CHARGING SPEED

The voltage on the left is the actual capacitor voltage and the voltage on the right is the set point. This was just a test with a 19Ohm resistor connected to the discharge terminal causing the discharge to be very slow when the set point is lowered. This will be much faster with a resistor bank with a lower resistance.

PCB TEST

I've spent this weekend putting the new PCB together( I actually had it built before Friday) and it was very easy to build. You will need magnifying glasses, a good light and a hot air soldering iron for the surface mount components. The rest of the components are soldered at the bottom side and the solder gets pulled into the holes so no soldering is necessary at the top.  There are two problems however, I screwed up on the solder mask on the Mosfets and you have to scratch the mask off around the solder points to get a bigger solder area and Diode 10 needs to be turned around.
The charging speed is so fast with a 12 Amp supply that when the capacitor reached it's set point and the mosfet kicks in when the voltage drops 0.1V that it actually overshoots the set point by 0.4V before turning the Mosfet off. I've been writing some really complicated code to try and fix this issue.

THE PCB'S ARRIVED

Well, the PCB's  finally came in. I have a very expensive camera and as you can see I'm not very good with taking photo's. This board is very solid and absolutely of high quality. I don't know why, but my camera makes the middle of the board look like its bent and some of the silver on the board look like it's black.

I will build this board this weekend and post more photos.

Just a peek at the Mosfet part of this welder. I am still waiting for parts

CAPACITOR DISCHARGING EXPLAINED

I was browsing the internet and found many sites where the guys think that they will get the same or better welders by making the voltage higher and the capacitance lower. Yes, it will be cheaper and easier to increase the voltage to get more Joules or Watt-second (1/2x capacitance x voltage x voltage) BUT here is the catch: The capacitance of your cap and the resistance that you weld, determine the length of your weld and not the WATT-SECOND. In other words if you have a 1 farad cap, charged to 35Volt (612Ws) then it will completely discharge in 15ms if you weld metal with a resistance of 0.003Ohm (0.005 nickel).
If you increase the voltage to 50V then you will have 1250Ws and your capacitor will still discharge in 15ms at the same resistance.
With a bigger capacitor, lets say 3farad at 20Volt (600Ws), will discharge over a 45ms period.
You can already see what is happening here: A higher voltage will give you more current discharged into your work piece in a shorter time. It will produce more heat, is very hard to control and will make welding thinner metals very difficult, meaning that 0.1ms can give you a nice weld and 0.2 might burn a hole in your work piece.
 With a lower voltage and bigger capacitance your weld will be more spread out and will have less current than above but it will give you a much better controlled weld and fuse your metals better and stronger together.
 The higher Ws makes a big difference but the capacitance should also be bigger to give longer and better controlled welds.The Volts and Capacitance needs to be balanced to make a good welder.
For battery packs, I will suggest the higher capacitance and that is what I'm building here.

ANY VOLTAGE, 60V AND OVER, AC OR DC CAN KILL YOU! VOLTAGES BETWEEN 50 AND 60V   MIGHT GIVE YOU A TICKLE BUT IT WON'T HURT YOU. THIS WELDERS WITH VOLTAGES OF 20V IS TOTALLY SAFE AND YOU CAN HOLD THE PROBES IN YOUR HAND WHILE 10000AMP IS FLOWING THROUGH IT WITHOUT FEELING A THING.

NOVEMBER 6Th

I finally have 3 boards on order. I ordered only 3 because of the overall high price (tooling amount) and will test them first before ordering more at a cheaper price and also to see how many of you guys will be interested.
I am waiting for parts to build I guess the part of this project that everyone is waiting for. I am trying to make this welder as cheap as possible and this weekend my calculator kept on spitting out data that I didn’t like. I have a circuit that turns my SCR’s off but to build it to work with all big SCR’s out there will be more difficult and expensive than just using Mosfets for the actual weld. I never wanted to use Mosfets but looking at the numbers made me change my mind.
Big SCR’s have an ON resistance of about 1.5mOhm (It differs). If we do a quick calculation you will see that if we make the resistance of the metal that we weld 0(dead short because we are trying to figure out the max current to protect our components) then we only need the Capacitor's ESR and the SCR’s ON resistance to work out the actual max current at the moment the switch is closed (we are not going to use the wire and weld probe resistance because they are variables)
Let’s say our Cap have an ESR  of 1.6mOhm. If we use the above SCR and charge our cap to 20V (max) then 1.6 + 1.5 = 0.0031Ohm. I = V/R 20/0.0031 = 6452Amps.
The Mosfets in parallel that I’m going to use will have a much lower ON resistance of 0.0002Ohm which will give us about 11111Amps for a split second(much higher than the SCR). The current will be less if we add the wire and probe resistances and also the metal that we are going to weld. The number of Mosfets in parallel will also give us a much bigger surface area to work with.
I should receive the PCB’s by the 17Th. I am busy designing this new Mosfet circuit and will post pictures and more information Tomorrow when I'm done.