Hi there

I have a client running two Kodak OG7.2 inverters in parallel with four Kodak FL5.2 batteries. System is completely off-grid so no utility connected. System has been running without issues for the past two years. An issue has recently started where a brownout occurs (power to load briefly drops out) when batteries reach 100%.

Anyone got any ideas what can cause this?

Is the inverter switching over modes when the batteries hit 100% SOC?

On 2025/07/26 at 12:22 AM, madness_za said:

s the inverter switching over modes when the batteries hit 100% SOC?

I doubt it, as the system is fully off-grid and no generator was mentioned. It would likely be staying in SBU output source priority (basically, it will stay in battery mode).

On 2025/07/22 at 9:50 PM, Blue Line Solar said:

An issue has recently started where a brownout occurs (power to load briefly drops out) when batteries reach 100%.

When the battery goes to float, there is a short period where the battery charge current goes to zero (depending on loads etc). At this point, the battery voltage is going to dip from the absorb voltage to the float voltage. The power flow will change from towards battery to away from the battery, so the buck converter will change from active (bucking) to "straight through". This will involve a change in bus voltage, I think. My guess is that the bus capacitors typically need to supply some of the load for a brief time; this could be the brown-out if they are not up to snuff.

Check for bulging of both bus capacitors, or any other signs of stress. Measure their capacitance if you can. Decent replacements are a bit pricy, so I hesitate to say just replace them and see what happens. I imagine that they could be awkward to desolder too.

The other possibility is some sort of problem with the buck transistor, its gate drive circuit, or the buck diode, though I think all that must be working for smoothly regulating the charge current. Perhaps those film capacitors on either side of the buck inductor.

Edited August 2, 2025Aug 2 by Coulomb