Charging a BEV with a Diversion Control system

[WillEert]

We are considering getting a Battery Electric Vehicle (BEV). I think the Chevrolet Bolt would be what we would get. As an off gridder I have to think about intergrating it's charging system into our house system. I feel we have enough power available for the miles we would use it to charge the BEV, if not we would have to put in more capacity - is that so bad? .

This is what I am thinking the charging system configuration could be. We would have anywhere from 0 to 4KW instanteaneously available to charge the BEV. Most of the BEV chargers are of larger capacity than that so I would PWM into the charging system. I could add a diversion inverter if need be (that I would prefer not to do but would do if need be) to add more charging KW which would give us up to 8KW or so of charging capability.

What I do not know is if the Lithium chemistry batteries the Bolt uses will charge fully at this low rate of charging over time. With my FLA if I don't give them enough amps then they seem to stay in bulk indefinitely and never reach a full charge. The Bolt battery bank is 60 KwHr. I don't know it's chemistry at this time. Would the BEV batteries reach a full state of charge eventually if their charge rate was 4KW max? Would this be "good" for the batteries? The idea is to do what it takes to charge the batteries in am acceptable fashion.

Thanks for any replies.

Will

[Westbranch]

Is it safe to assume that the PWM will output 120V AC?
Can the BEV accept other voltages ? Or Need other voltages?

[ClassicCrazy]

From what I know about lithium batteries - they don't sulfate like lead acid . So it doesn't matter if they are 20 % , 50%, or 80% full - it is not going to hurt the cells. And those modern vehicles have BMS battery protection devices to keep everything balanced and to the proper voltages.  So if you drive with a partially full battery as long as you have capacity to go there and back it isn't going to matter how full it is in the beginning.

So doesn't seem like it would matter how long  you take to charge them. 

As far as adding capacity to  your solar system - seems like there has never been a better time. I was at Midwest Renewable Energy Fair in Wisconsin last weekend. The Kyocera 270 watt panels that were selling last year for $1.10 a watt are selling for 0.74 a watt this year .

Larry

[Westbranch]

Larry, I am not worried about the SoC, but the total amount of charge, say overnight..  you need to have the capacity in the batteries to get you home or to recharge where you park overnight. 

A friend out here in the sticks has a TESLA , grrrrr... , said it's not going to his kids ( one already has his Tesla).  He upgraded his service to the garage and it is 230V for the fastest charge he can supply, but he mentioned there was a way for 480V ? (AFAIKR, may be off a bit) for an  even faster charge but the grid in his area can not supply that level...
That is why I was wondering about the inverter.... 

[WillEert]

I plan to PWM 240V ac to the charger.

Here is a link to the charger I may use. I thought we would likely get the "Home 25" model as I cannot see being able to provide any more KW to the charger than what that model will use.
https://www.chargepoint.com/files/home/home-install-guide.pdf

BEV can take a "level 3 charging" system if you get one with the correct fitting. It looks like this is a $750 optionon for the BOLT  but I think it would be worthwhile.  This is similiar to the Tesla supercharging system but is more generic. Level 3 charges with DC as I understand it. Level 3 is capable of adding 400 KmHr of range to the car if the battery can charge that fast. That leads to another question.  Might one charge the BEV battery bank with DC downstream from the Classic but upstream from the house  battery bank? I have not been able find out what voltage the Bolt battery bank operates at yet. I also do not want to risk the battery bank in this vehicle but it is a nice thought for an offgridder.

So if I understand the answer to the question it seems that one can charge Lithium batteries slowly at low amperage rates and acheive a full state of charge. I'm going to have to go and measure my diversion system voltage downstream of the SSR. I seem to remember that both the voltage and the amps varied with the PWM rate. If that is the case then I would not be supplying the charger with 240 V.  I wonder how it would like that?

Lots of learning on this project I think.

Will

[mike90045]

I think you need to plan to recharge your EV battery only while the sun is shining.  Building a 48v battery bank that can export 5 or 10 KWh overnight, would be a VERY large and expensive battery.

Say the vehicle battery is 15Kwh.  If it was only half depleted, it would suck 8 KWh out of your house battery overnight, plus any inverter losses.  48V @ 400ah is about 20Kwh max storage, 10kw usable.


The inverter that would be powering your 240VAC charger, would need to be a beefy inverter, capable of a large amount of power,  battery charging is a long continuous load, with no "time off" to cool down.   I have a 6Kw inverter that runs a water pump for 4 hours a day, and it gets quite hot after half hour of continuous 2Kw load

[WillEert]

Hi Mike,

The Bolt has a 60 KwHr battery bank. I would only charge it during sunlight hours. I would not expect to get a full charge ( depending how discharged the battery is) in one day.

