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Battery voltage - odd graph

porshuh

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Joined
Apr 28, 2021
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Has anyone noticed their LiFePO4 voltage acting like in the attached image? This is while using about 4.5kW from my 16kWh bank, using Ampinvt 5000/15000w pure sine wave inverter. The voltage range is so small that I can't really see this pattern using any other method. The graph below is produced by my Victron MPPT 250/100 solar charge controller.

The system has been great and everything seems to be working fine - just thought the pattern was a little odd

edit: one full cycle (one peak to one low, back to one peak) is about 2.5 minutes...

1637769691051.png
 
axes, scale? what is where? blue, brown line?

Welll - left to right is time, and the orange line is voltage. I will have to look when I get back from vacation but I believe the voltage delta is about 0.2 volts

I was posting more for anyone that might recognize that pattern that seems pretty neat (but odd), and they could chime in as to what creates that pattern.
 
Likely charge controller regulating float or absorb voltage. See if it disappears or greatly reduces when battery needs charging under constant bulk charging current.

Sinewave inverters also have ripple current at twice AC output frequency but without knowing time scale can only assume you are not at high enough time resolution to see effects of inverter load ripple current at 120 Hz rate.
 
Yeah that ripple frequency is between 2 and 2.5 minutes so I doubt it’s something caused by the inverter (which is why I find that wave so interesting).

The charge controller is in fact in bulk mode and charging as hard as it can. I believe at the time of the graph - it’s about 20a in and 90a out. So an overall 70a draw on the battery (pack is 16 * 3.2v * 310aH)
 
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