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Breakfast Know-It-All Electric Car Question

2182 Views 16 Replies 8 Participants Last post by  Yinzer
Ok, Good Morning! I have a table-full of self proclaimed experts on basically EVERYTHING!
Can anyone tell me what amperage a smart car pulls from your house power during a charge?
I have all kinds of answers here! Also, what about, say, a Tesla? Its a bigger, faster car so bigger battery??
Guys, I’ve got a breakfast riding on this!
Larry in East China Mi
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Forgot to mention: the type of "EV charger" being used should have the final word on how many amps will be drawn from the wall plug: check the input power rating of that charger.
Also, 240 volt household circuit outlets in the USA are typically either 30 (aka "clothes dryer circuit") or 50 amps (aka "kitchen stove circuit"). Each has a different style plug/receptacle so they are not mixed up.
Back to the very original question...
What the charger will pull depends on the charge controller box and the car. The actual charger is part of the car, and the controller box "negotiates" between what power is available and what the car can take. A US-spec Smart can take upto 30A at 240 V (7.2kW), but if you plug it into a 120 V household socket, it will pull what the controller box allows, which max out at around 14A, as they assume they are on a may 15 A circuit.

A Tesla plugged into the same charge controller box will get the same charge rate (which is why it takes days to recharge a Tesla plugged into the wall). Teslas also have DC fast-charge options (that the Smart cannot use) that charge at much higher rates (on the order of max 400 V at 80 Amps going from memory), but requires plugging into a DC supercharger.
There is no real "negotiation". The EVSE sends a +/-12V square wave signal to the car - the duty cycle of the square waves indicating the maximum current that can be drawn from it. The car will draw that maximum amount, or the maximum amount its on-board charger can draw, whichever is less.

For 451 ED's in the US/Canada, that maximum draw is about 14.5 to 15 amps - so the car, not the EVSE's circuit is dictating the draw since the 240 volt EVSE circuit is always going to be at least 30 amps ("clothes dryer" circuit), or 24 amps safe continuous (80% of the circuit breaker rating).

For the 453EQ in the US/Canada, the charger can draw 30 amps, so if the EVSE is connected to a 30 amp circuit and is properly set to only allow 80% of that, then the Smart 453 will draw 24 amps. but if it is a 50 amp circuit (40A continuous), it can draw the full 30 amps.
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Irregardless of all this Science, LOL, when I first got my 2016_ED I decided not to use the charging techniques that I have always used on my Teslas, ie charge as fast as possible using max current into the car. This to save the Smart battery by SLOW charging whenever possible. So this means 120 volts and "8 amps" instead of "12 amps" and or 240v. Also since the car does not allow setting a cut-off point to stop charging the Smart at say 80%, like you can easily do on a Tesla, I purchased an inexpensive rotary-dial 15 amp timer at Walmart to turn off the charger before it reaches 'full'. If needed I can fully charge the Smart just before leaving home, which results in no strain on the battery since you begin depleting as soon as you reached 'full charge'. Overkill perhaps but replacing a Smart hv batt is a pricey proposition indeed.

Note: if anyone knows how to stop charging the Smart prior to 100% please advise. I've read the owner's manual but can't find it.
There is no way to finish charging short of 100 percent - and having checked the cell volts (about 4.15 volts) at the end of charging, it IS 100%. I use a start/stop timer on my L2 Open EVSE so it is just finished charging about an hour before the car is used. Or for partial charging, plug it in close enough to the stop time so its does not get fully charged. As far as rate of charge, the maximum rate of charge on US/Canada Smarts is so low (about 9-10 DC amps or just C/5) that worrying about the deliterious effect of rapid charging is probably overkill. In Europe with their 400 volt 3-phase power available, the 22kw (1.2C) charging option is used all the time without apparently degrading the battery.

The US/Canada's 120/240 one-phase residential electrical standard - which was once arguably better than Europe's 230/400 volt 1 or 3 phase from an electrocution safety standpoint, is now definitely an inferior standard with the introduction of EVs.
My smart ED charges at 12 Amps every time I charge it...
Is that 120 volt (Level 1) charging? if it is 240 volt, then your "Charge Curr" setting in the "charge and depart" menu is set to "12A", not "Max".

The currents I was referring to in my recent in my post above are the DC amps into the battery which are lower than the AC amps because DC voltage is higher than the AC in voltage.
Normal operation. 12A is the most that you should be continuously drawing from a 15A circuit.
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