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?

No idea myself, but I need to learn. There is this:

http://ecomodder.com/forum/showthrea...ors-33661.html

Three pages of posts by oil pan 4, EVmetro and thingstodo. Check out EVmetro's build threads; he does really high-quality work.

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.

Are the wound rotors brushless?

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.

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.

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.

other than the propensity for arc flash at unexpected times, I see a chance of generating Gamma rays at 1 KV. shielding mitigates most of that, but expensive and heavy.

The other problem I see is physically maintaining insulation. lots of common and available stuff just isn't feasible above 600v. Hv stuff is expensive if you don't have space.

OTOH running 2 separate packs until just at the controller might work, kinda. isolating the 2 packs is an interesting thought puzzle. and extraneous leakage is just plain ugly.

oil pan 4:
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.

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.

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.

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".

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.

Piotrsko:

Whoops, didn't see yours until my previous posted.

Gamma, really? I thought x-rays came first. Odd. Source? If I can make Gamma rays with 1kV, the Mad Engineer wants to know...

This is a very legit concern - if I can't get parts without paying a hefty "high voltage" premium, then the whole thing isn't worth it. I'm trying to cut costs by re-using existing stuff, not give myself more expensive problems.

A single pack already needs to be isolated from ground, so I don't see isolating a second pack as any harder. What extra issues need to be figured out for a series connection over and above running two packs in parallel? Now, properly disconnecting them from each other to allow charging with available OEM chargers is a different problem. I don't really want to cover new ground there, if I can avoid it. Series-parallel battery switching has been done with relays, but I don't believe it has been done at these voltage levels.

Sounds to me like the trade-off is thinner wires with thicker insulation.

What vehicle is the 'one-off custom'? An FJ40? You could use two single-speed MGR instead of over-stressing one.

freebeard
That seems to be much of it, at least for the full voltage wires. Still need to figure out the insulation rating on the actual motor windings, though.

Yes, an FJ-40. I'm looking at using a Leaf motor because it will do 80kw continuous, based on ARNL(?) testing showing that rotor temperature seems to top out at 135C when driven at 7,000rpm at that power level. If it turns out that the high voltage is just is too much hassle, I may go the two-parallel-systems approach. That means two motors, but I'm not trying to run double the current through a stock motor. Maybe one of the "brain replacement" projects for OEM inverters will be available by the time I can do this build, which will lower the overall cost a bit.

I'm sticking with a transfercase and gearbox at the moment. Motors aren't quite there yet in power-density plus speed range for me to stick 1 per corner or 1 per axle and still have both rock-climbing ability and freeway speed capability without changing gears. With 35" tires, I need 576 RPM at 20kw continuous per wheel to do 60mph. To climb rock walls, I need 3250 ft-lbs per wheel (assumes full 6500 ft-lbs driveline torque in 1st-low with stock engine/gearing, and 2 tires in contact with the obstacle being climbed). Gimme a motor that can do that, at less than 100lbs per motor, and less than $2000 per motor/inverter set, and I'll seriously consider wires and cooling lines instead of driveshafts.

DC jumps gaps much better than AC.
Higher voltage DC will also establish an arc and will maintain the arc until the power is turned off. When dealing with batteries this presents an obvious problem.

I have seen double voltage starting only on direct drive. But I have seen inverter duty motors that have the option for parallel or double voltage starting.
Double voltage starting on inverter motors is out there but I have not seen it.

My DC stick welder that I built runs up to 125VDC open current. It can throw a pretty good arc.

Also most wire is only rated to 600v.

For anything up to around 144vdc I would just use a normal wrench wrapped with electric tape and welding protective gear for making the energized connections.
For 100s upon 100s of volts NFP70 arc flash stuff should be uses which is pretty much like wearing a bomb disposal set.

If I were going to build an electric vehicle I would stay between 48 and 144vdc since it is relatively easy to work with and all the parts are off the shelf.

oops didn't mean gamma rays.

look up typical magnet wire properties on Google. FWIW, I believe the higher voltage motors just use additional coats of varnish after winding.

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. You can also get motors rated for 408 vac which is almost 600 peak to peak. Some VFD's will run on DC, but make poor car controllers.

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 $$$$$.

Piotrsko:
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 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.

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.

Found one at 576VDC!
 

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.

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 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!

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

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


I would expect so - seems reasonable to me :thumbup:

oil pan 4:
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:
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.

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'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.

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)

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.

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.

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*.

