Charging a battery with a trolling motor!

drewmitch44

Lieutenant Commander
Joined
Jun 26, 2005
Messages
1,749
There was a thread a whyle back (maybee more than a year ago) that someone had asked "if you leave the trolling motor battery deployed will current run back to the battery?". Well i took my aluminum boat out the other day just to test a small outboard that im thinking about buying. Well this winter i never pulled the trolling motor off of the bow so it was on there when i was running this motor. I had taken my tool bag as a just in case type of thing. I was rooting through there to get a screwdriver and i saw that i had my digital multimeter. I tested the trolling battery and it was something like 12.4 V with nothing hooked up to it. The outboard that i was testing was a 9.9 and was pull start so nothing there was hooked up to the batter. i had hooked up the battery to the troller just to get me away from the edge of the pond so when i started up the motor i didnt suck up the pond scum and crap off the shallow bottom. The trolling motor is a older motorguide hand controlled one. I left it in speed "1" just to keep the boat going strait and away from the edge. It goes verry slow in speed 1. So i started up the gas motor and im letting it idle for a few min so it can warm up a little bit. I tested the battery with the multimeter with the troller on speed 1 and it read 11.23v. Well i left the multimeter hooked up to the battery that the troller was hooked up too. I went to the back to move the boat around a little with the gas outboard just to test how well it runs. Well i had still had the troller on speed 1 and i was using the gas motor a little and i looked at the multimeter and it read back to 12.4 with the speed on 1 and the troller running. So just for ****s and giggles i put the troller in reverse on speed "1" and left it deployed. I started to move the boat forward with the troller down and in reverse, but i was using the gas motor to go forward. Well i look at the multimeter and it was reading 14.05 volts!!! That meand that its charging the battery!! So i put the troller into speed "2" in reverse and went forward with the gas motor and the volts went higher still!!! Now when im saying this im not running fast or anything like plaining speed or nothing i just find it interesting that if you move the boat enough that it makes the troller blade turn the opposite direction that you have the controlls set to it sends current back to the battery! So i was joking on that thread a before when i had said "it most likely charges the battery up!" But it seems to me like it is quite possible that im getting a charge from the trolling motor! This was verry hard for me to explain but hopefulluy someone knows what im trying to say!!! Im going to take a break from talking about this and try again in a half an hour or so to word it better!!!
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Charging a battery with a trolling motor!

as you have shown it is possible, but it would take a strong shaft and a while to charge a battery.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,780
Re: Charging a battery with a trolling motor!

You have just proven to yourself that a motor and generator are basically the same critters. One consumes energy and produces work (energy consumed at some rate), and the other consumes work and produces energy. Course there are subtle differences between the two to meet their respective requirements on a continuously operational basis.

Obviously you don't want to be running around with your trolling motor in the water.

Mark
 

waterinthefuel

Commander
Joined
Nov 15, 2003
Messages
2,728
Re: Charging a battery with a trolling motor!

It is quite common. Battery regenerative circuitry. Trains use it. Even RC cars use it. I believe an electric scooter uses it. All you have to do is reverse the polarity (or switch it into reverse, same thing.)

I wish I could have seen that operation though, I have a feeling I would have laughed my butt off.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Charging a battery with a trolling motor!

Don't try that on an electronically controlled motor like a MK maximizer. Might burn up the controller.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,780
Re: Charging a battery with a trolling motor!

You get nothing free. It takes work (energy consumed at some rate) to produce energy to be consumed at a later time as work. Losses are involved.

About the best analogy I can give you is what hybrid car mfgrs are doing, and maybe trains, of which I am unaware.

If the vehicle is traveling at some speed, you have kinetic energy stored in this moving object; value of which is based upon weight and speed.

If you "brake" this vehicle by transferring this energy into a storage device (battery) you have in essence gotten something for nothing and saved wasting the "work" that you would have converted into heat in trying to stop the vehicle via a conventional braking system. This is one form of conservation of energy that really makes sense and I'm sure we'll be seeing more of it and as attention is focused on it, it will get more reliable and efficient.

Only question is, what price do you have to pay for this privilege, and does the price/weight/whatever cost, outweigh the attempted merits.

Mark
 

jtexas

Fleet Admiral
Joined
Oct 13, 2003
Messages
8,646
Re: Charging a battery with a trolling motor!

I can testify to another unintended consequence of running with the trolling motor deployed...
mg1.jpg


push the propeller backwards hard enough, it just unscrews itself!
mg2.jpg
 

EMM

Seaman Apprentice
Joined
Dec 24, 2007
Messages
42
Re: Charging a battery with a trolling motor!

Turbine engines on aircraft use a starter/generator which is close to what you describe. When power is applied it acts as a starter motor to start the engine. When the engine is running it is used to produce power for the aircraft. However it was built to do this.
 
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