T-Pain Is On A Boat: Re: [Electric Boats] Re: Building a lithium bank

Tuesday, April 24, 2012

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

1C would be emptying your pack in one hour. So in your case 1C would be 50ah cells at 144 volts for a 7200 watt pack. I have never even seen a LiFoPo cell that could not do at least 1C and I can't imagine with a 144 volt pack you would ever need 1C with any typical prismatic cells.

So the answer to do you need more then 1C not unless your planning on tiny 20 ah cells or something. With 20ah cells at 50a draw you would only be a little over 2C. But that is in spec on most prismatic cell anyways. So even then you would not have trouble finding 3c 20ah cells, if you wanted that little capacity.

With your 144 volt pack you can pretty much ignore C ratings, as at that voltage there is little chance you could ever draw enough amps to go over 1C. It is more of an issue with the folks using low voltage high amp motors.

For you it really just comes down to how much run time do you want. 100ah cells at 144 volts would be a 14.4kw pack. And you would be able to go full throttle for two hours! If that is enough run time for you then 48 100ah cells would do the trick. Figure about $6000. And you would run that pack at 1/2 C at your max 50amps. Or if that to pricey 50 ah cells would get you one hour at full throttle for half the price. If you got deep pockets 200ah cell would give you 4 hours at max speed! Just imagine that!

On Apr 24, 2012, at 1:06 PM, Steve Dolan <sdolan@scannersllc.com> wrote:

Thanks James for responding. Most of my questions were general in nature; I have a little bit different setup and will definitely be running a BMS. My Charger goes to the 144V pack and I have a PakTrakr and the HDM balancing system installed. My 144V pack then goes to a distribution strip where it can provide power to the 144V to 12V charger and the Advanced Motion Controllers for the motors so I think the BMS is required. The BMS system I purchase will both monitor and have the low/high voltage shutoffs. Currently my pack can be broken down to 72V for maintenance.

How about the C rating for a boat, 1C should do the trick correct? What would the recommended AH and Voltage for a 144V pack be since the max amperage of the motors is 50A?

Thanks again,

Steve in Solomons MD

Lagoon 410 SE

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