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.

the classification between 120v and 900v May be the same on the internet but your only seeing half the picture. potential energy is what counts not a textbook classification. i can tell you, nobody takes a 500v+ panel lightly whatsoever. green shields, cotton clothes with outer blast garments, leather covered in rubber gloves are the basics.

the potential energy built up in a 1500amp system at 800vdc is a freight train of pain. i know you don't like hearing this but truly stay away from these voltages unless you are certified. I've been doing high voltage electrical work for ten years, and your asking, on the internet,how to safely wire, insulate, and operate something that can kill you from 5 feet away...

Google search the requirements for entering a 10 calorie panel and ask yourself if you really think it's worth it still, because after all, i do believe this is where you would fall.

if you have a specific question ide gladly try and answer it for you, though.

:rolleyes:

MightyMirage, thanks again for commenting. I'll be responding to each bit below. Apologies for the length, I did try to edit it down!

Well, I wouldn't suggest anyone take a 500v+ panel lightly, nor myself. My point of them being "the same on the internet" (and yes, I am self-aware enough to know that where I'm coming from can look quite silly from an expert's perspective - trust me, I have had similar thoughts in other fields in which I'm more experienced than the commentor I'm reading!) is that I would need to apply the appropriate protective measures and isolation requirements for a 1500VDC system - and that DIYers who have 120VDC or greater battery packs who wish to follow the standards I've found *would need to do the same*. That and, if all I can find is that I need 1500V capable safety equipment, and I find that that equipment makes it difficult to impossible to do the work, I'll likely pick a lower voltage. Unfortunately, under the standards I've found to date, that sticks me under 120VDC. (or lower, see below) There's got to be some other intermediate ratings, or how do we get safe 144VDC DIY systems, let alone OEM 288-402VDC systems? AC forklifts are 80V to stay under certain codes, and previous DC forklifts were lower for similar reasons (I think the codes have changed in the interim).

I'm not ready to wire it yet, as I know I don't know enough. (And I don't have the budget yet, either.) This is why I ask questions. What's the difference in danger between a 200V/6000A capable system and an 800V/1500A capable system? Same potential energy, just 4 strings of 1500A short-circuit-capable batteries in parallel, rather than one series string. I'll have the same potential energy in the vehicle whatever voltage I pick - I need kwh for range.

Using 25 used 8V Leaf cells is 200V, each cell is ~62Ah rated, ~50Ah useable, so 10kwh. I want ~40kwh, so 4 strings. I can connect in parallel or series, but all those cells are there. Roughly 1.1 gallons gasoline equivalent, requires 2 wrecked Leaf battery packs. ~25C doesn't seem out of line for dead-short fault current on cells rated at 4-6C continuous.

As for certifications, I have yet to find the correct certs required to work safely on electric buses or the standards to which the internal components/shields/etc. have to be rated to in order to be worked on by an average garage mechanic, which are the closest parallel to what I am contemplating. They are available with 700-800VDC systems, and likely have quite a bit more amperage available - weight takes current to move.

Interesting search - once I weed out all the diet crap I find a lot of Arc Blast information, mostly from/about NFPA 70E. It looks like a 10 calorie panel would fall into the Hazard/Risk Category 3, requiring a multilayer FR coverall rated at 25 cal/cm^2 or better. Class 3 is, well, too high for hobby work.

I found a nice table on Approach Boundaries to Live Parts for Shock Protection that also appears to be geared to protection against Arc Flash, NFPA 70E table 130.2(C). In that table there *is* a more gradual set of steps. From 50-300VAC the chart sets the Limited Approach (have a trained person with you) Boundary at 3ft6in for a fixed, live circuit component. The Restricted Approach (be a trained person) and Prohibited Approach (is what it says on the tin - keep out) boundaries are just "Avoid Contact". Next step up, 301-750VAC is similar, but Restricted Approach is 1 foot, and Prohibited Approach is 1 inch. The next jump is good from 751VAC up to 15KVAC. This doesn't line up with the previous standards I found (no surprise - it is a patchwork out there...) and it sets the "not specified" boundary at 50VAC. That's pretty low.

I'd prefer not to have to design to 15,000V, so this sets an upper limit of 750V at full charge/peak regen. Hmm, it seems NFPA 70E-2012 Table 130.4(C)(b) covers DC, and pushes the 1 foot Restricted Approach Boundary up to include 1000VDC. Still no reason to go above 750VDC, though, to limit my AC voltage capability past the inverter. This also possibly shows why forklifts are the voltage they are, in that older charts were at 50VDC for "not specified" and the newer one I found pushes that up to 100VDC. That would track with an 80VDC AC forklift, as the post-inverter voltages ought to be 50VAC or less. This is still pretty low - I've seen no discussion about proper safety gear for working on common over-100VDC pack DIY EV conversions, and all sorts of pictures where if you open the hood you see bare battery connections, or bare controller connections, etc. I've never seen mention of an arc flash hood or coverall. This isn't to say I don't think it needed, just that the awareness isn't out there about it. Like pictures of people welding in flip-flops (ouch!).

