I have a trolling motor that is rated at 12 V. I want to double the speed of the motor.
If I change the armature wiring by using a thinner wire with more turns, will I able to use it on 24 V DC to get more speed?
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1\$\begingroup\$ can you share a datasheet or any other information about the motor? \$\endgroup\$– jwscCommented Jan 25, 2022 at 15:01
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1\$\begingroup\$ In theory yes but is it more RPM or torque you need, maybe a different prop is less stress on the bearings to propel the boat faster \$\endgroup\$– D.A.S.Commented Jan 25, 2022 at 15:09
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2\$\begingroup\$ If you double the turns you can certainly use it on 24V ... but at the original speed. You have halved the speed constant (RPM/V). To double the speed you'd need to run the existing motor on 24V ... but you'd need it to handle approx 4x the current, 8x the power. Which it won't ... unless it was designed to survive 24V in the first place. (A very few are. You can spot them by "12V/24V" in the specs) \$\endgroup\$– user16324Commented Jan 25, 2022 at 15:31
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1\$\begingroup\$ @jwsc it's an old Evinrude trolling motor having thrust around 40lbs that's all info I have. \$\endgroup\$– Dipendra GurungCommented Jan 26, 2022 at 4:16
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2 Answers
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If you have a 12 V DC permanent magnet brushed motor, the way to increase its speed by double is to supply it with 24 V, with no changes to the motor. If you rewind it with twice the number of turns of thinner wire, then it will run at the original speed with a 24 V supply.
You will need to keep the output torque similar, as motor heating goes as current squared. You will therefore need to reduce the size or pitch of the trolling prop accordingly. Loading it with more torque will draw more current, and quickly overheat the motor. Running the same torque at twice the speed will allow you to get twice the rated power out of the motor.
But for how long? Doubling the speed will reduce the life of the motor, more or less significantly, in a number of ways.
a) Sparking at the commutator will increase, increasing the wear on commutator and brushes
b) The bearings will wear faster
c) Twice the speed means four times the centrifugal force on the armature components. It may reduce the life to a fraction of a second as it flies apart through lack of strength.
Do you actually want to increase the speed of the motor, or do you want to increase the speed of the boat? It may be better to invest in a motor with a higher rated power, and couple it to a suitable prop.
A boat tends to require a power proportional to speed squared. If you want to double the speed of the boat, you need four times the power. Maybe your motor can run at twice the speed with twice the voltage (with a reduced life and reliability), but running at twice the torque will require twice the current, which means four times the heating. Unless the motor is rated at way over what is needed for its original 5 km/h, then it will not be able to manage 10 km/h, and will overheat. Does it have a ratings plate on the motor?
To paraphrase that famous (and I understand, unscripted) quote from 'Jaws', 'You're going to need a bigger motor'. Or at least, better cooled.
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1\$\begingroup\$ +10 for the answer! Yes, I want to increase the speed of the boat by increasing the speed of motor. The current trolling motor gives only a speed of 5kmph, I want to increase it to around 8~10kmph, if it possible by some modification on propellers or internal wirings. \$\endgroup\$ Commented Jan 26, 2022 at 4:40
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2\$\begingroup\$ @DipendraGurung You can increase the speed of the boat by increasing the power output of the motor, which from first principles, and according to this site, is proportional to boat speed squared. You can double a motor's maximum power by doubling the voltage, but not quadruple it. But, is your motor working at max at 5 km/h at the moment? Does your motor have a max current rating? Try it at 2x voltage with your present prop and measure the current. Remember you overheat if you run at much over the rated current. \$\endgroup\$– Neil_UKCommented Jan 26, 2022 at 6:17
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\$\begingroup\$ hollywoodreporter.com/news/general-news/… \$\endgroup\$ Commented Jan 26, 2022 at 8:53
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\$\begingroup\$ I got the motor from the scrap, the armature was burnt to black perhaps be due to overcurrent. Using youtube videos, I was able to rewind the armature using 20 SWG copper cable. When using at full speed, it draws around 30~35 Amps and gives a speed of 5~5.5kmph. The boat is wooden and made of Sal (Shorea robusta), which is quite heavy in weight. I am concluding that, either I need to change the boat design to lighter weight or upgrade the motor. \$\endgroup\$ Commented Jan 26, 2022 at 8:56
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1\$\begingroup\$ @DipendraGurung We aren't as good at hand winding as winding machines are, so you can bet that your rewound armature will have less copper on it than a new motor of the same dimensions, so will get hotter for the same power output. Weigh the motor. Now look in catalogues to see what sort of power ratings motors of a similar weight have. Use the site I linked to estimate the power required to propel your boat. Now see whether you need to buy a new motor. An ESC and a brushless motor will allow you a much smaller, more efficient motor, some have water cooling as well. \$\endgroup\$– Neil_UKCommented Jan 26, 2022 at 9:33
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- Sell 12 V motor on eBay
- With the money, buy a 24 V motor that is rated for the sped you want
answered Jan 25, 2022 at 15:19
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3\$\begingroup\$ Being an electronics enthusiast and learner, I asked here if we could increase the speed/power of motor. \$\endgroup\$ Commented Jan 26, 2022 at 4:34
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\$\begingroup\$ Just so you know: motors are electric. Not electronic. \$\endgroup\$ Commented Jan 27, 2022 at 21:52
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\$\begingroup\$ @DipendraGurung Importantly - in the comment above you mention wanting to increase the power of the motor - that is the only time that you have mentioned power and that adds quite a different aspect than increasing speed. For a trolling motor on a boat you may wish to increase speed to accommodate a different propellor - but not increase power. We do not know your aim or actual application. It would greatly help to know what you are actually wanting and the actual application. ... \$\endgroup\$– Russell McMahon ♦Commented Jan 29, 2022 at 10:27
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\$\begingroup\$ @DipendraGurung ... || Motor iron saturation may limit total power. More voltage and thinner wire may allow more amp-turns (same Increased V) but we need to know the "big picture". \$\endgroup\$– Russell McMahon ♦Commented Jan 29, 2022 at 10:27