Overkill Solar BMS Series Manual de usuario
Overkill Solar BMS Instruction Manual
Version: 0.1.0
Date: August 31, 2020
Table of Contents
Table of Contents 2
1. Introduction 5
1.1 What is a BMS 5
2. How to Build a Battery Pack 5
2.1 Safety Precautions 5
2.2 Planning 5
2.2.1 Gather Components 5
2.2.2 Gather Consumables 6
2.2.2 Gather Tools 7
2.3 Top Balancing 7
2.4 Assembly 9
2.4.1 Arranging the Cells 9
2.4.2 Connect the Balance Wires 10
2.4.3 Prepare BMS 11
2.4.3 Add BMS 11
2.4.5 Temperature Sensor 11
2.4.6 External Switch 12
2.4.7 Connectivity 13
2.4.7.1 Bluetooth Module 13
2.4.7.1 USB Interface 13
2.4.7.3 Arduino LCD Display 15
3. BMS Parameters 15
3.1 Protection Parameters 15
3.1.1 Cell over voltage 15
3.1.2 Cell under voltage 15
3.1.3 Battery over voltage 16
3.1.4 Battery under voltage 16
3.1.5 Charge over current 17
3.1.6 Discharge over current 17
3.1.7 Charge over temperature 18
3.1.8 Charge under temperature 18
3.1.9 Discharge over temperature 18
3.1.10 Discharge under temperature 18
3.2 Capacity Parameters 18
3.2.1 Designed Capacity 18
3.2.2 Cycle Capacity 19
3.2.3 Full Charge Voltage 19
3.2.4 End of Discharge Voltage 19
3.2.5 Discharge Rate 19
3.2.6 80%, 60%, 40%, 20% Capacity Voltage Levels 19
3.3 Balance Parameters 20
3.3.1 Start Voltage 20
3.3.2 Delta to balance 20
3.3.3 Balancer Enabled 20
3.3.4 Balance only when Charging 20
3.4 Other Parameters / Features 20
3.4.1 Switch 20
3.4.2 Load Detect 20
3.4.3 LED Enabled 20
3.4.4 LED Capacity 21
3.4.5 BMS Name 21
3.4.6 Barcode 21
3.4.7 NTC Settings 21
4. Periodic Maintenance 22
4.1 Periodic Cable Check 22
4.2. Periodic Voltage Check 22
5. Troubleshooting & FAQ 23
6. Technical Support, Return, and Refund Policy 27
Appendix 28
Appendix A: Recommended Parameters 28
A.1 General Settings 28
A.2: 12V Pack, 4 Cell, Using One 12V BMS and 100Ah LiFEPO4 cells 29
Mechanical Drawing 29
Bill of Materials 29
Wiring Diagram 31
BMS Configuration Parameters 31
A.3: 12V Pack, 8 Cell, Using One 12V BMS 32
A.4: 24V Pack, 8 Cell, Using One 24V BMS 32
A.5: 24V Pack, 8 Cell, Using Two 12V BMSs 33
A.6: 24V Pack, 16 Cell, Using One 24V BMS 33
A.7: 48V Pack, 16 Cell, Using Two 24V BMSs 33
Appendix B: Calibration 34
B.1 Voltage Calibration 34
B.2 Current Calibration 35
B.2.1 Idle Current Calibration 35
B.2.2 Charge Current Calibration 36
B.2.3 Discharge Current Calibration 38
Appendix C: About Cell Balancing 40
Appendix D: BMS Specifications 46
D.1. Pinouts 47
D.1.1 BMS Balance Connector (12V) 47
12V BMS connector: 47
24V BMS connector: 47
D.1.2 BMS Serial Interface Connector 48
D.1.3 BMS Switch Connector 49
D.1.4 BMS Temp Sensor Connector 50
Appendix E: BMS Application Usage 50
E.1. XiaoxiangBMS (iPhone) 50
E.2. Xiaoxiang (Android) 51
E.3. JBDTools (PC) 54
Appendix F: Wire and Lug Sizing 57
F.1 Wire Sizing Chart 57
F.2 Battery Bus Bar Sizing Chart 57
Appendix G: Glossary 58
Appendix H: Further Reading 59
H.1 Mobile Solar Power Made Easy! By Will Prowse 59
1. Introduction
1.1 What is a BMS
A battery management system, or BMS, is an electronic device that protects and manages rechargeable
battery cells.
2. How to Build a Battery Pack
2.1 Safety Precautions
●Keep metal tools away from exposed terminals
●Wear safety glasses
●Battery cells and electronics can overheat and cause fires or release toxic smoke, if they are
misconfigured or used incorrectly. Always keep a Class C fire extinguisher near the battery system,
and ensure that those around it are properly trained to use it.
●Ensure that the all electrical connections are screwed down tight and are not loose
●Battery systems are not a toy. Never let unsupervised children or pets near the battery system.
●Do not connect anything but the BMS’s B- cable to the cell negative BC0 terminal (the one exception
being the BC0 balance wire). The load negative must be wired to the BMS’s C- lead.
