# Wire sizing suggestions



## JRP3 (Mar 7, 2008)

I've been wondering how I should size the wiring on my project. 48 volt 400 amp Alltrax, I'll be using 4 gauge for the pack wiring, but what should I use for the switch to primary contactor, which will see 48 volts? Also what should I use for an ignition switch, will a 12 volt switch work?


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## major (Apr 4, 2008)

Hi JRP3,

Wire size is determined by the current (amps) and the insulation by the voltage. Most insulation is good for 48 volts. Get up over 100 volts, you'd better check it.

You should have two basic circuits. The 48 volt, high current circuit which includes the battery, fuse, contactor, controller and motor. And a control circuit which may be 12 volts, 48 volts or a combination. This control circuit has the switches, contactor coil, and other low power devices. These are usually a lot less than 10 amps, mostly like 1 or 2 amps.

For the high current circuit, 4 gauge is probably o.k. although it is not rated for 400 amps. But it may be suitable for you average current. Depends on your duty cycle (how you drive) and battery (how long you drive).

For the control circuit wiring, I like to use all 18 gauge. It is probably overkill, but nothing wrong with that. I find smaller wire hard to work with and prefer just to stock a variety of colors of 18 AWG.

Hope this helps,

major


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## frodus (Apr 12, 2008)

http://visforvoltage.org/forum/3111-wiring-brushless-etek-cable-guage#comment-17335

that might help a bit...

its all about how much current you'll need to carry. 400A is likely peak... but your cruising current won't be more than 150-200A... so size the cable to that. See my post in the above thread.


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## dataman19 (Oct 7, 2009)

Isn't there also specific wire type (I'm talking about wire flexibility, temperature and abrasive resistance).
I know welding wire is cheap - but not the better choice.
..
I'm asking all the other members- Which Wire Tyupe do you recommend?
..
Then I have to ask: Which wire type is the best?
...
dataman19


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## JRP3 (Mar 7, 2008)

Welding cable seems to meet the requirements since they need to be flexible and abrasion resistant. They'll see more action on a welder than on an EV.
As an update to my original post, the 4 gauge was fine for the battery wiring, but does get a bit warm under heavy load on the controller to motor wiring.


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## Sunking (Aug 10, 2009)

Ok I am a commercial electrical engineer and can help with wire strand type and insulation. 

Starting with insulation from my POV you want to look at either MTW (machine tool wire) or DLO (diesel loco automotive). Both are synthetic rubber compounds which means flexible, and resistant to heat and oil. Properties you need in a EV. I am sure the automotive industry has very similar insulation types.

As for wire stranding the finer the better. Not because it carries more current, but because it is much easier to bend around tight quarters and vibration resistance. Wire Class H and I are the finer or higher strand counts. FWIW the finer strand counts require much higher degree of termination techniques and tooling.


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## DIYguy (Sep 18, 2008)

dataman19 said:


> Isn't there also specific wire type (I'm talking about wire flexibility, temperature and abrasive resistance).
> I know welding wire is cheap - but not the better choice.
> ..
> I'm asking all the other members- Which Wire Tyupe do you recommend?
> ...


Welding cable really is the best for this application. Many small strands allows flexibility while overall cross sectional area provides current carrying capacity. The sheath on welding cable is very abrasion and oil resistant. Some sizes of welding cable come in a "Superflex" option,.. these ones have even more strands/flexibility. You likely don't need to go to Superflex... but if you had some, it would work fine. 
For a 400 amp peak application with up to 200 amp draw for longer time periods, I would use 2/0 cable. It may be a bit oversize... but better that than under.


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## JRP3 (Mar 7, 2008)

Another point. The cable I used was marine cable from work. Not quite as flexible as welding cable but better than standard automotive cable. Boats, speed boats at least, see much higher vibrations and shock loads than cars, and I've never seen cable fatigue issues on a boat. I'd think that any welding cable would be more than good enough.


