[EVDL List]

Hi Roger,
This might be very well true.
In fact, I would suspect that it is not the diode
in series with the 880 Ohm resistor in the Leaf
charger that gets damaged, because that would be
very pitiful, but there may be damage to the sensing
input (processor pin) that reads the voltage on the
Pilot wire that goes to the diode/resistor combination.
If an ESD discharge or a surge from contactor closing
happens to ride on that Pilot wire and runs straight
into the sensing pin (if it does not have enough filtering)
then that may be the reason it turns the Leaf "blind" to
the Pilot signal and no more charging is possible until
the charger (or that sensing circuit) is repaired.

This would indeed indicate a weakness in the Leaf
(J1772 charger interface) design, not so much an issue
caused by the WattStation, so there would be nothing
that GE can do except adding some protection on the
Pilot *output* to avoid they can pass a surge into
the Leaf - but then other charge stations may expose the
same weakness (at a lower rate) anyway.

Hmmm, maybe there is a market for Leaf surge protection
cords, to be inserted between any charging station and Leaf
(essentially a J1772 male/female plug on a short extension
cord with surge protection in line)

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On
Behalf Of Roger Stockton
Sent: Friday, July 20, 2012 9:49 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] EValert: GE WattStation Damages Leaf EVs = can
nolonger charge from any EVSE

[quote]Cor van de Water wrote:

> Since GE confirmed that they did something wrong,

The new items I've seen state only that GE is investigating the claims.

Bruce P is quick to vilify the GE Wattstation, but in one of his own
news items Nissan stated that only *some* of the Leaf failures had
occurred at GE Wattstations. That suggests that some Leafs have been
damaged while charging from non-GE EVSEs, and so there is more than a
passing chance that the problem is not the EVSE but rather a marginal
component choice or inadequate circuit protection in the Leaf charger.

> 2. The charging station causes signals on the Pilot that
> cause damage to the EV. Not likely as there are clear
> standard mandatory values to implement the signals
> and the 12V and resistance values only allow low current
> not likely to blow any diodes or cause other damage.

>From what I gather, the symptom is a failure of the vehicle side pilot
signal loading circuit such that the EVSE will not enable AC power to
the vehicle. It sounds as if the diode in the pilot signal circuit is
failing, so it is possible that the Leaf charger did not use a
sufficiently robust part. The J1772 standard cautions:

"The diode shown on the vehicle side is intended to be a common small
signal silicon diode. Reverse voltage ratings of at least 100V are
readily available and are recommended since this diode is exposed
directly to cable transients."

The EVSE pilot signal generator provides a +/-12V 1kHz square wave once
it detects that a vehicle is connected. There is a 1K resistor in
series with the signal generator, so the maximum current from the signal
generator is limited to 12mA into a short, and the vehicle side load
consists of a minimum of 880 ohms in series with the diode, so the
maximum current is actually limited to about 6mA. It seems unlikely
that the EVSE signal generator should be capable of damaging the diode.

However, J1772 also cautions:

"The cable capacitance from the Pilot wire to the Ground wire will
probably be around 25 pF per foot, and many cables are 15 to 20 feet
long. If the EVSE's contactor closes when the line voltage is near a
positive or negative peak, then the voltage on the contactor output can
rise from 0 to 170 V in just a few nanoseconds. This fast, high-voltage
transition can easily be coupled through the capacitance of the cable.
In addition, with the contactor closed during charging, any transients
such as might be generated by nearby industrial equipment or lightning
strikes can be coupled through. It is highly recommended that transient
protection be installed on both the EVSE output and the vehicle input."

IIRC, GE has stated that their EVSE includes all of the recommended
transient protection devices, however, it is not clear that the Leaf
charger does. It is possible that the Leaf charger lacks adequate (or
any) transient protection, and perhaps the GE EVSE has a higher than
average cable capacitance or is otherwise either more prone to
transients being coupled onto the pilot signal, or is prone to somewhat
more severe transients such that the Leaf charger is somewhat more
likely to be damaged while using this EVSE than others.

It is also possible that GE Wattstations happen to be particularly
successful in the marketplace, and so the reason that there may have
been more instances of Leafs failing while using GE EVSEs is simply that
there happen to be a larger number of Leafs using GE EVSEs.

Cheers,

Roger.


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[EVDL List]

[quote]Cor van de Water wrote:

> In fact, I would suspect that it is not the diode
> in series with the 880 Ohm resistor in the Leaf
> charger that gets damaged, because that would be
> very pitiful, but there may be damage to the sensing
> input (processor pin) that reads the voltage on the
> Pilot wire that goes to the diode/resistor combination.

The reason I suggest the diode failing is because at least one of the news wire items posted specifically stated that this is the failure that is occurring. The reports could certainly be wrong.

ESD damage to the processor input that monitors the duty cycle and frequency of the pilot signal is certainly a possibility and would appear to indicate a design flaw in the Leaf charger.

