watersnake slither on 4s li-ion?

[kdog]

hi
ive just bought an electric trolling motor, the watersnake slither with 44lb of thrust. i want to run it on 4s li-ion as i already have an 80ah battery at hand. unfortunately in the manual i came across 14.5v as stated max V and higher than this may damage the internals and void warranty etc.
i really only need about 2.0v above this stated max, i'm just wondering if anyone has exerience with over volting these critters just a tiny wee bit to run on 4s (at ~90%soc.)
ive only just bought it, so i dont really want to open it up in case i want to take it back.
TIA.
K

 

[amberwolf]

If it has a controller in it, it may have electronics that cannot handle more than that voltage.

If it has a battery built in, running it higher than that may damage the battery.

If it is just a simple brushed motor with no controller then it can probably be run on higher voltage, but it will run hotter and faster and be harder on the motor brushes.

If it's brushless then it has an electronic controller.

If it's brushed it could have a controller even if it is only on/off with no speed control.

The only certain way to know what voltage it can handle, outside of the warning already given by the manufacturer, is to open it up and verify the electronics design and component specs.

Or try it out and see if the smoke escapes.

 

[kdog]

ive done a bit of digging, the only info i can find online is for other models that are not particularly relavent to mine.
i carefully opened up the 'controller' unit and found a big old rotary switch that provides for the 5 foward speeds and 3 reverse- see pic attached.
im pretty sure its brushed, based on their other models, and it has 4 power carrying wires that exit the rotary switch and head down the shaft to the motor. so not a brushless controller as i was expecting and no internal battery.
so im not 100% sure how it controlls speed... there doesnt seem to be a brushed controller in the motor assembly if it has 4 power carrying wires heading to the motor from the rotary switch. these are the black, blue, yellow, red in the foreground, power from battery is in black at the rear.

maybe the motor has separate windings? is this a crude way of controlling power?
it does have permanent magnets, so no field windings.
maybe a brushed controller in the motor housing like in other models of this brand, but my previous brushed controllers are all two in two out which makes sense.
i tried it on 14.9V at virtually no load- so far so good

 

[kdog]

ive done some more reading which i probly should have done first, but someone can correct me if im wrong
the rotary switch selects several different taps on the windings for greater or less winding resistance (and bemf?) thereby determining power. i cant see any sensitive electronics in this apart from the lcd volt meter which i hope goes well above my req. so its just motor heat i need to worry about, and possibly early rotary switch failure.
it seems very similar to the min kota design if anyone has experience with them. (probably same factory).

 

[fechter]

I wouldn't worry too much about it. Once you start running it, the battery voltage is going to drop and get below 14.5v fairly quickly. I think the failure mode would be overheating of the windings or brushes. Another approach would be to drop the voltage using a big DC-DC converter, but that would be more expense and stuff to fail.

 

[amberwolf]

There are "schematics" (really an exploded diagram but sometiems including wiring) for various models at the manufaturer website. There are also parts lists, but there are no pictures on any of the parts pages to use for reference to know which part is actually which or to get a better idea of what they are.

I can't tell which model yours is closest to; you may have to ask them for a diagram / parts lists of yours if it's not like the listed ones.

i carefully opened up the 'controller' unit and found a big old rotary switch that provides for the 5 foward speeds and 3 reverse- see pic attached.

They could use a series of diodes to drop voltage, more diodes in series to drop more voltage for slower speed. Reverse would normally just be a contactor or relay that swaps + and - to the motor but if they have enough contacts and poles in the switch it could be done directly.

im pretty sure its brushed, based on their other models, and it has 4 power carrying wires that exit the rotary switch and head down the shaft to the motor.

Seems odd to have four wires, unless they have two separate sets of windings / brushes in the motor.

Note that brushed motors can have multiple sets of brushes; IIRC (been more than a decade since I worked much with them) you can get higher torque but lower speed by using more brushes on an otherwise similar motor, so perhaps the switch does this; using just one brush set for one speed, both for another, plus diodes for further refinement.

If it had a variable sped contrller (PWM), you'd probably have a knob for a throttle that would be really variable, not just a switch...but a switch could be used to just use a few possible positions of a "throttle" with different resistors. But such a speed controller would almost certainly have a visble heatsink or exposed metal casing, and with nothing like that visible in the picture, it's unlikely.

 

[kdog]

i watched method's tear down of his minnkota. im pretty sure the watersnake is exactly the same. the 5 forward sp/ 3 rev steps just select various resistors located down in the motor hub ( presumably for water to carry away heat).. so im going to run it on my 4s li-ion without too much concern and when it dies ill find a PWM controller for it...must admit i didnt think itd be quite this crap
just hoping it doesnt die on its inaugral trip with the wife and kids depending on it to get home

 

[kdog]

this is what im doing with this set up to make it more efficient.
ive unearthed an old brushed controller, and im bypassing the resistive speed control circuit. the fullspeed option for the rotary switch is just the normal motor wires so im popping them on to the controller output , hooking the pot up to the tiller and away we go. run smoothly, unfortunately ive only got a 350w controller atm but ill have a 500w arriving soon. dont really need to go much more above that at this stage so ill see how it goes and step up if need be.
sorry about the really crap photo i just quickly wired it up and snapped away