If customers want the savings (and why wouldn't they?), and are soon going to bid on every electric truck they can get their hands on, legacy truck builders will have no choice but to jump onto that market. Some already are. Just, Tesla makes a lot of noise about a product they intent to launch 3-4 years ahead of time. Many other brands only show a production sample at a car show, and the next day open doors for immediate deliveries. The competition may well have started their own development the first time Tesla hinted theirs, or even before that. It's not the most difficult math to work out, that electric will be cheaper for customers, considering the mileage their do. Fast charging is not so complicated to engineer, when you have as much as 1MWh of batteries. Even battery swap systems can be divised if so desired, alhough quicker it would require greater capital investments on the part of customers. Who may not like that too much. Most tractors can affford once of twice a half hour per 24h for charging/resting?
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Lets work out the Tesla Semi-Truck Technical Specs
- Thread starter lnpurnell
- Start date
Did Elon state the <2kWh/mi, 400 mile and 30 minutes in one breath? I bet 1kWh may be closer to typical (not to be confused with "worst case"), and would not be disappointed if the 400mi in 30 minutes would be in the 1-1.6kWh/mi range, so <1.28MW average.
An 800V charging rate would be a no-brainer, and knowing Tesla is not shy for big numbers, even 1600V if feasible. Even if drive potential remains <400V. A matter if some simple yet well managed switched.
An 800V charging rate would be a no-brainer, and knowing Tesla is not shy for big numbers, even 1600V if feasible. Even if drive potential remains <400V. A matter if some simple yet well managed switched.
I don't believe Tesla will increase voltage. Higher voltage increases risks and brings tighter security norms. Liquid cooled cables can transfer lot of power and charging snake can handle thick cables.
400 V batteries can be connected series for 800 V charging, but two high current switches are needed. Those are not very small or cheap. More possible failure points. Tesla keeps design as simple as possible, except on car doors.
Current kills, but current can only exist due to voltage. (and the current to kill is only 0.1 Amp or so (in the wrong place))
That's why a 12V car battery can put out 1000 amps, but you can touch both terminals without issue.
Current through body kills. Ordinary 12 V car battery can easily give 100 A, but cannot kill you. Rather high voltage is needed to push deadly current trough human body. I feel hardly anything, if I touch 40 VDC. I don't think 100 VDC would kill me. (Don't test. You could be more sensitive.) I would be careful with 400 VDC. I would be very afraid of 800 VDC.
800 V can travel easier through faulty insulator or break it. It can travel easier on dirty surface.
(AC is more dangerous than DC. One reason is that AC voltage is an average value. Our 230 VAC has peaks +-325 V. )
With strong contact 400 V is deadly. 800 V can push twice as much current trough a crack filled with dirty water. Current can also flow on moist surface. So in many real cases 800 V is deadly, 400 is not. I have got 230 VAC to finger tip. Of course I have never got it with strong grip. I'm sure this is most common situation. So 800 V is more than twice as deadly as 400 V.
400 V charging can be made faster than it is now. My guess is that even Tesla semi will use 400 V charging.
800 V is designed to limit competition. They can make it EU standard. Then they require that all chargers must be compatible with standard. This gives advantage for new cars build for 800 V.
Well the Megacharger connector we saw on the Semi has 8 charging pins. If the charge rate is 1.6MW, then we are looking at 400kW per charging line. That would be 1000 amps at 400 volts or 500 amps at 800 volts... (I'm using 1.6MW as the worst case if the Semi uses 2kWh per mile, it is going to be less than that but we don't know by how much.)
With so many amps, does it even matter how many volts a person is exposed to? Dead is dead.
I'd vote for 800V to reduce heat losses and need for copper to be hauled around.
An S8x400V, 300-500A cable is not going to be child's play to engage.
Yes the voltage is important. The available amps (takes less than 1 to kill) only matter once the voltage overcomes the resistance (or impedance in the case of AC). A car battery can supply 1000 amps, but 12V is insufficient to create that current flow, so sub-milliamp on contact with skin. Double the voltage is double the resultant current.
I like less copper, but the number of additional contactors is not trivial (for any topology I've come up with).
Sure isn't, especially in terms of contact seating force. It seems like if the cable is unwieldy to begin with, adding liquid cooling isn't a huge factor.
Also possible that the first trucks are only prototype connectors made to work with existing superchargers. (Slap four 3 systems together to get it working, add in control messages for four pack support, or a cable with pack selector...)
Voltage absolutely matters - matters far more than current. It's all about how good a connection you have with the wire and how much voltage it has. Things that can't hurt you normally can kill you if they hit a ring instead of bare skin. Things that would cause serious harm to a wet persons won't do anything if it's a wire resting on dry skin.
Doubling the voltage means minor faults in insulation that wouldn't cause a problem can kill. 400V is already enough to kill with a bare wire on dry skin, but insulation that mostly works on it might still leak enough to kill with 800V.
