Lets work out the Tesla Semi-Truck Technical Specs

[mongo]

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.

I get what you are saying, but doesn't that in itself imply the protections are not adequate? If a cable is safe, then the voltage in the cable does not matter. If it is not safe, then lower is better.

Can we all agree that:
If a protection system is adequate, the voltage does not matter in regards to human safety (because no one is exposed to the potential).
If a person is exposed to a voltage potential/ fault, typically high voltages are worse for the person.
?
And if not, can we move this to a high voltage v.s. low voltage/ Tesla v.s. Edison themed thread?

 

[Farmertom]

I think they should work on a standardized automated system , it doesn't need to be as complex as the one in the video. Drive over would still get my vote, the charge station would be surface mounted so no excavation required and greatly reduced chances of vehicle striking anything important when entering and leaving especially if the power supply is buried. The vehicle would be immobile while charging, chances of being electrocuted are virtually eliminated. And of course there is ground fault protection.

There must be materials produced today that are resistant to degradation from the elements, my Sonim phone is exposed to water, salt etc. all the time and it has no contact issues when charging. There are ways to keep flush mounted pads clean even in extreme conditions with some management in airflow and possibly heated pads.

The biggest issue with electrical safety is an incident happens in an instant. Dripping fuel is way safer than an electrical arc. There is also the issue that recharging is going to be happening at a much higher rate than refueling so it will have to be that much safer as well.

 

[Farmertom]

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.

Trying to wrap my mind around this. Are you implying Tesla's trucks are going to have enough energy reserve to actually transfer power power from one location to another?

 

[mongo]

I think they should work on a standardized automated system , it doesn't need to be as complex as the one in the video. Drive over would still get my vote, the charge station would be surface mounted so no excavation required and greatly reduced chances of vehicle striking anything important when entering and leaving especially if the power supply is buried. The vehicle would be immobile while charging, chances of being electrocuted are virtually eliminated. And of course there is ground fault protection.

There must be materials produced today that are resistant to degradation from the elements, my Sonim phone is exposed to water, salt etc. all the time and it has no contact issues when charging. There are ways to keep flush mounted pads clean even in extreme conditions with some management in airflow and possibly heated pads.

The biggest issue with electrical safety is an incident happens in an instant. Dripping fuel is way safer than an electrical arc. There is also the issue that recharging is going to be happening at a much higher rate than refueling so it will have to be that much safer as well.

I like it. A powered cover could keep both sides clean (truck side opens first for drip prevention). Self aligning, and also covers the case of semi-autonomous platoons.

Ground fault is a slightly different issue present in ground referenced AC systems. The DC charger feeds and pack are totally isolated from chassis and ground. The electronics can detect a single point fault of DC to chassis before there is any danger to people (no circuit until a person is in contact with both positive and negative). Internal shorts on the DC bus would need separate voltage/ current/ temperature monitoring, the same as a GFCI not detecting shorts from line to neutral.

 

[Farmertom]

I like it. A powered cover could keep both sides clean (truck side opens first for drip prevention). Self aligning, and also covers the case of semi-autonomous platoons.

Could still have cable plug in for overnight, long term charging, for areas that don't supply fast chargers or if the fast charger port goes down for some reason.

Ground fault is a slightly different issue present in ground referenced AC systems. The DC charger feeds and pack are totally isolated from chassis and ground. The electronics can detect a single point fault of DC to chassis before there is any danger to people (no circuit until a person is in contact with both positive and negative). Internal shorts on the DC bus would need separate voltage/ current/ temperature monitoring, the same as a GFCI not detecting shorts from line to neutral.

Makes sense, how would that work in the case where AC is being converted to DC? I suppose the DC circuit would still have to be closed positive and negative, the earth is still not involved...

So Tesla's cars have an inverter on board to convert AC to DC then for when you plug them into a household plug which makes sense. Are the fast chargers DC requiring a separate plug then? Will the trucks have this feature? It would take awhile to charge a truck at 220V 20A.

 

[jkn]

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.

