Having trouble testing maximum charge rate due to SOC & maybe MPPT configuration

[WorldwideDave]

Hello! I have been putting my BMS through the paces for the past 2 weeks. I can easily discharge at 150A continuous with no overheating. I do this by starting my pool pump, running it until the battery SOC is at 3%-0% range, then the sun comes out, charges it back up in 2 hours or so, then I discharge it all again, and repeat over and over and over until the sun is down. I cannot get the system to overheat or anything when discharging.
However, I am struggling to find a way to do an effective charging test. Here's why:
Charge scenario 1:
If I run the pump at the same time as the MPPT are charging (mid day, like now), I am producing almost 1.8kW of power from two arrays, generating over 140A of current to the system. The DC load is about the same - so 1700W in, 1700W out, so net zero to the battery/bms to make it over heat.
Charge scenario 2:
Get battery to zero percent SOC, turn on MPPTs to charge, it brings in 140A, and I can't get to 150A. I could add a 25A AC/DC charger or two, but either way, the battery is only 200Ah, and the MPPTs will refill the battery so fast (go from bulk to absorb) so quickly with no load, that it is not long enough to permit or cause the BMS to record any overheating.

I believe the issue is - and I may be wrong - that my MPPT settings are wrong (they are identical) and it hits about 40% SOC according to the shunt and switches into absorption mode, which i believe is restricting the current out of the MPPT or into the BMS.

I have posted the specs for the GFB 100Ah cells that are inside my battery.
12V, 8 cells configured in 2 series 4 parallel, 200Ah.
JBD 150A BMS.
Please correct me if I'm wrong with anything below:
They support 1C charge max (200A), and .5c charge standard (100A).
BMS settings are to stop charge at 3.65 (14.6V for my pack).
Looks like discharge until 2.5v (10V for my pack).

But my MPPTs I believe are going into absorption at 14.20V, and float at 13.50. Equalization is disabled.
Bulk has re-bulk voltage offset of 0.10V.
Absorption duration is fixed, time is 2 hours, tail current is disabled.

In my mind, it should be staying at bulk (?) longer, if that allows more current. But I'm not an expert.
It just seems that the battery is constantly not reaching close to 100% when there is more than enough solar (140A!) to fill a 200Ah battery pretty quickly I would think.

I'm just missing some knowledge about LiFePO4 and charging them I guess.

 

[Brucey]

Your battery which has a recommended charge rate of 100A and a max of 200A is settling at about 140A input. On a 150A BMS.

Seems normal to me. Are you overpanelled enough to get a solid 150A out of your sccs?

Also at 14.2V its fully charged its a fools errand to go higher for maybe 0.5% more capacity. Lfp doesnt need long absorbs like lead acid.

I would say if you are at 40% and your voltage is at shutdown levels it's more than likely an issue with your shunt settings, especially the default lead acid which sets things to 50%.

 

[WorldwideDave]

Your battery which has a recommended charge rate of 100A and a max of 200A is settling at about 140A input. On a 150A BMS.

Seems normal to me. Are you overpanelled enough to get a solid 150A out of your sccs?

Also at 14.2V its fully charged its a fools errand to go higher for maybe 0.5% more capacity. Lfp doesnt need long absorbs like lead acid.

I would say if you are at 40% and your voltage is at shutdown levels it's more than likely an issue with your shunt settings, especially the default lead acid which sets things to 50%.

Aha thank you...screen shot and open to suggestions:



right off the top looks like things such as Peukert and charged voltage and tail current may be wrong - open to your professional advice here!

