First major mistake on my tow boogie build -Help

EFOIL.builders Electronics (ESC, remote, batteries)
#1

So I am almost done building my battery for my tow boogie and now realise the LG M50LT are gonna probably impose some limitations due to the 10 -25C optimal operating range to get the max current draw of 14.4 amps. My pack is 14s8p

I didn’t realise this restriction at the time of planning and to make matters worse I live in NE florida where water temps in summer are around 29C / 85F. Yikes

I know @jkoljo is using them on his efoil and loving them but I think he rides in an area where ambient air and water are nice and mellow and he is also much lighter than I am (190lbs).

I guess my only options are to cut my losses and get the moli p42a’s or find a way to cool the battery compartment to within spec.

I have considered using a peltier connected to a water block on the outside of the case with a pump to dissipate heat quickly to the outside. On the inside a little 5v fan blowing on a coldsink.

Other thoughts are to just run a long coiled copper tube on the inside of case and use passive seawater from the nose cone. Not sure if the copper will be able to remove enough heat out the box this method.

I might also have to place the esc in a different housing separate from the battery which sucks coz I wanted it be AIO.

I am hoping all the brilliant minds on here will help me figure this out somehow.

ALoha.

#2

Batteries don’t choke like overheated germans, if it isn’t a small pack it’ll be fine. What kind of configuration do you plan?

#3

haha
Sorry forgot to mention its a 14s8p setup and already all welded together

#4

Yeah, checked some tests and see what you mean here, sorry. 8p and 7A, only 56A, i’ve seen about 60A logs for efoil starts but tow boogie must have like 1.5x the drag since it’s boogie plus board…

Battery IR would be 14*18/8=32 mohm, at 100A you’d need to get rid of most of 315W of heat after the first heating has gotten batteries up in temp… it’s too late here in sweden to do a calculation but my guess is the thermal mass of the battery will be enough to slow the heating down if you’re not towing at full current (by carving constantly, going upwind or whatever)

My plan would be to get a smart esc with temp sensing, set a current reduction from 60deg C and stop at 70 deg C to protect battery, then do some tests.

If need be, i’d try to find a close fitting ip67 alu box for the battery, fill it with oil and pump water on the box or on a cooling flange with a 12v pump.

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#5

Thanks so much Larsb,

Thats the info I needed. This build just got real.

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#6

On my boogie with a deep water start (34L board, I weigh 95kg) I pull 100amps from a 14s11p Samsung 40T pack. Slow cruising with a 1000cm2 wing is 30 amps, fast and having fun varies between 30 and 80.

My pack get to around 35°C after a session.

Your pack should be fine to use, if anything upgrade to a Bluetooth BMS so you can monitor internal temps before building a new pack.

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#7

On my tow boogie, with 13s9p 50E2, I’m only using 60A at the battery for water starts, and 12-16A for cruising. I’m using it to slingshot into swell, and don’t have much interest in flat water use, or going as fast as possible.

Having a 5’ 40L board or similar will make water starts much easier. Cruising with the 1201 ART Pro foil is very efficient at 600-700w. With a 1000cm2 HA foil, around 850w cruising. I’m into efficiency, so that I’m surfing and pumping in the waves for 3 hours in a session. The tow boogie does 25km range, and I foil about 50km in the session.

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#9

I’m so impressed with your efficiency - my Manta prop should arrive in a few days - hopefully it makes an improvement on the FR prop I’ve been using so I get numbers similar to yours!

#10

Those numbers are really good! What’s your weight and setup? (Board, wing, motor, esc, propeller?)

#11

35C is not bad, what’s your ambient?

Unfortunately the LGM50LT cells I chose drop down to 0.5 C in temps over 25C.

0.5c gives my pack 60 amps max discharge.

#12

That’s exactly how I intend to use mine most the time. Being able to tow myself in on unbroken swell a couple hundred yards out is the goal.

I have a 5”2 slingshot high roller which I think is about 42 liters. Also have a 7 10” x 20 x 140 sup board. That would be too easy.

#13

Didn’t opt for the manta unfortunately. The flite prop price shipped locally was too juicy.

Oh and btw, I have been thinking about your suggestion with some tweaks.

I couldn’t find an aluminum case in the size needed (that would be ideal) but I started thinking why not just use a pelican case like normal? I could cut a piece of acrylic sheet to shape and 5200 it in. All the space above the opening would just be used for battery connections and maybe the receiver. Battery and esc under the acrylic in the oil.

I could then put a little 12v diesel pump in the mineral oil and run 1/4” copper tubing to outside and make it go around the case a few times. The pump would circulate the mineral oil in the copper tubing and get cooled then return.

What are your thoughts?

#14

Around 20°C. Pack is usually inside to starts at 18°C.

“The preliminary datasheet for this cell lists a 14.4A “Max. Discharge Current” rating but that is only for 10°C-25°C room temperatures. At above 25°C the current rating starts dropping and is only 7.2A by the time the ambient temperature reaches 55°C…

Above 25 the rating doesn’t suddenly half, it tappers off until 55°C. At 35°C or 40°C you should still have 10amps per cell, which will be enough.

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#15

That makes more sense. I was hoping there was some flexibility.

#16

78kg, 4’5” 32L board, axis art pro 1201 (very efficient). Manta prop is more efficient than flite or flying rodeo 2 blade. I’m using a maker x hi100 with a 90mm fan cooling it, so there’s no fussing with water cooling. 65161 motor.

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#17

Is this the manta prop you’re using @Jatem?

#18

Yes. They’re a bit expensive for a fibre reinforced plastic prop, but they have good thrust and are efficient.

#19

Interesting wing, really wide high aspect. How is it in curves and general riding? I thought about testing a similar Gong YPRA xl but i fear it will just want to go in straight lines😄

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#20

The art pro 1201 turns well for a 1.2m wing. I can turn off a short period wave and get onto the wave immediately behind, or I can pump a long way out the back. The advanced fuse allows a good amount of yaw turning, and that helps initiate the turn. On smaller days it’s a brilliant wing, glides for ages, pumps well, and it has a big speed range. If you generally have powerful swell, it wouldn’t be the wing of choice.

#21

I was curious about wing WOW!

Can you comment how that would feel in flat water cruising use?

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