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DIY PW from 2 Tesla battery modules
#1
Given my lack of real world DYI powerwall experience, 3 weeks ago I started full retail (sorry!) with my solar setup:
  • 6x270W Jinko solar panels
  • Victron SmartSolar MPPT 250/60
  • Victron Multiplus II 48/3000/35-32 hybrid inverter
  • Venus GX for system monitoring
  • BYD B-Box 2.5kWh LiFePo4 battery

Before continuing the retail-way (that is, splashing money in expanding the BYD battery), I want to give the DYI a chance, when increasing my storage capacity to ~10kWh!

Can you please point out any red signs or shortcomings in the following plan?

Material:
  • 2 x 5,3KWH TESLA MODULE 6S74P. I would really prefer to connect them in series, so that my MPPT has headroom to install additional PV panels (it’s rated 60A => 1720W@24V and 3440W@48V)
  • Victron BMV-712 battery monitor
  • Cabling and fuses 

Connection diagram. 
Like this: http://evwest.com/support/EV%20West%20Of...k%20Up.pdf


Questions: 
  1. Will it be stupid not to have a BMS, if I connect the 2 modules in series?
    If so, would it be less stupid not to have a BMS if I connect the modules in parallel?
    By connecting in parallel and staying at 24V, I would lose the MPPT headroom for doubling the current number of solar panels (6x270W to 12x270W).
  2. Is there any way to have the BYD and the DIY PW connected at the same time to my inverter/MPPT? Or would I need to add a second Multiplus II inverter/charger?
    I can also part ways with the BYD, and end up only with the DIY PW.
  3. Using the BMV-712 battery monitor, will I still see a nice SoC % indicator throughout my Victron management software, like I see now? Would it be reliable, or not so much?
  4. Any other mistakes, shortcomings, warnings?

Thanks!!
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#2
5. Also, is the 12S configuration (2 modules in series) of the battery modules going to be a problem?
    I see people mentioning that 14S is the way to go.
    However, I was hoping that, through some tuning of the charger settings in the hybrid inverter, my system could handle the 12S configuration with no problems. 


  (picture isn't from my exact inverter model, but from a very similar one)

The inverter and MPPT have:
  • Charge voltage 'absorption' and ‘float’ ranges of: 48 - 64 V
  • DC Input voltage range 38 - 66 V (inverter only)

Each battery module has the following specs:
  • Voltage nominal: 3.8V/Cell, 22.8V/Module
  • Charge voltage cut-off: 4.2V/Cell, 25.2V/Module
  • Discharging cut-off: 3.3V/Cell, 19.8/Module
Will they "fit" together? Or is the 48V charge voltage lower limit, too high for the battery module?
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#3
Hello Rui,
IMO you should do a lot of reading in related fora on the subject, checking you-tube etc
before stepping into the next phase of your project.

If there is money, stick with your current more or less plug play set-up, and buy BYD expansion boxes
it works, and is easy to expand, be it at a cost

If you do plan to go the diy second-life route my thoughts are these:
1)do use a bms, always...
2)48V inverters even like the top end Victron will not be able to extract all energy from the serial connected Tesla modules, these are simply not designed for 48V system but 400VDC
3)24V works parallel works, but see 4)
4) you are faced connecting a bms to the Tesla modules that will be able to talk "can-protocol" to the inverter,
Batrium has a product in the pipeline (facebook.com/batrium), some others brands are out there too Orion, EVTV (http://store.evtv.me/products.php?cat=31)

Plus see this development from UK:
https://www.diyelectriccar.com/forums/sh...90266.html
https://www.diyelectriccar.com/forums/sh...ost1018477
Using the Simple BMS board requires a skillset ie these are not plug-play, you need to make a wiring harness to connect the modules + work with Arduino code to get it running, but to me this is major step forward using the Tesla oem slave boards, and others.

