[cajunfj40]

oil pan 4:

800 VDC presents an extreme arc flash hazard.
The other thing is can the motor insulation take double the voltage?
To me doubling the voltage and increasing the amount of heat put off by the windings is a recipe for short motor life.

Ah, there's the info: "extreme arc flash hazard." How much worse is it than at 400-650VDC? Is it that it can jump a longer distance to start the arc that causes the flash? In any case, there will be sufficient current behind whatever voltage chosen to vaporize wiring/busbar/terminal/etc and cause the resulting plasma to do very bad things. How much less dangerous is the common 144VDC system? In any case, I'll try to remember to invest in some fiberglass wrenches for dealing with battery terminals and the like. My shiny Craftsman wrenches will quite handily carry enough current to cause Serious Problems when dropped on top of some busbars.

I'll have to do some digging to figure out the insulation rating on the stators. Is there a relatively easy way to determine the peak transient voltages seen in a given motor/inverter system? That's the real issue - making sure a higher voltage system doesn't drive transients up to "blow a hole in the insulation every time you jam on the regen at freeway speeds" levels.

Doubling the voltage does not directly double the heat - generally heat is I^2R losses. I'm trying to go up in voltage to avoid going up in current. That said, without controls, doubling the voltage will likely double the current the motor will take (based on higher input voltage vs. BEMF at a given RPM). Either way, I am looking at more heating based on increased power output at a similar or slightly lower efficiency, depending on load and RPM. It'd be interesting to find out if that heating increase is more or less than mechanically paralleling two entire electrically separate motor/inverter systems. Using two systems would only double the total heating at any given operating point - though the two systems may run at a less efficient point lower on their operating curve than the one bigger system, thus increasing the nominal heating losses. I just want to make sure I keep the rotor below the point where the magnets get very unhappy. I'd prefer to go with an induction machine, but so far all the OEM's are still using IPM rotors to get the power density, IIRC.

Are the wound rotors brushless?

No, that was an analogy trying to say that spinning a Spark EV motor to near or above 7kRPM (vs. stock ~4,500RPM) ought not to be disastrous or even bad wear-wise if appropriate bearings are selected. DC brushed motors are often sped up quite a bit from design speeds in EV racing. Similar armature OD's exist to the Spark EV motor, and they run faster than the Spark EV motor does now. Failure is generally first at the commutator - which an OEM EV Motor of the type I am considering lacks - and banding strategies as applied to DC brushed armatures likely have similar applications on brushless. Most OEM motors now being IPM type where the magnets are fully contained makes banding probably un-neccessary.

In industrial motors only specialized ones can be started on double voltage. And this is only allowed for a few seconds.
Any normal motor would be damaged and quickly ruined by double voltage.

Is this true for VFD/speed controlled motors, or just direct-to-line motors? Is this for "squirrel cage" polyphase AC motors (usually 3 in industrial apps), permanent magnet brushless motors, or brushed DC motors? I can see a standard 208 3-phase motor being quite unhappy at 480V without the accompanying frequency change needed to make things "line up right electrically" inside. It would seem that having an inverter controlling the voltage/current/frequency that the motor "sees" would eliminate this problem, unless there are issues like the aforementioned insulation rating.

Also you should take into consideration that it appears that all these motor drive bits and pieces were designed to prevent anyone from swapping parts around like this.
With electric vehicle motors and drives these motor and drive sets appear to be designed specifically for each vehicle.

Well, yes. The OEM's have many reasons to want their kit to only work with their kit. Max efficiency can be obtained by designing the motor and inverter to work together, if the manufacturer takes the time to do so. Closer integration can eliminate redundant parts, having specialized plugs means making it harder for the wrong part to be installed in a repair shop, etc. DIY folks often have to work around this sort of thing when correct parts are no longer available, too costly, etc. There are many strides being made in cracking the CAN bus codes to be able to drive OEM parts outside their original settings - see the GEVCU, etc. MPaulHolmes' (and many other folks') inverter is a full-on removal of the usual CAN-bus controlled OEM inverter, bypassing all of that decoding. eldis over on the DIY Electric Car forum has a project he's working on for a "replacement brain" that will drive the OEM power stages in any given OEM inverter and thus also bypass the OEM CAN-bus stuff. People are figuring out how to swap new engines with full computer controls into older cars - hotrodding is not dead, just going high-tech out of necessity as people try to accomodate "wanting to have something cool" with "wanting decent fuel economy" and "not wanting to smog up the place".

Higher voltages are not inherently bad. Anything over about 90vdc is easily deadly.
It's once you start going over 600vdc that you go from deadly to spectacularly dead with bonus fireworks show when there is a fault.

Hence why I'm asking - I would like to try and plan ahead for how to prevent such accidents. If it requires larger spacing between components, I'll plan that in. If it needs a redundant extra layer of insulation, same. What I want to avoid is making it so hazardous that special precautions are needed for average service folks or emergency responders over and above what they are already trained for when dealing with electric/hybrid vehicles, when there is no clear way to make that knowledge generally available for a one-off custom.