Want advice on high current demanded 24V 280AH

[draghixa]

Hi all, need advice on high current demanded 25.6V 280AH battery bank for my boat bow thruster. The thruster motor is 24V and will pull up to 300A. My question is, should I build
a) one single 25.6V 280AH with 8 280AH cells in series and 400A BMS or
b) two 25.6V 140AH with 8 140AH cells in series and 200A BMS, and then connect them in parallel to install in boat?
Just want to know which option is better or safer for my case, thanks very much!

 

[snoobler]

In addition to BMS limits, cells themselves have limits. The typical LFP cell has a 1C discharge limit. In your examples, your 300A load exceeds the current limit of all cells.

Many cells allow for a transient "burst" of high current for short duration, and the 300A may be in this limit.

Additionally, motors have surge associated with them. Surge current is often 3-10X above the operating current. If 300A is the surge as measured by a clamp meter capable of "INRUSH" measurements or the absolute maximum current as specified by the manufacturer, then you're good. If you're uncertain of the actual inrush current, you need to nail that down.

 

[draghixa]

300A is very likely continuous current, may be I should make it 400Ah with 200Ah cells.

If using 200Ah cells, which layout would you suggest, 2p8s or 8s2p? I wouldn't mind to use 2 BMS if 8s2p is the better option, thanks for your advice.

 

[snoobler]

I would suggest you contact the manufacturer of your bow thruster to establish your actual design criteria.

 

[rotortalk]

Personally, I would select a BMS that uses contactors not MOSFETs, so you can get a nice chunky power draw without worrying about blowing up the BMS. Secondly, I would actually consider combining your house and bow thruster batteries, and running long chunky cables to the bow. I know a lot of boats put a separate bow thruster battery up front, for lots of good reasons. Voltage loss being the primary and weight distribution being a consideration, BUT having lots of lovely storage (6kWh) up front just to power the occasional use of the bow thruster seems such a waste. Convert your entire house bank to Li-ion and as I said, run chunky cables to the bow. You'll get the pleasure of a nice big house bank for extended periods at anchor and it will easily cope with your occasional 300A draw from the BT.

 

[Luthj]

The issue with multiple parallel BMS, is that if one drops out, or the current is balanced, then you can get a cascade overload, resulting in system failure due to a single failure point.

How is your bow thruster controlled? Does it have its own contactor set for switching current? If so, you might be able to route the contactor control power through the BMS, but not have the BMS carry the thrusters load. This has some risks, but you would know if the thruster was firing erroneously.

Since bow thrusters aren't run for very long, you can probably use a 280AH pack with contactor based BMS. Or if the thruster already has relays/contactors which you can control with the BMS main output, you may be able to chain those into the BMS scheme.

Is this thruster safety or mission critical? If so you may need to bypass the BMS for the load. For example have the thruster relay control switch powered through the BMS, but have a bypass/override switch for emergencies.

 

[CaptGregR]

I’ve been studying this also because my thruster is similar to yours, a 24v 8,000w which means it’ll be pulling 333A. If you look at most of the Lith batt specs it says that it’ll provide 1C continuous or 2C for 60 secs. At 280AH x 2C you should have the ability to supply short current demand of up to 580A. At least that’s the theory I’m building my system on. Hope it works!

 

[eXodus]

What about adding a Capacitor to reduce the inrush current? How long time of this high amps are you looking at?

Other idea: add a lead battery, those things can handle 5-10C discharge easy and recharge it with the lithium bank.

 

[DerpsyDoodler]

Hi all, need advice on high current demanded 25.6V 280AH battery bank for my boat bow thruster. The thruster motor is 24V and will pull up to 300A. My question is, should I build
a) one single 25.6V 280AH with 8 280AH cells in series and 400A BMS or
b) two 25.6V 140AH with 8 140AH cells in series and 200A BMS, and then connect them in parallel to install in boat?
Just want to know which option is better or safer for my case, thanks very much!

This same topic is being discussed here, as well. May be worth it for y’all to work together in your research here.