Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - 350-400VDC vs 700-800VDC?

cajunfj40 · 04-21-2016, 05:13 PM

Hello all,

I had posted a while back about trying to run two Leaf motors paralleled off a single inverter (short answer: not usually, but might be worth the experiment), and then asked a separate question about higher voltages that I think deserves to be split out on its own.

My questions are: what safety/regulatory implications arise from the increase, other than the vague "higher voltages are bad, m'kay?" I know from poking around at NFPA and similar regulations that it moves from a Level 2 risk to a Level 3 risk (for UPS battery systems), and that going to higher than 650V requires higher-rated tools like voltmeters and such to avoid internal tool damage. What extra risks are present on the EV itself?

Porsche recently unveiled an 800VDC EV concept, and I've found inverters/converters/etc. for 700-800VDC input continuous, 1000VDC transient, presumably for big transit buses, where the power levels make downsizing the current required really attractive.

I would intend to set it up so that the two packs only join up in either the inverter enclosure or a separate "high voltage control box" before going a short distance to the inverter, so no two wires in close proximity have 800VDC across them, and any single wire has at most 400VDC to ground or a nearby wire in case of a fault. I could re-use OEM plugs and sockets that way - no re-engineering needed. If the hazards aren't really any worse, nor a potential regulatory hurdle (for shops working on it? Dunno, I'd be DIY so not really subject to the regs) then that combiner box could be further away from the inverter box, potentially simplifying cable runs and parts layouts. Charge in parallel at "normal" OEM charger voltages, etc.

See, MPaulHolmes is working on his 200kW inverter, and to get that power (minus inefficiency) out of a single Leaf motor (or Volt motor, or other OEM motor of similar power ratings) without absurd phase currents, it would seem going to a higher voltage to allow extending the constant torque line up the RPM band would be "easier". Basically, take two OEM EV battery packs (Leaf, Volt, etc.) and connect in series, roughly doubling the RPM at which the constant torque can be maintained. I already want more range than one OEM pack can give me, so why not connect in series instead of parallel? 80kW is plenty for steady-state operation under most scenarios for my (still theoretical) planned build, and 100kW would not take much increase in cooling capacity either. Depending on how the efficienty islands act above the currently plotted ones for, say, the Leaf motor, running at higher power ratings at higher RPM's with the same phase current that it can handle 80kW at now shouldn't overheat it. I doubt I'd want to spin the motor much/any faster than stock RPM limit, though, because bearings/balance. (I wonder what an IPM rotor coming apart at 20kRPM would do? I think the stator and housing could contain it...) A Chevy Spark EV motor only spins 4500RPM now, so increasing that isn't too bad. (DC brushed motors with armatures that diameter spin up to 7K without too much extra work into them.)

Thoughts?

04-21-2016, 05:13 PM	#1 (permalink)
cajunfj40 Lurking Eco-wall-o-texter Join Date: Dec 2015 Location: MPLS, MN area Posts: 128 Thanks: 0 Thanked 65 Times in 45 Posts	350-400VDC vs 700-800VDC? Hello all, I had posted a while back about trying to run two Leaf motors paralleled off a single inverter (short answer: not usually, but might be worth the experiment), and then asked a separate question about higher voltages that I think deserves to be split out on its own. My questions are: what safety/regulatory implications arise from the increase, other than the vague "higher voltages are bad, m'kay?" I know from poking around at NFPA and similar regulations that it moves from a Level 2 risk to a Level 3 risk (for UPS battery systems), and that going to higher than 650V requires higher-rated tools like voltmeters and such to avoid internal tool damage. What extra risks are present on the EV itself? Porsche recently unveiled an 800VDC EV concept, and I've found inverters/converters/etc. for 700-800VDC input continuous, 1000VDC transient, presumably for big transit buses, where the power levels make downsizing the current required really attractive. I would intend to set it up so that the two packs only join up in either the inverter enclosure or a separate "high voltage control box" before going a short distance to the inverter, so no two wires in close proximity have 800VDC across them, and any single wire has at most 400VDC to ground or a nearby wire in case of a fault. I could re-use OEM plugs and sockets that way - no re-engineering needed. If the hazards aren't really any worse, nor a potential regulatory hurdle (for shops working on it? Dunno, I'd be DIY so not really subject to the regs) then that combiner box could be further away from the inverter box, potentially simplifying cable runs and parts layouts. Charge in parallel at "normal" OEM charger voltages, etc. See, MPaulHolmes is working on his 200kW inverter, and to get that power (minus inefficiency) out of a single Leaf motor (or Volt motor, or other OEM motor of similar power ratings) without absurd phase currents, it would seem going to a higher voltage to allow extending the constant torque line up the RPM band would be "easier". Basically, take two OEM EV battery packs (Leaf, Volt, etc.) and connect in series, roughly doubling the RPM at which the constant torque can be maintained. I already want more range than one OEM pack can give me, so why not connect in series instead of parallel? 80kW is plenty for steady-state operation under most scenarios for my (still theoretical) planned build, and 100kW would not take much increase in cooling capacity either. Depending on how the efficienty islands act above the currently plotted ones for, say, the Leaf motor, running at higher power ratings at higher RPM's with the same phase current that it can handle 80kW at now shouldn't overheat it. I doubt I'd want to spin the motor much/any faster than stock RPM limit, though, because bearings/balance. (I wonder what an IPM rotor coming apart at 20kRPM would do? I think the stator and housing could contain it...) A Chevy Spark EV motor only spins 4500RPM now, so increasing that isn't too bad. (DC brushed motors with armatures that diameter spin up to 7K without too much extra work into them.) Thoughts?