Interesting. Are there any relays or other inline components / connections between EV battery and MPPT input or just direct wiring?
And if just direct wiring, what wire gauge and what roundtrip length?
High Voltage DIY LiFePO4
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And if just direct wiring, what wire gauge and what roundtrip length?
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
Since I’m exporting, I would just control charge power to track EV excess export going to grid. EV battery can easily be topped-up during peak production hours daily…
In my case, I would only be connecting EV to hybrid at night once house battery is depleted, so EV and active solar sting would never be connected at the same time. Could even get away with a single HV MPPT and a couple high-voltage / high power relays / SSRs…
I’m pretty sure that as bidirectional chargers emerge / mature, there will be a way to get HVDC out (possibly with a bit of DIY hacking).
Again, with some DIY hacking, you’ll be able to precharge through a resistor and then bypass it for charging / use.
I’d be more worried about higher than maximum current during use and having enough inline resistance to make it easy for MPPT to throttle / control DC input power as needed…
Yes, a boost converter essentially provides a current limit. Assuring direct battery input does not exceed max current ratings and cause damage would be my biggest concern…
Hedges
I See Electromagnetic Fields!
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Only an issue when you connected battery to a particular PV MPPT circuit (microinverters in your case.)
The PV input is just a DC/DC converter with some control algorithm.
I would use an AC coupled Sunny Boy, older model with "turbine" and other modes. Input voltage can be constant, it just draws the current it wants.
Sunny Boy Storage appears to just be a bidirectional Sunny Boy, with "battery" (external bidirectional boost converter) input.
I would set its frequency-watts frequency range lower than the ones with PV, so power from HV battery is curtailed before PV. However, that could use HV battery to more rapidly recharge 48V battery, resulting in PV curtailment later in the day. OK for my application, because goal is to float lead-acid battery. For both of us, when PV curtailment starts to occur we want to send power to HV battery.
On the charging end, my plan is to use excess DC-coupled solar to charge house battery in morning and late afternoon and use both excess AC-coupled solar power being exported as well as DC-coupled solar power to top-off the EV battery during the peak production hours of ~1-3pm.
So my export will have a -1-2 hour ‘notch’ in it (depending on how much the EV battery has been drained by driving and/or overnight offset) right when export is least wanted by the grid.
So I should be able to avoid any curtailment and it will just be a reduction in daily export power from charging house battery and topping-off EV battery daily…
No need for frequency-shift curtailment in what I’m planning. Only DC-coupled curtailment once the house battery is fully charged but even that should pretty much never happen since the house battery is ~4-times bigger than excess daily DC-coupled energy…
yabert
Solar Enthusiast
Direct wiring... well I use the AC compressor output, so there is 30A fuse and the EV battery contactors inline, but they are there anyhow.
All details: https://diysolarforum.com/threads/360v-dc-input-split-phase-120v-240v-ac-inverter.15036/page-6
Not sure what the ‘AC compressor output is,’ but it seems as though you and others are successfully using HVDC out from battery to power 48VDC or 24VDC battery chargers and that is very cool.
Microinverters / inverters may have some difficulty / risk starting up off of HVDC batteries powering MPPTs intended for PV strings, but battery charging may be easier / more forgiving.
I wonder if anyone has tried using a straight-up HV SCC powered by HVDC battery to charge 24/48VDC batteries…
Does anyone offer a ~350VDC SCC that can charge at 24V or 48V?
Is there a relay between HV battery terminals and MPPT inputs somewhere (either within EV or anywhere else)?
Is there a BMS within the HV battery?
Can you estimate your round-trip cable length (and provide the gauge)?
Your 30A fuse assures your average current is under 30A but inrush could be well above that so I’m trying to get some estimate of inline resistance between HV battery and MPPT input…
Not clear to me how the stated 360VDC can be delivered by the stated maximum of 96S, but it’s close: https://m.aliexpress.com/item/1005001758226775.html
96S = at least 307VDC @ 3.2V / cell or 320VDC using 3.3 VDC per cell but only reaches 360VDC @ 3.75VDC per cell…
Still, these modular high-voltage BMSs are a thing now, so if 360V meeting your requirements is not available today, it’s just a matter of time (120S)…
yabert
Solar Enthusiast
All details in the link I give upper, and here:
Average 5-6A and no inrush. The precharge resistor inside EV battery do his job.
OffGridForGood
Catch, make or grow everything you can.
@yabert - thanks for all your posts, I have been following along - (and your link to TheSamba; WOW!) I am very interested in the high voltage DC set up you are using. May I ask what that VW Van-conversion to EV cost you? I can tell it was a lot of personal work on your own in a shop, but what did the cost of parts add up to?
