Overkill Solar 120A 4s 12V BMS, Instruction Manual

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5. Troubleshooting & FAQ
Q:​ Why is this so complicated?
A:​ Because it is. This equipment was not designed to be a consumer item or DIY project, but here we are.
Lithium batteries demand this level of control.
Q: ​I have a charge under-temperature warning. The sensor says -30 degrees Celsius?
A: ​Make sure that your temperature sensor is plugged in. An open-circuit temperature probe always reads as
-30c. If your probe is damaged you can set the under-temperature protection parameter to -40. This will
allow the BMS to operate until a new probe can be obtained.
Q:​ I don’t understand the wiring diagram. Why is the negative terminal the way it is?
A:​ This is a common question. The BMS is a glorified high-current automatic switch. It needs to be in series
with the battery somewhere in order to interrupt the current when it senses an issue with voltage, current, or
temperature. Your load (and charger(s) must therefore be placed ​after​ the BMS in the circuit.
Q:​ What is the quiescent current? What can I do for long-term storage?
A:​ The quiescent current is as follows:
●
5.5 milliamps with everything off, when the BMS is active, but no bluetooth.
●
15 milliamps with the bluetooth active (after about 10 seconds it drops to 0.8 milliamps. Reconnecting
it wakes it up again).
●
0.8 milliamps when the BMS is inactive.
So, assuming your battery setup is 100 amp hours, the BMS would run for 17 years. This proves that the
BMS can be connected for long periods of time without any fear of it draining the battery.
Unplugging the balance connector would ensure complete shutdown
NOTE: The cell’s self-discharge rate will always cause the battery to drain over time, which may be several
percent per month. This is simple chemistry and physics; there’s nothing that you or the BMS can do to avoid
the battery cells from self-discharging over time, other than to occasionally top up the batteries.
Q:​ I can’t get the bluetooth paired to my phone. Help!
A:​ In all cases, the bluetooth module should be selected from the monitoring app. NOT paired with the phone
or tablet device.
Q:​ My Android device says “Pairing Rejected”. What does that mean?
A:​ This can be resolved by setting the device’s location sensitivity to “High”. Also, make sure GPS location is
enabled.
Q:​ Why?
A:​ I don’t know, I use an iPhone.
Q:​ OK but why?
A:​ Android 5 and later requires access permission to the (coarse) location services. Otherwise it cannot scan
for bluetooth products. Besides permitting access, the location services may also need to be enabled. Note
that after enabling location services, the GPS can be switched off. Please be aware that this is a Google
Android phone quirk. The BMS does not require this information to work; nor does Overkill Solar care what