Off-grid EVSE

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jeffthewalker
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Off-grid EVSE

Post by jeffthewalker » Mon, 19 Dec 2016, 17:16

There is a dilemma for solar powered households (and especially off-grid one) with EVs.

I have had my LEAF for 15 months (and love it) and when at home I charge from the off-grid solar/battery system.

The solar setup grew to 2kW and at this level is sufficient for the household when the sun shines. It is adequate for some cloudy day(s) but a DC 20A/24V generator cuts in for 30 minutes automatically to keep the fridge(s) going when the battery level drops too far.

I have added another 1kW of solar and can (manually) single axis track the sun. This is still nowhere near enough to charge the LEAF without compromising the household. And if cloud comes over during a charge, all of the 2400 watts (10A 240V) will come from the battery (100A 24V). The 3000W PSW inverter handles it ok (gets a little warm). I start the charge (manually) when the batteries are about full. The batteries deplete their "fullness" on the 100A draw in about 15 minutes and I have to (manually) stop the EV charge.

My solution is to add yet another 1kW of solar (to a total of 4kW) and design an EVSE that will start when the battery bank is full. The EVSE will initially call for the LEAF to take only 1A (at 240V) while the EVSE monitors the battery voltage. If the voltage remains high, the EVSE will call for an extra amp (240V) up to the limit of 15A.

As the battery voltage drops, the EVSE will drop the current to eventually turn off altogether when the battery reaches (say) 24V.

I welcome all suggestion to this projected solution.

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Off-grid EVSE

Post by Johny » Mon, 19 Dec 2016, 17:26

Unfortunately the J1772 spec. only defines charge current down to 6A.

PWM duty cycle indicating ampere capacity[20]
PWM     SAE continuous     SAE short term
50%     30 A     36 A peak
40%     24 A     30 A peak
30%     18 A     22 A peak
25%     15 A     20 A peak
16%     9.6 A     
10%     6 A     

Source: https://en.wikipedia.org/wiki/SAE_J1772

Could you not use a simple voltage cut-in/cut-out on the battery bank and have a 6A EVSE. You could have it cut in when the float voltage was reached and have it cut out at some pre-determined voltage that you determine by experiment at the 6A charge current.

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Off-grid EVSE

Post by jeffthewalker » Mon, 19 Dec 2016, 18:51

Johny wrote: Unfortunately the J1772 spec. only defines charge current down to 6A.

PWM duty cycle indicating ampere capacity[20]
PWM     SAE continuous     SAE short term
50%     30 A     36 A peak
40%     24 A     30 A peak
30%     18 A     22 A peak
25%     15 A     20 A peak
16%     9.6 A     
10%     6 A     

Source: https://en.wikipedia.org/wiki/SAE_J1772

Could you not use a simple voltage cut-in/cut-out on the battery bank and have a 6A EVSE. You could have it cut in when the float voltage was reached and have it cut out at some pre-determined voltage that you determine by experiment at the 6A charge current.

Thanks for the input.

I did research the standard, looking for such limitations (minimum 6A) and I think I found somewhere a reference to 1A minimum. I have not found it again (yet). I can experiment. Hopefully, the table is just giving some levels and the LEAF can actually follow the PWM duty cycle.

I would like to have the ability to call up 1 to 15 amps so that I could take full advantage of the available sunshine/solar and to never overdraw the batteries.

6A is way too slow when 15A is available.

I will keep lookin' (dreamin').
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Off-grid EVSE

Post by jeffthewalker » Mon, 19 Dec 2016, 20:25

Johny wrote: Unfortunately the J1772 spec. only defines charge current down to 6A.

PWM duty cycle indicating ampere capacity[20]
PWM     SAE continuous     SAE short term
50%     30 A     36 A peak
40%     24 A     30 A peak
30%     18 A     22 A peak
25%     15 A     20 A peak
16%     9.6 A     
10%     6 A     

Source: https://en.wikipedia.org/wiki/SAE_J1772

Could you not use a simple voltage cut-in/cut-out on the battery bank and have a 6A EVSE. You could have it cut in when the float voltage was reached and have it cut out at some pre-determined voltage that you determine by experiment at the 6A charge current.

I could use the three values 6A, 9.6A and 15A and switch between them following battery condition.

