Assuming that your solar panel was powerful enough to run a trolling motor, then what would happen on a cloudy day?
The speed would be severely reduced or even stop. This is why a battery is commonly used in DIY solar kayak designs – it’s short-sighted to rely on solar panels only.
That said, with enough panel area, there is a way of running from solar without a battery. First of all, let’s talk about trolling motor currents.
A solar panel can run a trolling motor depending on the solar panel size and the motor power. It’s normal to run a trolling motor from a battery and a solar panel, but it is possible to remove the battery completely.
How Many Amps Does A Trolling Motor Take?
Trolling motor operating voltage is an important factor, so for this discussion I’ll consider a typical 30 pounds thrust model, which are almost always 12 volt.
Speed control is achieved in these basic models with a simple 5 position changeover switch. As you would imagine, each speed draws a different current from the battery. The chart below shows the current drawn from speed 1 to 5 for a typical 30lbs trolling motor:
|Thrust in lbs
|Current in Amps
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It’s immediately obvious that if we were willing to accept a slower speed, the motor current load can be cut substantially. For most trolling motor applications, fishing on a lake or powering an inflatable kayak, thrust is not too critical.
As long as your boat is small and you are not facing winds or waves, running the trolling motor at speed 3 or even 4 will have very little effect on speed, particularly if the craft is streamlined like a canoe or kayak.
Before moving on, let’s clear up some misconceptions about trolling motors – extra power and thrust does not equate to more speed. This also reflects on the current draw from the motor. Even on top speed a trolling motor will take much less than it’s maximum current if the boat is small and conditions are calm.
Will A Solar Panel Run A Trolling Motor By Itself?
This is a better question – can we run on solar without a battery?
This depends partly on the conditions described previously, the power output of the solar panel and one other secret ingredient – we need to talk about solar panel voltage.
The vast majority of so-called 12 volt solar panels have an open circuit voltage of about 21 volts, but this drops when connected directly to a load. A solar panel is basically a constant current supplier, and the amount of current will depend on the amount of sunlight and the panel area.
Assume that in Case 1 we have a solar panel that is too small for the load i.e. the motor. The motor will try to draw the current it needs to run, pulling the panel voltage down. It may run fitfully, or it may not run at all.
In Case 2 assume the panel area is much too big. There’s more than enough current to run the motor happily. In fact, the panel can supply more voltage than 12 volts. This means that the trolling motor can overvolt and draw more current than it is designed for.
Motors are rated in watts which is measured in volts x amps. If a motor’s power rating is exceeded by more than 10%, it is in danger of overheating and burning out.
How To Run A Trolling Motor Directly From A Solar Panel Safely
Looking at it simply, the fundamental problem is that the solar panel voltage is normally too high, so we need a way to regulate this. Luckily, there is a device which does exactly that.
The Buck Converter And Voltage Regulator
Buck converters take a wide variety of DC input volt and regulate it down to 12 volts, which is perfect for running a low-power electric trolling motor.
The buck converter I use in my own DIY solar inflatable kayak projects 15 volt to 40 volts and outputs 30 amps at 12 volt. 12 volts x 30 amps equals 360 watts, which is also the power rating of a standard 30lbs thrust trolling motor, so it’s perfect for the job!
The cool thing about buck converters is they convert any extra voltage over the 12 volt needed into current, so it effectively maximizes the solar panel’s output.
How Many Solar Panels To Run A Trolling Motor?
Now we have a means of safeguarding the motor we can focus on the solar panels required. As a general rule. we can say that approximately two thirds of the rate power can be converted into power in full sunshine, depending on solar panel type.
On my own solar powered kayak I mount two panels overhead, each rate at 150 watts. This means I can expect about 200 watts of power on a good day – I live in a very sunny country! Not only is the sun intense, but average sunshine across the year is 10 hours per day.
Dividing 200 watts by 12 volts we get 16.66 amperes. Checking on the speed/current chart we see that I should be able to run the motor comfortably at speed 3, which takes about 14 amps.
Conclusion: Could A Solar Panel Run Your Trolling Motor?
The Best Solution – Using Solar Panels And Small Battery To Run A Trolling Motor
Using a battery to run a trolling motor has one major disadvantage – they are very heavy, particularly if you want a decent run time. More than 90Ah is normally recommended. They also need charging after use – more lifting!
On the other hand, even if your small craft has enough room for solar panels, and you’re happy with the speed output, you will go nowhere if the sun doesn’t shine. Imagine a cloudy day when the sun disappears regularly – very frustrating.
An obvious solution is to use both solar and a battery. The beauty of solar panels is that the battery never becomes fully depleted. If you’re fishing, each time you stop after trolling, the panels are recharging the battery. You can use a battery one third of the size, say 30Ah, without problems.
It’s normally recommended to use a deep-cycle battery designed to be discharged up to 80% of it’s capacity, but I have an ordinary 40Ah car battery for many weeks with no problems. Auto batteries are designed to be discharge heavily for a very short period, after which they immediately begin to charge up. Normal discharge is never more than 5 to 10%.
How fast will a trolling motor go?
Trolling motors go about 5km/hour, regardless of their thrust. The larger motors are designed to develop more thrust for quickly positioning heavier boats.
How to make my trolling motor faster?
Normally a trolling motor is sold with a stock propeller. At the given RMP (determined by the voltage) the trolling motor will run at 5km/hr. There is nothing that can be done to speed it up, except perhaps a different propeller design.
What is a variable speed trolling motor?
Lower thrust trolling motors have a 5 position switch which changes the speed – normally there are 5 speeds. Variable speed, or soft start, is done by replacing a mechanical switch with an electronic circuit which increases the voltage progressively, thereby increasing the speed smoothly.