# Trolling motor power consumption?



## SteveON

I have a Minnkota Endura 50 that I use on a 20' Mirage sailboat. I use it mainly to motor in and out of the Marina (15 minutes max. each way) but I occasionally use it to troll around the cliff areas to fish (sails stowed of course). In that case I usually keep it on the the number 2-3 setting. I just bought a 720 cranking amps/115 amp hours 27 series deep cycle battery to power it. How long can I expect to use the trolling motor before I discharge the the battery? Can I use the motor several outings before I have to recharge the battery if I'm not taking much power away each trip or will I have to recharge it after every outing? Also wondering if one ican use a small solar charger to recharge/ maintain the battery while it's not being used? The battery is pretty heavy and hard to load/unload on the boat if I have to take it home each time to charge. The boat is dry stored on the trailer with no AC power available.
I had been using a 525amp battery (24 series a starting not deep cycle) but I decided to get the right kind and size to make sure I'm not left stranded. 
I'm open to any suggestions.
Thanks,
Steve


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## sailingdog

What is the amperage draw of the Minnkota? A Group 27 deep cycle wet cell battery has about 100-110 amp-hours at the 20 hour rate...or at a draw of about 5 amps per hour.

If the motor is providing 40 lbs. of thrust, that is about 2/3 of a HP or 500 watts or about 40 amps @ 12.6 VDC. This is based on the following:

746 W = 1 HP
58 lbs. thrust = 1 HP

If you're using the battery for .5 hours each time out, you're using 20 amp-hours (.5 hours * 40 amps).

The battery is rated for 100-110 amp-hours, but should not typically be discharged past the 50% point, so you have effectively 50 amp-hours, so ideally, you can use it for two trips before needing to recharge it. * I'd point out that the 100-110 amp-hour rating is a 20-hour rating or at a 5 amp draw. With a 40 amp-draw, it is likely to be a good deal less, and you'll probably really want to charge the battery after every trip.*

I'd point out that wet-cell batteries self-discharge during the warmer weather at a rate of up to 1% per day. So, if you leave the boat for two weeks, it will have lost possible 14 amp-hours from self discharge alone.

I would recommend getting a 30 watt solar panel to recharge the battery. A 30 watt panel, is about 2 amps per hour at 14.4 volts, and that will give you about 10 amp-hours of battery charging per day or so, especially if you're using a MPPT type charge controller. During the course of a week, it will return, on average, probably about 60 amp-hours to the battery, meaning that it will probably be able to handle your weekend usage of the boat each week.


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## SteveON

Sailingdog,
Thanks for your reply. Your answer makes perfect sense and I really appreciate the solar charger recommendation as well. I'll be search for a 30 watt panel with a MPPT type charger. Any suggestion where to start shopping? Ebay? Amazon? I might just have to suck it up until I find a setup and drag the battery home each time for now.
Thanks again!
Steve


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## sailingdog

You can probably find a 30 watt panel with a charge controller, but it will likely be a non-MPPT type charge controller. It should work fairly well, but you're not likely to find a MPPT-type charge controller in an affordable kit.

A 30 watt polycrystalline or monocrystalline panel on eBay will run about $90. A non-MPPT charge controller will run about $20.  I'd recommend you read the primer I wrote about *Solar Power On Boats* too.

You might also try Harbor Freight or Northern Tools. I got a 30 Watt panel that I use for winter battery maintenance at HF for not too much money and IIRC, it came with a small charge controller. I gave the charge controller to a friend, since I already have an MPPT one installed on my boat.


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## bobmcgov

What SD said. Those numbers square pretty well with my experience using a 40# Motorguide and a Group 27 (115AH) flooded batt. There's a ton of variables in play, however, so YMMV.