●Do not purposely short-circuit the battery pack
●Do not accidentally short-circuit the battery pack
●Do not submerge the battery pack
●Do not purposely connect the battery pack to a load that dissipates more than the BMS is rated to
handle.
2.2 Planning
2.2.1 Gather Components
●Battery cells (we recommend the Overkill Solar 100Ah LiFePO4 cells, which are the perfect size for our
BMS modules). We also give very detailed diagrams, mechanical drawings, bill-of-materials, and BMS
configuration parameters to ensure a smoother DIY experience.
●Bus bars (used to link the battery cells together. While it’s possible to use stranded insulated wire and
ring terminals, this is considered bad practice, and is arguably more expensive). The easiest approach is
to purchase properly-sized bus bars with your battery cells (Overkill Solar’s 100 Ah LiFePO4 cells
include bus bars). If you purchased other batteries that did not come with bus bars, they may be made
from copper bar or pipe; see Appendix F.2.
●The Overkill Solar BMS, which ships with the following items:
○Balancing lead
○Temperature sensors
○2-pin cable for external switch
○Quick-start guide
○Bluetooth module and cable (optional)
○USB module and cable (optional)
○The BMS may be ordered with optional cable upgrade (C- and B- cables can be upgraded to 8
AWG, 12” or 24” cables. see section 2.2.3 for why this may be useful). Crimped copper lugs
may also be specified at order-time.
●A pair of power distribution blocks, with two or more 3/8" lugs, rated for at least 150 amps (most
with 3/8" lugs will be rated for over 200 amps). We recommend a matched pair with one black for
negative, and one red for positive. These will be the interface between the battery pack, and the rest
of your system.
●An enclosure for your battery pack. Popular choices are:
○Overkill Solar sells a stainless steel frame for the 100Ah LiFePO4 batteries. This is arguably the
strongest and most durable way to build a battery pack, and would be suitable for mobile
installations, for example an RV.
○1/2" plywood is a very popular choice. This can be assembled in a few hours with very basic
tools. A pocket-hole jig (e.g.: Kreg K4) is the quickest and easiest way to attach 1/2" plywood
at 90 degree angles without splitting the material.
○Plastic snap-top battery boxes can be purchased for under $10.00, and are intended to be used
in a mobile setup (e.g. RV or boat). They have locking lids, adjustable dividers, two handles, a
recess for a mounting strap, and pass-throughs for large battery cables.
○Any large plastic box will suffice for a permanent, non-mobile installation. Storage boxes from
companies such as Rubbermaid and Sterilite are available in a multitude of shapes and sizes.
○Many DIYers will also choose to forgo the enclosure altogether. Typically, the electronic
components are mounted to a piece of vertical 1/2" plywood, and the batteries are usually
placed near the floor, but ideally elevated up a few inches. Sitting on a closet shelf is perfectly
fine. These cells do not offgas in normal operation, so they may be placed inside a living space.
Admittedly this setup isn’t for everyone, but it might be the right choice for some people.
2.2.2 Gather Consumables
●16-22 AWG Insulated ring terminals (needed for the balance leads). We include 3/8" ring terminals
with the Overkill Solar 100Ah LiFePO4 batteries, which have 10mm lugs. If purchasing other
batteries, you will need to provide your own.
●8-10 AWG ring terminals (needed to connect the BMS’s pig-tail leads to the battery). Crimped ring
terminals and longer pigtail leads are optional items for the BMS at the time of purchase. See the
Bill-of-materials in Appendix B for exact sizes.
●4 AWG, 2 AWG, 1 AWG, 1/0 AWG, or 2/0 AWG stranded insulated wire, 3/8" ring terminals, and
heat-shrink tubing (exact size will depend on the charge and discharge currents. See Appendix B for
bill-of-materials for specific configurations. See Appendix F for wire sizing guidelines).
●Kapton tape (needed to secure the temperature sensor(s). We recommend every DIYer to have Kapton
tape on hand. Buy it in assorted sizes). If you don’t have Kapton tape, or don’t want to buy it, you can
use whatever tape you have laying around.
●2” gaffer tape (optional; if you plan to tape your batteries together instead of fastening them inside of a
box or within a frame) We recommend gaffer tape because it does not leave a residue in most cases.
Duct tape works too, but gaffer tape is superior. And if you don’t have either of those, then any tape
will work in a pinch.
●Double-sided foam tape (optional; place between battery cells to prevent them from sliding around, and
also as a convenient way to attach the BMS to the battery pack. We recommend 3M™ VHB tape, and
this is what gets included with the 100Ah LiFePO4 frame kits).
●Light-duty 6” zip ties (for wire bundle management)
●Heavy-duty >12” zip ties (Optional; for mounting the BMS to the battery pack)
2.2.2 Gather Tools
●Ratcheting insulated terminal crimper (needed for crimping insulated ring terminals to the balance
leads). Most ratcheting crimpers will be rated for 10-22 AWG, and have three separate crimping
zones: red, blue, and yellow.
●Hammer lug crimper or hydraulic crimper (needed for crimping the heavy-gauge ring terminals)
●Cable-stripping knife (needed for stripping large-gauge wire) A razor blade or a knife are acceptable
substitutes, but aren’t as safe to use.
