Really? Which cars? Not Teslas as their packs are pretty much all 350v or 400v, no contactor to split them in half.
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Lets work out the Tesla Semi-Truck Technical Specs
- Thread starter lnpurnell
- Start date
Really? Which cars? Not Teslas as their packs are pretty much all 350v or 400v, no contactor to split them in half.
Are not. Before normal charging voltage and current is applied an insulation and current leak test is performed.
This test is performed at safe parameters. If something happens during charging, then charging just stops.
Therefore, due to these two failsafes, surface contamination is not dangerous.
Also I wouldn't agree on "all conductors" are exposed. Chademo, while mated, actually is sealed (I think IP66).
While not mated I can lick the connector, it is not energized (HV pins)
.People can't stop thinking charging cable does not have a dumb grid electricity in it. It's all HEAVILY monitored.
And piezo discharge is safe not only because it is limited current, but also limited time. Though yes.
Of course it was an example to stimulate some brains to think a little more
Actually, we have problems with ChaDeMo plugs in my country. We have a lot of bad weather and due to dew forming on
the plug, charging sessions often do not start. I've been in that situation many times. I literally have to clean/wipe the plug.
This is a good example how hard it is to kill yourself with "stuff" on the cable/plug. And 800V won't help me accomplish that.
Ahh s**t, it was manual disconnect and/or fuse, not contactor that operated all the time.
True, while mated they are not, before they are, so there is a surface path from the exposed conductor. Thinking rain/ snow or salt fog.
And this would be worse with higher voltage. All clearance/ creepage distances would need to increase along with contactor gap/ design.
Overall, I agree it would be hard to get shocked from a supercharger since you would to become a path between both conductors (batteries and charger are not earth referenced).
Important thing is that nobody reading this thread would actually believe they are in any way in higher danger when operating a 800V CCS station compared to regular 400V one. This is how stupid myths are born - some mildly educated hunks babbling about theoretical dangers and some Tesla-hating website picking this poop up as pure gold
Plugs here can have snow/salt fog in them. Like I said, they don't work. Same story with 800V. Safety tests are done at higher voltage anyway.
Plugs here can have snow/salt fog in them. Like I said, they don't work. Same story with 800V. Safety tests are done at higher voltage anyway.
I think I figured out why Tesla is offering a million mile warranty. I believe it is so they can use the semi battery for arbitrage and to move excess energy between locations customers.
The warranty overcomes the potential customer objection of battery degradation.
Customer buys truck. Customer signs long term PPA. Tesla buys, sells and moves energy as a secondary business to keeping the truck adequately powered. This is at no additional cost beyond software development and needing V2G in the semi and charger.
This is a debugged remake of Musk's original solarcity grand strategy.
The warranty overcomes the potential customer objection of battery degradation.
Customer buys truck. Customer signs long term PPA. Tesla buys, sells and moves energy as a secondary business to keeping the truck adequately powered. This is at no additional cost beyond software development and needing V2G in the semi and charger.
This is a debugged remake of Musk's original solarcity grand strategy.
Maybe for quick charging special drive over stations could be developed that are hydraulically actuated with big matching pins and sockets? No human interaction with the couplers at all and huge power transmission.
I'm going to guess that the utilization rate of non-OTR semi is 20% at most. Lowering the cost of running a semi a bit does not mean that McDonald's starts accepting deliveries at 1 am.
Musk/Solarcity has probably wanted to consolidate powerpacks for grid services since the beginning. That has proved impractical for a variety of reasons. But with Tesla semi they have giant batteries paid for by commercial customers. Many of these batteries are going to be plugged in for 12 hours weekdays and all weekend.
Any meaningful battery that is going to be plugged in longer than needed for its next scheduled duty, on a connection with menaingful throughput rating, of course can support grid fluctuations.
But only if the battery can commence its next duty with, say, 50 or 70% SOC when it's being called upon for primary duty. And if a battery is never needed to be more than a given SOC, it's just needlessly big which constitutes a waste of resources. But even 5% of reverse for the grid, having millions of big batteries spread over the world offering a bit of backup, can prove worth it.
The key word here is "never". A fleets battery capacity is going to be sized to the highest energy utilization day plus some reserve. That leaves on average substantial extra capacity, especially considering seasonality. Trucks running for Walmart in snow states are going to have substantial extra capacity in summer. Tesla solar dedicated to charging is also going to have excess. Than there are weekends.
