Hi All,
Around September last year I completed tests on IB cells, I compared the data with GP cells I already have. Below is the report I wrote about the tests and there is some graphs attached at the bottom. I think it was Mr Blonde who talked about the voltage curve differences had it exactly right. This was in the 3700 / 3800 thread
Chris.
IB / GP Cell comparison
Testing was conducted on my Pro Trak which was calibrated specifically for these cells to achieve the highest accuracy possible. I used various charge methods, discharge is fixed at 30A. The data was transferred from my Pro Trak to my old laptop as it was collected (or “Live”), then after the four cycle test run was complete I’d take that info and start another test run. I already had data collected from previous cycles of GP cells so I concentrated on obtaining info from the IB cells. If you will look at the pic (graph 1), this is a screenshot of the monitor program you will see the data from the first four cycle run and the second to fifth cycle on those cells. As you can see in Graph 1 the data looks pretty good, run time 471, Ave voltage 1.17/1.18, etc, all good data for a set of cells.
If you look Graph 1 you will notice that in the beginning of discharge the voltage is very high and slopes down gradually to the end of the discharge.
I ran off a few cycles using various charging methods but these cells seem to like a regular linear charge method best. All of the exotic charging techniques I tried did not improve any of the discharge data and in some cases the data was very slightly worse.
Voltage Comparison
The interesting information started to emerge when I compared the data between the two types of cells. Graph 2 shows a direct graphical comparison of pack voltage between the two sets of cells. As you can see the GP cells fall off faster at the beginning of discharge but as the cells get to the plateau the GP’s hold their voltage better than the IB’s.
Voltage Difference
After seeing graph 2 I wanted to know what the actual difference in voltage was at any given point in the discharge curve, Graph 3 emphasizes the difference between the two types of cells much more dramatically than a straight comparison of voltages. This graph looks a bit strange at first but if you look at the lines above the 0.0 point the red line is where the IB’s have more voltage than the GP’s and the blue line above the 0.0 point is where the GP’s have more voltage than the IB’s. The IB’s start off the run with more voltage than the GP’s but at the end of the run the GP’s have better voltage. Voltage translates directly into speed as the number of volts available to the motor determines what the max RPM of the motor is going to be. It will also have an effect on punch because when you start with lower volts, the voltage will depress more under heavy load.
The question to ask here is exactly how much run time you have left at the end of your race as looking at the graph will lead you to believe that if you have 130 seconds left when you finish the race then at no point will GPs’ have more voltage during the competitive race. However, if you go deep into discharge at the end of the run the GP cells appear to have better voltage.
IB Equalizing
Graph 4 speaks for itself.
You lose a lot of everything after equalizing these cells, run time (70 seconds), voltage (almost 0.2 at any given snapshot in time). I don’t think I need to add anything here. I have not collected any data on dead shorting at this time. You will notice that the voltage drops more abruptly at the end of discharge. This will give a false impression of higher average voltage. The calculated average for these cells was 1.18v but as you can see in reality these cells were not even close to either the GP’s or the unequalised IB’s (the same set of cells).
End Comments
What is clear is that both types of cells are very good, I know GP3700’s much better as I have been using them for 12 months or so and I’m very happy with them. I’m certain you will hear similar things about the IB cells particularly from sponsored drivers and matchers who use them. I like being able to equalize the GP cells as unequalized cells can get out of balance which may cause overcharging in certain cells within the pack. The advantage of IB cells is the run time which can be huge. I'll probably get IB's next time to give them a try but I think the durability of GP's will take me back to them next time. We shall see though.