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LiFePo4/Victron/Overkill Design

JacquesC

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Dec 15, 2020
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This is what I have in mind for my system, I have attatched my design, note, I havent drawn the plans for ground, but I believe connecting all the elements to a common ground will do the trick, right?

What I have so far is:

-Victron BlueSolar 100/50 MPPT
-Victron Multiplus Compact 24/2000/50-30 230v
-OverKillSolar 8s 100a BMS
-8X VariCore 3.2V 280Ah lifepo4 battery

What I need is:

-Solar Panels.. I'm thinking JA Solar 450w, but I'm wondering if 2 in series (VOC 49.70) will be too much for the MPPT?
-DC Fuse/Breaker 120 amp+ from Battery bank to Multiplus (positive)
-DC Fuse/Breaker 30 amp+ from Battery bank to MPPT (positive)
-Cables
-Earth spike
-Positive and Negative Busbars

What I think I should get is:

-VE Direct Bluetooh SmartDongle (to configure MPPT)
-Interface MK3-USB (to configure Multiplus)

What I hope I don't need:

-Shunt


So my queries are..

-Solar Panels- If I went 2S2P with the 450W, would the voltage be too high for the MPPT
-Is there any device that would allow me to configure settings for both Multiplus and BlueSolar MPPT
-Is the LiFePo setting on the MPPT good enough to keep my batteries protected or will I need a Smart Dongle if I want to make them last?
-Shunt- As long as I configure everything correctly, is there a need for one or would it just help me see the SOC
-Any advice or recommendations are appreciated, do you see any problems with my proposed system

TIA
 

Attachments

  • Solar Design.pdf
    1.3 MB · Views: 17
VOC would be too high.

Also don’t forget how you’re mounting those +60lb panels. The cost of a quality racking system isn’t cheap.
 
Shunt: Yes, I would install one.

Personal preferences is the Victron (Smartshunt or BMV), but there are good reports of the Chinese 'clones' of these as well.

Without shunt it will work just as fine, but you don't have any clue about your battery status. With the flat curve of LFP, it's basicly impossible to see if you're at 25% SOC or at 95% SOC. Unless that doesnt matter I would install a shunt to see where you're at.

As for the MK3-USB: See if you can use it from someone, it's only needed for initial configuration or troubleshooting. If everything works properly you don't need it, and it's not a $10 cable unfortunately.

For the solar panels: with 4 panels of 450W you will have 1800W of solar. At a 24V system that would be approx 75A. How are you planning on using a 50A controller for that?

And as stated, 2S is not possible due to the Voc of 49V. The Voc is even higher at lower temperatures, so take that into your calculations. a JA Solar 450W panel has a temperature coefficient of -0.272%/C (Just took a random datasheet from a 450W JA solar panel).
-10 celcius is a 35 degree difference. 35x 0,272 = 9.52%
So a 49V panel would output 49V + 9.5% = approx 54V in a low temp environment...

If in series, you're going to need a MPPT with higher voltage range, like the 150/85. That can also handle the 4 450W panels fine.

It's a general rule not to run any electronics at high loads for long periods. Leave some room. Causes them not to run at high load, thus less heat, and longer life. With 1800W of panels, its not likely you're getting the full 75A very frequently, it will be more like 60A at max generally (depending on the panel orientation) but still, I would prefer a 85A controller for 60A (and peak 75A) current.
 
-Victron BlueSolar 100/50 MPPT

-VE Direct Bluetooh SmartDongle (to configure MPPT)
Victron BlueSolar 100/50 = $295
VE.Direct Bluetooth SmartDongle = $49
Total = $344

Victron SmartSolar 100/50 = $320

Save $24 and have less wiring by buying the SmartSolar version.

As for the MK3-USB: See if you can use it from someone, it's only needed for initial configuration or troubleshooting. If everything works properly you don't need it, and it's not a $10 cable unfortunately.
I solved that by adding a Raspberry Pi running VenusOS. This requires the MK3-USB to be connected permanently. :)

If in series, you're going to need a MPPT with higher voltage range, like the 150/85. That can also handle the 4 450W panels fine.
The 150/70 will likely be enough. It will be a rare time that they get a full 1800W from the panels. Besides, the batteries are really in the 26V+ range most of the time. 70A x 26.5V = 1855W so the 150/85 would be overkill. Unlike the Voc which can't exceed the max input voltage, it's not a big deal if the max output battery current is exceeded a little. The SCC will just not give you quite as much current as might be possible at that moment. But again, in this case it will be very rare, if ever, that the panels could allow the SCC to produce over 70A.
 
FYI, if you don't want a shunt the overkill bms will do the same job of tracking soc just fine.

There are some minor bugs with it when changing settings (remaining capacity goes wonky) but it shouldn't be an issue as it will reset when charged apparently.

I just found this out myself.
 
VOC would be too high.

Also don’t forget how you’re mounting those +60lb panels. The cost of a quality racking system isn’t cheap.
I would like to know more about the mounting requirements for these larger panels? Are normal aluminium rail systems not suitable for these?

I am considering the 500W Longi LR5-66HPH panels which are similar dimensions and weight (and more suitable Voc for the Victron SCCs ~45Voc), and I was expecting I should be able to mount them the same way as smaller panels (wind loading shouldn't be such a big concern as we don't get the cyclones/hurricanes here in New Zealand)
 
Racking systems are a whole process of sizing and specs for roofs and add up quite quickly.

The larger panels are no issues to mount just need to set spacing and roof mounts to meet the load of the racking manufacturer specs. Also don’t forget grounding and combiner boxes and string breakers and roof penetrations.
 
As MPPT consider the new Victron MPPT RS
They can handle up to 450Wp with 2 strings
At the moment they are only in 48v, but that reduces the cable size (and money) even more
 
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