Charger says "Float" even though it's below Float voltage.

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coreyzev asked Feb 11, '22

Charger says "Float" even though it's below Float voltage.

I really feel like I should be understanding this better than I am. I already read a bunch of posts here. I understand how "Absorption/Float/Bulk" works in the sense of charging from zero to 100. But I'm confused about it right now, as it discharges and then charges up again from 65%.

I'm doing an initial slow cycling of my batteries to get them ready. And I'm a little confused by what I'm seeing here. Currently sitting at ~53.5 volts, below the float voltage, and it's charging my battery at my specified rate. Why does it still say float? There's something about Float/Absorption/Bulk that I'm not getting. Wouldn't this be a bulk phase since the voltage is lower?

Mostly, I'm just confused why it says "float" when it's charging at the bulk charge rate.

Specs:

Victron Multiplus
Absorption Voltage: 56.8v
Float Voltage: 54.0v
Battery: LiFePO4
- 300AH
- 48v

EDIT:
The voltage was previously down to 52.15v, and still said "float". That doesnt seem right.

Multiplus-II MPPT Controllers battery charging Lithium Battery float

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klim8skeptic ♦ commented · Feb 11, 2022 at 12:27 AM

Look at the re bulk voltage.

Should be in the manual.

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coreyzev klim8skeptic ♦ commented · Feb 11, 2022 at 12:45 AM

I cannot find them in the manual or anywhere else aside from this from another question:

The Multiplus re-bulk voltage is as follows (depends if 'Lithium batteries' is the selected 'battery type' in the VEConfigure 'charger' tab):

Lithium: Re-bulk Voltage = Vfloat - 0.2V (max 13.5V) - for 12V system, multiply by 2 for 24V systems & by 4 for 48V systems

But i cant confirm it anywhere.

Mostly I'm just confused why it says float, but it's charging as if it's on bulk. This might be a bug.

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klim8skeptic ♦ coreyzev commented · Feb 11, 2022 at 01:36 AM

In VRM under the "advanced" tab, open up the widget for the "VE Bus System", and select "VE Bus State".

You will be able to see the charge state of the Multi going back to the start of the day.

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coreyzev klim8skeptic ♦ commented · Feb 11, 2022 at 06:45 AM

Yes I'm aware of that. You're still not really answering the question. Which is "why does it say float, while it's clearly charging at the full amps i set it at?"

Also, this is what it says in that visual, which doesnt help answer my question:

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klim8skeptic ♦ coreyzev commented · Feb 11, 2022 at 08:01 AM

Well the charts are interesting at least..

You seem to have had a grid failure (genset ?) and the inverter has gone into AESS or search mode in the time that the inverter has synced to the input.

There is 1 period of power assist about when the power went off.

It looks like the multi has been switched off twice ??

the multi has not gone into bulk charge despite the voltage looking low enough to warrant a re bulk.

On the other hand, the voltage might have rebounded high enough that the multi did not start a re bulk charge. Thats my thinking.

What firmware are you running?

Why only an 8 amp charge current?

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Answer 1 · 2022-02-11T13:09:02Z

JohnC answered · Feb 11, 2022 at 01:09 PM

Hi @coreyzev

Just guessing here, but that LiFePO4 preset you're using has a Repeated Absorption Time of 7 days. So if it's already had it's once-per-week 1 hour Abs, then it won't be targetting Abs when it does get some charge.

Rather it will be targetting Float, and I suspect then it won't show Bulk on the way there. Bulk is normally considered to be the transition stage on the way to Absorb.

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coreyzev commented · Feb 11, 2022 at 03:47 PM

That's the best guess I've seen so far. I just restarted the entire system after I let it go overnight and it charged it up until the float voltage and that's it. Everything says 100% SOC now, but when I turned it on it went back to bulk charging.

I'm gonna make a new post with the whole issue better explained and tag someone from Victron cause this is just silly now.

Clearly a bug.

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JohnC ♦ coreyzev commented · Feb 12, 2022 at 07:58 AM

@coreyzev

If you've reset the Multi, then I'd expect it to attempt a new Abs period and show Bulk on the way there.

I suspect this isn't a bug, and is by design. Is it really so bad to see Float there for the rest of the week? At least it's signifying that your weekly cell-balance (Abs) is current and doesn't need repeating yet.

With Li's and a low charge rate you wouldn't see true Float target V achieved anyway until they're near 100% charged.

@Alexandra I don't think that 'Tail' issue applies here. Does it actually apply at all in a Multi (maybe in new firmware I haven't spotted yet)? :)

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Alexandra ♦ JohnC ♦ commented · Feb 12, 2022 at 08:17 AM

@JohnC
No nothing new you dont know about. If you dont know then I definitely don't.

What I was thinking is since the charge current is low the bulk charge state was not being triggered. I have seen on older mppts and other makes sometimes get 'triggered' into float when the person had insufficient solar installed and the charge current was low even when the battery was at rebulk voltage.

And as you say if restarting the system did not trigger bulk again then increasing charge current would be the next step.

But setting charge current so low maybe @coreyzev is not really prioritizing getting the large bank charged up in anycase?

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Answer 2 · 2022-02-11T19:57:03Z

Alexandra answered · Feb 11, 2022 at 07:57 PM

@coreyzev

Try charging at a slightly higher amps.

Because the different stages of charging are both voltage and amperage based, the tail current and other requirements of the charge algorithm may be getting "mixed signals". A 4% tail current on a 300AH battery is 12Amps. You are charging under that.

I am guessing you have 16kwh bank easliy there it is charging at 400/500w is a bit strange on a large bank. That is 30ish hours at a high DOD.

A bmv would help alot as well if you want to keep the charge current lower as the system would then know its target AH to replace. But the tail current issue will still be an issue.

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Answer 3 · 2022-04-14T15:32:24Z

goncalo answered · Apr 14, 2022 at 03:32 PM

Did you find what the problem was/how to solve it? I think I’m having a similar issue. The multi is always in float, never goes through bulk and absorption.

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