Electrodacus <> Growatt Charge & Discharge Questions

Thersom1948 · Nov 24, 2020

I just finished my first charge / discharge cycle under real usage and I had a couple of very specific questions.

You can see my generator build here.

Settings:
Max charge V: 28.2
Max Discharge V: 24
SBMS0 cell Max V: 3.53

I do not have the SBMS0 wired in to control the Growatt on/off switch yet, so they are operting "independently" at this point (Meaning the SBMS0 can't do what it wants re:start/stop inverter yet.)

I've very new at this so please bear with me

1. The Electrodacus and the Growatt do not show precisely the same battery Voltage. Usually the SMBS0 shows 0.1 to 0.25V higher regardless of whether it's sitting or discharging. During charge they are closer. Is this normal?

2. Due to #1 the electrodacus hit's "overvoltage" before the Growatt thinks charging is finished. Growatt is just getting to 28.2 and SBMS0 is at 28.3 and cells at 3.56-3.59 (so above the 3.53 "OV" setting). Should I adjust the Growatt down to match what the SBMS0 is seeing, or vice versa? or just live with it as is?

3. The Electrodacus offers a "Balance on Discharge" setting that is disabled by default. Should I enable this?

4. I ask #3 because during Discharge, one cell (#8) is ALWAYS one that is highlighted as "receiving' balance charge - it is always 0.005-0.02 below the others. Is this an early sign of a bad cell? or a bad balance? I also wondered if it could be due to the connection - Cell #8 is main (+) positive, so the SBMS0 lead is on top of the main battery lead, whereas the other aren't - Could this cause a slight measurement difference?

5. If I have both devices Max Charge set at 28.2, am I effectively charging to 90% cell capacity, even though the SMBS0 monitor says "100% charged" ?

6. Likewise, if I have Max Discharge set at 24V, am I effectively discharging to 10% cell capacity?

7. When the Growatt cuttoff at low voltage of 24V, the SBMS0 was reporting 6% remaining even (again slightly higher V reading). Is this expected?

8. The SBMS0 reported 265Ah used from 100% down to the inverter cutoff. Does this sound right based on the above?

Thank you for any input!

Chris61 · Nov 24, 2020

Thersom1948 said:
I just finished my first charge / discharge cycle under real usage and I had a couple of very specific questions.

You can see my generator build here.

Settings:
Max charge V: 28.2
Max Discharge V: 24
SBMS0 cell Max V: 3.53

I do not have the SBMS0 wired in to control the Growatt on/off switch yet, so they are operting "independently" at this point (Meaning the SBMS0 can't do what it wants re:start/stop inverter yet.)

I've very new at this so please bear with me

1. The Electrodacus and the Growatt do not show precisely the same battery Voltage. Usually the SMBS0 shows 0.1 to 0.25V higher regardless of whether it's sitting or discharging. During charge they are closer. Is this normal?

2. Due to #1 the electrodacus hit's "overvoltage" before the Growatt thinks charging is finished. Growatt is just getting to 28.2 and SBMS0 is at 28.3 and cells at 3.56-3.59 (so above the 3.53 "OV" setting). Should I adjust the Growatt down to match what the SBMS0 is seeing, or vice versa? or just live with it as is?

3. The Electrodacus offers a "Balance on Discharge" setting that is disabled by default. Should I enable this?

4. I ask #3 because during Discharge, one cell (#8) is ALWAYS one that is highlighted as "receiving' balance charge - it is always 0.005-0.02 below the others. Is this an early sign of a bad cell? or a bad balance? I also wondered if it could be due to the connection - Cell #8 is main (+) positive, so the SBMS0 lead is on top of the main battery lead, whereas the other aren't - Could this cause a slight measurement difference?

5. If I have both devices Max Charge set at 28.2, am I effectively charging to 90% cell capacity, even though the SMBS0 monitor says "100% charged" ?

6. Likewise, if I have Max Discharge set at 24V, am I effectively discharging to 10% cell capacity?

7. When the Growatt cuttoff at low voltage of 24V, the SBMS0 was reporting 6% remaining even (again slightly higher V reading). Is this expected?

