increase conductivity and reduce R (Full Version)

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incarus -> increase conductivity and reduce R (11/20/2007 7:50:18 PM)

I read all the post regarding building a123 packs and there are some concern on the 4 spot welds and their integrity under load. I am using a large motor with a voltage range of 10-37 volts with a recommended lipo set up of 8S.

I was planning on making a 6 cell and 4 cell A123 together to get the power needed.

has anyone tested just how much these spot weld will handle??

I am about to shrink tube the 6 cell pack I made and I want to know if I should beef it up before I complete the build...I dont want to take it apart later.

I was told that some have "wicked" up some solder under the tab(if your solder gun is hot enough)

is there any other foolproof method.

I read something about solderless cunductive epoxy....does something like this exist and where can I get it.

I hope I do not have to take the existing tabs off(pain)

I read on an other site that one person runnes there pack all day at 35volts with out problem

thanks for the input in advance.



A123 Racing -> RE: increase conductivity and reduce R (11/20/2007 11:13:41 PM)

Hello Icarus,

The tabs that are welded on the cells are solid nickel straps. They can handle all the power the cells can deliver, well over 70A continuous. Many people think these tans are attached using a spot welder which has caused some concern. They are in reality attached with a resistance welder. The tabs are welded to the cell with 4500A for a fraction of a second. This yields a weld that has a much lower resistance and allows for this high amount of power.

I would say use the tabs that are on there and save yourself some time and effort.

Power . Safety . Life

Brian

[image]http://www.a123racing.com/images/Animated-Banner_r0.gif[/image]



incarus -> RE: increase conductivity and reduce R (11/20/2007 11:49:40 PM)

thanks for the info. I was just concerened when I read some threads hear and elswhere that removed them and bridged the cells with heavy duty material using more stout bonding techniques. if it will handle up to 70A continuous....I quess I have nothing to worry about.

The 4 "welds" on the dewalt packs im using seem very flimsy but I will trust the experts



everydayflyer -> RE: increase conductivity and reduce R (11/22/2007 4:35:06 PM)

quote:

The 4 "welds" on the dewalt packs im using seem very flimsy but I will trust the experts

Not an expert just an experienced user.

I have ran a 3S pack in a MM powered Traxxas Rustler at over 100 amp. spikes. I have flown many flights with 4S and 5S 1P packs with spikes(burst) to over 70 amps. (just over 650 watts on 4S and over 900 watts on the 5Ss).

I did manage to short a 5S pack once and all I got for my trouble was a blown / melted strip of solder up braid which I had used to add the fifth cel to a former 4S pack.

FYI Some Heli flyers are useing the ten cell packs with stock DW interconnections in very high amp 3D ships.

Charles



cyclops2 -> RE: increase conductivity and reduce R (11/22/2007 10:51:59 PM)


I think a lot of people are forgetting how short of a distance that weld exists for.

We are talking .001" absolute maximum!! Then the big metal spreads the heat out and resistance is nothing again. So losses are nothing.

DO NOT do anything to the welded area. You will RUIN the chemicals and weaking the seals under the metal without reducing resistance.

Solder has more resistance than a spot weld. And your risk of damaging the cell is extremly high.

Do nothing. Enjoy what we have!!



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