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Mercer 5Kw 24 V shutting down


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Hi all

i don’t know why but  inverter shuts down literally at just over 40 min (every time for last couple of load shedding while load is around 225Watts in the period constantly, so not that much load I think, I have 2 12v 100ah AGM batteries linked to system, strange thing is when the system shuts down the victron bmv702 still shows battery capacity at 97% please help not sure why this is happening

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3 hours ago, JPR said:

I have 2 12v 100ah AGM batteries linked to system, strange thing is when the system shuts down the victron bmv702 still shows battery capacity at 97% 

The Victron can't know your actual battery capacity; it's probably programmed to assume an actual 100 Ah battery.

How old are the battery modules?

If you don't have patched firmware to fix the premature float bug, your battery may not be getting a full charge. That has two effects. Firstly, since the "tank never gets full", you'll have reduced run-time. But sadly, it also gradually ruins the battery, as lead acid really wants charging to full every cycle for reasonable life. Unfortunately, the default low battery voltage cutoff value (21.0 V) is way too low for the typical South African situation of regular load shedding.

You should check your battery voltage, both when charging and when discharging. Make sure the battery gets to about 56 V for about an hour each day; the net battery charge current should taper gradually for that hour down to a few amps.

On the discharge side, check that the battery voltage drops roughly linearly, with no sudden jumps (except at the start where it stops charging and starts discharging). So you should see a gradual decrease in battery voltage from about 25.6 V or so to the cutoff voltage, which should be about 24.0 V. If you are regularly draining the battery to about 21 V, that's going to kill a lead acid battery in about 2 months. Frustratingly, you have to leave about 50% of the available energy in the battery, to achieve normal life (2 years or more, maybe 10 years if the battery is good quality, and is always charged properly). You should also check that the two 12 V modules have about the same voltage (within about 0.1 V) at all times. If not, use a car battery charger to charge the one with the lower voltage, until the voltage at rest after about half an hour is close to the other one. Long term, a battery balancer seems to be a good idea.

If it gets a proper charge and discharges smoothly from ~25.6 to cutoff, then sadly the capacity is drastically curtailed. It looks like a 3-6 Ah battery at this point, depending on where your cutoff voltage is set.

100 Ah @ 24 V nominal is very light for a 5 kW system, even if you don't use anything like full power very often. Self consumption will be quite high for a 5 kW inverter, I'm guessing about 50 W, or some 2 A continuous drain.

Edited by Coulomb
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