Single vs. Dual charger?

Single vs. Dual charger?

What is the deal with the choice of buying a single vs. dual charger? It seems that the single charger handles 40 amps, and the dual 80 amps of 220 v AC. But why is this? Why is there any dedicated charger at all? Why isn't the PEM simply run in reverse to charge the battery, exactly the same way that it is done during regenerative breaking?

Tâm | 7 marzo 2016

Is this a serious question?

If so, what is "PEM"?

I google it up and it could be:

Portable Emissions Measurement
Privacy Enhanced Mail (1993 proposal for securing email using public-key cryptography)
Proton Exchange Membrane (for fuel cells)

Energy is just like shopping advertisement. When it's "free" or "save" that means you don't gain any money but you have to spend money to get those privileges.

The same principle with "regenerative" braking. You lose more energy then what you get back.

eric.zucker | 7 marzo 2016

Renault did exactly that with the Zoe, using the car's power electronics module as a charger. Saves weight on the car, may save some vehicle cost... BUT there is no electrical separation between the car's DC battery current and the AC input, which mandates the use of a much more expensive specific GFCI. (DDR type B in French).

Darryl | 8 marzo 2016

There is no single or dual option charger on a Model X on on Model S. Either you get a charge which can charge at 72 amp or one that can charge at 40. It all depends where you are charging at the capability of where you or charging.

eric.zucker | 8 marzo 2016

The 48A charger more or less fills up a 90kWh battery overnight (11kW for 8 hours is 88kWh). Note that the charge rate slows down as you get closer to a full charge. Going to a 72A charger means the same charge would take 5 1/2 hours, provided the feed in is sufficient (80A or more line and breaker for 72A charge).

It's been said numerous times, you can Supercharge no matter which charger is in the car.

psusi | 8 marzo 2016

@Tam: nothing you said makes any sense at all. PEM is apparently what Tesla calls the inverter module. As for losses, that is neither here nor there; the question is why have a separate inverter or rectifiler to convert AC to DC to charge the battery, when you can just use the same inverter you use to convert the DC into AC to drive the motor? It is used to convert the AC the motor generates during regenerative breaking into DC to charge the battery, so why not do the same from mains, like many commercial hybrid interver/charger battery backup systems do ( I'm talking whole house/buisiness ones, not your $100 computer UPS ).

@Eric.zucker: you have exactly the same separation that you get from a dedicated charger, and that has nothing to do with GFCI. GFCI is used for outlets in the bathroom or kitchen to immediately detect a short ( like that caused by a person completing the circuit from hot to ground ) and open the circuit. Yes, I understand the charge rates on both; my question is why isn't the 72A option the only option as the main inverter is quite capable of handling that much current.

@Darryl: They call the 40 amp version "single charger" and the upgrade to the 80 amp version "dual chargers" on the configuration page.

vperl | 8 marzo 2016

The MX has no 80 Amp Charger.

Read the information

psusi | 8 marzo 2016

@vperl: that's funny because when I got the invite to design my model X, there is an option there that reads "High amperage charger upgrade" and says:

Model X comes standard with a 48 amp onboard charger capable of charging at the rate of more than 25 miles of range for each hour of charge. This is sufficient to recharge Model X overnight when connected to a common NEMA 14-50 outlet or Tesla wall connector. Every Model X benefits from Tesla\\u2019s expanding Supercharger network for travel over long distances.\u003Cbr\\\/\u003E\u003Cbr\\\/\u003EThis option equips Model X with a 72 amp onboard charger for a 50% higher rate of charge when paired with a Tesla wall connector on a 100 amp circuit breaker. Charge rates when connected to 120 volt outlets, 240 volt outlets and Tesla Superchargers will be unaffected.

MrBuffer | 8 marzo 2016

I'm pretty sure if you run the Model X in reverse it recharges the battery.

Waldek | 8 marzo 2016

@psusi it is either 48 amp or 72 amp... not 40 and not 80 :)

eric.zucker | 8 marzo 2016

I just was last Thursday in an intensive training session for electricians installing EV charging infrastructures.

