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DIY LifePO4 16s 48v bank and Multi-II - So many questions


smurfdbn
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Hi All

In the process of putting together my first 16s 120AH LifePo bank, have found lots of great info in similar posts here but sadly, still have questions

My setup: Multi-II 5k, SmartSolar MPPT 150/100, CCGX with ESS.

Still a noob at this so to broaden my understanding, I have been exploring the various configs and I see charger settings in VE.Configure and then in Victron-Connect there are charger settings for the MPPT - Should these settings be the same? Which of these settings are used, when?  Does the Multi have overall control of charging?

As far as Charge parameters, the "docs" specify Cell Charge of 3.65v at 1C which equates 58.4v and then the BMS specs state max 80A.  If I select "Lithium-LifePO" in VE.Configure, charge voltage selected is 56.8v.  I read a suggestion from GerLach (same batteries) - "Pull a bit back on the charge volts to 54.2 or 53.8v so that the other get time to level out.".  Based on these varying suggestions, need some assistance with Charge parameters - perhaps @Gerlach would be kind enough to share...

I have a BMV702 - from what i've read here, the Multi can function without it - is there any benefit in connecting the BMV to this setup?

Thanks

Edited by smurfdbn
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4 hours ago, smurfdbn said:

Does the Multi have overall control of charging?

Depends. If you have a managed battery (ie the BMS can communicate with the CCGX using a can-bus connection), then the battery is in control of charging. Otherwise the Multi is in control (so whatever you set up in VE.Configure is also used by the solar chargers). It is however a good idea to set the MPPTs to the same values, just in case they end up running standalone at some point. With a 16s setup, there is usually not too much danger. With a 15s setup (eg Pylontech), people often forget to lower the voltage, and then the first time the solar chargers end up standalone they overvolt the battery 🙂

4 hours ago, smurfdbn said:

As far as Charge parameters, the "docs" specify Cell Charge of 3.65v at 1C which equates 58.4v and then the BMS specs state max 80A.  If I select "Lithium-LifePO" in VE.Configure, charge voltage selected is 56.8v.  I read a suggestion from GerLach (same batteries) - "Pull a bit back on the charge volts to 54.2 or 53.8v so that the other get time to level out.".  Based on these varying suggestions, need some assistance with Charge parameters - perhaps @Gerlach would be kind enough to share...

3.65V is very VERY highly charged. I would suggest you aim for 3.5V or max 3.55V per cell. Very little extra energy is stored above 3.45V per cell. As long as the voltage is high enough so that the balancer in the BMS can do its job, there is no reason to run at such high cell voltages. 56.8V is indeed a better voltage than 58.4... but I'd suggest 56V or even lower (but no lower than 55.2V).

4 hours ago, smurfdbn said:

I have a BMV702 - from what i've read here, the Multi can function without it - is there any benefit in connecting the BMV to this setup?

The BMV does better SOC tracking than the Multi. If you plug it in, the SOC of the BMV will be used in the system.  My suggestion is to use it.

 

Edited by plonkster
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@smurfdbn  which Battery Management System (BMS) does your battery work with? 3.65V is the very upper cell limit where your battery should protect your cells and stop charging. That should not be where you want to charge to. 3.5V per cell should be your aim for LiFePO4. So that is 56V for 16 cells, or 52.5 for 15 cells (absorption voltage). Float voltage should be 55.25 for 16 cells or 51.8 for 15 cells. If you charge your batteries for the first time the BMS might need to balance the cells so that they all at the same State Of Charge (SOC). For this I suggest limit your charge current to 5A or lower and make the absorption and float 1V lower and leave this on your charger for a week or two. Then when they are all the same up your charge current limits to what your battery can handle and set the absorption and float to the real values.

