Dumb Dual Charger Question

R²B · Oct 28, 2014

So as I understand it one would need a dual charger and an 80A (HPWC) connection at home to charge @ 58mph. Does this mean that one would need to get dual chargers to use the full capactiy of the Superchargers? Intuition tells me no, that all 85kw MSs can charge at the full rate (300mph or whatever) even with a single charger, but I don't understand why.

Can someone confirm...

Rockster · Oct 28, 2014

No. Superchargers do their thing without regard for how many onboard chargers you have. This is because the SC's dump DC current straight into the battery somehow, without using the car's onboard charger(s).

R²B · Oct 28, 2014

Thanks Rockster.

efusco · Oct 28, 2014

Rockster said:
No. Superchargers do their thing without regard for how many onboard chargers you have. This is because the SC's dump DC current straight into the battery somehow, without using the car's onboard charger(s).

Correct, remember that the chargers convert the wall AC to DC then to the battery. The SCs bypass that as the AC is converted to DC in the Super CHARGER.

gene · Oct 28, 2014

If you are trying to decide whether to order the dual chargers, I would say yes, do so. The HPWC I would say is not needed. The dual chargers are very nice to have when traveling out of the range of Super Chargers , yet in the range of 70 amp chargers (of which more and more are likely to be installed).

R²B · Oct 28, 2014

gene said:
If you are trying to decide whether to order the dual chargers, I would say yes, do so. The HPWC I would say is not needed. The dual chargers are very nice to have when traveling out of the range of Super Chargers , yet in the range of 70 amp chargers (of which more and more are likely to be installed).

That shipped has sailed for me (went with single charger). Looking back over the past 4 years of traveling I don't think I've ever been outside of the range of a Super Charger.

David99 · Oct 28, 2014

Think of the Supercharger as a giant external charger that bypasses your internal chargers.

pgiralt · Oct 28, 2014

The supercharger cabinet contains 12 of the onboard chargers inside the cabinet.

N4HHE · Oct 28, 2014

R²B said:
That shipped has sailed for me (went with single charger). Looking back over the past 4 years of traveling I don't think I've ever been outside of the range of a Super Charger.

Took 9 months before I was finally inside the range of a Supercharger. :-(
Maybe by the end of 2015 there will be a Supercharger in a direction I wish to travel. Even sweeter if there is another in my direction beyond the first.

- - - Updated - - -

David99 said:
Think of the Supercharger as a giant external charger that bypasses your internal chargers.

I think the difference between AC charging and DC charging is that with AC the EVSE tells the vehicle what is available. The chargers in the vehicle then limit their demands to what is offered, and convert and regulate according to what the battery cells need.

With a DC charger the vehicle tells the EVSE what it can accept and needs. Then the vehicle disconnects banks of cells as they reach the desired state of charge. Suspect this is why CHAdeMO is causing Tesla so much heartburn - that all CHAdeMO implementations do not work the same. That Tesla is having to learn their feedback loops to keep them from destroying our cars.

morbot · Oct 30, 2014

R²B said:
That shipped has sailed for me (went with single charger)

Well, you can always get it added by Tesla after the fact (albeit for more money than at delivery).

I opted out of the dual chargers because 95% of the time I'm going to be using the car for a daily commuter and not putting a ton of miles, an overnight charge should suffice. I originally passed on the HPWC too.

But, after thinking about only having the one charging cable... what would happen if it were to get stolen/damaged/etc while charging in the wild I'd be in trouble. Right as I was thinking that, the HPWC price dropped to be within range of a replacement cable, so I opted to pick one up, even if my car doesn't fully utilize it's maximum rate.

Saghost · Oct 30, 2014

N4HHE said:
Took 9 months before I was finally inside the range of a Supercharger. :-(
Maybe by the end of 2015 there will be a Supercharger in a direction I wish to travel. Even sweeter if there is another in my direction beyond the first.

- - - Updated - - -

I think the difference between AC charging and DC charging is that with AC the EVSE tells the vehicle what is available. The chargers in the vehicle then limit their demands to what is offered, and convert and regulate according to what the battery cells need.

