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Discussion in 'Model S: Battery & Charging' started by artsci, Sep 11, 2013.
Will having dual chargers further speed the charge with a supercharger? If so by how much?
No, they are separate. The supercharger DC power goes directly to the batteries and bypasses the on-board chargers.
superchargers use DC (direct current) directly into the battery bypassing any onboard chargers. you could have 0 chargers in the car or two non-functional dual chargers and supercharging would still pump 120kWh of juice into your batteries. the onboard chargers are for taking AC current and converting it to DC current for the batteries. with single charger the max you can pull is 40 amps from AC. with dual chargers the max you can pull is 80amps. so to answer your question no, it makes no difference. dual chargers only allow you to charge from higher than 40 amp AC sources.
I will add that the SuperCharger is actually manufactured with (12) of the same 10KW charging modules that are used inside the Model S... It's just the AC is fed to them directly, and their DC output is ganged together and sent to the Model S's charging port.
Their are internal switching relays that switch the input to the onboard charging modules directly to the nearly 400 VDC of the battery pack.
Gee, I also don't really know how Superchargers work. I know about the 10 kW chargers being stacked, but I don't know how it works to split the charge between two cars connected to the same Supercharger. I would like to know.
Well, for starters, having a dual charger or single charger on your MS has no impact on speed of charging at a Supercharger. None. No connection at all. Now, it is a different issue altogether when two cars are connected to Superchargers that are drawing from the same current, so that the second car charging usually is drawing far fewer amps and getting the short end of the stick. But that still has nothing to do with whether the car itself has single or dual chargers.
I'm no EE, but here's an attempt at a very simplified explanation of the different types of charging (basically a picture of what yobigd20 wrote). The reason it is complicated is that there are two "types" of electricity, AC and DC.
DC is the positive-and-negative type that you probably experimented with in 7th grade science. DC is what portable electronics use. It is simple and easy to store in batteries.
AC is a little more complicated because it switches back and forth, but its key advantage is that it can be transmitted better over long distances. So AC power is what comes in through the power lines in to your home, and is what is available at power outlets. Appliances that use electricity directly from socket and don't need to store it for portability (lamps, refrigerators, washing machines) use AC power.
But if outlets have easy-to-transmit AC, and your portable electronics use easy-to-store DC...somewhere, the electricity must get converted. This conversion happens in a magic black box called a rectifier. Your cell phone, iPad, laptop etc all have one: it's in the black box in the charging cord. You'll notice that the larger the device, the larger the rectifier is. Your car needs one (an even bigger one!) too. The key to understanding the different charging types is learning where the rectifier lives. Here is a simple diagram:
When you plug in to AC power (whether it's 120V or 240V - and whether you use an outlet or an EVSE) you use the rectifier in your car to do the conversion.
When you use a DC charging station like a Supercharger, the rectifier is in the charging station, so DC goes straight in to your battery (well, not really, but close enough).
Note that in both cases the power starts as AC and ends up as DC; the only qualitative difference between "AC charging" and "DC charging" is whether the AC electricity gets converted to DC before or after it goes in to your car. Quantitatively, AC charging is much easier to find, but DC charging is much faster.
So questions about Model S charging:
1. Why is the rectifier sometimes in the car, and sometimes in the charging station? Why not always have it in the same place?AC outlets are everywhere. To make charging convenient, your car should be able to plug in to them. But the only way for that to work is if the rectifier is in the car (or in a box that you carry in the car). So every EV has its own rectifier. But they are big, heavy, expensive, and give off a lot of heat. So nobody wants to put a REALLY HUGE rectifier in the car. A huge one wouldn't help anyway, as most outlets you are likely to run in to only have about 10kW of power (you can get a little more power fairly easily, like maybe 20kW; there are just not often plugs for them).
A DC station has special hookups so it can get way more power. And it needs REALLY big rectifiers to convert that power. So DC charging stations are very big; bigger than anything you want to carry in your car. But you can get a lot more power from them. (The smallest DC chargers I have seen are 25kW; Superchargers are up to 120kW).
In short, AC charging is convenient, but has limits on speed. DC charging is considerably faster, but not as plentiful and much more expensive to install. Most people want both.
2. Why do the 120V and 240V pictures look the same? Doesn't the EVSE (commonly called a "charger" but it's not really; Tesla calls their EVSE an HPWC) have a rectifier?No. An EVSE is just an outlet that is trying to not kill you - it doesn't expose you to 240V power (it uses a small 12V DC line to talk to the car, and won't turn on the 240V AC line until it knows it is plugged in). It doesn't have a rectifier or other things necessary to make it a "charger".
3. So what are Tesla's "twin chargers"?Simplifying greatly, it's two rectifiers in the car. So now you can convert 20kW of power from AC to DC instead of the standard 10kW. This limit was probably chosen because 10kW is all you're likely to be able to pull from regular outlets (240V * 40A = 9600W). You are only likely to get 20kW if you hard-wire in a special appliance, like an HPWC. All of this only matters if you plug in to AC power; it is not needed for DC charging because DC chargers have their own rectifiers.
Most other automakers only have 3.3 or 6.6kW rectifiers. The two main exceptions are the Toyota and Mercedes EVs that use a Tesla powertrain; they have Tesla's 10kW rectifier.
4. Ah, so is this what Tesla means when they mumble something about modular charging?Yep. Tesla makes 10kW rectifiers in large quantities. Every Model S gets one. If you buy twin chargers, you get two. And Superchargers have a stack of 12 of them. The rectifiers are the same; it's just a matter of where they live, and how many of them there are.
Thanks very much for the education.
Thanks, I know that on board chargers have nothing to do with the Superchargers. My comment was trying to get ckessel, who thought the OP was clueless, to explain, how the entire system works.
Guess he doesn't know.
Never mind, I know what I need to know.
Great post Chad!