350-400VDC vs 700-800VDC?

[cajunfj40]

Piotrsko:

Over on the DIYelectric site someone was commenting about some motor (honda?) has an inverter that doubled battery voltage to 500, so I would bet that 750 isn't unreasonable.

Toyota boosts their hybrid's battery pack to a DC Bus voltage of 500, for increased efficiency of the IPM motor at high RPM's. Apparently the efficiency gain and/or battery pack cost reduction is more than enough to offset the additional losses from the bidirectional DC-DC buck/boost converter between the DC Bus and the battery pack.

I still cant figure out a separation scheme for series batteries. based on my experiences, it is hard to not get full voltage leakage to somewhere. and high voltage high current stuff is $$$$$.

I don't discount that you've seen it, I just can't figure out how it happens. Note that I'm an ME, not an EE, so I may be looking at it all wrong. I know of things like capacative and inductive coupling, but don't really understand them. Any other sort of "leakage" I can think of implies a degraded or bypassed or otherwise faulty insulator. I'm having trouble figuring out how one can get full voltage leakage (or any voltage, for that matter) without at least two insulation faults in the otherwise isolated HV system. This isn't like the AC system in a building, where any voltage is *relative to earth ground* by design - so poke a wire at your peril. In an isolated EV HV system, that is not currently plugged into a charger, all points in the system should have zero volts *relative to earth ground*.

I guess it boils down to, which costs more: engineering a safe 720-800VDC EV system to raise the power of a single motor without excessive current/heating, or running dual motors to share the current at 360-400VDC - whether they parallel off a single inverter or have to use two separate ones. Either way, I hope to beat the ~$9550 for a 123kw peak/~56kw continuous output HPEVS system, consisting of an oil-cooled AC-35x2 (basically two AC-35 stators in one housing with two rotors on a common shaft) motor and dual water-cooled Curtis 144V/500A controllers. (oil pan 4 - this is the sealed regen-capable off-the-shelf solution I am trying to beat.) One Nissan Leaf motor can get me 80kW continuous - we don't know peak yet.

[redpoint5]

I have no expertise on this subject, but lots of interest in seeing someone give it a try!

There should be multiple safety systems in place to protect from these voltages. Even though I have been extremely attentive while handling supercapacitors, I have twice accidentally arc'd the pack with a brief but spectacular display of sparks... on just 13 volts.

The safety systems should allow a tired brain to make mistakes, forget things, and still remain safe.

How about making the double-voltage system and doing a series of increasing tests to verify all components are able to handle it? If some measured parameter approaches a limit, either engineer a solution, or abandon the idea and go dual motor / parallel batteries.

[cajunfj40]

Somebody did a higher-voltage DIY EV, in Australia!

Tuarn Brown's 1982 Suzuki Sierra SJ40

It's a 576VDC direct-to-transfercase AC Suzuki 4x4. Can do ~50mph at 4000RPM, which is apparently the limit for that motor/controller/voltage combination.

Built using industrial drive and motor. 6x 96V packs, tied together in a junction box by the drive to keep any single wire's potential as low as possible. Apparently has contactors in each 96V box to separate into a total of 12 48V modules. Can charge with 48V.

Started out as a 600VDC pack nominal, in two 300VDC strings, to keep the max voltage potentials outside the junction box basically the same as 240VAC mains (max peak of AC vs the DC). Dropped it to 576VDC due to not being able to use all the regen the drive was capable of. Voltage chosen to match the most common/least expensive industrial VFD's. I can't seem to find the thread where they went into the drive to get at the DC bus.

Huh, seems this person also at some point used a 240VAC-500VAC multitap transformer, plus a rectifier and some other bits, to feed voltage to the motor-side of the controller, and used it as a charger for the full 600VDC pack. Dropped it as being less efficient and more dangerous than charging at lower DC voltages to separate strings.

Red Suzi - The Australian Electric Vehicle Asn - Page 1

Very nice buildup - and exactly what I was thinking in terms of separating the pack, keeping the potential voltage across any given points as low as possible, etc. though the builder used common industrial boxes and conduits and such, rather than repurposed OEM bits.

576VDC at stock current levels ought to push a Leaf motor to ~118kw output without increasing heating overmuch. Now going to 200kw doesn't seem that much of an over-current push for short-term acceleration.

redpoint5 - as for build and test and rebuild and retest, well, I won't want to spend forever working on it. I will try to engineer it all up front. This Suzuki example - which passed Australia's somewhat stricter vehicle modification laws - seems to be as clean a setup as I can find. I can probably figure out how to start at a single pack voltage, then go to double pack voltage later, so long as I have two packs of similar condition so they work well in series.

[oil pan 4]

The industrial VFD I work with use up to 700vdc but that voltage is contained within the drive it's self and then only produces 480 volt 3 phase out to the motor.

[thingstodo]

Originally Posted by cajunfj40

Somebody did a higher-voltage DIY EV, in Australia!

