Todd Burch
14-Year Member
The supercharger is DC...so it bypasses the onboard Model S chargers. (2) applies regardless, and is due to the impacts of high charging rates on battery lifetime.
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Twin Chargers: Why?
- Thread starter smorgasbord
- Start date
Todd Burch
14-Year Member
Ah...misunderstood when you used the term "supercharging" 
I believe buried somewhere in the Roadster threads that the sweet spot for charging and battery life is in the range of 240V 40A, so I'd use a NEMA 14-50 over the HPC in that case. Of course, the chemistry of the 300mi pack is different and the Model S pack might behave a bit different in general.
Regardless, with the lower charging rate you won't waste as much energy cooling the battery while charging.
I believe buried somewhere in the Roadster threads that the sweet spot for charging and battery life is in the range of 240V 40A, so I'd use a NEMA 14-50 over the HPC in that case. Of course, the chemistry of the 300mi pack is different and the Model S pack might behave a bit different in general.
Regardless, with the lower charging rate you won't waste as much energy cooling the battery while charging.
I'm more worried about battery capacity and longevity for this concern, than efficiency of wall power consumption.Ah...misunderstood when you used the term "supercharging"
I believe buried somewhere in the Roadster threads that the sweet spot for charging and battery life is in the range of 240V 40A, so I'd use a NEMA 14-50 over the HPC in that case. Of course, the chemistry of the 300mi pack is different and the Model S pack might behave a bit different in general.
Regardless, with the lower charging rate you won't waste as much energy cooling the battery while charging.
If the HPC is only for periodic and/or range charging (rather than daily use) that makes it less compelling to me.
You can charge at 70A without degrading your batteries. However I don't usually do that as it makes my garage rather warm, and it is unnecessary.
Ah...misunderstood when you used the term "supercharging"
I believe buried somewhere in the Roadster threads that the sweet spot for charging and battery life is in the range of 240V 40A, so I'd use a NEMA 14-50 over the HPC in that case. Of course, the chemistry of the 300mi pack is different and the Model S pack might behave a bit different in general.
Regardless, with the lower charging rate you won't waste as much energy cooling the battery while charging.
We don't have enough data to know if charge rate affects battery life. Is is likely to be insignificant compared to depth of discharge, temperature, and max charge ( using range mode ).
Tom Saxton's experiments Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog found that 40amps to be optimal for energy efficiency.
Ambient temperature, cooling efficiency, charging efficiency of the Model S could easily make it different.
Mycroft
Life happens
The nice thing about the HPC is that you can program the car to draw at 40A most nights, but you'll have the full 80 whenever you need it.
Excellent. Do you have any links to detail this? They might help me with the decision. Thanks!
That's the way the Roadster works now. I have mine programmed to charge at 40A every night at 2 am. But if I ever want to charge fast I just hop in and dial it up to 70A.
Todd Burch
14-Year Member
Agreed...While 40A appears to be optimal for other reasons, I'm somewhat extrapolating that lower charging currents do less harm to the battery...but I agree that in the 40-80A range, it may have a very small to insignificant effect on battery life.
I could use some help. I am honestly confused. I am getting the 300 mile battery because there are about 10 days a year I drive about 200 miles in a day for work and will not have time to stop and charge. I will never take the car on a road trip. My wife would never have the patience to deal with charging. She is far too high strung. So, we will take her Mariner Hybrid. So, this charging issue has me confused. I plan on installing a 220 in the garage. How many chargers or what do I need. I was hoping just to plug it in to the 220 each night and top it off. I have also heard about a special charge for the 10 days I drive 200 miles. Please explain if you can. Thanks in advance. I would like to make this as simple as possible.
The way I understand it is twin chargers help when you're doing fast AC charging (60 miles returned per hour of charge vs 30 with one charger), but that requires a really high amp connection, such as the Tesla charger you can install in your house. So, in your case (and mine) you only need one charger. It's actually one of the reasons I chose to step down from the Sig because the 2nd charger was useless to me.
The "special" charge you mentioned is the quick charge, which is a DC charge and unrelated to whether you have the twin chargers (since those are AC). You don't need anything special for the DC quick charge except for the fact the 40kWh battery isn't supported, but you're getting the 85kWh so that's not a problem for you.
The "special" charge you mentioned is the quick charge, which is a DC charge and unrelated to whether you have the twin chargers (since those are AC). You don't need anything special for the DC quick charge except for the fact the 40kWh battery isn't supported, but you're getting the 85kWh so that's not a problem for you.
Mycroft
Life happens
You'll be installing a 50amp 240v receptacle in your garage and you will only need a *single* 10kw charger in the car for that receptacle.
Tesla hasn't said yet, but with the Roadster, there are two applicable charging modes. Standard and Range mode. The "standard" mode, which you would use daily maintains the battery at approximately a 75% charge. So a 300 mile pack would be normally charged such that you would have a 225 mile range. When you're going to be driving a longer distance, you set the charge the night before to "Range" mode. Then the batteries will be charged up to the top.
Edit: As ckessel says, to take advantage of the optional second 10kw charger in the car, you would have to use Tesla's HPC (High Power Connector), which will most likely use a 100amp circuit.
Tesla hasn't said yet, but with the Roadster, there are two applicable charging modes. Standard and Range mode. The "standard" mode, which you would use daily maintains the battery at approximately a 75% charge. So a 300 mile pack would be normally charged such that you would have a 225 mile range. When you're going to be driving a longer distance, you set the charge the night before to "Range" mode. Then the batteries will be charged up to the top.
Edit: As ckessel says, to take advantage of the optional second 10kw charger in the car, you would have to use Tesla's HPC (High Power Connector), which will most likely use a 100amp circuit.
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Thank you. I was very confused. It was starting to make me re-think even getting the car. Sometimes information overload leads to decision anxiety. I need this to be as simple as plugging it in every night. Anything more and I would lose all interest. I assume if I called an electrician and told him I wanted a 50amp 240v receptacle that he wold do that without any issue?
Pretty much. Just tell him you want the standard 14-50 socket. From a sheet Tesla has on their website about the charge adapter "Tesla recommends installing a NEMA 14-50R receptacle connected to a non GFCI 50A breaker".
I'd wait until the Model S charging sheet is formally released though just in case they have any changes, but in short, it should be a really simple, standard socket to have installed.
I've been told by a couple different Tesla employees that the standard cable included with the Model S will support the NEMA 14-50. It's cheap and easy to install at home, and ubiquitously found at RV Parks while on the road. Almost impossible to imagine them changing this.
BTW, don't tell your electrician that you're getting an electric car. Tell him you need the 14-50 for an RV you'll sometimes have there.
Mycroft
Life happens
I just remembered, make sure your electrician uses an RV style 50A receptacle and not a kitchen range style. The difference is that the RV style is designed to be plugged and unplugged relatively frequently while the less expensive kitchen range type is meant to be plugged in once and kept there. My understanding is that Tesla will have recommended receptacles available for purchase later.
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