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## Joey (Oct 12, 2007)

I'm at the point of selecting cable. I dug up this thread with a google search. The electrician at work recommends DLO cable. I looked into it. 4/0 AWG is rated for 405 amps, has good flexibility - min. bending radius is 3.1 inches, 550 strands of 24 AWG conductors, rated for 90 deg C, and the jacket has chemical resistance (PCE). The electrician is going to help me get it at the local supply house, which will include rental of the hydraulic crimping tool that they only loan out if you have an electrical license. Now the only drawback - as usual - price. I need to get a quote.


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## Ziggythewiz (May 16, 2010)

You don't need 4/0. If you want you could use it for the motor controller loop, but you don't need it anwhere else. You want wire rated for your average use, not peak.


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## major (Apr 4, 2008)

Joey said:


> I'm at the point of selecting cable.... 4/0 AWG is rated for 405 amps,....


Do you have a motor rated at 400 Amps continuous? Or 400Ah battery? If not, then 4/0 is way overkill.

http://www.diyelectriccar.com/forums/showpost.php?p=245897&postcount=6


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## Joey (Oct 12, 2007)

I picked a few worst case parameters - 400 whr/m, 80 mph, 2.0 v/cell under load, and the average current draw would be 270 amps on the battery side. The 2/0 AWG DLO cable is rated for 300 amps. Sounds like a good match.


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## major (Apr 4, 2008)

Joey said:


> I picked a few worst case parameters - 400 whr/m, 80 mph, 2.0 v/cell under load, and the average current draw would be 270 amps on the battery side. The 2/0 AWG DLO cable is rated for 300 amps. Sounds like a good match.


For how long? How many Ah are your cells? And what cell do you expect to run at 2.0V? How long can your motor run at 32 kW?

For average you need to use like one hour, or at least 30 minutes. Well, at least 2/0 sounds a lot better than 4/0. That will save you a lot of weight and money and be easier to install. I'd look at welding cable instead of that locomotive cable. It is a lot more flexible in my experience and makes the install better lookin'


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## evnz (Jul 24, 2010)

major said:


> Do you have a motor rated at 400 Amps continuous? Or 400Ah battery? If not, then 4/0 is way overkill.
> 
> http://www.diyelectriccar.com/forums/showpost.php?p=245897&postcount=6


i have 95mm2 what would the amp loading be on it ? have a sol 1 and was going to use it as high as i can ( drag racing) but only 300 amps continuous for the daliy driving
thanks 
owen


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## PStechPaul (May 1, 2012)

DLO cable is good, but probably overkill (rated at 2000V), and is quite expensive. 50 ft is almost $500: http://www.awcwire.com/Part.aspx?partname=DLO-2/0 

THHN building cable is about half the cost but not as flexible. However, it may be a good idea to use multiple conductors of a smaller gauge in parallel. http://www.mcmaster.com/#standard-electrical-wire/=je9mpx

Welding cable is probably the best choice. #2-0 is about $5/ft and good for 600V. http://www.mcmaster.com/#welding-cable/=je9p7z On the same page is 600V battery cable, available in red as well as black, for about the same price.


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## major (Apr 4, 2008)

evnz said:


> i have 95mm2 what would the amp loading be on it ? have a sol 1 and was going to use it as high as i can ( drag racing) but only 300 amps continuous for the daliy driving
> thanks
> owen


Even if the controller can do 300A continuous, what other components in your system can do that? Size the cable for the system average over an hour time period. Like I said here: http://www.diyelectriccar.com/forums/showpost.php?p=245897&postcount=6


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## Joey (Oct 12, 2007)

evnz said:


> i have 95mm2 what would the amp loading be on it ? have a sol 1 and was going to use it as high as i can ( drag racing) but only 300 amps continuous for the daliy driving
> thanks
> owen


95mm2 = 3/0 AWG. Ratings I see online range from 275 to 350 amps, but depends on the particular cable you have.



major said:


> For how long? How many Ah are your cells? And what cell do you expect to run at 2.0V? How long can your motor run at 32 kW?
> 
> For average you need to use like one hour, or at least 30 minutes. Well, at least 2/0 sounds a lot better than 4/0. That will save you a lot of weight and money and be easier to install. I'd look at welding cable instead of that locomotive cable. It is a lot more flexible in my experience and makes the install better lookin'


The cells are 180 Ah. 2C = 360 amps, 30 minutes The motor's continuous rating is 34 HP at 144 V. 34*750/144 = 180 amps. 

