Multi RS with Lifepo4 batteries with internal BMS settings, battery % out of sync

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nick5000 asked Apr 15, '24

Multi RS with Lifepo4 batteries with internal BMS settings, battery % out of sync

I have 3 x 48V 100AH "Great Power" lifepo4 batteries with internal "Dali" BMS.

My understanding is that the internal BMS will stop charging when full, and also cut off power if the voltage is too low or current too high.

The battery percentage indicator in VictronConnect is not always right, sometimes it jumps from 80% up to Float 100%, I assume because the batteries stops taking in current. I never see Absorption charge, maybe the BMS is doing a absorption charge without the Multi knows that?

Also, it has happened a few times that VictronConnect shows battery at 40% or so but then the aircon compressor turns on (I've seen 6kW when this happens sometimes) and the voltage goes too low, so I get a low voltage alarm, the inverter turns off and the battery is suddenly 0%. I don't know if the internatl BMS temporary shuts of one or more batteries, or if it's just the Multi.

Is it normal with lifepo4 that the voltage can drop 1-2V quite when there is suddenly a draw of 120A (@49V) and the batteries is around 40%?

Is this just the way it is with using batteries with internal BMS that doesn't communicate with the the Victron?

Could I optimise the settings to avoid the battery going to 0% when it's at 40%?

Relevant VictronConnect settings are:

Battery capacity 300ah

Max charge amp 70A

Absorption charge 57.6V (recommended for these batteries is 58V)

Float voltage 54V

Low battery shut off 47.8V (recommendation is 48V, however the internal BMS should shut it off before so it set the Multi slightly lower to avoid the alarm)

Low battery reset and alarm 48.1V

Peukert exponent 1.05

Charge efficient factor 99%

Discharge floor 15%

Thanks!

Lithium Battery 48v battery Multi RS

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Answer 1 · 2024-04-15T09:20:59Z

nickdb answered · Apr 15 at 09:20 AM

Without knowing the spec of the batteries, a large drop under load at lower SOC, is not normal. You would expect voltage drop under load, but that does sound like batteries that can't deliver what is required. Drop-ins tend to be designed to be cost-effective, so you're probably asking too much from them.

With great power, comes great voltage drop ;)

Your float seems low for lithium. Float and absorb are generally either the same or really close to one another (within 0.2V), so that won't be helping.

Without a managed BMS a BMV/shunt is recommended for better accuracy, it isn't clear if you have one.

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nick5000 commented · Apr 15 at 09:52 AM

Thanks, I can try to set float to the same as absorption.

I do have a soft start to the aircon, but sometimes when the generator is coming on I've seen (in Victronconnect) that the draw is 6kW for a second.

I don't notice any voltage drop normally, it's been only a few times when SOC is lowish and I have a high load. Maybe I could change the settings from 300AH to say 250AH in VictronConnect, to have a more realistic usable AH from the batteries?

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Answer 2 · 2024-04-15T09:39:54Z

Alexandra answered · Apr 15 at 09:39 AM

@nick5000

If SOC suddenly drops and batteries are off. The battery is shutting down. It can't do the surge at low end of SOC. Also 6k is a bit high at 48v anyway that is more 4800w territory so derated your loads for that.

Don't suppress the low alarm. That is counter intuitive, you wan the inverter to shut down before the batteries not the other way around.

The Dali has terrible balancing abilities. So maybe you are discharging before that is even happening. So cell imbalances are causing a whole lot of issues.

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nick5000 commented · Apr 15 at 09:57 AM

Tha batteries are supposed to be able to do 100AH each, so 300AH (@50V is 9kW), do you mean I should expect 48kW at lower SOC, or at any charge?

I need to read up on how cell balancing happens. You said I'm discharging before it happens. Is it supposed to happen at Float stage ? I'm generally at Float for hours every day.

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Alexandra ♦ nick5000 commented · Apr 15 at 07:21 PM

No balancing usually happens in absorption stage.

You will only get 300AH if you are getting 100A% DOD out of them. And then only if the cells are balanced.

The large drop at the end suggests a weal cell or cells that are reaching their low cut off before others.

You need a longer absorption time. The fox/fox from @nickdb works well for some batteries.

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Answer 3 · 2024-04-15T13:01:48Z

onrbikes answered · Apr 15 at 01:01 PM

Do you use the Daly app?

Do you have smart shunt.

I've just installed lifepo4 with a Daly. Mine is 24v so just double the numbers. I've used lead acid for 20 years and am fluent with offgrid.

I have an easy solar and smart shunt. I control all the settings via the 2apps. Some say the smartshunt isnt required, but it all works.

Both apps show a SOC within 5%. Even though the victron shows 100% the Daly will allow voltage in until it reaches full. So far night voltage never goes below 26.5v and after 16 days have 5 cycles on the Daly. By 10am charge hits 28.2v then goes to float mode 27.2v. I've just changed that to 27v

My system initially does go into absorption but i have that set to 20min. You should see your voltage in the victron trend graph.

The Daly is excellent. 2 other locals have one and they recommended one.

These are my settings..

