# Battery and Motor/Controller Cable



## PeterH (Mar 20, 2009)

This is a subject I wish I'd have investigated before I started my build, last August. In hind sight, I'd have used as heavy cables as I could in my battery boxes and anywhere else high current was going to flow. I used 00 welding cable through out my build and I wish I had used heavier cables. 

Why? I used the centralized version of the mini BMS in my build. It is working fine and I am glad I used it rather than the distributed version. However, in my build, I have 5 individual battery boxes and within 2 of the boxes, I had to use a short length of cable between batteries. This has caused a little extra apparent resistance and therefore I have a number of cells in my pack that appear to reach a higher voltage than their neighbors because of the extra resistance of the interconnecting power cables. In response, my BMS shunts power away from those cells near the end of the charge cycle unnecessarily. I'm not planning to change anything at this point. I've just passed 1000 miles since the 5th of July so I don't want to start over just when I have it working so nicely.

If you have one massive battery box without any interconnecting cables between cells, things are much simpler. In my case, I was determined to keep the cells out of sight and retain all of the seating in my vehicle so I had to split the batteries up and place them in so many boxes.

In my opinion, bigger is better when selecting power cables. 

Additionally, I did not use shielded cables so I haven't even tried (yet) to use a radio in my build... I expect a radio to be nearly useless because of RFI.

Hope this helps...
Pete


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## major (Apr 4, 2008)

SCEV said:


> What is a good size cable to use for the batteries and for the motor/controller? I've seen people say 1/0 is good for batteries and 2/0 is good for the motor controller...but I've also heard that is not enough.
> 
> I'm planning on a 230V pack of prismatics (probably the new CALB 100AH), a Solilton 1 controller and Warp 11 motor...so I'll be pulling around 1000A max for short bursts.
> 
> Also, does anyone know of any good sources for the cable/connectors...preferably one that pre-makes the cables for you if you tell them all the lengths you need?


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

And I don't buy into PeterH's story. Those devices work on charge, right? So at like 5 amps, with 3 feet of 2/0 cable, you get about 0.001 volt drop. I suspect you get more than that in your cable terminations and cell connections. The difficulty in using 4/0 cable would outweigh the advantage of a few tenths of a millivolt. But it is his project.


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## PeterH (Mar 20, 2009)

Hi Major, 

I'm sure you are correct...  I don't plan to re-do anything and sometimes tend to overthink things. I've never handled anything larger than 00 cable and I had enough trouble routing these 00 cables, that I find it easy to believe that anything larger would be a LOT more difficult to work with. (it might have been easier if I had known about a water based lubricant used to pull cables through conduit... my brother told me about it last night, months after it would have helped!)

I brought this up because I noticed a situation of extra resistance (very minor now) for specific cells caused by the combination of my mini BMS and the layout of my batteries. In my case one of those cells was connected to a short jumper (00 with crimped lugs) between cells in a box and than connection point wasn't making good contact with the terminal... the loose connection was causing way more resistance than that 2 inches of 00 cable. After discovering this and considering the theoretical implications for the rest of my battery boxes, I dove off the deep end of "how to do this better". Hence my possibly impractical recommendation.

Still, if I had it to do over, I'd try to redesign my battery layout so I had fewer interconnections and those that were necessary, would be of larger cable only IF it were practical to do so.  I'm not likely to have the budget to do this again so the world's supply of 0000 cable is safe.

Pete


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## PStechPaul (May 1, 2012)

You might want to contact these guys:
http://www.stormcopper.com/Flexible-Electrical-Bus-Bar-Connectors.htm










I've used them for special bent and machined bus bar components and their prices are very reasonable.

This is also some good stuff:
http://www.erico.com/products/FlexibarN.asp










I made a current capacity chart for AWG and bus bar that might be helpful. For single strips and wire in free air the current capacity is determined not only by cross sectional area but also surface area for cooling: www.pstech-inc.com/WireSize.xls

1/4"x1" bus bar should handle 500-1000 amps continuous. You can get 6 foot lengths of silver plated bus for $75:
http://www.mcmaster.com/#copper-alloy-110-bars/=iojv5q


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## dougingraham (Jul 26, 2011)

SCEV said:


> What is a good size cable to use for the batteries and for the motor/controller? I've seen people say 1/0 is good for batteries and 2/0 is good for the motor controller...but I've also heard that is not enough.
> 
> I'm planning on a 230V pack of prismatics (probably the new CALB 100AH), a Solilton 1 controller and Warp 11 motor...so I'll be pulling around 1000A max for short bursts.