But, I have 400Ah of Gel battery and don't like to draw more than 40A. One (or two) amp steps would be lovely.
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Off-grid EVSE

Post by jeffthewalker » Tue, 03 Jan 2017, 13:36

More discussion has taken place on the Google Groups EVSE forum.
https://groups.google.com/forum/#!categ ... r69kRiboqY
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Post by nuggetgalore » Tue, 24 Jan 2017, 17:57

jeffthewalker wrote:
Johny wrote: Unfortunately the J1772 spec.
Source: https://en.wikipedia.org/wiki/SAE_J1772
But, I have 400Ah of Gel battery and don't like to draw more than 40A. One (or two) amp steps would be lovely.


All very interesting but currently way to technical for me.
First I wish somebody would answer the following question: is there a basic problem to charge my iMiEV with a run of the mill DC to 240 V AC inverter (off grid solar +batts). Can it damage the onboard charger or the batteries of the EV?
I bought the EV to use the sun,but now somebody warned me it may be risky.
Thanks
Last edited by coulomb on Thu, 26 Jan 2017, 05:24, edited 1 time in total.
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Off-grid EVSE

Post by jeffthewalker » Thu, 26 Jan 2017, 16:38

nuggetgalore wrote:   

All very interesting but currently way to technical for me.
First I wish somebody would answer the following question: is there a basic problem to charge my iMiEV with a run of the mill DC to 240 V AC inverter (off grid solar +batts). Can it damage the onboard charger or the batteries of the EV?
I bought the EV to use the sun,but now somebody warned me it may be risky.
Thanks
"Run of the mill" inverter comes in two flavours. "Pure sine wave" and "Modified sine wave". I recommend only PSW. MSW may well be ok, but I don't want to take a chance with my car (LEAF).

I have been charging using solar/storage with a PSW inverter for over 12 months.

For my LEAF I have the original 10A EVSE and a JuiceBox 15A EVSE.

For the 10A 240V EVSE, I use a 3000W PSW inverter and would not recommend anything less (the 10A EVSE controls the power draw to about 2200W).

If the sun is shining and you have 2200W "excess" solar (more than the house needs), then you will be charging from solar. Anything less and you will be drawing (at least some) from the batteries.

If you draw too much from your batteries your house will get less (or not enough). If you draw too heavily from your batteries you could/would damage your batteries or lessen their life.

I started this thread as I am developing a "controlled" EVSE that only uses "excess" solar. That is, if the sun goes behind a cloud the new EVSE will draw less or shut down altogether. If others are interested I will consider supplying after I get my own one working.



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Re: Off-grid EVSE

Post by nuggetgalore » Sat, 09 Sep 2017, 06:27

Hi Jeff,
I just found this thread again.
Did you build one of these: " I would like to have the ability to call up 1 to 15 amps so that I could take full advantage of the available sunshine/solar and to never overdraw the batteries.

6A is way too slow when 15A is available.

I will keep lookin' (dreamin')."
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Re: Off-grid EVSE

Post by jeffthewalker » Sat, 16 Sep 2017, 05:35

Hi. I just got back to reading this forum. Since the layout change I had struggled to find the "new posts" option.

The answer is NO, I have not yet built this charger. I have moved my base temporarily to my newly acquired sapphire mining claim in Sapphire, Queensland. So far, I have installed just enough solar and battery to power the "shack". I charge once a week at a friend's "on-grid" claim.

However, I still feel that is a real need for a EVSE (charge controller) for off-gridders that will "follow the sun".

The J1772 protocol does not allow for current draws of less then 6A.

By monitoring the battery voltage and controlling the current to only pull to just below solar controller cut-off voltage, the EVSE would never draw from the batteries. In this way it would always (and only) use "excess" solar. So it would draw 15A if 15A was available as "excess".

I would love to push on with this project and will collaborate with other(s) with ideas and software/prototype hardware.
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Re: Off-grid EVSE

Post by nuggetgalore » Sun, 17 Sep 2017, 15:12

jeffthewalker wrote:
Sat, 16 Sep 2017, 05:35
Hi. I just got back to reading this forum. Since the layout change I had struggled to find the "new posts" option.

