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Hey all,
I was looking into moving my batteries around in my conversion, and I need a good length of wire to relocate them. I am currently using 2/0 cable for 72v @ 1000 amps, and plan to upgrade to 144v in the near future. I have access to 4/0 cable for next to nothing, can I just double up the wire runs and get the same effective throughput?
And I am positive this won't work, but you can't use the body of the vehicle as a ground, right? Like running the positive cable up from the trunk area and then going from the controller negative terminal to the body with the neg of the battery pack connected to it as well? It's a bit of a stretch but I figured I'd ask.
Thanks!
 

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can I just double up the wire runs and get the same effective throughput?
Electrically, yes. 2+2 = 4. Cross section is cross section. You could use a thumb-sized cable of Litz wire if you felt like it.

Mechanically, sure, don't see why not.

Typically more thinner wires is more expensive, but in your case, free is the great price.

And I am positive this won't work, but you can't use the body of the vehicle as a ground, right?
Stranded in the desert? You'll cross thousands of miles without a problem. But don't do it.

Safety nightmare if anything goes wrong, the goddamn shell of the vehicle is going to be energized with 144 volts.

You get 2/0 for nearly free. Use some 2/0.
 

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4/0 is bigger than 2/0 by the way.

The 12V system in a car is grounded because it's a safe voltage. I believe anything above 48V is required to be floating, at least in the automotive world.
The problem with grounding 72 or 144V is that if anyone touches a battery connector they're possibly toast, and definitely going to get a fun shock. Also a single wire faulting to ground creates a short.
OEM EV's monitor the isolation to make sure no HV is on the frame of the car.
 

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The longer your wires are from the battery to the inverter/speed controller, the better your chances are in killing the inverter/controller.

Not everything is ohm's law, which seems to be an obsession on this forum.

If you have substantially longer wires, the right way to do that relocation would be to increase the size of the capacitors at or in the inverter/controller in addition to running the 4/0.

Out of curiosity, what's the ratio in wire-run distances of original and proposed?
 

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The longer your wires are from the battery to the inverter/speed controller, the better your chances are in killing the inverter/controller.

Not everything is ohm's law, which seems to be an obsession on this forum.
I have a bit of trouble understanding this statement. Do you mean that longer wires are worse, but it's not exactly related to higher resistance (I'm assuming ohm's law is referring to the resistance part)? If so, what additional problem is there?

Or do you mean something else totally and I'm interpreting it totally wrong?
 

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Longer wires cause greater inductance. It's like a pipe full of water - if you suddenly shut off the water, you get a hammer effect from the momentum of the water.
So when your controller stops drawing current (which happens during every PWM cycle) the electricity tries to keep flowing. Voltage at the controller then can rise to extreme levels and destroy it.
This can be solved by shortening cables or adding capacitance.
 

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I am currently using 2/0 cable for 72v @ 1000 amps, and plan to upgrade to 144v in the near future. I have access to 4/0 cable for next to nothing, can I just double up the wire runs and get the same effective throughput?
I'm not sure what you're suggesting here. If you mean to ask if you can use smaller two conductors in parallel instead of one larger conductor, for the same length and current, the answer is yes as far as resistance is required. But as Issac97 mentioned, 2/0 is thinner than 4/0, so if 2/0 is adequate for your use and you can get 4/0 cheaply, then just use 4/0 for the new installation... there's no reason to double anything.

Electrically, yes. 2+2 = 4. Cross section is cross section.
Yes, so two conductors with a cross-sectional area of 2 square somethings each is the same as one conductor with a cross-sectional area of 4 square somethings. But American Wire Gauge is not cross section - it is not even directly proportional to cross section. 4/0 has about 60% more cross-sectional area than 2/0. (typo corrected here)
 

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2/0 has about 60% more cross-sectional area than 4/0.
I think you mean the other way around :)
107mm^2 for 4/0, 67mm^2 for 2/0.
A pair of 2/0 is probably easier to deal with because each will be more flexible. 4x 3-gauge is also about the same area.
 

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I think you mean the other way around :)
107mm^2 for 4/0, 67mm^2 for 2/0.
Yes, of course. :) I'll fix that.

A pair of 2/0 is probably easier to deal with because each will be more flexible. 4x 3-gauge is also about the same area.
True. But it certainly makes for more work on terminations. It is possible to bundle cables together into one connector, but that has its own problems.
 

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Yes, so two conductors with a cross-sectional area of 2 square somethings each is the same as one conductor with a cross-sectional area of 4 square somethings. But American Wire Gauge is not cross section - it is not even directly proportional to cross section. 4/0 has about 60% more cross-sectional area than 2/0. (typo corrected here)
Err, yes yes. Every 3 gauges of AWG is a doubling of cross-section, every 6 gauges is a doubling of diameter (and a 4x of cross-section). I know this off by heart from my wire weaving days...




I wasn't doing the math on the actual measurements between 2/0 and 4/0, just answering his question if he could use multiple strands of thinner wire instead of a single strand of thicker wire. My answer is yes, equivalent cross-sections are equivalent.

But you're correct, 2x 2/0 is not equal to 4/0. It's actually even thicker cross section than 4/0.
 
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