setting up a 'solar canoe' without battery, would like general info please.....

[dudevato]

   I have a 16 foot, 62 lb canoe with outriggers and 4ea. 130 watt Kyocera panels wired through 4 switches, direct to a 12 volt, 28 pounds of thrust Minkota trolling motor.  I'd like any and all info anyone would care to offer.
   The panels are wired in series, I think it is called.  All the +'s are wired together.  The tag on the back of the panels shows:
Pmax - 130w    UPmax - 17.6 volts   IPmax - 7.39a   Voc - 21.9v   Isc - 8.02
   I've had it out a few times and I can tell you it 'boogies'     I'm going to make a bumper sticker: Paddling Sucks!
   I've got a few questions that I'd like some input on, please:  Am I giving the motor too much volts?  I have the motor speed selector on 'full' and switch on/off my panels as I choose.
   Is there any way of figuring if another panel or 2 would increase my speed?  I'm not interested in using a battery. 
   I'm thinking I'm giving the motor some 28-30 amps, is this correct?
   I've seen an analog volt meter on line that shows the upper limit to be 16 volts, would I burn this out?  I'd also like an analog amp meter, to keep an eye on things and to make the dash board look cool.
   Again, thank you for any and all input on this fun project.  I've a pretty neat pic of the setup at the lake I can email if anyone interested in seeing it.  I'm in southern california, so there's plenty of sun.  thanks for your knowledge & typing. dudevato@yahoo.com     Gary 

[Rover]

If all the + wires are together its parallel , not series, which would make sense since if they were series then voltage would be 4x the panel voltage, as wired it is 1x panel voltage, and right onthe border of the tolerance fo the motor. The motor probably has amp draw figures, please post them.

Figure in perfect conditions the panels tell you in series ... rougly 29-30 amps , but your probably not in perfect conditions.. so in this scenario , without  battery figure 80% would be my guess .


As wired .. with the 4 switches, I can only assume its to prevent over current on the motor or play the position of a blocking diode for a shaed panel, but on a craft that small I'd go with the over current since more than likely that all solar panels are receiving sunlight equaly unless differentially angled.

...as far as increasing speed... need to know the max draw of the motor as I said above.. is it posible.. maybe.. .could also add another minkota and more panels. I would love to see a picture of the craft.

You might also want to put n ammeter in line to the motor to see what you are actually getting out of the panels, these can be bought/made cheaply for under 30$

I'm actually in the design stage of doing something similar with a hobbie cat catamaran hull ( I don't have the hull set yet, but thats the easy part)

[Rover]

I menat in parallel 29-30 amps

[klsmurf]

Yes, Please post a picture. I'ld really like to see this set up.

[Rover]

...sorry one more thing, I am designing mine around a battery bank... and you might think of adding at least one battery to the mix to get you through temporary cloud cover, your motor is going to react directly in proportion to the output of the panels, clouds goes over an your wine glass may tip over as the motor drops rpms. In your case , think of it as a power buffer, I know you don't have the hull length and beam to support a banks weight, but a sole battery can get you through the cloudy spots for a bit.

[dudevato]

R, thanks for your response. I use the 4 switches only to control the speed, I've no idea about Over Supplying the motor with electricity. The more switches I turn on, the faster I go.  I don't want to do anything that will shorten the life of the motor.  Again I don't want a battery, there are no clouds in california    The sun is pretty much straight overhead and clear sky/no clouds.
   I checked the motor and there are no specs on it as far as amps drawn.
   Thanks for correcting me about series/parallel.  So I've done the parallel thing.
   If I am about at the limit as far as supplying the motor with 16 volts, is there some cheap/easy way to limit the 'supply' to 12 volts?
   The pic I have of the boat is 825 kb's, 'much more than the 150 limit here.  'Don't know how to get around that.  I'll send a couple of pics attached to an email if you get in touch. 
   As things are set up now I have 2 panels on each side of the canoe, at gunnel level, running parallel with the boat.  I plan on moving them 'over the canoe' to provide shade.  The only thing worse than paddling is setting in the sun 
Again, thanks for the info.  Gary - Lancaster, Ca.  dudevato@yahoo.com 

[Rover]

Hi Dudevato,

Ok no reason to start a new thread .... people are interested in the whole thing.  Also I'm not worried about your motor overspeeding, I don't see that happening.

[Rover]

Hi D,
I think we would be much better informed with a pic of the vessel... I'm pretty sure there is information about on how to reduce the picture size. However, if you just want to email the pic to rover at symbol  (@)  rovr1.com , I will post it for you.