That is all true. But do those safety mechanisms work in all possible situations? Fire, crash, mishandled old equipment, old cars repaired by home mechanic (if that is not allowed, car prices of old cars will drop to zero.), ... I don't think I can imagine all possible failures.

Of course I cannot imagine accident causing double fault and prevent fuse to blow. I imagine my self as a fireman standing on a pool of water and spraying more to a burning EV or as a medical personnel helping injured driver. Worst case 400 VDC or 800 VDC would make big difference to me. 400 VDC is almost inherently safe. I have got 230 VAC to my fingertip. If I had to rescue somebody and only way to test if there is 400 VDC or not is my fingertip, I would do it.

Relays connecting two 400 V batteries to 800 V for charging have to handle 800 V and very high current with 400 V are not small and easy to do.

If we have to go to 800 V then we'll go. I don't think we have to. At least not before this:
Fisker claims solid-state battery ‘breakthrough’ for electric cars with ‘500 miles range and 1 min charging’
500 mile range, 1 minute charging time.

 

[scaesare]

Perhaps we need to simply set the bar as: "Hey, it's safer than Hydrogen refueling!"

Then Telsa can go ahead and install 3,200V charging stations in wet locations with a few wraps of electrical tape as insulation.

 

[mongo]

Could still have cable plug in for overnight, long term charging, for areas that don't supply fast chargers or if the fast charger port goes down for some reason.

If there is an on-board charger, it can have it's own AC connection. Internal charger could can be shared across packs, or one per...

Makes sense, how would that work in the case where AC is being converted to DC? I suppose the DC circuit would still have to be closed positive and negative, the earth is still not involved...

The AC to DC conversion likely takes place across a transformer which provides the isolation.

So Tesla's cars have an inverter on board to convert AC to DC then for when you plug them into a household plug which makes sense. Are the fast chargers DC requiring a separate plug then? Will the trucks have this feature? It would take awhile to charge a truck at 220V 20A.

Current Tesla DC fast charger uses the same connector and the high voltage junction box either routes the charger port to the batteries (DC) or the chargers (AC). If Semi has Mega on bottom, the side AC connector could go straight to the chargers. 240 or three phase are possibilities.

 

[mongo]

That is all true. But do those safety mechanisms work in all possible situations? Fire, crash, mishandled old equipment, old cars repaired by home mechanic (if that is not allowed, car prices of old cars will drop to zero.), ... I don't think I can imagine all possible failures.

Of course I cannot imagine accident causing double fault and prevent fuse to blow. I imagine my self as a fireman standing on a pool of water and spraying more to a burning EV or as a medical personnel helping injured driver. Worst case 400 VDC or 800 VDC would make big difference to me. 400 VDC is almost inherently safe. I have got 230 VAC to my fingertip. If I had to rescue somebody and only way to test if there is 400 VDC or not is my fingertip, I would do it.

Relays connecting two 400 V batteries to 800 V for charging have to handle 800 V and very high current with 400 V are not small and easy to do.

If we have to go to 800 V then we'll go. I don't think we have to. At least not before this:
Fisker claims solid-state battery ‘breakthrough’ for electric cars with ‘500 miles range and 1 min charging’
500 mile range, 1 minute charging time.

Agreed, ruptured battery pack fire is the most uncontrollable scenario for voltage exposure.
Also agreed, increasing voltage makes the electronics, mechanics, and elctro-mechanics more challenging.
Speaking from an eco-system point of view, other than charge current, I see no advantage to Tesla going above 400V, especially with their equipment being fed from 480V.

Tip: if anyone really needs to check for voltage using their body, use the back of your right hand and keep your left in your pocket.

 

[zecar]

Trying to wrap my mind around this. Are you implying Tesla's trucks are going to have enough energy reserve to actually transfer power power from one location to another?

Yes, but more importantly they will have enough capacity for the customer can decide where and when to charge. It's a form of demand response.

One of the ways Musk probably gets to 7 cents is the truck charging directly off of 3 cent solar when the sun is shining. To often charge off of optimal conditions requires flexibility in timing as well as optimization software. Although each market area will require a different solution to 7 cents.

