BetterLeaf
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BareEVSE - an EVSE circuit for under $5

Tue Feb 05, 2013 2:54 am

OK, with fantastic solutions like OpenEVSE around, here is something with a different design goal:

A bare minimum circuit to successfully charge a Nissan Leaf with components that just sit idle in your parts box.
No programming required. Well, here it is:

Image

It's a good old NE555 that's putting out the 1 kHz PWM pilot signal. You can adjust the duty cycle and therefore control the maximum current that the Leaf onboard charger will draw.
It is small enough to fit into a J1772 plug. No more clunky in-cable box!

Pros: A great 2nd cable for top up charges while traveling. Easy to repair. No great loss if stolen. No in-cable box.
Cons: Must be present to start charging. No preheating or timer charges, no 80% charges. DTC warning code can be logged.

Hate the cons? Then continue reading to the end for the no-cons relay version.

The minimum components for the circuit are
a NE555,
any two diodes (1N4148, 1N4001...),
two 1k resistors (>=1/8 Watt, <=5%),
a 10nF capacitor
a 100k and
a 10k potentiometer (any type will do but precision pots are preferable).

a 12 Volt switching power supply that operates on 100-240 Volts. As the circuit draws less than 15 mA any type will do. Verify that it is well designed and isolated. Check the temperature.
So far you are looking at less than $5.

The bummer is the J1772 EV plug that sets you back a $130. With some good quality cable and a mains plug you are still under $170.
In this first version the mains plug is directly and permanently connected to J1772 plug!

The US electrical code for example, allows this only for devices up to 125V, 15A or 20A. For other countries please check you local electrical code if 240V 16A are acceptable.

So why does this technically work???

Well, there is the elaborate J1772 protocol but the Nissan Leaf does not enforce all requirements. Might be because it results in a better user experience if charging with all the non-compliant EVSEs around actually works.
The spec says the pilot should be a constant 12V in the idle state. The Leaf does not particularly care. It's happy even if the PWM is provided right away on the first plug in.
The spec says the pilot signal that the EVSE generates should alternate between -12V and 12V a thousand times per second. The Leaf does not care about the -12V. Alternating 0V and 12V is fine. The standard actually requires a diode so it can be assumed that most cars behave that way.
The spec says the power should be switched on only after the car drops the pilot voltage further and the Leaf onboard charger tests for this but there is a 10 second grace period. This is documented in the service manual.

So if you plug in the J1772 connector first, you have 10 seconds to turn on or plug in the mains. If you can fulfill that requirement, the Leaf will charge. It will slowly increase the power as usual. There will be no arcing when you plug in the mains. If you miss the 10 secs you can repeat the procedure by unplugging the Leaf. The Leaf will shut off normally after the batteries are full.

Now to unplug before the batteries are full, it is good practice with all EVSEs to unplug the J1772 first. If you press the proximity switch on the J1772 connector the Leaf will immediately stop drawing power. (Actually it drops to 70 Watts). If you disconnect the mains first, it will arc at the mains plug. Same thing happens on the standard EVSE, so generally it's a good idea to do it that way.

Now for the mains connection you must use a GFCI plug rated for your intended voltage and current. Preferably one that also contains a fuse or acts as circuit breaker. The nice thing here is that you can use it as an on-switch. That's faster than plugging in. There are units that automatically disconnect on power loss. That's even more convenient because you know the switch is always off when you plug in.

Is it safe???
Technically it is just as safe as the billons of other 220V-240V every-day household appliances worldwide (like electric stoves, (dish)washers, dryers, A/C units, electric lawn mowers). All of these require a good ground connection and follow code but none of these use a pilot signal and relay at the power source. It's up to you to figure it out! Technically the charge cable is just an over-priced extension cord.

Of course, the -12 V and the relays provide an extra safety margin.


The AC part is high voltage which can kill or burn down your house, so please only attempt to build this if you are qualified to do so. General rule: If you do not know what you are doing then please don't do it. Buy an EVSE and live.

It is your decision and you are doing so at your own risk!

Please do not violate your local electrical code!
The US electrical code only allows systems rated up to 125V 20A to be used without a relay located at the mains connection.

GFCI saves lives and is a must!
Some people think using no relay can kill your Leaf's on-board charger. Include a relay as shown below. Your choice, your risk.


Don't use this design with a car that is capable of drawing more current than the specs of your cable and plugs unless properly fused.

Note that the EVSE DTC code B29C1 can be logged if you miss the 10 sec grace period or sometimes if the battery is full. They just cause a display of the yellow warning symbol the next time the car is turned on. This will automatically go away when the car is turned off and on again. They cause no damage of loss of functionality.

The schematics:
Image

R2 is optional and not populated. R1 can also be dropped if you use and need a resistor to adjust the supply voltage closer to 12V like the PCB in the photo.
Pin 1 of JP2 connects to the pilot signal. R3 is important and must be 1K. No substitutions.

