# Re: [EVDL] battery tab welding



## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

Hello Minh,

I just saw a segment ON HOW ITS MADE and there was showing different welding 
technics. They was doing a high temperature 1000 F silver soldering welding 
using a tack welder. A ribbon of silver solder that was coming off a reel, 
was inserted between the two contact alloys that was being welded together.

A tack or contact weld point may be only a little spot of the two alloys 
that are welded together, but then the silver solder is melted between and 
also bonded to the metals between the metals that was being welded together. 
This increase the conductivity of that weld joint, instead of just a little 
tack spot.

You could go to a welding supply company and see what type of products are 
best for what you want to do.

Roland


----- Original Message ----- 
From: "minhd" <[email protected]>
To: <[email protected]>
Sent: Sunday, February 03, 2008 12:09 AM
Subject: [EVDL] battery tab welding


>
> Does anyone have a recommendations for a capacitive discharge welding 
> service
> in Southern California? I would like to build a battery pack using the
> LiFePo4 26650 cells. I don't want to invest in purchasing a CD welding
> system at this time. Any ideas how much I should expect to pay to have 
> two
> tab welded onto each cell?
>
> Minh
> -- 
> View this message in context: 
> http://www.nabble.com/battery-tab-welding-tp15251122p15251122.html
> Sent from the Electric Vehicle Discussion List mailing list archive at 
> Nabble.com.
>
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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*



> Bill Dube wrote:
> > You need an inverter type welder that is capable of 4,000 amps. You
> > can fudge this down a bit, and get away with 3700 amps and a bit
> > longer duration, but it MUST be an inverter welder, not a capacitive
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

Please elaborate. Why does CD(capacitive discharge) welding cause cell
damage? Is it due to the need to minimize heating to the battery housing?
If the duration of heat application needs to be minimized, then perhaps
using a silver solder as Roland suggested could minimize the needed heat to
braze the tab to the cell. Both CD and inverter welding methods produce a
lot of heat over a short duration. 

Does anyone know if the K2 cells or the Headway cells have the same tab
welding issue? Has anyone try to weld tabs to K2 or Headway cells? If yes,
please help me understand the process and equipment involved? 

Regards,
Minh





> Dan Frederiksen-2 wrote:
> >
> > Bill Dube wrote:
> >> You need an inverter type welder that is capable of 4,000 amps. You
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*



> minhd wrote:
> > Please elaborate. Why does CD(capacitive discharge) welding cause cell
> > damage? Is it due to the need to minimize heating to the battery housing?
> > If the duration of heat application needs to be minimized, then perhaps
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

the previous cell connection thread does not answer the fundamental question
I had. Why does the A123 cells have to be resistance welded (inverter ...)? 
The capacitive discharge welders does essentially the same thing. I don't
think the CD welders have the fancy pulse duration adjustments!

Minh



Tom Parker-12 wrote:
> 
>


> minhd wrote:
> >> Please elaborate. Why does CD(capacitive discharge) welding cause cell
> >> damage? Is it due to the need to minimize heating to the battery
> >> housing?
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*



> minhd wrote:
> > the previous cell connection thread does not answer the fundamental question
> > I had. Why does the A123 cells have to be resistance welded (inverter ...)?
> > The capacitive discharge welders does essentially the same thing. I don't
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

I neglected to explicitly say you need an inverter welder, Bill is right
.
While the HF25 is an inverter welder, I didn't realize that it is only
2400A max.
Bill, with thin tabs, can you get by with 2400 Amps? Obviously this
would only be good for scooters,bikes or an EV that has a LOT in parallel

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

While an inverter welder is by far the best way to
weld tabs onto cells, I'd say that a home made cap.
discharge welder is a _lot_ better than soldering. 
But for me, after seeing the results of countless
different attempts at cell interconnects, I wouldn't
consider anything but an inverter welder for any pack
larger than a dozen cells or more. That's all I am
willing to risk with unproven methods. On YouTube
there are several videos of different welding
techniques. Derek has some videos of using an
inverter welder. I hear there are videos of home made
cap discharge welders making up A123 packs for RC
cars. Our battlepack NiCd pack for our battle bot was
soldered to cells, but quickly "frosted", indicating
cell damage. Early versions of the Killacycle (using
boulder cells) were not reliable until the battery
manufacture supplied sub modules with copper braid
(inverter) spot welded to each cell. Bill tried
several soldering techniques, pressure contacts, etc.
with various levels of failure.

There are several web sites showing how to home brew a
cap discharge welder using large SCRs or Triacs. It
would be interesting to try one with two sets of SCRs.
One to turn on the welding pulse, and one to short
out the cap bank after the welding is done, to reduce
the long tail. But since I know people with inverter
welders, trying this personally is a bit low on my
project list.

- Steven Ciciora




> --- Bill Dube <[email protected]> wrote:
> 
> > The goal is to minimize cell terminal heating.
> >
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

I spoke with Aaron from http://sunstoneengineering.com/site/pages/products . 
He explained that their CD welder do have a pulse width setting to cut off
the tail end of the weld pulse. This produces an inverter like square wave
energy pulse. 
I understand now that the inverter welders are the ideal tool to use for
welding tabs onto the cells reliably without causing damage to the cells. 

Thanks for all your insightful comments.





> Steven Ciciora wrote:
> >
> > While an inverter welder is by far the best way to
> > weld tabs onto cells, I'd say that a home made cap.
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*



> Steven Ciciora wrote:
> >
> > While an inverter welder is by far the best way to
> > weld tabs onto cells, I'd say that a home made cap.
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

.2 seconds (wondering how you measure this) is 200ms. The recommended
maximum is more like 8-10ms and is why the single phase inverter
welders are not recommended for lithium ion. (They use zero crossing as
the minimum pulse width, and in this country that is 16ms.)

Car stereo Caps have terrible ESR.

I am surprised it works well for you. Do you have any idea how many amps
you are putting out?


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

200V 300A .2 seconds is 12,000 watt seconds. ( I think
Amps*Volts*time=watt seconds)

4000A @ 12V .008 is 384 watt seconds

I wonder If both of these were getting max amps(and volts) to the weld
then is it true that the cell is seeing 31 times more energy?

I know the heads arn't rated for even 384 watt seconds. (250 for miyachi
88A)

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] battery tab welding*

I think he meant 20V - not 200V. Most car cap are rated at 20 to 24V. 
Also, car audio capacitor are notorious for hyping the capacitance of the
unit. Bill is right about using the MFG recommended welding process when
one is building a large EV pack. The other thing to note about home built
CD welder is that the weldor can not apply pressure to the weld tab as
consistently as the machine. Unless you are willing to develop a pneumatic
electrode actuator with a pressure regulator to adjust the pinch pressure, I
don't think it is wise to build an EV pack with manual electrodes.

Experiment wisely!

Minh






> Jeff Shanab wrote:
> >
> > 200V 300A .2 seconds is 12,000 watt seconds. ( I think
> > Amps*Volts*time=watt seconds)
> ...


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