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Old 02-19-2017, 10:08 AM   #1
AccuXperT
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AccuXperT is on a distinguished road
 
Join Date: Jul 2014
Location: Germany
Posts: 25
5 yr Member
Default NEW: Bluetooth for Segway-Batteries

After I had presented the mobile diagnostic device for Segway batteries here in the forum, I would like to deprive the worthy forum community of my current innovation no longer: Full diagnostic adapter for Segway batteries with bidirectional Bluetooth functionality.

BT1 - Im Vordergrund der BT-Adapter - P1100152.JPG

0.0) Motivation

After completion of the development work on the project "mobile diagnostic device" presented here - the luxury variant with a high-quality color TFT display - I had searched for a possibility to measure the values ​​of a Segway battery which are important for a user and to display them on a tablet / smartphone. In addition, there was the desire for a measuring device which is as small as possible and more cost-effective without having to dispense with the functionality known from the mobile diagnostic device or aspects of device and operational safety.

The result is a highly innovative "Bluetooth measuring device for Segway batteries", which I will briefly call "BT adapter" in the following (BT = Bluetooth).

1.0) Principle

It is known that the Segway battery communicates with the Segway Base via a system bus and various data are exchanged. After attaching the BT adapter to the Segway battery to be tested, the BT adapter connects to the battery via the system bus, reads out the relevant data from the battery and holds it for forwarding via Bluetooth. After a tablet / smartphone is connected to the BT adapter (BT connected), the data is sent and output to the tablet / smartphone.

The recording of the individual measured values ​​is largely carried out by the Segway battery (BMS) itself and transmitted via the system bus to the BT adapter - the procedure corresponds to that of the TFT diagnostic device. For checking, the BT adapter has a measuring circuit independent of it, with which important voltages are cross-checked again (redundancy).

This concept also has a great value on security and network independence, the device is directly supplied by the Segway battery: unlike other devices, the advantage of the network independence is that the BT adapter requires no 120V power supply or internal batteries. The current consumption through the BT adapter is relatively low: 6 mA flow after plugging the adapter on the battery (BT inactive), approx. 15 mA during operation (BT active).

Furthermore, various commands have been implemented, which can be entered via the tablet / smartphone and sent to the BT adapter, whereby the flow and display mode can be influenced by the user. The user thus has the possibility to arrange the individual values ​​according to relevance and best possible legibility, to omit individual values, to insert additional blank lines, etc.
Of course, the changes made by the user are stored internally and are retained for the next session in the event of a power failure (ie after the BT adapter has been removed).

2.0) Features

The battery values ​​are output either on demand by the user (= On Demand) or continuously updated (= Free Run) and in one of three selectable display modes:

- MINI = minimum output of the relevant battery values
- MAXI = maximum output of the battery values ​​including the 23 individual cell voltages
- USER = user defined; The user can define values ​​and output order themselves

The status transmitted by the battery (normally to the Segway Base) can be permanently visualized, which can be used in advance to determine whether the base accepts a battery as fault-free or not. In addition, an acoustic alarm device warns the user of a critical operating condition or indicates a possible fault situation.

The following values ​​are transmitted by the BT adapter via Bluetooth:

- Status bytes (corresponds exactly to the data stream battery <-> Base)
- Battery status (OK / FAIL)
- Display the battery error code at status = FAIL
- 23 cell voltages, accuracy +/- 0.5 %
- Maximum cell difference in mV (Cell-drift)
- Average cell voltage in mV (AVG)
- Lithium cell with the highest voltage, with the cell no. (MAX)
- Lithium cell with lowest voltage, with the cell no. (MIN)
- Total voltage in V (measurement by battery BMS), accuracy +/- 0.5 %
- Total voltage, measured by BT adapter internal ADC, accuracy +/- 0.5 %
- pos. Current in mA (unloading), accuracy +/- 1 %
- Total battery temperature in °C
- Charge state SOC (State Of Charge) in %

Other features or functions of the BT adapter:

- Acoustic alarm function for under- / overvoltage
- Acoustic alarm function for status = FAIL (with error code display)
- Data transfer to tablet / smartphone via Bluetooth (On Demand / Free Run)
- User programmable sequence control
- Changes made by the user remain permanently (EEPROM)
- The last selection remains permanently (EEPROM)
- Self test function
- Device function in the range 48 ... 88 V
- Genuine Segway connectors (gold-plated)
- BT adapter installed in the impact-resistant ABS small housing (9 x 5 x 3 cm)

3.0) Redundant voltage measurement

As with the TFT diagnostic device, several protection mechanisms have been provided to protect both the BT adapter and a contacted battery as best as possible.

An additional plus of security is ensured by the integrated redundancy by double-voltage measuring circuits: The BT adapter performs internal voltage measurements through internal AD converters. That means that the battery terminal voltage is permanently measured with an accuracy of +/- 0.5 % and checked for critical limits (U_ADC).
This allows a reliable comparison to the total battery voltage determined by the battery BMS and transferred via the system bus (U_I/O). This means that not only the voltage values ​​can be checked for plausibility, even if the system bus is faulty, the BT adapter is always aware of the actual battery voltage.

4.0) Photos

The BT adapter sends the battery values ​​in the display mode MINI (MIN / MAX / AVG):

BT2 - MINI-Darstellung - P1100139 (1).JPG

The BT adapter sends the battery values ​​in the MAXI display mode (including the 23 individual cells):

BT3 - MAXI-Darstellung mit 23 Einzelzellen (1).JPG

The BT adapter sends the battery values ​​in the display type USER (example with blank & copyright):

BT4 - USER-Darstellung - P1100160 (1).JPG

Example for the measurement accuracy of the BT adapter and the plausibility of the individual voltage values: With an actual battery terminal voltage of 76.0 V (FLUKE, unloaded measurement), the BT adapter has a value of U (ADC) = 76.05 V . The measurement error is 50 mV, the accuracy is better than + 0.1 % (FLUKE = reference with a basic accuracy of +/- 0.05 %):

BT5 - 50mV Messgenauigkeit - Fluke wurde kalibriert mit 0,05% BT (1).jpg

5.0) Outlook

The entire knowledge from the development of the TFT diagnostic device could be successfully implemented with the BT adapter. The BT adapter is simply plugged onto the Segway battery to be tested, the data from the battery are read out and sent via Bluetooth - Well done.

At this point, the question arises whether the BT adapter could be installed directly into the battery. Thus all relevant values ​​from the battery could be checked, without the necessity to dismantle the battery from the Segway. It is technically actually possible (and I have already been implemented by myself) to install the PCB with the BT transmitter module DIRECTLY IN THE BATTERY! This means that all the relevant data of the two batteries can be visualized during the ride - here, in particular, the load-dependent current level should be interesting. For this, it is necessary to use the system bus from / to the battery together with the base in a time-delayed manner - quasi a multi-master system. Studies in running Segway operation have shown that the internal system bus to the battery is actually not used for the greatest time, so it is possible to communicate with the battery during the breaks between the base activity itself. The procedure used for this is somewhat tricky, a continuous parallel operation is still possible in my experience, without the additional communication overloading the accumulator μC (more inquiries) or the Base with a fault in the emergency shutdown (unexpected bus activity).

For this I am sure there will be further developments.

6.0) Further documentation

A video about the functionality of the BT adapter can be found in my international YT channel :
(Tip: There can be an additional description activated by clicking on the below Button "SEE MORE")


Last edited by AccuXperT; 02-19-2017 at 10:59 AM..
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