ripple4
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automatically ajusting EVSE for off-grid/current sensing

Sun Apr 28, 2019 5:21 am

This idea is related to the grid-interactive, but not grid-tied, hybrid inverter that I talked about in this post. (viewtopic.php?f=45&t=27295)

I thought this had enough merit or potential other uses to stand on its own and wanted to see if someone had anything to add. The basic idea is to have an EVSE that can sense some amount of current flow, somewhere else, and then increase or decrease car charging dynamically to not exceed some limit. there is a commercial solution for this from some .au address, Zappi, but it's $800. there is also an instrutable for an all-arduino EVSE. What i'm talking about is sort of the best of both worlds, low cost, moderate effort and moderate finish quality.

The issue that I’m wrestling with is how to balance car charging with a off grid inverter without exceeding the power limits of the inverter. The root problem is that if the array/charger/inverter is sized for the car in the winter then there will be an overproduction in the summer, so to use that, it would be great to run an air conditioning unit and house hold loads. However, when I come home in the afternoon I don’t want to have to unplug the AC and click a bunch of transfer switches. Nor do I want to always be limited to 240v/6A when there is full sun and nothing else is running. So the idea I have is to buy a EVSE that is very finely adjustable from 6-16 amps (my 2012 only charges at 16a max) and then put a current transformer on the output of the inverter. Then when the power demand is low for AC and house loads then EVSE will go up to 16a, but when the A/C kicks on or a bunch of loads come on, it will dial it back to 6A. all within the 2 seconds the inverter says it can handle a surge load.

How I think this can be done is buying an inexpensive EVSE replacement brick and sort of hacking it to be microcontroller, well, controlled. The one I’m going to experiment on had LED lights for each current level and a membrade dry contact push button to increase current. So if I tap into the LED signal wires and push button wires into a Arduino, with CNY17F optical isolation and a proper pull down signal conditioning on the digital inputs I will be able to make IF/THEN chain that cycles thought the various current levels and monitor that its at the right one. On the input side of the equation I see myself installing a split core current transfer OR a hall effect current sensor on the output of the inverter and that will measure the current flow going to all the loads added up. I would prefer a turn-key split core CT, unfortunately there is not a 20A signal conditioned CT on eBay that I can find, so the hardest part of all of this for me will be learning to build a CT signal conditioner that the Arduino can read.

I’ve made quite a few Arduino robots around the house, one that turns porch lights on and off with the sunrise/set (https://www.thingiverse.com/make:356106). Ones that runs stepper motors, 8x20 LCDS, SCRs and pneumatic valves, but I always seem to have problems signal conditioning random sensor when it comes to fighting EMI. solenoids and LCD combinations are the worst, i think the LCD is like an antenna right into the CPU. Just to be clear i'm linking to the sources i bought from as a courtesy to interested people, these are not seller links.

$80 adjustable EVSE brick
https://www.aliexpress.com/item/Electri ... 4c4dDXr0i8

CT sensor
https://www.ebay.com/itm/YHDC-SCT013-02 ... 2749.l2649

Hall sensor
https://www.ebay.com/itm/Current-Sensor ... 2749.l2649

Zappi comercial current sensing evse
https://www.ebay.com/itm/myenergi-Zappi ... Sw2Wtbfz85

all arduino EVSE ( not adjustable as presented, but could be with additional PWM code and selector button)
https://www.instructables.com/id/Arduin ... g-Station/

Oilpan4
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Re: automatically ajusting EVSE for off-grid/current sensing

Sun Apr 28, 2019 8:53 am

The surge load is only if the batteries can handle it too. The surge refers to the inverter being able to handle a starting load that exceeds the normal continuous rating.
But only if the battery can handle it too.

So you are wanting an evse that ramps up and down from 6 to 16 amps?
Is that even an option for J1772?
I was under the impression that it went 6, 8, 12, 16 amps, ect orjumped by whole amps. Can you dial one into say 7.5 amps?
Then have it slowly ramp up to say 9.3 amps as the sun gets higher in the sky?


The best thing you can do for going off grid is not get an electric vehicle, unless you drive it very little.
Or if you must, a plug in hybrid, that way you don't have to charge it to get around.