The answer is NO, I have not yet built this charger. I have moved my base temporarily to my newly acquired sapphire mining claim in Sapphire, Queensland. So far, I have installed just enough solar and battery to power the "shack". I charge once a week at a friend's "on-grid" claim.

However, I still feel that is a real need for a EVSE (charge controller) for off-gridders that will "follow the sun".

The J1772 protocol does not allow for current draws of less then 6A.

By monitoring the battery voltage and controlling the current to only pull to just below solar controller cut-off voltage, the EVSE would never draw from the batteries. In this way it would always (and only) use "excess" solar. So it would draw 15A if 15A was available as "excess".

I would love to push on with this project and will collaborate with other(s) with ideas and software/prototype hardware.
Thanks for that. Yes I might have to get the 15/10/6 amp EVSE (have to go and check if it works with my 2010 iMiEV.

PS:.I know Sapphire rather well, was gold mining in Clermont for 30 Years and bought some equipment in Rubyvale/Sapphire . In the good ole days when red tape was not as omnipresent as is today.
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Re: Off-grid EVSE

Post by coulomb » Sun, 17 Sep 2017, 20:27

nuggetgalore wrote:
Sun, 17 Sep 2017, 15:12
Yes I might have to get the 15/10/6 amp EVSE (have to go and check if it works with my 2010 iMiEV.
It might not. It really depends on how the modification works. My guess is that they would have done the bare minimum to make it work, and they may not have included any means to control the charge rate.

So yes, definitely check that out carefully before purchasing a fancy EVSE. If the existing modification doesn't control the charge rate (e.g. it always charges at 13 A), it may still be possible to achieve a variable charge rate, but with some technical fiddling. You might be able to end up with a pot on the dash, or a switch, to select various charge rates, possibly lower than 6 A. Of course, you'd rather it was controlled automatically by your solar charging system, which might require a small computer with a wireless interface of some sort.

Then again, it's possible that the 2010 charger simply doesn't allow for variable rate charging at all. I would hope that's not the case, but it's possible.
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Re: Off-grid EVSE

Post by Paul9 » Mon, 18 Sep 2017, 11:45

In my off grid place west of Sydney I use a Plasmatronics PL30 Regulator to control my battery bank. I am aware that this regulator is capable of charging a second battery bank or turning on lights or running irrigation pumps etc etc depending on criteria the user sets in the regulator. And the criteria that can be used are quite extensive.

For instance it will charge a second battery bank but only if the primary battery bank is at 95% (or whatever % the user sets) SOC or more.

As I understand the issue, this regulator may solve the problem of charging the vehicle only when the main battery bank is full or above a predetermined voltage. Any processes can also be turned off when either the main or secondary battery banks drop to a certain voltage or SOC.

If you google Plasmatronics PL30 User Manual and PL30 Reference Manual you will find the info on the above in Section 7 of the Reference Manual.

Hope it helps
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Re: Off-grid EVSE

Post by nuggetgalore » Mon, 18 Sep 2017, 20:50

Thanks for the tips.
I will post what that EVSE does to both my 2010 and the 2012's of my mates ( when I find the time to drive to Oakleigh ).
Cheers
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Re: Off-grid EVSE

Post by jeffthewalker » Tue, 19 Sep 2017, 07:01

Paul9 wrote:
Mon, 18 Sep 2017, 11:45

As I understand the issue, this regulator may solve the problem of charging the vehicle only when the main battery bank is full or above a predetermined voltage. Any processes can also be turned off when either the main or secondary battery banks drop to a certain voltage or SOC.

If you google Plasmatronics PL30 User Manual and PL30 Reference Manual you will find the info on the above in Section 7 of the Reference Manual.
I had a good (but quick) read through the "user manual". It is able to control a load on and off following the battery voltage (or other parameter).

However, in an off grid situation, the supply of sunshine and the household load on the batteries is variable.

If the EVSE is pulling 2000W and a cloud covers the sun, the "excess" solar could drop to 1000W. With an EVSE that could lower the load, but not cut it off altogether, the EVSE would continue to supply the EV with excess solar.

The J1772 protocol allows for this and an EVSE can be designed to accomplish it.
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Re: Off-grid EVSE

Post by coulomb » Tue, 19 Sep 2017, 08:55

jeffthewalker wrote:
Tue, 19 Sep 2017, 07:01
I had a good (but quick) read through the "user manual". It is able to control a load on and off following the battery voltage (or other parameter).

