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Dual Chargers

I am unsure on whether to get the dual charger option. My expected driving pattern from home is not enough to justify getting this option with the High Power Connector for home use, but I am unsure about longer road trips to places that may not have the Supercharger access. As I understand it, many J-1772 charging stations are set up with relatively low current circuits that are fine for the Nissan Leaf, but would not support the full 20 kW dual chargers for the Model S using the proper connector. I have checked all the online sites (Recaro, Plug Share & Car Station) and can find no details on which J-1772 charging stations would support an 80 to 100 amp circuit necessary for medium fast (60 mile per hour of connection) charging.

Does anybody have thoughts on this? The core question is how to find out where the high current J-1772 stations are located to make the decision on dual chargers for someone like me who only needs this function on the road and not at home.

I'm 99% sure that I wont bother with dual chargers. Since they are not a requirement for supercharging and I drive on average less than 60km (35miles) per day it's pointless.

Here in Australia the standard wall sockets are 230V, 10A. This will give about 2kW, so around 12-15km/h charging rate. With the car being parked for at least 12 hours overnight every day it would recharge more than double what I use.

I'm looking at putting a 20A or 32A (230V) outlet in the garage that would give me up to 7.2kW. Still less than the 10kW single charger but enough to recharge the car from empty overnight.

The only consideration that would change this is if there were a lot of 20kW chargers on the open road where there weren't superchargers. At the moment its a moot point as there aren't even many 32A 230V chargers around.

Given your apparent requirements, I wouldn't get the dual chargers. Even if you plug into a high amperage charger, the negotiation between the charger and the car would just limit the current automatically anyway. The only worry would be someone who comes along and wants to use the full current.

I'll add that everyone at Tesla that I've talked to feels that the second charger can be added after you purchase the car for about the same cost as purchasing it with the car. Just about all also suggest waiting. That being said I am going to get both initially because the of the road trips I do and the ability to charge off of 70/80 Amp Tesla HPC's along the way. I don't have much hope of finding many if any J1772 chargers greater than 30A.


"about the same cost as purchasing it with the car"
From a materials perspective, I believe we've heard that stated officially from Tesla.

From a labor perspective, installing it after *has* to cost Tesla more .. so I'll presume they'll charge a bit more, accordingly.

If you have the money: get it.

If you don't, then don't.

It's a simple question really.

I'm thinking that I'll get them for two reasons: resale/trade-in value, and I think that the car will be such a pleasure to drive that I will want to do many more "day trips." With the money I save in gas, I can drive a few hours, go out to lunch while charging, and then make my way home.

Resale value may be the best reason to have the dual chargers. By the time you're ready to part with your car, assuming BEVs really take off, high power J1772 chargers will be much more common. If your car cannot take full advantage of those chargers, that reduces its value relative to other cars on the market.

Here's my thoughts and how I made my decision to get the dual chargers.

#1--the cost differential was fairly minimal
#2--I've never owned an EV before and have some range anxiety/concerns
#3--I do hope to use my Model S for some longer highway trips that will almost certainly require at least a partial top-up prior to getting to my destination or home.
#4--I think we are in some rapidly changing times and that there will be more and more higher capacity chargers available over the next several years. I intend to keep this car for at least the next 7 years and probably closer to 10 yrs. The ability to recharge 62 miles in an hour is significantly greater than 31 when you're traveling and using a charger.
#5--At times I need to make quick turn arounds...perhaps commuting to work, home and immediately needing to leave for a more remote destination. The ability to top up the charge in a very short period of time will be handy at those times.

I was very close to not going with the HPC and twin chargers and I think that for most people they won't be "necessary". But I also suspect there may be a time or two for everyone where you wish you had it.

+1 @EFusco. I am already wired with a 100A/230V outlet in my garage, and had decided to go dual chargers when Tesla called me re Sig waiting list. That made the premium for sig more reasonable to me since dual chargers etc. are of course included.

I don't have that many long trips planned, but home to/from the beach is a 220 mile trip, which I fully intend to drive in a 'spirited' fashion.... and it will be comforting to know that the car will be fully recharged always the next morning even after a long weekend.

The charge adapters supplied with the model S are 10k capable. The dual chargers are only necessary if you get the home charger unit which is 20k capable. Third level charging does not require dual chargers because the DC voltage is fed directly to the batteries.

@stephen.kamichi - correct, when I said "outlet in my garage" I mean wires to connect my HPWC. Yes, my order includes the HP wall connector.

Twin charges (even without HPWC in your garage) is for "future proofing", resale value, and best available technology access while traveling reasons as others have posted.

I am looking at the 40kwh battery and in my mind this almost requires the twin charger for that just incase time when you have to wait to top off to get home. This would 1/2 the wait time.

