question

Christian Brenna avatar image
Christian Brenna asked

What conditions makes my multiplus go from float to storage

I have a multiplus 12/3000/230 connected to a 390Ah AGM bank with a maximum of 0,2C charging current. Some times when the depth of disharge is not to deep, the charger goes to rapid from float to storage. The charging current can be as high as 7A/13,8V float when charger goes over to storage mode. I have read that it should take 24 hours before the charger goes to storage mode. On my charger this happens after a few hours if DOD when the charging started was less than 20%. The result is 95% SOC when the charger goes in storage mode. What conditions should be met to go from float to storage? The multiplus is used as inverter/charger in a sailboat.

battery charging
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5 Answers
mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi @Christian Br., thats explained here:

https://www.victronenergy.com/upload/documents/Adaptive_charging_how_it_works.pdf


(ps sorry that no one was able to answer your question sooner!)



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The storage mode kicks in after very short time, not 24 hours as mentioned in user manuals. The result is that multipluss works like a 3 step charger without topping up the last 1-2% SOC. At the moment SOC is 98,6% after a 10 hours power disconnection in the harbour. I have two equal battery systems onboard, the other system is charged with a mastervolt chargemaster. The mastervolt charger float charges its batteries easily to 100% again, while multipluss fails after small discharges. As I can see the reason is that my multiplus steps down to storage to quickly. It would have been easyer if multipluss float charged for 24 hours according to the manual before storage mode kicked in.

So if it isn’t a 24 hour timer, what makes my multipluss go from float to storage after less than 30 minutes? When SOC is only 95%?

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Hi @Christian Br.

The unit does only go out of storage mode when the voltage drops enough that it would go back to the Bulk phase, when the battery is not discharged enough, it doesn't to back to Bulk to prevent over-charging the batteries.

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Christian Brenna avatar image Christian Brenna Daniël Boekel (Victron Energy Staff) ♦♦ ·

But if we disconnects the shorepower at 100% SOC, and sails for 24 hours. Then at 85% SOC should we then see storage before 24 hours? The multipluss we have goes to storage in approx. 1-2 hours after connecting of the shore power in this example. The result is AGM batteries that never charges more than 85-95% without my manual help. Because of this storage can not be used. This is a little bit sad, because I bought this multiplus to replace a mastervolt because of the storage mode.

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Also, never forget that SOC is a calculated figure, and you have choices how to set it up how that's done.


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In this answer I can read the following:

We have therefore introduced a fourth stage: the Storage mode. The Storage mode kicks in whenever the battery has not been subjected to discharge during 24 hours. In the Storage mode float voltage is reduced to 2,2 V/cell (13,2 V for a 12 V battery), which is close to the open circuit voltage of a fully charged battery.

••••

My multiplus is never charging with more than 1 hour of float before it switches to storage. Do I have a malfunction, or is this «victron standard». As the situasion is now i consider to go back to my old mastervolt chargemaster 12/70-3. The main reason for changing to victron was the 4 step with storage mode. As the situation is now my multipluss will not automatically top charge our 380Ah (c20) AGM bank.

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I still have this problem after two years! It is very hard to find anyone that can tell me anything about why the multiplus fails in top charging the batteries. The only time the multipluss does a perfect recharge is when the batteries has been extremely deep discharged. Today we came back to the harbour and connected the shore power. SOC was approximately 85%, the charger started with bulk, went quickly to absorption mode, and after 10 minutes with 0,1C charging current to the AGM batteries, the multiplus went to float. I have removed the storage mode, because the charger then normaly enters the storage mode after less than 1 hour. If that happens the batteries ends up as approx. 90% SOC. Normally max current setpoint is 0,2C. (77A). The multipluss doesn’t manage to top charge with this setting. Even with the 45A setting today the multiplus fails in top charging the batteries. I also have a identical battery system charged with a mastervolt chargemaster, and the mastervolt charges perfect. The reason is that mastervolt enters float mode at a minimum charging current level or after a given min/max time. When the boat has been discharging without shore power for several hours/days, the storage mode should not be seen before after minimum 24 hours as I can read from the manual. Is that correct?

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Christian Brenna avatar image
Christian Brenna answered ·

If the discharge is quite small, like 5% DOD, the multipluss starts with absorption, and goes relatively quickly to float. That is well done I think, now it can floatcharge for 24 hours, but then after less than 1 hour the storage mode kicks in again, at 98-99% SOC. As we speak the SOC onboard is 99% after a couple of days charging. The other identical twin AGM bank charged with 3 step charger is now 100%. When the multipluss was bought, the plan was to floatcharge for 24 hours, and then let the batteries rest in the storage mode. The plan was not to use storage mode as a charging mode.

What conditions makes storage kick inn after small discharges? Is it only after bulk charging that 24 hours of float will be done? The multipluss lost the shore power for 15 hours this week, and when it started it went straight to storage mode 13,25V/5A. I would have preferred 24 hours of float voltage, but maybe there is something that I have missed in the manual. As the multipluss charges now, the mastervolt 3 step chargemaster charges identical batteries 1-2% more (VRM with 2x BMV712).

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Christian Brenna avatar image
Christian Brenna answered ·

I still have the same problem, and today after a weekend in the sailboat, the shore power was connected at approx. 80% SOC. The multipluss charged the 380Ah AGM batteries with 14,25V and approx. 45A absorprion for about 10 minutes, and then switched down to float 13,8V. A little bit to early I think. The multipluss charger is hard to understand. After another hour the storage mode kicks in during 13,8V with 21A charging current. The batteries will not top charge at 13,2V. I do understand that absorption time is calculated from the bulk time, but what happens with the 24 hours of float charge before the storage? What makes the storage kick in when SOC is 88% and current on float is 21A? To fully charge I have to force absorption charge, and that is not the best solution.... (system is on VRM).


The absorption calculation is ok, but how does multipluss calculate the float time? Do I really have to switch off the storage mode to fully charge my batteries?

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Christian Brenna avatar image
Christian Brenna answered ·

Am I the only one having this problem? Is the way my multiplus charges the normal way of victron to charge AGM batteries? I am no longer using storage mode, as the multiplus is unable to top charge the batteries with storage mode activated. It has taken med 3 years to not find any answear on this question.

When should storage mode be activated? In my opinion it should never be activated before 24 hours after the multiplus is powered up. Multiplus should be able to fully charge the batteries before the storage mode. This question is still not answered after all these years.




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mr-g avatar image
mr-g answered ·

Good day. I think we have to go back and think about the definition of what is 100% full battery. Hence it was noted that the SOC is a calculated value (more like a assumption). The clever guys at Victron must re think this point at what time the battery must be reset to 100% SOC! Think about this. "If a battery pulls no more charge current at the float voltage for an Hour then battery is considdered as full, then system must reset SOC to 100% and switch to Storage mode. Because all of electrons already moved over to the plates. (We can also dive deeper in the chemical reaction if needed.)


Thus there is nothing wrong with the charging of the multiplus, it is just at which point the multiplus must say when the battery is really at 100% and switch over to storage mode. I hope this helps all engineers at Victron and users to better understand and interpret what is really a full 100% SOC battery.

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