It's a 576VDC direct-to-transfercase AC Suzuki 4x4. Can do ~50mph at 4000RPM, which is apparently the limit for that motor/controller/voltage combination.

I would expect this to be quite reliable - using off-the-shelf parts, staying within the design window for the individual parts.

It may be a bit heavier than it needs to be, so it may take a bit more power to move it. But if you are building a daily drive that you need to be reliable .. over-built with much room for error is GREAT!

Built using industrial drive and motor. 6x 96V packs, tied together in a junction box by the drive to keep any single wire's potential as low as possible. Apparently has contactors in each 96V box to separate into a total of 12 48V modules. Can charge with 48V.

13 contactors is a lot of contactors for the series string. Does that mean 24 contactors to put the packs in parallel? WOW.

I can't seem to find the thread where they went into the drive to get at the DC bus.

I think the DC bus is a set of terminals on the Variable Frequency Drive.

Here's the manual - page 51 shows DC+ and DC- terminals on the drive

http://206.72.118.208/legacy%20liter...n%20Manual.pdf

576VDC at stock current levels ought to push a Leaf motor to ~118kw output without increasing heating overmuch. Now going to 200kw doesn't seem that much of an over-current push for short-term acceleration.

I would expect so - seems reasonable to me

[cajunfj40]

oil pan 4:

The industrial VFD I work with use up to 700vdc but that voltage is contained within the drive it's self and then only produces 480 volt 3 phase out to the motor.

I think the one the Red Suzi uses is similar - it can't rev very high due to not being able to get enough voltage to match an increase in frequency. They described in the thread I linked that they later had the motor rewound and rewired to give them a lower design voltage. I don't understand it all, but it influenced how fast the motor could rev with a given DC bus voltage and had other beneficial effects on torque as well.

thingstodo:

I would expect this to be quite reliable - using off-the-shelf parts, staying within the design window for the individual parts.

It may be a bit heavier than it needs to be, so it may take a bit more power to move it. But if you are building a daily drive that you need to be reliable .. over-built with much room for error is GREAT!

Apparently the unit ran great, and wasn't terribly heavy - ~2500lbs, IIRC? It is in the thread somewhere. The motor itself wasn't very big or heavy - nominal 11kw at 415V/50hz. A lot of the motivation was "proof of concept" and getting real-world data to go with a *ton* of theoretical work that had been done in other threads on that forum. Further steps, most likely in other threads, were to go with a more powerful drive (higher current capability) and LiFePO4 type batteries, in a more aerodynamic chassis, though I think they ended up buying an iMiev instead and tweaked the Red Suzi more. The thread I linked was from 2008.

[QUOTE]13 contactors is a lot of contactors for the series string. Does that mean 24 contactors to put the packs in parallel? WOW.[\QUOTE]

Maybe? Not sure - posted total drop through all the contactors, cables, etc. in series was only ~2V tops. Peak current to the motor was 97A, so they are not large contactors.

I think the DC bus is a set of terminals on the Variable Frequency Drive.

Later in the thread - which I read after I posted - it was mentioned that this drive was meant to run off a common DC bus, so no hacking needed.

I would expect so - seems reasonable to me

I'd prefer not to push lots of excess current through the motor. I'll need to figure out some way to monitor rotor as well as stator and water jacket temperature to avoid cooking the rotor magnets and/or windings if I run a modified/aftermarket inverter that can really whack the power into it. One of the major reasons I am looking exclusively at brushless designs is to get the ability for near-continuous locked or really slow rotor torque without the fear of burning up the commutator. It won't be as high as 1000A into an 11" brushed DC motor would give, but the wider total speed range means the lower gear needed to multiply out that torque will go faster, likely meaning only a single gear reduction setup would be needed for good street performance, rather than having to shift. Low range is still available for off-road - either using the 2 speeds already present in the transfercase with a gear reduction box in front of it, or using a 2-speed transmission ahead of a transfercase modified to have a 3:1 or 4:1 or so low range gearset that is locked in - and better bearings to handle the continuous high-speed usage.

[MightyMirage]

800volts is extremely dangerous. it would be very hard for you too achieve this safely. understand that copper expands too 64,000 times its volume when its vaporized by an arc flash. this can easily maim you, and easily kill you.

i suggest sticking to lower voltages, because one mistake at this level could easily lead you too being stuck in a 6v EV for the remainder of your days. (powerchair)

[cajunfj40]

MightyMirage:

Thank you for your reply - caution is merited here.

Apologies if this comes across as a bit snippy: I understand that it is dangerous, I'm looking for more detail on that danger. There are plenty of responses in this thread and others already that say "high voltage is dangerous". So is gasoline, and people blithely handle pumping equipment spewing gallons-per-minute of the stuff every time they fill up their car. The amperage available in an EV battery pack can already cause flash-arc damage or similar effects at much lower voltages - drop a copper bus-bar or a wrench on a battery pack and you're going to have a bad day as the dead-short current capability of modern batteries throws a plasma party.

