220V vs. 240V

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Rat

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Can one of you engineer or electrician types explain to me why all the current (no pun intended) references to the charger are for 240 V? Until recently I always heard that home circuits and sockets were 110V and 220V. Now all I hear on the EV boards are about 120 / 240. Are these really the same thing - i.e. 110=120 and 220=240? Why the different terminology? I have a 220V home dryer plug in my garage, but is this too wimpy to support the charging station? I am concerned that the electrician will charge me to run an entirely new circuit from my panel to the garage, which are at opposite ends of the house.
 
Line voltage in the US was generally 220v or 230v with a center tap for 110v or 115v up until some time (2-3 decades?) ago. It was increased to a standard 240v/120v +-5% in north America. I can't tell you why, maybe someone else knows.

Many people still refer to line voltage as 110 or 220 out of colloquial habit. But it's usually actually 240 or 120v. US appliances are designed to operate at 120v +-10% (108-132v) or 240v +- 10% (208-264v).

A "220v" dryer plug is most likely operating at 240v nominal. It is probably energized by a 30 amp circuit breaker. The current vague information is that the 2011 Leaf can only draw 3.3Kw from the 240v outlet, which is less than 15 amps. Later Leafs are rumored to be able to accept up to 6.6kW (almost 30 amps at 240v). But electrical codes limit steady current draw from a circuit breaker to 80% or less of the breaker's rating, 12A for a 15A breaker, or 24A for a 30A breaker.

We don't know yet if the Leaf's EVSE (wall unit) can be programmed to limit 240v draw to say 15A or 20A. If it can't, then you'd want to have a 30-amp capable circuit installed to operate it (40 amp breaker). If the EVSE can be set to 15A or 20A, your dryer outlet can probably be repurposed (hard wired) as your EVSE supply.

EDIT: fixed incorrect breaker current fraction
 
Minor details:
I have read that 80% is the "permitted" continuous load on a breaker, so 24 amps from a 30-amp breaker.

Also, I believe that the power "standard voltage" is 120v (or 240v) +0% -10% rather than +-5%.

But, if you measure the "110" with a voltmeter in a relatively new neighborhood, you will probably find just over 119v in the (lightly loaded) morning, and rarely below 113 or 114 volts in the afternoon. But at the long end of a heavily-loaded supply wire or cord, it can easily drop to 110 volts.
 
I can't seem to find the source right now, but I remember reading that Nissan (or maybe some code) is going to insist the 240V EVSE must be installed on a dedicated 40A circuit, so your existing dryer line would not be acceptable, even though it can carry enough current for the 3.3kWh charger the first Volts will have.

And I'm sure most people know this, but you also can't just replace the 30A circuit breaker with a 40A breaker. You need to have thicker wires out to the garage.
 
Here is a little history...

http://wiki.answers.com/Q/Why_was_120V_chosen_as_the_standard_voltage_of_homes_in_the_US_and_not_some_other_voltage

In the United States, the electricity utility powerlines going to residential streets and roads are operated from 2300 to 2400 volts. With a 2400 volt supply, it is very convenient and easy to design and build pole transformers that have a 10-to-1 step-down ratio, thus providing 240 volts to the houses. The transformers also have a center tap to provide 120 volts from each 240-volt leg to the center point. This center point tap also provides a convenient point for a grounding connection. The actual measured voltage in your house receptacle circuits will normally be 120 to 125 volts. All appliances are rated for the minimum operating voltage (110-115), thus there is much confusion about the actual level of the supply voltages."
 
Good summary explanation by DeaneG, except for the 75%. As garygid points out, it is 80%.

Confusion arises partly due to the 80%, which, unless it is specifically referenced, causes trouble especially for the 30A number, because the breakers are rated in 10A increments (except for the lowly 15A single pole). So, the 30A breaker should be used to supply 24A, not 30A. In order to make use of the 30A continuous current you DO need a 40A breaker, but the actual allowable current is 80% of 40 = 32A. I have even seen erroneous references to the 30A draw in connection with some J1772 equipment. But the J1772 does not have a pilot signal for 30A ... the signal is 32A (as it should be, and in which case, gues what, it should sit on a 40A breaker).