 

[jkn]

I think they should work on a standardized automated system , it doesn't need to be as complex as the one in the video. Drive over would still get my vote, the charge station would be surface mounted so no excavation required and greatly reduced chances of vehicle striking anything important when entering and leaving especially if the power supply is buried. The vehicle would be immobile while charging, chances of being electrocuted are virtually eliminated. And of course there is ground fault protection.

There must be materials produced today that are resistant to degradation from the elements, my Sonim phone is exposed to water, salt etc. all the time and it has no contact issues when charging. There are ways to keep flush mounted pads clean even in extreme conditions with some management in airflow and possibly heated pads.

The biggest issue with electrical safety is an incident happens in an instant. Dripping fuel is way safer than an electrical arc. There is also the issue that recharging is going to be happening at a much higher rate than refueling so it will have to be that much safer as well.

I don't like drive over system because of snow, ice and water dripping (or being stuck in) from bottom of the truck. I have been many times waiting train on station and watching them cleaning electrical contacts with a broom. (Trains from east and north continued as one train to south.) Of course contacts were in a closed box. It didn't stop dust like snow.

Electrical system can detect leak and cut current very fast. Fueling system cannot react that fast. At least fuel in the hose will leak.

Battery fire is much slower and less energetic than fuel fire. Battery fire does not produce large explosion, only many small pops when cells explode.

I would say even 800 VDC system is safer than fuel system, except I can see when fuel is burning. I cannot see if there is an electrical leak.

Perhaps we need to simply set the bar as: "Hey, it's safer than Hydrogen refueling!"

Then Telsa can go ahead and install 3,200V charging stations in wet locations with a few wraps of electrical tape as insulation.

Hydrogen leak in closed space is a bomb. Hydrogen leak in open area is harmless. Even hydrogen fire in open area is not so bad, because most burning would happen high up.

 

[mongo]

I don't like drive over system because of snow, ice and water dripping (or being stuck in) from bottom of the truck. I have been many times waiting train on station and watching them cleaning electrical contacts with a broom. (Trains from east and north continued as one train to south.) Of course contacts were in a closed box. It didn't stop dust like snow.

This is concern of mine also, but I think it is manageable in terms of snow/ slush. If the truck side opens first, that creates a clean space, so they are no drips when the charge side opens. Bigger issue I see I flooding and such. Having the charge system at/near/ below ground level makes a sump super critical.

 

[arnis]

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!

So much talk about what will happen in case of xxx voltage.
Well, have you ever seen 2500A DC transfer? You should understand that 400V and 800V are both low voltages and 2500A
is extremely, EXTREMELY HIGH current. Almost nothing uses these currents. These currents hardly have any useful fuses to blow. And even worse, it requires gigantic clamping force. I'm talking about few pairs of bolts sized like your thumb each. Each and every connection.
Low Voltage - upto 1000V
Medium Voltage - 1000V to 35kV
High Voltage - 35kV to 230 kV
Extra High Voltage - above 230 kV.
If we compared 400V DC vs 34 000V DC then I would think a little bit. But not when we compare 400V with 800V.

This skin dielectric breakdown has no effect on safety, like others have mentioned, there are fault detection methods.... and it never get's to skin contact at all. Have we ever observed charging station fault where human was zapped (except static electricity)? If not, why even consider 400V?
You do understand that Porsche is likely using 800V on passenger vehicle.
And I said, that up to 1000V, everything has been super-duper verified and legislated to be absolutely safe. From 60V DC up to 1000V DC, absolutely no difference.

If all your safety related information is based on few Wiki articles, then I wouldn't like to hear any more of that.

DC current at 400V with "few amps" doesn't act like it does with AAA battery and LED's.

Try to stop that arc at 2500A 400V DC.

