High Voltage DIY LiFePO4

[OffGridForGood]

So,...If i DIY an EV conversion, and then use the same HV battery voltage for a HVDC off grid solar set up, and build the EV conversion with suitable connections to act as a battery extension to the home solar, then I am "Good to go"
Sounds like it should be do-able,
No idea how to make it thou.

 

[Ampster]

then I am "Good to go"

Yes, as long as you remember to unplug it.

 

[OffGridForGood]

"Hunny - don't forget to unplug the HVDC connection before taking the car out for a drive, remember what happened last time"

 

[OffGridForGood]

To plan such a DIY set up, with the main Solar ESS battery bank using DC voltage identical to the DIY-EV battery (the mobile battery), we would need an Inverter capable of about 380 volts DC -right?
But the only ones I see like this (Deye) are actually 3-phase inverters.
Are there any single phase 240V (60hz) high voltage inverters on the market at this point in time?
Something about 20kW would be good.

 

[Hedges]

Sunny Boy Storage is 6kW, and has 3 battery inputs.
I would like to do this, but having SBS AC coupled to my SI.
With auto-transformer it could do 120/240V split-phase. Without that, I'm not sure whether it would do 240V single phase (may look for neutral in the middle like GT PV, but since it also says 50 Hz, it may support single phase.)

The new 10kW 120/240V SMA hybrid I expect will also use HV battery (they have a 3-phase model already in Europe.)

 

[zanydroid]

FWIW modifying your HVDC traction battery to use as a temporary ESS is close to black and white prohibited by code if you are under IRC 2021

R328.10 Electric Vehicle Use
The temporary use of an owner or occupant's electric-powered vehicle to power a dwelling unit while parked in an attached or detached garage or outdoors shall comply with the vehicle manufacturer's instructions and the California Electrical Code.

(All California did was reword NEC to CEC)

 

[Hedges]

There might be some wiggle room if you have a carport. Or a room or building that is not a garage (e.g. barn)

Or if it is a self-driving Tesla and you get it to roll back and forth continuously (not parked).

Or if you put the vehicle up on blocks or on a trailer (not parked).

Or leave it continuously connected (not temporary). Some issue with using an extension cord because those aren't allowed as permanent.

Or powering your workshop (not a dwelling unit). What if the workshop has a 48V battery charger, which charges the battery of your home system?

It seems they want you to use a vehicle that the manufacturer says can supply AC.

 

[zanydroid]

It seems they want you to use a vehicle that the manufacturer says can supply AC.

I think it’s definitely fine with CCS2 or other V2X. I think it’s probably fine with V2L, I actually read one EV manual this weekend to see if they have any incompatibilities with feeding a house and it read like a generator manual.

As for the other loopholes… well building code is not written by lawyers so some interpretation by AHJ is needed to plug them. If the building code were written by lawyers to plug all of these loopholes… it would be unusable. Or you would need to hire a lawyer to read it.

 

[dcg9381]

High dc voltage means an awful lot of battery cells.
Monitoring, protection, and balancing starts to become both complex and expensive.
Unless the power level is really high, I cannot see any advantage for off grid.

Is there any reason we don't see big 48V batteries connected in series? The only reason I can think of is that our inverters play nice with 48V.
One advantage I see is EV charging. As soon as you DC battery voltage to the same voltage as the car (or potentially the grid) it's less lossy to convert that power to usable output.

 

[dcg9381]

well building code is not written by lawyers so some interpretation by AHJ is needed to plug them.

I disagree. NEC is specific as hell. Discussed by electricians and argued with AHJ everywhere: if it is not EXPRESSLY PROHIBITED, it's allowed.
Want to site me for a violation? You have to cite code. Can't do that, you may be able fail me "just because" but I'd eventually win on the legal side.

That being said, I never piss of the AHJ inspectors. I play dumb and let them "educate me". It's less expensive that way.

 

[Hedges]

Is there any reason we don't see big 48V batteries connected in series?

Other reason would be allowed (negative) voltage seen by 48V battery BMS if it open circuits while in series with others.
A bypass diode could fix that.

Then looks at isolation voltage of circuits used for data com, and any filter or TVS devices to chassis.

 

[dcg9381]

Other reason would be allowed (negative) voltage seen by 48V battery BMS if it open circuits while in series with others.

So I'm not sure about this. I'm not claiming different because I'm just now buying batteries that have internal BMS systems.
If you have a series of batteries:

neg - 48v + - 48v + positive = 96v.

IF this circuit opens, BMS internally continues to see individual cells, but it's going to see any output voltage, as there is no continuity.

neg - 48v + <open> - 48v + = 0v

Let me know what I've got wrong.

 

[Ampster]

it's less lossy to convert that power to usable output.

Do we even know how "lossy" onboard chargers are? Any DC fast charger has to have a DC to DC converter. Do we know how "lossy" those are compared to the onboard chargers?

 

[dcg9381]

Do we even know how "lossy" onboard chargers are? Any DC fast charger has to have a DC to DC converter. Do we know how "lossy" those are compared to the onboard chargers?

I do not, but as an electrical rule, the farther off target voltage you are, the more it's going to cost in efficiency to move towards that target voltage.

 

[fafrd]

Actually, they do exist and they are cheap. Just not fully (or at all) integrated for bidirectional.

EV HV DC fed to PV input of cheap hybrid draws power as needed to make AC and charge 48V battery.
AC output of hybrid feeds PV battery charger.

