100 Ah 48 Volt LFP (LiFePo4) Battery Construction

About: Too much free time!

Battery Usage.

This battery is meant to drive a 2500 Kilowatt Inverter or more producing 240 Volts AC for Homes ,Boats, Cars ,RV's etc.

Source the cells.

I bit the bullet and went with the best I could find on Ali-express even though its a punt at the best of times. The cells I settled on were 100 Ah from

Shenzhen Cozemate company Store

The producer of the cells seems to be a large player in Jiangxi province China

Gangfengbattery.com

Cycle life:1500~6000cycles

Cost $2581 for 16 delivered to my door.

Note- Ali-Express as the name implies seems strange in the way they do things. I ordered and paid for these with a credit card . Payment was accepted and off I went . A day later I received a message on Ali that my payment had been declined and I should send them details of my Drivers licence,passport,copies of the statements and a copy of the card. Now that may just be a scam operating on their site but I had no intention of sending any such data anywhere on the internet so I just ignored them. Thinking that was that I started looking around again . In the meantime I got a message from the seller giving me a tracking number and when I tried to find that number it was not there. Oh false number I thought . The seller is trying to keep the sale alive giving me that.

In fact the tracking number was correct and was with Startrack and the cells arrived by truck from Kingsgrove NSW marked PCA express. Star Track Express Pty Ltd.

I'm in Cairns in Far North Queensland and they took just on one week to get here after payment being sent from from NSW ? Packaging was robust and well done . The outside cardboard boxing was plain except for the addressing parts. The notices about Lithium and safety etc were completely isolated inside the box so no one knew what they were I suppose. They were marked "Ganfeng battery Technology Co Ltd"

There were two boxes and inside each two more ,each containing 4 cells in foam packing. Package had to be damaged 2 inches deep to even touch the cells. Weight was 19.3 kilos each box.Each cell weighs 2.13 Kilos.

A disappointment though - No Connectors and No Screws ? Screws are M6 in Stainless and 10mm should be long enough. I'll make bus bars from copper tube and use stainless plain washers. 1/2 inch soft copper tube is flattened then holes drilled appropriately. Gives 4 surface areas which is better for the electrons to flow in the surface layer.

A surprise - Terminals are Positive Black and Negative Fawn- A blob of red paint went on very quickly

Checking the voltage of each cell confirmed they were all essentially the same at 3.278 Volts each.

So what to do ? Discharge them to 2.5V and bottom balance ? Or Charge them up carefully as recommended by most manufacturers to 3.65 Volts the first time on receipt. I decided to charge them up with a BMS and an active cell balancer attached and did them in two banks of 24V nominal as that's what I'm set up for at present. I decided to just get each cell over on 3.65 volts and start using them .

It should be understood that on initial charge to 3.65 Volts each cell magically lays down a protective SEI (Solid Electrolyte Interface) layer of electrolyte coated lithium ions reacting with the solvent in the electrolyte and depositing it on the carbon side of the separator.Later this protects the battery's electrolyte separator from damage from the electrons stored on that side when charged . Taking the cells back up to 3.65 Volts again afterwards is frowned upon as more plating with lithium metal occurs eventually sealing off the carbon and the charge carriers can't pass through as I understand it so far.

The 24V BMS I am using atm is 24V BMS

I will go to 48V BMS

The 24V active cell balancer is 24V ACB

I will go to 48V ACB

As I put more on this system I will update it. I am presently arranging side compression which is a must before using at large amps.

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Step 1: Putting It Together and Charging

This is with 1/2 inch copper pipe connectors done and placeholder nuts and bolts . All going and charging at 8.5 Amps. Because of the weight ,(18 Kilos+) I'll keep it in two lots of 8 cells and later cable them in series for 48V .

When I compress them slightly I'll remove the connectors and file just a little sideways clearance into the connectors with a dremmel.

I used paddle pop sticks to separate the cells and allow air to flow for cooling.Not much with just 1 paddlepop ,about 1mm but I'll try 2 glued frist on the second string. The compression sides are set up not to compress which might damage the cases but simply a thread or two tight just to restrict expansion. Its plywood and stainless rods through.

Step 2: Connect to Your Inverter

I am using this as two strings of 8 cells giving 27 volts roughly and driving a 2500 watt inverter. Flat out it is drawing 100 amps @ 27V . Giving roughly 10 amps @ 240 V.

Now 16 cells at 3.65V upper limit is 58.4 volts which is way over 48V nominal for inverters etc.16 cells at 3 Volts lower voltage then would be 48 Volts . Seems tops for 48V Inverter is about 60Volts DC input so given they are not built to be operating around that voltage all the time it might be better to drop one cell.

Considering each cell lives most of its life at 3.2V as its discharging I might opt to remove one cell and keep as a spare . Corresponding voltages for a string of 15 cells would then be 54.75 and 45 Volts keeping it a little lower so as not to blow the inverter or connected devices.

The inverters that I have researched so far seem to have a top voltage of about 60V . Not much headroom at 58.4V. better at 54.75V.

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