However, in an off grid situation, the supply of sunshine and the household load on the batteries is variable.

If the EVSE is pulling 2000W and a cloud covers the sun, the "excess" solar could drop to 1000W. With an EVSE that could lower the load, but not cut it off altogether, the EVSE would continue to supply the EV with excess solar.
But that could be another way to do it, if you don't mind working your batteries a bit.

In the situation of 1000 W solar power and 2000 W EV charging, if the SOC is say above 80% the EV could be charging. The battery will slowly drain, however, and at 80% SOC you could get the EV charging to turn off. If the SOC rises to say 90%, you can continue charging again. Worst case, you still have 80% SOC in your battery for night time use. You could fiddle the SOC setpoints to fine tune the balance to your liking. Then it doesn't matter how fast the EV charges, as long as your inverter can supply it and any other loads. In effect, the Plasmatronic or other controller will do a very slow (half hour on, 25 minutes off say) pulse width modulation of the EV charge, and it will adapt to the cloud conditions.

It seems better to just use the exact amount of excess power that you have at the time, rather than "banking" some solar charge in the battery, but if that's not feasible, this could be the next best thing.

I'm assuming a battery system here. Without a battery, then yes, you do need more or less instantaneous control. However, if you know you will end up charging the EV at least partly from the grid anyway, you could afford some periods where the grid provided some of the EV charging. For example, 1600 W average solar power over say a 2 minute window and 2000 W load would be OK if you knew from experience that at least 20% of the charge had to come from the grid anyway. You have to have either batteries or the grid; as far as I know it's not possible to use only solar power to power a 230 V load like an EV charger.
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Re: Off-grid EVSE

Post by jeffthewalker » Tue, 19 Sep 2017, 13:06

Yes, I can see that it would be like PWM with the controller cutting in and out.

As I would be doing the EVSE controller from scratch (PIC microprocessor) I much prefer to "follow the sun" with 1A resolution. I am happy to use the battery voltage as the indication of state of charge. I have a separate 24VDC to 120VAC PSW inverter dedicated to the EV so that at 6A (lower limit of J1772 protocol), I can get down to 720w (6A X 120V) which I think would be available on most days.

With a solar/storage system that is 2kW nominal solar for the dwelling and 2kW additional to cater for the EV all is well while the sun is shining and the batteries (6kWh) happy. Feeding the EV with 2.4kW when it is solar available is great and wonderful. But when the sun is (relatively) quickly covered by cloud, at 24V the batteries now have to provide 100A (2.4kW) until the controller calls it quits. I am trying to avoid this heavy battery draw.
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Re: Off-grid EVSE

Post by nuggetgalore » Wed, 04 Oct 2017, 19:53

coulomb wrote:
Sun, 17 Sep 2017, 20:27
nuggetgalore wrote:
Sun, 17 Sep 2017, 15:12
Yes I might have to get the 15/10/6 amp EVSE (have to go and check if it works with my 2010 iMiEV.
It might not. It really depends on how the modification works. My guess is that they would have done the bare minimum to make it work, and they may not have included any means to control the charge rate.

So yes, definitely check that out carefully before purchasing a fancy EVSE. If the existing modification doesn't control the charge rate (e.g. it always charges at 13 A), it may still be possible to achieve a variable charge rate, but with some technical fiddling. You might be able to end up with a pot on the dash, or a switch, to select various charge rates, possibly lower than 6 A. Of course, you'd rather it was controlled automatically by your solar charging system, which might require a small computer with a wireless interface of some sort.

Then again, it's possible that the 2010 charger simply doesn't allow for variable rate charging at all. I would hope that's not the case, but it's possible.
At long last we found time to check this 6/10/15 Amp EVSE.
Sadly on my 2010 model iMiEV it does not work on the 6 and 10 amp settings as the onboard charger ramps up to the "normal 12.5 A and then the EVSE trips.
So back to to the question of how to modify the charge rate settings on a 2010?
The 2012 we also took there "normally charges with 8.5 A with the charging cable with the brick. it accepted the 3 different amp rates of the "EVolution " EVSE.
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