Android tablet and battery progress

I’ve decided to go a different direction with regard to the gauges in the center console below the stereo.  The “old” plan shown below was a pair of blue digital gauges that would show battery voltage and current.

BUT out with the old and in with the new!!

EMW ( is working on an android app and hardware to collect useful EV data and send it via bluetooth to any android tablet or phone.  I picked up a 7″ Samsung tablet that will be permanently installed in place of the stereo to act as Stereo/Navigation/Gauges as well as all the normal stuff you can do on a tablet.


Below is a screen shot from the basic version of the app (set up with my personal idea of a useful layout).

They are working on an “EV Control System” that will provide all of the existing functionality plus control and interface to other hardware in the EV.  I’m looking forward to making the tablet a center piece in the car, I kind of wish I could fit in a 10″ tablet.  I will still have existing hardware gauges that will show battery voltage/current, state of charge etc.  So while using the tablet as a navigation system for example I won’t loose all access to critical information.  The tablet will however provide much more information in an attractive single location.

They are still in development so I asked about including touch screen switches that would allow custom use of unused arduino pins to turn things on and off.  They like the idea, so hopefully it makes it in the final software version!  I think this would be great for the heated seats that I would like to add to the car.  All of the kits that I’ve found use round switches, and I must be too picky because round switches just won’t match the rectangular switches (shown above) that are located below the stereo.  Having touch screen switches would solve this problem.  Other features could be set up in a similar manner to turn on the main heater etc.  I’m also going to talk to the developers about having some on screen “LED’s” that could be used as indicators tied to arduino inputs to show an alarm event on screen.

I’m an Iphone user, but I’m really starting to enjoy this Android tablet.   It’s only running Honeycomb (3.2), but there is talk that samsung will be making an upgrade to Ice Cream Sandwich (4.0) for this and their other dual core tablets that came out recently.  Apparently ICS streamlines the interface making the tablet faster and giving some new features.

After some reading and reviews I’ve decided to try Sygic as my navigation app.  I don’t have the car up and running yet, however just playing with the app it seems to work very well and looks great too.  It was around 12 Euros for the Canadian map version and has free app and map upgrades.  (this was important to me because the Nav system in my ’07 InfinitI is locked in late 2006 map data and cost a small fortune to update).  Although I don’t really need a Nav system for my day to day driving, simply being able to calculate the distance to a destination will let me venture closer to my range limits with confidence.

I’m testing apps to use as the main music player, I like winamp however the “default” app has the mini tray app that can be used over top of either the Nav or Gauges without requiring you to switch apps to change music etc.  I’m not sure about the size and usability yet though, that’s something that will probably have to be played with after I get the car running.


I have a system worth of stereo components that I put together for use in my F150, however since we don’t drive the truck very much I decided not to go that big with the stereo.  A slightly smaller/lighter version of that sound quality system may end up in the EV.

There are also browsers and movie players that would let me entertain myself or passengers while not driving.  The tablet connects nicely with my Iphone to provide 3G internet while on the go, however the gauges, music and Nav systems won’t require any internet access for normal operation.


Battery testing is coming along slow and steady.  Once I had 76 cells tested I decided it was a large enough sample group to let me calculate the average capacity and start grouping the cells.

The final ideal 3P group size is 55.451Ah so I played some Battery Sudoku and with some help from Excel grouped 72 of the cells into 24 groups each totalling either 55.45 or 55.46Ah.  Although this is a pain and time consuming it gives me the ideal battery modules that should all perform virtually the same.  Internal resistance was also measured and any high cells were weeded out of the groupings.  I’ve got some friends and co-workers playing with a software solution that would group the cells automatically however it seems that mental number crunching provides the best results.


Total Variance
A 18.50 18.55 18.41 55.46 0.01
B 18.81 18.56 18.08 55.45 0.00
C 17.95 18.79 18.72 55.46 0.01
D 18.06 18.69 18.70 55.45 0.00
E 18.60 18.39 18.47 55.46 0.01
F 18.11 18.51 18.83 55.45 0.00
G 18.13 18.51 18.81 55.45 0.00
H 18.26 18.52 18.67 55.45 0.00
I 18.25 18.49 18.71 55.45 0.00
J 18.62 18.84 17.99 55.45 0.00
K 18.27 18.55 18.63 55.45 0.00
L 18.28 18.56 18.61 55.45 0.00
M 18.33 18.56 18.56 55.45 0.00
N 18.62 18.69 18.15 55.46 0.01
O 18.34 18.33 18.78 55.45 0.00
P 18.34 18.57 18.54 55.45 0.00
Q 18.35 18.59 18.51 55.45 0.00
R 18.36 18.59 18.50 55.45 0.00
S 18.44 18.62 18.40 55.46 0.01
T 18.41 18.61 18.44 55.46 0.01
U 17.84 18.73 18.88 55.45 0.00
V 17.82 18.73 18.90 55.45 0.00
W 17.78 18.75 18.92 55.45 0.00
X 17.76 18.77 18.93 55.46 0.01

I picked up a second PowerLab 6 to help me speed up the process so that I can test 2 cells at a time, which should cut the testing time in half.  I have to catch up on preparing the cell terminals though so progress has slowed at the moment.


I’m also in the process of welding the battery box.  I decided to switch from bolted aluminium to a welded steel frame that will have aluminium panels riveted in to complete the box.  Below is the outline of the box, there will be some triangulated cross braces added to stiffen up the finished box.  The basic frame is shown below, the odd shape is due to the location of the transmission and transmission mount in the rear of the car.

This should make a fairly lightweight but strong battery box.  The total weight of the pack will be in the range of 300lbs plus dc/dc converters and chargers so the box should be plenty strong enough.  The finished box will be bolted to the car for future serviceability.  The box will be insulated with 1/2″ foam and have heaters installed in the bottom.  I’ve gone back to the original design of 96 series cells partly because the new layout should fill the battery box evenly and completely.


I have completed the design on two PCB’s which are currently being manufactured.  The first is a cell log 8 breakout board which will allow easy connection and monitoring for up to 32 cells per board using 4 Cell Log 8’s.  There are relays and alarm outputs to allow easier use and mounting of the popular and inexpensive Cell Log 8S and 8M.  The PCB’s should ship to me any day now and once I get to test them out I will make them available to anyone who wants a simple and inexpensive cell level monitoring system.


The 2nd PCB is a much simplified version of the DC/DC converter charging PCB that can also be used as a platform for a pack voltage to 12v dc/dc converter with the correct configuration.

The simplification allows for multiple uses and I will probably use it for both cell preparation (charging and balancing) as well as act as a dc/dc converter that will keep the 12v system battery charged and balanced all at the same time.  This requires more wiring both at the HV pack level as well as the 12v output, however the extra protection that it provides is easily worthwhile.  Each module can run off of either a range of 36-75V OR 72-150v.  Using 1 1/2 boards would allow 108-225v input range which would cover many of the common builds and put out 12-15V @ 75A.  I haven’t decided on final packaging yet but an integrated fan will be required.  The on board mounting for the Cell Log 8 has been removed, however there is a location where a JST-HX style connector can be soldered to the PCB to allow the use of a Cell Log 8 with this board.

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