Hmm, are there any rough guidelines as to how to get a DIY EV system down into the Class 1 (or lower) Hazard/Risk category, in terms of voltage and current capability, or am I committed to at least Class 2 at the common 96-144VDC level and the short-circuit capability of modern LiFePO4 batteries of sufficient capacity for acceptable range/acceleration? I'm shooting for 100-200kW acceleration capability and ~80kw continuous. (a Leaf motor is capable of 80kW continuous without overheating, by way of comparison). Class 1 PPE is pretty reasonable - 12.8oz denim or thicker is "good enough" for many organizatons, though a coverall labeled with the appropriate arc rating would be cheap insurance. Safety glasses are needed anyway for auto work, and it doesn't take much to add a pair of rubber gloves and some insulated tools for the electrical work. If I have to wear an arc hood (Class 2 PPE), or insist that auto mechanics do so, that would likely be an effective barrier to my implementing a Class 2 Hazard/Risk rated installation. Can proper enclosures and de-energizing procedures lower the Hazard/Risk category? There's got to be some way - Nissan mechanics don't wear arc flash hoods when working on Nissan Leafs.

Thank you for your willingness to answer questions! I hope I don't exhaust said willingness. Part of the insistence on finding the correct codes/standards/etc. for the contemplated voltages is so that I can still take the completed vehicle to a garage for routine non-ev maintenance work without exposing those workers to a hazard they are not trained/equipped to handle.

See, I want to do it right, and a big part of that is doing it safely, and I have trouble letting go of an idea if I can't understand *why* it isn't safe. (NB - doesn't mean I'll do it if I don't understand, just that I'll keep digging until I do understand - or understand that the time required to understand is greater than I am willing to put in - and can then make an informed decision as to whether to proceed.)

Books/internet are not real life, yes - but they are the collected wisdom of the experts that have gone before, and provide valuable background information so I can go get practical knowledge of the appropriate type - including certification if necessary - and/or hire out the bits I cannot do safely to someone who can, and/or find out that the requirements make it budget/time prohibitive to move forward.

Thanks again, this is very useful info!

On a somewhat related note, this has got me wondering about the time as an intern that I got to watch a 15KV substation fed by two separate power grids (the 4 power conduits running from this substation to the plant I interned at were probably 6-8" in diameter) get shut down by the electricians. I had safety glasses, maybe a hardhat. I don't recall any arc flash type gear - everyone else had safety glasses, gloves, maybe a hardhat. I was close enough to see the details of how they used a drill motor powered by an isolated DC system to crank open each set of contacts (in a closed cabinet, motor attached on outside) in the correct sequence. They were safety interlocked so you couldn't crank them down out of sequence without having to deliberately break something first. From your comments, I probably should have been kept much further away, and the rest of the folks there probably should have been wearing a lot more gear...

Average mechanics rarely work on anything higher than 24volt and pretty much never work on anything over 48 volts.

Hello oil pan 4,

That is generally true, insofar as the vast majority of cars on the road that an average mechanic is likely to see are plain ICE types. The number of hybrids are growing, though, and my independent mechanic says there are a few in his client base already. My point is that the car's systems need to be safe enough that an average mechanic can do average under-hood and under-chassis service work - to the brake system, the steering system, the suspension system, etc. - without being at an unknown/above average risk. I seriously doubt that any OEM would let a car out on the road that required full arc-flash safety gear for routine maintenance - I aim not to, either. How do they make it safe? Same question for the higher voltage buses.

I don't think I'd be able to convince even my good, independent mechanic to do any work directly on the high-voltage portions of any DIY system, and I don't aim to. It'll be on me to keep those parts working, or a local EV conversion shop/garage/specialist if I can find one.

From what little I have seen on the hybrid systems the manufactures build go way out of their way to make it extra hard to screw up.
Yeah once you make a really high voltage setup you are not going to find any one to work on it.
If you built a standard 144v system some place like what EVmetro has might work on it. But they are pretty rare. Don't know if they would mess with unusually high voltages.