8. The SBMS0 reported 265Ah used from 100% down to the inverter cutoff. Does this sound right based on the above?

Thank you for any input!

Another newbie here with no expertise to speak of and using a 12v system, so only offering some of my settings. I have set charging to 13.8v, so well within upper limits and showing 99% charged, maybe somewhere to start

Thersom1948 · Nov 25, 2020

Chris61 said:
Another newbie here with no expertise to speak of and using a 12v system, so only offering some of my settings. I have set charging to 13.8v, so well within upper limits and showing 99% charged, maybe somewhere to start

Thanks for the data - So it sounds like the Electrodacus just flags whatever you set at Max Charge V to be 100% on the meter. Good to know!

Chris61 · Nov 25, 2020

Thersom1948 said:
Thanks for the data - So it sounds like the Electrodacus just flags whatever you set at Max Charge V to be 100% on the meter. Good to know!

I wouldn't say that. Set your limits conservatively. The Electrodacus is there as a safeguard if things go wrong

Thersom1948 · Nov 30, 2020

Chris61 said:
I wouldn't say that. Set your limits conservatively. The Electrodacus is there as a safeguard if things go wrong

Agreed. I'm setting my max charge V to 28.2

I'm saying from a programming perspective of the Electrodacus: Whatever you tell it is your Max Charge V is what it will make the charge meter show 100%

Set Max Charve V to 28.2. Charge to 28.2 = Electrodacus Meter says 100%
Set Max Charge V to 29.0. Charge to 29.0 = Electrodacus Meter says 100%

Chris61 · Dec 1, 2020

Thersom1948 said:
Agreed. I'm setting my max charge V to 28.2

I'm saying from a programming perspective of the Electrodacus: Whatever you tell it is your Max Charge V is what it will make the charge meter show 100%

Set Max Charve V to 28.2. Charge to 28.2 = Electrodacus Meter says 100%
Set Max Charge V to 29.0. Charge to 29.0 = Electrodacus Meter says 100%

What I did
Set max charge to 14.1v Charge to 13.8v = Electrodacus Meter says 99%
If I disconnect BMS, I have to charge towards 14.1 to set 100%, as it resets on 49%
BMS only triggers if stuff goes wrong, cell delta stays mostly in single digit figures

Close enough for me, others may not agree

FilterGuy · Dec 1, 2020

Thersom1948 said:
1. The Electrodacus and the Growatt do not show precisely the same battery Voltage. Usually the SMBS0 shows 0.1 to 0.25V higher regardless of whether it's sitting or discharging. During charge they are closer. Is this normal?

.1V difference between two different meeters is not at all unusual. .25V difference is a bit high but certainly not unheard of.
It could be due to voltage drops across wires and connections. Do they agree when the system is static (No charge or discharge)?

Thersom1948 said:
2. Due to #1 the electrodacus hit's "overvoltage" before the Growatt thinks charging is finished. Growatt is just getting to 28.2 and SBMS0 is at 28.3 and cells at 3.56-3.59 (so above the 3.53 "OV" setting). Should I adjust the Growatt down to match what the SBMS0 is seeing, or vice versa? or just live with it as is?

You want your chargers to stop before the BMS does. You may need to adjust the two devices to have a wider gap. Perhaps set the SBMS0 to 28.5 or so. The other option is to drop the Growatt voltage.

This is a classic tradeoff problem. To get the most out of your batteries you want the set the voltages as high as possible. However, the higher you set your charger voltage, the less wiggle room you have for setting the BMS system and voltage settings.

BTW: Did you balance the cells? Balanced cells can help with setting small gaps between the charger and BMS settings.

Thersom1948 said:
3. The Electrodacus offers a "Balance on Discharge" setting that is disabled by default. Should I enable this?

I don't usually turn on Balance on Discharge.....but would be hard pressed to explain why.

Thersom1948 said:
4. I ask #3 because during Discharge, one cell (#8) is ALWAYS one that is highlighted as "receiving' balance charge - it is always 0.005-0.02 below the others. Is this an early sign of a bad cell? or a bad balance? I also wondered if it could be due to the connection - Cell #8 is main (+) positive, so the SBMS0 lead is on top of the main battery lead, whereas the other aren't - Could this cause a slight measurement difference?