The battery will not run at 2.0 V. I picked the worst conceivable parameters to get a current that would have margin.

I should pick something between:
2 AWG, 190 amps, 5% margin
2/0 AWG, 300 amps, 40% margin



PStechPaul said:


> DLO cable is good, but probably overkill (rated at 2000V), and is quite expensive. 50 ft is almost $500: http://www.awcwire.com/Part.aspx?partname=DLO-2/0
> 
> THHN building cable is about half the cost but not as flexible. However, it may be a good idea to use multiple conductors of a smaller gauge in parallel. http://www.mcmaster.com/#standard-electrical-wire/=je9mpx
> 
> Welding cable is probably the best choice. #2-0 is about $5/ft and good for 600V. http://www.mcmaster.com/#welding-cable/=je9p7z On the same page is 600V battery cable, available in red as well as black, for about the same price.


Thanks for the links. The HD welding cable has the same chemical and abrasion resistant jacket (PCE) as the DLO. The welding cable has 34 AWG strands, and the DLO has 24 AWG. Welding cable looks like a winner. 

Thanks for the input everyone.


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## major (Apr 4, 2008)

Joey said:


> The cells are 180 Ah. 2C = 360 amps, 30 minutes The motor's continuous rating is 34 HP at 144 V. 34*750/144 = 180 amps.
> 
> The battery will not run at 2.0 V. I picked the worst conceivable parameters to get a current that would have margin.
> 
> ...


Hi Joey,

Since the motor current is always greater (or equal) than the battery current, you would overheat (probably smoke) the motor if you ran your batteries out in 1/2 hour (2C). So why size the cable for that condition? If you expect to run at high speed for most of a battery charge, then the battery and motor currents could be about the same and you'd want to use the same size cable for both circuits. 

The sizing of the cables depends on the average current for heating and also the insulation rating for temperature, so check the ampacity charts for your particular cable choice. And as I mentioned before, if you have very long runs (cable length) or the cables in an enclosed conduit or raceway or bundled with the return cable, cooling may be an issue causing you to choose a gauge heavier.

The opposite is also true. If you have very short length cables which are well ventilated you can use a gauge smaller. But then if you want to use a single size for the whole job, make it handle the one hour current rating of the motor plus a reasonable safety factor (maybe 20%).

Using too large of cable can cause more issues than benefits. That made me cringe when you talked of 4/0 loco cable. I've used 4/0 on 38,000 pound electric buses. It is a bitch. The lug ends are huge. On the bus, they fit the other equipment. In you car, large cable and lugs like that can stress the terminals they connect to like your controller and battery terminals. The heavy cable is hard to bend and route so may in fact require longer pieces. It weighs more and costs more.

Regards,

major


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## evnz (Jul 24, 2010)

QUOTE=Joey;95mm2 = 3/0 AWG. Ratings I see online range from 275 to 350 amps,

This is a continuous rating ?
So what would the peak be for 95mm cable (3/0) please ?


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## major (Apr 4, 2008)

evnz said:


> QUOTE=Joey;95mm2 = 3/0 AWG. Ratings I see online range from 275 to 350 amps,
> 
> This is a continuous rating ?
> So what would the peak be for 95mm cable (3/0) please ?


That is reasonable for a continuous rating. The peak would be like 10,000 Amps. Current ratings take on an exponential relationship with time. The shorter time period or pulse, the higher the current. Very high current can be tolerated for short durations. So you rarely see a _peak_ current rating for wire or cable.


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