Tuesday, August 5, 2014

New Batteries (Off Grid System)

Finally, the new forklift batteries for my off-grid system arrived. After 7 years of service from my old forklift battery set, it was time to replace them since the old batteries were showing signs of fatigue & started failing. I had already replaced 3 of my old cells and the overall reduced capacity was a clear sign that the batteries had reached their end of their service life.
A short history about my old battery set. They were not new at all but had been scrapped from a factory since they were removed from a fork lifter. A good friend (and neighbour) Mario who used to work there, suggested to me to take them in and give them a try. I selected the best 12 cells (out of 24) and kept the remaining good batteries as spare. Well, it was really a good decision to keep them since the 12+ cells which I salvaged gave me 7 years of service.

The new batteries I purchased are of the same time. These are:-

Brand: Fulmen Forklift Batteries
Voltage: 2.11v per cell
Amp Hour: 680AH
Storage Capacity: 2.11v x 680AH x 12(Cells) = 17217.6WH or 17.21KWH
                             At a max of 50% DOD, 8608WH or 8.60KWH of usable capacity.

Width: 20cm
Depth: 12cm
Height: 46cm
Weight: Very heavy ~ 30Kg each!

Below is a photo of the installed batteries inside my existing battery box. Note the additional wiring which I have prepared to tap and measure each individual cell voltage.
Every month, I perform a check on the batteries and besides reading the SG of all cells, I need to also check the individual cell voltages. From these two measurements I'll be able to decided when an Equalisation charge is needed.

And next to the battery box, The photo below is showing the fuse box and the battery desulpahtors. One of the desulpahtors is 24v connected to the new battery set while the other desulpahtor is connected to my 12v battery system.

The new battery monitoring system.  I installed a digital voltage meter across all the 12 cells. These voltmeters can measure a DC voltage from 0v to 10v with an accuracy of +-0.1%. The supply voltage is quite flexible 4v - 30v.

And below a photo of the cell voltages during an equalisation charge...

The picture below is displaying a set of 12 fuses which I built using the tracks of the vero-board as the fuse wire. Since I have a wire running from each battery cell going into the battery voltage box, I needed to independently fuse each battery cell just in case! Instead of purchasing 12 separate inline fuse holders and fuses, I opted for the vero board track which is rated for 5amps.
Below is the circuit diagram of the battery monitoring system. I used two separate power supplies to power the 12 digital meters.
The digital voltmeter connections are pretty straightforward. Each voltmeter will measure a cell voltage and therefore the negative (-) and sense wires need to go across the individual cells.


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