[salva]

Hello, I am collecting info and stuff to start on an E-Boat proyect, she is a 7mtrs boat with a 1.5ton displacement. My plan is to get the following performance:

Max speed: 5 to 6 knots
Range at optimal speed: 10 to 12 miles

To get that I plan to use a 10Kw/h 48V battery pack, motor will be an small 8Kw AC motor with a curtis controler.

I have two option on batteries, either going to a EpZS (traction) battery bank with 24 2V cells, or going to 4 big AGM 270Ah battery set. Either case the weigth is around 300Kg.

What is the preferred tecnology AGM or Traction battery?

In case of AGM I have seen that many people use BMS to get an equal charge when using several AGM's in series. Does 4 batteries in series still need BMS under your experience?

In forklift application with big 2V cells I have never seen a BMS, just raw charger voltage applied to the pack, why do you think they don't use BMS?

Thanks for your help.

 

[Alexander_B]

first the bms question: because AGM's are sealed, they can't vent gas, and you can't add water. this means you can't purposefully overcharge them to equalize them (and then add water back to fix the cell balance) therefore, a computer system that checks the level of charge on the batts to see if one isn't overcharged (wich could lead to expensive damage) for a 4 agm setup tho, its not really a point, easy way out would be to use 4 seperate 12v chargers (modified to not make a ground fault from one batt to the next)

on with the traction versus agm. agm's require little maintenance, only a float charge if left for long periods, and you can use about 60-80% of the rated capacity per charge, this way they will last about a 1000 cycles. (if you use more, the life is strongly reduced, this goes for all lead based batteries) traction batteries can/should only be used to <50% of their rated capacity, but if you take care and maintain them well, they will have a long and healthy life, perhaps even up to 3000 cycles and over 10 years, if you have quality thick plate traction batteries and maintain them well. you take a pick, service life versus ease of maintenance.

 

[DIYguy]

In case of AGM I have seen that many people use BMS to get an equal charge when using several AGM's in series. Does 4 batteries in series still need BMS under your experience?

http://www.hdm-sys.com/products/equalizer.php

In forklift application with big 2V cells I have never seen a BMS, just raw charger voltage applied to the pack, why do you think they don't use BMS?

forklift batteries are flooded. They boil them to equalize.

 

[GerhardRP]

In a boat, I wouldbe very concerned about spillage in rough seas. Go with sealed batteries.