Re: [Electric Boats] Re: Building a lithium bank

 

In regards to the needing or not needing a BMS.  If you are going to go the no BMS route only hook two things to your pack: the motor controller and make sure the low voltage cutoff is set high on it, and the charger and make sure the high voltage cutoff is set low.  Do not hook up anything else especially not a pack voltage to 12v transformer or any monitoring equipment that draws from the pack.  And plan on ever few months setting some time aside to check the balance of each sell.   One bad cell could cause a run away failure of cells other wise. 

With a per cell BMS you can be a lot more lax, as it would give you warning, and cut off charging if even one cell get to high or low. So you can set the low and high voltage cutoffs more aggressive.  Therefor getting more ah from the same pack. 

Either case works just depends on your comfort level doing the bi-monthly balance check. If I remember right you run a 144 volt pack so be extra careful when you are testing each cell.   If I were you and not going to use a BMS I would set your pack up so you can brake it down to 48 volt packs for the testing. 

Personally I run a BMS on my current EV because I really do not want to think about the pack when I am not using it.   But that just me. 

On Apr 18, 2012, at 10:23 AM, Steve Dolan <sdolan@scannersllc.com> wrote:

 

This is probably to Eric but anyone with input is welcome.
I have been at the Car forums mentioned and been looking at the replacement to my AGM's in hopefully a few years. At the DIY Car forum there are a few things I don't understand that may or may not apply to a boat.
In most cases the car is going to very in speed a lot more than a boat. Our usage maintains a rather linear use therefore a steady decrease in power over time. On the other hand a car starts and stops, coasts and accelerates much harder than a boat will see.
It seems that Car battery LiPo4 packs are exceeding the rated Voltages of the motor. Probably not the motor controller to a certain extent or damage would occur but it seems that people are adding batteries 10% to 15% above the rated pack voltage. A 48V pack may be increased to say 56V of batteries. I know that I bulk charge my AGM 144V pack to 174V. What is the thought behind this increase in batteries?
The Selection of Amp Hours seems to be all over the place. I see people buying 100AH batteries at a C4 or higher rating. Wouldn't the average boater be fine at a C1 Rating and 200AH batteries? Our discharge rate wouldn't be as high as cars since we wouldn't be drag racing the boat (At least not mine) and I tend to max out at 50A at the 144V. I must be missing something here.
As far as BMS's go, again we tend to be more linear in use and abuse. Since a lot of people are saying for a car BMS may not be necessary wouldn't this be more true with boats?
And then in general, what would differentiate a car pack from a boat pack in selection of batteries or for that matter even equipment when it comes to LiPo4's?

Thanks for your help on this.
Steve in Solomons MD
Lagoon 410 SE

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