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noel1968 avatar image
noel1968 asked

Battery charging in float stage

Hi - If somebody can help on this.. If you see below my battery is on float state and reading shows 54.9V. But the setting in the configuration for float is 55.2V. But the charge never goes beyond 54.9V and its always charging. When I check the voltage at the battery terminal its at 55.2V.

Is this an issue if its always charging or why does it no go beyond 54.9. The distance between the battery and the Easy solar is less than a feet. How do I correct this?

batterybattery system voltage
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1 Answer
Mark avatar image
Mark answered ·

Need some more info to properly assess and provide feedback - particularly battery type, battery capacity, charge voltage temp coefficient, typical ambient temperature, what your using as the battery monitor (Multi or a BMV) & where it's measuring the voltage.

The charge voltage set points are normally compensated for temperature so I'm assuming that the temperature might be higher than 25degC if the actual charge voltage is lower than what is set. If so this is normal and expected.

Any difference in battery monitor voltage and what you measure directly at the battery terminals could be due to a variance between the cable losses between the 2 different measurement points and the actual measurement equipment.

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noel1968 avatar image noel1968 commented ·

Hi - This is the screen shots from the VE configure. I dont have a BMV but from the Console the readings are calculated and displayed. You can also see the other parameters in https://vrm.victronenergy.com/installation/34053/share/47db99b3.


Hope this helps



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Mark avatar image Mark ♦♦ noel1968 commented ·

As you are running an ESS assistant the MPPT would be a slave to the Multiplus. I'm not too familiar with ESS, but recall a ESS symbol that should appear & I can't see this with your remote console screen - what firmware are you running in the Multiplus, MPPT & CCGX? It may be good to update it all to the latest version.

Do you have the Multiplus temp sensor connected?

Can you check the battery temperature during the day using the CCGX/remote console? (with the recent FW it's now reported).

If its over 25degC I'm thinking that the charge voltage is a little lower than what you have specified due to temperature compensation.

Are you using the voltage sense terminals of the Multiplus and if so where are the wires connected directly to the battery? There may be some cable losses depending how it's all connected and exactly where you take the voltage reading with you multimeter vs the Multiplus source.

In terms of some charge going in during float, that's generally normal in order to maintain the float voltage setpoint. Probably somewhere about 0.5% of the battery capacity which is ~1A for a 200Ah battery bank - which is about what you have going in.

With your setting's, what type of batteries are you using?

If lead acid based the max absorption time that of 2h that you have set may be low, this is typically set to ~6h (for most lead acid based batteries) but the Multiplus will determine the actual time with the 'adaptive' setting. Setting the SOC to 95% after bulk also seems high, this is typically set to ~85% for lead acid based batteries. So your batteries may be a little undercharged/lower than the indicated SOC. But please refer to the battery manufacturers data sheet for some of these specs.

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noel1968 avatar image noel1968 Mark ♦♦ commented ·

Thank you very much will check and revert with information

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noel1968 avatar image noel1968 Mark ♦♦ commented ·

1. ESS is connected and configured..


2. Battery Temperature


3. My battery is lead acid - I plan to change the absorption time to 6 hours

4. Voltage sense terminals - I will install one

Post which I will come back with findings


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Mark avatar image Mark ♦♦ noel1968 commented ·

Well the lower voltage makes sense then, as the measured battery temperature is 30.5degC. The default temperature compensation is -64mV/degC (for a 48V system) in relation to 25degC nominal temperature.

So -0.064V x 5.5 degC = -0.35V (correction to charge voltage setpoint).

This is exactly the difference you have seen (55.2V vs 54.9V).

In addition to increasing the absorption time I would also recommend to change the 'State of charge when bulk finished' setting to ~85% if you are using lead acid batteries - that way it will track the batteries true SOC better.

Connecting the voltage sense wiring will also further eliminate any small voltage drop error in the DC power cables.

