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I know that on an ICE car, the alternator keeps the 12v battery charged. How is the 12v battery charged on our electrics? If the 12v battery gets discharged from leaving the lights on for example and the car gets a jump to get it going, how long must the car be driven to make sure it has enough juice to start it up again? I know the 12v battery doesn't have to work hard if no accessories are being used, but I'm curious on what precautions should be taken.

Len
2014 EV Coupe 14,500 miles
2014 EV Cabriolet 4,000 miles
 

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.... feel free to correct me if i'm wrong.... but does the ED even HAVE a standard car battery? I mean... it doesn't seem like it logically would, since it doesn't have to rely on a spark to get the engine going, and anything electrical can just run off the other batteries. Don't even think there's actually a way to jump start a car, since there's nothing to really "jump". It's just batteries, an "ignition", and an electric motor.

Again... feel free to correct me if i'm wrong. I'm getting ready for work, and don't really have the time to dig deeper... just going by my understanding of the whole thing.
 

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.... feel free to correct me if i'm wrong.... but does the ED even HAVE a standard car battery?
Short answer, YES ED has a 12V battery located in the same place as the ICE version.

The 12V powers the accessories while the HV battery pack is the Traction (or propulsion) Battery.
 

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Short answer, YES ED has a 12V battery located in the same place as the ICE version.

The 12V powers the accessories while the HV battery pack is the Traction (or propulsion) Battery.
Then why does turning on an accessory (eg., Heating/AC) diminish the estimated range of the vehicle? I see my estimated range drop by 2-3 miles when I start the fan, and when I stop it, the range goes up again.

2015 451 ED
 

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Huh - glad I asked the question. Looks like I'm not the only one with questions about the 12v battery. Here is why I asked the question.

I got a call the other day from a Smart ED owner. He told me he left his lights on and when he went to start his car the next morning, it was basically dead. He had to use the key to unlock the door, etc. So he proceeded to jump the battery per the instructions in the owners manual using another car and jumper cables just like one would jump an ICE vehicle. So he was able to start his car and drive it five miles to work where he plugged it in to recharge the "big" battery. A few hours later he goes by to check things and all is apparently well again with the 12v battery. So did the 12v battery get charged during that short drive or did it get charged along with the "big" battery?

Len
2014 EV Coupe 14,500 miles
2014 EV Cabriolet 4,000 miles
 

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Then why does turning on an accessory (eg., Heating/AC) diminish the estimated range of the vehicle?
HVAC is a "major draw" component and while it it is likely 12V, receives its (stepped down) power from the HV.

The HV battery pack and regeneration is the source of the 12V recharge when not on EVSE.

12V Accessories = management computers/relays, lights, radio, power windows, butt warmers and circulation fan.
 

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A few hours later he goes by to check things and all is apparently well again with the 12v battery. So did the 12v battery get charged during that short drive or did it get charged along with the "big" battery?
Probably a combination of both to include regeneration?

When ED's were new to the market, I nearly scored an ED at DEEP DISCOUNT from a rather naive non-MB dealer.

He thought that the HV battery was "bricked" not knowing that there are TWO batteries and with the 12V dead the management computers are in deep sleep.
 

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Short answer, YES ED has a 12V battery located in the same place as the ICE version.
The 12V powers the accessories while the HV battery pack is the Traction (or propulsion) Battery.
If you think about the engineering to make an electric 451 when you've already engineered the gasser, you want to concentrate your efforts on the things that make the electric drive different and share as much bog-standard parts with the gas car as possible. All of the low voltage systems have an expectation of voltage ranges and stability (and you're already buying thousands of them for the gas cars) that is met in the case of the gasoline car with the large battery acting as a buffer and voltage stabilizer.

You could try to engineer a buck converter and capacitor bank to provide the same level of stability and feed the 12V systems directly off the traction pack, but that also would require the main contactor to be closed (which is a small safety concern of sorts as well as an additional drain on the traction pack). You're also building maybe 1000 smart electric drives, so you don't want to spend NRE costs on something that you don't have to.

Instead, the cheaper (and very good) engineering solution is to have the 12V battery charged (most likely from a buck converter setup) only when the main battery is "in use" (meaning the car is running or charging) and otherwise completely isolate the traction battery. This allows anything engineered for the gas smart cars to "just work", allows people to add 12V accessories without (much) worry about how to interface them to the car, and the only penalty is that you have to periodically "use" the car somehow every so often, else you risk having a flat 12V battery, which isn't all that different from an ICE car.

See the last Q here for a (tiny?) bit more information: https://www.smartusa.com/resources/downloads/manuals/electric-drive/battery_faq.pdf
 

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Jim S.

Good explanation.

The safety requirement to totally isolate the high voltage inside the traction battery pack case when the car isn't in drive mode seems to be the main reason for the separate 12V battery - which only gets charged when the car is turned on (which requires 12 volts) and being driven (or charged?). But still, in the days of home-built electric car conversions - everybody just used a DC-DC converter. And, electric motorcycles and scooters use just a DC-DC converter.

But yes, I had to charge the 12V battery on my Smart just once after I left the lights on....

Oh, and regarding your link and its stern admonition against using extension cords with the 120 volt charging adapter - that's just ridiculous. The 120V charging adapter (which, when I turn my Smart in in 6 weeks will have only been used once) is practically unusable without an extension cord. The Smart owner just needs to make sure the extension cord is good for 15A and it will be fine.
 

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HVAC is a "major draw" component and while it it is likely 12V, receives its (stepped down) power from the HV.

The HV battery pack and regeneration is the source of the 12V recharge when not on EVSE.

12V Accessories = management computers/relays, lights, radio, power windows, butt warmers and circulation fan.
The HV battery also directly powers the heater element and the AC compressor. Using 12 volts to power these multi-thousand watt components would not be practical. But yes, every other accessory, including the blower motor and optional heated seats are 12 volt.
 

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My Tesla driving friend uses a 10 gauge 50' extension cord
to charge his Model S and, neither the cord or circuit breaker
get even slightly warm...
 

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Yeah, I think the no extension cord admonition is CYA on the part of the manufacturer. There are some dodgy extension cords out there, but any reasonable quality extension cord wouldn’t give me cause for concern.

But it’s easier to blanket recommend against than to try to educate consumers on wiring gauge, copper vs CCA, etc.

I cited the FAQ just as reference for the anyone who doubted there was a 12V battery in car.
 

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Regarding extension cords....

All wires have some internal resistance. Typically, the larger the diameter, the lower the resistance. Manufacturers size cables based on current draw, plus a little overhead for safety. Adding an extension cord increases the resistance of the circuit. In extreme cases, an insufficiency sized cord causes enough resistance to cause increased current draw and possible component damage.

Additionally, using undersized extension cords, particularly for high current loads can cause the extension cord to become hot enough to start a fire.
 

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Yes, but... What's the difference between a 12/2 romex cable running an extra 20' to an outlet and a 12/2 extension cord running the same 20' from an outlet? The only difference I can see is a plug connection instead of twisted wires.
 

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Yes, but... What's the difference between a 12/2 romex cable running an extra 20' to an outlet and a 12/2 extension cord running the same 20' from an outlet? The only difference I can see is a plug connection instead of twisted wires.
It's because your 12/2 romex cable doesn't move around the house and get beat up like your extension cord. Your extension cord is getting twisted over time which causes the copper strands to break. That causes more resistance. In time, your extension cord can become a hazard. Especially after you've been using it a few years without issue. You forget to feel it and see if it's warming up. It's a hot day and someone laid something on just one part of the cable.
 
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