You are saying that with a bidirectional charger supporting HVDC out, you can feed that into an HV MPPT of a hybrid inverter I rented to connect to a solar string and is will successfully charge a 48V battery at whatever maximum charge power it supports???

Has anyone done that?

Switch connecting HV DC enables discharge as needed.

That would have to be an HV switch supporting full max charge power x 120%…

A switch connecting AC to charger would enable fixed charge rate. Preferable would be variable charge rate using only surplus PV (which could connected to second MPPT input.)

Not concerned about controlling charging the EV, it is alternate use of HVDC out of the EV that interests me. It’s an interesting idea ti use an HV string input but I suspect a current limiter or some solution to limit HVDC current would be required…

Neither of those switches would be required if EV charger was varied according to surplus PV. For a battery inverter that does frequency shift, charger just needs to respond to frequency.

This makes EV part of your ESS. Ensuring EV is recharged for your driving needs could require additional controls.

If hybrid requires floating battery (like transformerless inverters require floating PV), that could be a problem.

Again, most interested in potential problems related to use of HVDC out only…

So what requirements might there be on an HV MPPT string input needed to allow it to function with an HVDC output from a bi-directional charger?

 

[zanydroid]

You are saying that with a bidirectional charger supporting HVDC out, you can feed that into an HV MPPT of a hybrid inverter I rented to connect to a solar string and is will successfully charge a 48V battery at whatever maximum charge power it supports???

Has anyone done that?

The Vanabolt has been plugged into an inverter this way:

Bidirectional storage with EV.

Ohmconnect is not a VPP but it does operate in the framework of resources designed to relieve pressure on the grid. OhmConnect tracks your usage and then when there is an Ohm hour they pay you for reducing your consumption below your previous average during that period. I used them for a few...

diysolarforum.com

 

[OffGridForGood]

(All California did was reword NEC to CEC)

"CEC" was already in use for the Canadian Electrical Code.
(although we have see confusion before, ie" CA" used to identify California and Canada)

 

[OffGridForGood]

There might be some wiggle room if you have a carport. Or a room or building that is not a garage (e.g. barn)

Or if it is a self-driving Tesla and you get it to roll back and forth continuously (not parked).

Or if you put the vehicle up on blocks or on a trailer (not parked).

Or leave it continuously connected (not temporary). Some issue with using an extension cord because those aren't allowed as permanent.

Or powering your workshop (not a dwelling unit). What if the workshop has a 48V battery charger, which charges the battery of your home system?

It seems they want you to use a vehicle that the manufacturer says can supply AC.

Or DIY a Conversion ICE to EV, and write up a manual for the EV's HVDC use when connected to a home ESS, since your effectively the manufacturer...
Or,
Make the EV battery easily slide out on rails with a forklift, move to a dedicated support and plug in the garage? (I am considering a small pickup truck for a conversion, and make the battery just a large flat pack that fits the truck box, easily removed, heavy duty clamps hold it in place during use) Two packs would allow one in the truck and one in the rack during the day for use/charging at the same time. At night switch the two batteries around from shelf to truck with a forklift...gets around the rules?
One Flat pack battery = range for commutting short trips,
Two Flat pack batteries stacked in the truck box = long range (but removes box storage space) for long trips when needed, elliminate the need to carry the two batteries (weight) for most days, when only short range is needed...yeah just thoughts at the moment. Where is MattB

 

[Hedges]

You are saying that with a bidirectional charger supporting HVDC out, you can feed that into an HV MPPT of a hybrid inverter I rented to connect to a solar string and is will successfully charge a 48V battery at whatever maximum charge power it supports???

Has anyone done that?

By the end of the thread, this guy got a cheap hybrid with 48V worth of car batteries drawing from HV EV battery into PV MPPT input, and operating his Skilsaw.

UTILIZING GRID TIE INVERTER OFF GRID - $100 REWARD FOR SOLUTION

The property is off grid using a Prius as a generator to power an off grid tiny home Inverter being used: Aurora PVI6000 Prius traction battery voltage: 220 DC Ran wire from Prius to pvi6000 Inverter turned on and said "Missing Grid" This is grid tie inverter and needs to be connected to...

diysolarforum.com

The missing piece is transferring PV to car battery. So I suggest actual PV into other PV MPPT input, and inverter feeds vehicle charger when desired.

Issue with HV EV battery feeding MPPT would seem to be that if you have battery and actual PV connected, you want to draw from PV first, only drain EV battery if necessary.

So what requirements might there be on an HV MPPT string input needed to allow it to function with an HVDC output from a bi-directional charger?

Maybe its algorithm? Some just have PV MPPT function. Some are constant voltage, or otherwise adapted to fuel cell, hydro, wind.

I'm not sure how you control the bidirectional charger. He connected battery directly.

I would be concerned with precharge inrush using battery directly. Also fault current. (Sunny Boy Storage specifies 30A max available current to its battery inputs, and their supported batteries, some models at least, are lower voltage battery with boost converter. Not direct battery.

 

[yabert]

You are saying that with a bidirectional charger supporting HVDC out, you can feed that into an HV MPPT of a hybrid inverter I rented to connect to a solar string and is will successfully charge a 48V battery at whatever maximum charge power it supports???

Has anyone done that?

The Vanabolt has been plugged into an inverter this way:

I confirm! Here a picture of the 360Vdc EV battery (Chevy Bolt) connect to the MPPT of the Inverter and a small 24V battery connect to the battery input of the inverter.