36V battery for 29.6V outboard?

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Alex M
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36V battery for 29.6V outboard?

Post by Alex M » Dec 08, 2017 3:43 pm

Good day, people. I hope this is the right place to ask.
Considering electric outboard on a kayak - I'm tired of my 2.5 HP four-stroke Suzuki. Nice motor, runs forever on 1 liter of gas at 6 mph speed, but... 2.5 HP is more than I need, plenty of noise (quieter than 2-strokes, but I'm sitting next to it, side-mounted), and 30 lbs is heavy on the side (this is THE lightest water-cooled 4-stroke).

Surprisingly, E-outboard market is in poor shape. Zillions of lame Minn Kota - forgive me, anglers on a quite lake standing upright in 150 lbs canoe - I'm in coastal sea waters, need more than 40 lbs thrust, and operate from seating position. Majority of them are either 12V (arrghh, heavy led batteries). Or, if it's 24V and/or thrust > 40 lbs, then it has inconvenient 40"-50" long shaft and weigh as much as my gas motor or even more (yes, without battery).

I'm looking at Torqueedo Ultralight 403 - If I'll come up with THAT much money.

Geared motor max. input power 400W (doesn't sound like much, but propeller thrust is comparable to 1 HP gas motor).
Battery Li-ion 915 Wh, $US 800 (!!!). This is upgrade, stock battery on the motor is merely 320 Wh and you HAVE to buy it with 320 Wh.

Here is the problem: odd voltage
Nominal voltage 29.6
Final charging voltage 33.6
Final discharge voltage 24.0 (what the heck is "final discharge", must be BMS cut-off voltage).

So... If I get 36V*700WH Li-ion or Li-Po ebike battery for $300-400, with max voltage 42V and BMS cut-off 28V, and charge it to 33.6V and run down to to 28V - what will it be in terms of % charge - from 0% to 70%? Though, running it down to 0% is bad, bad.

dustNbone
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Re: 36V battery for 29.6V outboard?

Post by dustNbone » Dec 08, 2017 10:58 pm

A 36V Li-Ion battery will be 10 cells in series, so at 33.6V each cell will be at 3.36V

Image

If you look at this graph you can see that at 3.36V a Li-Ion cell is basically dead, or just about to die. It's full at 4.1 or 4.2V, so I 36V battery that's full is 41 or 42V.

A 24V Li-Ion pack is usually 7 cells in series, so 29.4V full and 21V or so empty.

I guess about ideal would be an 8S pack, 33.6V full and 24V or so empty. That's probably what they're using.

Alex M
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Re: 36V battery for 29.6V outboard?

Post by Alex M » Dec 08, 2017 11:31 pm

I see on this graph that 33.6V means that 2000 mah was drawn out of 3000 mah cell? So I will only have 1/3 of 700 WH to play with.
Not worth the trouble.

And then, I will kill it if I run it down to 2.8V. Below 3.2V it can't support the load anymore, the graph just drops down.

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Re: 36V battery for 29.6V outboard?

Post by Monstarr » Dec 15, 2017 4:17 am

haswing protruar 2.0 rs ?

Image

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Re: 36V battery for 29.6V outboard?

Post by Alex M » Dec 15, 2017 2:25 pm

Didn't know about this Haswing. Thanks.
2,000 Euro, but it is 24V!
One thing makes it unsuitable for me - "fresh water only".
18 lbs weight is reasonable, but on a kayak this outboard means - side mount, and then it's a bit heavy on the side, though not as heavy as my current 30 lbs gas motor. OTH, Torqueedo 403 is more centrally mounted (close to centerline, close to stern), weighs 5 lbs without battery, though it's weak and slow @1 HP (and again, weird 33.6 voltage).

I looked around - yes, 33.6V must be 8s battery, plenty of chargers and BMS but nobody sells complete 8s packs with BMS and enclosure, except for very small 8s for RC products.

Here is an idea - an alternative to $$$ 33.6V battery - refill it when it dies. There are few companies in the US that do this for ebikes, cost less than a new battery, hopefully they will do it for this one too. They pack it with new 3.7V cells. Oh boy, they got us by the balls with proprietary batteries in EV-Ebikes industry too...

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Re: 36V battery for 29.6V outboard?

Post by justin_le » Dec 16, 2017 8:41 pm

The other possibility is to run a DC-DC converter that will take any 36V-48V nominal ebike battery pack and then step that down to a 29V output for your torqueedo motor. That has the most flexibility in terms of battery supply. We recently did something similar for some dealers of the VIVAX assist minimalist conversion kits in the US. This system is also designed around an 8S pack arrangement which is rare in the world of ebikes, and their motor controllers have an upper voltage shuttoff prevention so that they don't operate if the supply is over 33V.