The 10k pot adjusts the frequency. The 100k pot adjusts the duty cycle. 25% at 12V is about 15A, 26.66% would be 16A. The Leaf should never go over 18A regardless of what the EVSE pilot advertises. (At 120V the maximum is 12A, so the same cable works for both voltages).
Please use a scope or multimeter that is capable of measuring frequency and duty cycle to adjust the pots.

And yes the signal is dynamic. The Leaf will adjust it's charging current and slowly follow the signal's duty cycle.

The Leaf charger does not care too much about the accuracy of the 1 kHz pilot, so the usual temperature drift of the NE555 RC based oscillator does not seem to affect it.

Here's what it could look like. The PCB is on the left, the 12V switching power supply on the right under the wires. Both warped in self-vulcanizing electrical tape rated at >200F and >400V.

Wiring up the proximity switch is a must! There are some pictures of how to assemble the cable on the web.

Image

But wait there is more...
... the relay version of course. Add a few more standard components and turn this into a more complete EVSE with none of the cons. Here's the right hand side of the schematics:

Image

The upper OP amp switches the 1 kHz signal on when the car says so. Puts out a constant 12V on idle as per spec.
The lower OP amp switches the power relay connected to JP3 on when the car requests it.

If you can find a proper >=16A relay that fits into the J1772 plug you can have your cake and eat it too. Make sure the transistor (and also the power supply) is rated properly for the required coil current.
For the Leaf to be happy it is sufficient to switch only one phase. No more DTCs. If you can find the space you can switch both.

Again, for 240V operation in the US both AC lines must be contain a relay and it must be near or in the mains plug.

Note that with this solution the relay will still be switched on if the pilot is shorted out.

Enjoy!
Last edited by BetterLeaf on Fri Feb 08, 2013 7:44 am, edited 3 times in total.

DanBaldwin
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Re: BareEVSE - an EVSE circuit for under $5

Tue Feb 05, 2013 9:05 am

Where can you get the J1772 plug and cord for $100.00? The cheapest I've seen is about $140.00.

Herm
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Re: BareEVSE - an EVSE circuit for under $5

Tue Feb 05, 2013 11:59 am

The relay is probably a good idea if you drop the 1772 plug into a puddle of water.. hopefully the GFI in the 240V plug will prevent a shock.

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Ingineer
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Re: BareEVSE - an EVSE circuit for under $5

Tue Feb 05, 2013 1:12 pm

BetterLeaf wrote:The Leaf will pull about an amp less of what the EVSE pilot advertises. It will never go over 16A regardless of the pilot. (At 110V the maximum is 12A, so the same cable works for both voltages).
The Leaf's OBC (On-Board charger) can pull up to around 18A. It most definitely goes over 16A when on lower voltages (such as 3-Phase wye here in the US, which is 208v). It most definitely does not draw 1 amp less than the pilot! I would surmise you have bad instrumentation.

Nissan will definitely void your warranty on your OBC and your Inlet if you use this device that is "always hot", which has been proven to destroy on-board chargers. It can also cause arcing and damage to your inlet. If you are concerned about multi-thousand dollar repair bills, I would avoid this!

There is a reason why the Leaf sets a DTC and lights up a warning! Connecting power to an asleep charger defeats the internal pre-charge system and if this happens, it can be catastrophic! Since there is nothing preventing this from happening except for a specific manual sequence, it's bound to happen at some point.

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/ - - - - Like us on Facebook: EVSE Upgrade

BetterLeaf
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Re: BareEVSE - an EVSE circuit for under $5

Wed Feb 06, 2013 3:06 am

DanBaldwin wrote:Where can you get the J1772 plug and cord for $100.00? The cheapest I've seen is about $140.00.


I was refering to the plug alone. You are right, with a cord it is $134 at Leviton. I thought I saw the plug alone there some time ago for a little over $100. It's definately no longer offered now.

I paid a discounted rate at whole seller 8 months ago for a couple of plugs. Since this deal is also no longer available I corrected my estimation in my initial post just to avoid any confusion.

Thanks for bringing this to my attention.

BetterLeaf
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Joined: Wed Jan 30, 2013 10:53 am

Re: BareEVSE - an EVSE circuit for under $5

Wed Feb 06, 2013 3:22 am

I have read many of your posts during the past year and I certainly value your opinion.

So, thank you for responding.

I'd like to point out that both of the presented circuit versions were built around 8 months ago and have been tested almost daily with no adverse effects.
Ingineer wrote:The Leaf's OBC (On-Board charger) can pull up to around 18A.

Yes, you are right of course. I have corrected that. Thanks for pointing that out.
Ingineer wrote:It most definitely does not draw 1 amp less than the pilot! I would surmise you have bad instrumentation.

I've used a calibrated scope and also a multimeter on the pilot. Both showed identical values for the duty cycle. So that should be correct. I've used a cheap consumer device for measuring power and current consumption and that was .7A lower than what the pilot suggested. So maybe it was inaccurate. I've removed that statement. Thank you.
Ingineer wrote:if you use this device that is "always hot",

As described in my initial post the J1772 connector is certainly not hot when plugged into the Leaf. The GPCI plug will ensure that if is always off. You need to manually reset before it will energize the J1772 plug.
Ingineer wrote:It can also cause arcing and damage to your inlet.