 

[ricardocello]

see Eggo:
Thread 'Victron Shunt Settings (concept and some settings may apply to others)'
https://diysolarforum.com/threads/v...-and-some-settings-may-apply-to-others.97606/

 

[WorldwideDave]

see Eggo:
Thread 'Victron Shunt Settings (concept and some settings may apply to others)'
https://diysolarforum.com/threads/v...-and-some-settings-may-apply-to-others.97606/

Think we chatted about that a while back.
Battery charged voltage is set to 14.0V.
He wrote, "If you EVER charge with solar, set it to 0.2-0.3V below absorption."
With my MPPTs set at 13.5 absorb and float at 14.2, I guess I should be setting this charged voltage to 13.2? Please confirm.
Sounds like instead of 4% on tail current, he wants me to set to 6%?
Peukert is set to 1.00; @sunshine_eggo wants it at 1.05, but makes argument for closer to 1.01. It's at 1.
Sorry to bug you all about this.
Just to confirm -
I have absorb and float set right on MPPT?
I have battery charged voltage set too high at 14, should be 13.2?
Raise tail current from 4 to 6%?
Peukert change from 1 to ?

Shunt's current settings:


MPPT settings:


Sorry everyone - just want to get this right. Haven't changed this since last chat, which I cannot find prior PMs.

 

[sunshine_eggo]

Think we chatted about that a while back.
Battery charged voltage is set to 14.0V.
He wrote, "If you EVER charge with solar, set it to 0.2-0.3V below absorption."
With my MPPTs set at 13.5 absorb and float at 14.2, I guess I should be setting this charged voltage to 13.2? Please confirm.

No. You have mislabeled your voltages above, but they are correct in the settings.

Sounds like instead of 4% on tail current, he wants me to set to 6%?

I waffle on this a little. It's not that important.

Peukert is set to 1.00; @sunshine_eggo wants it at 1.05, but makes argument for closer to 1.01. It's at 1.

This was specifically because you were seeing notable differences in SoC between the battery BMS and the shunt. Peukert has more effect the higher the C rate, so I thought it might be influencing it.

Sorry to bug you all about this.
Just to confirm -
I have absorb and float set right on MPPT?

Yes

I have battery charged voltage set too high at 14, should be 13.2?

No.

Raise tail current from 4 to 6%?

Meh. This is only something I would change if you struggle to sync.

Peukert change from 1 to ?

No.

 

[WorldwideDave]

No. You have mislabeled your voltages above, but they are correct in the settings.

where? Tell me what to fix in the post.

No.

So that I understand, you want me to change nothing in MPPTs or battery, and it all looks fine, and there isn't any problem?
I have not had SOC get to 100% since these changes. Open to suggestions. Here is this month.
You can see SOC dropping 12% or so daily with no loads other than idle standby. You can see a downward trend due to low sun.

Either way, I still have the issue where the BMS and victron SOC aren't close particularly. Seperate issue though.

This issue I'm trying to address here is that it seems that - and maybe I'm wrong - when I discharge the battery, the MPPTs stop charging early.
Battery hits 14 V, goes into absorb for 2 hours (?) load goes on, drains battery, and repeats.



But even in float, never reaches full 100% SOC anymore over 7 days:

 

[sunshine_eggo]

where? Tell me what to fix in the post.

Think we chatted about that a while back.
Battery charged voltage is set to 14.0V.
He wrote, "If you EVER charge with solar, set it to 0.2-0.3V below absorption."
With my MPPTs set at 13.5 absorb and float at 14.2, I guess I should be setting this charged voltage to 13.2? Please confirm.

So that I understand, you want me to change nothing in MPPTs or battery, and it all looks fine, and there isn't any problem?
I have not had SOC get to 100% since these changes. Open to suggestions. Here is this month.
You can see SOC dropping 12% or so daily with no loads other than idle standby. You can see a downward trend due to low sun.

Please provide a full size zoom in of only this charge:

 

[WorldwideDave]

Please provide a full size zoom in of only this charge:

Here's what I think is happening in that timeframe (fairly sure, but been 3 days or so):
wake up, come outside, click the pool on manually and tell it to discharge at 150A or so until almost dead. That's about an hour at 150A with my 200Ah battery at about 1800W going through the shunt. I think.
Next I stop the load for a bit, then once voltage higher up again, though SOC reads low, I fire up the normal pool cycle which runs fast for 5 minutes to prime (1500W) then mellows out to about 650W and runs for a few hours. At some point I may have come back out and told it to run a 'quick clean' cycle at a faster speed (1500W) for about an hour, saw that it was going to hit 0 SOC, and turned it off and let it charge up to almost 100% SOC - just never got there. So then ran pool again, probably at 1500W, but the sun was helping out a lot more then, so SOC didn't drop down, then just left it alone - not sure if pool pump ran again or not, but some hiccups there in voltage so maybe a few more test when pump ran at 500W but PV was cranking out 1200W so raised SOC slowly. Just a guess. Or I could have turned off PV isolator to move some panels not sure.