4.1 mOhms x 30-feet x 2 (roundtrip) = 246 mOhms, so than helps.
If the EV includes a precharge resistor, how is it by bypassed after precharge is complete?
In any case, that makes it easy and 6A through 246 mOhms is less than 9W of I^2R losses, so over 99.5% efficiency from battery to hybrid…
Hedges
I See Electromagnetic Fields!
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Schneider 600V solar charge controller:
Schneider Electric 865-1034 Conext MPPT 100 Amp 600VDC Solar Charge Controller
NOTE: In order to program this controller, you will need the Schneider InsightHome Energy Management Device 865-0330.
www.solar-electric.com
Midnight 600V:
Victron 450V or 8x battery float:
Victron Energy SmartSolar MPPT RS 450/200-Tr Solar Charge Controller
Note: This charge controller is no longer available, Please look at the SmartSolar MPPT RS 450/200-MC4 Part Number: SCC145120410 This charge controller is for 48V systems. When designing for PV array open circuit voltage. The maximum open circuit voltage of the PV array must be less than 8 times...
www.solar-electric.com
OffGridForGood
Catch, make or grow everything you can.
I believe he just means "inverter" - ie DC to inverted to AC output.
Thanks, but if spending over $1250, it seems like getting an inverter and AC battery charger thrown into the mix would be worth a modest premium…Schneider 600V solar charge controller:
Schneider Electric 865-1034 Conext MPPT 100 Amp 600VDC Solar Charge Controller
NOTE: In order to program this controller, you will need the Schneider InsightHome Energy Management Device 865-0330.
Midnight 600V:
Victron 450V or 8x battery float:
Victron Energy SmartSolar MPPT RS 450/200-Tr Solar Charge Controller
Note: This charge controller is no longer available, Please look at the SmartSolar MPPT RS 450/200-MC4 Part Number: SCC145120410 This charge controller is for 48V systems. When designing for PV array open circuit voltage. The maximum open circuit voltage of the PV array must be less than 8 times...
You’ve convinced me that HVDC charging of LVDC batteries is a thing (at least at 48VDC) so hopefully it’ll be just a matter of time before we see 48V versions of HVDC MPPT storage hybrids like this: https://www.renvu.com/Solis-5kW-S6-HV-Single-Phase-Hybrid-Inverter-with-Tigo-Transmitter
yabert
Solar Enthusiast
25k$ CAD because 5 years ago a crashed 2017 Bolt cost 18k$ deliver in my driveway.
Today, with a bit of luck you can have crash EV with 50-90 kWh battery for 5-10k$. So do your calculs and you could realise how low cost is it.
This bring me to the main subject of this thread (High Voltage DIY LiFePO4). Why DIY when car manufacturers put billion in development of high voltage battery who including high quality cells, BMS, contactors and all the engineering and security stuff inside battery who finish at scrap yard everyday?
To me it clear, simply use those high quality batteries and stop throwing money to have low quality chinese cells and BMS.
If NMC of NCA chemistry fear you, I have good news for you because Tesla, Ford, GM and other start to use LFP cells in their cars
yabert
Solar Enthusiast
Contactors. Precharge contactor and then battery traction contactors (the high current ones).
yabert
Solar Enthusiast
No, I really mean air conditioner compressor.
On EV's the compresor generally work at the traction battery voltage. As I don't integrated the AC compressor in my Vanabolt, I simply use this 360V output to powered my house... well, power go to my inverter who powered my house.
zanydroid
Solar Wizard
This is cool, but IMO by the time surplus LFP modules from EVs become available in quantity there’s a very good chance stationary storage will be commoditized. IMO stationary storage probably requires less expensive materials and engineering than EVs to support the same cells.If NMC of NCA chemistry fear you, I have good news for you because Tesla, Ford, GM and other start to use LFP cells in their cars
OffGridForGood
Catch, make or grow everything you can.
True, however we are discussing repurposed EV cells, not new. Rather than these being wasted or torn apart for recycle, use surplus (wrecked EV cars) battery packs to supply low cost stationary battery storage. As was pointed out, these can supply a high voltage MPP input to charge regular 48-volt DC rack batteries, or perhaps high voltage DC ESS with an inverter designed for this DC voltage.
zanydroid
Solar Wizard
Do NMC modules work out cheaper today than server rack batteries? Referring to the modules sold on recycling websites
Do the NMC modules have value in servicing EVs?
Do the NMC modules become deemed unfit for onroad use after being in a wreck?
Trying to build a mental model for why they would drop in value.
Do the NMC modules have value in servicing EVs?
Do the NMC modules become deemed unfit for onroad use after being in a wreck?
Trying to build a mental model for why they would drop in value.