solar panel ratings

[Dawgfish]

Is there a solar panel thats able to charge batteries and run a trolling motor?

[Phil M]

Charge batteries - yes. Charge batteries and run a trolling motor from the batteries - yes. Buy a deep cycle battery and smaller trolling motor. There are several discussions here if you search the forum for solar panels and how to properly hook them up to a deep cycle battery.

Phil M

[Divecoz]

All Depends..
Hours of Sunlight available and consumption of trolling motor..? How often between charges , are you in hopes of using the Trolling motor? and on and on and on..

[nedmiller]

There are lots of factors here. Are you starting with fully charged batteries every morning and just using the trolling motor to get you out of the dock, or are you thinking you will run the trolling motor much of the day (probably not going to work).

A really rough estimate of power usage can be obtained by using a bit less than 1 amp draw for each # of force your trolling motor uses. So if you have a 50# trolling motor you might burn 45 amps. You will have to have a big battery bank and/or a huge solar array (500+ watts) to run a trolling motor all day. If you have 75 watt solar panels in full sun all day, you can use the trolling motor an hour or so if you are not using other electricity.

Using a new Minnkota (with a maximizer) will allow you to go less than full speed and save amps. If it is an old trolling motor, running at lower than max speed may not save you many amps since I think they used a resistor for speed control.

SILK

[Phil M]

Using a new Minnkota (with a maximizer) will allow you to go less than full speed and save amps. If it is an old trolling motor, running at lower than max speed may not save you many amps since I think they used a resistor for speed control.
SILK

Hmmm. I use an older Minnkota trolling motor, and should test that theory out. It never occurred to me that going slower would NOT save on amp usage.

My trolling motor and dinghy are used sparingly, and for short hauls only.

Phil M

[nedmiller]

Someone more knowledgeable should weigh in now, but I'm under the impression that the reason the older models get really warm when running slowly is because they used a potentiometer (?) to regulate the speed--ie increased resistance. The newer models that say PWM (maximizer) regulate the speed by rapidly turning the current on and off--thus saving your battery.
If you have an old model and need to go a certain distance, do it at full thrust.
SILK

[Catigale]

I dont think the older models used a resisitor to dump the excess amperage at low speed. Dumping hundreds of watts of electrical power isn't easy and would require water cooling.

Not an expert on this, but there are lots of ways to run an electric motor at low power more elegantly.

[mastreb]

I dont think the older models used a resisitor to dump the excess amperage at low speed. Dumping hundreds of watts of electrical power isn't easy and would require water cooling.

Not an expert on this, but there are lots of ways to run an electric motor at low power more elegantly.

Controlling DC electrical motor speed efficiently actually was pretty hard before the advent of cheap microcontrollers. The options were:

1) Potentiometer, essentially a variable resister that resists current flow but does heat up to do so. The heat is lost power. They are cheap and effective but inefficient. Older continuously variable trolling motors used this method.
2) Variac, a variable transformer that allows you to reduce voltage and thereby reduce the power and draw without generating a lot of heat. The problem with variacs is that they are very large and expensive. I doubt anyone ever put one on a trolling motor. These were used for example on model trains as the throttle.
3) Multi-tap transformers which would allow you to switch between a small number of engine speeds. As efficient as a variac, but not continuously variable. Medium cost. Trolling motors that had three or five speeds used this technique, and were efficient but were not continuously variable.

With silicon controlled rectifiers and small microcontrollers, you can do a "pulse width modulator" that sends timed bursts of power to push the motor at the most efficient possible time, and when they're off there's little lost to heat. These work by rapidly switching a silicon power switch that is timed to the shaft's rotation (via a shaft position sensor) so that the pulses occur and the point of maximum potential efficiency.

This is how modern dimming switches work for incandescent lights, which is why they make ceiling fans "hum" at different volumes as they're dimmed--at "efficient" points in the rotation, the hum is minimal, and when the fan is "singing" pulses are coming through at a rate that causes the motor to be pushed and pulled, setting up a resonant vibration.

