350-400VDC vs 700-800VDC?

[MightyMirage]

Originally Posted by cajunfj40

MightyMirage:

Thank you for your reply - caution is merited here.

.

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.

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.

Originally Posted by freebeard

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

] g.

[cajunfj40]

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

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.

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).

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...

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.

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.

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.

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

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...

[oil pan 4]

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

[cajunfj40]

Originally Posted by oil pan 4

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.

[oil pan 4]

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.

[thingstodo]

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.

Originally Posted by MightyMirage

the classification between 120v and 900v May be the same on the internet but your only seeing half the picture.

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.

potential energy is what counts not a textbook classification.

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

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.

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.

the potential energy built up in a 1500amp system at 800vdc is a freight train of pain.

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.

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...

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

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.

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.

[e*clipse]

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.
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!

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

[thingstodo]

Originally Posted by e*clipse

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.

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.

[MPaulHolmes]

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.

[cajunfj40]

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

Originally posted by e*clipse: First I'd like to thank cajunfj40 for this EXTREMELY valuable and interesting thread.

Glad to be getting a good conversation going!

I'd also like to thank thingstodo and MightyMirage for their expertise, experience, and contributions on this topic.

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".