question

coreyzev avatar image
coreyzev asked

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


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

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Multiplus-IIMPPT Controllersbattery chargingLithium Batteryfloat
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5 comments
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Look at the re bulk voltage.

Should be in the manual.

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coreyzev avatar image coreyzev klim8skeptic ♦ commented ·

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 avatar image klim8skeptic ♦ coreyzev commented ·
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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3 Answers
JohnC avatar image
JohnC answered ·

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 avatar image coreyzev commented ·
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 avatar image JohnC ♦ coreyzev commented ·
@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 avatar image Alexandra ♦ JohnC ♦ commented ·
@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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Alexandra avatar image
Alexandra answered ·

@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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goncalo avatar image
goncalo answered ·

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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