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Deerhunter2

I Have Two Trolling Motors, Which One Would You Use?

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I have a Minn Kota 55AT - it is 12 volt and 55 lbs thrust. I also have a Motorguide model 750 - it is 12/24 volt and says 41 lbs thrust. Why does the one that will run on 24 volt list a smaller thrust and wouldn't it be stronger on 24v than it would be on 12v? Any input will be appreciated.

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Dusky, I know the Min Kota is only 12 volt. I am wondering why the motorguide has less thrust when it WILL run on 24 volt.

LogPerch, I understand the 24 volt Motorguide will last longer but how would it be stronger when it only says 41 lbs on it and the Minn Kota says 55 lbs?

My confusion is: Why would the 24 volt motor be rated at a smaller thrust than the 12 volt one.

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20 years or so ago, many of the manufacturers had their own individual way to rate TM thrust, and there was no standardized way to measure it. Some rated it at what I'll call the initial surge of electric power, some at the power it put out after that initial surge, etc. Some rated it at the propellor, and some didnt. It was not unusual to find a "weaker" TM which actually had a lot more thrust than a TM with a higher thrust number. As one example, the old Evinrude foot control TMs had a lot of thrust for a 24 v motor even though the rated amount of thrust on them looked pretty poor. This may still be taking place though MG and MK are about the only remaining manufacturers.

Wrench or one of the other good mechanics could probably elaborate on this.

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Pounds of thrust does not equal ft./lbs. #Thrust is a unit of force, while a foot-pound is a unit of torque.

Trolling motors are rated at their maximum thrust.

Power (expressed in horsepower) is another thing altogether. Power, as it pertains to propeller drives, is torque times rpm. The actual pounds of thrust from any given horsepower will vary depending on a number of factors, including prop diameter, number of blades, inherant flex of the blades, and pitch.

For what it's worth, rating electric motors by power would be more meaningful than thrust ratings. If you change the pitch of the prop, for example, you could increase or decrease the thrust of the same trolling motor. So, a 54 lb maximum thrust motor would not always give you a maximum of 54 lbs of thrust.

I have a working understanding of all of this but not well enough to "teach it"..... so here's a link that serves as a good baseline for choosing the proper system for any need.

http://www.trollingmotors.net/trolling-motor-resources

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One other thing....

Your old 12/24 is probably "constant current controlled". More modern TM's are "modulated" so that voltage is pulsed to increase battery life after the initial start up.

So....in a modulated unit the thrust rating is the MAX THRUST AT STARTUP, so once you stand on the button a few seconds the actual thrust will fall off somewhat.

Some MK and MG 24v units have a "HBP" (high bypass) switch that bypasses the module giving the brushes constant (non-pulsed) voltage for continuous max power. Operating like that for more than a few minutes at a time though will really heat things up and suck your batterys down with a quickness.

Does that make ANY sense at all? I have it solid in my head but be dammed if I can think of a better way to explain it.

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i would try the 12volt first then try the 24volt and see what works best.Its gonna depend on what kind of boat you have.I had a 15ft fiberglass bass boat that had a 56lb 12/24 volt trolling motor that had 5speeds.When it was in the 5th speed in 24volt it would really jerk the boat.When it was in 5th speed in 12volt it was about equal to when it was in 2nd or third speed in24volt.I would say since there is 14 lbs difference that they would be about equal.If i had to choose i would use the 12volt t-motor with the two batteries that you would have used for the 24volt t-motor and use them together for longer running time.But i would try them both first cause its gonna depend on how big your boat is....I could be wrong but that is what i think.

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