OK to reverse polarity?

[Joolz]

Have a Shakespeare Glider 32 trolling motor that is used regularly in the powerboat, transom mounted. Would like to use it my wooden boat, bow mounted. Instead of switching the head around (would need to be done each time I switched boats) could I just reverse the polarity? Today I run a quick test and this worked just fine: reversing the connections to the battery reversed the prop and all speeds worked just fine. A 1 second job contrary to switching the head's direction. Tried calling their customer support line but it's hopeless. They never pick up and I tried more than once. Besides, this is likely a call centre in India or the Philippines that handles dozens of products for different companies, so they'd likely be reading their answers off a generic script anyhow.

So has anyone here tried this with success? As in, not causing any sort of damage. These seem to be just basic electric motors with virtually no electronics involved. But before frying it, figured I asked first.

 

[Joolz]

After a subsequent 40 min on hold, spoke to a rep. As expected, his answers were the typical 'we don't recommend doing this', adding that switching the head around would also void my 2 year warranty. Not that it matters, think this motor was bought exactly 2 years ago anyhow.

So the question remains: will switch polarity damage this electric motor? Hoping to hit the lake tomorrow morning as forecast calls for a very hot afternoon, so hoping to go in the early morning to try this new boat out with the trolling motor. If someone can chime in before then, that'd be great.

 

[Grub54891]

You raise an interesting question. I do have an older one I could try that on, but it would take me a few weeks to go out and get it to do. If it fails, I would not care as it's old and I never use it. in theory it might work. Weather it would burn out diodes, or circuit boards..... dunno...

 

[Redfred1]

This might help! Had a situation come up with a TM that had a busted prop. Couldn't find a replacement anywhere. Got one to fit; only problem it ran backwards. (F was R; Rwas F). Got curious; tore it open; found that that switch was a simple SPDT switch center post hot; outside was direction. I just swapped the wires on the switch. I don't have a clue how it would effect the other working parts (Speed control;etc). Will keep track with what goes down. Good Luck!!

 

[Joolz]

It does help in confirming my suspicion that it should be fine. And FYI when I tested mine earlier today, all the speeds worked just fine, and in both directions. In fact there were no signs of anything being off. Had I not seen the prop rotating the opposite direction, I'd be none the wiser.

It would surprise me if these weren't designed with the thought that a boater would at one time or another inadvertently swap the wires while connecting these to the boat's battery. If these would blow then, there'd be much cry from pissed off buyers of these.
Think I'll take the chance and give it a try in the morning. Meanwhile if someone can stop me in time, please do so by sharing your horror story.

 

[dingbat]

Switching polarities is how you control direction of rotation on a D.C. motor.

Can't think of a situation where a gear drive would be sensitive to direction of rotation unless it has a ratchet brake. You would know immediately if it did

 

[Silvertip]

Although this may not be an issue with trollers that use "speed coils" for speed control, trollers with "Maximizers" (Minnkota) or others using similar technology may not like reversed polarity. PWM units utilize solid state components that are polarity sensitive can be damaged.

 

[Joolz]

Here's an update on how it went: just fine, having the polarity reversed. My passenger didn't really cooperate so it was a very short run (she's 1) but I did try out all the speeds and spent some 20 min in the water. Shocked by how slow a 32lbs thrust motor is. My gps indicated a speed of 3.5km/h max (that's just over 2mph). Boat is a tiny 2.3m long wood skiff, flat bottomed. But weight was poorly distributed, bow heavy. Since the lady in the boat didn't want to let go of me, I couldn't just place her near the stern for a little better balance, nor did she allow me the chance to place the trolling motor on the transom (which would have mean proper polarity and the blades rotating the "right" way). But having it at the bow, pinned at max speed and only getting a mediocre 3.3km/h average was disappointing, on a windless, wakeless day. I actually row this boat faster than this using 6.5' oars that I built myself.

Is this what one can expect from a 32lbs thrust motor? Would a 50 do much better? If so I may have to look to upgrade this motor. Really, this is useless seeing how I could simply row faster while keeping the boat a lot lighter and getting some exercise in the process.

Today's much anticipated test was a true disappointment :grumpy:

 

[Joolz]

No Title

To help answer the question of how fast a 32lbs thrust motor should push a small wooden skiff, here's a pic and a bit more detail. As noted above I was surprised by how slow the experience was, seeing how this same motor is used to dock our heavy 15' FB boat with a 115hp outboard and it does so just fine. So I had anticipated that it would propel a flat bottom skiff weighing less than 40kg (empty) a lot faster than the 3.5km/h I was getting while pinned - in calm, windless conditions. Is this the norm for these trolling motors?

