8i20 DC power supply companion board.

I've recently decommissioned an 8i20 I was using on my mill due to some issues and the fact that I was never really thrilled about the power supply solution I was using, it took up too much space, too many wires and start up current issues, I always meant to whip up a PCB to handle this a bit neater but never quite got around to it. I am a fan of the 8i20 so I'd like to get a more proper setup for when I recommision it. I'm just thinking it up at the moment, I haven't really dove in yet. Once done I'll slap the project on github.

Power components aren't my strong suit but assuming everything is specified for the max 2200w I'd like to get a couple suggestions on the following if anyone has any:
1) filter cap values and quantity
2) best way to handle initial inrush current of charging the caps on power on
3)on board brake resistors.

The brake resistors I'm not sure about. Trying to figure what a good minimum power resistor setup looks like and fit on a PCB. This would be heatsunk and have a thermostat or some other thermal device connected to an SSR to disconnect drive input power if the brake resistors were overheating.

I'm trying to avoid controlling the power supply with hal, other than an enable signal. Any particular reason for the 10,000uf capacitor? From what I know about drives this size I would assume say 4 x 470uf caps is sufficient, which is the setup I was using previously. I did have a few 4700uf 450v caps laying around that I tried, and besides being huge, the inrush was pretty serious. What value and power rating did you use for the inrush limiting resistor?

I got to playing with a schematic just so I can visualize the idea and came up with this. Missing some passives and probably a diode between the igbt and INA138 but I just wanted to get it on paper at the moment so I can get some advice. I'm not sure that I'll use any discharge circuit, waiting 5 minutes until the HV LED on the 8i20 goes out before playing with stuff hasn't really bothered me.

Thoughts.....or just plain wrong?

"Why?"

Just a philosophy thing. While there is nothing wrong with having hal control something like this, if hardware logic is not controlling it then hal must control it. Which means a configuration issue becomes a safety issue. Besides that it requires more wiring from the controller to the Power supply/drive area. Though I'm not exactly an electronics wizard myself I hope to come up with something small-ish and once the board is designed I slap it together and don't think about it much.

"I have more capacitance, and why would the caps discharge at all with the drives disabled?"
Caps aren't batteries, they cannot hold a charge indefinately. Just the passive circuitry on the 8i20 does in fact fully discharge the motor power caps...albeit slowly. The higher capacitance of your setup will take much longer to discharge but it will in fact discharge just sitting with the motor leads connected to the 8i20 (without the relay). There is a small benefit to the fact that if the caps have not discharged fully there is no inrush to deal with anyway.

Ignore that first drawing not sure what I was thinking putting the transistor before the rectifier.

"Important note: I am just sharing what I did. I have no qualifications to indicate that what I did was what should be done."
well me neither lol. I design boards as a hobby and have been relatively successful. I myself am not "qualified" to design a HV PCB but I will seek advice and play with it until I feel it is safe to test. I also seek advice for stuff like this on electronics forums and if we are lucky enough, maybe the grand wizard PCW himself will grace us with some advice.

Maybe slightly more proper schematic:

I used the shunt as that is what the INA138 application notes refer to. It's pretty likely I won't be able to find a suitable shunt anyway so a resister-zener or something similar is more likely. I have to do a bit more research as to what's available for handling that voltage which is why I haven't bothered to try to calculate the passives to set the gain for the INA138.

I'm looking at replacing the INA138 and shunt with a diode and IGBT gate driver which might take a bit of guesswork out of it. I use a Fet driver on another PCB I make but that's for switching speed wheres this is more for isolation.

After educating myself just a bit this is where I'm going at the moment. Still not quite sure how to derive the voltage reference to operate the gate of the IGBT but I'm working on that.

andypugh wrote:

blazini36 wrote:

Still not quite sure how to derive the voltage reference to operate the gate of the IGBT but I'm working on that.

That might be why I decided to do it in HAL, as the 8i20 reports back bus voltage.

And again there's nothing wrong with that, just not what I have in mind for this particular thing. Main issue I have with that is if the hal config gets messed up and doesn't switch the bypass then the NTC or whatever just turns into a heater.

As I look into this I start to realize what the idea of the 8i20 probably was. If you have multiple motors/8i20's in a single system, you might throw together a large single DC bus supply. Control the input with a contactor and do exactly as you have done, using one of the 8i20's bus voltage pins to control the inrush bypass through hal. More or less how I was doing it previously but I never quite got to the inrush limiting device, just limited the bus caps so I could use a reasonable input fuse. I did come across PCB mount relays that can handle controlling an inrush current limiter on the AC side If I can't figure out the solid state device but I still need to derive the voltage reference to control the relay.