When the battery is flat

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ScottinOregon

Member
Joined
Dec 7, 2014
Messages
20
I'm constantly (maybe twice a year) ALMOST making it home when the battery gives out. I call a neighbor and they tow me the last mile, and that works ok, but getting the car positioned to be towed, or the times I've run out in parking lots just meters from a public charger, I've noticed being in neutral does NOT mean the car rolls freely. I've had four guys pushing on flat ground and we can barely move it even though it says it's in neutral. Is there a known explanation for this, or some way to get the thing into proper free-rolling neutral?
 
Electric cars, unlike their gasoline or diesel counterparts, don't have a neutral position in the transmission. They can go forwards or backwards, but when they're not doing either the motor is still connected to the wheels - it just doesn't have any power driving it. Putting an electric car in "Neutral" just means no power is being sent to the electric motor driving the wheels.

The neutral position in a regular car means that should your car need to be towed, it's fairly simple to do so and the car can be towed freely without rotating transmission or engine components. This is not the case with an electric car - when the wheels turn, they'll turn the motor with it and this can result in damage to the motor. Particularly in vehicles with a liquid cooling system, turning the motor at high RPM without this system working can overheat the motor to destruction.

From the BMW i3 Rescue Guidelines manual:
• The vehicle may not be towed by the axles, as the electric motor could supply current to the high-voltage system. The car may only be transported on a flatbed vehicle.
• To bring the vehicle out of a danger zone, you may pull it extremely slowly over a short distance of no more than 500 m. If possible, make it rollable first by switching the selector lever to N.
• Secure the vehicle during transport, for example using tension straps pulled through the wheel rims. • Please observe national regulations.
 
Hummm,
  1. I regularly coast in "N" without a problem. I do this to avoid regeneration/generation loads.
  2. If in "D", the car will 'hold' the car on a slope without using the brake.
  3. If in "P", there is a gear lock that keeps the rear wheels from turning.
Later today, I'll stop on a slope; shift to "N", and; release the foot brake. I would expect the car to start rolling down the grade. But if it doesn't, this suggests the 'hill hold' mode may be active.

Bob Wilson
 
In"D" there is an electronic hold that prevents the car rolling backward, and in "R" there is an electronic hold that prevents the car rolling forward. In "N" there is no electronic hold, so the car can roll either direction (and in "N" no electricity going to the motor, so no "resistance" in turning), but the wheels are connected to the electric motor, and it turns when the wheels turn. "P" engages a mechanical hold.
 
Rather than coasting in "N" why not simply lift your foot from the go pedal just enough to neutralize the power meter reading on the main display?
 
jbrinsfi said:
Rather than coasting in "N" why not simply lift your foot from the go pedal just enough to neutralize the power meter reading on the main display?
That's what I do. There seems to be a fairly wide power pedal position range where the power meter remains at 0 (i.e., no power and no regen, therefore, coasting).
 
MKH said:
(and in "N" no electricity going to the motor, so no "resistance" in turning)
Because an i3's motor contains permanent magnets, I'm pretty certain that their magnetic field will prevent the motor from rotating without resistance even when the motor's coils aren't powered. This probably explains why it's not easy to push an i3.
 
I find my I3 rolls very easily in neutral, when it has a enough charge. I suspect it is electronically mimicking holding the accelerator right between calling for power and regen. Without sufficient charge, it cannot do that, and so the spinning motor becomes the generator. See if your I3 rolls more easily now that it is charged to confirm this.
 
A new twist on me almost running out of juice before I get home (which drives my family members crazy). I find that when I try to charge at a public charger with a low charge it won't complete the car-charger handshake and so won't charge. Very frustrating to have public chargers I sometimes depend on working fine ... except when I really need them. Yesterday I had a farmer neighbor haul me home on a flatbed trailer with 6% battery after three different stations 8 miles from home failed to connect with the car, and my home charger worked perfectly. Any thoughts on why?
 
If they were CCS Combo Level 3 DC fast chargers, the usual reason is because the cables are too heavy and pull the connector down in the car's socket. Try holding the cable up until it finishes handshaking.....
 