Victron-Connect and VE.Configure are both writing the settings to the inverter. Which ever you used last will override the other. VictronConnect is a bit "easier" with less options, but if you set up ESS then you have to use VE.Configure to be able to load the ESS assistant. Then once you have loaded ESS assistant and your SmartSolar is also connected, then the Charge settings will come from the Smart Solar. The Inverter settings will always come from the inverter (so VE.Configure/Victron Connect)

If you add the BMV and connect that to your setup, then the battery voltage and current will come from the BMV instead of what the Multi measures. It is a bit better that not having anything, but nothing more than the basic stats.

If you want more information from the battery BMS then you need something that can communicate with the inverter and battery and get cell level values from the battery. This assumes that your DIY battery's BMS does have some sort of communication interface and that you can get the commands for that BMS (you normally can get it from the manufacturer).

 

Hardware option
In this thread Justin is busy creating a hardware item (Adriuno micro computer based) that can read his battery and create Canbus messages that most inverters can then read. Canbus works on Victron Multiplus systems, so that should work, once it is finished. 

Software option
I have been creating a software driver that you add to your GX device. So this will only work with Victron inverters (any GX type device or Raspberry Pi that run the VenusOS). You can then connect your battery using a USB-serial interface to read the battery data. This is already working for my battery, but I still need to make the install easier and more generic to work on other batteries. 

 

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@plonkster, @Louisvdw, thank you for your comments, much appreciated

The BMS is a basic unit, no comms - may look at upgrading this as we expand the setup.  So 3.5v per cell it is - will start out with suggested voltage ranges, keep a watchful eye on proceedings.

12 hours ago, plonkster said:

The BMV does better SOC tracking than the Multi. If you plug it in, the SOC of the BMV will be used in the system.  My suggestion is to use it.

Was leaning that way thanks...

12 hours ago, Louisvdw said:

For this I suggest limit your charge current to 5A or lower and make the absorption and float 1V lower and leave this on your charger for a week or two

Thanks for this tip.

12 hours ago, Louisvdw said:

up your charge current limits to what your battery can handle

As for final operational charge current, i'm generally nervous around currents settings so tend to err on the side of caution. 

Docs state: Standard Charge Current: 1C - also saw this in another discussion on these cells: "My cells can, with no problem handle the 0.5c and 1c charge" - BMS spec is 80A (assume this is max), Multi is rated at 70A so i'm thinking 50A or 60A?  As i'm not fluent in battery speak, would appreciate some guidance on this aspect.

 

12 hours ago, Louisvdw said:

I have been creating a software driver that you add to your GX device.

All the best with your project...

Thanks again

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4 minutes ago, smurfdbn said:

BMS is a basic unit, no comms

When you upgrade my driver might help you :) 

5 minutes ago, smurfdbn said:

Multi is rated at 70A

This can be a bit confusing. There is input power and output power.

The Multi can charge(IN) at 70A, but it will draw much more when inverting. (70A x 48V = ~3.3kW)

Discharge (OUT) is rated as 4000W with a peak of 9000W , so that will (4000W / 48V = 83A or 9000W / 48V = ~ 185A)

 

With only 1 battery at 80A max you need to make sure to set your Multi to only draw up to the limit the battery can handle (thus 80A). You did not tell us what BMS you use so I am not sure if your BMS can handle 80A full load or if that is just peak. Most of the time the rating is full load for a BMS.

Then we normally charge the batteries at 0.5C which is half their discharge rating. 50A or 60A should be good there.

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1 hour ago, Louisvdw said:

Then we normally charge the batteries at 0.5C which is half their discharge rating. 50A or 60A should be good there.

Yeah. This is a bit different to lead acid. With lead acid there is a recommended charge rate, and coming in too low is a problem. With LiFePO4, there is a limit which you should preferably not exceed (1C), but charging slowly is much less of a problem. So in this case you can just throw the full 70A from the inverter/charger into the battery and not worry about it (it is under 1C). But as Louis said, discharge is another matter. If the BMS wants you to stay under 80A, you risk a battery disconnection with sustained power levels above around 3.6kW (if we leave room for a bit of losses).

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3 hours ago, Louisvdw said:

When you upgrade my driver might help you :) 

Will keep that in mind 😊

3 hours ago, Louisvdw said:

Then we normally charge the batteries at 0.5C which is half their discharge rating. 50A or 60A should be good there.