This in mind I am now confused when I look at the web site and after speaking with a Tesla badged gentleman who was at the NY test drive and said he was hired to install the DC quick charge stations.

First the web site states two conflicting specs for the mobile charger:
The Mobile Connector is included with every Model S and allows you to charge almost anywhere.

2. 10 kW capable Universal Mobile Connector with 110 V, 240 V, and J1772 adapters
3. Public charging station adapter (J1772, 80 amp capable)

Then the Tesla gentleman also said 40 amp only. He also did not think the DC stations were going to have the standard tesla chargers to let us twin-chargers top off. This would be a great disappointment and rather shocking if they did not have 2-3 twin-chargers at each.

So this makes me think:
1. it does not support more than 40 amp
2. it does support 80 amp
3. it does but with a separate 80 amp adapter

It would be nice to know.

The mobile connector only supports 40A (9.6kW). To get the full 20kW you need the HPWC or a public 80A J1772 EVSE. I don't think finding >40A public connectors would be very easy anyway.

The DC quick chargers have nothing to do with single or twin chargers. It bypasses them entirely. Teslas quick charger ("Supercharger") is basically 9 10kW chargers in a big box, feeding DC to your battery. The quick charger has the proper cable attached already, nothing else needed.

But a 40kWh battery will not allow DC quick charging.

I had a thought about the twin charger after driving the S. I commented that the car's regen didn't seem very strong, the Tesla employee said at higher speeds, the car couldn't convert the kinetic energy back to electricity fast enough to slow the car at the same rate as it does at lower speeds. Does it follow then that with the twin charger, regen has the potential to be twice as agressive?

I don't think that follows. It's unlikely that the regeneration path goes through the chargers.

Bear in mind that regeneration throws aways some of the kinetic energy as heat so while it's better than throwing all of the energy aways as heat (the way friction brakes do) it's not as good as gliding to a lower speed (or stop) where a larger portion of the kinetic energy gets converted into forward motion.

I don't know if that follows, but seems worth asking. I think regeneration has to go through the charger(s), since the AC motor running ias a generator (regen mode) produces alternating current, which must be converted to DC to charge the batteries.

I suspect the 85kwh battery can accept charge faster than the 40kwh, so would have stronger regen, too. In Doug's (?) video, the car was slowed to 45mph, and dropping going downhill with just regen. And all the cars made so far are 85kwh.

I believe the "inverter" is what converts DC (battery) to AC (3 phase for the motor) and also converts AC (3 phase from the motor when acting as a generator) to DC back into the battery.

Think of the single or twin chargers simply as the "wall bug" that comes with your computer or phone: it exists only to convert house current (be that 110VAC or 240VAC, at 10-80A depending on your configuration) to DC strictly for the purpose of charging the battery.

Yep, the charger(s) have nothing to do with regen.

At higher speeds, much more energy needs to be dissipated to slow the car down. Regen is simply limited by how fast the battery can accept the charge and the grip of the rear wheels.

Regen should theoretically be limited in around the same scale as the energy transfer the other direction (i.e. Acceleration). Currently this is incredibly higher than the "high" regen setting. I would not want 60-0 when releasing my foot from the accelerator in 4.4 seconds however, so "full" regen is probably not practical.

You'd need a VERY heavily padded steering wheel. And strong shoulders. ;)

I opted for no dual or charging station. These are pretty much the only options I didn't get. I will use supercharger on the road and saved 3k. I'm leaving my car plugged in all night anyway so who cares if it charges a bit faster.

Leofingal: Nope. Most batteries can deliver way more energy than they can accept from a charger. 4C discharge/1C charge is fairly common.

And with braking comes weight transfer forward. Too high regen and the rear wheels will lose their grip.

- And with braking comes weight transfer forward

In the Model S the center of gravity is about the same height as the centre of the axle. Weight transfer is close to zero--it might even be negative. Note that the rear brakes on the Model S are are larger diameter than the front brakes.

Agreed about the rate of charge vs. discharge. Charging is much lower.

Ok, I'll accept a factor of 4, but that is still a lot faster than current settings, so it is a software limit.

@pilotSteve (et. al.) - Thanks for clearing up the regen functionality not using the charger!

Just when I think I really have a handle on how this car works, I find out how wrong I am. I guess it doesn't pay to get cocky.

@Leofingal - Since you can essentially drain your battery in an hour or a little less (at 100+mph), and full power charging from the HPWC takes 4:43 according to Tesla's calculator, it probably closer to a factor of 5.

I think that's about right; the max from an HPWC is a touch over 60 miles of range per hour charging. Not a straight line, though; the last 20% takes a lot longer than the first 20%!

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