Never reaching the charge absorption voltage

[nicholas38]

I have the Victron Multi RS Solar, 5x550W panels and 3 x 48V chinese lifepo4 100ah batteries with internal BMS and no bluetooth. I watched Will's recent videos about charing voltages etc, and I'm wondering if it's a problem that I normally don't reach the absorption voltage.

I've set absorption charge in the Victron settings to 58V. It normally starts the day around 51V and increases to around 54V when it gets to 100%. My Float setting is set to 54V, so they stay at 54V. Sometimes the victron app says absorption charging for a few seconds or half a minute, before going to Float. Maybe those times the voltage actually reaches 58V, but that's normally not happening. My feeling is that the batteries BMS are not always in sync with the Victron and they stop accepting charge before Victron wants to. However Victron is normally right and says 99% then 100% just before going to Float.

In Victron settings I could do a manual equalisation, would that achieve the same goal as the absorption charge? What else could I do?

 

[AshleyL]

........chinese lfp batt?
Okay.....it is 15s or 16s battery?
MultiVac from Asimov story will reply "Insufficient data for meaningful answer"

 

[nicholas38]

........chinese lfp batt?
Okay.....it is 15s or 16s battery?
MultiVac from Asimov story will reply "Insufficient data for meaningful answer"

16 cell lifepo4 battery with Dali BMS. Charging voltage specified as 58.4V

 

[AshleyL]

16 cell lifepo4 battery with Dali BMS. Charging voltage specified as 58.4V

Daly BMS? Now that explained everything.

One or maybe all of your battery packs has out-of-balance cells that trigger overvoltage disconnect.

When the BMS is doing a hard disconnect, there will be a voltage surge (can be very high at 60-65V and might damage the inverter charging component) at the inverter. The inverter interpretes the voltage surge as bulk charging phase completed and the sudden lack of current (tail current) as absorption phase completed, therefore entering floating phase immediately.

Daly BMS only has "charge balance" method as its passive balancer. (30ma or 150ma balance current depending on the model).
"Charge balance" means the passive balancer only works when the BMS detect there is current flowing into the battery.

Good luck on balancing those cells. You should read more on how to top balance those cells/battery pack/

 

[nicholas38]

Daly BMS? Now that explained everything.

One or maybe all of your battery packs has out-of-balance cells that trigger overvoltage disconnect.

When the BMS is doing a hard disconnect, there will be a voltage surge (can be very high at 60-65V and might damage the inverter charging component) at the inverter. The inverter interpretes the voltage surge as bulk charging phase completed and the sudden lack of current (tail current) as absorption phase completed, therefore entering floating phase immediately.

Daly BMS only has "charge balance" method as its passive balancer. (30ma or 150ma balance current depending on the model).
"Charge balance" means the passive balancer only works when the BMS detect there is current flowing into the battery.

Good luck on balancing those cells. You should read more on how to top balance those cells/battery pack/

Thanks for your reply! However, I've never seen this high voltage in the Victron app. Shouldn't I see it there?

 

[AshleyL]

Thanks for your reply! However, I've never seen this high voltage in the Victron app. Shouldn't I see it there?

Depend on your Victron data sampling rate. Blink and you will miss it.

Trust me, you don't want the BMS to perform hard disconnect very often due to cell overvoltage protection being activated.

You should find some way to view the Daly BMS data instead......and configure some settings. By default, Daly BMS starts balance at 3.3v which is a bad idea, it should start balance at higher voltage 3.42 or 3.45v

Balancing earlier can be detrimental since it will undo the top balance.

 

[nicholas38]

By default, Daly BMS starts balance at 3.3v which is a bad idea, it should start balance at higher voltage 3.42 or 3.45v

Balancing earlier can be detrimental since it will undo the top balance.

Do you mean that the Dali balancing from 3.3V will be detrimental if I use separate active top balance?
I've understood that Dali BMS balance very slowly, so wouldn't starting earlier be a good thing then?

Would it help the balancing time if I increase float voltage from 54V to 55-56V ?

