24v 2000ah parallel wiring issue

[JaredG]

I’m new and looking at upgrading my boats house battery to lithium from 1300 ah of agm to 2000 or more of lithium. System is 24v and I am looking at using 24v batteries if possible for simplicity. Most 24v batteries I look at are 100 to 200ah and and don’t recommend more than 4 batteries in parallel which does not meet my total needs. What hardware or systems including any separate BMS will I need to research and implement to build a larger system? Currently I have victron multiplus 5kw and cerbo and about 3000watts of solar and victron mppts going to my agm bank. Also open to suggestions for good marine 24v batteries and any diagrams/sizes between batteries and inverter if fuses/busbars/switches are recommended. I have 16kw genset going to inverter for charging as well as the solar is usually not enough for usage needs.

 

[robbob2112]

The reason they don't want you to parallel more than 4 batteries is the BMS can't shutdown if there is a problem. I.e. if a cell in one battery shorts the other 3 dump current into it. The mosfets on the batteries can't handle that much current/voltage and turn it off. So you end with a vent and a fire.

To get more than 4 in parallel, we'll consider it for any parallel, you need a class T fuse on the positive wire from each battery to the bus bar used to bring them together. This way if the fault from above happens the class T with a high AIC is capable of blocking the arc that would happen.

If you dig through other batteries with the same limit it will say the overcurrent protection will be exceeded.

If I did say 8 in parallel I would use a class T for each and also put a contactor on each with all the coils controlled by switches so I could shut the whole thing down at once or one at a time to work on them.

Something like this

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

Basically I would do a control panel with a master switch plus a switch for each. The contactors are NO so if power is removed from the coil they disconnect.

I would also add some kind of automatic precharge circuit to charge the inverter caps anytime any battery is connected.

1300ah x 25.6 = 33280Whrs * .5 (usable capacity) = 16640Whrs usable

25.6 x 230 = 5888Wh

So you would need 3 of them, or 4.. you can run them from 100% to 0%, but will get better life stopping at 20%... so still way more than the AGM can provide

23552Wh From 4.. $3744... and you don't exceed the 4 limit.

Post in thread 'Li Time 24v 230ah 20% off until Nov 11'

Oct 31, 2024

Ok, that is a good deal...

Litime black Friday month of deals should start soon. I got some very good deals then too.

• robbob2112

• 

If you want to build from scratch you need to understand bus bars, bms, cells, cabling, compression, and a few other topics.

You will need a YR1035 meter, a good dmm preferably a clamp meter that reads DC amps and inrush, torque screwdriver and wrench, bench powersupply, and a few other bits. And a thermal camera.

There is a forum that is just about diy batteries, read up... and realize while it isn't hard to do but you are risking a fire or explosion if you aren't perfect.

DIY LiFePO4 Battery Banks

Advanced user discussion on BMS/ Cell Configurations/ Temperature Regulation/ Cell Sources and more

diysolarforum.com

 

[l00semarble]

I’m new and looking at upgrading my boats house battery to lithium from 1300 ah of agm to 2000 or more of lithium. System is 24v and I am looking at using 24v batteries if possible for simplicity. Most 24v batteries I look at are 100 to 200ah and and don’t recommend more than 4 batteries in parallel which does not meet my total needs. What hardware or systems including any separate BMS will I need to research and implement to build a larger system? Currently I have victron multiplus 5kw and cerbo and about 3000watts of solar and victron mppts going to my agm bank. Also open to suggestions for good marine 24v batteries and any diagrams/sizes between batteries and inverter if fuses/busbars/switches are recommended. I have 16kw genset going to inverter for charging as well as the solar is usually not enough for usage needs.

2,000ah * 25.6v = 51kwh of energy. That is a LOT for a system with just a 5kva inverter and 3kw solar. How big is this boat? What you running? How will you use the boat and what are the goals of the system? I'm trying to imagine the scenario where a battery this large relative to that inverter and PV makes sense. We have no details on your situation so I may be making assumptions that are worthless.

You mention that solar does not meet your needs and you have to run the genset. The multiplus 5kva has a 120A charger, right? So if you have 2,000ah that is a 0.06C charging rate which is trivial. If you draw that battery down to 20% SOC you would need to put back 1,600ah. Even if the Multiplus could do 120A consistently (which it can't) it would take 13.3 hours of genset run time to recharge to 100%. In reality this could take 15-17 hours of generator time. Why not just run the generator once per day rather than wait and run it for excessive periods later? You need to create all the power you use either way so why not settle into a 24 hour rhythm and save money/space/weight on an oversized battery. The battery does not create energy, it only stores it.

Of course there are use cases such as "I like to leave the dock on Friday morning and not have to think about power until I get back to the dock on Sunday night." "As long as I can get through three days I can recharge when back at dock. "

But if full time cruising (off the dock) I see a point at which a larger and larger battery doesn't really improve the situation. You would be better off spending the money on more Solar (if it could fit somewhere.)

But to answer your original question the Victron Smart Lithium NG (next generation) batteries are able to be done up to 50 in parallel. They have a massive 24v/300ah battery so 6 or 7 of them in parallel would get you the bank you want. And they are nice too because even though many in parallel there is only one BMS controlling everything incluidng monitoring/balancing every cell.