Cable guage

[Helirich]

I'm in the middle of upgrading my car from 36 to 48V with 500 amp controller. I have two carts to use for parts. All the cables are either 4 or 6 Guage. They arnt in the best of shape, but I got it working. The lengths are not ideal either. So I want to make all new cables. I know a lot of people upgrade their 6 Guage cables to 4. Since I'm making all new, I can do whatever I want.

What I'm asking is "if big is good, is bigger is better". LOL. Of course, there's a limit to everything. Is there any reason to go with 2 Guage (or bigger) or is that useless overkill?

[tag50]

500 amp is the tipping point to have 2ga. cables.

.

[Lochlin]

I just did my cart the same way. My thoughts were that the 2G cables were, literally, only a few bucks more than the 4G in total. Why not go bigger even if it is overkill?

[JohnnieB]

Originally Posted by Helirich

I'm in the middle of upgrading my car from 36 to 48V with 500 amp controller. I have two carts to use for parts. All the cables are either 4 or 6 Guage. They arnt in the best of shape, but I got it working. The lengths are not ideal either. So I want to make all new cables. I know a lot of people upgrade their 6 Guage cables to 4. Since I'm making all new, I can do whatever I want.

What I'm asking is "if big is good, is bigger is better". LOL. Of course, there's a limit to everything. Is there any reason to go with 2 Guage (or bigger) or is that useless overkill?

Overkill is underrated.

Electrically, bigger is better, but mechanically there are practical limits. Cables thicker than 1/0Ga are likely to be impractical because probably you can't bend them to fit were they need to go with out a cable bender.


Electrically, all cables have resistance and the thinner the conductor is, the more resistance it has and the more resistance, the more of the amp flow through it is converted to heat, which is power wasted in the amp delivery system rather than being converted to motion by the motor.

A 36V PDS or DCS cart that has been upgraded 48V with a 6 x 8V battery pack has a total of about 20' of high current cables. The following is the resistance for the copper conductors alone.

20' 6Ga = 0.007902Ω
20' 4Ga = 0.004970Ω
20' 2Ga = 0.003126Ω

A few milliohms does appear to be very much until you start pumping 500A though that resistance since W = I^2 x R.

Power loss at 500A for 20' 6Ga = 1975.5W
Power loss at 500A for 20' 4Ga = 1242.5W
Power loss at 500A for 20' 2Ga = 781.5W

Since 746W = 1HP, the cable loss can also be stated as follows:

Horse Power loss at 500A for 20' 6Ga = 2.65HP
Horse Power loss at 500A for 20' 4Ga = 1.67HP
Horse Power loss at 500A for 20' 2Ga = 1.05HP

Of course, your motor will only draw 500A for a brief period of time and will only be drawing someplace between 50A to 100A most of the time, but the loss ratios are the same.

For a 500A controller, go with 2Ga.

FWIW: My first upgrade was 2Ga cables on a otherwise stock 36V PDS that was only three years old at the time and I had a noticeable improvement if low end performance.

[mondo]

Great info^^^^^^^

[rottie]

I would also say be aware of you connections as there is resistance there too.

If there is a weak connection, then heat is generated there which causes a vicious cycle. As a connection gets hotter the resistance goes up, causing more heat, etc, etc, etc.
So look at the whole system, not just individual components.

[JohnnieB]

Originally Posted by rottie

I would also say be aware of you connections as there is resistance there too.

If there is a weak connection, then heat is generated there which causes a vicious cycle. As a connection gets hotter the resistance goes up, causing more heat, etc, etc, etc.
So look at the whole system, not just individual components.

However, the whole system is made up from individual components, so one must address each component individually to create a whole system.

The SepEx (PDS and DCS) high current cable system I used as an illustration consists of 10 lengths of cable that have a heavy gauge ring terminal at each end, so the are 30 individual components. The cables are part of a series circuit, so if any one of the individual components is not up to par with the rest, or improperly installed, the whole system is lacking.

The devil is in the details.

[scottyb]

I agree

[Volt_Ampere]

If you are going to upgrade, go to 2g!

[JohnnieB]

Originally Posted by scottyb

I agree

Another true believer.

The one with the tinfoil hat, that is.