(More confusion: many receptacles and plug have a maximum rating of 250V printed on them.)

My house is "overvolted" ... we share a transformer with only one other neighbor. Even under load my "240V" (nominal) supply runs 242V in the mornings and 247V in the afternoons. I have seen as high as 249V, but rarely. I have seen open-circuit voltages (volt meter, no load) on the "120V" (nominal) as low as 115, but usually running 119-122V.

edit: Note: I am getting all sorts of conflicting info in researching about the 30A versus 32A pilot signal in the J1772 spec. (Also see my reply a few posts down.)
 
The OP is actually a very good question. Maybe it's a good time to start a sticky FAQ thread, since some of our assumed info is becoming fact?
 
Maybe AndyH can check a recent copy of the J1772 standard and see if the "max current" (duty cycle of a square wave) signal has discrete allowed values, or is a more-or-less "continuous" value.

A graph I "saw" (or maybe only imagined) of duty cycle vs max current was a continuous slope, rather than a series of "allowed" values. But, it might have been old, or only "suggestive" of the meaning of the signal.

If only 6-amp "steps" are allowed, then 12 (from a 15-amp breaker) might be allowed, but the popular 15 (or 16) amps from a 20-amp breaker would not be available.

So, I suspect that mandating only 6-amp steps would be a (another) poor choice for this standard.
 
http://en.wikipedia.org/wiki/Mains_electricity

Edison selected 100 volts for the lamp as a compromise between distribution costs and lamp costs. Generation was maintained at 110 volts to allow for a voltage drop between generator and lamp.
 
I am hitting a bunch of conflicting info on the pilot signal meaning. ( I edited my timeout/note above. ) Yes, I've seen the graph that shows 6amp increments (from 6 to 48). But I am certain that older Avcons can provide 32A and rely on the 2001 version of the Standard. It's certainly possible that the 2010 version has changed the meaning of the signal, but unlikely. I don't have access to or am willing to pay for access to the actual standard. If AndyH could help here ... that would be great :)
 
I received a confirming email reply from a trusted and informed source. As I had suspected The 2010 J1772 Standard is designed around the 80% of breaker ratings for the ranges 30A-80A (meaning 24, 32, 40, 48, 56, 64 amp current draw). The 90A breaker, allowing 72A is reduced to 70A for a special reason encountered with the Tesla: 72A would have required the next larger wire size in the vehicle.

Some info on the 30A/32A confusion: for inexplicable reasons the UL approval for the J1772 connector was done at (and is listed at) 30A, rather than the closest 80% equivalent pilot signal (32A on 40A breaker). At least one EVSE mfg is ignoring the 2A difference.

(Side notes: By implication, the 2001 J1772 Standard is obsolete. A highly rare 35A breaker was ignored in the signaling choices. In the email reply: no mention was made of 100A*80%=80A draw, and signaling below 24A was not addressed (because that's Level 1 ?).)
 
LEAFer said:
I received a confirming email reply from a trusted and informed source. As I had suspected The 2010 J1772 Standard is designed around the 80% of breaker ratings for the ranges 30A-80A (meaning 24, 32, 40, 48, 56, 64 amp current draw). The 90A breaker, allowing 72A is reduced to 70A for a special reason encountered with the Tesla: 72A would have required the next larger wire size in the vehicle.

Hmm, this all seem somewhat "american" to me. In Europe (at least Scandinavia) we do not have the "80%" rule, we can draw what the breaker allows continously. The most common outlet is 230V 16A which the standard really should accomodate. The next most common one is 230V 10A. Next one after that would be 230V 32A I guess, no problem here. Though it's nearly always 3-phase at >25A but there should be no problem using just one of the phases...?
 
jkirkebo said:
Hmm, this all seem somewhat "american" to me. In Europe (at least Scandinavia) we do not have the "80%" rule, we can draw what the breaker allows continously.

