question

jimgeier avatar image
jimgeier asked

Why does my Multiplus not ever indicate float?

My Victron Multiplus doesn’t ever appear to reach float state and continues to indicate absorption continuously. I’ve heard that float is disabled for lithium batteries, so maybe seeing absorption indicated is normal? I have Victron smart lithium batteries (4 X 200AH in parallel). I have the multiplus configured for lithium, fixed charge curve, 14.2 V absorption, 13.5 float, 2 hours absorption time and 7 day absorption interval, 14.0 charged voltage. The system includes a Lynx BMS, Cerbo and 3 Lynx distributors.

BMSfloatmultipus
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agroventuresperu avatar image agroventuresperu commented ·
Where are the Victron smart lithium batteries manufactured, and what specific lithium chemistry are they?
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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ agroventuresperu commented ·
@AgroVenturesPeru

From the sticker on the batteries they are produced in India and chemistry is LiFePO4.

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marekp avatar image marekp Stefanie (Victron Energy Staff) ♦♦ commented ·
@Stefanie

I heard that inside are Winston cells.

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ marekp commented ·

Is that a question or a statement? ;-)

I have no idea.

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1 Answer
Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

@jimgeier@wireless-nets.com

This is absolutely normal and nothing to worry about. The MultiPlus is controlled by DVCC and the Lynx Smart BMS, sending a charge voltage limit to the Multi. With the Lynx Smart BMS the Multi is no longer using its internal charge algorithm.

What matters are the settings in your Lynx Smart BMS.

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marekp avatar image marekp commented ·
@Stefanie

Is this absorption stage same as absorption when under MP control?

Is battery held for hours at the absorption voltage until charging is done?

Usually absorption lasts 1 hour and than voltage drops to "Float" until end of charging cycle.

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ marekp commented ·

Almost.

>Is battery held for hours at the absorption voltage until charging is done?<

It should be until balancing (and this usually can take up to 2 hours, sometimes even longer) is done because that's the whole purpose of 'absorption'. The battery is fully charged when absorption voltage has been reached. Quite different compared to lead-acid batteries where the battery is only at roughly 80% at that point.

Under MP control: bulk > max. current until voltage at 14.20V > absorption until absorption time limited reached > float (13.50V)

Under BMS control: CVL 14.20V=bulk=max. current until voltage hits 14.20V > absorption until absorption time limited is reached > CVL drops to 13.50V - but MP remains in absorption.

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jimgeier avatar image jimgeier commented ·
Very helpful. Thanks!
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