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Multiplus not bulk charging

Hi. I have a new install MP2 3kVA with victron gel batteries (4 x 220AH in series).

I did an initial discharge test down to what the system believed was 70% or 48.9V.

When I cut back power, the charger went straight into float, not bulk.

It has slowly charged back to 85% and is now in storage mode.

Any ideas why it would not have bulk charged?

Should I just run another (longer) discharge cycle and see if it corrects itself?

Multiplus-IIbattery charging
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3 Answers
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dgnevans answered ·

The other work at wound is to turn off storage mode under charge I believe. Then it will go through the normal cycles when charging.

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Thank you for your reply. Storage mode is not selected in the VEconfig.

I just raised the float voltage to 55.2V and after some use the system then went into a bulk charge. Subsequently reduced it again.

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vbelijohn answered ·

Hello! I have the same problem with a Multiplus 24/5000. I have attached the diagram of the voltage. You can see that the first day, the systems enters bulk-absorption-float. The second day it is only on float! My batteries are OPZs and I noticed that the second day the voltage during the night did not fall under 24,2 V . So if you formula is correct, my float voltage is 26,8V, If we take of 1,3 V for a 12V system than for my 24 V system the rebulk volatge is 26,8-1,3*2= 24,2 V.

So it is normal to not trigger a new charging cycle?


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Mark avatar image
Mark answered ·

It can be a pain/issue for off grid setups, but there is a minimum voltage that the battery must fall below, in order to trigger a new charge cycle, after an initial charge cycle has been completed.

This is the case even when the AC input has been disconnected and reinstated days later - such as when charging with a generator.

For a 48V system the battery must fall below Float voltage - 5.2V (for lead acid batteries).

There is a work around, which is to switch the Multiplus OFF and then back ON. Then it will go into bulk charge phase immediately, regardless of the battery voltage.


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What is the minimum charge value for 12v lead acid batteries and can it be altered in settings?

The 12v system re-Bulk voltage is in the screen image attached above: Float voltage - 1.3V (with a maximum of 12.9V).

Mark, can this be adjusted in settings? It seems lots of adjustments for off grid living!

Unfortunately it's hardcoded and the behaviour can't be disabled or adjusted - unless Victron update the logic in the firmware.

PS. If you have a lithium battery selected, for a 12V system the Rebulk voltage is float -0.2V (13.5V max). But you shouldn't use this as a work around for lead acid batteries as temperature compensation is disabled and the absorption time is fixed.

Improving this is something that I would like as well, since every time I want to recharge/top up the batteries in my off grid system with a charge from the generator, unless I do a semi-deep discharge I need to turn the Multiplus off then back on to reset the logic.

Mark, just discharged 336 amps out of the batteries and started the genny, it went to bulk for a min or so and then into absorbtion. All well and good, but as bulk is the more efficient charge protocol, am I damaging the batteries or just extending the charging time by not having a meaningful bulk?

There are a number of contributing factors that effect the bulk time, mainly;

- Battery capacity (which degrades over time)

- Level of discharge

- Charge current

The duration of the bulk phase is not particularly important, but if it is extremely short after a deep discharge, it could be a sign that something is wrong (bad batteries or excessive charge current).

For most lead acid type batteries, you should aim to charge with a charge current between 10 to 30% of the the battery capacity in Ah; so for a 1000Ah battery bank, a charge current of 100A to 300A would normally be appropriate.

Now if the same 1000Ah battery bank is discharged to the same level and then charged at say 50A, 100A or 300A, the bulk phase duration and also the state of charge when bulk is completed will be very different.

At a lower charge current the bulk phase will take much longer to increase the battery voltage up to the absorption voltage and the state of charge when bulk phase is completed will also be higher, so as a result the 'required' absorption time will actually be shorter (but the total charge time will be much longer).

The important points are to:

a) Recharge at a suitable charge current for the battery bank

b) Ensure that the absorption phase continues until the charge current required to maintain the absorption voltage has dropped to ~1 to 2% of the battery capacity in Ah; so 10A to 20A for a 1000Ah battery bank.

The adaptive absorption time logic in the Victron MultiPlus/Quattro units references the bulk phase duration and sets the absorption stage duration as 20x bulk phase duration.

Normally this works out quite well, but you really need to check what the charge current into the battery is just before absorption phase finishes (just before it moves in to float phase).

If the charge current at that time is more than ~2% of battery capacity, then it might be a good idea to try a slightly lower charge current, in order to ensure that the battery bank fully recharges to 100% SOC. A lower charge current will increase the bulk phase duration and as a result also increase the absorption phase duration.

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