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ben avatar image

How do Quattro and MultiPlus decide to switch from float back to bulk charging?

What is the voltage drop required for the inverters to switch back to bulk charging? For each of {Quattro, MultiPlus} and for each of {12, 24, 48}V nominal ranges?

MultiPlus Quattro Inverter Charger
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3 Answers
mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi @ben, sorry for the slow reply! I actually queried internally to find the proper answer, and then forgot to translate it and post it here.

Here it goes, this is for a 12V system. Multiply by 2 for 24V and by 4 for 48V.

For lead batteries, the system switches back to bulk when the voltage drops 1.3V, or more, below the configured float voltage.

For lithium batteries, the system switches back to bulk when the voltage drops 0.2V, or more, below the configured float voltage.






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scubasail answered ·

Halleluja! Thanks for the info! I was pulling my hair out trying to figure out why my 100/30 is not going into bulk mode and signed up just to reply here.

However, I have a "user defined preset", so neither FLA nor LFP preset, although it's an LFP batt bank. Because I'm not on the boat at the moment I want to keep the LFPs at a mid-level of charge. Hence I had set float to 13.1V and absorp to 13.5V (max absorb time 1 minute) but the charger always dropped off after the first hour of charging in the morning to 13.1V. I now want to use the boat more and keep the fridge running, so I upped it to 13.3 and 13.7 V respectively.

So far, after 3 days, it's not going above 13.2V.

I'll attach a graph of the voltage and currents involved, if possible.

Fair winds,

heinz, SV TiMantra


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Hi @scubasail,

We wonder if we have a similar issue to yours. Our 100/30 Victron MPPT controller NEVER returns to bulk during the day. We have three 2-month-old Lifeline 12V AGM batteries that have very little load on them. Cellphone charging, some water pump usage, and NO refrigeration. At the end of the day the voltage reads 12.9 volts but not the target voltage of 13.8. The Victron controller is on the default preset setting of #2 which defines the absorption volts to 14.4 and float volts to 13.8. Why doesn't the controller sense that it should switch back to bulk during the day while there is still sunlight available? At night, the bulk LED appropriately blinks blue every three seconds when there is insufficient power to start charging. All comments welcome! S/V Endless Summer

scubasail avatar image
scubasail answered ·

Hello SV Endless Summer, @EndlessSummer

As mentioned in another thread, I'm developing a boat management system myself which, amongst other things, also monitors the batts. Hence I understand Victron's difficulty as to when the MPPT should go back to bulk mode. If the threshold is too low, the MPPT will jump back to bulk too often, which could prematurely age the batts as bulk is followed by absorption, which holds the batts at a fairly high voltage.

Having said that, 12.9V resting voltage for an AGM batt might be the 100% charged level. You would need to check the datasheet (DS) for that, but it sounds about right. Hence this is normal and expected behaviour. You could increase the float voltage on the MPPT to the level that the DS says is the resting voltage at 100% SOC but rising it too high above 12.9V might reduce the lifespan of the batts.

Hope this helps and fair winds,

SV Ti Mantra


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