Quote:
Originally Posted by Fl_Fyr_Fytr
So what is the voltage of three of these in series? It won't be the 7.2v of stock, right? Is it 11.1v (3.7x3)?
|
The nominal voltage is 3.3v per cell so 9.9v per 3 in series, although the voltage of the three doesnt matter really. it's the toal voltage of the entire pack which is relevant.
I'm going to try with 48 (158V) cells initally but could move upto 52 (171V) if required.
You have to use enough cells to cope with the high regen currents and voltages of the stock system.
Quote:
Originally Posted by Fl_Fyr_Fytr
Why couldn't only two be used per tube and then large copper spacers to make up the room to the connector board (7.4v subpacks)?
|
That would only be 40 cells in total as there are only 20 tubes 2 per tube (Well 21 actually but that last one is blanked off) Not enough voltage for the system IMO as under heavy loads (100A) the cells will sag, but to what extent and to what effect on the system we don't know yet.
Quote:
Originally Posted by Fl_Fyr_Fytr
An increase in capasity while saving on weight would be great! Also, I had always thought that at least two sets in parallel would more reliable than all cells in series and there is also an unused tube in there...
|
The pack will weight less than the standard 22kg.
48 cells weighs 14kg
52 cells weighs 15.5kg
There is not enough room for 48 cells x 2 strings in parallel in the stock case.
The stock case will hold upto 63 x 8ah cells if the spare blocked tube is also machined out (21 tubes x 3 cells)
We need between 48-52 cells based on my experience with Lifepo4 cells so far.
(48 or 51 cells) are the best numbers as that is 16 or 17 sticks of three cells.
Quote:
Originally Posted by Fl_Fyr_Fytr
Is it possible to slightly grind down the negative end to make more room? Possibly enough to use the stock orange end? I realize that that would cut down on the stronger side of the cells, but what physical stresses would these be under?
|
Not practicable IMO they would have to be machined flat and cutting down would reduce thread depth as well for the studs. It may be possible to use the orange ends by using some aluminium washer/spacer on the end of the cell to extend the terminal so they fit into the orange board cell terminal recesses, we need to add about 3-5mm to enable it to butt up against the orange connector boards. A lot depends on the layout of the cells and how they line up with the connection points on the relay board. I intend using those stock connection points. The cell layout won't exactly follow the stock layout as we will only have 16 or 17 sticks, but it may be possible to keep it fairly simple. I need some 20mm diameter 3-5mm thick aluminium spacers with an M6 hole in the middle for experimenting.
Quote:
Originally Posted by Fl_Fyr_Fytr
Will you be using a modified BCM?
|
I will be testing it with the stock BCM, but the BCM fooler resistor Potential divider is required because.
1) There arent enough cells unless you use exactly 50 cells to get the correct voltage taps
2) The fooler provides a perfectly balanced battery to the BCM, so the voltage the BCM sees at the taps will be proportional to the pack total voltage. This will helps us find out if there is an overall low voltage error point.
Quote:
Originally Posted by Fl_Fyr_Fytr
Does special care need to be taken charging these as compared to stock?
|
Yes they need an independent BMS which can overide the stock system if required.
Quote:
Originally Posted by Fl_Fyr_Fytr
Sorry for all the questions. My thought is that it would be great if someone could offer a total cell replacement and even have it much better than stock. I bet it could be done cheaper than having the battery replaced at a dealer too.
|
I agree but that won't be me, there will only be this thread and the information it contains, people can follow my example if they wish and build there own replacement battery. They could use cheaper Headway cells if they wish as well.
Peter
Lifebatt 8ah OEM Battery Case Install
