Hi,
I'm interested in building a cheap DIY spotwelder using a 12V lead-acid car battery, a heavy duty contactor (Tyco EV200 rated at 500A continuous, max 650A make current to avoid contact welding but break current could be up to 2000A) and controlling the timing with an Arduino board.
My goal is to know whether I could spotweld 0.2mm pure nickel strips using a max current of e.g. 600A in order to stay below the safe limit of 650A for the make current of the contactor or whether I would definitely have to dump >1000A to spotweld such strips and thus run the risk of getting the contactor sticking (which is basically what everyone who uses a solenoid for spotwelding is doing...).
I understand that, in theory, it's better to dump >1000A during 5ms than use 600A during a longer pulse time. But if you look at e.g the Sunkko 709AD spotwelder which gets pretty decent reviews, this unit has been verified to output 690A (https://m.youtube.com/watch?v=Y3LX5CYB99g). So I was thinking that by limiting the current to about 600A (e.g. by choosing an appropriately sized car battery and/or using some resistor wire in the circuit), I may still get results that are decent and inline with those that could be achieved with a Sunkko 709AD unit. Don't know if the Sunkko 709AD can spotweld 0.2mm thick pure nickel though ..
I may play with 2 different car batteries: a 340A CCA or a 610A CCA. I understand that CCA (cold cranking amps) is an important rating. However all it does tell is how many amps a battery can output at -18 deg celsius while maintaining its voltage above 7.2V, which is not directly relevant for spotwelding for 2 reasons:
A) no matter my motivation, there is no way I'm going to spotweld at -18 degree
I'll probably do it at about 20-25 degrees (and outside for safety reasons). Rather than CCA, some batteries also indicate HCA (hot cranking amps) which are measured at 25 degrees. It seems it's possible to convert CCA to HCA by multiplying CCA by 1.66 (https://www.batteryequivalents.com/battery-terms-and-abbreviations-glossary.html). So a 340CCA battery may theoretically output 340x1.66=564A at 25 degrees, which would remain in the safe area for the contactor. On the other hand, the 610CCA battery may theoretically output >1000A at 25 degrees which may cause the contactor to fail at some point when making contact, unless I use some resistor wire to drop the current down to 600A.
B) when spotwelding, we are essentially shorting the car battery. In that condition, I guess the battery voltage may drop much lower than the 7.2V used in both CCA and HCA ratings and thus the output current may be much larger than the one mentionned by those ratings...in which case even the 340CCA=564HCA battery may still be "unsafe" for the contactor.
So back to my questions:
1) do you think that a welding current of 600A (for as long of a pulse duration is needed) is enough to weld 0.2mm thick pure nickel?
2) for those who have actually built a DIY spotwelder using a car battery/solenoid: have you actually measured the welding current that your setup is capable of outputting (e g. using a clamp meter) and how much you overload the solenoid?
3) for resistive spotwelding, we want high amps (I) as this is what produces the heat and we don't necessarily consider voltage (V). Many DIY MOT spotwelders run at 1-2V but can dump >1000A. However, isn't it power (P) rather than amps which is producing heat??? I understand that since P=RI^2, this is mostly the same thing since the resistance (R) is given by the circuit characteristics. But we also have P=VI and so even if the car battery voltage drops down to e.g. 4V while outputing 600A, that is equivalent to 2400W which is roughly the same amount of power a MOT spotwelder would output with 1000A at 2V. So should we focus on power or amps??
4) according to the datasheet, the Tyco EV200's main limitation is the max 650A make current (to avoid contact welding) but the break current could be as high as 2000A @12V. I thought that arcing (which degrades the contact surface overtime) would mostly occur when breaking the connection but not when making it so why would the make current be the main limitation whereas the contactor can handle much higher break current?
The alternative is to replace the contactor with some parallel power mosfets or directly buy a Malectrics or Kweld. But since I'm planning to build a single ebike pack with this spotwelder, I'd like to first experiment with the cheap and easy solenoid/car battery route. But I'll definitely use a 300A fuse on the battery, work outside, and first do tons of tests before ever attempting to spotweld anything onto an actual 18650 cell...
Thanks for your insight!
