Solar System for 4s 16.8v NMC Lithium Ion Batteries

Cedar

Hi all,

I am designing a custom solar system setup and want to be sure it will work.

Here's details on all components

Solar Panels - Two 12v panels at 115 W each (already owned)

Charge Controller - Victron BlueSolar MPPT 100/30

• https://www.amazon.com/Victron-Energy-BlueSolar-Charge-Controller/dp/B076N5PTBN/ref=sr_1_3?dchild=1&keywords=victron+bluesolar+100/30&qid=1590864560&sr=8-3

Batteries with BMS - Nissan Leaf Generation 2 Battery Module Lithium Ion NMC

• https://www.techdirectclub.com/nissan-leaf-generation-2-battery-module-lithium-ion-1-kwh-per-set-66-amp-h-12-volt-configuration-w-option-lot-of-2/

• 2 units at 500 Wh each = 1000Wh x 70% usable = 700Wh usable. These batteries are 60-70% usable capacity (I guess because BMS limits it?)

• BMS - https://www.techdirectclub.com/4s-bms-30-amps-assembly-kit-for-2-nissan-leaf-lithium-ion-battery-g1-g2/

Inverter - Victron Phoenix 12V 500W

• https://www.amazon.com/Victron-Energy-Sinewave-Inverter-VE-Direct/dp/B01N4J9OOM

Wall Charger - 54.6V 9A YALANCHA

• https://www.amazon.com/Charger-Battery-Aluminum-Electronic-Wheelchair/dp/B07RQS96W5/ref=sr_1_2?dchild=1&keywords=48v+9a+charger&qid=1590814661&sr=8-2&th=1

My goal is to disconnect the solar panels and connect the wall charger (powered by generator) on cloudy days. The reason I chose a 48v charger is because I will eventually get a 48v battery for an electric bike so I'd need it anyway. I calculate that I can plug this charger into the inverter to charge the bike battery from the Nissan Leaf batteries. What do you think my potential issues are? Thanks a ton!

mike95490

>  What do you think my potential issues are?

Battery management.  EV batteries are prone to "Venting Flame" much more so than the safer LFP batteries.
https://batteryuniversity.com/learn/article/types_of_lithium_ion
  and often need thermal control (coolant) in cars.  If you willl not be placing any demanding load on them that would cause them to heat, you might be OK

What is your containment structure for them ?

A small bike battery charger will take days to recharge the large battery bank

Raj174

I don't think you can use a 48 volt charger as a DC input for a mppt charge controller. The mppt function will not work. A pwm CC will work in this configuration.

Cedar

Thanks Mike & Raj for replying. I made a mistake in the diagram, it's a 1000 Wh battery (not 2000) and the seller's site says its 60% useable so more like 600 Wh. I want to connect the panels in series so I can generate above 16v when cloudy but I understand that in doing this, even shading one cell of one panel would drop the output of both panels a lot. Is there any way to connect in series while still having panels independent?

mike95490
I was originally thinking a wood box but now that you mention fire maybe a metal box? The max input from controller would be 30A (more like 10A with only 2 panels hooked up) and the max draw would be 500W. Would that still generate a dangerous amount of heat/fumes? I can go with LifePo4 if needed but would be fun to create a system with the much cheaper Nissan Leaf modules. Also I calculate that this 48v 9a bike charger would charge the 1000Wh battery in 2.3hr is that correct?

@Raj174
Could you explain why this charger won't work? I'm not sure what you mean by "MPPT function", I would need the controller to accept 48v, (54v to be exact, 48v is just the nominal rating), buck it to 16v (increasing amps from 9 to 30), and give it to the battery. And if the battery is discharged to say 13v it would convert the excess to heat as I am assuming controllers do. Thoughts?

mike95490

merely charging a Li battery does not present any heat/fume problems .   It's when the battery decides to fail, either from mfg defect, being overly discharged, or overcharged, that the heat/fumes/flame becomes a problem.  You have seen the reports of cell phones and laptops "bursting into flames" and those were well engineered systems and mostly attributable to internal defects in the battery.

Most MPPT chargers regulate themselves by shifting the Max Power Point around - which works great with PV panels as they are a current source.  But a battery or power supply is a voltage source and unable to be managed the way a solar charge controller expects to manage the charging.   You are planning to operate outside the design specs for the chargers, so expect excitement.

Raj174

@Raj174
Could you explain why this charger won't work? I'm not sure what you mean by "MPPT function", I would need the controller to accept 48v, (54v to be exact, 48v is just the nominal rating), buck it to 16v (increasing amps from 9 to 30), and give it to the battery. And if the battery is discharged to say 13v it would convert the excess to heat as I am assuming controllers do. Thoughts?

It appears that I have advised you incorrectly. Take a look at this thread for more information.

https://forum.solar-electric.com/discussion/351215/dc-dc-battery-charging-using-a-charge-controller