How does a Supercharger work?

[FlasherZ]

Assuming the Gen2 cabinets are configured similarly, that would mean if each cabinet is rated at 135kW total, then the max output per car would only be 101.25kW. Aren't some clocked as putting 120kW out per car?

118.8 kW on my trip earlier this week (@ 24 mi rated SOC).

I think they mean kW, not kWh in that diagram. Not sure if the same DC switching logic is used in gen2. If I start with the AC side of things, I get 9 charger units * 48A * 277V = 120 kW (more or less) but it doesn't take into account efficiency losses, so we still don't get 120 kW there (probably more like 110 kWish). Perhaps the switching is more fine-grained?

To get a full 120 kW, you'd need 12 modules with switching granularity of 1 ((135/12)*11=123.75 kW), or 18 modules with switching granularity of 2 ((135/18)*16 = 120 kW). I suspect they may have just bitten the bullet to do switching at a granularity of 1.

 

[Ingineer]

Yeah, I bet they changed it so there are 2 additional sets of contactors at the top and bottom. This would increase safety, and allow the whole cabinet of 12 shelves to be used on one car.

 

[Ingineer]

By the way, here's the label from the Gen 2 charger:

Note the voltage range. It also has 3 separate AC input connections, each protected by it's own fuse. This also confirms the reports of 3-phase capability. It also means that this should be able to put out quite a bit more than 10kW when it's used in a SC cabinet, if they kept the same configuration, that means 11250kW.

 

[miimura]

Clearly you meant 11,250W, not 11250kW. How did you get that number?

By my estimation, if they used it in a Supercharger, it would be on 277VAC and draw up to 13,296W (277 * 48). 85% efficient operation should deliver up to 11.3kW to the DC side. It could deliver that power as low as 251VDC to remain within the 45A output limit.

 

[tom66]

Or, look at it another way. The SpC is limited to 330A over 12 chargers, which is 27.5A DC output per charger or 120kW maximum at around 363V. If there's some derating to allow for a failed charger (330 / 11 chargers is 30A per charger, allowing one failed charger in the stack without derating of output current) then 41.2A/charger or 495A total would be possible. This is around 180kW peak charging, with all else remaining the same. Of course the line input current will be the limit at that point, so the charger current will likely peak earlier in the voltage curve, maybe realistically around 150kW charging.

 

[Ingineer]

Clearly you meant 11,250W, not 11250kW. How did you get that number?

By my estimation, if they used it in a Supercharger, it would be on 277VAC and draw up to 13,296W (277 * 48). 85% efficient operation should deliver up to 11.3kW to the DC side. It could deliver that power as low as 251VDC to remain within the 45A output limit.

Yes the "k" was a goof. The Gen 2 SC cabinet has 12 modules. according to Tesla, they can put out 135kW, so 135kW / 12 = 11.25kW. This makes everything work, and the new modules have 3-phase input, so they can remain in balance across all 3 legs in any configuration.

I've noticed in my car I can feed in higher voltages than 240, and the charger produces more output. US cars with single chargers are limited to 40A max, but I was able to feed in 267V with a boost transformer and the output went up by about 1kW. Not much, but hey, it's essentially "free" and well within the voltage range.

 

[scaesare]

Yes the "k" was a goof. The Gen 2 SC cabinet has 12 modules. according to Tesla, they can put out 135kW, so 135kW / 12 = 11.25kW. This makes everything work, and the new modules have 3-phase input, so they can remain in balance across all 3 legs in any configuration.

I've noticed in my car I can feed in higher voltages than 240, and the charger produces more output. US cars with single chargers are limited to 40A max, but I was able to feed in 267V with a boost transformer and the output went up by about 1kW. Not much, but hey, it's essentially "free" and well within the voltage range.

I suspect an in-car module would accept 277 just fine.

 

[Ingineer]

I suspect an in-car module would accept 277 just fine.

The G1 module has a max of 277v listed, while G2 (shown above) is 300v. I had to do some work to make sure the HPWC only sees 240v, as it runs hot as it is. Unfortunately my boost transformer only gets to 267v.

 

[scaesare]

The G1 module has a max of 277v listed, while G2 (shown above) is 300v. I had to do some work to make sure the HPWC only sees 240v, as it runs hot as it is. Unfortunately my boost transformer only gets to 267v.

Out of curiosity, how did you do that with the HPWC? Use it's contactors to trigger another set feeding the boost xfrmr and from there to the car?

 

[mackgoo]

It isn't FIFO like some people believe. I followed a Supercharger tech from Colorado to Kansas and chatted with him along the way. B is indeed a slave to the A side and it will give up most of its power if the need is on the A side. If you're plugged into B and someone plugs their car into A and it needs more than is leftover from your car charging, it will take it. The only way the B side would get almost no power is if someone pulled into the A slot with an almost dead battery ("Charge Now")

Sorry if this has been resolved but I didn't want to read through. It is FIFO. I know because the other day I pulled into an "A" stall and was severely depressed until the "B" stall starting tapering due to end of charge. Finally when they finished it kicked up. That's real life operation.

 

[Ingineer]

OT, but I completely redid the inside of the HPWC, including adding an enconomizer circuit for the contactor coil so it doesn't get so hot. I ditched the fuses and redid the wiring terminations using copper bus bars. It runs massively cooler now and with less voltage drop.

Before I get attacked about removing the fuses, keep in mind it's protected by a fast-acting breaker (I didn't heed the 125% rule either), and the car is also individually fused on each of it's 3 inputs per charger.

 

[FlasherZ]

I don't have a problem with the fuses being removed, although it does invalidate its listing, which may be an issue for your insurance company if anything happens, along with the failure to observe continuous load rules (unless you're using a 100% rated breaker, or you're talking about using a breaker in the HPWC itself). If that's the risk you're willing to take (insurance/liability), it's your decision. I would take exception if you recommended that others violate the law, though.

