# Cable sizing



## Salty9 (Jul 13, 2009)

You can look it up: http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity


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## ElectriCar (Jun 15, 2008)

Your amperage is the only thing determinant of wire size. Voltage is immaterial. I have a 500A controller and originally had parallel 1/0 cable. I since removed it all and went with aluminum 4/0. Look into it, it's MUCH lighter and as of last week, 3/0 Copper (cu) was 3.3X the cost of 4/0 aluminum. I did it all for the weight savings as I'm in a hilly area, quite a bit of stop and go at times which is where weight is a factor.

4/0 is fine for me as most of my driving now is less than 100A. The only time I exceed that is up a hill or accelerating and then it only goes up for a few seconds. 

If you're going to be pulling close to 800A for long periods, like several minutes you may need 3X 4/0. It all depends on your amp draw and the duration of that current draw. A little vague I know. Give us more details.


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## altair909 (Feb 6, 2011)

Thanks for the replies. Aluminum eh? I magine they transfer heat better too? 

I don't think I would be drawing 800 amps all that much. Just to get on freeways and whatnot. People drive crazy around here!! So I need to be able to punch it every now and again. I also just read something that lead acid may not be able to deliver the kind of amperage my controller can draw. Don't really know what the continous current draw is since I am pretty new to this. I live in michigan. Not very hilly. The car weighs approx 2500 lbs with the ice in it. Probably gonna add 1000 lbs in battery(12 x 12 v lead acid).


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## cruisin (Jun 3, 2009)

ElectriCar said:


> Your amperage is the only thing determinant of wire size. Voltage is immaterial. I have a 500A controller and originally had parallel 1/0 cable. I since removed it all and went with aluminum 4/0. Look into it, it's MUCH lighter and as of last week, 3/0 Copper (cu) was 3.3X the cost of 4/0 aluminum. I did it all for the weight savings as I'm in a hilly area, quite a bit of stop and go at times which is where weight is a factor.
> 
> 4/0 is fine for me as most of my driving now is less than 100A. The only time I exceed that is up a hill or accelerating and then it only goes up for a few seconds.
> 
> If you're going to be pulling close to 800A for long periods, like several minutes you may need 3X 4/0. It all depends on your amp draw and the duration of that current draw. A little vague I know. Give us more details.


Boy, if in a hilly area, a AC system would be just what the doctor ordered for you. I converted to AC and dont have a lot of hills around me, but a lot of starting and stopping never using the disks, only regen. Sometimes I go back home and have almost the same voltage that I left with. I probably could have saved a lot of monies by not converting to disk brakes, and downsizing the 225ah Li-ion batteries to maybe about 180ah.


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## major (Apr 4, 2008)

altair909 said:


> .......Don't really know what the continous current draw is since I am pretty new to this. ....... Probably gonna add 1000 lbs in battery(12 x 12 v lead acid).


Hi alt,

Cable size questions come up often. Maybe there is (or should be) something in the wiki. A lot of guys go too heavy in my opinion. You should size your cable to the average current for the circuit. If you have very long cable runs or if the cable is in an air tight conduit, you should go one gauge larger.

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. 

For a Warp9, lead acid installation I used 2/0 for the motor circuit (short lengths) and 1/0 for the battery circuit (a couple of long lengths and some inside conduit).

Use a good quality welding cable, copper, not aluminum. 

Regards,

major


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## EVfun (Mar 14, 2010)

I'm going to second Major here. I use 1/0 in the battery loop and 2/0 on the motor loop (motor current is often higher than battery current but never lower.) I would be comfortable with these sizings in copper cable to about 1000 peak amps. 10 feel of 1/0 cable has about one milliohm (0.001 ohm) of resistance. Most of a vehicles operation will be well under peak current.


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## DavidDymaxion (Dec 1, 2008)

Major, LiFePO4 battery electrolyte boils at just 77C (way below an electric motor's max temp). It's also a sudden onset kind of problem that permanently damages the batteries. It seems like you'd need to size for the max temperature the cables would hit at max current to not cook the batteries. Does sizing the copper wire for the relatively low 1C rate of the batteries cover that? I tried a quick search for tables of wire temperature vs. current, but had no luck -- can you point me the right way (maybe just need the right keywords for a search)? Thanks.


major said:


> ... 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.
> 
> For a Warp9, lead acid installation I used 2/0 for the motor circuit (short lengths) and 1/0 for the battery circuit (a couple of long lengths and some inside conduit). ...


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## major (Apr 4, 2008)

DavidDymaxion said:


> Does sizing the copper wire for the relatively low 1C rate of the batteries cover that?


I would think so. The internal resistance of the cell is certainly much greater than the resistance of the connecting cable and lug and contact patch on the battery terminal if properly assembled. True, there is a difference in mass and thermal conductivity and radiating surface area and surrounding temperature. All this needs to be considered when designing the system. If needed, the cables can be oversized to sink heat out of the cell, or the cell connector designed as a finned heat sink with air over (I've done this on ultracapacitor cells). But in most cases, I think my advice sound. Afterall, the OP is in Michigan using lead acid presumably for a commuter. No indication of unusual conditions like extreme ambient


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## Newbiee (Feb 16, 2011)

For the average vehicle conversion how many feet of cable would u guys recommend to be sufficient when making a purchase? 50'?


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