Victron Multiplus II - "stuck" in storage mode

[admiral]

I have a Multiplus II 48/3000/35-32 - it is used as a UPS for my house and has no solar etc. connected. The only way for it to charge the batteries is using the grid. I have storage mode enabled as the batteries does nothing for long times until there is a power failure.

The battery state of charge started at 100 % , and the inverter was in storage mode.  We then had a 2.5 hour power failure, and the battery state of charge went down to 91 % .  The grid came online, and the Multiplus II just went back into storage mode. The problem with this is that the batteries are charging very slowly, and they will never charge back up to 100 % - the only way for that to happen is to restart the inverter.

We've had a few power failures since the last one, and the battery state of charge went down to 83 % this morning - and still the inverter went back into storage mode after the 2.5 hour power failure. It appears as if it is "stuck" in storage mode - and this is not how I understood storage mode to work at all.

Any thoughts, or ideas on how to fix this?

Storage mode description from Victron documentation:  "After completion of the absorption period the battery should be fully charged, and the voltage is lowered to the
float or standby level. If no discharge occurs during the next 24 hours, the voltage is reduced even further and the battery goes into storage mode. The lower storage voltage reduces corrosion of the positive plates. Once every week the charge voltage is increased to the absorption level for a short period to compensate for selfdischarge (Battery Refresh mode)."

[Jaco De Jongh]

32 minutes ago, admiral said:

Any thoughts, or ideas on how to fix this?

Have send you a PM..

[___]

Disable storage mode.

So here is the thing. Before the charger will change into a different mode, the voltage has to drop by some amount, so very often a complaint of "stuck in float" or "stuck in storage" is because the voltage doesn't drop low enough to start another bulk/absorb cycle.

Storage mode is to reduce unnecessary off-gassing on lead acid batteries (float voltage is high enough to cause some off-gassing), so after 24 hours at float the charger will drop to storage mode, a voltage high enough to maintain the battery but not charge it. The voltage in storage mode is not enough to completely counter self-discharge, so a periodic re-absorb is done every few days.

For batteries that are frequently cycled, such as now with load shedding, or where solar is involved, storage mode is pointless. Just turn it off.

[admiral]

@plonkster - how much does the voltage have to drop for the charger to change into bulk / absorb?

My batteries are not really cycled - they are only used in load shedding, so storage mode is really not a bad idea *if* we don't have a lot of load shedding.  And, by the way, the charger does *not* wait 24 hours to go into storage mode - it was way quicker than that after a full bulk / absorb / float cycle.  An hour or so.

[___]

5 hours ago, admiral said:

 - how much does the voltage have to drop for the charger to change into bulk / absorb?

Around 5V if I recall, but there is a minimum value too which I cannot remember.

[admiral]

@plonkster Allegedly 5.2 volts:  https://community.victronenergy.com/questions/175/how-do-quattro-and-multiplus-decide-to-switch-from.html?childToView=372#answer-372

I still don't understand why it sticks around in storage mode - it does not do what the manual says   E.g. it *definitely* does not stay in float for 24 hours before it goes to storage - it almost immediately jumps from float into storage.  Eh - where is the source code for this

Edited December 9, 2019 by admiral

[admiral]

I adjusted the float voltage upwards a bit, as an experiment to see if this will make it go into bulk earlier.  After doing that the charger went into absorption mode for a while - and guess what - it just skips float and goes into storage.  This is buggy, or some very strange behaviour.

[admiral]

Setting it to float does look as if the batteries charge a bit better - and it got almost back to the same state of charge as before the load ejection.

Storage mode would be great if it worked as advertised - but only after say 24 hours, and then it must go out of storage into float immediately after any inverting.