To respond to the original question:

- higher voltage makes leakage current more of a concern. I have yet to find a frame leakage or ground fault system that I would put in a car. I plan to install 100 Kilo-ohm resistors and contactors on either end of my Leaf battery pack and measure for current across a 1K resistor. That should give me about 4V if there is an un-intentional connection to the frame while I am running the test. Much less if there is not a solid connection to the frame.

One of the links below shows how much current is uncomfortable through to damaging for the human body. My goal is to use any reasonable means to reduce the likelihood of a shock, or the severity of a shock if it is not reasonable to avoid it completely.


For AC, I think it's the same classification from 50 VAC to 1000 VAC - low voltage

For DC, there appears to be no low voltage, medium voltage, and high voltage classifications similar to AC. Low voltage is mentioned as 48V and below (now it seems like 100V and below), but since they discuss mostly lead-acid ... it's more like 55V charged and almost 60V for the floating charge.

125VDC, which is what a lot of electrical switch gear uses in substations, does not get described as a classification in what I have read. Most of the people who deal with this voltage work for power companies ... and they don't have to follow electrical code for some reason ... maybe they don't want their systems to have arc flash categories.

This document, listing just the changes for DC and arc flash, sets the shock rating at 100 VDC. I don't remember this one, I must admit.

http://www.ieee-pes.org/presentations/gm2014/2756.pdf

There are some guidelines for calculating arc flash on DC, but batteries are not common in industry above 125 VDC. The DC buss on VFDs or ASDs, DC drives ... plus larger installations of solar arrays. I have asked for some rules of thumb and our consultants have a few. And as the document above mentions, they are quite conservative.

- use contactors to isolate packs and sources
- use fuses to limit arc flash risk
- fuses should trigger in 5 cycles, or about 1/10 of a second, for a large overload (10X expected current)
- review the fuse curves whenever anything is changed on the system to make sure they are still going to protect you

We don't do arc flash calculations on any AC source of 208V three phase below 75 KVa, since it does not sustain an arc and the transformers involved don't have the thousands of amps (KA) that appear to be a big part of the energy in an arc flash.

DC is a different fish - the voltage does not cross 0V 60 times per second so once an arc is established it does not extinguish as quickly without outside help - from a fuse, or a contactor, or a breaker ... or vaporized copper.

I would argue that amps are the enemy, but voltage causes amps to flow. Perhaps I am splitting hairs.

At 8+ calories, you missed the bella clava and the face shield unless that's what 'green shields' means. And I think the leather is on the outside to protect the rubber insulation on the gloves from damage.

1500A for an intentional load on a battery system is quite large. Even at 50C on a lithium cobalt battery chemistry - you'd need 30 a-h cells. And about 200 of them to reach 800V. A small fortune indeed. Easily controlled by a properly sized fuse.

However, 1500A into a short circuit is not all that much. If you expect 1500A on your system for 5 seconds (I can't imagine the speed you'd be going after 5 seconds of acceleration at 1500 amps), have the fuse trigger (melt and clear the fault) at 1500 amps for .. 7 or 8 seconds,

It is *FAR* easier to get 1500+ amps from a 144V lithium iron pack (10C is only 150 a-h cells), or parallel packs of cells, or any of a host of lithium chemistries that people are using. The amps give you the heat, which gives you the blast. Voltage gives you the safe distance between un-insulated conductors or terminals.

Perhaps a bit dramatic, but a warning that should be listened to and protected against.

Here is another reference from industry

http://www.battcon.com/PapersFinal20...rc%20Flash.pdf

From what I have read, and what I have experienced:
- size your fuses well. Make sure that the fuses will interrupt the voltages you are using. And make sure that your pack can supply enough current to trigger the fuse element in a reasonable time. Like the 1/10 of a second I mentioned earlier. A 1000 amp fuse is useless if your used Leaf pack can only put out 800 amps!
- split your pack into lower voltages. I thought 48V was reasonable, but it appears that 100V is OK as well. The separate packs connect in series when you turn the key or start the charger. Split the pack segments with contactors.
- use vacuum contactors, rated for the TOTAL voltage you are using, + 25%. If you are a paranoid (like I am) use one on the positive pack and one on the negative pack plus one between each pack segment. Make sure that the main contactors both open. I'd like the contactors that split the packs to verify open as well but I'm not sure how to measure that one. Perhaps that will be part of the leak detection or Ground fault.
- I'd add a DC breaker as well. It's harder to find these at higher voltages, but they exist. A 300A, 125V DC breaker on the battery side will let the controller do 1000 amps of motor current for a 5 second acceleration

There have been very few tests of DC for arc flash. The two that I've seen video of (I don't have links) were based on NO FUSES since they were for 125 VDC in a substation. With no fuses and no other protection, the flash and the bang are impressive. So USE FUSES! In my opinion, that is what will keep you from death, or from skin burns bad enough that you'll wish you were dead.

