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LTLFTcomposite
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Re: Q: 120V emergency cord

Fri Jun 25, 2010 7:15 am

For most of these discussions it's helpful to think in terms of watts, not volts or amps. How fast you can charge is a function of how many watts you can pump into the car.

The advantage of higher voltages is you can deliver more watts over a given wire size. You could step up the voltage coming out of a wall outlet (perfect use for those old tube TV's, don't they step up to like 100,000 volts?) but you still don't get any more watts out of it.
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AndyH
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Re: Q: 120V emergency cord

Fri Jun 25, 2010 7:31 am

garygid wrote:The EVSE "handshaking" (the Control Pilot wire) probably carries a different "DC" voltage to the car (maybe just one different resistor in the EVSE) to indicate 120v power instead of 240v power.

With "no" pilot signal (or perhaps some minimal, fixed-voltage pilot signal) from the EVSE, I think the car is to expect 120v and draw no more than 12 amps after the J-Plug is in place.

Someone with the J1772 specs (AndyH) might be able to tell us for sure.

I would look if I had the standards document.
Gary,

I can't find anything in the J1772 Jan '10 document that suggests the EVSE can signal the car about input voltage. I suspect the on-board charger is an 85V-265v input device like many off-board chargers.

The purpose and functions of the pilot signal are clearly defined and signalling supply voltage is not one of them.

Andy

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garygid
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Re: Q: 120V emergency cord

Fri Jun 25, 2010 9:07 am

The Control Pilot signal is used by the EVSE primarily to tell the car what max AC current is available. It can also signal that there has been an "EVSE-Error" to the car.

The car uses the same line primarily to ask the EVSE to "turn ON/OFF" the AC power lines from the EVSE to the car. The line also informs the EVSE that the car requires ventilation (or not) while charging.

With the LEAF's sealed batteries, no "ventilation" is needed. Lead-Acid batteries (that might produce hydrogen) should request ventilation.

The EVSE "should have" a specific-value resistor between its Pilot Voltage generator and the Pilot signal's exit from the EVSE, and the EVSE (and car) can monitor that "Pilot Voltage". The resistor might vary between a 120v EVSE and a 240v EVSE. Maybe AndyH knows the value, or values.

I assume that a zero Pilot voltage indicates there is not a "Live" EVSE available. Apparently a steady non-zero Pilot voltage and a 1kHz square wave are the other two possibilities.

Depending upon the values of resistors in the car and the one in the EVSE, several different "conditions" are indicated.
The 1kHz square-wave's duty cycle, from around 10% to 90%, indicate to the car that about 6 to 80 amps of AC is available (details posted elsewhere).

The car uses different values of resistance to tell the EVSE that ventilation is required, and to signal (ask for) power ON and OFF.

I need details of the resistor values and timing of the signaling (like "connect") sequences to do more.

It is OK (legal, I believe) to share the information contained in the standards document, but one must buy (about $60) the document itself.
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AndyH
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Re: Q: 120V emergency cord

Fri Jun 25, 2010 9:35 am

Part of your answer is in the post immediately above yours.

The internal processes of the EVSE appear to be based on the 12VDC supply in the EVSE. That suggests that there are no resistors to swap based on input voltage. As an EE - would it make sense to you that a device designed to operate from 208-240VAC would require resistor tweaks when the voltage changes? ;)

I've posted the info on what J1772 does with the pilot signal in another thread. If I can find it, I'll duplicate it here.

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Re: Q: 120V emergency cord

Fri Jun 25, 2010 9:56 am

No, no resistor change from 208 to 260v, but perhaps a change between 120 and 240?
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AndyH
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Re: Q: 120V emergency cord

Fri Jun 25, 2010 10:24 am

No resistor changes because of voltage changes.

No signaling from the EVSE to the car about EVSE-input voltage. The EV charger is directly connected to AC thru the EVSE. The AC wiring - for both L1 and L2 - runs directly from the AC source (120V outlet or 208-240VAC hard-line) thru the J1772 connector to the car's charger.

According to the SAE J1772 document, the EVSE for both L1 and L2 has internal control electronics that uses 12VDC. The signaling resistors and pilot signal 'buss' are fed from the 12VDC-operated control electronics 'module'.

Sorry Gary - I don't want to come across snarky, but there are only so many ways to say it...

Andy

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Re: Q: 120V emergency cord

Fri Jun 25, 2010 11:01 am

AndyH wrote:The AC wiring - for both L1 and L2 - runs directly from the AC source (120V outlet or 208-240VAC hard-line) thru the J1772 connector to the car's charger.
So how does max current setting work ?
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Re: Q: 120V emergency cord

Fri Jun 25, 2010 11:01 am

OK, I did not expect to standard to be so "limited".

However, it might make it easier to "convert" the "included" 120v EVSE to 240v operation, at least at its default max current (possibly 12 amps). Of course, use of the modified EVSE would not be completely legal, I suspect.

Apparently all J1772-complient vehicles either need to accept 100 volts to 260 volts AC as input, or do their own voltage-checking before "connecting" internally to the car's internal charger.

Since a "120v-only" charger in a car (or a "240v-only" charger) cannot determine the supply voltage until after it "turns ON" the AC power through the EVSE, the car would need to isolate the input from the one-voltage charger, turn ON the AC power, check for an acceptable voltage, and then either connect the charger and begin charging, or refuse to charge (and probably shut OFF the EVSE).

What are the resistor values specified for the EVSE, the "nozzle", and the car?
Thanks.
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Re: Q: 120V emergency cord

Fri Jun 25, 2010 11:03 am

AndyH wrote:No resistor changes because of voltage changes.

No signaling from the EVSE to the car about EVSE-input voltage. The EV charger is directly connected to AC thru the EVSE. The AC wiring - for both L1 and L2 - runs directly from the AC source (120V outlet or 208-240VAC hard-line) thru the J1772 connector to the car's charger.

According to the SAE J1772 document, the EVSE for both L1 and L2 has internal control electronics that uses 12VDC. The signaling resistors and pilot signal 'buss' are fed from the 12VDC-operated control electronics 'module'.

Sorry Gary - I don't want to come across snarky, but there are only so many ways to say it...

Andy

This makes complete sense and is similar to the AVCON chargers, I used a resistor and cap to tell the unit to engage and start charging.

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Re: Q: 120V emergency cord

Fri Jun 25, 2010 11:06 am

The "maximum available" current is indicated by the EVSE to the car using the duty-cycle of a square-wave signal on the Control Pilot line.

It is up to the car to regulate how much current it actually draws.
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