The 80% rule is indeed american and comes from UL safety standards. Fuses, breakers, etc are sized to barely carry their rated load at 25C, oops, 77 degrees. If they are in a hot environment, they may eventually trip at rated load (you have to scrutinize the manufacturer's data sheet). So as cowboy engineers we derate to 80%.

In the rest of the world, where things seem to be better thought out (CE standards), fuses and breakers are rated to carry 100% of load over their working temperature range.
 
DeaneG said:
Sure would be nice to get specs on the "Nissan" EVSE: is the pilot signal programmable to 24A, or fixed at 32A?
The pilot signal is the EVSE telling the charger on the car what the MAXIMUM available current is. The car can decide to use less (and it should NOT decide to use more!).

Some EVSEs are a] user-programmable to select the maximum current (not necessarily something convenient) and/or b] field technician programmable (rarely adjusted). Much more convenient would be to do the programming on the car's user interface. For example, on a Tesla there's a screen where you can "dial-down" the amount of current to draw from the maximum signaled; and it also has an auto-start-time option for lower night-time rates.

YES! Get us the specs already, Nissan !
 
LEAFer said:
The pilot signal is the EVSE telling the charger on the car what the MAXIMUM available current is. The car can decide to use less (and it should NOT decide to use more!)....YES! Get us the specs already, Nissan !
Right, I was thinking of the people who want to repurpose an existing 240V/30A dryer outlet or circuit. Easy enough if the EVSE can be programmed to signal 24A max.

Or will Nissan mandate a 40A circuit with 32A EVSE signalling in anticipation of a 6.6kW update to the early Leafs?
 
I have a copy of the J1772 recommended practice from Jan 2010. I haven't yet played with any hardware designed to use this standard, so cannot say how EVSE manufacturers are actually using the info in the J1772 doc.

According to the document, the Control Pilot signal performs multiple functions. It allows the EVSE to properly detect that a vehicle is connected. The EV receives a signal that the EVSE is ready to supply energy. The EVSE is notified if the charge area needs ventilation. Finally, the EVSE signals the EV, by modulating the pilot duty cycle, to communicate the maximum available continuous current capacity.

5.3.5.1 IF the EV/PHEV reads a duty cycle of 3-7%, the EV/PHEV shall interpret this as a valid digital communications command.

5.3.5.2 IF the EV/PHEV reads a duty cycle between 8% and less than 10%, the EV/PHEV should interpret this as a valid 10% duty cycle.

5.3.5.3 IF the EV reads a duty cycle less than or equal to 85.0% the EV/PHEV should base the current on the Amps = (% duty cycle) * 0.6 formula.

5.3.5.4 If the EV reads a duty cycle greater than 85.0%, the EV/PHEV should base the current on the Amps = (% duty cycle - 64) * 2.5 formula.

5.3.5.5 IF the EV reads a duty cycle of 97%, it is recommended the EV/PHEV consider this as a valid 96% duty cycle.

dutycycle2.jpg


dutycycle.jpg


edit: added duty cycle interpretation table
 
DeaneG said:
Right, I was thinking of the people who want to repurpose an existing 240V/30A dryer outlet or circuit. Easy enough if the EVSE can be programmed to signal 24A max.

Or will Nissan mandate a 40A circuit with 32A EVSE signalling in anticipation of a 6.6kW update to the early Leafs?

The beauty of adopting a standard is that the vehicle manufacturer doesn't have to waste their time mandating much of anything. ;)

The EVSE can tell the car that anything up to 80A is available, and the car can say "I'm tired today - I only feel like 11.47A. Wake me when we're done."** :D

**Non-technical dramatization - not to be construed as an endorsement of either anthropomorphism or AI in ground vehicles. :lol:
 
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