It could be a number of things. You mentioned a couple possibilities. It might just be a mismatched cell. I would adjust your voltages to make the system work and then watch that cell.... it keeps getting worse it might be bad.

Thersom1948 said:
5. If I have both devices Max Charge set at 28.2, am I effectively charging to 90% cell capacity, even though the SMBS0 monitor says "100% charged"

The charge curve is sooooo flat it is hard to put an exact percentage on 28.2V, but it is definitly not 100% charged. The SMS0 is measuring the current in and out and figuring out when it should be full.... It probably set itself to 100% when it hit the over-voltage cut-off. Consequently, it thinks the battery is fully charged even though there is a little room left in the cells for more.

Thersom1948 said:
6. Likewise, if I have Max Discharge set at 24V, am I effectively discharging to 10% cell capacity?

The charge curve is so flat it is hard to put an exact percentage on 24V, but it is definitely not 100% discharged.

Thersom1948 said:
7. When the Growatt cuttoff at low voltage of 24V, the SBMS0 was reporting 6% remaining even (again slightly higher V reading). Is this expected?

That is probably about right... When you set up the SBMS0, you told it the Ah of your battery bank. The SBMS0 counts the Ah in and out to calculate what is left.

Thersom1948 said:
8. The SBMS0 reported 265Ah used from 100% down to the inverter cutoff. Does this sound right based on the above?

Without knowing the Ah of the battery, I can't tell.

Thersom1948 · Dec 3, 2020

Thank you for the detailed answers!!

FilterGuy said:
.1V difference between two different meeters is not at all unusual. .25V difference is a bit high but certainly not unheard of.
It could be due to voltage drops across wires and connections. Do they agree when the system is static (No charge or discharge)?

Not really - pretty much always 0.1-0.25 difference. They are closest when it is Utility charging.

and weirdly - the SMBS0, with the tiny tiny wires on the shunt, reads 0.1 to 0.25 HIGHER than the 1/0 welding cable going to the Growatt that are my main battery leads. How would those massive cables than are less than 12 inches each be showing that much voltage drop when the tiny SMBS0 leads don't?

FilterGuy said:
You want your chargers to stop before the BMS does. You may need to adjust the two devices to have a wider gap. Perhaps set the SBMS0 to 28.5 or so. The other option is to drop the Growatt voltage.

This is a classic tradeoff problem. To get the most out of your batteries you want the set the voltages as high as possible. However, the higher you set your charger voltage, the less wiggle room you have for setting the BMS system and voltage settings.

Got it. I may lower the Growatt down to 28.0 for now. I don't need to pull full capacity all the time, this is just a backup / light load system.

FilterGuy said:
BTW: Did you balance the cells? Balanced cells can help with setting small gaps between the charger and BMS settings.

Yes - I balanced with a desktop power supply up to 3.55 until current dropped to zero. I even let them rest overnight and then did it again, twice.

FilterGuy said:
I don't usually turn on Balance on Discharge.....but would be hard pressed to explain why.

haha, ok - Maybe I will email Dacian and ask him.

FilterGuy said:
It could be a number of things. You mentioned a couple possibilities. It might just be a mismatched cell. I would adjust your voltages to make the system work and then watch that cell.... it keeps getting worse it might be bad.

I should have mentioned even though #8 is always the different one, the total delta between all cells as reported by the SBMS0 is almost always just 7-12mv.

I will try adjusting the charge V and putting the BMS lead under the Main Positive Lead (so directly touching the Main Positive battery terminal) and see if that changes anything.

FilterGuy said:
The charge curve is sooooo flat it is hard to put an exact percentage on 28.2V, but it is definitly not 100% charged. The SMS0 is measuring the current in and out and figuring out when it should be full.... It probably set itself to 100% when it hit the over-voltage cut-off. Consequently, it thinks the battery is fully charged even though there is a little room left in the cells for more.

Perfect - that's exactly what I want it to do. I don't need to max out capacity right now.

FilterGuy said:
The charge curve is so flat it is hard to put an exact percentage on 24V, but it is definitely not 100% discharged.

