06. Batteries
It's up to you to decide which battery you want to use. Here is some instructions how to use different ones.
The Lead Acid one is a simple battery to use. The controller card is prepared for this type of battery and you can connect it directly to the B+ and B- points. Charging will be done via the controller card in this case so the charging pins can be connected to the controller card.
The Lead Acid battery does not need any special protection or balancing circuit. A good battery to use could be the Biltema 4.5Ah 12V accumulator pack. It is a bit on the heavy side but will provide the cutter with plenty of cutting time.
Another advantage with this chemistry is that it is good for delivering and accepting large currents. It can be charged quickly.
When using Lead Acid you should be careful not to drain the battery too much. As a guideline try to stay above 50% charge. It is possible to drain the pack more, but it will shorten the lifetime.
Enable the LeadAcid battery type in the software when using this option.
This type of battery is rapidly replacing LeadAcid and NiMh types. The costs are dropping quickly.
If you want cheap cells and is prepared to build your own pack, try to visit any shop selling electrical bicycles or toys. If you are lucky they normally have faulty battery packs available for a low cost purchase. The normal case with these packs is that only a few of the cells are bad and the rest quite good.
We use a screw driver battery as a default in Liam. The pack contains three 18650 batteries and a charging / protection circuit. The only issue with this pack is that is has its own charging socket.
If you have laptop packs lying around, some of them actually accept charging directly on a couple of the pins in the pack. This is a great and simple way to get a battery for low cost.
You can build your own pack using 18650 cells
Dissecting battery packs from e-bikes or toys allows you to find them. Another source for completely new cells is NKON. They have a large range to select from at competitive prices.
Another source can be to buy and dissect a power bank. BANK
You will also need a protection and balancing circuit.
Once you have both a circuit and battery cells you can connect them up. The main connection will take the power. You should connect the cells in series. The normal case is 3S which means three cells connected in series. 4P3S means you have four cells in parallel which in turn is connected in series. This is what you can see here.
Between each cell connection point there is a wire to the balancing board. This is beacause the board needs to be able to read the voltage over each cell in order to make sure they all have the same voltage.
The balancing / protection board can be purchased on EBAY at low cost. Look for 3S protection balancing and you will get a nice list of boards.
Most of these boards will cut off the charging when the voltage or current is too high. They will do the same at discharge. I have found that when assembling packs, the connection is normally by default "dead" until you do a little charging of the pack though the leads. This "wakes" the board up and it is ready for use.
Here is a picture showing how easy the connection can be to the battery. This type of connection applies to all batteries which can be charged in the same connections as drained.
http://www.microcutter.se/articles/batteri-och-hur-man-staller-in-potentiometern
Lead acid batteries can be charged with high current. 5Amps is normally no problem. Use 15V charger or power supply for a good result. The lead acid battery will automatically rise up in voltage when it is getting full and it will not be damaged if it stays connected to the 15V unless it is for a very long time.
Lithium Ion batteries should ideally be charged with a CCCV method (Constant Current Constant Voltage). This means that a highly discharged battery should be charged with a constant current. Normally of 1C until it is approaching full SoC. At this point the charge current should drop and the charger should aim to keep the voltage level constant instead.
In the Liam design we just skip all this and go for charging with what the power supply gives. 15V and 1A is a good specification. This assumes of course that you have a battery with a protection and balancing to prevent risk of over charging the battery.
A little about the C definition. The C stands for the charge rate that the batteri is suited for. If the capacity of the cell is 1Ah (1000 mAh), a charge rating of 1C means that we can charge the cell with 1Ah*1C = 1A A cell with the capatity of 2000mAh can then take 2A when charged at 1C
Most cells can safely be charged at 1C and most of them are at 1300mAh or higher.
If you are really interested in this and would like to make a proper LiIon charger, here is a link to how you can make one.