Also if you would ... please post the model # of the minkota  , might be able to dredge up the current draw.

[Rover]

Ahh the 4 switches are a rudimentary throttle control, I guess the throttle on the minkota is locked wide open, or removed etc. Last night I stated "prevent over current" this was a gaff on my part, you won't overcurrent the motor. A 28 lb thust Minkota is also one of the smallest thrust motors they make.

Once again, feel free to email me the pic

[ghurd]

I bet you are not getting full speed.

Is there prop cavitation?
Have you made something to stop cavitation, like a little Dolphin motor plate or something? (I always wanted to, never did)

I don't know how much drag the outriggers add.  Not much?

I have a Minn Kota MX65.  #36 thrust?
Fiberglass canoe is #210, 18' and ~45" wide.
2 adults, child, G27 battery, cooler, etc.
At about half throttle, the shaft separates the water until the air reaches the prop.  Have to almost completely stop the prop to let the air out.

If half throttle on an MX65 is #18 (2/3rds of your motor's max), and mine is heavier but a bit longer, seems like your system must not getting full motor speed?
If it is not getting full speed, then it is not getting enough amps.
I don't see how regulating to '12V' (14V) will help.

Might check the voltage at the motor in great sun at noon with all 4 PVs and full throttle.
12 or 15V would be good.
8 or 10V is a lot slower.

Sounds fun!
G-

[Rover]

Ghurd,
Thinking about the drag/displacement , you are probably worse of than one with outriggers. There some  math involved, and although one would think that the outriggers would create more drag, you can't really think in terms of drag. For a given weight fully loaded with roughly the same displacement there is the benefit of increased water line.

Your's full loaded is basically a displacement hull pushing more water. I think part of your cavitation issue is that you can't get boat up to a speed to match what the prop wants to do, if there was increased water flow through the prop, I think cavitation woud decrease.  I'd be interested to see if your cavitation issue remains the same with a lighter load, allowing you to go faster until it cavitates.

My trawler is a true displacement hull with a keel and 36 hp diesel motor, If I start out full throttle, my prob cavitates until I get up to about 4 knots.
 

[ghurd]

I figured mine was worse, but the motor cavitation issue is all speed.
The motor is in clean water, well off to the side of the canoe (way too far for comfort, but I can turn left!), and the prop is maybe 24" deep.

I can start out at full throttle with no problems, but as speed increases, the air pocket behind the shaft gets deeper and deeper, until it reaches the prop.
There is very little speed difference between the air behind the shaft only being a few inches down, to being all the way down.
A tin can and hose clamp would fix it (I think).  Then it could get up on plane.   

My line of thinking is if Gary's is better, meaning it can go faster with less power, I doubt his motor is getting full power, or it would have the same issues as mine.
Make sense to you?

My back is too old and bad anymore to be wrangling 18x4' #210 on and off the truck cap/shell anyway... haven't used it in 10 years.
G-

[Rover]

Hmm... interesting... I'm not so sure you're actually experiencing cavitation, which is kinda like boiling water. If you see it as your speed increases, to what you might think as a plane, does your stern drop lower in the water?, if it does, you're not planning. It might may also me due to trapped air below the vessel is being forced under the craft , as you increase speed the bow raises a bit,  trapping more air (depends on hull design a flat bottom may be more prone to this than a v-hull),  this air may be force downwards to the prop.

I can make a prob cavitate by going full throttle in my slip, not going anywhere, water boiling, it is not introduced air from the surface.


This is all fun , but I want to see a pic of Gary's .... interested in how long the outriggers are, etc.

[ghurd]

OK- wrong word?
Mine goes fast enough the shaft plows the water out of the way to the extent there is air behind the shaft, and at a critical speed, the air reaches down to the prop.
Once it catches a bit of air, the boat speed goes to 'still moving some'.  Have to almost completely stop the motor to let it out.

The canoe makes a bit of a wake, but it is well behind the motor.  No air in the prop is coming from hull disturbances.

On plane was a joke.
G-

[Rover]

Was actually hoping you managed a plane with a trolling motor

I'd like to know the amp draw of Gary's minkota, been to the minkota website... kinda light on technical details, sure lbs thrust ... (actually a prettty useless measurement, further research shows opinins that they like to state output in lbs thrust as it more marketable than actual hp, and there realy is no direct correlation, least not one I could find ) , and voltage. 

so at a possible 20-30 amp max output from solar (wide variation , water reflection may help), we still don't know the current draw of the motor. The original question being about voltage adding another panel, I can't see it hurting  in parallel since it will be the same as he has now, but is it a waste?.. don't know .