 

[Skypower]

The only thing that I would try is to reduce the charge current very low to keep the bms’s from going into high cell voltage protection yet get the balance function time to balance (on charge only). If the battery disconnects charge, back off and try again. This could take days. I probably won’t have the patience for that so I’d either (A) return it if there’s any warranty, (B) carefully oscillating saw the top off and manually bring up the lower cell voltage with a bench top power supply or (C) just replace the bms with a jk if the cells are worth the effort. Flying blind and not being able to see into a battery (no Bluetooth) is unfathomable now and I guess you found out now too

 

[AshleyL]

Do you mean that the Dali balancing from 3.3V will be detrimental if I use separate active top balance?
I've understood that Dali BMS balance very slowly, so wouldn't starting earlier be a good thing then?

Would it help the balancing time if I increase float voltage from 54V to 55-56V ?

Yes, unless if you can access the Daly BMS setting to change the balance start from 3.3 to higher 3.45v, even with separate active balancer, it will undo the top balance over time.

Starting at 3.3v is way too early, 3.4v is the earliest you could start at due to how LFP chemistry works.

What kind of active balancer you use? Don't tell me it is Daly useless active balancer 1A/5A again.........

 

[nicholas38]

The only thing that I would try is to reduce the charge current very low to keep the bms’s from going into high cell voltage protection yet get the balance function time to balance (on charge only). If the battery disconnects charge, back off and try again. This could take days. I probably won’t have the patience for that so I’d either (A) return it if there’s any warranty, (B) carefully oscillating saw the top off and manually bring up the lower cell voltage with a bench top power supply or (C) just replace the bms with a jk if the cells are worth the effort. Flying blind and not being able to see into a battery (no Bluetooth) is unfathomable now and I guess you found out now too

Ok I see! I could set the max charge current in Victron to for example 1A (?) after I've reached say 53.5V.
As there is 3 batteries in parallel, how would I know if one battery disconnects charging?.

 

[nicholas38]

Yes, unless if you can access the Daly BMS setting to change the balance start from 3.3 to higher 3.45v, even with separate active balancer, it will undo the top balance over time.

Starting at 3.3v is way too early, 3.4v is the earliest you could start at due to how LFP chemistry works.

What kind of active balancer you use? Don't tell me it is Daly useless active balancer 1A/5A again.........

I don't have any active balancer.

 

[Skypower]

Ok I see! I could set the max charge current in Victron to for example 1A (?) after I've reached say 53.5V.
As there is 3 batteries in parallel, how would I know if one battery disconnects charging?.

Yes, see how much current it’ll take without the BMS disconnecting. You could try to isolate the batteries or use a clamp meter to find out what each battery is or isn’t taking.

 

[Skypower]

How did you know that there’s a Daly in there, documentation or does it have a removable cover?

 

[AshleyL]

Ok I see! I could set the max charge current in Victron to for example 1A (?) after I've reached say 53.5V.

3 parallel packs? You might want to increase total current flow to 5A.
Reason being Daly BMS cheap shunt cannot detect amperage lower than 1A. I owned few Daly BMS before I put them away.
In parallel configuration, assuming each of your 3 pack receives equal amperage, at least 5A / 3 = 1.67A still flowing into each pack.

I don't have any active balancer.

.......Hmm...no comment.

 

[nicholas38]

How did you know that there’s a Daly in there, documentation or does it have a removable cover?

The seller stated that. It doesn't have a removable cover.

 

[Skypower]

The seller stated that. It doesn't have a removable cover.

 

[Skypower]

3 parallel packs? You might want to increase total current flow to 5A.
Reason being Daly BMS cheap shunt cannot detect amperage lower than 1A.

Great point, I’d forgotten about that.

 

[nicholas38]

I asked them again, they say it's the Daly 16S 48V 100A, non smart BMS. From the specs it shows balance detect 3.5V and current 30mA.

If I manage to balance it a few hours each day, then how many days would it take to balance if some cells are very unbalanced, when balancing at only 30mA? I don't know how to calculate or estimate that..

I tried yesterday to set charging current to 5A once I got to 90%. It seemed to work ok, I reached 98% by sunset. However the voltage displayed in victron went down from ~54.3V when charging at 35A to around 53.6V when charging at 5A. Why does this happen, is it Victron that decides that? It went up to 53.9V just before sunset at 98%.

Also, I'm wondering if I should use the manual absorption mode setting instead of adaptive absorption in the Victron. Will that help with balancing?