Large BIFRC spot welder case with battery

thingiverse

This is a large case for a BIFRC battery tab spot welder PCB. This is the successor to my previous small spot welder case (https://www.thingiverse.com/thing:4809772). This one is larger and has room for a 4S 14.4V LiPo RC battery inside. BIFRC_large_case_body.stl is the body by itself BIFRC_large_case_lid.stl is the lid by itself s2tIC8ndth.stl is both body and lid in one file The BIFRC is installed in and becomes part of the front panel, eliminating the problems getting to the program button or the mode and trigger LEDs. On the left side of the front panel is a voltmeter to monitor the battery state. On the right side there are holes for a toggle off-on switch and an RJ11 telephone jack used to attach a foot pedal (I used https://www.thingiverse.com/thing:3152310) to the welder via an old telephone cord. A pair of 6mm holes at the bottom right are where the welding cables emerge from the case. I used 7/8" long 4-40 screws as hinge pins for the lid, though the bores are generic 2mm in the body and 3mm in the lid (so the lid moves freely around the hinge pins). M2 screws longer than 18mm should work fine. The hinge barrel is oversized because, well, PLA is not as robust as metal. The hinge is located in the front of the case to avoid interfering with access to the battery. Simple detents lock the lid in place, and thumb relief divots on the back give you a place to push up on the lid to release and open it. There are cooling vents in the back, but I haven't noticed the battery getting hot. There is an access hole in the back to get to the balance charge pigtail on the battery, though I'm not sure how useful that is. To install a BIFRC PCB, I made all attachments on its back-side. I changed the PCB-mounted XT60 connector to an in-line XT60 connector on a short pigtail. The foot pedal connections are to the G and R through-holes (bottom-left corner of the PCB, near the GND and KEY pads, respectively) on the BIFRC. The XT60 battery negative pin is wired to the BIFRC "-" (or gnd) pad. The negative welding cable is attached to the BIFRC "OUT-" pad. In this design, the positive welding cable is attached directly to the XT60 battery connector positive pin, and only a small (20 gauge) wire attaches through the front panel toggle switch to the BIFRC card VCC pin. The voltmeter ground is attached to the battery ground on the BIFRC. The voltmeter power and test leads both attach to the VCC pad on the BIFRC, so the meter is off when the toggle switch is off. The toggle switch turns off power to the BIFRC PCB control circuitry only. The MOS Tube on the BIFRC isolates the welding negative probe, effectively turning the welding probes off. Designed in Tinkercad, Advantages: The PCB and battery combined (with a little help from rubber feet glued to the bottom of the case) stay put when I'm welding batteries. The other case was so light that the cables dragged it around, which bugged me. This design has a power switch, though I caution that if something goes wrong with your BIFRC, it's possible that turning off the BIFRC won't turn off the probes. The programming button and the MODE and WORKING (I call it "Trigger") LEDs are all easily accessible. Disadvantages/improvements I should have used a rocker switch to make it less easy to accidentally turn it on. An improvement would be a pair of barriers on either side of the switch to prevent that. There is no place to store the probes when not in use. Perhaps if I grew the right side out another centimeter or two and added bore holes to insert the probes into... I think it could use a handle. It would have to attach at the sides, because the lid detent is not reliably strong enough (depending on material, resolution, individual printer qualities) to hold the weight of the welder and battery. From sad experience, the MOSFETs need heatsinks. The photos don't show them.