It is also possible that if the charger uses a transistor switch to connect the additional load resistance required to request power from the EVSE, that this switch could fail and so prevent the charger from asking for AC power.

Lots of possibilities. Since the news item states that the diode used to load the pilot signal is being damaged, for now I must assume that to be the case ;^>

Cheers,

Roger.


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[EVDL List]

If they say it's the diode used to load the pilot signal, that makes me
think of a SOT-23 Zener diode that pulls the signal down to 6V (relying on
the resistance of the signal to limit current) and can't handle the heat.

Or the resistor and diode are both SMT and share a single copper pour for
cooling, and the resistor is overheating and transferring its heat to the
diode.

Maybe the GE WattStation has a slightly higher voltage or lower resistance
than other charge stations, or maybe it's just coincidence that it's been
noticed more on the GE unit.

Just some more possibilities.

-Morgan LaMoore

[quote] Roger Stockton <xxx@xxx.xxx>wrote:

> Cor van de Water wrote:
>
> > In fact, I would suspect that it is not the diode
> > in series with the 880 Ohm resistor in the Leaf
> > charger that gets damaged, because that would be
> > very pitiful, but there may be damage to the sensing
> > input (processor pin) that reads the voltage on the
> > Pilot wire that goes to the diode/resistor combination.
>
> The reason I suggest the diode failing is because at least one of the news
> wire items posted specifically stated that this is the failure that is
> occurring. The reports could certainly be wrong.
>
> ESD damage to the processor input that monitors the duty cycle and
> frequency of the pilot signal is certainly a possibility and would appear
> to indicate a design flaw in the Leaf charger.
>
> It is also possible that if the charger uses a transistor switch to
> connect the additional load resistance required to request power from the
> EVSE, that this switch could fail and so prevent the charger from asking
> for AC power.
>
> Lots of possibilities. Since the news item states that the diode used to
> load the pilot signal is being damaged, for now I must assume that to be
> the case ;^>
>
> Cheers,
>
> Roger.
>
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere. Thanks.
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[EVDL List]

It can't be the steady state heat as the charging
station is required by standard to supply the 12V
through a 1kOhm resistor and the vehicle adds a
880 Ohm resistor, so we are talking about approx
6mA which may lead to a meager 5mW dissipation
in the diode and about 30mW in the 880 Ohm resistor,
not a power level that will kill even an SMD part.
I think it is the spike caused by contact closure
that sends a capacitive coupled 100+ Volts surge to
the pilot that can cause a breakdown.
Though I still expect that it damages the sensing
of the pilot instead of blowing the diode, although
a good surge that goes well over the breakdown voltage
of say 100V can create an instantaneous power spike in
the order of 10W or so. Most parts will survive a short
spike like that but it is possible that the diode in
the Leaf is more sensitive than usual and breaks down
permanently, which automatically disables charging
on compliant charge stations.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On
Behalf Of Morgan LaMoore
Sent: Monday, July 23, 2012 8:03 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] EValert: GE WattStation Damages Leaf?

If they say it's the diode used to load the pilot signal, that makes me
think of a SOT-23 Zener diode that pulls the signal down to 6V (relying
on the resistance of the signal to limit current) and can't handle the
heat.

Or the resistor and diode are both SMT and share a single copper pour
for cooling, and the resistor is overheating and transferring its heat
to the diode.

Maybe the GE WattStation has a slightly higher voltage or lower
resistance than other charge stations, or maybe it's just coincidence
that it's been noticed more on the GE unit.

Just some more possibilities.

-Morgan LaMoore

On Fri, Jul 20, 2012 at 6:18 PM, Roger Stockton
[quote]<xxx@xxx.xxx>wrote:

> Cor van de Water wrote:
>
> > In fact, I would suspect that it is not the diode in series with the

> > 880 Ohm resistor in the Leaf charger that gets damaged, because that

> > would be very pitiful, but there may be damage to the sensing input
> > (processor pin) that reads the voltage on the Pilot wire that goes
> > to the diode/resistor combination.
>
> The reason I suggest the diode failing is because at least one of the
> news wire items posted specifically stated that this is the failure
> that is occurring. The reports could certainly be wrong.
>
> ESD damage to the processor input that monitors the duty cycle and
> frequency of the pilot signal is certainly a possibility and would
> appear to indicate a design flaw in the Leaf charger.
>
> It is also possible that if the charger uses a transistor switch to
> connect the additional load resistance required to request power from
> the EVSE, that this switch could fail and so prevent the charger from
> asking for AC power.
>
> Lots of possibilities. Since the news item states that the diode used

> to load the pilot signal is being damaged, for now I must assume that
> to be the case ;^>
>
> Cheers,
>
> Roger.
>
>
> _______________________________________________
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[EVDL List]

[quote] Cor van de Water <xxx@xxx.xxx>wrote:

> Hi Roger,
> This might be very well true.
> In fact, I would suspect that it is not the diode
> in series with the 880 Ohm resistor in the Leaf
> charger that gets damaged, because that would be
> very pitiful, but there may be damage to the sensing
> input (processor pin) that reads the voltage on the
> Pilot wire that goes to the diode/resistor combination.
> If an ESD discharge or a surge from contactor closing
> happens to ride on that Pilot wire and runs straight
> into the sensing pin (if it does not have enough filtering)
> then that may be the reason it turns the Leaf "blind" to
> the Pilot signal and no more charging is possible until
> the charger (or that sensing circuit) is repaired.
>
> This would indeed indicate a weakness in the Leaf
> (J1772 charger interface) design, not so much an issue
> caused by the WattStation, so there would be nothing
> that GE can do except adding some protection on the
> Pilot *output* to avoid they can pass a surge into
> the Leaf - but then other charge stations may expose the
> same weakness (at a lower rate) anyway.
>
> Hmmm, maybe there is a market for Leaf surge protection
> cords, to be inserted between any charging station and Leaf
> (essentially a J1772 male/female plug on a short extension
> cord with surge protection in line)
>
> Cor van de Water
> Chief Scientist
> Proxim Wireless Corporation http://www.proxim.com
> Email: xxx@xxx.xxx Private: http://www.cvandewater.com
> Skype: cor_van_de_water XoIP: +31877841130
> Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203
>
> -----Original Message-----
> From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On
> Behalf Of Roger Stockton
> Sent: Friday, July 20, 2012 9:49 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] EValert: GE WattStation Damages Leaf EVs = can
> nolonger charge from any EVSE
>
> Cor van de Water wrote:
>
> > Since GE confirmed that they did something wrong,
>
> The new items I've seen state only that GE is investigating the claims.
>
> Bruce P is quick to vilify the GE Wattstation, but in one of his own
> news items Nissan stated that only *some* of the Leaf failures had
> occurred at GE Wattstations. That suggests that some Leafs have been
> damaged while charging from non-GE EVSEs, and so there is more than a
> passing chance that the problem is not the EVSE but rather a marginal
> component choice or inadequate circuit protection in the Leaf charger.
>
> > 2. The charging station causes signals on the Pilot that
> > cause damage to the EV. Not likely as there are clear
> > standard mandatory values to implement the signals
> > and the 12V and resistance values only allow low current
> > not likely to blow any diodes or cause other damage.
>
> >From what I gather, the symptom is a failure of the vehicle side pilot
> signal loading circuit such that the EVSE will not enable AC power to
> the vehicle. It sounds as if the diode in the pilot signal circuit is
> failing, so it is possible that the Leaf charger did not use a
> sufficiently robust part. The J1772 standard cautions:
>
> "The diode shown on the vehicle side is intended to be a common small
> signal silicon diode. Reverse voltage ratings of at least 100V are
> readily available and are recommended since this diode is exposed
> directly to cable transients."
>
> The EVSE pilot signal generator provides a +/-12V 1kHz square wave once
> it detects that a vehicle is connected. There is a 1K resistor in
> series with the signal generator, so the maximum current from the signal
> generator is limited to 12mA into a short, and the vehicle side load
> consists of a minimum of 880 ohms in series with the diode, so the
> maximum current is actually limited to about 6mA. It seems unlikely
> that the EVSE signal generator should be capable of damaging the diode.
>
> However, J1772 also cautions:
>
> "The cable capacitance from the Pilot wire to the Ground wire will
> probably be around 25 pF per foot, and many cables are 15 to 20 feet
> long. If the EVSE's contactor closes when the line voltage is near a
> positive or negative peak, then the voltage on the contactor output can
> rise from 0 to 170 V in just a few nanoseconds. This fast, high-voltage
> transition can easily be coupled through the capacitance of the cable.
> In addition, with the contactor closed during charging, any transients
> such as might be generated by nearby industrial equipment or lightning
> strikes can be coupled through. It is highly recommended that transient
> protection be installed on both the EVSE output and the vehicle input."
>
> IIRC, GE has stated that their EVSE includes all of the recommended
> transient protection devices, however, it is not clear that the Leaf
> charger does. It is possible that the Leaf charger lacks adequate (or
> any) transient protection, and perhaps the GE EVSE has a higher than
> average cable capacitance or is otherwise either more prone to
> transients being coupled onto the pilot signal, or is prone to somewhat
> more severe transients such that the Leaf charger is somewhat more
> likely to be damaged while using this EVSE than others.
>
> It is also possible that GE Wattstations happen to be particularly
> successful in the marketplace, and so the reason that there may have
> been more instances of Leafs failing while using GE EVSEs is simply that
> there happen to be a larger number of Leafs using GE EVSEs.
>
>

We've had sort of the opposite situation here - EVSEs blowing up due to
"incorrect voltage" on the pilot or plug present signal, and it was being
blamed on miswired 3rd party charging cable, but a cable which mysteriously
works most of the time so can't be grossly miswired (like pilot to 240V, as
was suggested).

I did wonder if it was actually a transient, aggravated by a slightly
longer or different construction of cable, causing a protection component
to permanently short out or open up, however it's done.
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