 

[jkn]

So much talk about what will happen in case of xxx voltage.
Well, have you ever seen 2500A DC transfer? You should understand that 400V and 800V are both low voltages and 2500A
is extremely, EXTREMELY HIGH current. Almost nothing uses these currents. These currents hardly have any useful fuses to blow. And even worse, it requires gigantic clamping force. I'm talking about few pairs of bolts sized like your thumb each. Each and every connection.
Low Voltage - upto 1000V
Medium Voltage - 1000V to 35kV
High Voltage - 35kV to 230 kV
Extra High Voltage - above 230 kV.
If we compared 400V DC vs 34 000V DC then I would think a little bit. But not when we compare 400V with 800V.

This skin dielectric breakdown has no effect on safety, like others have mentioned, there are fault detection methods.... and it never get's to skin contact at all. Have we ever observed charging station fault where human was zapped (except static electricity)? If not, why even consider 400V?
You do understand that Porsche is likely using 800V on passenger vehicle.
And I said, that up to 1000V, everything has been super-duper verified and legislated to be absolutely safe. From 60V DC up to 1000V DC, absolutely no difference.

If all your safety related information is based on few Wiki articles, then I wouldn't like to hear any more of that.

DC current at 400V with "few amps" doesn't act like it does with AAA battery and LED's.

Try to stop that arc at 2500A 400V DC.

AC is more dangerous than DC because it messes with nerve system.
"More than 30 mA of AC or 300 – 500 mA of DC at high voltage can cause fibrillation."

Fibrillation = heard stops pumping blood. -> Quick death if there is no defibrillation equipment nearby.

For AC even 40 V can cause fibrillation. For DC about 400 V is needed.

That is why 800 VDC is much more dangerous than 400 VDC.
400 VDC is close to deadly limit, so not much extra resistance is needed. (Body's resistance is almost enough.) 800 VDC is far above it.

If human body is part of circuit, then that circuit does not carry 2500 A current even with 800 V.

Dielectric break down causes resistance to be lower for higher voltage. That increases danger of 800 V even more.

 

[arnis]

AC is more dangerous than DC because it messes with nerve system.
"More than 30 mA of AC or 300 – 500 mA of DC at high voltage can cause fibrillation."

Fibrillation = heard stops pumping blood. -> Quick death if there is no defibrillation equipment nearby.

For AC even 40 V can cause fibrillation. For DC about 400 V is needed.

That is why 800 VDC is much more dangerous than 400 VDC.
400 VDC is close to deadly limit, so not much extra resistance is needed. (Body's resistance is almost enough.) 800 VDC is far above it.

If human body is part of circuit, then that circuit does not carry 2500 A current even with 800 V.

Dielectric break down causes resistance to be lower for higher voltage. That increases danger of 800 V even more.

All this has little to do with charging stations. As in both cases (400V, 800V), these voltages do not have contact with human operator.
That means it does not apply to this topic.

 

[jkn]

All this has little to do with charging stations. As in both cases (400V, 800V), these voltages do not have contact with human operator.
That means it does not apply to this topic.

Yes, if everything works as planned. Crash, fire, bad maintenance,... can change situation. For safety worst case is only interesting case.

 

[mongo]

For safety worst case is only interesting case.

Assuming good engineering

 

[Saghost]

All this has little to do with charging stations. As in both cases (400V, 800V), these voltages do not have contact with human operator.
That means it does not apply to this topic.

Just because you design it not to contact the operator doesn't mean it won't. The whole point of this discussion is how dangerous things are when something goes wrong - and 800V is much more dangerous if something goes wrong, in part because things don't have to go as far wrong to be dangerous.

 

[Model 3]

All this has little to do with charging stations. As in both cases (400V, 800V), these voltages do not have contact with human operator.
That means it does not apply to this topic.

"Anything that can go wrong will go wrong".

 

[arnis]

and 800V is much more dangerous

How much? Give me some numbers.

"Anything that can go wrong will go wrong".

Can it? I mean safety only. Yes we can break the station itself. We can also blow up charger with lightning strike.
But let's isolate "can go wrong" in terms of extra 400V minus 50% of amps.
Can it go wrong? For example it is not realistic expectation that plug is powered when disconnected.
It's also not realistic to expect system will be functional when switched off.