 

[Rover]

cause I'm kinda bored today, found an interesting  thread on here http://forums.iboats.com/showthread.php?t=229711

based on the discussion, look like amp draw is in the range of 20-30 amps

Ghurd, hehehe, in the same thread one guy also discusesses cavitation issues, and placing the prop deeper

So... I may go with another panel , but I still like a battery buffer ( On switch connects battery to panels to motor , (diodes on the solar) , this could be improved with a controller , but I'm thinking if the battery is fully charged , when on ... basically direct draw from solar.)

Not knowing if the vessel is being use on a large body of water or small, hate to see anything go out solely based on solar, without some kind of small reserve

[Ungrounded Lightning Rod]

You might try switching the panels into a series-parallel configuration (two groups of two parallel panels with the groups hooked in series) to see if that gives you an even faster drive.

I'm not sure how trolling motors are set up:  Are they permanent-magnet motors, series wound, parallel wound, or what?

I'd assume either PM or series wound.  A PM would go faster with more voltage if there was adequate current.  Excessive voltage is only an issue for brushes (if it's low enough not to break through the insulation - which this would be).  The main burnout factor in a motor is overheating from excessive current.  So I wouldn't sweat hooking the panels in series to boost the voltage unless there are semiconductors in the trolling motor's control box.

[ghurd]

"Excessive voltage is only an issue for brushes"
Not necessarily.

I would want to have a deeper look at the speed control circuit before connecting it up for anything higher than the high end of 12V.

My MX series has a 'Maximizer' circuit.  And it really works.
According to the sales pitch at the time, there are points in the motor rotation where the current really does not do anything but drain the battery.
The Maximizer detects these points and stops current during those periods.  It was supposed to have a larger positive effect at lower RPM.
It sort of sounded like a synchronized PWM control, and maximizer equipped motors were variable speed instead of 5(?) fixed speeds.
I believe they also sold a maximizer circuit as a separate unit for use with non-MX motors.
Later, IIRC, they claimed to include this circuit in all of their motors.

If they still do that, not sure 24V (42Voc) is a great idea.
G-

[TomW]

Hey, guys, shoot me if I am wrong but...

Doesn't Ohms law still apply?

The motor will only draw as many amps as it needs to satisfy that at a given voltage, regardless of the amps available.

Same reason your car battery can drive a few amps into a light bulb and 500 amps into the starter. Massive current is available in a battery but each device only satisfies Ohms law on current draw.

I would not worry about a few volts over rating on the motor until you get a lot more panels driving it. The control may be another story if it is electronic. Lots of those components don't like excess voltage. Others won't care.

Or not??

Tom

[Rover]

I agree Tom, which is why I back tracked from my 'prevent over current " statement

[Ungrounded Lightning Rod]

Hey, guys, shoot me if I am wrong but...

Doesn't Ohms law still apply?

Motors are a special case because the dominant factor is the back-EMF generated by their rotation.  Ohm's law still applies - to the difference in voltage between the battery and the armature (or whatever).

Motors are wound with very low resistance to minimize losses.  When they're not spinning you apply Ohm's law straight to this low resistance and the supply current - and get the "inrush" current for a stalled motor.  As they spin up the generated voltage fights the supply voltage and the current drops.

What happens in detail depends on what type of motor it is and how it's connected.  For commutated DC motors:
 - For a PM motor with the armature straight across the supply voltage, RPM is essentially proportional to applied voltage.;  (It would be EXACTlY proportional to voltage if the thing was made with superconductors.  B-) )
 - For a parallel-connected motor the field strength also rises in proportion to the applied voltage.  So the RPM is essentially constant despite voltage variations.
 - For a series-wound motor the field strength is strongest when the motor is stalled.  These are sort of trying for constant HP under varying load conditions and provide max torque at stall.  Raising the available voltage raises the available HP.  (Not a likely arrangement for a trolling motor.)
 - The series-parallel hybrid has two sets of field coils, getting much of the series motor's high stall torque but achieving the parallel motor's voltage-independent unloaded speed limitation.

All of that completely ignores the controller, of course.  As was pointed out above, that's likely to be made of semiconductors and unhappy (perhaps to the "magic smoke runs away" stage) with input voltages above its ratings.