Voltage drop and Charger voltage settings

[Raikoh]

Hello, before i ask my question i would like to say, this forum is really apreciated and helped me very much to first build a small off grid lead acid system inside a cabin and now im building lifepo4 to power a house. Very good content to spend hours and hours reading. Thanks a lot

Im currently setting up 16x280ah lifepo4 and i could not find an answer anywhere so i'll try to post it here.

The issue i have is with the charger not reading the "true" voltage of the battery, so i have some values

Charger measurement/display: 55.2 volts
Actual measurement at batt terminals: 54.7 volts

The charger is off by like 0.5v, do i need to do 55.2 + 0.5 = 55.7v in the settings of my charger to have the value i want for the cells?

The videos i looked at doesn't do it like that, i also read that 0.5v difference is "normal" to have on a 48v system.

I could use some help

 

[sunshine_eggo]

1. Have you confirmed these readings with a separate voltmeter?
2. Are all crimped connections of high quality and all fastened connections properly torqued?
3. Have you confirmed there is nothing pinched (shrink wrap, a washer, debris) between terminals or otherwise interrupting the current path?
4. How is the charger attached to the battery?
5. What is the gauge of wire between the charger and the battery?
6. when you observe 0.5V difference, how much current is flowing?

 

[TacomaJoe]

Voltage drop is a function of the current flow. If you drop 0.5V with 40A flowing, part of me thinks bump up the charge voltage to make up the difference, which is good until you approach 100% SOC and the current drops. Now the bumped up voltage is being applied to the battery. You may be able to find the sweet spot that covers the high current voltage drop without overvolting the battery during low current.

 

[Raikoh]

I've currently build it with cables i had around, not every connection is high quality, i've done the best i could while im waiting on tools. But theoretically, i've read that the charger will most likely not have the same voltage as the battery or even BMS, how to choose the right value to set on the charger then?

I've seen people on this forum post their values, as an example:

Charger measurement/display: 53.5 volts
Actual measurement at charger terminals: 53.03 volts
BMS measurement/display: 52.93 volts
Actual measurement at batt terminals (after BMS/shunt) 52.86 volts


I'll wait to make proper connection with my tool and see how much it improved.

 

[Raikoh]

Voltage drop is a function of the current flow. If you drop 0.5V with 40A flowing, part of me thinks bump up the charge voltage to make up the difference, which is good until you approach 100% SOC and the current drops. Now the bumped up voltage is being applied to the battery. You may be able to find the sweet spot that covers the high current voltage drop without overvolting the battery during low current.

Alright, that's interesting, i think i get it, thanks.