ben avatar image

Force charger into bulk?

Occasionally, for various reasons, I find it preferable to force a Multiplus from Float back into Bulk.

I understand that it will do this automatically when configured for "Lithium Battery" at a delta of {0.2V, 0.4V, 0.8V} below the configured float voltage for the {12V, 24V, 48V} charger.

But, if I wanted to force it to bulk anyway, regardless of the voltage, without resetting it and losing the pass-through/inverted output, is this possible? Has anyone come up with a trick to convince it to switch back?

I am aware of the special "forced absorption" toggle switch operation. I am looking for essentially the same thing, but for "forced bulk."

MultiPlus Quattro Inverter Chargercharging
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Re the restart of the bulk mode from float, so the restart voltage for 48v systems are

Lithium: restart-bulk-voltage = Vfloat - 0.8V to 3v (max 54V) range is this correct?

For my system settings are set to 57v for Absorb and float 57v as well, so when it falls below the 57v level down by 0.8 to 56.2v it should reset to bulk mode, or the max setting which is 54v. when mine falls below 56.2v it does not go into bulk charge mode it stays in float mode and charges in float only. Unless i do system reset or use more energy from my battery pack until i falls below the 54v level. What determines this value?

Is there away to change this setting in vebus config file?

Please advise


Rob D


I don’t know if this applies to a Multiplus, but with the smaller Bluetooth chargers like the 75/15’s I have, you can force them into Bulk by turning them off using the App then turning them back on.

It does apply to a Multiplus or a Quattro, but the problem is that, unlike an MPPT, the inverters are also supporting loads at the same time. So, turning them off is not an option for me, unless I want my home to go dark. :-)

2 Answers
mvader (Victron Energy) avatar image

Hi both; Force Absorption is indeed nearly the same as force to bulk would be; but not 100% the same. And the difference is indeed in the timing.

Other than that all I can say now is yes nice; and yes not a lot of work to add; and yes there is a 1000 things not a lot of work to add; and also some important things on that backlog that are a lot of work to add ;-).

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Yeah. And the other issue with forced absorption is that the slightest mistake in timing on the button toggle switch will shut the entire system down, powering down my whole house. So it is "exciting" even to engage it!

@ben don't you have a Venus device? you can start equalization through the remote control panel.

Hi, I happen to know Ben has a Venus device and is a software developer; so Ben; please search for /VebusSetChargeState here:

(only one of those exposed to the user interface is the Start equalize. You're welcome to put in a PR for the Gui to start absorption (and a way out of it)).

ben avatar image ben ♦ mvader (Victron Energy) ♦♦ ·

Ah, that's great -- at least I can force to absorption this way without using the toggle! Thanks for calling this out.

Yeah equalization is not something I'd want to engage for my lithium battery. But programmatic control of float, absorb, and bulk are all beneficial to have. Cheers!

Hi @mvader, I did 'expect' the absorption time to be independent from the bulk phase & time - BUT the description in the manual about 'battery safe' doesn't seem to support this...

"Battery Safe

The applied voltage to the battery is raised gradually until the set Absorption voltage is reached. The Battery Safe Mode is part of the calculated absorption time."

I interpreted this (posibly incorrectly) as that 'battery safe' is active during the bulk phase (since that's the phase/period when battery voltage rises to the absorption voltage) and that this time/phase is included as part of the total absorption time calculated (based on the words "is part of the calculated absorption time" .

Any chance that you can elaborate on the actual logic & how I 'should' interpret this explanation in the manual?

Thanks in advance, Mark.

Ah, now I see you mean with BatterySafe. I haven't enabled that feature, so I don't know much about it or how it works. Can't help you here!

BatterySafe is calculated as part of the absorption time; in the Multis and Quattros

(Hi! :-) )

Mark avatar image

I think that 'forced absorption' function will probably have the same effect for you.

I say this because 'bulk' is just a term given to the period of time when max availabe current is provided until the absorption voltage setpoint is achieved.

The absorption phase CAN vary the current (ANYWHERE between max & 0) as required to maintain the absorption voltage (which is identical to the bulk voltage).

So... if the battery voltage is below absorption voltage at the time you manually force 'absorption' phase then I would expect the charger to provide MAX current until the time that absorption voltage is achieved - just like it wold if it was 'called' bulk.

Try it & see.

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Quite true: it works exactly the same in terms of voltage. Except... the absorption phase is limited by a timer, and the bulk phase is not. In my case I have the absorption phase minimized for day-to-day use. Triggering it manually results in a very short charge. (Unfortunately.)

I understand what your saying & it is normally true (ie. with a MPPT).

BUT I just had a another quick look at my multiplus manual & it 'seems' that the multiplus charge profile actually includes BOTH the bulk & absorption period within the 'absorption TIME'...

The rate of V batt rise is also limited during the bulk phase - termed 'battery safe'.

Refer to extract;

Are you saying that you are sure it's NOT performing this way during a normal charge (not forced absorption)? Maybe double check...

If so maybe a Victron tech will need to confirm this point.

The main thing to see is if there is still a reasonable current entering the batteries at the end of absorption / the time of the switch to float.

Right, when you do forced absorption you get CV charging for the duration of your configured absorption time period. For those of us with short absorption periods, that means even if the battery is well below the CV threshold (and it is, when I would want to engage bulk), we can't actually get a full charge with just that short interval.