Regulation mandates to have a GFCI on the circuit that charges your car (at least the little box on the mobile charging cable), so your life is protected if the car body somehow should not be properly grounded.
Cars do get wet when it rains. A GFCI detects minute differences (10 to 30 milliamperes to protect human life here) in current flow between live and neutral. If electrons are missing, they have found another path to Earth, which can be through a human body. Ground Fault Circuit Interrupt.

I will not speculate if Renault's Zoe charger is well designed or not, the fact is that you can't charge on a line with a standard GFCI.

Red Sage ca us | 8 marzo 2016

MrBuffer: Only downhill. During gale force winds. On Tuesdays.


johnse | 8 marzo 2016

@psusi Yes, there are two charger options on the Model X, a 48A unit and a 72A unit. There is no "dual charger" option as there is on the Model S--it's a single unit of one capacity or another.

The question you are asking, if I may restate it to be sure I understand, is why have a separate charger unit at all. Since the charger is used to convert AC to DC to charge the battery, and the regenerative breaking also converts AC to DC to charge the battery, why can't this circuitry be dual-purposed.

In theory, you could do this. However, I suspect this would significantly complicate the circuit. The two systems have very different characteristics. Here are just a few (here I am speaking from a US-centric view. Some details would be different in Europe):
1) In the US, the 240V power most often used to charge the car is single-phase (often also known as split-phase since the single 240V line is used to power two 120V branches 180 degrees out of phase with each other).
2) The AC induction motor is a 3-phase AC device. The voltage generated will vary significantly based on how fast the motor is turning.
3) AC mains voltage and frequency are constant. Regen breaking is extremely variable.
4) The Charger needs to communicate with the EVSE to determine the current it is allowed to draw (For example, it can't draw 11kw from a 6.6kw Level 2 charger. If it tried, it would trip breakers and/or damage equipment.)
5) The regen circuit needs to handle much higher currents. It is challenging to produce circuits which handle significantly different current ranges (and we're probably talking at least an order of magnitude difference) and have acceptable efficiencies throughout the range.
6) Efficiency counts more when charging from EVSE than during regen breaking.

I suspect that it is much easier to design two circuits, each tailored to their purposes, rather than a single circuit which has to handle both cases. I also suspect that the dedicated charger is able to do a more efficient job (and possibly better battery management and cell balancing) than the regen breaking circuitry.

(BTW: I think some people misinterpreted your question to be another of the perpetual-motion "questions" which arise here too often when someone thinks they can charge the car by running a generator off the wheels while driving down the highway.)

@eric I think that the GFCI concerns would be taken care of by using an isolating transformer. Such is probably also used in the onboard charger anyway. But these other issues are probably the determining factors.

Tâm | 9 marzo 2016


Thanks for clarifying your question.

I misunderstood it as "why would I need to an unnecessary charger for my car when a built-in regenerative braking system would cover that problem as in a perpetual motion/perpetual generator concept?"

I didn't know what PEM mean which didn't help to understand your question.

I was further confused when you mentioned "Single vs. Dual charger" in Model X forum because as others explained that Model X has an option of 48 OR 72 A charger only, not dual, not 2 chargers.

It would be clearer if the title would be:

Can you use the motor AC-to-DC inverter to task both 1) regenerative braking charging on the road and also 2) stationary household AC charging?

I do not know the answer but @Johnse explained it well.

However, my preference is to have separate systems for:

1) Regenerative braking charging.
2) Household voltage charging.
3) Supercharging.

That way, if one system fails, others can still perform their jobs independently.

psusi | 9 marzo 2016

Single/dual vs. large/small; six in one, half a dozen in the other. I guess it was the S that they called single/dual and was 40/80... slightly differnet for the X, but same concept.

Supercharging is done by not using any charger at all and connecting the supercharger directly to the battery, pumping DC into the car instead of AC. This is why the superchargers are so expensive; they have to produce whatever voltage the battery pack asks for, and at very high current. The other chargers just connect mains to the car and let the car worry about converting it to DC.