Set victron Lifepo4

Absorption 28.4v

Charged voltage 28.2v ( this needs to be .2 less than Absorption)

Float 27.2v

Discharge floor %30

Tail current disabled

Peukert 1.04

Charge efficiency %99

Daly settings

Sleep set time 65535S ( this is a important one)

Balanced open diff volt .02v

Diff volt protect .1v

Balancing happens all the time.

Hope this helps

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nick5000 commented · Apr 15 at 01:47 PM

Thanks! I don't have any bluetooth or other way to connect to the Daly BMS, and no smart shunt as the Multi RS is directly connected to the batteries, nothing else connected to the batteries, I only use the VictronConnect app to monitor and control the Multi RS.

My battery cell's specs says:

Standard charge: 0.33C constant current, 3.65V constant voltage, charge to 3.65V, continue charging till current deadline to ≤0.05C,

Standard discharge: 0.33C constant current discharge to 2.5V,

Max continuous charge/discharge: 1C

So your batteries are 27.2V when fully charged and only goes down to 26.5V at the lowest? What state of charge are you at then?

Victron connect says over a few days that my max voltage is ~58V and min ~50.8V, however the max voltage is the charging voltage, the float is at 54V, so the batteries are between 54.0-50.X V when not charging (when I dont have the issue of low voltage. Last time that happened it shows as min 47.47V).

My Victron absorption settings says adaptive duration, max 8h, tail current 3.0A, but it appears that only the Daly is doing the absorption charge, the few times I see it it only last for a minute or less.

I don't have any setting for "Charged voltage" on the Multi RS/Victron connect. Only absorption, flot, equalization and storage.

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Answer 4 · 2024-04-16T00:00:49Z

onrbikes answered · Apr 16 at 12:00 AM

The charged voltage is on my smartshunt so you won't have v that

You really need to get at the Daly settings to see what's happening.

When you access the victron app via bluetooth fires the daly show up?

This is a long shot but if you, download the Dalybms app. Default code is 123456. It may show up

47.5v is %8 SOC

50v is%15

That 54v to 50v is too large as .1v makes a big difference.

3.65v is absolute highest. That %100 charging.

3.4v is resting voltage, when fully charged

When my batteries float at 27.2v they're at %100.

In the morning they're at %70 and 26.4v, just like the chart sets says.

Mind you my draw is seriously minimal. At night only the fridge freezer is on, and no phantom loads.

What country are you?

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nick5000 commented · Apr 16 at 03:50 AM

Thanks, my Daly doesn't have Bluetooth, I guess it's an older model.

Isn't differernt battery brands and manufactures different in the voltage range etc? Mine seems to want a quite high charging voltage. They ask for 3.65V (58.4V for 48V), I've set it slightly lower to 57.6V.

I'll check again what voltage I have when the solar charging has completely cut out, I think it's less than than 54V actually, as 54V is the floating voltage I've set. Nickdb above said that 54V float seemed low, so I'm trying to change this to 56V today.

Can I determine the battery percentage from the voltage?

I'm in Thailand at the moment.

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screenshot-2024-04-16-at-054909.png (312.4 KiB)

Answer 5 · 2024-04-16T06:22:16Z

onrbikes answered · Apr 16 at 06:22 AM

A shame you're unable to see what the battery is doing. As stated above a cell may be weak and out of balance.

From the graph the Absorption is very little before it goes into float.

You can go into expert mode and adjust the time. It may be set to adaptive or a very short time period. It'd be interesting to know what the time is set at.

May want to set it for 58.4 as stated but let it sit there.

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nick5000 commented · Apr 16 at 06:55 AM

Thanks, the absorption time is set to adaptive. I could try to set it to 30min for exampel, however I think the battery itself is refusing further absorption charge, that why Victron goes to Float quickly. If I'd want more absorption time, should I start it earlier, by reducing absorption voltage? Edit: As it says "Battery is charging with maximum current until absorption voltage is reached"

Just not I reached float, and I tried to disable the solar, and the battery voltage then went right down to ~54.4V (I set float to 56V today). But very quickly while drawing 5A went to to 53.66V (in 5 minutes). Now at 53.6X it goes down 0.01 every 7 seconds or so. When I turn on the aircon and draw 21A then the voltage goes down to 53.1V.

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Answer 6 · 2024-04-16T10:03:34Z

onrbikes answered · Apr 16 at 10:03 AM

What if you increased the float charge by .1 and v see what happens.

If you ho from adaptive to set time absorption it stay there. Could try that for 30min and see what happens

How old are the batteries?

Are they getting warm?

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nick5000 commented · Apr 17 at 05:01 AM

Batteries are not warm, around 6 months now. I could try to set a fixed absorption time, but if the Daly stops taking in charge then I don't see how it matter what I set the Victron to? It would only make a difference if it changed to absorption before the battery is fully charged. It appears from the Victron text that it changes to absorption charging when the absorption voltage is reached (which is set to 57.6V in my case), but then the batteries are already full.

Edit, tried changing absorption time to 30min, but it only lasted 2 minutes before going to Float (because batteries didn't take in any current).

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Answer 7 · 2024-04-17T06:46:51Z

onrbikes answered · Apr 17 at 06:46 AM

Hmmm.

What about removing one battery at a time to see if you have a faulty one.

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