Hello friends,
I am trying to make a basic spot welder for small home usage. I built the following circuit below but I can only get 2 amps from output. I am using high discharge rate INR li-ion batteries as power source. They are 4x in parallel. The mosfet is IRF2804 ( 40V 280A ) Please help me to figure out this.
What is the A-h (or mA-h) rating of the batteries?How about using a DC high current SSR instead of a mosfet? All said spot welding needs a lot of current - something only a car battery can provide (it can dump more than 200A into a short, enough to make an iron wrench red hot)
Batteries are rated as 2500mah each. Each battery is capable of supplying 30A continious current. I have mosfet in hand.
30A probably won't work - see the edit to my previous reply.
You need something capable of supplying in excess of 200A at a low voltage.
I guess you need a charge-discharge kind of system where upon contact a large current is dumped into the spot weld contact point and then when the contact is withdrawn it charges back...
You are missing the point, my problem is, why I can only draw 2A from mosfet ?
While I can draw only 2A from mosfet what is the point of using 200A power supply ?
PS: Each battery can supply 30A continious and can supply much more than that on momentary usage. And I have 4 of them in parallel. So, I do not think I have have power supply issue.
Could be its 'ON' resistance Rds(on)...check the mosfet's datasheet.
Its rated max current of 280A means that it needs that much voltage on its drain. If it has an ON resistance of 0.1 ohms, a short circuit current of 200A will require a drain voltage (and supply) capable of providing 200A at 20V
I found the problem, In datasheet Vgs is mentioned as 10V. I apply 4V to the gate, thats why less current passes through mosfet. I supplied 10V to the gate and it worked.
Look into using capacitors to supply the final welding current.