The key is scheduling and routing software for truck management to meet the customers requirement.
If you can accept a 10 minute charge stop on days when you run higher on consumption, that takes away need for the reserve you mentioned. To be used only a few times per year, on cold days or with unusually strong head winds.
Weekend are a good point, but if I had a large fleet to manage, I'd make sure at least the Tesla was driving for me somewhere, as it would save cost.
I think that would be an easy fix compared to manhandling huge cables and sockets. It's possible to also have the receivers built into the front or sides. Special covered plugs through the front bumpers could be a solution as long as they retract into a position that could be driven over or beside when done.
Reading all these posts about the infrastructure required to run trucks it's easy to see the costs of operation parallelling or exceeding current petroleum powered equipment. And this is just for trucks, they can travel to charging stations, imagine remote stationed equipment where you have to take the energy to them...
Support for heavy cables/ objects is solved problem. See seat/ tire/ dash installation in factories. Electric or spring counterbalance is all that is needed.
Megacharagers can be time shared. Local overnight charging only requires a suitable electrical connection if the truck has a charger.
Remote, non-self powered equipment could be an issue, unless they create an extreme range, lower net payload option.
One Powerpack gives an additional 210kWh @3600 lbs. So double the range for worst case ~15k pounds, more likely <10k for purpose built pack.
Socket on the side is easier to manually clean from snow and ice when needed. Charging snake could handle heavy cables:
800 V is safe when everything goes as planned. If not, it is much more dangerous than 400 V. So it should be avoided if possible:
1 MW charger 400 V -> 2.5 kA.
Copper cable 5 cm wide 1 cm thick (easier to bend in one direction). For 1 m cable resistance = 16.78 / (0.01 * 0.05) = 33560 nΩ
Power loss P=I*I*R = 2.5 * 2.5 * 33.560 = 210 W
+ & - cables, length 3 m -> 1260 W power loss. About 0.1 % of total power. Cooling is needed.
1 m would weight 0.05 * 0.01 * 8960 = 4.48 kg + & - cables, length 3 m -> 27 kg Spring support would be enough.
Tesla semi has separate circuit for each battery. So split cable to four separate cables with separate plugs. Spring support is not needed.
I have explained it. We don't live in binary world. There are more than two situations: 1 No connection to power line, 2 Zero resistance connection to power line.
Read Electric shock - Wikipedia and stop producing BS.
"More than 30 mA of AC or 300 – 500 mA of DC at high voltage can cause fibrillation."
"If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs."
That means: Skin changes from being insulator to conductor. That happens on other materials also.
"Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms".
Page has a table for human resistances for different voltages. Yes, in this case resistance depends on voltage! Table is for AC, DC is less dangerous. Resistance values should be roughly same. For 50% of people resistance with 220 V is 1350 ohm. Deadly current for DC is 300 mA. 1350 ohm * 0.3 a = 405 V is needed push deadly current trough human body. It is not an exact result, because resistance for 400 V is lower. Based on this some humans would survive direct connection with 400 VDC. Again AC is 10* more DANGEROUS!
Thanks for the calculations. I ran 250 mcm welding cable in a 4 pack/1.6kWh/mile scenario (1.28 MW charger) and get about 2.1kW of loss for a 3 meter cable. So liquid cooling would be reasonable. Insulated cable weight of 82 lbs/ 27kg of which half would be inherterly supported by the station.
Regarding the voltage discussion. Higher voltage is typically more dangerous, but we need to look at the system as a whole.
The only way to be exposed to the potential is to make contact with both cables (a double fault). If the megacharger has shielded cables and guard/ shield rings on the connectors, it will know instantly if there is leakage from either of the main conductors (a single fault). So it can shutdown at the first sign of trouble, long before people are exposed.
Current electronics also check for wiring faults to chassis. As long as the vehicle blows its pyro fuse (crash case) and opens the contactors, pack voltage is not a concern. Unless the pack is breached, in which case each {max safe fire fighting voltage} section would need pyro fused.
Edit: early submit click.
I don't think anyone is arguing that with enough precautions an 800V system can't be made safe enough here - safer than refueling a car at a gas station, for instance.
The argument we've been having is whether an 800V system is inherently more dangerous than a 400V system with the same precautions, which I thought was self evident but one party refuses to accept so far.
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