(...and yes, I'm aware the UMC isn't listed which would seem to defy NEC requirements requiring NRTL listing for electrical equipment, not appliances.)

 

[Ingineer]

See, I knew it! =)

 

[deonb]

How do you guys think that the current limiting works?

Is it purely based on varying the voltage, or is either the charger or battery somehow changing its internal resistance?


And if its the chargers changing their internal resistance, the chargers would have to all change it in parallel, but when a charger is removed from the system (e.g. to go from 'A' to 'B'), all the other chargers would have to bump their internal resistance back up, then ramp down again. However, this causes spikes each time a charger is turned off, and we don't see those spikes.

 

[Moonwick]

I've noticed in my car I can feed in higher voltages than 240, and the charger produces more output. US cars with single chargers are limited to 40A max, but I was able to feed in 267V with a boost transformer and the output went up by about 1kW. Not much, but hey, it's essentially "free" and well within the voltage range.

This thread had me wondering about this, and it's neat to hear that someone's actually tried it. Too bad it'd probably set off some alarm bells over at Tesla if something went wrong and they had to pull the logs, since I'm certain the wall voltage shows up there. I'm also guessing that the efficiency loss from using the boost transformer really wouldn't make the extra 10-25% kW (25% if you could actually get all the way to 300V) worth the trouble.

 

[Ingineer]

How do you guys think that the current limiting works?

Is it purely based on varying the voltage, or is either the charger or battery somehow changing its internal resistance?


And if its the chargers changing their internal resistance, the chargers would have to all change it in parallel, but when a charger is removed from the system (e.g. to go from 'A' to 'B'), all the other chargers would have to bump their internal resistance back up, then ramp down again. However, this causes spikes each time a charger is turned off, and we don't see those spikes.

The bank of 12 SC charger modules are the same ones used in the cars, just a lot more of them. The BMS controller located in your battery pack determines the maximum safe charge current and voltage and instructs the SC cabinet over it's CAN interface to deliver what's requested to the battery. The BMS is always "in charge", (pun hehe) as it has all the facts about cell module condition, voltage, SOC, temp, etc.

The way in which the 12 modules are connected to the A/B stations on the 135kW cabinets is still being debated, but in the older 120kW 1st generation design, the modules were arranged in 4 sub-banks with 3 modules each. Up to 3 sub-banks could be connected to either A or B, with the remainder being connected to the other side. As a car began tapering and a sub-bank was not needed, it was switched back to the other side or off if nobody was using that side. It's likely the 2nd generation 135kW systems work exactly the same way, we just don't know for sure yet.

 

[deonb]

The bank of 12 SC charger modules are the same ones used in the cars, just a lot more of them. The BMS controller located in your battery pack determines the maximum safe charge current and voltage and instructs the SC cabinet over it's CAN interface to deliver what's requested to the battery. The BMS is always "in charge", (pun hehe) as it has all the facts about cell module condition, voltage, SOC, temp, etc.

Yes, but how? Current is drawn, not delivered.

For the charger module to restrict the maximum current that can get drawn, it would either have to change its output voltage (causing the battery to draw less current), or change its own internal resistance.

Or there has to be something between the charger and the battery that can dynamically change resistance.

 

[Ingineer]

Yes, but how? Current is drawn, not delivered.

For the charger module to restrict the maximum current that can get drawn, it would either have to change its output voltage (causing the battery to draw less current), or change its own internal resistance.

Or there has to be something between the charger and the battery that can dynamically change resistance.

The charger is a switch mode power supply. It changes output voltage by adjusting PWM duty cycle. The phases of Lithium-Ion charging are monitored and if the algorithm calls for CV (Constant Voltage), the PWM is controlled from sampled voltage. If the algorithm needs to limit to CC (Constant Current), then the current shunt is sampled as the input for the error amp, thus dropping PWM duty cycle until the current is under the demanded threshold. This causes the output voltage to regulate based on current, thus achieving the commanded constant current. If the BMS deems the pack temp is too hot, the PWM then gets a secondary (or tertiary) limiting factor.

 

[deonb]

The charger is a switch mode power supply. It changes output voltage by adjusting PWM duty cycle. The phases of Lithium-Ion charging are monitored and if the algorithm calls for CV (Constant Voltage), the PWM is controlled from sampled voltage. If the algorithm needs to limit to CC (Constant Current), then the current shunt is sampled as the input for the error amp, thus dropping PWM duty cycle until the current is under the demanded threshold. This causes the output voltage to regulate based on current, thus achieving the commanded constant current. If the BMS deems the pack temp is too hot, the PWM then gets a secondary (or tertiary) limiting factor.

Ok, but interestingly then, when you're connected to AC, the car shows AC voltage, where if you're connected to DC, it shows DC voltage.

What I would expect, is that if you're charging from e.g. 9 chargers, during tapering the 9 chargers would progressively step down their DC voltage, then 1 charger will fall away - which changes the internal resistance of the remaining chargers. The remaining chargers would then have to up the voltage again to compensate, and the progressively step down again.

In other words I expect the DC voltage to go down and back up around 12 times during charging. But it doesn't?

 

[FlasherZ]

This thread had me wondering about this, and it's neat to hear that someone's actually tried it. Too bad it'd probably set off some alarm bells over at Tesla if something went wrong and they had to pull the logs, since I'm certain the wall voltage shows up there. I'm also guessing that the efficiency loss from using the boost transformer really wouldn't make the extra 10-25% kW (25% if you could actually get all the way to 300V) worth the trouble.

Someone had reported that the US chargers will step down amps at higher voltages to keep a max power of 10 kW... I admit I haven't tried it.