For example, the Minnkota Endura 50 is an analog troller -- the 5 FWD/3 REV is your clue. That is to say, it achieves lower-than-maximum speeds by putting a bloody rheostat (dimmer-switch resistor) in line with the motor. The result is that *analog trollers use nearly the same juice at any speed setting* -- at low speeds, they burn off surplus amps as heat.

Digital trollers (like the Maxxum or Great White series) use electronic speed control. These can yield up to 3x improved run time at reduced speeds over analog models, tho at WOT there's no real advantage. They typically have infinite speed settings.

Another variable is discharge rate -- how fast you are pulling amps measured as a fraction of the battery's capacity. For most trollers, that's well inside the 8-hour discharge rate. Most batteries are labeled with their 20-hour discharge rate, which may be half again the 8-hr rate. What that means is the faster you discharge a battery, the smaller it behaves. So you should discount that 115 AH to maybe 80 AH as a derated capacity; then, as SD proposes, halve that to 40 AH for your functional capacity, and that means you get 1 hour of run time at 40A draw.

Now, there's a school of thought that says it's false economy to nurse batteries this way. That by limiting yourself to 50% DoD or less, you are leaving half your useful capacity on the table. Sure, driving a battery to its full 80% DoD may halve its life span -- *but you will have gotten twice as much work out of it*, so you come out even in the dollars-per-mile calculus. A decent deep-cycle lead antimony batt should withstand 1500 cycles between the eighties (80% DoD to 80% SoC). These contrarians, whom we might call the "Rented Mule" school, propose it's better to utilize more of the battery's capacity and accept a shorter service life. The advantage is, you carry around less battery mass in the meanwhile. And entropy being what it is, batteries decay even when babied or unused ... so why not ride em hard & put em away wet, buy new ones when these die?

A 30W mono- or polycrystalline solar panel will recharge your Group 27 in about 1 sunny day following 1-2 normal days' use, so it is a good match. You probably should add a charge controller, just a simple one, to keep from boiling the battery dry once it is charged. I got this one on eBay for $15 and like it just fine.

Cheers!


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## SteveON

sailingdog-I'll take the time to read the primer you wrote and then start my search for the right panel for the job.

bobmcgov- thanks for your response. Lots to think about. Im of the school of thought that I would have no problem running the battery down to 80%. It has a two year free replacement warranty if it fails. I normally replace the batteries in my car, truck and motorcycles about every two years anyway. The heat here in San Antonio, Texas can be brutal on batteries. 

I will probably have to wait until the first of Oct to buy a solar panel. I have a wedding I have to pay for comming up soon. Not sure my daughter would understand her wedding "gift" was a new solar panel for her dad's boat...LOL.
Steve


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## sailingdog

A wise decision... women can be so sensitive about their weddings... 


SteveON said:


> I will probably have to wait until the first of Oct to buy a solar panel. I have a wedding I have to pay for comming up soon. Not sure my daughter would understand her wedding "gift" was a new solar panel for her dad's boat...LOL.
> Steve


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## schepp

Very confused on the topic of analog trolling motor using the same amount of power whether on low speed or high. I have an old 46 lb thrust motorguide and with a voltage meter attached I can see the voltage drastically vary between the low speed and high speed setting. If it was drawing the same amperage regardless of speed the voltage level would remain the same, no?


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## Rocky Mountain Breeze

Rheostat controls work by adding load to the circuit to reduce the voltage. The greater the resistance on a given circuit the less the voltage delivered to the load. This is how the heater fan control worked on cars prior to the modern age.


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## schepp

Thank you Rocky, however can you explain that in laymens terms to me please. My basic understanding is that more load, regardless of whether it was a rheostat or 1 light bulb vs 5, would equal more power used and more voltage too(meter would show a decrease in voltage based upon load, battery etc.). If there is less voltage shown being used (speed 1 vs 5) and being measured at the battery, then I thought that would mean less amps, watts, power being used, and the longer the amount of available battery storage. If the same amount of power, amps (watts) is being used regardless of speed, then why does it state right on the label of many of these analog motors it states on speed 1 you will get 20 hours , speed 3 you will get 12 hours and speed 5 you will get 5 hours , all based on the same sized power source(all approx but I think you get my point),,,please , thank you.


