# Selecting the right Cable and Busbar?



## major (Apr 4, 2008)

Planky said:


> Not Selecting -> choosing, i don´t know how to change the title of the thread, Sorry.
> 
> Need your experience.
> I have a Soliton 1, Kostov K10 that can handle 270A Continuously.
> ...


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

http://www.powerstream.com/Wire_Size.htm 

A couple of links.


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## DJBecker (Nov 3, 2010)

Planky said:


> I have a Soliton 1, Kostov K10 that can handle 270A Continuously.
> My Battery Pack is 144V 180Ah.
> I will have 2 longer (more resistance) Battery cables from the front to the back of the car as i have to split the pack because of weight/space distribution.
> ... As the Motor can handle nearly 100kW peak (short short time) the upcoming currents would be around 660A+.


In much of the world the bus bar cross section is specified in mm^2, but there is a good chance the cables is still in AWG.

You should ignore all wire sizing guides intended for fixed installations. The rating is based on the long-term temperature rise with constant current inside a conduit.

You should select the cable based on current and how well it will be cooled once installed. At 144V you may find that 3 gauge is sufficient for battery cables, with twice the cross section area (0 gauge) for the motor cables. Thicker cable will reduce the resistive power loss, but adds weight and costs more. A warm cable might be more efficient than carrying around extra pounds of expensive copper.

Some people mistakenly think that longer runs requires thicker cable. Their logic is faulty. If you are using 2 gauge for the short battery-to-battery jumpers, you might as well use 2 gauge for the longer back-to-front cables. The only reason to use a different gauge is for physical reasons. You may want thicker jumper cables to help remove heat from the batteries, or may need to go a bit thinner to get a small bend radius in a tight location. You'll often see battery connections made of stacked copper sheets, both for cooling and to reduce the mechanical stress.

Contactors are another component that requires heavier cables to remove the heat.


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## Planky (Aug 22, 2011)

thanks, for info.

so your recommendation is to use AWG 3 for Battery and AWG 0 for Motor?
Why using different ones? i can pull more then 180A from Battery (C value), right?

regards
Andreas


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## EVfun (Mar 14, 2010)

I wouldn't recommend (or use) cable that small with a 144 volt system. It may meet the needs from a temperature rise standpoint, but there is no need for the losses at high current. 

I use 1/0 for the battery loop and 2/0 for the motor loop. Very large cars or race cars may need larger cable. High voltage systems may allow the use of smaller cable in the battery loop.


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## DJBecker (Nov 3, 2010)

Planky said:


> so your recommendation is to use AWG 3 for Battery and AWG 0 for Motor?
> Why using different ones? i can pull more then 180A from Battery (C value), right?


I'm suggesting that you remain open to the possibility that 3 gauge or 4 gauge may work, not that it's necessarily the best size. It depends on the cable sheath thermal conductivity, where it's installed (air flow or other cooling), and actual current draw in your installation.

The loop from the controller to motor will have a higher current than the battery loop. During acceleration from a stop it may have 10x the current. A rule-of-thumb is to make it 2x the cross section (3 AWG sizes larger), but that's just a guess. A higher voltage battery or higher current controller suggests a bigger factor, while mostly constant speed highway cruising allows a lower factor.

To put some real numbers:

At 144V you might draw 100 amps at cruise (efficient small car at 50MPH). 20 feet of 4-AWG cable will drop 0.5V at 100 amps. That's 50 watts wasted when the motor is using 14000 watts. Doubling the cross section would only save you 25 watts.

If the motor loop has 500 amps while accelerating, a 6 foot controller-motor loop of 4-AWG cable will drop about 0.8V. That's 400 watts of heat. The cable will get really hot, really quickly. Doubling the cross section to 1-AWG drops 0.4V, resulting in only 200 watts with twice the thermal mass. It's still going to get pretty hot, but you'll have 4x the time before the insulation starts smoking. You'll probably want to go even larger if you are in stop-and-go traffic which repeatedly puts a high torque load on the motor, resulting in high I^2R losses.


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## sourcefinder (Dec 17, 2010)

I run a constant current of 300 A and used 35mm2 which was very small.
You always have to think on two points:

1) how much energy to you loose in your cables
2) is it safe

As my cables got warm, I took a look to the standard which says 95mm2 for 300A.

First of all I just thought about the cables, but there is another important point: most batterie-copper-connectors are not built for this current.

In my case I have a cable length of 12m and a copper-connector length of 9m. So make sure the copper-connectors are also right.
I will double them to reach 88mm2.

Von wo aus Österreich bist du, Planky?
Bin aus Salzburg


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## Planky (Aug 22, 2011)

Danke für die Infos.
Thanks for Info.

Bin eben von Wien wieder zurück nach Vorarlberg gezogen und beginne nun mein "kleines Projekt".
I just moved from Vienna back to Vorarlberg and starting my "little project".

I have some more question, am i allowed to write you a PM? -> it´s about terminals with screws and the Austrian TÜV.


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## sourcefinder (Dec 17, 2010)

Zum österreichischen tüv kann ich leider nicht viel sagen, hab das system in einem boot installiert.
Denke aber dass die auch in der norm nachschauen werden. Der elektriker in deinem ort kann dir sagen, was sicher ist vom querschnitt. Dazu dann noch polabdeckungen damit nichts auf den polen scheurn kann...


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