The dealer really wanted to use our LiGo battery modules so we made this item here:
http://www.ebikes.ca/shop/electric-bicy ... vivax.html

The operating efficiency is in the 94-95% range, so you take a small hit there but not much. This one is only for 200 watts of continuous power output so it wouldn't work with your torqueedo drive at full power, but if you search ebay or aliexpress for dc-dc converters with 36-48V input ranges and an adjustable output voltage you should be able to find plenty that would do the trick, like this
https://www.ebay.com/itm/112519878057

Just be prepared that published spec's on china sourced products like this are often grossly overstated, so normally you'd want to source something that is rated at like twice the current than what you'll actually be drawing.
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Alex M
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Re: 36V battery for 29.6V outboard?

Post by Alex M » Dec 16, 2017 9:07 pm

Thanks, Justin. 95% DC-DC is impressive, didn't know this was possible, most converters are under 75% efficiency. Yes, 200W output is below 400W of that Torqy 403. One more connector is also a minus, on water.

I understand what Germans were thinking with Torqy 403 - more volts, less amps - but why not going all the way to 36V nominal :)...

Yes, ebay and ali-express batteries are toss a coin. There are few "more-less" established companies in the US and Hong, to get batteries from. Though, with better quality the price difference shrinks quickly.

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Re: 36V battery for 29.6V outboard?

Post by justin_le » Dec 16, 2017 9:51 pm

Alex M wrote:
Dec 16, 2017 9:07 pm
Thanks, Justin. 95% DC-DC is impressive, didn't know this was possible, most converters are under 75% efficiency.
Normally it's more like 80-90%, not 75%, but in any case that's because most converters would have their components cost optimized for the current & power level required using the inductors and mosfets at the edge of their designed operating area. If you optimize the design for max efficiency with minimal losses, then you end up with much less current through the power electronics and magnetics than what they can handle, so you spend more and have a larger/bulkier package for the power output. It's not that difficult to make a DC-DC with high efficiency, it's just not very economical when people are comparing specs / $$.
Yes, 200W output is below 400W of that Torqy 403.
If your goal is powering a kayak though, you might be surprised at how pointless it is to even put 400 watts of power into the engine. You can pretty effectively get up to hull speed with like 200 watts in an efficient boat hull like this, and the incremental gains in speed make it fairly pointless to drive the power much higher. You end up with like another 0.5 kph in your speed and cut your range in half.

I was playing around last weekend in my rowing wherry with an RC plane propeller powered from an electric skateboard hub motor on a long shaft, it was crazy how well you can cruise from even 70-100 watts of power, and how little each additional 100 watts added after that.
Yes, ebay and ali-express batteries are toss a coin.
I was referring more to their dc-dc converters than batteries, but yeah the same thing generally applies across the board! For the DC-DC's, as a rule divide their claimed current output by 2 or 3 to get a reasonable continuous amps rating (at least that's what we found on half a dozen various samples).

In any case I'll be curious which way you go and how this all pans out with the Torqueedo unit. There really is a dearth of good options for electric boat assist in this power range. It's all either lame trolling motors or large outboard replacements. The other option that I've liked the look of is electricpaddle
https://www.electricpaddle.com/

Even though it's a 24V battery system that they offer, their motor controller works just fine with 36V and 48V packs, if my memory is correct from when we chatted with them at the port townsend boat festival.
Big Dummy Frame (yes This One, thanks ES!) with prototype 26" Grin all-axle front hub, Phaserunner controller, and 52V 11Ah Cellman triangle pack
My website: http://www.ebikes.ca
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Alex M
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Re: 36V battery for 29.6V outboard?

Post by Alex M » Dec 17, 2017 2:18 pm

I am aware of problems with speed on water. Resistance to boat movement increases 8 times when you increase speed 2 times, so every additional 0.5 km/hour results in huge drop of range. Besides, Torqueedo 400W motor has peak efficiency - don't remember - at 200W or less. Its max speed is 8-9km with user-added "airfoil" on the motor leg, but at this speed the range is about 2 km.

The bottom line - with this Torqy 403, to move at reasonable 6km/hour (4 mph), for a reasonable distance, with enough margins for headwinds and opposing currents (when I need help the most), 800-900 WH battery is a must. They sell it with mandatory 300WH battery - this could still change, I'm not in a hurry with this project - hey, it's a kayak, can propel it without any motor :)

I've researched all the existing salt-water outboards by now - yes,Townsend EP too. He does say his motor works at any battery voltage - this is very unusual. It has a bit loud whining sound in the videos. Propeller is huge 14", so it has to be very far on the side mount on kayak. The tiller is attached too high, his 1st model from 2013 looked better in this respect. In a kayak you're sitting at waterline (or lower yet), so this tiller ends up at your eye-brows. His motor is a good solution for dinghies and rowing boats though.

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