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

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in discharge protection mode. If you don’t have access to shore power, then use either the second or the third
method below.
The second method is to “jump-start” the battery pack with another battery, which can be a lead-acid car or
deep-cycle battery (if you’ve got a large-capacity lithium battery laying around, that would work too, but lead
acid batteries are more common). Just ensure that the voltage of the jump-start battery has the same nominal
voltage as the battery pack in need of the charge.
The third method is a bit more clever, and doesn’t require lugging a battery around. You can do it from your
smartphone, if you have the optional Bluetooth module. Pull up the BMS configuration app (XiaoxiangBMS on
iPhone). Go into the protection parameter settings page. Write down the undervoltage protection numbers
or take a screenshot of them. ​Temporarily​ lower the cell undervoltage release value. For example, for
LiFePO4, lower it from 3000 to 2800). This will allow the discharge FET to activate (remember we disabled all
loads, so the only thing that should be allowed to discharge is the MPPT controller). This should give the
MPPT charge controller power, which will start charging your battery pack, assuming that the cells are in full
sunlight. Wait until the batteries have recovered a bit of charge, and then go back into the BMS configuration
app, and return the undervoltage parameters to their original value.
Q:​ Why doesn’t it charge high enough?
A:​ The BMS does not control the charge voltage. This needs to be configured in the settings of your charger.
Q:​ Can I use a lead-acid charger to charge a LiFePO4 battery pack? Or do I need one that supports LiFePO4?
A: ​Well that’s a deep subject.
"a lead acid charger" can be a lot of different things.
smart, dumb, adjustable/programmable....
Short answer is yes, the battery will tolerate it.
Long answer, possible failures:
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Some won’t charge to a high enough voltage.
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Some will be overloaded by the low internal resistance of the battery(similarly to alternators.)
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Some will charge too high if they do an equalization cycle.
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Dumb unregulated chargers will charge too high.
Charging too high could damage connected equipment. Because this is a common port BMS, everything in the
system is connected together. When the BMS disconnects for overvoltage, the charger is still active and
connected to the rest of the system, possibly resulting in a damaging unregulated voltage spike.
We suggest only using regulated chargers and/or power supplies. Set the upper voltage limit to 14-14.4v
If the charger only offers battery profiles, choose the setting for AGM batteries.
A lab CC/CV (constant-current, constant-voltage) power supply also makes a good charger. Set CV to
14-14.4v
If there are absolutely no other options but a dumb charger, connect a healthy lead acid battery in parallel with
the system. If the lithium pack disconnects, the lead acid battery will continue to regulate the system.