That is probably about right... When you set up the SBMS0, you told it the Ah of your battery bank. The SBMS0 counts the Ah in and out to calculate what is left.

Excellent! That's exactly what I want.

FilterGuy said:
Without knowing the Ah of the battery, I can't tell.

280ah 24V. 8 EVE 280AH cells in 8S

FilterGuy · Dec 3, 2020

Thersom1948 said:
...and putting the BMS lead under the Main Positive Lead

Do *not* put the bms lead under the main. It is very unlikely to make a difference and would create a poor connection for the main lead.

Thersom1948 · Dec 3, 2020

I emailed Dacian of Electrodacus and he said I could post his responses here for the community:

My email:

quick question for you

System: 8 EVE 280AH cells in 8S. Growatt24V SPF3000TL.

The SBMS0 and the Growatt never show the same battery Voltage. Usually the SMBS0 shows 0.1 to 0.25V higher regardless of whether it's sitting or discharging. During charge they are closer but still off. Is this normal?

This is obviously causing problems with charging and OV cutoff. The SBMS0 is showing OV at 28.3 (3.56-3.60 per cell) when the Growatt has not even gotten to 28.2 yet and is still charging.

I'm using a 300A shunt (to meet the 66% rule), and 1/0 welding cable for the main battery leads that are less than 12 inches, so I think V drop is minimal.

His response:

Growatt has lower accuracy as it is not that critical since it was designed for Lead Acid and under load it will be normal for it to read lower due to some voltage drop on the cables.

Growatt is a close on MPP Solar and has no remote ON/OFF for charging so you can not charge with that unless you add a solid state relay on the AC input line and allow the SBMS0 to control that with the EXT IO4 set as type 1

The only inverter charger that was designed for Lithium is Victron Multiplus and that has separate remote ON/OFF for inverter and charger and can work as a proper UPS details about that here https://www.victronenergy.com/uploa...battery-systems-to-Multis-and-Quattros-EN.pdf

The SBMS0 need to be able to control ON/OFF all charge sources and what happens since you do not have the remote ON/OFF for the charger is that cells are overcharged (go above the 3.55V limit) and likely secondary limit is reached the overvoltage Lock and that will turn your inverter OFF as if Over voltage lock is reached it means there is a hardware fault (in your case incorrect installation) so it will turn OFF also the Load's so the EXT IO3 set as type 2 that should only control the inverter part.

So you need to find a way to allow the SBMS0 to control the charger. The simple option as mentioned is a Solid State Relay in series with the AC input line controlled by EXT IO4 thus allowing SBMS0 to stop the charging by disconnecting the AC input. This is not as elegant as the Victron Multiplus where AC input remains connected and only battery charging is stopped.

I'm having a little trouble parsing all of his responses.

FilterGuy · Dec 3, 2020

FilterGuy said:
Do *not* put the bms lead under the main. It is very unlikely to make a difference and would create a poor connection for the main lead.

FYI: The primary current path is between the pad and the flat of the lug. Some current will flow through the stud, but the stud is there to mechanically hold the lug down on the pad, not carry current. If there is anything between the lug and the pad, it adds resistance and that is a bad thing.

Thersom1948 · Dec 3, 2020

Thersom1948 said:
I emailed Dacian of Electrodacus and he said I could post his responses here for the community:

My email:

His response:

I'm having a little trouble parsing all of his responses.

If I am reading him correctly, I should:

1. Connect SBMS0 EXTIO3 to Growatt Inverter On/Off switch to disable inverter at High or Low Voltage. (This I knew, seen in Will's video)

2. Connect solid state relay from SBMS0 to EXTIO4 to AC Input to Allow SBMS0 to control AC charge and disable on OV.

FilterGuy · Dec 3, 2020

Thersom1948 said:
I'm having a little trouble parsing all of his responses.

OK.... let me try to expand on it.

>Growatt has lower accuracy as it is not that critical since it was designed for Lead Acid.
Lead acid batteries are less sensitive to minor voltage differences so the accuracy of the volt meter can be less.

>under load it will be normal for it to read lower due to some voltage drop on the cables.
The cables have a small resistance, so the current running through the cables will create a small voltage drop. If you put a volt meter on the cable, you would see a small voltage between the battery connection and the inverter connection when the system is under load. The higher the load, the higher the voltage drop.

