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Discussion Starter #1
The EPA rates the Bolt range at 238 miles. That gives 238/60 = 3.97 mi/kwh (and that seems perfectly correct).

One computes MPGe by multiplying miles per kWh by 33.7 kWh/gallon: that gives 133.
Yet the EPA MPGe rating is 128 city, 110 highway, 119 combined. That 119 figure gives 3.53 mi/kWh or range of 211 miles. And the 128 gives 227.

So there is an inconsistency here that is not small. Does anyone know how that happens?
 

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Discussion Starter #3
Duh. Perfect explanation. Thanks! Another matter: I would imagine the dome lights are run off the 12 V battery. In theory that could be drained. Does the existence of the charged battery with many kWh in it make this irrelevant -- or could one stupidly drain the 12 V battery by leaving a light on, or a trunk ajar, as many of us have done once in our life?
 

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Duh. Perfect explanation. Thanks! Another matter: I would imagine the dome lights are run off the 12 V battery. In theory that could be drained. Does the existence of the charged battery with many kWh in it make this irrelevant -- or could one stupidly drain the 12 V battery by leaving a light on, or a trunk ajar, as many of us have done once in our life?
The traction battery is physically disconnected whenever the car is "off" and not actively charging. So yes, one could drain the 12v battery by leaving a light on.

I replace all interior lights with LEDs on my vehicles to prevent the battery from running low.
 

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2017 Chevrolet Bolt Application for Certification

EPA Test Procedure for EVs

Normally they take the charge depleting UDDS test from the rolling road dyno and scale it by 0.7 to arrive at the range ratings, and scale the recharge Wh/mile by the same factor. This would have given the Bolt a 255 mile rating and a 128 MPGe rating. Chevrolet requested a further ~6.7% decrease, presumably satisfying bullet point 4 "using adjustment factors which are based on in-use data (with prior EPA approval)"
 

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And more to the point, if the 12V is drained, the computer can't boot and switch on the traction battery....the car will seem 'dead'.

In this case a quick 'jump' from another 12V battery will bring the system up, and the Bolt will then recharge its own 12V from the traction battery.

make sense?
 

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I would imagine the dome lights are run off the 12 V battery. In theory that could be drained. Does the existence of the charged battery with many kWh in it make this irrelevant -- or could one stupidly drain the 12 V battery by leaving a light on, or a trunk ajar, as many of us have done once in our life?
The operation of the 12V battery is a lot more complex than you might imagine. DrDiesel posted the charging algorithm here.

When the car is turned off it does check the 12V battery status from time to time, and it will engage the high voltage battery to recharge it if necessary. But it doesn't check that often and it looks to me like the intention is just to handle the load of the vehicle's control computers in their idle state. An additional load like an interior light being left on might well be enough to drain the battery between the intervals where the car checks its status.
 

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Are the interior lights not computer controlled to shut off after some time? I traded a 2012 Cruze for the Bolt all it's lighting was computer controlled, making it impossible to run the battery down by leaving a light on.

Ron
 

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Discussion Starter #9
I guess I need to do an experiment on the Dome lights. Turn on. Check in an hour. Easy enough.

Knowing that, in worst case, a quick jump or trickle charge will work fine is comforting.

All the posted info is interesting, especially the comment that the traction battery might occasionally put some juice into the 12V. And thanks for the comment about how EPA gets its ratings. All very interesting. I glanced at the docs. Not crystal clear why the multiply by 0.7. If they are running the thing on a wheel without actual motion then I suppose it could be for the lack of wind resistance. In any case, I am happy to now understand why MPGe is off by 10%.
 

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Are the interior lights not computer controlled to shut off after some time? I traded a 2012 Cruze for the Bolt all it's lighting was computer controlled, making it impossible to run the battery down by leaving a light on.

Ron
Very close. Page 154 of the owner’s manual, or search for "rundown” most (all?) GM cars have had for year’s battery rundown protection. This works by monitoring current draw on the 12V battery and if tripped, disconnecting circuits for headlights, interior lights, etc that are draining the battery.
 

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Discussion Starter #11
Excellent. The exact quote is this: The battery saver feature is designed to protect the vehicle's 12-volt battery.
If some interior lamps and/or the headlamps are left on and the vehicle is turned off, the battery rundown protection system
automatically turns the lamp off after some time.

And now that I understand MPGe more clearly, I get what these ratings mean. Bolt = 119; Tesla 3 = 126; Tesla S = 104. Nissan Leaf = 112.
 
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