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chbrandt avatar image
chbrandt asked

LiFePo4 Charge Settings

I recently purchased a 120w solar panel to charge my LiFePo4 cells in the bottom of my telescope. The cells are managed by an overkill solar BMS. I have a Bluetti 120w panel with MC4 connectors to the Victron Energy 75 | 15 MPPT controller (PV) then a cable from there (Battery) to the BMS for charging via an Anderson connection. Here's my question. I have my absorption voltage set to 14.6v in the Victron battery settings. When my battery is only charged to 13.6, or about 50% per the BMS bluetooth app, the Victron controller is going into the absorption phase. That seems wrong, but I'm thinking perhaps it's because the voltage reading from the controller is higher under a charge and maybe my BMS is showing actual? My second question, under absorption, it's charging at 14.6v and sending only 5.6 amps through to the battery. If I change the absorption voltage to 14.7, it immediately jumps to bulk and starts sending more amps and my solar panel wattage goes up. My question is, if my solar panel is able to bring in more watts than 14.6x5.6 (82 watts), which it is, why is it not pushing more amps than 5.6, even when in absorption? I would like to push about 6.8 amps at 14.6 or more if my panel can bring it in. Any thoughts would be very helpful!

battery charging
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1 Answer
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wkirby answered ·

If the MPPT is hitting its Absorb Voltage but the BMS is reading a lower Voltage then there must be some resistance between the MPPT and the actual battery terminals. Maybe the BMS is doing something that we don't know about. Maybe the BMS has prevented charge and gone high impedance to charging current and in turn the MPPT has gone to float?

Ohm's law is very strict and cannot be broken.
If the internal resistance of your battery means that a current of 5.6A results in a Voltage of 14.6V at the terminals then you can't change that. More current will mean that the Voltage will increase and vica versa. You already tried this by changing your target Voltage to 14.7V and you noticed that more current was required to reach that higher Voltage.
If you have reached your target Voltage then why do you want more current to flow into your battery?

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