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noel1968 avatar image noel1968 Mark ♦♦ commented ·

Thanks Mark for patiently responding. Will try this and revert with findings

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noel1968 avatar image noel1968 Mark ♦♦ commented ·

Mark - I changed the values to 85% SOC and absorption to 6 hours. The charge never went beyond absorption and got only till about 93% of charge. I also checked with my battery manufacturer and he told 2 hours is max absorption time.

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Mark avatar image Mark ♦♦ noel1968 commented ·

Hi Noel,

Generically speaking, for a lead acid based battery the bulk phase charges the battery from X% to ~85% SOC, then the absorption phase completes the last ~15% of recharge.

The 'adaptive' charge curve selected in the Multiplus VE Configure settings means that the Multiplus adjusts the ACTUAL absorption time to suit each individual cycle.

The absorption phase normally does NOT run for the 'maximum absorption time' specified - this is just a max time limit, that might only ever be reached after a very deep discharge and/or with an undersized charger.

The Multiplus calculates the actual absorption time (for each indicidual charge cycle) based on the duration of the preceding bulk phase and then multiplies the bulk time by a factor of 5.

This is logic is described further in this whitepaper;

https://www.victronenergy.com/upload/documents/Adaptive_charging_how_it_works.pdf

Are you able to share the data sheet from the battery manufacturer so that I could review it? 2h as the maximum allowable absorption time sounds like it could leave your battery undercharged during some deeper charge cycles.

Attached is a 'generic' recommended charge curve for deep cycle lead acid based batteries;

As an example, this charge curve recommends a maximum absorption time of 8 hours, BUT the absorption phase should normally be ended much earlier - as soon as the charge current has dropped down to below ~2% (or even <1%) of your battery capacity.

So if your using a 200Ah battery bank the charge current should drop below <4A (=2%) or lower (<2A=1%) to consider the battery as fully recharged and enter float phase.

So I recommend that you check what the charge current drops to just BEFORE the abortion stage ends to see if you are charging with sufficient absorption time or not. If there is still a reasonable charge current flowing into the battery just BEFORE the absorption phase ends then your batteries are probably not being fully recharged and this is probably your main issue with the SOC% not indicating as you 'expect'.

This is also some more generic info from the 'Rolls' battery manual;

Its also important to note that the battery monitor functionality is not perfect and wont be as accurate as a dedicated BMV battery monitor where the shunt measures all current flow in to and out of the battery.

In the end its up to you and your installer to determine what charge setting you feel are most appropriate for your system. Please treat my comments as information only.

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noel1968 avatar image noel1968 Mark ♦♦ commented ·
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noel1968 avatar image noel1968 noel1968 commented ·

Mark just to give you an update... earlier with 2 hours absorption time and when the monitor indicates its in float, I checked the battery charge at the battery terminal it would indicate 55.2, but remains the same till the discharge starts. But the monitor will indicate 54.8v only

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Mark avatar image Mark ♦♦ noel1968 commented ·

Hi Noel,

Regarding any voltage 'reading' differences, get some wiring hooked up to the 'voltage sense' terminals of the Multiplus and see if that resolves this delta. Based on resistance in the power cabling and connections it's normal for there to be some small error between voltage measurements at 2 different points, particularly under higher loads.

Regarding the SOC% tracking and absorption time, the first step should be to confirm that the batteries are being fully charged, so you need to look at some logs to see exactly what the charge current is just before the end of absorption phase. If this current divided by your battery bank capacity is >2% then you should extend the absorption time. I did not see anything in the battery data sheet that states not to charge with >2h of absorption time, if it is required.

If the charge current at the end of absorption phase / battery capacity is <2% then you can consider the batteries to be fully charged and will probably need to try adjusting the Multiplus battery monitor parameters in an attempt for it to track the true SOC % better.

If you don't cycle your batteries down very deeply each night then you may need to revert the change I initially recommended with setting 'state of charge when bulk finished' to 85%... - you could try to raise it slowly by a few % at a time and monitoring the outcome with SOC % tracking. As you already have the 'charge efficiency' set to 100% there is no more scope left to adjust this parameter.

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