Tesla Motors Club

Tdave said:

The MC240 draws 30 amps only because there are no 40 amp GFCIs for Tesla to use. So they use a 30 amp GFCI and limit draw to 30 amps. Once they can source a 40 amp GFCI, the MC240 will be upgraded to 40 amps.

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beepayz said:

I just had the firmware 3.3.1 update to address the MC120 GFCI tripping issue... It still trips.

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There is a new Tesla Roadster Firmware update that addresses nuisance GFCI tripping when using the Tesla MC120 mobile charge cord. Sweet!

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Cottonwood said:

A GFCI only looks at current differences between Line and Neutral for 110V apps, and between the two lines for 220V apps. For this reason, voltage differences between Neutral and Ground should not matter. If it did, then ground faults on other circuits would induce false alarms on good circuits.

From GFCI Basics:

A GFCI protection device operates on the principle of monitoring the imbalance of current between the circuit's ungrounded (hot) and grounded (neutral) conductor. It does not monitor the grounding conductor, and so it will still operate in a circuit without a ground.

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billarnett said:

I removed the GFI from my 120v charger. And ran a full charge cycle with it (35 hours :-( No problems.

Note: I did not stand in a puddle while handling the cord. I did not stick my fingers in the socket. I did not chew on the cord while it was charging. YMMV

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...At the beginning I assumed that any electric vehicle would use a switching power supply as its charger. This is not necessarily the case. It's an interesting coincidence that the EV1's battery pack voltage, 312 volts, is not much below that produced by direct rectification of the 240 VAC power line (340 volts). Given that the EV1's inverter (the electronic circuit that converts DC into AC for the induction motor) looks very much like a DC switching power supply in reverse, it's possible to feed 240V AC line current directly back into the inverter. This would use the inverter as if it were doing regenerative braking -- with the AC power line taking the place of the motor/generator. This approach, called reductive charging by Alan Cocconi (one of the original EV1 designers) has the advantage of requiring neither an offboard charger like the Magnecharger or the nearly equivalent onboard charger. The inverter would double as the charger, and with its existing liquid cooling system it could probably handle some fairly high charging power levels -- at least as high as those encountered in highway cruising.
This approach would dictate a conductive interface.
For safety's sake, this approach would require the complete isolation of the propulsion battery and all related circuitry from the chassis of the car. Both the negative and positive lines from the propulsion battery would be "hot" with AC with respect to ground while charging. The EV1 is already designed this way. But Cocconi reports that even with this isolation, small leakage currents can exist that will trip a GFCI in the supply circuit and careful design of the drive motor is required to eliminate them.
As an alternative, a stationary AC isolation transformer could be provided on the outlet used for charging. But because this would have to be a 60 Hz transformer rated for full charging power, it would be physically large and heavy. It could easily be heavier and possibly even more expensive than the existing Magnecharger.
The existing switch-mode chargers, for all their faults, do provide AC ground isolation "for free" through their high-frequency transformers -- either the one built into the car (conductive approach) or the one formed by the paddle and coupler in the inductive approach. And they do adapt readily to changes in AC line voltages. Both problems would have to be solved in any direct AC charging scheme...

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...
it is a consequence of using a high-frequency switcher for your
charger and/or controller.

Every wire in your EV's high voltage propulsion system has capacitance to
ground. Large conductors, laying right against the metal body, for long
distances, all conspire to create relatively large capacitances.

If you use a plain old 60 Hz transformer-based charger, and a plain old
contactor controller, the AC current in all these capacitors is low enough to
ignore. It won't reach 5ma, and won't trip a GFCI, and won't represent a
shock hazard if, for example, the ground wire breaks while you are charging
and someone touches the car body and actual earth ground.

If you have a high-frequency switcher for a charger, then this same stray
capacitance can carry a substantially higher current. Now you *can* get over
5ma, trip the GFCI, or get a shock...

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...In my RV (and concession stand) I carry an "electrical survival kit" that
enables me to bypass GFIs when there is no other option. Such as staying at a
friend's house for a couple of days. There is a "reverse jesus" cord that
consists of a female 30 amp outlet, a short length of SO cord and heavy gator
clips. I simply pop the cover off the GFI outlet, optionally loosen the
mounting screws a little and tap onto the incoming terminals. Viola! Instant
bypass. I have been known to move the wires from the "LINE" side to the
"LOAD" side of the GFI which makes it still appear to work but it doesn't cut
off the juice...

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