I'm interested in building a cheap DIY spotwelder using a 12V lead-acid car battery, a heavy duty contactor (Tyco EV200 rated at 500A continuous, max 650A make current to avoid contact welding but break current could be up to 2000A) and controlling the timing with an Arduino board.
My goal is to know whether I could spotweld 0.2mm pure nickel strips using a max current of e.g. 600A in order to stay below the safe limit of 650A for the make current of the contactor or whether I would definitely have to dump >1000A to spotweld such strips and thus run the risk of getting the contactor sticking (which is basically what everyone who uses a solenoid for spotwelding is doing...).
I understand that, in theory, it's better to dump >1000A during 5ms than use 600A during a longer pulse time. But if you look at e.g the Sunkko 709AD spotwelder which gets pretty decent reviews, this unit has been verified to output 690A (https://m.youtube.com/watch?v=Y3LX5CYB99g). So I was thinking that by limiting the current to about 600A (e.g. by choosing an appropriately sized car battery and/or using some resistor wire in the circuit), I may still get results that are decent and inline with those that could be achieved with a Sunkko 709AD unit. Don't know if the Sunkko 709AD can spotweld 0.2mm thick pure nickel though ..
I may play with 2 different car batteries: a 340A CCA or a 610A CCA. I understand that CCA (cold cranking amps) is an important rating. However all it does tell is how many amps a battery can output at -18 deg celsius while maintaining its voltage above 7.2V, which is not directly relevant for spotwelding for 2 reasons:
A) no matter my motivation, there is no way I'm going to spotweld at -18 degree
I'll probably do it at about 20-25 degrees (and outside for safety reasons). Rather than CCA, some batteries also indicate HCA (hot cranking amps) which are measured at 25 degrees. It seems it's possible to convert CCA to HCA by multiplying CCA by 1.66 (https://www.batteryequivalents.com/battery-terms-and-abbreviations-glossary.html). So a 340CCA battery may theoretically output 340x1.66=564A at 25 degrees, which would remain in the safe area for the contactor. On the other hand, the 610CCA battery may theoretically output >1000A at 25 degrees which may cause the contactor to fail at some point when making contact, unless I use some resistor wire to drop the current down to 600A.B) when spotwelding, we are essentially shorting the car battery. In that condition, I guess the battery voltage may drop much lower than the 7.2V used in both CCA and HCA ratings and thus the output current may be much larger than the one mentionned by those ratings...in which case even the 340CCA=564HCA battery may still be "unsafe" for the contactor.
So back to my questions:
1) do you think that a welding current of 600A (for as long of a pulse duration is needed) is enough to weld 0.2mm thick pure nickel?
2) for those who have actually built a DIY spotwelder using a car battery/solenoid: have you actually measured the welding current that your setup is capable of outputting (e g. using a clamp meter) and how much you overload the solenoid?
3) for resistive spotwelding, we want high amps (I) as this is what produces the heat and we don't necessarily consider voltage (V). Many DIY MOT spotwelders run at 1-2V but can dump >1000A. However, isn't it power (P) rather than amps which is producing heat??? I understand that since P=RI^2, this is mostly the same thing since the resistance (R) is given by the circuit characteristics. But we also have P=VI and so even if the car battery voltage drops down to e.g. 4V while outputing 600A, that is equivalent to 2400W which is roughly the same amount of power a MOT spotwelder would output with 1000A at 2V. So should we focus on power or amps??
4) according to the datasheet, the Tyco EV200's main limitation is the max 650A make current (to avoid contact welding) but the break current could be as high as 2000A @12V. I thought that arcing (which degrades the contact surface overtime) would mostly occur when breaking the connection but not when making it so why would the make current be the main limitation whereas the contactor can handle much higher break current?
The alternative is to replace the contactor with some parallel power mosfets or directly buy a Malectrics or Kweld. But since I'm planning to build a single ebike pack with this spotwelder, I'd like to first experiment with the cheap and easy solenoid/car battery route. But I'll definitely use a 300A fuse on the battery, work outside, and first do tons of tests before ever attempting to spotweld anything onto an actual 18650 cell...
Thanks for your insight!
