12v Solar to 24v Tesla batteries

LoCoSqurriel · June 2018

Good day to All,

I am new here and new to solar. I have 4 100w Renogy panels (specs below), and I want to charge 2 - 24v 5.3kWH 250AH batteries. I will also have them being charged by the engine alternator while I am driving. I am wondering how is the best way to connect them and how long it would take to charge them. I was thinking 2 panels in series and then connected to the charge controller. I was hoping with the higher voltage connected this way would get the batteries charging sooner in the day. Just looking for thoughts and concerns.

Thank you for any assistance in advance! Cheers

Electrical Data Maximum Power at STC* Optimum Operating Voltage (Vmp) Optimum Operating Current (Imp) Open Circuit Voltage (Voc) Short Circuit Voltage (Isc) Maximum System Voltage Maximum Series Fuse Rating 100 W 18.9 V 5.29 A 22.5 V 5.75 A Module Efficiency 15.47% 600 VDC UL 15 A

mcgivor · June 2018

Being that the battery is 24V you would have to series the panels, PV voltage muse always be greater than battery nominal. The 400W would produce ~ 320W which is extremely small given the capacity of the battery, for off grid about double that would be in the ballpark. The amount of time to charge would be in proportion to the amount they are discharged, given there are no figures it's impossible to speculate. Lithium-Ion batteries need a specific charge controller, with the exception of some drop in replacement type, others will need a battery monitoring system or BMS, to safely charge them as they are sensitive to overcharging and over discharge. Can you provide more details on the batteries as well as charge controller you intend to use, there are others here who have more experience than I do and will be able to assist in the specific niche of Lithium technology.

LoCoSqurriel · June 2018

I was going to only use one of these batteries, however, I was just wanting the ability to stay off grid longer during the days with limited sun. Due to limited roof space, I was starting with 4 panels, I might be able to add more or adding a small wind turbine. A BMS will be used as well as a temperature monitoring system as they shouldn’t be charged or discharged within certain temps.

The Charge controller I am looking to use:

https://www.amazon.com/gp/product/B0719PGGBS/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=tntmtb-20&creative=9325&linkCode=as2&creativeASIN=B0719PGGBS&linkId=4bdd4bb0f96c45191b14810fb40ff9e3

This is all I have for the details on the Tesla Battery:

The modules consist of 444 Panasonic 18650 cells of about 3200 mAh nominal capacity.

The cells are configured 6s74p, Voltage range for the whole module is about:

18.6V soc 0%

23.1V soc 70%

24.9V soc 100%

capacity ~233Ah, ~5.2kWh

dimensions:

length 27”/685mm

total width with mounting fins 11 13/16”/300mm

width without mounting fins 11”/280mm

height 3”/75mm

mounting fin at 2”/50mm

terminals apart 9”/230mm

tubing 5/16” 8mm

weight about 55lbs / 25kg

Estragon · June 2018

Properly tilted in full sun, the 2 strings of panels may produce ~10a, for ~40-50 amp-hours in a typical day.

Wind probably isn't a viable alternative, unless you expect to park in quite windy (as in your hat needs to be tied on) conditions.

Assuming consumpton is likely to be more than the solar will support, I'd consider a small inverter type generator, such as Honda eu2000i. The battery likely has a fairly high charge acceptance rate, so an hour or so of generator run time in the morning would probably get much of the charging done, with the solar finishing over the remainder of the day. These generators are relatively small, lightweight, quiet, and fuel efficient (as generators go).

12v Solar to 24v Tesla batteries

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