solar panel wired direct to a brushed motor?

[parajared]

Would it be a bad idea to run raw solar amperage direct from panel to a brushed motor; no esc, no solar charge controller, no battery?

I've gotten into multi-day kayak touring and I have a decently efficient boat but the possibly hairbrained notion of a solar panel assisting with overall effort has taken it's hold. I imagine a fixed-position motor mounted to the existing rudder mount while I provide the steering and the rest of the momentum with a paddle. There would be no power levels, no steering the motor, no battery storage, just a simple on/off relay that cuts motor power when I don't want it.

Here's what I'm worried about:
1) It seems like there might need to be some kind of circuitry other than an on/off relay needed between panel and motor, would something overload?
2) the panel voltage I currently have is "12 volts" and the trolling motor I am considering is also "12 volts" but since my solar panel reads 18 volts in direct sun and I'm not sure if the "12 volt" motor could handle that. I'm looking at an old 8lb thrust Minn Kota on Craigslist but haven't bought it.

 

[JackFlorey]

It works OK, but you run into the problems of:

1) the motor collapsing the panel to a very low-power state and having it stay there
2) Poor match between panel and motor (such that you are only getting 10% of the power you could)

Most 12V systems will work from 9-16V. The load will likely keep the panel's voltage lower than its Voc measurement.

 

[harrisonpatm]

This would "work" with a small motor. I'm assuming you're imagining a motor and a propeller sticking in the water? If so, you could do tests to see how much current is required by the motor to push you along. I'm assuming it's a decent amount; water creates a Decent amount of drag. If so, the motor will attempt to pull more current from the panel then what it's able to provide, at which point the voltage will collapse and the motor will stall.

But if it's a small motor/propeller, the current draw might not be too high. Downside is of course that a small motor = weak motor, and you aren't going to see much propulsion.

I like the idea a lot though, it being a very simple a basic propulsion assist. In think this concept would work better for something like a trolling motor, rather than effective propulsion.

I'd love to see what you come up with, if you do end up trying it. Sounds like you already have the parts, why not just give it a test and report back? Worse that would happen is it just wouldn't go.

 

[harrisonpatm]

How would the motor work without an esc?

Brused DC motors just need a DC voltage source to run. If you give it it's rated voltage, it'll spin at a certain speed and try to stay at said speed depending on load.

In an application where you want to control speed of a brushed motor, you would want some type of ESC, yes (though you could also get a very rough control of speed by adjusting input voltage yourself). What OP is suggesting is that he doesn't care about specific speed in his case, he just wants sun-powered go juice, as much as his solar panel can provide, and his paddles will take care of the rest.

 

[fill]

you could do it with a bldc too just use 3 panels and sit them under a shade with a 1 panel sized slot,
attach the motor to a central pole supporting the shade and start it spinning, each panel exposed will fire one phase of the motor.......

 

[amberwolf]

It works for the little solar powered personal fans...but I don't know how well it will work for a kayak propulsion.

If you didn't already have the panel, you could do some testing of how much current
the motor will take in various situations under the real load it will have, with the prop you'll use, etc., directly from a battery of the expected panel voltage. Once you have that, then you can see if the panel you would use could support that load.

If you already have the panel and motor, you could just test it and see if it works. It shouldn't hurt anything, but it might not work (if panel can't support the load).

The one condition it could hurt things is if the panel can create enough current to overheat the motor windings without bringing it out of stall condition, but not enough to actually spin it under load.

Remember also that as the panel angle changes, or it is shaded, etc., it's output will change.

 

[parajared]

I have the solar panels but not the motor. The Craigslist trolling motor I'm interested in is $22 but it is in rough shape and also looks ancient.

The 30lb thrust Minn Kota's maximum amperage is 30amps but I can't find amperage specs on the old 8lb thrust Minn Kota 10 that's currently on Craigslist.

It seems I can mount a comfortable max of 150 watts of solar on the back of the kayak in such a way that it won't interfere with paddling so that would be a max amperage of about 9 if I mounted all three 50w panels.

In a youtube video (FovKYNA7HkY) a guy pulls 8 amps to run a 12v trolling motor paired to a kayak to 3mph with no paddling so it seems worthwhile to mount all three panels.

According to Johnson Outdoor all trolling motors max out at 5mph and one should calculate for 2 lbs of thrust needed for every 100 lbs of boat weight. When I'm fully loaded up for kayak touring my total weight would be about 325lbs (including the weight of the boat). I'm not sure if 150 watts would exceed 3lbs of thrust or not but I feel inclined to put all 150 watts on and gamble away my $22 on the Craigslist motor.

I'll let you know how it goes

Edit: also it would be better to do a safety switch instead of a wireless relay in case I fall out of the kayak. Don't want the kayak to keep going without me lol.

 

[parajared]

you could do it with a bldc too just use 3 panels and sit them under a shade with a 1 panel sized slot,
attach the motor to a central pole supporting the shade and start it spinning, each panel exposed will fire one phase of the motor.......

Lol,
Like this?

 

[harrisonpatm]

I have the solar panels but not the motor. The Craigslist trolling motor I'm interested in is $22 but it is in rough shape and also looks ancient.

The 30lb thrust Minn Kota's maximum amperage is 30amps but I can't find amperage specs on the old 8lb thrust Minn Kota 10 that's currently on Craigslist.

It seems I can mount a comfortable max of 150 watts of solar on the back of the kayak in such a way that it won't interfere with paddling so that would be a max amperage of about 9 if I mounted all three 50w panels.

In a youtube video (FovKYNA7HkY) a guy pulls 8 amps to run a 12v trolling motor paired to a kayak to 3mph with no paddling so it seems worthwhile to mount all three panels.

According to Johnson Outdoor all trolling motors max out at 5mph and one should calculate for 2 lbs of thrust needed for every 100 lbs of boat weight. When I'm fully loaded up for kayak touring my total weight would be about 325lbs (including the weight of the boat). I'm not sure if 150 watts would exceed 3lbs of thrust or not but I feel inclined to put all 150 watts on and gamble away my $22 on the Craigslist motor.

I'll let you know how it goes

Edit: also it would be better to do a safety switch instead of a wireless relay in case I fall out of the kayak. Don't want the kayak to keep going without me lol.

Not only does it sound like you've done your homework, it sounds like you don't have unreasonable high expectations for speed. Go for it.

 

[amberwolf]

It seems I can mount a comfortable max of 150 watts of solar on the back of the kayak in such a way that it won't interfere with paddling so that would be a max amperage of about 9 if I mounted all three 50w panels.

do you know what output they will actually have in your usage where you are going to use them? (different lattitudes/seasons/etc get differnet amonts of sun, and weather/time of day,e tc)

Edit: also it would be better to do a safety switch instead of a wireless relay in case I fall out of the kayak. Don't want the kayak to keep going without me lol.

you could use an anderson pair as a loop key in eihter positive or negative, then tie the loop key to your lifejacket so if you fall out it yanks it off.

 

[Hwy89]

Interesting project Jared, hope to hear how it works. My thought is that adding a small battery to the circuit to buffer the fluctuations in solar output would help protect the motor from heating up in near stall conditions and provide a bit smoother and more predictable performance.

 

[glennb]

I like the idea in principle (albeit, I think sails are more practical).

Finding/making/modifying the prop is crucial though, and I can’t envisage a test rig you could fashion to acquire the data.

I’d want to be assisting the motor directly (or vice versa) by way of a linked drivetrain I.e. motorised Hobie style propulsion as opposed to paddling.