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Electric propulsion 101


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Mirage drive gives you an unlimited range and a nice gentle leg exercise. It requires some muscles and functioning knees. Most folx with Mirage drives dont use trolling motors. 


I like tinkering with things, so I do have a trolling motor, but still carry Mirage with me for JIC.


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Went on the water yesterday and loved the results.



1. About 5/3 Minn Kota switch. She is a funny thing. I guess Minn kota motor design is such that they connect more speed coils in parallel, to increase the speed. As opposed to using (admittedly more wasteful) method of having dedicated coils for each speed. So the switch behaves accordingly - as you rotate the knob, it engages more contacts





2. Since I have a lathe, I turned my own control knob out of 1.5" Delrin. Drilled a blind .250 hole, D&T 10/24 set screw 



3. The whole thing is mounted inside of Lowes 4x4x4 watertight enclosure (look by electrical conduits, it is grey-ish plastic)



4. Watersnake, as opposed to Minn Kota, does use 2 coils, connecting only 1 at a time, for Hi and Low speed. Due to switch design, I had to hope that it wouldn't mind both coils connected in parallel when in High Speed. After measuring the current, it appeared to work (as tested by motor in a pail of water). Tests on the water confirmed the results. Top current didn't change. With some chop and wind, I am drawing 18A out of 24lb motor at Hi (with both coils in parallel).



One day I gotta take my GPS phone with me, to measure the top speed, but I am satisfied with it so far. Where I fish, I put on about 7 miles during average fishing trip and speed is fast enough for my needs.


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Quote:

Originally Posted by Dee View Post

Do you guys prefer electric over peddle ? Let's say the new predator xl, the predator 13 with torqeedo or hobie outback or pro angler. Which would you prefer and why





To me the perfect setup in terms of overall functionality is a Hobie with the Mirage drive coupled with the Torqeedo Ultralight 403 drive. The Ultralight 403 is designed to be installed using a single ball mount on the stern of the kayak and to connect to a rudder if one is installed so you continue to use the rudder as usual and when the rudder is turned it also turns the Ultralight 403 drive.


With this setup you can pedal with the Mirage drive or use the paddle or use the Torqeedo drive or use the motor and the Mirage drive or the motor and the paddle. If I need to fight a strong current I can use the Mirage with the Torqeedo for maximum forward speed.


Total weight for the Torqeedo with its battery is 15 lbs.   The 22NF 50 Ah battery for a different motor will weigh 40 lbs by itself. I can take a long a second battery that weighs another 8 lbs. or get the one with nearly twice the Amp hours for $100 more that weighs only 9 lbs.  These a lithium batteries that can be recharged endlessly.


The only advantages of the AGM and Gel type batteries is that they do not have to be vented to the outside air and they can be used while laying on their sides. For kayak use a 22NF sealed lead acid will be good enough and cost half as much. They can be charged with a standard auto battery type charger at 2 or 4 amps and a good charger will shut off when the battery reaches 100% DOD and not overcharge the battery.


I would not worry overly about the gauge wiring used. With DC the total distance affects the current loss. On a kayak the battery to motor distance is going to be 6 feet or less for a total of 12 feet at 12v DC and 10ga is adequate. With the connectors get marine type that have an adhesive lined shrink wrap tubing segment included with the terminal.


The Torqeedo Ultralight 403 may seem ultra expensive but I paid as much for the last 6HP outboard I bought to use as a kicker on my bass boat. A 50 Ah lithium battery sells for $700 and that does not include the GPS that is incorporated into the Torqeedo battery. There are much cheaper ways to go about adding electric drive power to a kayak but they also do not provide the same level of functionality. Out on a small lake it would not matter but for going way out into the ocean and through the surf zone it can make a difference.


Every hour an American soldier commits suicide and every hour two soldiers are raped by their fellow soldiers.
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  • 1 year later...
  • 2 years later...

OK, quick update, about 5 years later. 

 

One of my LiFePo4 batteries, about 6 years old (bought it used),  has decided to act up - stopped taking charge, blinking light changed from green to yellow.

 

Few weeks before it happened, it was showing nice 40AH actual on-the-water capacity, right where it should be

 

Dusted off my Electronics degree, opened her up: peel away the top sticker, exposes 6 screw openings, Torx of some size.

 

Quality BMS (battery management system), microcontroller and all. No signs/smells of burned out elements.

 

Into the PCB (BMS) plug in 2 cables: one for a number of temp sensors, all wires being black, and another one, with may be 5 different colored leads. That's the balancing & sensing circuit, that lets the BMS measure voltage of each of 4 multi-cells individually and same connections are used to balance the cells.

 

Logic is simple: each cell needs to be in comfort range of voltage. Less than that  on any of the cells and BMS will shut down the battery. Likewise if range is exceeded. Both are there to protect the battery from overdischarge and overcharge.

 

Chemistry being LiFePo4, cells are MUCH more robust as compared to "regular" lithium in phones, laptops etc.

 

Anyway, proceeded to measure voltage on each of the 4 multi-cells (4 of these in series, each at about 3.4v, is what produces the output voltage of about 13V+).  You unplug the cell connector and using some thin wires, probe voltage between 2 adjacent leads, starting from black wire and on.

 

One of the cells was at 0v, while the other 3 sat at 3.2v. Clearly, over many charge/discharge cycles cell balance was  deteriorating till this occured. No worry, got my bench power supply at 3.2v (to match other cells), limited current to 1A and started charging the dead cell (with cell connector unplugged from the PCB). She took charge, voltage begun to rise. Bumped the amps to about 5 and may be in 20min the cell got to 3.2v. 

 

At this point plugged everything back and connected the main charger and battery came back to life, started taking charge. Back in biz !

