Battery Monitors

It has been a long time but EV's are in the news more now than ever. For many, building your own EV is still viable especially compared to the cost of a new Leaf or Volt. I did a quick search for battery monitor systems from http://evalbum.com and here are some numbers, which by the way are not scientific but do offer some insite into what others are using.

• Paktrakr 144


• Curtis Fuel Gauge 74


• Xantrex 30


• Westberg 29


• Evision 25


• TBS E-Xpert Pro 25


• Elite Power 22


• Elithion 19


• Trakr 16


• Mini BMS 9


• Victran 3

FOR SALE: Paktrakr 800

I'm selling my Paktrak 800 with current sensor, serial cable, 4 foot remote extension cable and 6 remotes programmed for Lithium (48 cells). It was originally $751 and I'm asking $590. It is all in very good working condition. This would make a very cost effective battery monitoring system along with a BMS board like the EV Works BMS Cell Module or a shunt board like the Volt Blocher. Let me know if you are interested.

Bluetooth onboard

With a 5v voltage regulator connected to the keyed 12v the IOGEAR Bluetooth adapter on the Paktrakr now works without the 5v Kelly. I'll have to wrap up all the loose wires.

Bluetooth & test drive

We finally got some warmer weather, which motivated me to wire the IOGEAR Bluetooth adapter into the 5v output of the Kelly controller temporarily to allow the EV Dashboard to connect to the Paktrakr. I drove 10 miles and didn't find any EM interference from the engine or controller with the Bluetooth connection. The Kelly can only consistently put out a max of 120-130 amps but no more. The acceleration from the line was good, but not great. Also, at about 4500 RPM, in any gear the motor made a high pitched whine and reduced power. The SOC% went from 88% down to 52% for 10 miles.

One thing did suprise me, while accelerating, the LFP cells all dipped well into the "low" range below 2.75v (120v pack total). And they snapped back up to 3.2v (144v) when I let off the gas pedal. That's still a usable term isn't it? "gas pedal". This indicates that a low-voltage cut-off on the controller at anything above 2.75v would fail.



After adjusting the throttle and changing the Paktrakr amp sensor I drove it again, 10 miles. It topped out at 68 MPH and could sustain 140 amps. Better, but not the 250 amps in the Kelly specs, which I thought it could do.

New controller & single cell charger

Kelly Controls sent a new KDH15600B, which is 11" long compared to the 7" KDH14401A. It fits into the same spot as the smaller model with only one new cable needed. Notice the paktrakr resting there. I'm waiting for an extension cable to run from the last remote in the trunk. Then I'll strap the remotes and display in a permanent location.



Single Cell Charger
After the initial charge to the TS cells and they rested the voltages were all between 3.32V and 3.36, which is pretty good. I bought a single cell LiFePo4 6A charger to manually balance the cells in the interim before I can find an inexpensive and adequate BMS. The single charger has a 3.8V cut-off and each cell charged for 1-2 hours then after rest the cells are all at 3.50V. The weather was a little colder the past few days, -5F and the garage was cold too and each cell appeared to dip a little to 3.48V. I expect when they warm up they might come back to 3.5V.

According to the ThunderSky charging curve 3.8V is 75% charged and the remaining part of the charge curve is at 4.2V with a tapering current for about 30-90 minutes. So, I'm not sure that shunt style BMS that limits part of the current to 3.8V is appropriate unless it can "release" all the cells once they are balanced to finish the charging cycle.

EV Dashboard

EV Dashboard is a Windows Mobile application that also runs on a Windows CE 5.0 based dash mounted GPS device like the one below.

This is a GPS touchscreen from dealextreme.com. Notice the catchy phrase on the side. It also says "Very Good Very Powerful" across the top.



After finding the time over a couple weeks to connect the Paktrakr up to the TS cells I was able to get the EV Dashboard connected. There were only a few differences between my test data and the live data from the Paktrakr so I only had a few tweaks to the display. I'll mount it in the car next.

It is pretty easy to see that cell 7 on Remote 4 is under charged. (I haven't activated the cells yet). There are 45 cells (20 in the trunk and 25 up front) and Remote 3 has only 5 cells on it and is split with 4 in the back and 1 under the hood. This required a single wire strung back to the remote in the trunk. Also, the remote's lead is not quite long enough so Ken Hall from Paktrakr is making an extension.

Here is the setup tab. You can select the battery type, select logging to the SD card and run back your data in simulation mode.




Contact me if you are interested in using the EV Dashboard. I'll can just send you the beta bits. Also let me know if you can build a low power bluetooth serial cable for the Paktrakr. That would save some power and $ for the IOGEAR Serial to Bluetooth adapter and DC adapter and it would be a more elegant solution. This previous post has some setup details.

EV Dashboard

I've written a Windows CE app, which will also run on a Windows Mobile 5 and 6 device, to display data from the Paktrakr. It reads the data from a bluetooth adapter on the serial cable. I've got it running on a dashboard mounted GPS. On the main tab it displays amps, volts, temp, soc% and kWh. And on the second tab it has a bar chart of the batteries or cells with voltages. It has a simulation mode and can log data to the SD card.

Display:

I found a cheap 5" GPS display running Windows CE 5.0 Core with Bluetooth that can run apps. http://www.dealextreme.com/details.dx/sku.22067 It includes a bracket to mount on the dashboard.

The application should also run on any Windows CE 5.0 Core device with bluetooth including the Magellan Maestro 4250 and the Mio C520. These devices may, however, require renaming some of the installed files.

USB:

There is only one USB port on this type of device and it doesn't provide power. So it can't power a serial to USB adapter. Even more, because of limited battery on the device the USB is needed for charging. Perhaps there is a USB splitter that would charge from one side and communicate from the other, but I couldn't find one.

Bluetooth:

The device doesn't have pairing software for remote bluetooth devices so I had to discover devices and open a stream to the bluetooth device directly instead of through a virtual COM port. I used a IOGEAR Serial to Bluetooth adapter that has an AC power cable (output is 5V and .35A). To get it to work on the Paktrakr serial cable. Hopefully I can find a car adapter to fit it. Then I had to solder a wire between pin4 and pin7 on the 9pin serial cable coming from the paktrakr.

While this wasn't an ideal solution it does work.

Better Bluetooth Cable:

I ordered a couple bluetooth usb dongles from Amazon for 99 cents each. They run the Broadcom 2045 chipset which has very low power requirements. So, I believe it wouldn't be too hard or expensive to build a cable from Paktrakr. I'll be looking for some help with this since it is out of my comfort zone.

http://www.broadcom.com/products/Bluetooth/Bluetooth-RF-Silicon-and-Software-Solutions/BCM2045

GPS:

Microsoft has a GPS Intermediate Driver (GPSID) that is available on Windows Mobile 5 and later. This allows multiple apps to share the GPS hardware. This GPS device doesn't ship with GPSID and I can't find a way to set it up. So, watthour/mile will have to wait for the "advanced" version.