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

cajunfj40 · 06-17-2016, 01:05 PM

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.

06-17-2016, 01:05 PM	#18 (permalink)
cajunfj40 Lurking Eco-wall-o-texter Join Date: Dec 2015 Location: MPLS, MN area Posts: 128 Thanks: 0 Thanked 65 Times in 45 Posts	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.