ScottinOregon said:
I find that when I try to charge at a public charger with a low charge it won't complete the car-charger handshake and so won't charge.
Are these public charging stations AC Level 2 EVSE's or DC Fast Chargers?

ScottinOregon said:
Yesterday I had a farmer neighbor haul me home on a flatbed trailer with 6% battery after three different stations 8 miles from home failed to connect with the car, and my home charger worked perfectly. Any thoughts on why?
Unfortunately, I don't have an explanation. I don't know whether charging is prevented by some EVSE's or DC chargers if the battery pack's voltage is below a certain limit. I don't understand why it would be, however.

Had your power meter lost any gray chiclets (i.e., was power being limited because the battery management system determined that the actual charge level was considerably less than 6%)? Even if the charge level were actually lower than that displayed, I don't know any reason why charging would be prevented.
 
Ya,I feel like some of those level-3 cables are going to pull the whole charging port right out of the car, especially when they aren't long enough to drape along the ground. But that's not it, my failed charging machines were all level-2 with surprisingly skinny cables. They would say "connecting" ... then I'd get blue flashing on the car and "charging" on the machine ... then a few seconds later "connection failed" or, an eye roller, "charge complete."
 
And, Art, ya, I had enough charge to still drive a few miles, so it seems like it shouldn't have caused the battery management system to give up. I've wondered if the 12V system might be handling the handshake management but there was nothing that would have drained that battery this time (unlike last time when I had emergency flashers on for a couple of hours). And the fact remains that my home charger (which admittedly might be "dumber" than public chargers) shook hands and was off the the races charging the car with even less EV charge than when I was trying with the public chargers.
 
With the signalling on an EVSE, there's no 'digital' data exchanged in the normal sense. There are some interlocks and a PWM wave that tells the car how much power is available. Make sure that the plug is seated all the way in since the interlock on the latch needs to be closed, indicating to the EVSE that the plug is fully inserted. That switch can be quite sensitive and give intermittent results if it's not fully latched.

If there's any moisture in the plug or socket, while the pins are generally gold plated, things can be a bit problematic. On mine, I find that a shot of WD40 can make a difference as it does what the acronym means - Water Displacement. If there's any crud on the latch, it might clean that off, too, and make that switch function more reliably. I tend to give mine a shot maybe every 2-3 months or so. Won't hurt anything (just don't let it drip all over, it can attract dust).

With a CCS connection, two of the acv power pins become a serial data path to describe to the CCS unit what voltage the car wants. The CCS unit is actually a variable DC power supply. Some of the newer ones can also charge 800-volt battery packs, so knowing what the vehicle wants is important.
 
ScottinOregon –

I've had a number of issues with public Level 3 DCFC charging, most caused by the failure of the charge port locking pin solenoid. With that now repaired most of my L3 charging attempts are successful.

Regarding L2 charging, I rarely use a public station for this but when I've done so I've had a 100% success rate – until last month.

With about 20% battery left (2014 BEV) I parked at a public Chargepoint L2 station. After authorizing with an RFID card and plugging in I heard the EVSE's contactor close and then – a second later – open. The car wasn't charging (based on the instrument panel), the EVSE wasn't delivering power (based on its built-in display), yet its timer was counting up as if it was supplying power to my i3.

Of the four EVSEs at this location, I tried three. All would authorize with my card but not one would deliver power.

This is the first time I've run into this.
 
Frictioncircle: your L2 experience is EXACTLY mine except now you're scaring me that public chargers won't charge me when I'm down to merely 20% instead of the close-to-zero experiences I've had! Nothing like having a public charging system that works wonderfully ... unless you actually NEED the juice!
 
frictioncircle said:
...at a public Chargepoint L2 station. After authorizing with an RFID card and plugging in I heard the EVSE's contactor close and then – a second later – open. The car wasn't charging (based on the instrument panel), the EVSE wasn't delivering power (based on its built-in display), yet its timer was counting up as if it was supplying power to my i3.

Off topic, but I noticed similar behavior at a Charge Point station a couple of weeks ago. I forget the exact details -- I may have logged in / authorized my session before plugging in -- but whatever, I noticed that the Charge Point clock was counting before I ever plugged in. They don't seem to care whether the juice is flowing to run their clock.
 
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