The lead acid batteries will do a fairly good job of eating the back-emf there and, yes, a series diode would protect the PSU whilst the lead acid protects the motor controller from overvoltage, like a pair of really heavy capacitors. I’d put a small WW resistor across the PSU output before the diode to give it a non-zero load to regulate into and you’d still want the noise smoothing caps on the motor drive input for stability.
The other ‘advantage’ would be the enormous arc flash you would get on a power electronics failure with the 1000A + delivery of those batteries so a big, fat, sand-filled fuse would be your friend
Yeah, the lovely tang of vaporised MOSFET seasoned with vaporised epoxy potting compound and exotic compounds of copper and aluminimum, marinaded in air plasma, nothing like it.
More seriously, the short circuit or fault mode current delivery from series lead acid batteries is more than enough to establish an arc that can permanently blind you or at least give you the fastest sunburn you’ve ever seen. There’s not many welding torches that run in the kA range. The sizes of the wires in this case are likely to be the limiting factor on arc current, they’ll just catch fire after a few seconds of limiting the arc to a few hundred amps.
Sand (and other stuff) filling of fuses is a method of quenching the arc that builds up when you have high voltage or high current flows to break with the fuse.
Yep, you probably could, looks like those are rated for a sufficient interrupting current. I got in the habit of glass filled because I had them, they were cheap and the things I was feeding 48V and 96V into from stacked car / truck batteries could send back significant voltage from angry inductors when you tried to cut their power.
Well apparently the V3 ODrives have a limitation in that they can really only use about 70% of your kV rating which is why I am hitting the limit at 24V. V4 will be able to use all of it. This is because V3’s primary design goal was for positional control and not for velocity control. If I overvolt my PS to 27V I should be able to get to 30k. The single channel V4 ODrives should be out beginning of next year.
So my PS can be over volted to 30V. At 30V I can easily hit 35k RPM. Only issue is my cooling fan for my electronics enclosure is not happy at that voltage. Might switch it to run off the Carbide Motion Board.
On the motor windings (stator), since the Makita’s housing is insulated from it. But the rotor will also heat up from eddy currents. RC community blogs suggest that it needs to be kept below 60 degrees C to prevent de-magnetization and/or glue failure - but who really knows?
So I have the code running well enough now that I do not need to set the RPM in ODrivetool. It does it automatically from the PWM output. Soooo much nicer than having to fuck with a router control knob or typing in commands.
Need to work on the fault handling and the temperature monitoring of the motor coils.
I received another email from Harvey Tool today about their high speed endmill/drills that reminded me of your earlier post about drill/endmills.
Does O-Drive use the hall sensors?
It works with Hall Sensors yes. It is not working with the Makita above 10k RPM for some reason. Hopefully will be hooking the motor up to an oscilloscope today to try to figure out why.
I was surfing youtube and saw the new Bantam cnc is using a hobby grade outrunner BLDC motor to drive their spindle.
When I suggested a chip guard to prevent conductive chips from being sucked into the motor windings I got the best response that could only come from a sales rep that has no idea about what I was referring to
Bantam Tools
Hi there! We future-proofed the machine to accept an air blast system to help with chip evacuation. Be on the lookout for that accessory later this fall!