The main inverter does have to handle very high current during regen, as well as variable voltage and frequency, but it is not limited to only high current; you can have your foot on the accelerator to limit the regen and slow the car gently. That means the inverter has to regulate its current output based on the accelerator. It could just as easily do that in response to the current limiting requests of either the charging station or the on screen setting that lets you limit it further. Since it is already capable of handling a broad range of voltage, frequency, and current, it should be easy for it to accept the constant voltage and frequency of the mains, at a much lower current than happens with regen.

As for the split phase issue, that is still true with a dedicated charger and it is handled by simply leaving one of the three phases dead and only powering two of them. That's why you charge faster from a 3 phase charging station than a split phase one: you are getting the rated current on all 3 lines instead of only two.

eric.zucker | 9 marzo 2016

In principle it's doable. Now how about thermal management? Regen is unlikely to be happening for hours on end in a stationary situation.
Add risks to the vehicle in case of brownout or power spikes. If lightning fried the charging unit, it may be easier to replace than the PEM. Dead charger, you might be able to drive to a SC. Dead PEM...

vperl | 9 marzo 2016

To be clear, the MX does Not have dual CHARGERS.

This is the X forum

Hooking up to a TESLA Supercharger bypasses any Charger. The DC flows into the BP, the Charger on the X does nothing.

AC charging is controlled by the low voltage Charger by itself . If one orders the optional high power charger built in separately in the X the AC charging is faster.

milesbb | 9 marzo 2016


Bill Howland at this site:

Bill claims AC Propulsion has a patent in the US and will SUE anyone trying to do that here. Tesla does this "somewhat silly " thing because they don't want to be Sucked Dry by AC Propulsion

ian | 10 marzo 2016

@psusi - The superchargers do indeed use chargers, in fact, they are the very same chargers found in the S just a bunch of them stacked together located in boxes near the charging station. That is how they convert the AC from the utility feed to DC to dump into the battery.

psusi | 19 marzo 2016

@milesbb, if they do have a patent on it then that is yet another example of how broken our patent system is. If it was so obvious to this armchair engineer that I can't believe everyone isn't doing it, then it isn't a novel invention worthy of a patent. There is also plenty of prior art of using an inverter to both charge the battery from mains, and convert back to AC when mains fails to invalidate such a patent in other applications outside of automotive.

@ian, yes, that is exactly what I said -- the supercharger is its own external charger, rather than using the on board charger that non supercharger stations use. The question is why do we have to pay extra for a high capacity charger in the car, as well as the 100 amp capacity charge station in the garage. The latter I understand, but the former I do not.

vperl | 19 marzo 2016


The single on board , ( either the small or larger Amp Charger) is a single Charger for AC.

The SUPERCHARGER system delivers Direct Current only straight to the battery.

If you live in a developed country AC is more readily available.

But, that might not be your concern

natalee | 10 luglio 2019

When considering buying a used Model S I want to ensure that that car has Dual Chargers. Does anyone know of a way to confirm that before purchase? I don't want to buy a car that charges at a slower pace. | 10 luglio 2019

@natesdesigns - If they provide the window sticker, it should be listed on it. You could also try to charge it at a destination charger, but many are limited to 40 amps, so that will not tell you much. You could lift out the rear bottom seat and look at the two charger boxes. I found pulling the rear bottom seat to be difficult.

If you're new to EVs, while a few owners enjoy the dual charger, very few owners really need it (and is one reason Tesla discontinued it). If you charge at home, you'll usually have 8 hours at night when it charges. A single charger car at 40 amps, will always be full when you leave. If you use Superchargers during travels, the dual/single charger in the car is not used - so it doesn't matter there.

One scenario that helps, is if you travel towards the end of the range (250 miles or so) during the day, you come home for a few hours, and then go out for another 100+ miles, having dual chargers may be of value. Can't say the situation ever came up for me in 6+ years of Tesla ownership, but that's just me.

iefbr14 | 10 luglio 2019

Charge Current field on the charging screen on my dual charger MS85 shows 80A max; presume a single charger would show 40A max.

jjgunn | 10 luglio 2019

Tesla service centers seem to have the 240v @72 Amps. I've seen it in action & it's a "nice to have" in the Model X. Beaver found some destination chargers in South Dakota that ramp up to 72 Amps too. But they're few & far between.

TBH....240v/48 Amps is probably more than you'll ever need for home charging.