DC motor power requirements

Electronics aren't my thing, yet. I'm an mechanical millwright. Newest project is possibly an electric jetdrive kayak if I can get a grasp of the requirements. Pretty sure I've found the drive and motor but don't know how to figure out how big of a battery I'll need to get sufficient run time. Been "researching" this alien language, if you'd call it that. Need real people help. I have mild restrictions on weight. I was thinking Lifepo4 battery running 48 or 52v. Run time at full throttle would be <1hr.

At a recreational lake we liked to rent a boat (like a canoe or rowboat) with an attached electric motor and propeller. It was powered by a 12V lead-acid 'marine' battery. It's designed for less stressful and longer charge/discharge cycles than a car battery goes through.

Usually an attendant carried a freshly-charged battery to the boat dock and clipped it to the motor. 40 or 50 lbs. It didn't carry two or three of us extremely fast. But it was fun that we didn't have to row.

There were a few times we rowed and reached higher speed. Once we were in a kayak. We were barely at the waterline and I got wet where I sat. Any battery you choose for your kayak ought to be lightweight so you stay afloat. The lighter it is the more transportable it is between boat and charging station.

BradtheRad said:

At a recreational lake we liked to rent a boat (like a canoe or rowboat) with an attached electric motor and propeller. It was powered by a 12V lead-acid 'marine' battery. It's designed for less stressful and longer charge/discharge cycles than a car battery goes through.

Usually an attendant carried a freshly-charged battery to the boat dock and clipped it to the motor. 40 or 50 lbs. It didn't carry two or three of us extremely fast. But it was fun that we didn't have to row.

There were a few times we rowed and reached higher speed. Once we were in a kayak. We were barely at the waterline and I got wet where I sat. Any battery you choose for your kayak ought to be lightweight so you stay afloat. The lighter it is the more transportable it is between boat and charging station.

Click to expand...

The kayak I plan to use is a hybrid. It has a 700lb capacity. With these electric motors my understanding is rpm is determined by V. Based off the specs of the motor in my pic how long would a 100-150ah 48v battery last me at full throttle?

Our own rental times lasted 30 or 60 minutes. Motor speed never seemed to slow in that time. A crude estimate compares horsepower to Watts (720W per). I heard a human being can produce up to 1/2 horsepower. So I suppose our trolling motor ran on 360 W. (12V at 30A.)

I imagine your 48V 100A could last two or three hours (4800W).

Your chart lists very high figures for Amperes and RPM. An ampacity table states 400A should be carried in 000 or 0000 gauge (same thickness as for starting a car).
At 100A we're talking about 2 gauge.

I suspect you can get by with fewer Amps and lesser RPM (or gearing down to fewer RPM).

Possibly lesser voltage. Do you have plans to charge 48V worth of battery packs?

Hi,

physically:
* you need a force to throw your boat with the desired speed (not only depends on speed but also on weigth and shape of boat and surface condition)
* this force is provided by a propeller
* Maybe the propeller is driven by a gear
* the gear/propeller is driven by a motor
* the motor is controlled by a motor controller
* the motor controller is powered by a battery
Each of these converts energy .. and each of these has losses ... you have to care for in your math.

So if you know all these (if you don´t know, nobody else will know) you know the required battery power to run the boat.
Multiply this power by time and you get the required battery energy.

And I guess one of the most "problematic" parameters is speed. I expect it to extremely influence the required power.
This means: twice the speed does not mean twice the power ... I would not be surprised if it is more than 4x the power.
--> the higher the speed the (extremely) higher the required energy.

*****
Forum section:
I don´t know what these "social discussions" sections is meant for.
Usually there is the forum section for technical questions. Where 99% of the questions are asked.
And I don´t see what your question has to do with "RC" or "microcontrollers". So don´t be surprised if some people simply don´t find your question.
As far as I understand your question is about calculating energy ... from mechanical, to electrical. Motor and battery.

Klaus