I'm primarily interested in whether there is a difference in the danger other than the ability to jump a larger gap and sustain an arc over said larger gap.

The referenced "Red Suzi" thread has some really good detail on minimizing the potential voltage between any two nearby parts, and thus reducing the chance of an arc flash incident. That builder was attempting to keep the DC voltage potential in any given battery box at 24 or 48 volts, to keep it in the "Safety Extra Low Voltage" range below 25VAC/60VDC (though not explicitly stated as such, that was the effect) where no contact protection is required (IEC 60449). Contact protection is required between 25-50VAC and 60-120VDC, per the same standard, but it is still classed as "Extra Low Voltage Class III". It appears that anything above 50VAC/120VDC goes to "Low Voltage Class II", and that rating and protection class are good up to 1500VDC/1000VAC (EN 50110). I'd make sure I'd meet or exceed any contact protection needs, insulation needs, etc.

Basically, the reason for the question is that the common 144VDC DIY battery pack size, and common OEM 300-400VDC battery pack size are already in the "Dangerous - special gear required" range - and the exact same standards apply for the full range of 120VDC to 1500VDC. I want to know what the actual additional hazards are when moving from 350-400VDC to 700-800VDC, given that said voltage is still within the same hazard class per international standards. I can read technical standards and documents, but I don't know about all of them - if you can point to reports showing a "danger curve" or similar WRT the voltage in a system, I'd very much appreciate it. All I can find are the aforementioned standards that are biased towards grid-connected wiring, and some Arc Flash Potential calculations that assume 25,000A available fault current. I won't have that much. Maybe 2500A, more likely 1500A or less, since I'll likely be using 50-80AH batteries.

Remember also that a properly designed EV battery system will never see full voltage potential anywhere in the HV wiring system when compared to the frame or body panels or 12v wiring system of the vehicle - at least, it won't if there is only 1 insulation fault. The only places you can get the full potential are between the two ends of the battery pack string and associated HV wiring. Have those opposite potential connections enter a control box at opposite ends and the potential for danger outside that control box is minimized. That, as far as I can tell, is the only additional thing to worry about - wider separation between parts. I'd minimize the chance of a short across the pack at any voltage anyway, so it isn't that much more of a hassle.

[freebeard]

Originally Posted by MightyMirage

i suggest sticking to lower voltages...

I suggest fewer 'o's in your 'too's.

cajunfj40 -- It's an excellent question and I support your asking it. You're looking for the known unknowns and the unknown unknowns, pace Rumsfeld.

I've always wondered about electric boats. Somehow they manage while immersed in an electrical conductor. Jack Rickard, on EVTV, compared the shore line for an aircraft carrier to a Tesla Supercharger cable. Pretty much the same thing.

[cajunfj40]

cajunfj40 -- It's an excellent question and I support your asking it. You're looking for the known unknowns and the unknown unknowns, pace Rumsfeld.

Thanks, freebeard. I don't know what I don't know, so I ask, especially when research comes up short and I hit things like "50-1000VAC and 120-1500VDC are Low Voltage" in *international safety standards documents*.

I've always wondered about electric boats. Somehow they manage while immersed in an electrical conductor. Jack Rickard, on EVTV, compared the shore line for an aircraft carrier to a Tesla Supercharger cable. Pretty much the same thing.

Battery-electric boats have the same protections as battery-electric vehicles for other mediums: the high-current main propulsion circuit is isolated from the hull and other electrical circuits, so that any current leakage has to be due to at least 2 insulation faults. The current-carrying conductors are generally not touching the water, either, so there's nothing for the water to conduct. Of course, if you fill the battery compartment or motor compartment with water and it gets between terminals, you're going to see some current drain. If saltwater, quite a bit of it, and accompanying hydrogen/oxygen generation and explosion hazard. Freshwater (ie, not seawater) actually isn't all that great a conductor - it is the impurities that do the conducting. Ultra-pure DI water is used as a direct-contact-with-conductor coolant for laser power supplies. When it trips out for current leakage, the conductivity of the water's gone up too high and you have to drain and replace.

For ship to shore cables, you have IP-ratings for the connectors, proper insulation and environmental ratings for the cable itself, corrosion-resistant terminals, over-current and ground-fault protection circuits (commonly GFI's), etc. A GFI for an EV would probably be a good idea if you have a properly built battery box and you are running greater than 120VDC, though you might drive yourself batty chasing down all the current leaks after a few salt-road winters...

I would plan on IP-65+ or NEMA type 6+ or similar liquid-tight style conduit, glands and boxes for all wiring. UL listing for the common liquid-tight conduit is 600V or less, except in neon signs where 1000V is allowed. There may be higher ratings available. 600V might be "enough" of a boost over 350-400V to get where I want, though. that's ~417 amps for 200kw power output from an 80% efficient motor/controller setup. UL may not be the "correct" rating to go by for a car, though - they are looking from a building safety standpoint generally.