That is unlikely to happen. I've never observed any significant arcing on any kind of connect. The charge current is raised very slowly by the Leaf.
On disconnect: When the proximity switch is pressed to release the charge handle the Leaf's power consumption will drop instantly to ~70 Watts. I am sure it has not escaped your attention that even with the original Nissan EVSE the Leaf's onboard charger will still not instruct the EVSE to open the relay. It will continue to draw a little power. On the pulling the plug the disconnection of the pilot pin will open the relay. If done quickly enough there is chance that the AC pins will still be hot even though they are longer connected.
Ingineer wrote:If you are concerned about multi-thousand dollar repair bills, I would avoid this!

Absolutely and I would go as far as to generalize that:
If you are concerned about multi-thousand dollar repair bills I would certainly avoid driving any type of car.
Ingineer wrote:There is a reason why the Leaf sets a DTC and lights up a warning!

Yes, of course: to detect and alert the driver about a stuck or broken EVSE relay.
I trust the Nissan engineers were smart enough to design a on-board charger that can cope with this likely event. The DTC seems to indicate that are at least aware of that condition.
Ingineer wrote:Connecting power to an asleep charger defeats the internal pre-charge system and if this happens, it can be catastrophic!

The proximity detect is there, time to wake up!
During initial tests even hot plugging AC alone while asleep did not cause any damage, although I would never recommend doing that.
Ingineer wrote:Since there is nothing preventing this from happening except for a specific manual sequence, it's bound to happen at some point.

Again, the same word of caution applies to driving a car. This involves a complicated manual sequence of pressing the correct pedals at just the right time.

No seriously, everything you have said should be taken into consideration and putting in a relay as shown in the add-on circuit is preferable.

Anyways, I have no commercial interest here, I just thought it would be good to share my ideas and my observations.

So thanks again and take care!

EdmondLeaf
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Re: BareEVSE - an EVSE circuit for under $5

Wed Feb 06, 2013 10:53 am

Like with other things, having more choices, and knowing more is great.

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Ingineer
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Re: BareEVSE - an EVSE circuit for under $5

Wed Feb 06, 2013 12:16 pm

I'm not just being alarmist: Because I'm in this business, I get lots of reports of when something goes wrong, such as the GE Wattstation EVSE problems. While still relatively rare, your $5 EVSE is still likely to cause OBC failure, and if a handful of people build these and use them daily, I'm sure we'll see them sooner or later. I'd just hate to see someone get burned with an OBC replacement. If you happen to be reading this and your OBC has failed, please post so others will know what I'm attempting to warn about.

Driving a car is not the same as connecting the car in a special sequence. This may be fine if the car has only one user, but if there is a family situation with kids and spouses, it could easily be forgotten or skipped. With your always-hot circuit, All it takes is one power failure or dip, and BOOM!

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/ - - - - Like us on Facebook: EVSE Upgrade

GregH
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Re: BareEVSE - an EVSE circuit for under $5

Wed Feb 06, 2013 12:45 pm

I think this micro EVSE circuit is fantastic! Not something I would use every day but if I had a 2013 Leaf with a 6kW charger I could see making a simple device like this for use at RV parks for longer trips. I wouldn't even bother with the relays... Of course with 3.3kW I personally don't consider those long trips viable. A moderate EVSE is a lot smaller than the 70lb Magnechargers we used to lug out of the trunks of our EV1s, but still a cable with no box on it at all would be awesome!
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EVDRIVER
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Re: BareEVSE - an EVSE circuit for under $5

Wed Feb 06, 2013 12:57 pm

Besides that fact that a plug in 240V, 20A GFCI is almost impossible to find it is likely that someone will either skip using it or leave it behind even if it is available. I personally know of at least six instances of cords that have been cut for various reasons, two of which were very small dogs that ate the cord. This happens often with the LEAF EVSE believe it or not. I wonder how that is going to feel with a live cord energized? These type of "cheater" EVSE circuits have been around a long time but I would not use on on a modern EV or at all for the many reasons stated before. Besides, it defeats the main function of what the EVSE is supposed to do and opens one up for serious liability. Sure doing this in Europe is far less of a risk then in the states but I can also post all sorts of ways to cut corners and make electrical devices cheap and unsafe but that is not the point. I'm sure that if you were a US resident or had more concern for the safety of others and their property you would be less likely to make these irresponsible postings with cheap "hacks". Besides the lack of concern for safety, things like this almost always come back to reflect poorly on EVs in general once someone gets burned in every sense of the word.

This idea is nothing new and has been done before but just watch how "I told you so" comes up as well as a bunch of wining from those that ignored common sense and screw up their EV. Perhaps EV Charge America can start selling these...

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