I cant freaking decide what voltages to set for charging with my 48v Victron Inverter/Charger, pls help

[coreyzev]

I've read all the things, especially @FilterGuy's resource on voltages. I previously had it set according to that: Absorption: 56.8V, Float: 54.4V. But it felt like the system was acting weird when I "barely" used the battery, which is often the case, and then it either did or didn't charge.

The default for Victron for LiFePo4 batteries is Absorption 56.8, Float 54. But because we in theory want it to NOT float at all for LiFePo4, I set float to match Absorption, which in theory would cut it out entirely... but doesnt seem right. (Also I feel like FilterGuy would've said something if that were better to do).

To be clear, the main [internal] controversy here is where to put my Float voltage for the best health of my batteries which will likely be cycled frequently. But also often used along w/ a 30A 120V system.

So now I feel kinda at a loss. Components will be listed below. Would love suggestions from y'all. Thank you.

System:
Battery: DIY 48v 16s3p 300Ah LiFePo4
Inverter Charger: Victron Multiplus-ii 48v/3000VA/30-50 120V
Shore Power: 30A 120V

Current settings:

 

[John Frum]

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

 

[time2roll]

Absorption 55.2 but 56.8 is OK. I would cut the absorption to .2 or .5 hours
Float 52.0 this will allow the battery to actually cycle.

Charge current 30 amps seems low unless the generator is small or that is the max. Again I would reduce absorption time.

I would definitely check to box to not charge below 0C, maybe 5C depending on if there is a heater and what it is set to come on. Temp sensor on the battery.

 

[pau1phi11ips]

It was my understanding that, although float isn't required for the battery chemistry, the float time is handy for giving the BMS some time to balance the cells.

 

[John Frum]

It was my understanding that, although float isn't required for the battery chemistry, the float time is handy for giving the BMS some time to balance the cells.

It causes unnecessary voltage stress to float above the high knee.
Balancing below the high knee can undo the top balance.

 

[HighTechLab]

Are you on the latest firmware (V 494)? The algorithm for how the inverter handles charging has changed drastically since V. 483

 

[coreyzev]

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

Thank you. This was helpful. I just set my float to 52.5V. I want it to cycle sometimes. There are a ton of terms in that document that would benefit from a bit more detailed explanation but I could've googled if i wanted. it was still helpful.

It causes unnecessary voltage stress to float above the high knee.
Balancing below the high knee can undo the top balance.

What is the high knee?

Are you on the latest firmware

Hi, thanks. I have been on 494 for a while. gonna update to 496 tomorrow when I'm not using the system.

 

[John Frum]

There are a ton of terms in that document that would benefit from a bit more detailed explanation but I could've googled if i wanted. it was still helpful.

Which ones?
Help me make the doco better.

What is the high knee?

This is a representative charge curve for an LFP cell as prepared by Andy of the Off Grid Garage.

100Ah Cell - Test 1

Shared with Dropbox

www.dropbox.com

Notice how the voltage shoots up at the end of the charge cycle.

 

[Taem]

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

This url is broken. Can you update it?
I have the same issue with charger setting and i hope that info will be very helpful.
Thanks

 

[Taem]

I've read all the things, especially @FilterGuy's resource on voltages. I previously had it set according to that: Absorption: 56.8V, Float: 54.4V. But it felt like the system was acting weird when I "barely" used the battery, which is often the case, and then it either did or didn't charge.

The default for Victron for LiFePo4 batteries is Absorption 56.8, Float 54. But because we in theory want it to NOT float at all for LiFePo4, I set float to match Absorption, which in theory would cut it out entirely... but doesnt seem right. (Also I feel like FilterGuy would've said something if that were better to do).

To be clear, the main [internal] controversy here is where to put my Float voltage for the best health of my batteries which will likely be cycled frequently. But also often used along w/ a 30A 120V system.

So now I feel kinda at a loss. Components will be listed below. Would love suggestions from y'all. Thank you.

System:
Battery: DIY 48v 16s3p 300Ah LiFePo4
Inverter Charger: Victron Multiplus-ii 48v/3000VA/30-50 120V
Shore Power: 30A 120V

Current settings:
View attachment 88219

Hi,
Can you send your final setting for LifePo4 charging please:
Absortion
Float
Repeated absortion interval, day, time
Charge curve
Do you use "BatterySafe"?
Thank you in advance )

 

[John Frum]

This url is broken. Can you update it?
I have the same issue with charger setting and i hope that info will be very helpful.
Thanks

Doco attached.
If you have any questions I'm glad to answer.

 

[TomC4306]

Float 52.0

No. Too low.
The battery will cycle overnight.
It doesn't need to cycle during the day when solar is available which is what this float voltage would do.

 

[TomC4306]

Charge to full.
Disconnect battery. Measure voltage after resting a few hours. Set that as float.
In my case, 54.2v.
When you enter float mode the battery stays at 100% at a lower voltage but the mppt's can service the load. If you set float to 52 volts the battery must discharge to 52 volts before the mppts will cover any load.

 

[John Frum]

I have the same issue with charger setting and i hope that info will be very helpful.

What is your issue?

 

[time2roll]

No. Too low.
The battery will cycle overnight.
It doesn't need to cycle during the day when solar is available which is what this float voltage would do.

I thought that was the point to use battery power at night that was collected from solar during the day. Then solar recharges again next day and minimizes grid usage overnight.

 

[John Frum]

I thought that was the point to use battery power at night that was collected from solar during the day. Then solar recharges again next day and minimizes grid usage overnight.

Float is only relevant when there is a charge source that is providing float voltage.
Solar generally doesn't provide float voltage after the sun goes down.

 

[TomC4306]

I thought that was the point to use battery power at night that was collected from solar during the day. Then solar recharges again next day and minimizes grid usage overnight.

That is the point. But it won't be achieved setting float at 52 volts. Your solar charge controller charges your battery to full during the day and then falls back to float voltage of 52 volts. Now, while the sun is still out, you are discharging your battery to 52 volts forgoing the available solar to run your loads. Keep the battery at 100% at a slightly reduced voltage until the sun goes down. Then, draw down the battery overnight that is the point.

 

[time2roll]

Float is only relevant when there is a charge source that is providing float voltage.
Solar generally doesn't provide float voltage after the sun goes down.

I did not realize the Multiplus-II was a solar controller.

 

[John Frum]

I did not realize the Multiplus-II was a solar controller.

My mistake, got my threads mixed up.

 

[Taem]

What is your issue?

Thanks for pdf file with instruction. I will try to figure out with settings.