You can see it did hit float eventually in the evening:

I may have also had a ac/dc charger wired up that day but don't think I did.

 

[sunshine_eggo]

I really can't read any of that.

This is the full size button:

 

[WorldwideDave]

I really can't read any of that.

This is the full size button:

View attachment 284817

I did that my friend, one post up.

 

[WorldwideDave]

The bigger issue still remains, however. @sunshine_eggo as you saw last night I was going to bed with zero SOC last night. Today it is raining and cloudy, and solar is at 300W across all 19 panels. Can't fix that I know...but voltage is reading 14.2V, in absorption already (how can this be?) and the SOC says 20%. That's the part that is baffling me. Shouldn't it be in bulk until battery is at 80% SOC?

It is almost as if the battery (JBD BMS custom pack, 8 cells, 2s4p, 200Ah, 12V) is telling the shunt something wrong.

I have all loads off today trying to reach 100% SOC.

Also remember the shunt & battery SOC are way, way off from each other. I'm okay with that per your advice to focus on the shunt's SOC only because it measures true in and out, and it is saying 205Ah were consumed/discharged, and now says 161 Ah left to go to reach 100%. If this is all true, shouldn't it be in bulk still, not absorb?

Battery shows 20A coming in from MPPTs right now, FYI

Even if okay to stay in absorb, doesn't absorb slow down the rate of the charge/limit current from MPPTs?

I can hook up a AC/DC victron 25A charger as well, but raining so rather not.
Now:

 

[Brucey]

Is every negative going thru the smartshunt?

No ve.smart bt networks enabled on anything?

 

[WorldwideDave]

Is every negative going thru the smartshunt?

Yes.
Cerbo GX 'positive' source -->small Victron provided fuse -->positive bus bar
Cerbo GX 'negative' source -->negative bus bar

12VDC Battery positive -->t-class fuse-->60V kill switch-->positive bus bar
12VDC Battery negative -->Battery shunt-->negative bus bar
Battery shunt 'positive' source -->small Victron provided fuse -->positive bus bar
Battery shunt communications -->VE.Direct to Cerbo GX

MPPT 150/100 positive-->MRBF-->positive bus bar
MPPT 150/100 negative-->negative bus bar
MPPT 150/100 communications --> VE.Can to Cerbo GX

MPPT 250/70 positive-->MRBF-->positive bus bar
MPPT 250/70 negative-->negative bus bar
MPPT 250/70 communications --> VE.Can to Cerbo GX

Giandel Inverter positive-->MRBF-->positive bus bar
Giandel Inverter negative -->Inverter shunt-->negative bus bar
Giandel Inverter Shunt 'positive' source -->small Victron provided fuse -->positive bus bar, same post as inverter and Cerbo GX
Inverter shunt communications -->VE.Direct to Cerbo GX

No ve.smart bt networks enabled on anything?

Great question, thanks. No it is not. I will verify by connecting to each device (2 shunts - one for the inverter, one for the battery), and the MPPTs directly over bluetooth, as they are 'smart' and not 'blue'. Wish you could do that while on the LAN connected to VictronConnect instead of walking outside.

 

[Brucey]

What are the rest of your shunt settings?

