Battery installation

Wiring a battery to a Lithiumind™ BMS

Connect the cells together to form the battery.

If the battery uses cells in parallel, then parallel the cells directly ("buddy pair"), and then connect in series these parallel sets. Don't make separate series strings and the connect them in parallel: that will not work with this BMS, as it can only monitor one string of cells.

If using cells that are not cylindrical (such as prismatic or pouch), place the cells in a box that will squeeze them to retain their shape, even as they expand when they are full.

The battery B- point (at the battery, not some ways away from it) is the reference for the BMS. Many devices that are connected to the BMS will be returned to this point (they use this poin tas their ground, or common). This is what is commonly referred to as a start ground.

In order to measure the battery current, the B- cable must be connected to the 'B-' screw on the BMS controller.

Use a wire gauge that is appropriate for the average current. At minimum:

• 16 A: 18 AWG
• 22 A: 16 AWG
• 32 A: 14 AWG
• 40 A: 12 AWG
• 50 A: 10 AWG
• 75 A: 8 AWG
• 100 A: 6 AWG
• 135 A: 4 AWG
• 180 A: 2 AWG
• 245 A: 0 AWG

Use a ring terminal with these specifications:

• For #10 (5 mm) stud
• Maximum O.D. of 0.500" (13 mm)
• Insulated is best, but uninsulated is OK, as long as you use heat shrink tubing on it to insulate it
• A wire crimp barrel size that is appropriate for the wire gauge

Here are some suggestions:

• 18 AWG, insulated
• 14, 16 AWG, insulated
• 12, 10 AWG, insulated
• 8 AWG, uninsulated
• 6 AWG, uninsulated
• 4 AWG, uninsulated

You will not find any terminals for larger wire that can fit the BMS. If you need to do so, you will have to fashion an adapter between a larger terminal and the smaller screw on the BMS.

Note, however, that the BMS can only handle a battery current with an average value of 50 A. So, go ahead and use 4 AWG wire if you want, just don't use more than 50 A average through the BMS.

Having said that, there is a neat solution to using this BMS with systems that use more than 50 A average current: a current divider.
Use multiple wires to carry the current, and have only one of them go through the BMS.
For example, for a motor controller that uses 200 A average, use 4 identical wires (same gauge, same length) between the battery B- terminal and the motor controller B- terminal. Then cut one of the 4 wires in half, put ring terminals on the ends you just cut, and connect them to the BMS controller.
Now, 50 A will go through the BMS controller, while 150 A will go through the uncut wires.

Procedure:

1. Strip the 'B-' wire as required by the ring terminal barrel
2. Crimp the teriminal
3. Remove the M5 screw and washer from the BMS's B- location
4. Insert the terminal on the screw (leaving the washer between the screw head and the terminal)
5. Screw the screw back into the BMS controller

In order to protect individual cells, the BMS needs to know each cell's voltage. It does so through a set of wires (for N cells in series, it uses N+1 wires). These wires are called "taps".

The BMS controller can handle any wiring mistake, in any permutation, without damage. But the wires going to the BMS cannot survive a short circuit. For that reason, it is important to use a fuse on each tap wire, and to place it on the cell end of the wire.

The fuses should have the following specifications:

• At least 0.5 A, as high as possible (for best BMS performance) but no more than the rating of the wire:
  • 16 A max for 18 AWG wire
  • 11 A max for 20 AWG wire
  • 7 A max for 22 AWG wire
  • 3.5 A max for 24 AWG wire
• Slow blow is fine, but fast acting is better
• Max voltage greater than the full battery voltage, DC rated (125 Vdd fuses will work in all cases)

Here are some suggestions:

• LittelFuse 0251005.MXL - 5 A, 125 V, fast PicoFuse with wire leads
• Cooper Bussmann BK/GMC-10-R - 10 A, 125 V, 5 x 20 mm cartridge fuse (requires fuse holder)

The wire size is not critical: anything between 24 and 18 AWG will do. However:

• For reliability reasons, go for the largest gauge
• If you are not going to use fuses, go for the smallest gauge, so that the wire will fuse easily in case of short circuit

Wire color is not critical. However:

• Certan safety standards (which may not aply to your application) require that all high voltage wires be safety orange; but, as this BMS is not isolated, every single wire in the application would have to be orange!
• The tap wires could be any color, but it would be a good idea to make the tap to the B- terminal black, and the one to the B+ terminal red

If the number of cells is not known a priori, the BMS will not come with a terminal block for the taps.

A single, long connector for as many tap wires as your system has may be hard to find. Instead, smaller connectors may be combined to achieve the desired number of circuits.

Stackable, pluggable terminal block plug (Tyco / Buchanan)

• 282830-4 - 4 positions
• 282830-5 - 5 positions
• 282830-8 - 8 positions
• 1-282830-0 - 10 positions
• 1-282830-2 - 12 positions
• 2-282830-6 - 25 positions (special order)

If you wish, you can glue adjacent plugs together, to form a single connector. Though, be advised that larger connectors will be hard to unplug from the BMS (you cannot use a metal tool to pry it out, as it will make a short circuit).

For highest reliability, ferrules can be used on the wire ends that are clamped into the terminal block, such as:

• 24 AWG
• 22 AWG
• 20 AWG
• 18 AWG

1. Install the fuses on each battery terminal (N+1 fuses for N cells in series)
2. Cut each tap wire to the desired length
3. Connect each tap wire to its fuse
4. Strip each wire 1/4" (6 mm)
5. If used, crimp a ferrule on each wire
6. Insert the wires in the terminal blocks:
   • The B- tap wire goes to pin 1, square pad on the PCB, closest to the adjustment trimmers
   • The tap wire to the '+' terminal of the most negative cell goes to pin 2
   • Etc., all the way to the 'B+' tap (note that, if using less than 24 cells, there will be unused circuits at the end of the PCB connector closest to the end of the BMS)
7. With a voltmeter, make sure that the voltages on the terminal blog plug are correct
   • The voltage between the last tap and pin 1 is the full battery voltage, with pin being the negative side
   • The voltage between each pair of adjacent taps is equal to a cell voltage
8. Install the terminal blog plug onto the BMS, making sure it is aligned properly

A thermistor is required to detect the battery temperature, to reducing the chance that the pack is operated outside its temperature range.

While it is possible to operate without a thermsitor (by replacing it with a 10 Kω resistor), doing so will endanger the pack, and is strongly discouraged.

Because each application is different, the BMS does not come with a thermistor, so you have to select and buy one that will work well in your application.

The thermistor must have the following specifications:

• Resistance: 10 KΩ at 25 °C, NTC (Negative Temperature Coefficient)
• B25/50: 3380K

Suggestions for thermistors (Cantherm)

• CWF4B103G3380
• CWF3AA103G3380
• MF52C103F3380
• CWF1B103F3380
• CWF1B103G3380
• MF52C1103F3380

1. Install the tip of the thermistor onto a cell in the battery pack, using a method appropriate for the style of thermistor (do not let oit make electrocal connection with a live part of the battery)
2. Connect either one of the thermistor wires to the battery B-, as close as possible to the battery
3. Connect the other thermistor wire to pin 3 of the 12-screw terminal block on the BMS, labeled "THERM"