AC motors are a different story entirely, but not particularly useful on boats.

Motors designed from the outset to be driven efficiently by digital pulse streams are called Switched Reluctance Motors (SWMs), and are essentially a purpose-built type of stepper motor. Likely the next generation of trolling motors will use these. I think the Torqueedo motors already do, but that's just a suspicion based on how much more efficient they are than a typical trolling motor.

[Catigale]

I stand corrected. Actually, it's 2330 and I'm lying down corrected...just caught the last PHL to ALB bus

[seahouse]

I use an older Minnkota trolling motor, and should test that theory out. It never occurred to me that going slower would NOT save on amp usage.

Hey Phil!

Your amp draw will be less, because the resistor slows/reduces the current leaving your battery. Not all of the power difference is lost as heat in the resistor, just some of it, which makes it less efficient, but it still will extend battery life over running full "throttle"; in two ways.

One, you will be using less power from the battery immediately, and two, the battery longer-term longevity will be improved because you will be drawing less amperage from it, making it run cooler (elevated operating temperature is reduced, a good thing).

BTW - Good post mastreb!

[mastreb]

To amplify seahouse's post, it's important to remember that the energy required to accelerate a mass increases at the square of the speed, i.e., if it costs 4 watts to get to 2mph, it will cost 16 watts to get to 4 mph.

Thrust is acceleration resisted by the sum of all other forces, mostly drag and inertia. So even if you don't feel like you're accelerating, this basic scientific law applies but the curve changes from a pure square law increase to whatever the sum of all forces winds up being in your particular case. This is why going 12 knots with an ETEC-60 costs you about 3X the fuel that covering the same ground at 6 knots will cost you (the drag changes a lot between displacement and planing, so before anyone tells me I'm oversimplifying, yes, I'm over simplifying).

So while it's true that going WOT on an electrical motor that is more efficient than resisting down the power because less wattage is lost to heat, it's not going to get you farther over ground because vastly more wattage is lost to speed if that speed is not necessary.

There is some speed at which you will be losing more power to heat in the resistor that you are putting power to the motor, but hopefully that speed is vanishingly small, and hopefully the throttle clicks to off before it will let you just radiate your power to heat. Other than that effect, the slower you go with an electric motor, the longer your power will last. The optimal speed is that speed which will drain the battery just as you pull up to the recharger, with some margin for error. YMMV (literally).

So don't go WOT thinking you'll cover more ground before your battery dies. You won't. You'll just get almost there faster.

[Catigale]

Just to put it in perspective...you need a couple of HP minimum to move a Mac off a dock..this number applies to both gas and electric of course. 1 HP is 750 watts, so you need a 1500 watt solar panel to be solar powered completely..would double nicely as a solid spinnaker...or a siliconakker maybe?

[K9Kampers]

..would double nicely as a solid spinnaker...or a siliconakker maybe?

...or the solar panel that doubles nicely as a no-solar paddle!!

[Dawgfish]

I was only planning on using trolling motor for "hurry up & turn" & " parallel parking " & possibly the solar paddel mentioned above!
anyone ever use a trolling motor to charge batteries while sailin by rewiring it slightly?

[2BonC]

Here a picture of my solar panel to give You an idea about the size (and cost) of it:

It´s a really big one and covers almost the complete sliding hatch (80 x 65 cm- I can´t give You the tech. spec., in GE it says something about 272Wh/d on a sunny day)) . However I´m quite disappointed as far as the performance is concerned.
During a bright sunny day the generated electrical power is not sufficient to operate a Lawrance Plotter, a Raymarine ST40 Wind and a Raymarine SPX5 Auto Steering system. The SPX 5 reported "Low battery" after about 4 hours of operation. So don´t exspect to much!
I must say that the panel is mounted flat (curved) on the hatch and was partially covered by the main sail.

By the way can one give me the size of the plexi-cover of a - table ? At the moment I don´t have access to my boat but I want to prepare a map to put under the plexi cover.

rainer