 

[GA_Boater]

Don't forget the TM on the bow is pulling instead of pushing, the opposite of what it is designed to do. Move it to the transom and test the speed. But don't be surprised if it isn't much faster. 32# of thrust is all that much.

 

[Joolz]

Thanks, this helps qualm my expectations. Yep, I really wanted to do a quick test with the motor in the transom but the 1yo wasn't happy being out there with me (read without her mommy). Was also hesitant to mount it to the transom initially as the back of the boat would be only some 4" above the water line. All I needed is the wake of a speeding ski boat to potentially have a disaster in my hands.

I'm confused on where the TM should be mounted for most efficiency. Have read that they work better in the bow, as pulling is more efficient than pushing. Hope this isn't the case and that I can mount it to the transom and while have weight distributed so that the bow isn't so high up - and get more useful speeds then what this initial test showed. Since this would be a 150km roundtrip drive to the lake to test it out, it may be some time till I get the chance. Meanwhile will keep an eye open for a used 55#. Like you said, this 32# mounted to the transom may not be that much better.

 

[GA_Boater]

The motor housing is pointed on the leading end to streamline the water flow to the prop. The prop end is basically flat causing maximum drag.

You can even spin the TM around on the bow to see if using as designed makes a difference.

You should leave the 1 year old at home if the transom is only 4 inches above water. No matter where the motor is mounted, any wave action can swamp the boat.

 

[Joolz]

Good point on the drag caused by the back of the housing. Hadn't considered this at the time. Suppose a proper test would have meant switching the head around, but since this motor is to be used mainly on the FB boat at the transom, opted against the mod.

To clarify, while rowing the weight is distributed so that the waterline is about an inch off the flat bottom, from bow to stern, leaving plenty of room ( or some 11" at the transom, more at the bow). If I were to sit at the transom thwart to operate the trolling motor, there'd only be about 4" to spare, which is the reason why I chose to mount the TM to the bow. If I had been given the chance, the test would have been done right next to shore, ensuring no other boats were around. Naturally we all wear PFDs at all times while on the boat.

Thankfully the place I take the kids to is only 10 min from home, a huge in-town reservoir that doesn't allow for motors of any kind (not even TM). No wake worries there, the only "wake" you get is from passing kayakers, so a safe place to introduce baby to boating (other than our FB, which she and the boys love).
But even if I was doing a solo run at the lake pictured above - could the wake of a passing-by ski boat sink this little skiff? This is stuff I need to know ahead of time, as some guys out there are true a-holes that don't seem to care or have a clue of how wake affects those on canoes, kayaks or smaller boats. And yet these idiots got their boating licenses...

 

[SOG3]

My Sears Diehard built by Minn Kota will not run with reversed polarity. Connected it backwards by mistake and couldn't figure out why it wouldn't run ,got my buddy to check and sure enough,it was backward, My battery is located at the bow for weight purposes.

 

[ondarvr]

The prop is designed to spin one direction more efficiently than the other, so it makes perfect sense that spinning it backwards would be slower. That's why people turn the top around.

 

[ArnyLogan]

Hi...i am a new user here. As per my knowledge when you took the voltage readings, was this was done with the engine at idle? Try the same again but rev the motor and see what voltages you then get.Where you do have a major problem is in the way your 3 way fridge is wired.
It should not be connected to the house battery but should have it’s own seperate twin cable power supply, run from the cranking battery to the fridge.And as has already been pointed out, you need move the earth return from the cranking battery’s negative terminal to the earth point for the earth cable coming from the cranking battery, where it earths to the body/chassis.

 

[GA_Boater]

Hi...i am a new user here. As per my knowledge when you took the voltage readings, was this was done with the engine at idle? Try the same again but rev the motor and see what voltages you then get.Where you do have a major problem is in the way your 3 way fridge is wired.
It should not be connected to the house battery but should have it’s own seperate twin cable power supply, run from the cranking battery to the fridge.And as has already been pointed out, you need move the earth return from the cranking battery’s negative terminal to the earth point for the earth cable coming from the cranking battery, where it earths to the body/chassis.

Did you post in the wrong thread? The OP's boat has no power except a trolling motor and no fridge in his dinghy, so it must be for another thread.

Also this thread is inactive and now closed.