just grab some numbers out of the air like a 144 volts, 600 amps, 5 feet 1-way cable distance or 10 feet loop, and 1% (1.4 volts). 

CM = [22.2 x 600 x 5] / 1.4 = 4757 circular mills of copper. Requires a 12 AWG cable. However a 12 AWG fusing current is 235 amps, so it will not work.

What I am stumped on is for an EV is what standards do you use to determine minimum cable size vs current? 

Cannot be NEC as it is way to conservative, and does not list the cable insulation that would be used in EV's, and is based on over current protection device like a fuse.. At 600 amps the minimum requirement for a single conductor in free air is 400 Kcm which is considerable larger than 4/0 which is rated for 400 amps.


----------



## major (Apr 4, 2008)

Sunking said:


> IWhat I am stumped on is for an EV is what standards do you use to determine minimum cable size vs current?


From my previous post: 



> A good guide for average current is the motor rating. For the 9 inch DC motors and even the 11, the one hour rating is in the range of 200 to maybe 240 amps. Size your cables to this. If you draw more current than this on the average, you will overheat your motor. This will apply to the motor circuit. For the battery circuit, take the Peukert adjusted ampere hour rating for your battery for a one hour discharge. Use that number for the average current for cable sizing.


Then refer to the rating for your cable of choice. Here is such a guide: http://en.wikipedia.org/wiki/American_wire_gauge Guides for welding cable are usually based on duty cycle, not continuous. So for 1/0, 150 amperes would be conservatively safe. 

At 150 amps, 1/0 cable will have 48 mV drop per meter, IMMIC (If My Math Is Correct ). So the voltage drop in the battery cables should be well below 1% of battery voltage.

Regards,

major


----------



## Sunking (Aug 10, 2009)

major said:


> Then refer to the rating for your cable of choice. Here is such a guide: http://en.wikipedia.org/wiki/American_wire_gauge Guides for welding cable are usually based on duty cycle, not continuous. So for 1/0, 150 amperes would be conservatively safe.


Major I am familiar with the AWG table, but as I eluded too that table uses NEC values which is way to conservative and is based on building light and power wire.

I guess what I am asking is their an Automotive standard for wire and current sizes? 

I would suspect automotive or EV would use much higher temperature rated insulation, which would mean for example you could run 1/0 at much higher current levels than NEC maximum of 150 amps. 

One thing I know is I have bot a golf cart and a NEV made by EVE Fairplay. The NEV is factory with a 48 volts 400 amp controller and uses 4 AWG cable powering a 6 HP 4.2 Kw motor.


----------



## major (Apr 4, 2008)

Sunking said:


> I guess what I am asking is their an Automotive standard for wire and current sizes?


I think I explained my reasoning fairly well. 



> Then refer to the rating for your cable of choice.


If you use a cable with higher temperature insulation, then yes, you can run higher current density and will see increased voltage drop. It is your choice.

Reread my post and see that you need to use average current, not current limit values when sizing cable. And the golf carts you refer to are notorious for undersize cable IMO because of duty cycle (stopping often while the golfer plays his ball) and for cost reduction.


----------