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## schepp

picture showing power consumption arc


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## schepp

and another chart


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## schepp

Still would enjoy some more explanations. In my real world test, on a 3 hour kayak ride with a 46lb thrust old Motorguide, my stats certainly are closer to what the manufactures states*in the above pictures). At lower speeds the motor uses significantly less power and battery storage than at high speeds, resulting in longer run time. I used up about 20 ah of battery power in that 3 hours , mostly on speeds 1, 2, and 3. So I averaged about 7ah running on those 3 speeds within a 3 hour period. I guarantee that my 46lb thrust old Motorguide , if utilizing full power for 3 hours as suggested regardless of speed setting, that my 65ah my battery would have been dead, and my wiring melted.


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## tschmidty

It's incorrect to say it is going to draw full power all the time but it does basically use resistance to add load to the circuit. Think pinching a garden hose. It's less efficient since that resistor is not actually doing anything but getting hot so drawing excess energy that is not being supplied to the motor. 

A much more efficient way is when the motor controller uses PWM (pulse width modulation). A fancy way to say it blinks power at the motor. So the motor gets full power but only, say, 50% of the time at half throttle. For Minn Kota the tech is called Maximizer.


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## TakeFive

It would be nice if someone could draw an electrical schematic and do the power calculations to see how much energy is wasted in the Rheostat design. Seems to me that voltage across a load dissipates energy, whether in the form of mechanical energy to the prop, or wasted by heating up the resistor. Either way it's the same amount of energy, which doesn't match up with the observation that running at slower speed leads to longer run time. Perhaps it's just that there's less viscous drag on the boat at slower speed, and W=F*d, so the total of energy used + energy wasted is less. Same lousy efficiency, but less energy transferred from the boat to the water.

I'll try to do some calcs someday, but for now I'm going sailing!


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## Rocky Mountain Breeze

Schepp: When a rheostat is used for speed control it is in series with the motor, so the motor sees lower voltage as the control is set at a lower speed setting and higher voltage as the resistance is decreased for a higher speed setting. tschmidty is correct in his description of more modern speed control devices which open and close the circuit very rapidly depending on the amount of power desired at the device. As to your manufacturers charts, who knows. Truth often yields to hype in the advertising world and unless the product is subjected to independent testing and verification there is little risk to the manufacturer's reputation except by the purchaser. When the deception is recognized by the marketplace the product is then reintroduced as "New and Improved!".


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## schepp

Thanks for the info, and I have looked into the PWM. regardless, what is the role of the speed control then?... I assume the speed control is limiting the amount power (the faucet, in the garden hose analogy. ) that is being fed to the motor. So yes a schematic would certainly help understand why there is a waste of energy. I am assuming if I measured the output of the speed control it would vary, in amps, from speed 1 to speed 5. So lets say if the speed control is letting 2 amps pass through at speed 1, (even though there is much more available from the battery) and 40 amps at speed 5, where is there wasted energy? I love electric motors, have hobbied with them and I thought they will they will use up whatever amount of power you feed it, to it's capacity. My thoughts on the analogy is that the speed control is the faucet control for the hose which has a sprinkler at the end, so the more I open the faucet, the more the sprinkler can spray, with little waste. Your analogy is that the faucet is almost always totally open, and the sprinkler has a two way split with a control on it, where a lot of water shoots out the side and very little goes through the sprinkler, if the sprinkler control is on low. 

So is the speed control between the battery and the motor or is the speed control between the motor and the prop?


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## tschmidty

Speed control is between battery and motor of course. So with a rheostat type, you get heat loss from the resistor and lower voltage at the motor. The difference is something like 15% give or take 15% :=)

With PWM you get full voltage at the motor. The efficiency comes from the fact that the transistors used to modulate the power have a much lower voltage drop. That voltage drop is what produces the waste heat on a resistor. 