Thanks, definitely eases my mind

Sorry for the incomplete info - BMS pic attached - rating for charge is 80A, discharge is 120A

BMS.thumb.jpg.9bafae5e1b978dcf68f8c0d6018f9e38.jpg 😊


 

1 hour ago, plonkster said:

If the BMS wants you to stay under 80A, you risk a battery disconnection with sustained power levels above around 3.6kW

Was so focused on getting the Charge parameters right, hadn't got to the discharge side, my bad - 120A discharge should comfortably handle our loads without a disconnect 🤞

Thanks again Gents 
 

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2 hours ago, smurfdbn said:

Sorry for the incomplete info - BMS pic attached - rating for charge is 80A, discharge is 120A

Does this BMS perhaps have dry contacts to indicate stop-charge and stop-discharge conditions?

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5 minutes ago, smurfdbn said:

No dry contacts, just the basic BMS

That's a shame. Cause you can go a long way if you have those dry contacts, and it is usually significantly cheaper than full CAN-bus comms.

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1 hour ago, Louisvdw said:

OK. That is a Daly BMS. Pretty solid, but that version is without comms. There is a "smart" version with RS485 communications out now as well. It is what Justin is using for his hardware CANbus driver.

I did see the post on Justin's system - for now, just getting my feet wet with this diy build - at the price, worthwhile battling a bit to learn the ropes. 😊

Must say, it would be a damn sight harder if not for the knowledgeable and generous members on this forum 😉

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Just now, plonkster said:

That's a shame. Cause you can go a long way if you have those dry contacts, and it is usually significantly cheaper than full CAN-bus comms.

I did see a thread on this but I don't know that i'm anywhere near being able to put that together yet, hopefully one day when i'm big 😊

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Hi @smurfdbn sorry for the late responds. Got a new born in the house so now need to put my attention with him till i get time to post.

To respond on your question, I founded  charging on this settings my inverter and mppt worked at the best for my combination. I just check now, my 1ste battery is running 212 days now with out problems. In the beginning I kept a constant eye doing adjustments till i founded that the best spot was 54.6v on bulk and 53.6v float. Solar MD is using the same settings on there units. 

I see you using a DALY bms with your build with a Victron. @plonkster knows the background of problems TTT had with his Victron system with a DALY bms and 150ah lifepo4s. He had a problem where if the battery gets full and the bms switches  the charge fits off, then there is a spike, because he was running hi charging volts. I told him to turn it down. Then there is this ripple errors he keeps getting. It happens when the battery is fully charge, charging Fit's will close, system will idol, then when there is demand on the inverter for a short birst, the mppt will supply the demand but the Fits on the the bms is still open because the Fits only close on 3.55 volts. Just to short, so know the mppt sits with a bunch of power that runs between the inverter and mppt up and down till it calms down. 

I did a test on my system were it turn it up with 1.5v on Bulk and charge and kept a eye, and boy oooooooo boy!!! The inverter was super unhappy and the mppt because the when the Fit's close on the bms, I got Volt spike to 60v on the mppt and inverter side and the mppt resets the MPPT volt sweep, sounded like electrical fence. I turned my settings back to my old settings and my system run normal again, so i'm staying on this, and i'm running 2 sets of lifepo4's with there own BMS and 2 mppts. 

Other thing that i founded, if you charge the bank at 54.6v, fully charge you can leave and it will drop all the way on 53.8v and stay there for days.

This is my findings and my DIY is running with out problems.    

Edited by Gerlach
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@Gerlach 

19 minutes ago, Gerlach said:

Got a new born in the house so now need to put my attention with him till i get time to post.

No worries and Congratulations!

It was actually the original post about your DIY build that got me going - thank you for your input to my question, confirms my course of action.

I did see the comments on TTT's issues so will be erring on the side of caution

As always @plonkster and @Louisvdw were very helpful, I believe I am on the right road for now...

Thanks again

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