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Old 02-11-2024, 07:49 PM   #1
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kernwig's Avatar
Join Date: Sep 2020
Location: Silverado, California
Trailer: 2017 Escape 21C "S.S. Iceburg"
Posts: 133
MQTT charger requirements for LiFePO4

Briefly: What MQTT charger profile is needed to charge a LiFePO4 battery?

I bought an LiTime (AKA: Ampere Time) 12V 100Ah battery on a black Friday sale and replaced my failing dual 6V AGM batteries.

A few years ago I did a solar install an intentionally bought the EPEVER MPPT Solar Charge Controller 30A because it is listed at Lithium compatible. This same Chinese unit is sold by Renogy and lots of other brand names. I researched the configuration options and the float is set for 13.6V. (Full list of option at the end of this post.)

After plopping in the new LiTime battery and hooking up my external 100W solar panel for a week, the battery was still at just 12.8V. A couple days out being charged from the tow vehicle and 180W of solar on the roof in the desert sun, and still only 12.8V.

LiTime support claims that the MQTT controller I have isn't up to the job, and and course suggests their unit. I find this a bit suspect and don't understand the explanation. I also like the remote display on the controller I have and don't want to remove it and leave a hole in my cabinet!

Here's what LiTime says:

Regarding the controll you are using, we have checked the manual and found that it was not compatible for the LiFePO4 battery charging.
( The charging voltage cannot be set at 14.2V and above; if it is set at 14.2-14.6V according to the instruction manual, the BMS cuts off at about 14.02V during the absorption stage of charging, and it is necessary to set the charging voltage at 14V in order to continue charging with the tail current 6A.) Then the battery will always met the charging cut off issues.

We would recommend another solar charge controller with the lithium mode : absorption voltage within 14.4-14.6V.
If you do not mind, you could try LiTime 12/24V 30A solar charge controller MPPT.
Are they feeding my a line, or do I need to replace my charge controller?

Here are my MPPT Solar Charge Controller settings:

Over Voltage Disconnect Voltage: 14.8
Over Voltage Reconnected Voltage: 14.2
Charging Limit Voltage: 14.4
Equalize Charging Voltage: 14.4
Boost Charging Voltage: 14.4
Float Charging Voltage: 13.6 (resting level)
Boost Reconnect Charging Voltage: 13.3
Low Voltage Reconnect: 12.4
Under Voltage Warning Reconnect: 12.4
Under Voltage Warning: 12.0
Low Voltage Disconnect Voltage: 11.6
Discharging Limit Voltage: 11.2
Equalize Duration: 0
Boost Duration: 30
Temperature Compensation Coefficient: 0
Low temp cut-off: 5 C

Here's what LiTime support recommended, before claiming that my charge controller isn't up to the task:

Charging Limit Voltage: 14.6V
Over Voltage Disconnect Voltage:15V
Over Voltage Reconnect Voltage:14.2V
Equalizer Charging Voltage:14V
Float Charging Voltage:13.8V
Boost Charging Voltage:14.4V
Boost Reconnect Charging Voltage:13.2V
Low Voltage Disconnect Voltage:10.8V
Low Voltage Reconnect Voltage:12.4V
Under Voltage Warning Voltage:11.6V
Under Voltage Warning Reconnect Voltage:12V
Discharging Limit Voltage:10.4V
Over Discharge Disconnect Voltage:10.4V
Over Discharge Reconnect Voltage:11.6V
Over-Discharge Delay Time:0.8S
Equalize Duration:120MINS
Boost Duration:120MINS
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