 

Anyway, cell balancing is very tricky due to  very flat voltage curve of LiFePo4. For example, 4 cells could all be at 3.4v, yet one could be 20% charged, other 40% and so on. Due to series connection, all cells are charged at the same rate. So say the cell that was at 60% charge, will get 40% more and be at 100%. BMS will sense that and stop the charge (for the entire battery- ie ALL cells), but the cell that was only at 20% charge, received the same 40% of extra charge and got only  to 60% of charge.

 

There's a balancing mechanism in BMS that attempts to even out the cell charge levels. Battery must be connected to the charger for it to work, so keep the charger connected to the battery for few days if possible. But even then you can still get out of balance over years of use, abuse and neglect.

 

Most folx swear by bottom balancing cells once in a while - basically dropping these into state of low charge, where voltage curve is much steeper and thus you can be sure that all the cells now at the same state of (dis)charge.

 

You can imagine how crazy this balancing act can get when you deal with thousands of cells - like in Tesla.

 

Anyway, these batteries WANT TO BE STORED WHILE FULLY CHARGED.

 

Dont let them just sit there unattended for months at a time. Charge em at earliest after having used them in an outing.

 

But, should things go into whacky state, now you know how to fix it .

 

Edited by r111
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Cool input Rashid, tx ... the real test is whether that cell charges equally during your next recharging cycle.

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Very interesting.  I'm guessing this situation is why most high end RC LiPo batteries and chargers have a charge lead and a separate balance lead build in?  If I understand correctly, you manually went in and balanced the batteries, since no balance leads were built in?

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The battery pack (cells) inside of these does have the balance connector, which plugs into the BMS. That's how I got to individual nnP cells w/o exposing the actual cells - that will require a heat gun.

 

The green versions of the battery provide ez access to the BMS, 6 torx screws under the top sticky decal. Black versions are older and the top lid is hot glued in.

 

FIY, factory also places a separate , hidden, serial number sticker under top decal (some ebay sellers remove the externally visible serial #). 

 

LiFePo4 have extremely stable chemistry and are effectively an eternal battery, esp  if you can provide some manual balancing TLC as I described. Specifically, LiFePo4 are nearly immune to death-by-overcharge/discharge. Still BMS makes sure the cells stay in comfort zone. For Lifepo4, it means you dont want these dropping below 2.7v when in use or going above 3.9v when charging.

 

Valence has something like 6 temp sensors, spread out throughout the battery enclosure, BMS  disconnects the battery should temp rise out of spec.

 

And bonus section on cells.

 

State-of-the-art cells now come in capacity of up to 15AH per cell. Such cell could be about 2" in OD and 6" long and could provide up to 100A current (for about 10mins with 15AH cells) - thats almost 1/2 HP from one cell! Tesla cells are much smaller, about 6AH capacity.

 

Say we want to make  60AH 12V pack using 15AH cells.

 

We'd get 4 cells and connect them in parallel , that will provide the required 60AH, but  at 3.4V - which is the sweet voltage spot for lifepo4 . These 4 cells will always auto-balance due to parallel connection, you will not have to individually balance em and in most setups, these would be spot WELDED together, so you'd have no way to even get at individual cell. The resulting mini-pack is called 4P, for "4 cells in parallel"

 

To get the required 12V, we need to connect the 4 of 4P packs in series. The resulting configuration would be called 4S4P, using total of 16 cells (Tesla uses thousands of indiv cells !).  It is the individual 4P mini-packs that require balancing to maximize overall charge.

 

Since we can draw 60A for 1hr at 12V (thats what 60AH means for 12V batts), such battery would be rated as 60x12 = 720WHr. In reality, most of the power delivery will happen at lifepo4 sweet voltage of ~3.4v per cell, meaning even higher WHr (4 x 3.4v x 60A)

 

Enthusiasts are going crazy with the high capacity cells, building state of the art power packs for solar, bikes, bicycles, portable and other uses.

Edited by r111
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Been reading that they've developed the fluoride ion battery a bit,  doesn't need the extreme temp to operate as they once did, .they got it to operate at room temperature....

 

More energy storage,  less volatile without risk of over heating...... of course it's in the developmental stage but sounds like a promising jump in the technology..... 

 

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Lets discuss the trolling motors.

 

The bees knees are the RC brushless motors, optionally coupled to reducing gear box.  Simply insane amt of torque, extremely well proven through years of RC models - both the motors and the controllers, very small in size. 

 

2 designs have emerged: one is Torqeedo, with planetary gear reduction box, driving a largish, very aggressive high pitch custom prop, max RPM about 1500 (~$1500, includes fancy throttle controller w/ display,  battery). The baby 403 size develops about 30lb of thrust (?)

 

#2:  thruster type,  direct drive of a small turbine inside of a shroud - Bixpy, ~$1000 (battery + wrist mounted wireless controller). These rev much higher, probably north of 15K, so no need for gear box, can be driven directly by the motor. ~20lb of thrust - mostly limited due to self-imposed size limit and safety considerations (these same propulsion units  could be used for diving).

 

I hope that an enterprising type in China sees an opportunity here and gives us something like a barebone propulsion kit, Torqeedo style head (motor + planetary gear) with your choice of shaft length (say 1" OD in 18" and  24"), separate (not shaft-mounted) sealed ESC controller, your choice of props: 2 or 3 blade, with say 3-4 pcs included in the kit. Or do a thruster-type head instead. May be 35-40lb of thrust

 

You'd use your own battery with it (most RC motors are very voltage friendly, anything from 6v on to 24v+). Be probably $50 in parts, sell it for $200. Design it so that shaft seal is user-replaceable.  Heck, may be even the motor - but those are practically eternal, no brushes to replace. These would sell like hot cakes, world-wide. Aliexpress ! :)

 

 

 

 

 

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