Maybe it's necessary or the best technical path, but it certainly isn't "the same" in terms of safety risk, except that you want to be very careful with both of them.
Amps to battery and amps through human body are completely separate. How much is needed to kill is a complex story: Electric shock - Wikipedia
AC is much more dangerous than DC: 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 for other materials also.
Higher voltage would reduce copper usage. I don't want to calculate it now. Since wires are short, energy loss is not a problem, but produced heat is. 0.1% loss of 1 MW = 1 kW, would melt wire without good cooling.
AC is much more dangerous than DC: 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 for other materials also.
Higher voltage would reduce copper usage. I don't want to calculate it now. Since wires are short, energy loss is not a problem, but produced heat is. 0.1% loss of 1 MW = 1 kW, would melt wire without good cooling.
This is based on nothing else than very thin line between good cable and a cable with a "crack" measured in micrometers.
Makes as much sense as measuring insulation cracks in micrometers.
It's not how electricity works.
Take a piezo element from cigarette lighter and hit yourself with thousands of volts.
If you die, I buy you some flowers
Voltage does not matter in our case of "dangerous cable". Difference between 400V and 800V is as important as crack in the insulation being either 35um or 70um - both are unrealistic scenarios because the thickness of insulation is in the order of magnitude thicker, often thicker on 800V rated cable (depends what cable is used today) and cracks do not stay in those margins - either there is no crack or it gets huge upon breakdown. Also cables are double-insulated.
I've not heard a single incident of charging station ever zapping an operator. Also, AFAIK, they do measure leakage in case of a fault.
Talking about dangerous electricity is fine for children. But not to people who design charging stations and have some real knowledge between ears. 1000V DC is already determined as suitable for regular DC charging stations (and has been for some time now). It's not refutable without new data (which has to prove old data incorrect as well) you guys did not provide.
And no, we can't use more copper. And no we can't also cool 4pairs due to the same reason we can't use more copper.
400 - 800 V safety is not only about charger safety. Cars do get into accidents. Which can damage insulation in many ways.This is based on nothing else than very thin line between good cable and a cable with a "crack" measured in micrometers.
Makes as much sense as measuring insulation cracks in micrometers.
It's not how electricity works.
Take a piezo element from cigarette lighter and hit yourself with thousands of volts.
If you die, I buy you some flowers
Voltage does not matter in our case of "dangerous cable". Difference between 400V and 800V is as important as crack in the insulation being either 35um or 70um - both are unrealistic scenarios because the thickness of insulation is in the order of magnitude thicker, often thicker on 800V rated cable (depends what cable is used today) and cracks do not stay in those margins - either there is no crack or it gets huge upon breakdown. Also cables are double-insulated.
I've not heard a single incident of charging station ever zapping an operator. Also, AFAIK, they do measure leakage in case of a fault.
Talking about dangerous electricity is fine for children. But not to people who design charging stations and have some real knowledge between ears. 1000V DC is already determined as suitable for regular DC charging stations (and has been for some time now). It's not refutable without new data (which has to prove old data incorrect as well) you guys did not provide.
And no, we can't use more copper. And no we can't also cool 4pairs due to the same reason we can't use more copper.
Of course everything is safe on new system. What is situation with 20 years old equipment? Those charger cables are often mishandled.
If we want save copper, we can make cables inside car from aluminum. Electricity comes to this house in aluminum cables. (Al is not good in flexible cable.)
If Semi uses 800V, it will likely be only while megacharging. Also batteries have contactors separating into halves (regular cars have 200V halves). Tesla truck likely has all 4 batteries running in parallel when driven on roads.
Don't care about 20 year old equipment. Like I said, leakage is measured by charging stations.
Nobody cares about copper. Aluminium cables will be gigantic at those amps. Also problems with connectors between copper and aluminium.
Cables inside this house are copper, outside aluminum (have been 30 years). No problems in connection. Al cables would be thick, but not so heavy.
Largest current is from battery to motor(s). So large part of 800 V advantage is lost with 400 V motors. If battery back has connectors to switch it to 800 V mode, you cannot prove it is in 400 V mode after every accident.
I don't think 20 years is too long lifetime for equipment. So I do care.
Tesla semi will probably have one pack for each motor. Charging connector looked like it has separate pins for each back. So it has 4 completely separate circuits.
Makes as much sense as measuring insulation cracks in micrometers.
It's not how electricity works.
Take a piezo element from cigarette lighter and hit yourself with thousands of volts.
If you die, I buy you some flowers
A piezo is a energy limited high voltage source, just like a static shock in winter is. The peak current is too low to cause lasting effects (in most cases).
All conductors are exposed at some point (unless it's an inductive charger). Therefore, surface contamination effects are important to consider.
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