 

[WorldwideDave]

Yes.
Cerbo GX 'positive' source -->small Victron provided fuse -->positive bus bar
Cerbo GX 'negative' source -->negative bus bar

12VDC Battery positive -->t-class fuse-->60V kill switch-->positive bus bar
12VDC Battery negative -->Battery shunt-->negative bus bar
Battery shunt 'positive' source -->small Victron provided fuse -->positive bus bar
Battery shunt communications -->VE.Direct to Cerbo GX

MPPT 150/100 positive-->MRBF-->positive bus bar
MPPT 150/100 negative-->negative bus bar
MPPT 150/100 communications --> VE.Can to Cerbo GX

MPPT 250/70 positive-->MRBF-->positive bus bar
MPPT 250/70 negative-->negative bus bar
MPPT 250/70 communications --> VE.Can to Cerbo GX

Giandel Inverter positive-->MRBF-->positive bus bar
Giandel Inverter negative -->Inverter shunt-->negative bus bar
Giandel Inverter Shunt 'positive' source -->small Victron provided fuse -->positive bus bar, same post as inverter and Cerbo GX
Inverter shunt communications -->VE.Direct to Cerbo GX



Great question, thanks. No it is not. I will verify by connecting to each device (2 shunts - one for the inverter, one for the battery), and the MPPTs directly over bluetooth, as they are 'smart' and not 'blue'. Wish you could do that while on the LAN connected to VictronConnect instead of walking outside.

All three devices (MPPT, MPPT, and battery shunt) are prompting to create or to join a network. Also, the Cerbo GX does not have the wireless access point option turned on. The inverter shunt does not list the networking as an option. I believe that is because it is in a different mode “DC Energy Meter” “Inverter” than a “battery meter” mode. Either way it doesn’t appear as an option for the IP 65 500 amp inverter the way I have it currently configured.

 

[WorldwideDave]

What are the rest of your shunt settings?

 

[Brucey]

This is the problem, it won't reset to 100% when it hits 14V


Change it to "Set to 100%"

 

[WorldwideDave]

This is the problem, it won't reset to 100% when it hits 14V
View attachment 284992

Change it to "Set to 100%"

Notice how it says 13.5 V and everything is in float and yet as you can see the state of charge is still really low. I will definitely try that. See attachment.

 

[WorldwideDave]

This is the problem, it won't reset to 100% when it hits 14V
View attachment 284992

Change it to "Set to 100%"

Ok did that and MPPT in float for both.
I guess I’m not sure what the setting you just had me change does. But I believe you. Isn’t the issue now that it is in float and it thinks that it’s charged? In other words, not likely to go back into bulk unless I drained down some of the battery?

 

[Brucey]

Ok did that and MPPT in float for both.
I guess I’m not sure what the setting you just had me change does. But I believe you. Isn’t the issue now that it is in float and it thinks that it’s charged? In other words, not likely to go back into bulk unless I drained down some of the battery?

The soc percentage doesnt affect the charging at all.

Basically with the previous setting, the shunt would detect when voltage hit 14V. But it never would reset back to 100%. Which is how you get strange things like 21% at 14.2V.

 

[Brucey]

Let it do a full charge cycle without any load for it to figure itself out.

 

[WorldwideDave]

The soc percentage doesnt affect the charging at all.

I did not think that it did - which is why it would sit at 0 percent and run for 30 minutes instead of killing the inverter. Cerbo GX would send out alerts and I'd rush out there and system would still be up and running. The voltage would be at 12V. Very odd.

Basically with the previous setting, the shunt would detect when voltage hit 14V. But it never would reset back to 100%. Which is how you get strange things like 21% at 14.2V.

thank you for explaining this. Though unsure how after I reset the shunt it got to that setting.

 

[WorldwideDave]

Let it do a full charge cycle without any load for it to figure itself out.

I would be happy to. Okay that DC loads are at 22W (idle consumption) while we wait for sun to come out and charge back up? The thing is that the current SOC reads 38%, but volts is reading 13.5.

It's been a cruddy day.


I wanted to see if running short load for a few minutes would change state. Here it is zoomed in. You can see that it went from float to bulk, but is reporting back in float right now.



What I can do is run down the battery for a bit, plug in a AC to DC charger, and just let that run until morning, and at some point, the SOC should reset to 100%?

 

[Brucey]

Just let solar do it's thing and at 14V the soc should reset to 100% yes idle load is fine.