Hmmm yea. Oooopsy[emoji16] again that wouldn’t be accurate but would give an idea of it.
How about using the fuse as a shunt? Does the resistance of the fuse change much from one to another, or does the temperature rise of the fuse contribute too much to resistance instability?
For what it's worth, I have found that Infineon MOSFETs have pretty accurate resistance values, maybe within 10% or better, and the tempco is well specified. My experience has mostly been 100V FETs and above, so it may not be directly applicable here.
I would guess that if you know the FET temp, you can do a pretty good job. For those who have to know, there could be an option to calibrate the current using an external shunt. Not sure if it would be worthwhile, because I suspect the current varies a lot during the weld process.
In the end, kWeld has proven to make very repeatable welding results, and that's all it has to do
For what it's worth, I have found that Infineon MOSFETs have pretty accurate resistance values, maybe within 10% or better, and the tempco is well specified. My experience has mostly been 100V FETs and above, so it may not be directly applicable here.Did you find this by measuring, or were these datasheet figures?
Is there a problem with using the relationship among capacitance, charge and voltage to determine the energy of a pulse that I have overlooked? This seems to me a good bit easier and more accurate. One still has heating losses, but those should not be too hard to measure or estimate using suitably placed thermistors.
ESR is measurable as is the cable resistance. The relationship between charge and voltage for a LiPo is more complex than the linear relationship of a capacitor, but I don't see why it is harder than the time variant Rds(on) of a MOSFET passing a large current for a short period of time.
A comparison to the measurement of CPU drains is fatuous at best. That does not involve going from 0 to 1000A and back in a fraction of a heartbeat.
As I understand it, you're discharging a capacitor bank and you're measuring the energy of the pulse by measuring the current. The accuracy of the measurement is limited by the difficulty of measuring a large current under dynamic conditions.
If the charging current is disconnected prior to the pulse and the capacitor bank voltage measured before and after the pulse that should give an accurate measure of the energy from first principles. There is likely some voltage variation after the pulse is cutoff related to the degree to which the capacitors do not discharge uniformly. However, this might provide a means for assessing the condition of the capacitor bank.
Is there a problem with using the relationship among capacitance, charge and voltage to determine the energy of a pulse that I have overlooked? This seems to me a good bit easier and more accurate. One still has heating losses, but those should not be too hard to measure or estimate using suitably placed thermistors.
ESR is measurable as is the cable resistance.
I have purchased two Maxwell 58F units to build two different welders and power my Arduino Spot Welder, and I also hope to use them with my future Kweld !
this design: https://www.thingiverse.com/thing:2588371
In the electrical diagram of the article where these capacitors are used, I have seen that there are 2 resistors of 10ohm and 100W in parallel with the capacitors.
I thought that the purpose of the resistors was only to discharge the capacitors after using the soldering iron. Maybe they are necessary for it to work properly?
I'm sorry, but my knowledge of electronics is still very basic.
if you sell them directly.
It has arrived today
How many mOhms (approximately) will it lose when using thicker cables and solder the cables (partly) directly to the board?