Oh okay, will do that from now on. Sorry about that.

I should also say that in addition to the hearing protection, a polycarbonate face shield is also a good idea. Safety glasses are good but a face shield is better. A chunk of resin from an exploding fet will damage any part of you it collides with and it is not impossible when you get to higher voltages that a fault could turn your bus bars into molten projectiles.

 

S

Sorry for my long absence and hope I didn't leave you in the lurch. Slight altercation with a moderator with questionable social skills. I really do have to learn to ignore these things ;-)
You have learned a very great deal and you are absolutely correct with what you have done and your experiments. I am impressed. I have spent years in power electronics and known many engineers who don't understand it as you now do. So, enough with the admiration society ;-) and down to business:
With batteries in series, the problem can be if one is weak then the others will force it into reverse polarity which can be explosive, and boost converters, you have set them up well but beware of same issue: if one goes into current limit the other and the load may force it into a reverse bias situation which can also be explosive.
With the power semiconductors you are using, especially with batteries as the power source that probably have fault current ratings in the hundreds or low thousands of amps, if you have a catastrophic failure that 'blows' the semiconductor the resulting bang could make you permanently deaf. Industrial deafness is not uncommon among power electronics engineers. Besides precautions to prevent splats, hearing protection is a very good idea.
As you already know, slowing down the switch transitions will reduce the spikes at the expense of higher switching losses. But the spikes may well return when the load current comes up. My advice would be to keep the switch speed high initially and determine the snubber elements you need for your given layout then slow the transitions down again if you want to.
My 'trick' for determining the parasitics your snubber has to compensate for is simply this:
At a low operating voltage but enough current to make the ringing readily discernible, add a capacitance in the snubber location that shifts the frequency of the ringing by a factor of 5 or more. Now you could say that the ringing frequency is a function of your applied capacitance and the parasitic inductance and so you can calculate that inductance. Now remove your cap and remeasure the ringing frequency. you know the parasitic inductance and the frequency so calculate the parasitic capacitance. It is pretty simple technique but the results are damn near perfect. I don't have it patented yet so shhhh, don't tell anyone!
Your snubber cap wants to be big enough to swamp the parasitic capacitance and the resistors wants to be sized to set the damping factor to around 0.8. Trial a few resistances with the circuit still at low volts. You may be surprised that the resistor is a higher value than you may have expected. I suggest starting at 100R and see how you go. The final value might be under 10R, or more like 220R. Suck it and see is perfectly reasonable for this bit of the operation as other factors often come to light in the process as you have already found from what you have already done.
I suspect you are correct in that your original layout prior to the 1000uF experiments are about as good as it is going to get and a lot of your parasitics are an unavoidable consequence of the packages the semiconductors are in and the physical size of the capacitors etc etc.
And on that topic, how did you size the capacitor bank and what ripple current rating and frequency are you designing for? I'm just wondering if you need so much capacitance or maybe need more or better caps as brushed motors can be a bit brutal as a load I think.

No worries, I was pretty curious where you disappeared to, but I figured it was either something important or something out of your control. Great to hear that I've done well so far!

As far as the batteries in series goes now, I have decided to switch to lithium ion batteries that I'll be building using 18650 cells. I obtained 297 identical cells recently with 2800mAh capacity that are C2 rated. I plan on using 240 of them to create a 144v 16.8Ah battery pack. I plan on using something like PTC reset fuses between each cell. Haven't done enough research on the BMS side of things yet, but I understand the concept of how they work. I know these things can combust if they get too hot, so that's part of the reason I'm going with PTC reset fuses. I don't really like the idea of changing out individual fuses if something happens, but if the PTC reset fuse idea doesn't work out, then I may not have any other choice. (It seems like I have a thing for dangerous projects, haha)

Also on my boost converters, I have diodes set up in series preventing reverse currents. I actually learned my lesson when I didn't previously have diodes... I was using them to charge my 144v lead acid battery packs, and ended up blowing a fet and a trace vaporized right off the board.

I'll be testing all of my 18650 cells using an ESR meter and a capacitor in series, that way I can get a good rough estimate of their internal resistance, and keep all of their internal resistances withing a small range. Course I know it's not the best way of testing them, and it won't be 100% accurate, but i happen to already have an ESR meter, and saw a guy using this method to check if cells were good or not, so I figured I'd give it a go.

Thanks for the advice on the hearing and face protection, didn't actually know people have gone deaf due to exploding semiconductors. I value my hearing, so I'll wear some headphones or something while I'm testing in the future. I have a welding mask on hand, so it might be a little ridiculous, but I could use that for face protection.

Also I did some testing under load, the spike raise a little bit, but it was still pretty smooth and didn't seem too bad. I actually recently tested all the way up to 170V. The spike didn't increase linearly with voltage like I thought it would. I can't remember the exact results, but I believe all the way up there it was only a difference of 2V, which seems pretty acceptable to me. I tested my load up to 23A on 12V, by physically trying to stop the motor with a rubber handle, spike was hardly a spike anymore.

I also implemented current limiting on the controller recently, and "manufactured" my own little PCB, using a CNC, to put the current sensor and some capacitors on, that way I could have it be inline with the bus bars. It turned out pretty decent. The limiting works pretty decent as well. The current does go over by 2A sometimes, but quickly decreases to the set limit, which also seemed fine by me.

And yeah, that is a pretty simple sounding way of determining a snubber! Sounds way easier than the ways I was reading about. I'm gonna have to give that a go! Don't worry, your secret is safe with me, and the other users on this forum, haha.

I'm going to be straight forward here, when I was sizing the capacitors, I hardly knew anything about ripple currents. The capacitors I'm using are rated for 2185ma of ripple current each. How I sized the bank was probably not the best way, but it was at least a fairly educated guess. I looked at motor controllers that drive motors with similar ratings. Most commonly, the treadmill controller. I figured these controller may have been a little under-rated, so I took the amount of capacitance, and doubled the amount... instead I added 3x the capacitance just in case I were to use a motor that pulls more current at some point. There's obviously more for me to learn here, I would greatly appreciate it if you could explain this a bit more in depth.

 

I should also say that in addition to the hearing protection, a polycarbonate face shield is also a good idea. Safety glasses are good but a face shield is better. A chunk of resin from an exploding fet will damage any part of you it collides with and it is not impossible when you get to higher voltages that a fault could turn your bus bars into molten projectiles.

I figured you might appreciate some pictures of the current sensor PCB and the 18650 cells I plan on using for the new battery. I'll be re-wrapping all of them, as their current wraps are either ripped from the process of removing them from batteries, or covered in epoxy. All of the cells I'm using are identical models. ICR-18650M by Moli Energy to be exact. These cells are only 3 years old. I don't know exactly how many cycles they've had, but I'm certain they're going to be in good, usable condition. I'll be testing them all over the next few weeks.