●Wire strippers, capable of stripping 26 AWG, Klein Tools 11057 or similar (needed to strip the balance
leads)
●Wire shears, Klein Tools 63050 or similar (needed to cut the large-gauge cables)
●Socket and wrench set (needed to tighten the battery lugs). The recommended Overkill Solar 100Ah
LiFePO4 cells come with 17mm nylon-insert locking nuts.
●A phone, tablet with Bluetooth, or a laptop with USB (Optional; Can be used for programming the
BMS. Programming is not needed for common configurations). See Appendix A for recommended
parameters, and Appendix E for installation and usage.
●A felt-tip pen or label maker for labelling the cells and balance leads
●A lab CC-CV power supply capable of around 10 amps or LiFePO4 battery charger capable of
charging a single cell (one or the other is needed for top-balancing the cells). Note that if you ordered
the cells from Overkill Solar 100Ah LiFePO4 cells, and they were all ordered at the same time, the
top-balancing step can be skipped because it was done before they were shipped to you. The top
balancing procedure is covered in Section 2.3.
●A handheld voltmeter for troubleshooting and BMS calibration. If you plan to calibrate your BMS, the
voltmeter needs to be accurate to at least 1 millivolt. If you use a cheap or badly-calibrated voltmeter,
you will only make your calibration worse.
●A clamp-style current meter (optional; but required for BMS calibration). Most handheld multimeters
will only measure DC current up to 10 amps; these are not sufficient. We recommend a clamp meter
capable of measuring DC current at greater than 100 amps, at an accuracy better than +/- 2.0%. If
purchasing a new clamp meter, always make 100% sure that it will measure DC current. Cheaper
models only measure AC current.
2.3 Top Balancing
Before the battery pack is assembled, lithium battery cells must be top-balanced, if the factory or vendor did
not do so before shipment [1]. This is an essential step, and should never be skipped. If you have been told
differently, or don’t believe us, please read Appendix C, where we explain why.
[1] Overkill Solar 100Ah LiFePO4 cells are shipped top-balanced. If you purchased all cells at the same time,
from Overkill Solar, then there you can skip this section.
With that out of the way, it’s time to top-balance the battery cells.
Note that this process will take some time. It could take a few days, depending on how many cells you plan on
using, and where the state of charge was in each cell before they shipped. Typically cells are shipped at lower
than 50% charge, but don’t count on this. Assuming your charger or power supply is rated at 10 amps, it will
take five hours per cell. Do not leave the cells unattended during the balancing process. Plan your day
accordingly.
1. Obtain a lab CC/CV (constant-current, constant-voltage) regulated power supply capable of providing
at least 10 amps.
2. If you already jumped ahead and wired your battery pack up, disconnect everything now (remove the
BMS, the bus bars, temp sensor, double-sided tape, everything.
3. Wire all cells in parallel, using the bus bars (all positives wired together, and all negatives wired
together). If you do not have enough bus bars, you may use 10-12 AWG cable with crimped ring
terminals. Be extremely careful to ensure that all cells are connected together with the proper polarity.
4. Configure the power supply for 3.65V, and set the current to around 1/10 C rate (e.g: For a 100A
battery, set the current to 10 amps). Lower currents will work, but will take longer. Higher currents
may work, but could affect accuracy, as the discharge curves vary depending on the current draw.
5. If the power supply does not have a voltage readout, then connect a digital multimeter to the positive
and negative bus bars. This will need to be monitored throughout the test.
6. If the power supply does not have a current readout (in amps), then connect a digital current meter in
series with the circuit, or use a clamp-style meter clamped onto the lead between the supply and the
battery (clamp to either positive or negative lead is fine, but not both).
7. Shut the power supply off.
8. Connect the battery positive lead to the power supply positive terminal.
9. Connect the battery negative lead to the power supply negative terminal.
10. Now, turn on the power supply.
11. Wait until the current readout goes to zero. This may take many hours. If the voltage ever exceeds
3.65, stop immediately.
12. At this point, your cells have been top-balanced. Disconnect the power supply leads, and disconnect
the bus bars.
WARNING: If the lab power supply polarity is reversed by accident, a tug-of-war between the batteries and
the power supply will ensue. The batteries will win, and the power supply will likely be permanently
damaged. Use caution.
Figure 2.3.1: Top-balancing cells in parallel (power supply connection not shown)
Figure 2.4.1.1: 12V 4-cell battery configuration, top-down view
Figure 2.4.1.2: 24V 8-cell battery configuration, top-down view
Use a felt-tip pen (or a label maker) to label each cell, and each terminal on the battery. This will reduce the
risk of making mistakes when connecting and reconnecting things. Also, some batteries do not label the +
and - terminals very well. Consider using a red marker or red fingernail polish to mark the red terminal (being
careful not to get any on the threads or lug contact area).
At this time, mount the cells together. There are many ways to do this. The simplest option is to wrap tape
around the cells (gaffer tape is a great choice). Double-sided foam tape between cells is also a good choice. If
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