Because now that I have the leaf I can't even really think about going off grid.
With out the leaf a 50 kwh battery would probably work fine for me. Now that I have the leaf, nope better not even think about it till I can get a 100kwh battery or more.
Or make the leaf a secondary vehicle and burn gasoline or diesel, then charge and drive the leaf as electricity is available.
2011 white SL leaf with 2014 batt.
Chargers: Panasonic brick moded for 240v, duosida 16a 240v and a 10kw setec portable CHAdeMO
Location: 88103

WetEV
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Re: automatically ajusting EVSE for off-grid/current sensing

Sun Apr 28, 2019 2:17 pm

Oilpan4 wrote:So you are wanting an evse that ramps up and down from 6 to 16 amps?
Is that even an option for J1772?
Why don't you read the standard?
11.) The EVSE may modify the pilot signal pulse width at any time, commanding the EV to increase or decrease the maximum AC current draw. The vehicle must adhere to the maximum response time in order guarantee universal compatibility with the external controlling equipment. (see Table 6, specification 10)
Oilpan4 wrote:I was under the impression that it went 6, 8, 12, 16 amps, ect orjumped by whole amps. Can you dial one into say 7.5 amps?
Since you don't know, why are you wasting bandwidth?
5.3.5 EVSE Current Capacity - The EVSE provides the maximum available continuous current capacity, and by inference the rating of the protective circuit breaker, to the EV by modulating the pulse width as described in TABLE 4 and shown in FIGURE 8. The available line current is linearly proportional to the pulse width by the following equation:

Ampacity = (0.6 amps x pulse width, in usec) / 10 usec, from 100 to 800 usec.
Oilpan4 wrote:The best thing you can do for going off grid is not get an electric vehicle, unless you drive it very little.
Maybe, and maybe not. Depends on driving time patterns as well. Are you often home during the day? Or not?
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ripple4
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Re: automatically ajusting EVSE for off-grid/current sensing

Mon Apr 29, 2019 5:04 am

I could have explained this better, as the other poster indicated the standard allows for many discrete steps of charging current, its not infinitely variable. As I understand it the car’s onboard charger is the device that actually permits more or less current to be drawn, and it can change dynamically. The EVSE provided a variable pulse width pilot signal to the car letting the on-board charger know what current level to consume. the evse can include programing for as many discrete settings as are allowed by that formula, or as few as a practical. I am not a historian on the SAE j1772 spec, maybe someone can share why is was designed that way, because it seems unnecessary, why would the charge current need to change dynamically? Maybe they anticipated smart houses that could tune EV current draw to align with home usage, I really have no idea, but in my case it's going to work out great.

By finely adjustable I was drawing a difference between, for example the ZENCAR 16a EVSE, which has 8,10 and 16amp settings. And the ZWET box I linked to that has 6,8,10,12 and 16 amp settings. I know clipper creek is a forum sponsor, but I don’t see that they offer any adjustable units to include in this comparison.

Oilpan4
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Re: automatically ajusting EVSE for off-grid/current sensing

Mon Apr 29, 2019 9:20 am

ripple4 wrote:I could have explained this better, as the other poster indicated the standard allows for many discrete steps of charging current, its not infinitely variable. As I understand it the car’s onboard charger is the device that actually permits more or less current to be drawn, and it can change dynamically. The EVSE provided a variable pulse width pilot signal to the car letting the on-board charger know what current level to consume. the evse can include programing for as many discrete settings as are allowed by that formula, or as few as a practical. I am not a historian on the SAE j1772 spec, maybe someone can share why is was designed that way, because it seems unnecessary, why would the charge current need to change dynamically? Maybe they anticipated smart houses that could tune EV current draw to align with home usage, I really have no idea, but in my case it's going to work out great.

By finely adjustable I was drawing a difference between, for example the ZENCAR 16a EVSE, which has 8,10 and 16amp settings. And the ZWET box I linked to that has 6,8,10,12 and 16 amp settings. I know clipper creek is a forum sponsor, but I don’t see that they offer any adjustable units to include in this comparison.
I too am not a j1772 historian and technical spec junky. I had no idea j1772 could do that.
It could be more useful than the 6, 8, 10, 12, 16 amp stair step. It's good to know.