5) perhaps have a loook at other second life drivepack from brands as Nissan Mitsubishi etc. 
These may fit better to a 14/15SmultiP system making a 48V battery.
see this rather long thread, but this where it all started for me:
https://www.photovoltaikforum.com/speich...02414.html

regards,
Carel Hassink

gregoinc and hbpowerwall like this post
pro-LOX, Carel Hassink, 
Obdam, Netherlands
36Kw ESS, 320 Yuasa LEV40 cells
14.2Kwp Ciggs solar panels, 2 Goodwe 3phase inverters
SMA SI 8.0 single phase + controls, REC BMS

second life ev/phev li-on batteries
follow me on facebook.com/Carel1956
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#4
(08-28-2018, 07:09 AM)CarelHassink Wrote: Hello Rui,
IMO you should do a lot of reading in related fora on the subject, checking you-tube etc
before stepping into the next phase of your project.

If there is money, stick with your current more or less plug play set-up, and buy BYD expansion boxes
it works, and is easy to expand, be it at a cost

If you do plan to go the diy second-life route my thoughts are these:
1)do use a bms, always...
2)48V inverters even like the top end Victron will not be able to extract all energy from the serial connected Tesla modules, these are simply not designed for 48V system but 400VDC
3)24V works parallel works, but see 4)
4) you are faced connecting a bms to the Tesla modules that will be able to talk "can-protocol" to the inverter,
Batrium has a product in the pipeline (facebook.com/batrium), some others brands are out there too Orion, EVTV (http://store.evtv.me/products.php?cat=31)

Plus see this development from UK:
https://www.diyelectriccar.com/forums/sh...90266.html
https://www.diyelectriccar.com/forums/sh...ost1018477
Using the Simple BMS board requires a skillset ie these are not plug-play, you need to make a wiring harness to connect the modules + work with Arduino code to get it running, but to me this is major step forward using the Tesla oem slave boards, and others.

5) perhaps have a loook at other second life drivepack from brands as Nissan Mitsubishi etc. 
These may fit better to a 14/15SmultiP system making a 48V battery.
see this rather long thread, but this where it all started for me:
https://www.photovoltaikforum.com/speich...02414.html

regards,
Carel Hassink


Carel, man, huge thanks for your post!

Your first advice (stick with BYD expansion) is super wise.
I'm hoping to reach a +10kWh storage, spending less than the €4.500(+VAT) needed for the BYD-route, with a comparable cycle life count. 
2 Tesla battery modules + Batrium + Fuses and cabling will probably be around €3.000.
Considering the absence of warranty, time consumed and risk, I'm also not sure of this path. 
Maybe by finding a sweeter deal on the battery of a wrecked EV it'll become a more interesting path.

Anyway, I've been away from the DIY Powerwalling world for almost 9 months and it's HUGE to see the developments in Batrium. Had no idea it now integrates with Victron GX and of the Watchmon4/5/6 pipeline. That way, I can trash the buy of a Victron BMV-712 battery monitor, and use that money to go full-Batrium.

Question: Using 2 Tesla battery modules in series, they'll combine to form a 37-50 V battery. 
               The inverter has a 38-66V discharge rate, so no problems there, right? 
                Additionally, the inverter as a 48-60 V charge voltage range... so.... is this 48V min. voltage charge rate too high for the battery? I was under the impression that the voltage charge rate could be higher (don't know by how much, though) than the battery's voltage.
              To preserve battery life, I wouldn't be doing 0-100 DoD. Maybe 20-80. Would that solve the voltage "compatibility" with my inverter?


Will read the thread you suggested on photovoltaikforum!
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#5
Rui,
anytime,
best
Carel
gregoinc likes this post
pro-LOX, Carel Hassink, 
Obdam, Netherlands
36Kw ESS, 320 Yuasa LEV40 cells
14.2Kwp Ciggs solar panels, 2 Goodwe 3phase inverters
SMA SI 8.0 single phase + controls, REC BMS

second life ev/phev li-on batteries
follow me on facebook.com/Carel1956
Reply
#6
Is the plan to put this in parallel with the BYD B-Box 2.5kWh LiFePo4 battery you already have then you will run into some voltage mismatch, unfortunately the Tesla cells in series are still 2s shy of playing nice with your existing battery.

On the plus side, you got a bunch of nice Victron stuff... that's the route I would like to go myself.
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