Multiplus II charge profile help

[Lasertrapper]

For my van build, I built 4 12v packs using 16 CATL 302ah cells, each pack has its' own JK 200amp BMS with 2amp auto balance. The 4 12v packs are wired in parallel to the Victron multiplus. I've cycled the system a few times first with modest load, then with moderately heavy load, and no surprises so far. I monitored the connections temp with a laser and all remained 105f or less, cell voltages are within 0.015 or less.
My question is whether the Victron charge profile should be set to LiFePO4 (which it currently is) since the 4 BMS are regulating the charge profile?

 

[sunshine_eggo]

For my van build, I built 4 12v packs using 16 CATL 302ah cells, each pack has its' own JK 200amp BMS with 2amp auto balance. The 4 12v packs are wired in parallel to the Victron multiplus. I've cycled the system a few times first with modest load, then with moderately heavy load, and no surprises so far. I monitored the connections temp with a laser and all remained 105f or less, cell voltages are within 0.015 or less.
My question is whether the Victron charge profile should be set to LiFePO4 (which it currently is) since the 4 BMS are regulating the charge profile?

BMS do not regulate charge cycles UNLESS they are interfaced with a Cerbo GX and in control of charging.

Otherwise, in almost all cases, BMS are ON/OFF switches (like your JKs). If you exceed any of the ratings, they cut you off.

The Victron LFP charge profile is 14.2V absorption, 1 hour and 13.5V float, and it enables low temp charge protection if a temperature sensor is present, and your firmware version is high enough. If your batteries are not triggering over-voltage protection, I would leave it as-is or even reduce absorption to 13.8V with a 4 hour duration to reduce charging stress and maximize cycle life, though I wouldn't do that in the case of generator charging. Stick with 14.2V or even bump it up to 14.4V and cut absorption time as low as it will go.

 

[Lasertrapper]

Thank you so much! I do have Cerbo GX and have been considering connecting my JK BMS's. Apparently can be done via RS485 dongle and some Venus script but looks not to be for the faint of heart.

Do you think it might be worth doing? I guess the suggested method is to do debugging via Raspberry Pi since mistakes can render the Cerbo GX useless?

 

[sunshine_eggo]

Thank you so much! I do have Cerbo GX and have been considering connecting my JK BMS's. Apparently can be done via RS485 dongle and some Venus script but looks not to be for the faint of heart.

Do you think it might be worth doing? I guess the suggested method is to do debugging via Raspberry Pi since mistakes can render the Cerbo GX useless?

GitHub - Louisvdw/dbus-serialbattery: Battery Monitor driver for serial battery in VenusOS GX systems

Battery Monitor driver for serial battery in VenusOS GX systems - Louisvdw/dbus-serialbattery

github.com

I used it with my JBD with a UART to USB adapter on a Raspberry Pi running Venus OS (poor man's Cerbo). According to the github, JK is the most frequently used BMS with that driver.

If you have the "Inverter" JK BMS, I don't know how that works.

 

[Lasertrapper]

Couple questions

How long can I leave batteries fully charged on Multiplus "float"?

One more question after much deliberation;
I have the 4 12v packs, each with its' own JK BMS parallel connected to the Multiplus via Victron Lynx (see picture). The setup is temporary to facilitate testing. The 4 packs will slide into a welded aluminum cage with 2 packs on top, 2 packs below. Each pack is surrounded with 3/16 Delrin sheet to prevent chafing, and is compression loaded so shouldn't move much if at all. The cage will be rigidly bolted to the floor and sidewalls of my van where space is at a premium.

Each pack is fused at 150amps via megafuse in the lynx, and current limited to 100amps via BMS. Because of space limitations, it would be extremely difficult to add either MRBF or fast class T fuses to the cables proximal to the battery packs. My question is this: if I add a warning placard that states to "MATCH STATE OF CHARGE BEFORE RETURNING ANY BATTERY PACK TO SERVICE," would I need another fuse for each pack?

 

[740GLE]

For 12v id fell fine with just the mega fuse per pack.

I wouldn’t add any other fusing.

As for matching SOC on each pack when connecting them, matching SOC is pointless. If I were you I’d match voltage .1v to .2v when connecting.

The JK BMS SOC tracking isn’t the best unless you hit 100% frequently, even then I have one JK that I can’t get to hit 100% even though each cell hits 3.45v and absorbs for 2hr.

As for the Multiplus and letting the batteries float, what are you float settings? I think if you leave the packs at 3.35v/cell with (zero current) indefinitely without damage and you’d be very very close to 100%.

Do you have a smart shunt to track SOC all 4 packs?

 

[740GLE]

For 12v i’d fell fine with just the mega fuse per pack. I use just mega fuses for my 24v packs.

I wouldn’t add any other fusing.

As for matching SOC on each pack when connecting them, matching SOC is pointless. If I were you I’d match voltage .1v to .2v when conencting.

The JK BMS SOC tracking isn’t the best unless you hit 100% frequently, even then I have one pack that won’t hit 100% even though each cell hits 3.45v.

For the multiplus what’s your float voltage? I’d set it for 3.375/cell and let it go.

 

[sunshine_eggo]

For 12v i’d fell fine with just the mega fuse per pack. I use just mega fuses for my 24v packs.

I wouldn’t add any other fusing.

As for matching SOC on each pack when connecting them, matching SOC is pointless. If I were you I’d match voltage .1v to .2v when conencting.

The JK BMS SOC tracking isn’t the best unless you hit 100% frequently, even then I have one pack that won’t hit 100% even though each cell hits 3.45v.

For the multiplus what’s your float voltage? I’d set it for 3.375/cell and let it go.

On the MP, it might be worthwhile to run a repeated absorption cycle every 7-14 days for an hour to give some balance time and reset to true 100%:

 

[Lasertrapper]

Thank you !!!!!!!

I will reword my warning placard, ""MATCH VOLTAGE BEFORE RETURNING ANY BATTERY PACK TO SERVICE"

 

[sunshine_eggo]

Thank you !!!!!!!

I will reword my warning placard, ""MATCH VOLTAGE BEFORE RETURNING ANY BATTERY PACK TO SERVICE"

Really... 0.2V is more than adequate. When you make the initial connection, the lack of clamping pressure means there's a lot of resistance, and there is very little current flow. It increases as you tighten nut/bolt and clamping force increases.

Andy put a 0% SoC cell in parallel with a 100% SoC cell, and while the current transfer was initially high, the voltage gap narrowed quickly, and the current became very reasonable.