Sunday, November 16, 2014

Buidling a Mini Energy Storage System - ESS - to Store More Energy at Night during Winter

You probably followed my AESC / LEAF Battery Modules adventures since last March: Ordering them from Las Vegas, Bottom Balancing them, Wiring them in Series and Testing them for month in my bedroom with a 24V 10A LiFePO4 charger and a SUN 250G Grid Tie Inverter

Here is a link to all these previous posts on the same subject :

In October I finally decided to pack of this "mess" into a compact Mini ESS - Energy Storage System - and below are the steps I went through, using a Bordeaux 6-bootle wooden crate - we are in France ;) -

This small unit is now upstairs in the living and used every day and every night, mostly to store as much Energy as we can at night when Electricity is half price during 8 hours with our TOU plan from EDF

This Mini AESC / LEAF Battery Modules ESS is storing 1.5 kWh of Energy at night and is pushing it back into our home grid during the day :)

So I started with these 3 LEAF battery modules, wired in series, and tested over 6 months

The idea was to find an enclosure that fit the modules almost perfectly and I thought about a 6-bottle wine crate to do the job

Warning: be extremely careful when using metallic tools with exposed battery connections !! a short could cause massive damage to you since the power output is HUGE !

So it fit almost but the tabs were sticking out a bit, an opening would be necessary anyways to access them to be able to check the voltage and access the connections when needed

Let's cut out this window

and pill up the 3 AESC modules

Now it is time to dismount the whole charge and discharge control system and install it inside the box, on top of the modules: it is made of a dual relay programmable voltmeter, and 2 Tyco Kilovac contactors - overkill for this system, but it's always better -

I did not want to put all these components directly on top of the modules so I added a small piece of wood, cut it to fit in length and did not cover the whole surface to let the modules breathe a little even if they do not heat up at all, they just get lukewarm towards the end of the charge around 4.1V per half modules

After came the fitment of all the rest: the 250W Grid Tie Inverter, same one used in my big DIY ESS upstairs, a 10A 24V - actually 29.2V - LiFePO4 charger and all the cables and wires
The 2 Kilovacs will face each other taking minimum space like this

Then we need to rewire the modules in series, but this time with connections using new 6mm lugs, add the main breaker in the middle of the pack for safety - and long time storage -

Soldering all the cables, using 2.5mm2 solid copper, too big for carrying 10A in both charge and discharge modes on short distances, but it is always better - and I can always double or triple the current later upgrading with other chargers and grid tie inverters -

First test after rewiring everything : it works, good !

At this point I brought the Mini ESS upstairs and put it next to the big one

I quickly protected exposed connections with a plastic cover, switched on the charger and it completed its first night charge - using half price electricity -

I forgot to talk about the main switch which simply allows, OFF in the center, Charger ON upper position, and Discharge through the Grid Tie Inverter in lower position
Bot Charge and Discharge modes are cut off automatically when the upper and lower Pack voltage limits are reached : 24.9V for full down to 21.6V for empty (6 half modules with voltage from 4.15V down to 3.6V)

The next week end I looked for a way to cover the whole unit and found a plastic box cover that fit perfectly

Tall wood screws will be perfect to hold it in place leaving some space to let the warm air from both charger and GTI get out

I screwed the small plastic box cover on the connections and this should be fine to protect - small holes will be drilled to be able to check the modules voltage, even if this is not moving at all, as I learned during the last 6 months test period -
The main DC breaker here is used to break the pack in two if unusual high current is reached in case of a short circuit for example, and to avoid any drain of the voltmeter if the Mini ESS is not used for long periods of time - holidays for example -

Now it remains here in the living room, next to the other ESS which has been running for a year and a half now with solar

Here is the UStream channel where I can watch both Generation and Net Usage at home anytime remotly (link on the upper right)

and screenshots of the Wattson Anywhere portal providing graphs (link on the upper right too)

So this little unit is helping the big one by adding an extra 1.5kWh of storage at home

and they both try to keep our NEt Usage as close to 0W as possible ;)

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