Something like that. Not sure about the exact physic behind it but for sure it didn't seem to work. (tried some years ago)
Too short a pulse might evaporate metal before the melt can spread I guess.
I will be having 100mm long probes for my kWeld.
I'd love to see a "shot counter". This would make it great for evaluating the state of the battery (or other power source). If the number of shots starts to decrease dramatically, we know the battery is dying.
I'd love to see a "shot counter". This would make it great for evaluating the state of the battery (or other power source). If the number of shots starts to decrease dramatically, we know the battery is dying.Thanks, very good idea! I've directly put this on my todo list. I'll make it an input energy meter, and I'll also implement a function that measures the battery ESR.
I was thinking of ordering some supercapacitors and use those as a power source. I'm unsure how the capacitors will cope with the high discharge rates. The Maxwell ones I've looked at is rated at 250A maximum, with an internal resistance of 2,2 mOhm and 2,5V nominel.
I was thinking of using 6 in series, which would result in just under 60F at 15V, for a total of ~6.5kJ. I'm not sure if the current capabilities of these are sufficient.
For the supercaps, how about those carbattery psu's they are quite beefy and with a good voltage (13-14V).
Perhaps some form of current limiter between the psu and supercaps ?
It is not the voltage that needs to be limited but the current.
I am not sure if a pc psu likes these giant currentjumps, they might shut down on OCP.
Perhaps some form of current limiter between the psu and supercaps ?
With this circuit, a low dynamic resistance thyristor isn't terribly expensive and could handle the current.
Easier to use a PSU with a current limiter rather than an ATX PSU. If you want to charge at max power with an ATX supply you would have to use a buck converter with an input filter to smooth the current.
You cannot switch DC with a thyristor.
I am looking for the solution at lowest possible price. The buck converter will cost maybe 20-30€, the ATX PSU another 30-40€, totaling 50-70€. Can you can recommend a 12V / 40A PSU that can easily be sourced and meets this price.
That's not how capacitive discharge works. You charge the capacitor with a low current switching converter, then you dump all the energy from the capacitor with the thyristor. When the current drops to zero the thyristor turns off.
That's not how capacitive discharge works. You charge the capacitor with a low current switching converter, then you dump all the energy from the capacitor with the thyristor. When the current drops to zero the thyristor turns off.The main idea behind my welder is that it measures the amount of energy that is dumped into the weld spot, and stops the current when a user adjustable threshold is exceeded. This provides very consistent welds. This can only be achieved with MOSFETs.
Aha. I was wondering why you didn't use thyristors instead of MOSFETs, since they come in rather large packages that can handle several thousands of amps, while being relatively cheap.
Have you looked into forced commutation? Possibly a class D commutation setup might do it.
Aha. I was wondering why you didn't use thyristors instead of MOSFETs, since they come in rather large packages that can handle several thousands of amps, while being relatively cheap.
Have you looked into forced commutation? Possibly a class D commutation setup might do it.I had considered them, and there were several reasons why I decided against them:
- a 300A SCR would probably have done the job, these are ~30€ which is same cost as I have now
- I was concerned if I would be able to design a reliable forced communitation circuit - it it fails to turn off the SCR, then the fuse is the last hope to prevent something from catching fire
- the voltage drop of the SCR would probably be 2V @ 1000A, which is more than 10 times of what it is now
- they are much bigger and I wanted to integrate everything on a circuit board
- last but not least, my knowledge of MOSFETs is several decades higher than that of SCRs
Does the wire need to be silicon?
I can find 10 and 16mm2 awg7 and awg5 i believe in flexible wire for in the power cabinet.
a 1500W 45A digital VC and CC controlled power supply
If that deal is happening then I am seriously looking for some 5 or 6 supercapacitors, I am only not sure how many F's they should have ? Any link besides Ebay or suggestion is welcome
I also see some protection boards with loadbalancing and current limiting, what is that about? Since we do not want current limiting in this application is it safe to use supercapacitors this way or could they also explode as LiPos?
I chose silicone high flex because a) it eases electrode handling and b) it is 200°C rated and won't immediately burst into flames when something unwanted happens.
I dream of one of these
I have some Maxwell BCAP0310 P270 T10 here,I'll keep you updated!
Supercapacitors don't like being overcharged, similar to Lipos. In a similar way, they need balancers when connected in series. For low current applications, that can be a simple resistor, but in our cases we need an active circuit. Typically that is a (e.g. 2.6V) comparator that switches a transistor which connects a resistor in parallel with the cell.