2/0 from battery to controller should be fine. If the controller is close to the motor then 2/0 from controller to motor should be fine. If the distance from controller to motor is more than a few feet consider 4/0. The problem is that 4/0 even in the flexible forms is still more difficult to work with and it is heavy.

If all you are doing is stop and go driving around town then 1/0 from battery to motor and 2/0 from controller to motor would be more than adequate. If you are doing lots of highway driving where the continuous current is higher then go with the 2/0 between battery and controller. If you are drag racing then more will almost always help.

There are really only two considerations here. They are voltage drop and overheating. Voltage drop is going to limit your top speed if it is excessive. Not something you really need to worry about too much. Overheating of the conductors is of greater concern. The currents between the controller and motor will be higher than between the battery and controller. This is because speed is controlled by lowering the voltage. The load on the motor controls the current that is drawn. So for idling around a parking lot the battery current might be 50 amps but the motor current could be 500 or more. The battery current will not exceed the motor current. They can be the same if the controller is running wide open but otherwise the battery current will always be less.

2/0 wire is rated for 190 amps in power transmission mode. 2/0 has resistance of a little less than 0.00008 ohms per foot. At 190 amps this is a waste heat of 2.9 watts per foot of cable. At 1000 amps this would be 80 watts per foot of cable. The cable can easily handle this for several minutes. 1/0 wire is rated for 150 amps in power transmission mode. 1/0 has a resistance of a little less than 0.0001 ohms per foot. At the same 190 amps in the above example the there would be a waste heat of 3.61 watts per foot. At 1000 amps this would be 100 watts per foot. 4/0 cable has a resistance of a little less than 0.00005 ohms per foot. The cable is rated at 302 amps in power transmission mode. At 190 amps it would have a waste heat of 1.8 watts per foot. At 1000 amps there would be 50 watts of waste heat per foot. In both cases the waste heat in the cable is going to be quite a lot less than the waste heat found in the battery interconnects. I have measured the battery interconnect resistance on my GBS cells at 0.0000041 ohms. This is from post to post over about a 2.5 inch length. At 1000 amps the heat going into the battery from the losses in the interconnects is 4.1 watts. The bulk of this heat will go into the battery with a little heating the air.

Don't worry overly much about this. It is a car and your high current bursts are short. If this was a plane where you can run 75% power for 90% of the time then you would be running 4/0 or larger everywhere.


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## dladd (Jun 1, 2011)

fwiw, I still have a few short lengths of 2awg cable in my battery loop (1-2 feet long each, 3 cables). The long runs and the motor cables are 2/0. I routinely pull 500 battery amps, but my continuous usage is more like 100-130a on the freeway. I've not noticed the 2awg cables getting any hotter than the 2/0 cables in my usage. I'm sure I have a small voltage loss, and at some point plan to replace the 2awg with 2/0, but realistically I think they are working fine.

I pull up to 700a beween the motor and controller, but it's only for seconds at a time. The 2/0 motor cables have never gotten hot, even on these 100+ degree days they are getting only moderately warm to the touch (how's that for precision measuring?  ).


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## EVfun (Mar 14, 2010)

PStechPaul said:


> This is also some good stuff:
> http://www.erico.com/products/FlexibarN.asp


Do you happen to have a supplier for this stuff? It is easy to find from industrial suppliers, but I didn't find any place dealing is small retail quantities.


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## PStechPaul (May 1, 2012)

You might try this:
http://store.electrical-insulators-and-copper-ground-bars.com/cable-jumpers-tin-plated-lugs.html

and
http://store.electrical-insulators-and-copper-ground-bars.com/flexible-insulated-busbar.html

It's rather expensive, however. You might be able to find some heavy copper braid and use copper pipe to make your own a lot cheaper. Check eBay:
http://www.ebay.com/itm/AlphaWire-Tinned-Copper-Tubular-Flat-Braid-1-165amp-/220822204278


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