Confusing Lipo wires (on a portable Spot Welder)!

[sonnetg]

Hello,
I am planning on upgrading the lipo with 18650 cell pack on my Kerpu Spot Welder (3.7v). Before I take out and replace the Lipo battery, would anyone happen to know what these two extra wires coming out from the lipo for (circled red in the attached images)? Underneath the circuit board, it says R29. Some kinds of resistor maybe? That would be a bit odd.

I have attached the images.

 

[sonnetg]

Another attachment with close up.

 

[E-HP]

Is there voltage between the two wires, or voltage between each and ground?

 

[sonnetg]

Is there voltage between the two wires, or voltage between each and ground?

Interesting. The voltage of the battery reads 4.08v, and there is no voltage between the two thin red (R29) wires coming out of the lipo in to the R29 slot. However, there is voltage between the ground and one of the wires, and the voltage reas 3.98v. It could be resistor or a shunt maybe? I have never seen anything like this when dealing with lipo. But my knowledge of EE is very limited. I have attached a image of the other side of the circuit board.

 

[docw009]

Might be a temperature sensor, You could always peel back the heat shrink and see what it is. It's probably not part of of the Lipo cells. Use it again for the new Lipo,

 

[sonnetg]

Might be a temperature sensor, You could always peel back the heat shrink and see what it is. It's probably not part of of the Lipo cells. Use it again for the new Lipo,

Thanks. Here is a video I found which seems to be helpful. I also notice the two red wires in the video. It could very well be a temperature sensor (thermistor). Let me investigate a bit more.

 

[E-HP]

Put it in the fridge for a while the measure the resistance as it come back up to room temp when you take it out

 

[sonnetg]

Put it in the fridge for a while the measure the resistance as it come back up to room temp when you take it out

Great idea. I am pretty sure this is a thermistor. I will certainly try it out before I yank anything out. Good thing thermistors do not have any polarity, so I should be able to remove easily and re-solder when needed. The Kerpu compact spot welder was quite decent when it was new few years back, but the lipo definitely needs to go now. I plan to hook it up with Samsung 25R lion pack and see how it goes. Thank you.

 

[sonnetg]

Just to update. This is indeed a temperature sensor (thermistor). I disconnected it, and the spot welder would not work. The error on the screen was: "Abnormal Temperature detected". Whew! mystery solved. Learned something new

 

[docw009]

You may learn something new when you try to run it on 18650 cells. No one sells any units like that, I threw my Seesil and BIRFC integrated welders away when the internal lipos got too weak to weld. I fiddled around with prism cells and the big Life cans, but couldn't get the current you get from a Lipo pouch. I hope it works out though.

 

[sonnetg]

You may learn something new when you try to run it on 18650 cells. No one sells any units like that, I threw my Seesil and BIRFC integrated welders away when the internal lipos got too weak to weld. I fiddled around with prism cells and the big Life cans, but couldn't get the current you get from a Lipo pouch. I hope it works out though.

Yeah....there is always something. The kerpu is an awful unit. They made it very difficult for anyone to disassemble or upgrade. I think the unit is built to be disposable unit. I will try Samsung 25R in a 1S10P configuration, and see if it does any better. 10P configuration should be able to provide 200A or burst of more if needed. I use this spot welder for small jobs and it still works, but I want a backup plan if the lipo gets too weak. If not, I will switch to capacitor based spot welder.