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Discussion Starter #1
Hey all,

I have been doing some research on EV's over the past couple of months and I feel like I am finally ready to build my project, a small electric boat.

Planning on fitting an electric motor to something small, like a 14' john boat for example and having fun out on the water for a few hours.

I started with the motor and since I'd like the boat to get on plane, I decided a 5KW motor should be able to do the trick. After searching around, I found this one online and priced pretty low. https://www.goldenmotor.com/frame-bldcmotor.htm


Now I am thinking what kind/size battery do I need?

Trying to keep the battery as small as possible I decided to go with 48v and after taking a look at the data curve, I noticed that this thing can draw up to 200A. So using that and assuming I will only be using the motor intermittently and rarely at full throttle, I decided to opt for a 200ah battery. This should provide at least a couple of hours out on the water.

I am interested in building my own battery out of 18650 cells, and upon further research found that this will require between 1000-1500 cells depending on manufacturer (13s, 70-120p)

Now that I have my specs in order, I am interested in adding BMS to the pack so I don't blow up my garage during charging or my boat while I'm on the lake. Problem is, I can't find a BMS that will work for 13s and a draw of up to 200A during discharge.

I figured you guys in the EV conversion world must have some advice that can help a newbie out.

Oh, my background, I have pretty good mechanical and electrical knowledge, but batteries are new to me. And computer programming is basically a foreign language at this point.

Thanks in advance!
Kevin
 

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Search electric outboard motors to see what's available commercially and DIY conversion-wise. You could think of it as an overgrown trolling motor.
 

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Discussion Starter #3
Great idea, I had searched for something that would work commercially before going to DIY route.

After shopping around, the price you pay for one of these systems doesn't seem worth it to me.

Torqueedo does sell a 48v battery that can do the job with BMS included, but it is over $5,000. Hoping I can put mine together for less than half of that. Just need to find a BMS that can handle a battery that size.
 

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Hi Kevin

Just what do you want a BMS to do?

IMHO a BMS is useful to monitor the charging sequence and possibly to balance the cells

But during actual USE - it does nothing so the discharge current is irrelevent
 

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Discussion Starter #5
I was under the impression that a bms would ensure all cells are discharged at the same rate, preventing over discharge of any single cell? If I’m wrong here that makes my life a lot simpler
 

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I was under the impression that a bms would ensure all cells are discharged at the same rate, preventing over discharge of any single cell? If I’m wrong here that makes my life a lot simpler
I have never even heard of a BMS that could do that!

The basic functions are
Warning if a cell is overcharged or over discharged
Balancing the pack so that when fully charged all cells are the same
 
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