I have found this charger.

http://openevse.com/

It can use  "OpenEVSE fully support SAE J1772 which specifys 120 or 240v @ 6A to 80A 50 or 60hz." It also has an adjustable maximum charge rate. It seems that you can write a 0 - 5V dc to the controller that adjusts the charge rate in 1 amp increments. If that is the case then I would , using an Arduino, divert power to it.

My system uses Magnum MS4448 PAE inverters. I am not completely satisfied with them however so far my diversion inverter which operates at 4kw output, making hot water,  has only crispy crittered the cooling fans. I have two load inverters and am thinking that I would use these to charge the car, changing the charge rate every minute or so in response to battery voltage. This still very preliminary.

These people are doing what I hope to be able to do.

https://community.openenergymonitor.org/t/diverting-solar-pv-to-ev-using-openeevse-mqtt-and-nodered/3411

Lots to learn. It is very hard to purchase a Bolt in Canada. Looks like at least a 6 -8 month wait which would mean delivery in winter. That is not good timing for me.

[Westbranch]

will wrote
''I have two load inverters and am thinking that I would use these to charge the car, ''

Are these not the Magnum4448's?

[ClassicCrazy]

If you have any problems with those Magnum Inverters - contact Ryan - he is working at Magnum now and told me at the Energy Fair he is happy to help with Magnum issues.

Larry

[WillEert]

The load inverters (2 of) and the diversion inverter (1 of) are Magnum MS4448PAE's. My old system before the Magnums had an Apollo Solar 4048. This inverter worked well and is still hanging on the wall of my shop. My only complaint with Magnums is that they are slow. By that I mean my lights flicker when the fridge (not the freezer starts). With the Apollo this did not happen. Also the stove causes flickeration. I don't know how the Apollo wpuld have handled the stove because we did not try to operate one with a 4kw system. the flickering is why I split the inverters up. The diversion inverter only does the PWM diversion or charging with the generator while the load inverters just support the house load. This works quite well.

For the car I am thinking that when the diversion inverter is at max diversion (4KW) I will turn the car charging on using the load inverters to produce the AC 240V required. The minumum charge rate is 6A which @ 240V is 1440W. The PWM diversion will reduce by this amount. If the sunshine permits when the PWM diversion is close to max again then the car could be increased in 1A steps. When available power diminishes then at a certain point the car charging would be turned off. I have lots of learning to do to be able to write the dynamic charge limit to the charger. The actual charge rate is set by the car in response to a signal from the charger so I have to be able to manipulate the signal from the charger to the car or have the charger code do that. I see this being done in England with this charger by I know nothing about emonpi or node red. The OpenEVSE charger is programed in C++ and appears to be an Arduino Uno so I should be able to figure out an Arduino based program.

Will

[WillEert]

I have sent away for my OpenEVSE charger. It will communicate by TTL serial so I should be able to make it work with my diversion control. It has commands to start charging, end charging and alter the charge rate. With any luck I can get it working by the time I get the car - whenever that might be.

Will

[ClassicCrazy]

I have sent away for my OpenEVSE charger. It will communicate by TTL serial so I should be able to make it work with my diversion control. It has commands to start charging, end charging and alter the charge rate. With any luck I can get it working by the time I get the car - whenever that might be.

Will

That is great Will - will look forward to your new controls .
Larry

[WillEert]

One thing I have encountered in the car world of charging Lithiums is the idea that at lower charge rates charge efficiency drops. Some people quote a charge efficiency in the 60% range for the Nissan Leaf. Any thoughts on this?

I floated the idea past my associate in life that in order to get enough energy to use our new car as much as we would like we might have to put in more power. I was considering an equipment shed with a roof like the firewood storage. I am starting to run out of ports of the megas so integrating a third charge controller into the system means I would have to give up my dedicated upload port however it would be done.
This concept was not taken well.........

Will

[ClassicCrazy]

At the Energy Fair in Wisconsin a couple weeks ago - the Kyocera PV panels that were selling for $1.10 a watt last  year are down to .74 a watt this year . Seems like great time to add more PV with prices so low.

I don't get why efficiency would be so low charging lower rate - just a bad charger design ? 

Larry

[WillEert]

Unexpectedly a Bolt appeared that was available so one came home with us last night. All I have to charge it is a 12A 120 EVSE cord   (standard issue). I am plugging it in to a standard receptacle 15A as needed.  So far I have learned:

If you turn your power off while the Bolt is charging, but not full,  it "chirps" endlessly until you unplug it.

Sometimes I wonder about people who develop modern stuff. Why would you do that?  I am hoping that the OpenEVSE charger I have ordered will not cause the chirping to occur. It has code and hardware buttons that lets you "sleep" it or "wake" it up. If the new charger won't cure the chirping I am sure some wire cutters will. Another thing about modern vehicles seems to be however that it is difficult to determine what is connected to what - casually cutting the chirper wires may have bad consequences.

I do like how it drives however. Very fun.

Will