# Battery connection: solid metal vs wire



## Vanquizor (Nov 17, 2009)

I didn't think skin effect applied in DC circuits...


----------



## akseminole (Jan 5, 2014)

Thank you.


----------



## GerhardRP (Nov 17, 2009)

Vanquizor said:


> I didn't think skin effect applied in DC circuits...


I think the issue in EVs is that solid connectors tend to stress the batteries more in the vibration environment compared to stranded connectors.


----------



## Sunking (Aug 10, 2009)

Most commercial applications of stationary batteries use buss bars for intercell and term post connections like you see below. Its a rather small battery bank of 24 volts @ 1800 AH used in a small cell site. From the battery if you look closely will notice a pair of 2/0 on each polarity for distribution. The 2/0 is extra flexible Class H Stranding. It is used because it is much easier to work with vs Class B stranding.

EV is a different application with two different requirements where higher strand count can be justified expense.

1. Most importantly is mechanical stress cause from vibrations and lateral acceleration. A Class B stranding uses annealed copper, and it would become fatigued in a short period of time at the point where compression terminals barrel ends on the wire. 

2. Between controller and motor although it is DC, it has a high frequency AC component if using PWM controller, or is AC if using a VFD inverter. AC current tends to flow on the outside of conductors. 

In an EV like my golf cart in the second picture i am using LFP and the intercell connectors and term post are buss bars.


----------



## major (Apr 4, 2008)

Sunking said:


> In an EV like my golf cart in the second picture i am using LFP and the intercell connectors and term post are buss bars.


So Sunking,

What are the circuit cards on every cell pair?

And to aksem,

One of the primary reasons solid connectors are used for battery or cell connections is the difficulty and reliability of attaching terminal lugs to both ends of stranded cable for all the numerous short connectors required. A flat copper busbar with a hole at each end has 2 contacts; one at each cell terminal. A cable has a contact between the strands and lug at each end as well as with the cell terminal, so has double the contact surface to surface interfaces, each being a possible source of high resistance and corrosion.

When solid busbars are used it is imperative that the cells be secured so there is no movement relative to each other. That would cause stress on the terminals and compromise the contact with the busbar or the terminal seal in the cell. Laminated busbars or braided straps are often used to allow for vibration.

major


----------



## Sunking (Aug 10, 2009)

major said:


> So Sunking,
> 
> What are the circuit cards on every cell pair?


Cell Balancer. It is a 48 volt 200 AH pack. I have rearranged the setup to eliminate the pair of 6 AWG used to connect the two 24 volt packs in series with a inter-cell bus bar. Will try to post another picture of finished setup. I am not using BMS to balance charge every cycle.


----------