If I was going to go off grid I would want to be able to use my home chademo at least occasionally, which peaks at just about 8kw.
I normally use my 12 amp 240v converted Panasonic brick for home charging.
I could probably go as low as 6 amps at 240v for most over night charging.

My leaf is pushing about 400kwh for the moth of april, mostly charging after 7pm.

I'm with you. I would love to go off grid, but have to do so affordablely and with out taking out a huge loan.

What size is your battery?
2011 white SL leaf with 2014 batt.
Chargers: Panasonic brick moded for 240v, duosida 16a 240v and a 10kw setec portable CHAdeMO
Location: 88103

ripple4
Posts: 82
Joined: Tue Sep 18, 2018 1:45 pm
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Location: Toledo, Ohio

Re: automatically ajusting EVSE for off-grid/current sensing

Mon Apr 29, 2019 3:11 pm

My project is not off-grid, its 'grid interactive', short of grid-tie. it can draw utility power when needed, but cannot put power into the utility. still the utility pass through feature of the hybrid inverter is breaker limited to 5kw, so i need this auto-adjustable charger if the solar is producing or not.

I'm planning on a 48v 410ah bank of 16x GC2 golf cart batteries. I choose that size to hold the 10kwh i need on a daily basis for the leaf and keep the DOD at around 50% which should give a 2000+cycle life. but in terms of raw capacity it's only a 1 day supply.

smkettner
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Re: automatically ajusting EVSE for off-grid/current sensing

Mon Apr 29, 2019 4:09 pm

ripple4 wrote:My project is not off-grid, its 'grid interactive', short of grid-tie. it can draw utility power when needed, but cannot put power into the utility. still the utility pass through feature of the hybrid inverter is breaker limited to 5kw, so i need this auto-adjustable charger if the solar is producing or not.

I'm planning on a 48v 410ah bank of 16x GC2 golf cart batteries. I choose that size to hold the 10kwh i need on a daily basis for the leaf and keep the DOD at around 50% which should give a 2000+cycle life. but in terms of raw capacity it's only a 1 day supply.
Why make it complicated? I would aim for fixed 4kW and see if there is an issue.
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BrockWI
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Re: automatically ajusting EVSE for off-grid/current sensing

Mon Apr 29, 2019 4:20 pm

I went the simple route and if it is sunny I just set the EVSE for 10 amps @ 240 vac or 2400 watts. Our array is just over 3000w but if I start charging and it isn't solar noon, the array will produce less and as we pass noon a bit more, plus the house loads in there. Sometimes if I am in a hurry I set it to 20 amps @ 240 vac, which will draw down the house bank but knowing I am going to be gone and the bank will get topped back up later in the afternoon.

My understanding is once the charging session starts you can't change the pilot signal? It stays at the initial rate. Maybe if you set the car to always charge, it could disconnect every 15 minutes and check mppt and reset the pilot signal and start charging again? That was my intent long ago, but I just ball park it now and have had pretty good luck.
3 kw solar pv - XW6048 - eight L16's
4 ton GSHP - 1 ton ASHP
2003 VW TDI 200k miles - 52 mpg lifetime
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lost first bar @ 72k
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WetEV
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Re: automatically ajusting EVSE for off-grid/current sensing

Mon Apr 29, 2019 5:32 pm

BrockWI wrote:My understanding is once the charging session starts you can't change the pilot signal?
I have a charging station that I can change currents on and measure the current on. With my 2014 LEAF, right now.

The current changes as you would expect. Both up and down. As fast as the web page updates, which is about 15 seconds.
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BrockWI
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Re: automatically ajusting EVSE for off-grid/current sensing

Mon Apr 29, 2019 5:38 pm

interesting but totally makes sense, my open evse won't do that, if I scroll up 2 amps suddenly the car will just stop charging :)
3 kw solar pv - XW6048 - eight L16's
4 ton GSHP - 1 ton ASHP
2003 VW TDI 200k miles - 52 mpg lifetime
EVSE level 2 - Clipper Creek HSC-40
2013 S model with QC package Mar of 2013
lost first bar @ 72k
@90k miles - 54.71Ahr - 83.64SOH - 78.44Hx - 237GID

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