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avontuur avatar image
avontuur asked

settings for a lithium system

New to a recently installed and working lithium system on a canal barge and trying to understand the interplay of all the settings.

I have installed a Multiplus 12/3000/120 with 2-wire assistant controlled by the 123SmartBMS, 3x Smartsolar MPPT 100/50s, about 1660 watts of solar, BMV712 controlling an EV200 main bus shut off solenoid, BP220 to control the PV charge wired as a relay controlled from the 123SmartBMS and BP100 set up to control 12v loads, 123SmartBMS, 800 Ah of Winston cells in a 2p4s configuration.

The Multiplus was set up with the 2-wire assistant and the default lithium settings of Abs 14.2v and Float 13.5v; the 123SmartBMS was set to default Vmin 2.95v, Vmax 3.45v, Vbypass 3.4v. MPPTs to Lithium setting.

Charge Restart 95%, Discharge Restart 20% .I really don't understand what these mean in practice in terms of cell voltage. Please help.

The battery hovered around the float voltage of 13.5v.

With the above settings and connected to shore power the battery discharged from about 13.5v (3.5v/cell) to 13.0v more quickly than desireable and did not increase in voltage above the absorption setting of so a lot of potential power went unrealized.

I then raised the 123SmartBMS to Vmax and Vbypass each to 3.5 v/cell (battery voltage 14.0v) and the Multiplus to Abs 14.2v and Float 13.80v which gave me a greater capacity for discharge.

Now the battery hovers around the float votage of 13.80v (shore power).

When switching on the solar to this installation (and disconnecting shore power) from a battery charged to 13.8v I have to wait until the battery discharges down to 13.23v before the 123SmartBMS charge relay switches on to charge the battery from the PV panels. The problem is that by this time I have missed all the morning sunshine that could have been pouring into the battery.

What needs to be done to take advantage of all the day's sun?

Thanks in advance, I have found this site very helpful for my design.


BMS
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Bump.

"Charge Restart 95%, Discharge Restart 20%"

These would seem to be set the wrong way around?

Are you only using the 123SmartBMS, and not a CCGX/Venus with ESS/assistants?

13.8 float voltage is too high. Maybe set the mppt at 13.5v, and the Multi at 13.4v.

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avontuur avatar image avontuur klim8skeptic ♦ commented ·

@klim8skeptic

Thanks for the reply.

I forgor to add to my list that I do have a Venus GX to integrate all the readings.

The Load and Charge relays of the 123SmartBms go through opto-isolators and controlt the Multiplus through the 2-wire assistant and also seperately control the remote switches of a BP220 for charging from PV panels and also a BP100 to control 12v loads.

The boat is mainly set up with 240v AC use with navigation lights and instruments run at 12v.

The Mutiplus consistently reports that 13.8v is too high yet the manual of the 123SmartBMS battery curve indicates that the cel l Vmax to be 3,.5v ( x4=14.0v) and Vbypass to be 3.45v ( x4=13.80v) and Vmin to be 2.8v although 2.8v seems rather low for safety and looking at the battery curve 3.38/3.30v would seem safer for Vmin.

Link to 123SmartBms manual :

https://123electric.eu/wp-content/uploads/2018/07/123SmartBMS_manual_1v3.pdf

Your link to the battery curves from Shenzen also show a max cell voltage of 3.5v at 100% SOC and 3.4v at 10% SOC

I have not looked at ESS assistants because I thought they were only for grid-tied installations. My installation is designed to be stand alone (as on a boat) and to use shore power if available.

Are there any other assistants that could help me?

Cheers

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kai avatar image kai ♦ commented ·

Do you have a link to your cell's nominal SOC vs V curve from the manufacturer? There may not be much energy stored in the voltage range above 3.4v or so. There's a plateau in the curve which is where the bulk of the energy is stored. Once you go above that, the charge and discharge actions will result in relatively large changes in voltage but not much change in terms of actual capacity.

Any optimisation needs to be with reference to what the cell chemistry can support.

Also, check the absorption voltage. The victron defaults iirc are for victron smart lithiums which have integral electronics and the voltage range is not identical to bare cells. I can't find the relevant docs, someone else might correct me on this.

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adev answered ·

As the others have said, there’s a plateau in the discharge voltage curve and not much energy above 13.3 or so.


And 13.8 is indeed too high as a float voltage. Lithium should not have a float charge at all in the way lead acid does, so a 13.5v float is effectively switching float stage off, as it should be.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

Winston cells are readily available.

Info is available, but you need to understand the voltage differences at different C rates. http://en.winston-battery.com/index.php/products/power-battery/item/wb-lyp400aha?category_id=176


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