2020 UTA College of Engineering Innovation Day April 22, 2020

Senior Design Battery Tab Spot Welder

Executive Summary Conceptual Design Phase

Background: Resistance Welders

When physical connections between metallicsurfaces require stronger bonds, welding servesas an optional solution. Methods and magnitudeof energy transfer differ by materials andconnections desired. Our design results in asystem intended for resistance welding Li-Ioncells and producing thermocouples. Energytransfer is facilitated by a capacitive dischargedpulse, and can be adjusted by the voltage levelat which the weld occurs.

Detailed Design Phase

Prototype & Test

References

Conclusions

We were tasked with developing a resistance welder that functions by capacitive discharge. This system tailors to connecting Li-Ion cells for assembling larger battery supply packs. We’ve presented the specific range our welder must perform; and included an extended range for optional energy welds. Simulations and testing confirm our theorized values. At present circuit boards and assembly are underway as we continue towards a professional finished product.

Hornsby, Alan; Alvidrez, Jose; Rodriguez, Juan; Saine, Pa Demba

• Welders transfer current to generateheat, fusing materials at the intendedweld location

• Materials fused together providedurable connections with lessimpedance than methods which addmaterial to the connection

• Dual pulse welds preferred sinceinitial pulse cleans and pre-welds thematerials for secondary pulse

• Systems developed for uniquewelding needs, offering flexiblesettings and operation to remaincompetitive

• Technology within comparablecommercial products facilitateconsumers to design and fabricatetheir own welding systems at orbelow MSRP

• Intended user frequently needs 18650and 26650 Li-Ion cells for battery packcreation

1. https://www.amazon.com/DROK-Adjustable-Regulator-Stabilizer-Transformer/dp/B0744BT79M2. https://www.americanelements.com/meltingpoint.html3. https://www.spotweldingconsultants.com/capacitive-discharge-welders/dual-pulse-ins.htm4. https://www.keenlab.de/index.php/portfolio-item/kweld/

5. 𝐴!"#$%!&"' (%')*!+ = ∫,! & $&"#$%&''(

; Dr. Wetz, University of Texas at Arlington

6. W., Valvano Jonathan. Embedded Systems. Real-Time Interfacing to the MSP432 Microcontroller. 2nd ed., vol. 2, Jonathan W. Valvano., 2018

Constraint Value UnitV_source 120 VrmsI_source 15 A

Weld Signal Capacitive Pulse

Weld MaterialLevel

Calculated Unit

Nickel 6.7 V

Iron 6.5 V

Ni-Cr 7.1 V

Ni-Al 6.0 V

Copper 6.5 V

Our system must usestandardized AC power andweld via a capacitor bank, as inTable 1. Expected energy needsfound in Table 2 werecalculated by solving for theneeded temp. rise of the massat the intended weld location.Using 𝐸 = '

(∗ 𝐶 ∗ 𝑉(, we

determine the requiredvoltages our welder shouldoutput as in Table 2. A footpedal welding trigger results ina micro-controller performinga dual pulse weld by managingisolated gate drivers toMOSFETS. This results from aPWM signal to each driver.

Table 1: Initial Design Constraints

Table 2: Welding voltage requirements

Each AUIRF1324 MOSFET operates inlow-side, where the electrodes andwelding occurs before the drain.Welding causes the MOSFETS toallow current from drain to source,operating as the final switch. TheMSP-EXP432P401R modulates apulse with a frequency of 10kHz,resulting in peak output of 1.16A ofpeak current to each MOSFET. Thislogic is shown along with the natureof our dual pulse in Fig. 1. By way ofa DROK DC-DC regulating [1] supplyour user can adjust both weldenergy and charge time by settingthe output voltage and currentrespectively in a compact display.With this module we lose the abilityto adjust the width of each pulse.Weld successes are determined bythe energy delivered in this regard.An example of the expected currentof a weld at maximum energy, 105.8J at 23V shown in Fig. 2 sets the hardlimits that parts must be rated tohandle. This allows opportunity toattempt higher energy welds.

Fig. 1: Isolate gate driver modulated input signal

Fig. 2: Maximum condition discharge simulation

Fig. 3: Example of welding tabs to alkaline D-cells

Fig. 5: Overhead view of weld assembly model

Fig. 4: Angle view of weld assembly modle

A full system operating simulation hasn’t been recorded due to lack ofpart information in software such as OrCAD Capture lite. Hardware testsconfirm the energy output of the welding system as in Fig. 3. Each D-cellbatterie have a nickel tab welded to the positive terminal from an 8.65Vweld. CAD software models our assembly in Fig. 4 & 5 while circuit boarddesign reaches finalization. Once the circuit board dimensions arecomplete a full assembly update can occur.

Alan Hornsby Jose Alvidrez Juan Rodriguez Pa Demba Saine