I'm a bit worried about water-proofing where people normally put battery packs. I have opted to put the batteries in the cabin with me, replacing the back seat. There is a sturdy frame around the batteries, a lexan cover to keep conductive stuff from falling inside, etc. But my my provincial insurance rep (the last one I asked) mentioned that I would have to seal the battery case and vent it outside the cabin. That would be inconvenient, and would effectively make the batteries the same temperature as outside ... which means no driving the car in winter. When I get it done, I will put the car in front of a vehicle inspector and get a written list of things they want changed ... and I hope I can convince them that the venting thing is not required since the electrolyte is quite non-toxic. If the batteries start to vent, I need to get out in a hurry ... and whether they are vented internal or external to the car will not matter much.

Like redpoint5, I don't have much expertise, but a lot of interest in the subject.

First I'd like to thank cajunfj40 for this EXTREMELY valuable and interesting thread. :thumbup:
I'd also like to thank thingstodo and MightyMirage for their expertise, experience, and contributions on this topic.

My specific interest in this topic is developing a system that uses multiple Toyota MGR's, or possibly the Prius motors. The new versions appear to be designed for higher voltages in about 2010 ( and have been tested by ORNL ) In these tests, the bus voltage (DC link voltage) was boosted to 650V at 5kHz, NOT using the boost converter. For the Prius, the BEMF was just over 500VRMS at 14000 rpm. This would imply a peak internal voltage of over 700V. With field weakening, ORNL was able to test the motor up to 13,000 rpm with a 650V bus. When the bus voltage was reduced to 500VDC, they were only able to run to motor up to 8000 rpm, and 5000 rpm at 225VDC.

For my project, I'd like to spin the motors as fast as ORNL did, - not limited by a low bus voltage - maybe sanity - LOL! :p

Because I don't know what I'm doing, I always spec components with significantly higher voltage ratings than the one I'm actually using. When one looks at a $$/kW perspective, generally higher voltage (lower current) components are lighter and less expensive.

One mystery to me is "why do certain plastics have significantly better voltage ratings as insulators than others?" For example, you can get big cables for cars, where they can handle hundreds of amps, but they are only rated for 60V. :( You can then go to home depot and get a same guage wire with similar thickness insulation, and it will be rated for 600V.

- E*clipse

I don't feel qualified to comment on this topic. Materials science is not a strong point for me. I do know that the lower voltage rated insulation on the cables that I deal with is quite a bit easier to cut with a knife than the higher rated insulation is. I would assume that the lower rated insulation is also cheaper to produce. It makes sense to me that the manufacturers would use the least expensive product that does the job.

When our electricians are handling 5000V rated cable, or 15000V rated cable, the knives that they use to strip the insulation look positively wicked. It also appears that the insulation is less flexible.

I was recently using some "anti corona" or something cable that was very flexible, and used in my job's transformers. It was stranded 11 gauge, and had a working voltage of 5000v I think. I also used some 15,000v wire. It felt flexible, but when I would strip the black insulation, it was like it used to be stranded, but looked welded together. Strange. Oh well. I don't know the cost of it, but it was off of a 5000 foot roll I think. I would look to companies that make components for PDUs for high voltage parts. (power distribution units). My company recently made an on/off switch that's rated for like 100,000v. There's a whole world out there where high voltage is no impediment. So, I know you could reliably get a 800v or whatever controller safely working in a car.

Wow, this thread took off while I was away! Lots of good info here, thanks!

Glad to be getting a good conversation going!

I'd like to echo this thanks as well.

I found a bit more info on the 7.6V/60Ah (2S2P) LiMn2O4 with LiNiO2 Leaf battery modules. They offer 240A continuous, 540A pulse discharge rate. (per Hybrid Auto Center's website). From the Nissan Leaf First Responders Guide, I find 403.2V as the max pack voltage. (48 modules at 8.4V each). I can't find the dead-short current capacity of a module or pack, but it would likely be a bit higher than 540A. What would those more educated in lithium battery chemistry guess at here? Volt modules are rated a bit lower, being similar chemistry but only 45Ah per 1S3P "blade".

I don't know about the Leaf, but Spark EV used A123 batteries, and someone recently sent me a 95v module of them, and they can do 1500 amp.