Besides the efficiency, you can also get a more powerful thrust at lower speeds. Think impact wrench versus just yanking on a lug wrench since the motor is seeing full voltage at the times it is being powered. This is how they can claim "up to 5 times" more power. Basically no, it isn't. You gain probably 20-25% more using PWM. In some perfect scenario of power used, throttle position and mars being in alignment might give you 5 times more power on a piece of paper. Real world it won't happen.

For your sprinkler analogy, (yes the faucet/battery is always on full and must be restricted down the line) think more that the extra water is shuffled along back into the faucet. It requires some energy to recycle that water as it is going through another hose back to the faucet and that is where your losses come from.


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## JimsCAL

The simplistic answer is the power and thus the speed is reduced by reducing the current (amps) being delivered from the battery. Note power in watts is volts times amps, and 746 watts is 1 HP. The electronic PWM device is more efficient than the rheostat in reducing the current. So at low powers when the current is being reduced, the PWM controlled motor will have much lower losses and the battery will last longer. Wide open, there should be little or no difference.


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## Rocky Mountain Breeze

I was going to use the illustration that the water hose would have part of the water flow (current or amperage) diverted to another hose thus reducing the amount of water to the original destination. Using the water analogy the pressure of the water would be voltage, the flow rate would be amperage, and the total GPM delivered through the faucet would be the wattage. The rheostat converts the excess flow into heat at the rheostat which is why the current (and thus the power generated by the motor is less) actually used by the motor is less, although the current drawn from the source is relatively constant. Sorry but I do not have the internet technical ability to post a wiring diagram although I could draw you one on a piece of paper if we were together. The PWM variation would be like turning the faucet on and off very quickly to reduce the flow of water without wasting any of it.


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## JimsCAL

Rocky Mountain Breeze said:


> The rheostat converts the excess flow into heat at the rheostat which is why the current (and thus the power generated by the motor is less) actually used by the motor is less, although the current drawn from the source is relatively constant.


This is wrong. The rheostat or PWM circuitry are in series with the motor, not in parallel. As the current is reduced, it is reduced for both exactly the same.


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## schepp

Thank you, I understand the benefits of using PWM. Still not clear on the rheostat power hogging that much power. I'm looking at my 12v mini electric bike I have, trying to draw comparisons to my trolling motor. It has a battery and a controller and an electric motor. The controller has a heat sink on it, which I assume is where the rheostat is located, as part of the controller. With trolling motors, I read the wasted energy is withing the motor housing, creating heat , which gets cooled due to it being in the water. So in a trolling motor is the rheostat in the small controller or is it located in the motor housing? I can believe a possible 15% waste of power but I still don't see the controller consistently drawing almost full power from the battery - The manufactures spec don't even read like that. With my trolling motor, On speed 1 my controller gets warm. On Speed 5 it would probably eventually blow a fuse or melt (this could just be poor wiring) SO, in a side topic, does the dimmer switch connected to a light bulb (120 v AC) waste electricity in the same manner? AND is there an off-the-shelf PWM that I can purchase in Ontario (I'm in Muskoka)?


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## travlin-easy

While some electric trolling motors use a variable resistor that is in series with the battery to control speed, some have up to 10 windings on the motor that change the speed via a smooth switching system and a series of diodes. None of the speed controllers result in increased power consumption from the controller itself.

Gary


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## schepp

So how does the speed control on the Vintage Shark 410 trolling motor work? Its has a single 3 -way Toggle switch, Low - Off - High...


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## travlin-easy

Windings.


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## neeqness

Well another way to look at it is heat generated is energy loss. There are amps lost when that heat is generated.

While I do not know the percentage lost, I imagine this knowledge to be sufficient to convince me that it is less efficient.

