Trolling Motor Woes

I got an open box Intex 40lb trolling motor to throw on my inflatable. Seems to work well on 12V lead acid.

I used some leftover 18650 cells to make a 3S 60AH battery to power the thing. It ran great in my pool, giving me almost 2 hours of thrust at full speed until it cut off. The voltage on the battery was 11V when it cut off, about 3.67V per cell bank.

I have no problem running down to 3.0 V per cell, and in theory I should get at least another 2 hours but the low voltage cutoff of the motor makes that impossible. I get it, it is trying to protect a lead acid battery from going too low.

So I ripped the battery back apart and reconfigured it into a 4S. I figured the loss of amp hours will be made up for by being able to use more of the battery before LVC.

And of course, now the motor just blinks at me with a warning that the manual says is too high of voltage!

:x

My RC discharger will discharge the battery at a 1 amp an hour, which would take forever to discharge it down to 13 volts, which is what I assume the motor will start to work at. I hook up a few 12 volt Motors left over from old razor scooter to the battery and let it run all day long, but only got it down about half a volt.

Well my new plan was I'm going to bypass the relay board in the motor and hook up my own pwm controller (still on it's way from Ebay). I opened up the top of the trolling motor and bypassed the relay board entirely, connecting the positive battery lead directly to the lead going down the shaft to the motor. I disconnected all of the other wires going to the relay board, including the one to the LED display, the control on the handle, and several wires going down to the motor. I assumed these wires were for the temperature sensor and to control the LED display, as if there does not appear to be any integrated circuit in the relay board.

But now, if I connect directly to either a 12 volt battery or my 16 volt battery, the motor does nothing.

Its a red and black 12 gauge wire going down to the motor... not three wires like I would expect from a brushless motor. However there are another 12 wires or so that head down in a tidy little ribbon cable... I'm not quite sure why the motor doesn't spin I suspect that needs some sort of feedback from the ribbon cable and there are more advanced electronics closer to the motor itself.

If anybody has dissected the Intex 40 lb trolling motor, I would really appreciate some ideas. I want to bypass it's high and low voltage cut off completely.

Otherwise, I guess my next recourse would be to try a dc-to-dc buck converter, to take my 4S down to a steady 12 volt, and just use the built-in controller on the motor. I don't prefer this method, as I feel like I will be losing power off the top that I would rather just send to the motor... I guess I could always add a switch that turns off the buck converter when I get closer to the voltage that the motor will take directly.

Or I just buy a lead acid lol

Just put a few diodes series on the + battery rail, then have a switch to short them out. When you first power on the diodes will drop the voltage about 1.8 volts (ie 16 to 14.2 volts) and the motor will start up. Then once it's running use the switch to short out the diodes. The voltage drop caused by the current draw will then let the motor continue running.

Once the voltage has dropped a bit on the battery you can leave the switch closed.

At the very least the diodes would let me test if the "high voltage" cutoff is active all the time or just at startup... and since the motor isn't running at startup, the current would be very low on the diodes...

Otherwise I would need about a 60 amp solar diode if I want to run the motor with the diode in line, right?

I would love to find out where the motor senses the voltage, and just put the diode there. I'm sure that sensor is probably always low current, and that way I could forgoe the switch.

Telemachus said:

At the very least the diodes would let me test if the "high voltage" cutoff is active all the time or just at startup... and since the motor isn't running at startup, the current would be very low on the diodes... Otherwise I would need about a 60 amp solar diode if I want to run the motor with the diode in line, right?

Click to expand...

Something like that. Heatsinking would be minimal because you would switch them out of the circuit very quickly. New those diodes are $1.80 at Digikey, but you could use any diodes (like the rectifiers from an old switchmode power supply.)

I would love to find out where the motor senses the voltage, and just put the diode there. I'm sure that sensor is probably always low current, and that way I could forgoe the switch.

Click to expand...

Keep in mind that there may be an actual reason they have a HVD.

Yes I've thought about that.

I don't think it is to protect the motor... likely some sort of voltage regulator drops the 12V down to 3v or 5v for the IC. That's why I was hoping I could bypass it all with my own PWM controller in case I blow the whole control board.

Telemachus said:

I don't think it is to protect the motor... likely some sort of voltage regulator drops the 12V down to 3v or 5v for the IC.

Click to expand...

Yep, and 16V is a very common max voltage for electrolytic caps, and a common "abs max" for higher voltage IC's. So bringing that 16.8V down to 15V might get you over the hump.

High current diodes and heat sinks will be cheaper than a buck converter...

This one isn't too badly priced and would likely work with 16.8V input... at least down to the point where I could bypass it and run the motor directly.

uxcell New BIG-Size Voltage Converter Regulator DC/DC DC 24V Step-Down to DC 12V 40A 480W Buck Transformer Waterproof https://www.amazon.com/dp/B01LYK6G2Y/ref=cm_sw_r_cp_apa_i_iO4qEb621NBQN

Other than the cost Factor, do you see the advantage of one over the other?

Telemachus said:

uxcell New BIG-Size Voltage Converter Regulator DC/DC DC 24V Step-Down to DC 12V 40A 480W Buck Transformer Waterproof https://www.amazon.com/dp/B01LYK6G2Y/ref=cm_sw_r_cp_apa_i_iO4qEb621NBQN

Click to expand...

I am suspicious:

" If you use the pulsed DC power provided by the generator, please filter it with capacitor before connecting it to the converter."

Sounds like an unfiltered converter. You'd need a pretty large cap and the converter might not work with 16V since it is designed for 24V.

Hmmm... I figured they were suggesting to filter the input to keep it stable. My battery would supply a pretty clean input signal.

Yes the question is whether or not it could do anything with <17V.

And also, is the output just a pwm switched version of 16.8 volt? If so, my motor probably still won't be happy with it.

I tried it with two simple diodes in series (15.2V on my multimeter) and BINGO. My battery is sitting at 16V right now so it might end up needing 3 in series when it is fully charged.

Thanks the idea. Did you have any particular diodes at digi key that you suggest?

Telemachus said:

Thanks the idea. Did you have any particular diodes at digi key that you suggest?

Click to expand...

Not specifically. I'd go with the cheapest diodes that:
1) meet the current rating
2) have the right forward voltage loss. Usually they are around .5 to .7 volts.

Don't forget the switch to bypass them once you start drawing significant power, otherwise you will drop a lot of power across those diodes. (.6 volts at 40 amps = 24 watts.) The switch can have almost any voltage rating as long as it's rated for the current.

I I was thinking about that. I think if the connection gets broken at all, the motor will turn off. So I need a switch that will short the diodes but never break the connection... once it is shorted, all the current should follow the path of least resistance and skip the diodes, correct?

I'm a little bit worried about the electronics in the motor once I skip the diode, but like you said it appears to drop half a volt to three-quarters of a volt when the motor is running

Just to close the loop on this thread in case anyone else ever gets into a bind with the intex 40lb trolling motor...

I played with different ways to insert diodes to take 16.8V (which the motor can easily handle) and eventually ended up killing the onboard electronics (plugged a ribbon cable in backwards during testing!)

That motivated me to dig deeper and I found that the majority of the electronics is just behind the motor in the bottom. I was able to bypass all of it and now control the motor with a cheap PWM motor controller from Ebay. It will let me throw whatever voltage I want at the motor with finer control and very little wasted heat and much longer run times... and I get to choose my HVC and LVC.

Bill thanks for your ideas.