With a DC charger the vehicle tells the EVSE what it can accept and needs. Then the vehicle disconnects banks of cells as they reach the desired state of charge. Suspect this is why CHAdeMO is causing Tesla so much heartburn - that all CHAdeMO implementations do not work the same. That Tesla is having to learn their feedback loops to keep them from destroying our cars.

"Disconnects banks of cells as they reach desired state of charge?"

Do you have a source for that? I've never seen a battery system that worked that way, and I didn't see parts that seemed suited in the model S battery tear down thread.

I had assumed the slower charge rate as the car reached higher states of charge was for the usual reason - the charge voltage difference was being reduced to keep from overcharging individual cells, and the lower voltage difference means less current flow to each of the cells, all of which are still connected.

I'm not an expert on the model S, though - if it works differently I'll be interested to read all about it.

Walter

cpa · Oct 30, 2014

When I would watch the charging rates on the touchscreen, the voltage remained fairly constant; it was the amperes that started out high and then slowly tapered down to 15-20A with still 350+ V.

Cottonwood · Oct 31, 2014

cpa said:
When I would watch the charging rates on the touchscreen, the voltage remained fairly constant; it was the amperes that started out high and then slowly tapered down to 15-20A with still 350+ V.

It depends on the model. The 60 has 84 cells in series and tops out at about 350 Volts at the end of the taper. The 85 has 96 cells in series and tops out at about 400 Volts at the end of the taper. Both of those numbers correspond to a fully charged cell of about 4.17 Volts.

Saghost · Oct 31, 2014

cpa said:
When I would watch the charging rates on the touchscreen, the voltage remained fairly constant; it was the amperes that started out high and then slowly tapered down to 15-20A with still 350+ V.

That's why I said the voltage differential - the difference between the cell voltage and the charge voltage you're feeding it. Typical modern charging techniques have a constant current phase at the beginning and then move to a constant voltage phase as the battery gets closer to charged - meaning the charger feeds a constant voltage and as the cell fills up, the difference between the cell's voltage and that constant voltage drops, which is why the current flow falls off.

I think. I'm not an expert in batteries, but that's the way I've been taught it works.
Walter

Cottonwood · Oct 31, 2014

Saghost said:
That's why I said the voltage differential - the difference between the cell voltage and the charge voltage you're feeding it. Typical modern charging techniques have a constant current phase at the beginning and then move to a constant voltage phase as the battery gets closer to charged - meaning the charger feeds a constant voltage and as the cell fills up, the difference between the cell's voltage and that constant voltage drops, which is why the current flow falls off.

I think. I'm not an expert in batteries, but that's the way I've been taught it works.
Walter

Constant current to constant Voltage is old school lead acid charging technique. The Tesla Taper is much more sophisticated, with an steady taper of total charge power as SoC increases; the Voltage steadily increases as the current steadily decreases. At the very end, the Voltage is relatively constant as the current decreases.

dhrivnak · Oct 31, 2014

R²B said:
That shipped has sailed for me (went with single charger). Looking back over the past 4 years of traveling I don't think I've ever been outside of the range of a Super Charger.

You are fortunate as I have yet to travel by a Super Charger, or a charger above 30 amps in the past 3.5 years and 28,000 miles. I guess location is everything.

jerry33 · Nov 1, 2014

dhrivnak said:
You are fortunate as I have yet to travel by a Super Charger, or a charger above 30 amps in the past 3.5 years and 28,000 miles. I guess location is everything.

Right. After close to 35,000 miles, I've been able to use a Supercharger four times.

ACDriveMotor · Nov 2, 2014

1 year and I've not yet been to a SC. More a consequence of busy-ness than anything else. I need to find a free half a day to get up to Burlington just to make sure it works.

morbot · Nov 2, 2014

First priority upon taking delivery for me is getting some paint protection wrap put on. Second priority is finding a day to take a roadtrip to one of the superchargers outside Seattle. Just to give it a try and make sure everything works as expected, and to spend a little quality time driving the car.

Now I just need to decide which way to go... North, South or East? Seeing as it's gonna be December, I might avoid the pass as I'm inexperienced driving in the snow.

Dumb Dual Charger Question

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