Building 4 x 3P8S 24v battery-pack from 96 Fortune cells

[BillCaswell]

Hello All,

Due to the access to the battery box in my sailboat, I am working through plans to build 4 battery packs. Each pack will be configured for 24 volts and consist of 24 Fortune cells. 4 batt packs x 24 cells/pack = 96 cells. The attached diagram shows my thinking on how to wire each cell together for a 24 volt configuration that will easily fit through the access under the nav station. The size of the battery pack is similar to the LifeLine 8D size batteries. The weight is similar so the pulley system (not shown) will work.

I am looking for some suggestions: (I'm peddling as fast as possible to come to speed... including searching the DIY forum for previous discussions)

- Does this arrangement of 3P8S look correct? I found some examples online so followed the same pattern.

- Each cell can produce 2C or 200 amps continuous. Does 3P8S mean that each battery will provide 600 amps continuous at 24 volts?

- Is my thinking correct that I need to find cells-to-cell bus bars that can handle 200 amps or do I need to use higher capacity bus bars because the batteries will provide 6C peak for 10 seconds? Suggestions?

- I plan to use contactors controlled by a BMS to protect each battery. I am looking at the REC BMS with their slave units unless there are other recommendations to look at? I have been reading the DIY Solar forums and am overwhelmed by the many choices and people suggesting their favorite BMS.

- Lastly, because I need to lower each battery down into the battery box, I need to make boxes for each of the four battery groups. I'm trying to decide between aluminum, 316 stainless steel as each battery will weigh nearly 160 lbs. Thoughts and any suggestions for sourcing the boxes other than going to a local metal fabricator?

- I want to use as much UL components as possible, making sure to build these packs to ABYC and USCG standards. Does anyone have experience with this? Gotchas or advice?

- I am repeating some of the same questions from my thread in the Beginners Forum but I think that I've made progress in my understanding, so wanted to post in this thread where I saw similar questions.

Thanks in advance for any guidance or suggestions!

 

[time2roll]

Yes three in parallel with each rated 200 amps means 600 amps potential from each battery. Although will be limited by the BMS. And at 2C they will be flat dead in less than 30 minutes. Best to fuse the battery to limit the current to the components used.

 

[MisterSandals]

because the batteries will provide 6C peak for 10 seconds? Suggestions?

Lemme guess...

Search results for query: bow thruster

diysolarforum.com

 

[BillCaswell]

Lemme guess...

Search results for query: bow thruster

diysolarforum.com

sorry, not sure that I understand your point.

 

[MisterSandals]

sorry, not sure that I understand your point.

I did not mean to be cryptic, sorry. The sailboat questions that include drawing really high amps are often for bow thrusters. I provided a link to the threads about bow thrusters. It was a guess on my part.

 

[BillCaswell]

I did not mean to be cryptic, sorry. The sailboat questions that include drawing really high amps are often for bow thrusters. I provided a link to the threads about bow thrusters. It was a guess on my part.

Ah, got it. Sometimes, I am too literal.

Yes, I need to power a box thruster that is powered by the house bank. It is a bit of a beast. It's a 20hp electric motor powering a 14 kw hydraulic bow thruster. The motor draws 650-700 amps when running. The use of the bow thruster is normally limited to 3-10 second bursts.

I also need to factor in the startup and inrush current. I've spoken to a friend that is more knowledgable about electric motors and such (he runs an avionics shop and works on commercial aircraft) and thinks that the inrush current is likely running current + 40%, or 980-1000A for a few milliseconds until the motor overcomes its inertia and starts spinning. The motor is fed by two x 4/0 battery cables, drawing 325 amps each protected by 400 amp fuses. If I'm mistaken, 4/0 battery cable is rated at 440 amps.

I'm looking for a BMS system that can handle this load, so have bought the KikoVac 500 amp contactors. I will run two in parallel.