Sent from my LG-H918 using Tapatalk


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## schepp

hey Gary , travlin-easy... could you please elaborate on what you wrote : "None of the speed controllers result in increased power consumption from the controller itself"


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## Rocky Mountain Breeze

AC and DC motors are different in how they convert electricity to motion. Most AC dimmers today just "clip" the flow of electrons, again using the analogy of rapidly flipping a switch on and off. I doubt that the controller on your motor has a rheostat in it as it would generate too much heat for a small device to release. It probably uses a bank of resistors to reduce the flow of electrons which would generate some heat but not nearly as much as a rheostat and would also reduce the amount of current drawn from the power source. I will wait for JimsCal to misinterpret this again.........


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## schepp

I have a question concerning power consumption etc, and with the wiring. Typically there are 4 wires that lead into the shaft and to motor. Thick red and Black, and smaller gauge blue and yellow. From what I gathered the blue and yellow wires are present to provide the speeds, based on the controller setting, through some type of resistance inside the motor housing, which is being controlled by the controller, and the red and black provide the power. When I disconnect the red and black wires from the controller and then simply connect them , JUST the Red and Black wires (+ and -), direct to a battery the motor turns at what I assume is full power to the motor, with no power or heat loss, no resistance, correct? (other than what my wiring might effect and load etc). Effectively I could completely bypass the controller and run the TM at full speed forward using a 50a toggle switch. If I wanted full speed reverse too, I could use a DPDT switch and have a choice between the two. Correct?


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## tschmidty

My guess would be the blue and yellow wires actually tell the controller the speed the motor is turning out so that it can cut off power if the motor is stuck for example. And yes connecting full power directly to the motor is fine, but is also what happens when your controller is on high so I don't see much benefit.


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## schepp

Thanks tschmidty. I am experimenting with mounting a trolling motor on a kayak, ( so re-wiring is required) so I am extending controller wiring from the stern to the cockpit, and the battery wire to a battery in the front hidden compartment of the kayak. Even though I am using large gauge wiring, on setting setting 3 and above the controller is getting too hot. Since I am only looking to go as fast as the motor can go , the most basic setup with as little wiring as possible would be a toggle switch. The 46lb thrust i have installed now is too much for the kayak to run at full speed continuosly, but I have a 26 pound model I was thinking of switching too. I am figuring 26 pounds would be a better match.. I guess it could be that I am incorrect with my wiring, is too long for the gauge or the controller is old and failing.


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## tschmidty

You are using the stock controller as in the one on top of the trolling motor? You could try using a different controller as well, something like this: https://www.amazon.com/ELEGIANT-10-50V-Controller-Driver-Extension/dp/B01HEXJUX8/ref=cm_cr_arp_d_product_top?ie=UTF8

A lot of times the wiring in the controller itself can be pretty small.


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## schepp

yes stock controller. So this PWM you linked me (thank you) is as simple as connecting positive and negative from battery and then only the + / - that leads into the shaft ( I am asking this as I see four screw connectors.)..


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## schepp

how does reverse work with this PWM


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## schepp

any experience with this product? it has a reverse switch DC 10-55V 12V 24V 48V 60A PWM DC Motor Speed Controller CW CCW Reversible Switch | eBay


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## TakeFive

Pimp my kayak!


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## schepp

Found a local supplier here in Canada ,,, This should do the trick I hope..https://abra-electronics.com/roboti...-modules/psm-247-40a-dc-motor-controller.html


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## tschmidty

Yep, looks good. Nice that it has on/off/reverse built in. 

This would work for the 26. a little marginal for the 46. 1 amp per pound of thrust is usually a pretty good rule of thumb.


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## schepp

WOW.. Incredible the difference in using a PWM controller vs Analog speed control. Certainly uses up at least 4 times less power storage. However my first run seemed to indicate the need to put a small fan on the heatsink to dissipate the built up heat in the controller. Works like a charm. Thank you.


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