>The only inverter charger that was designed for Lithium is Victron Multiplus and that has separate remote ON/OFF for inverter and charger and can work as a proper UPS details about that here https://www.victronenergy.com/uploa...battery-systems-to-Multis-and-Quattros-EN.pdf
I would not go as far as to say it is the only inverter/charger that was designed for Lithium, but it is the only one I know of that works really well with the way the SBMS0 is intended to operate. It is the only one I know of that can be set up with an external signal to turn charge on and off and a separate external signal to turn the Inverter function on and off. The other inverters have no external signal or an external signal that turns both the charger and inverter on/off.

>The SBMS0 need to be able to control ON/OFF all charge sources and what happens since you do not have the remote ON/OFF for the charger is that cells are overcharged (go above the 3.55V limit) and likely secondary limit is reached the overvoltage Lock and that will turn your inverter OFF as if Over voltage lock is reached it means there is a hardware fault (in your case incorrect installation) so it will turn OFF also the Load's so the EXT IO3 set as type 2 that should only control the inverter part.

Hmmm... that is one big run-on sentence. I think it boils down to this: Since the SBMS0 is not controlling the charge function, the batteries are getting over charged.

> So you need to find a way to allow the SBMS0 to control the charger. The simple option as mentioned is a Solid State Relay in series with the AC input line controlled by EXT IO4 thus allowing SBMS0 to stop the charging by disconnecting the AC input. This is not as elegant as the Victron Multiplus where AC input remains connected and only battery charging is stopped.

He is saying to turn off the charge function by switching off the AC in. That is an interesting solution, but it means that you can not use the AC in once the batteries are full.

FilterGuy · Dec 3, 2020

Thersom1948 said:
If I am reading him correctly, I should:

1. Connect SBMS0 EXTIO3 to Growatt Inverter On/Off switch to disable inverter at High or Low Voltage. (This I knew, seen in Will's video)

2. Connect solid state relay from SBMS0 to EXTIO4 to AC Input to Allow SBMS0 to control AC charge and disable on OV.

That sounds about right.

FilterGuy · Dec 3, 2020

FilterGuy said:
> So you need to find a way to allow the SBMS0 to control the charger. The simple option as mentioned is a Solid State Relay in series with the AC input line controlled by EXT IO4 thus allowing SBMS0 to stop the charging by disconnecting the AC input. This is not as elegant as the Victron Multiplus where AC input remains connected and only battery charging is stopped.

He is saying to turn off the charge function by switching off the AC in. That is an interesting solution, but it means that you can not use the AC in once the batteries are full.

Actually, as I think about it, it might not be as bad as I thought. Once you get your voltages adjusted, the inverter/charger should cut out before the SBMS0 does. Consequently it should be a rare event that the SBMS0 cuts off the AC into the Inverter/charger.

Thersom1948 · Dec 4, 2020

@FilterGuy thank you for all of the detailed responses, I really appreciate it!

I'm exploring the AC/DC solid state relay, but all of the AC ones of sufficient amperage or crazy expensive. Like $200-$400.

I think I'll just adjust the charge voltage on the Growatt and live with it. I manually charge via any AC anyway, I never just plug it in and leave it all the time. My installation is semi-portable, it's not grid-tied.

HeartNSoul · Jul 22, 2021

So has anyone gotten a SBMS0 or DBMS40 to work with a Growatt?
I am building my 24V system right now and Ian, where I got my Growatt, says the Growatt doesn't work with any BMS ( I have a SBMS40 ), that I should just have them both run seperately as stand alones? What did you end up doing? How did it work? Are your batteries protected from solar panel charging over voltage?
I have 8x 3.2 280Ah Lichen LiFePO4s
Appreciate any response.

HeartNSoul · Jul 24, 2021

I meant "SMBS40" not DBMS40 in my question: "So has anyone gotten a SBMS0 or DBMS40 to work with a Growatt?"

Electrodacus <> Growatt Charge & Discharge Questions

Thersom1948

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FilterGuy

Solar Engineering Consultant - EG4 and Consumers

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