150 Amps on a 72v efoil enough?


I have already covered my boat outboard to a lion 72v 5.4kwh system from gasoline.

So I like speed and I thought I’m about 94kg heavy and I’m gonna need a big motor for my gun case efoil project.

Now I just read in a post that it doesn’t matter what voltage you run on, it’s gonna be the same amps to get you up on foil (he wrote normally around 180amps).

Is this really correct? I mean at full charge 180amps times 84v that’s… 15 darn kw being drawn.

I hadn’t thought about that, so I had only ordered a 150A Daly BMS, but I need to double check if that’s enough or not with the community. Thinking of building the pack with 4000mW molicell batteries (30A)… But do I need get a beefier BMS? I was hoping to get up and flying at around 100A, but I got no experience of foils (only building that outsized electric outboard conversion - where things are pretty similar in many ways)…

You can bypass the bms for discharging and only use it for charging. Like this the only limmit is the battery.

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Lift power is about 3kW so at 72V about 40A battery current is needed. Motor current, which is handled by the ESC, is roughly 100-150A (but could be more depending on the setup used.)

You won’t need a more powerful BMS than 150A since BMS is handling battery current.

Beware, 20s is a lethal voltage and it’s even worse in damp conditions, can’t be recommended. It only takes one death and then we’re all going to be heavily regulated so please go with a lower voltage - and don’t screw up! I’ve unfortunately tried frying fingers on my 72V ebike and it’s not nice… really not.

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Thanks for the reply. And yes - this high voltage and the nature of this being very close to water vs my outboard does scare me. I have huge respect for it in this project.

I’m cool with lowering the voltage, what should I strive for then? Below 50v?

I know high voltage does play a role in increasing the risks of having the electricity being being lead out ways that can suddenly lead to the body. The voltage is what makes it easier for an accident to happen but it’s the amps (current that does the damage). Corrosion is speed up by higher voltage which is another reason.

But any voltage over 30v will usually break the skin barrier too.

I know it’s all about minimizing risks. But is a 60v that much more safe than say 72v when we have these batteries being able to push huge amounts of current to us.

So I’m all about safety and I was actually hoping the game here A LOT when it comes to safe connectors. My plan is to used double o-ring heavy duty water proof connectors. Also the other designs I’ve seen has only two layers between the sea and the cells/ESC. I was thinking of three layers; the outside case, a second 3D printed water tight box and then both the Flipsky water proof ESC and the battery in special designed water proof cases I’ll print with my new enclosed heated 3D printer, printed with Nylon. Thus upping the game to three layers.

Do you know if I can use my new 20S BMS with say 14S battery pack? I know it’s not recommended but I heard some of these BMSs can be reprogrammed to use fewer of the balancing wires etc. I just don’t know if the Daly one can be used with fewer/reprogrammed.

So… What voltage is considered safe here and should I just sell my 150A BMS and get another one? I’m not particularly keen on running a ESC directly to the battery without a BMS and just use a BMS for charging and rely on ESC + battery fuse.

Safety depends on how you handle things but let’s say you don’t handle connections being wet or salty, then 60V is about what skin will isolate. I run 12s but would consider 14s ok, even though technically both these voltages are too high in salt water.

I think dual isolation is good enough, as current will take the easiest path, with a plastic enclosure there’s nothing that leads current with you being the shortest path. That relies on you not tinkering in the box while out on the water though😀

Well if salt water (yes that’s the use case here in western sweden) enters box one, theres now only one layer between me and leads carrying current. Anyway each to their own on that.

Hmm… I ordered the strongest Flipsky motor with peak 19500w, but I don’t really care about top speed since this is gonna be my first efoil build. So high voltage here isn’t a priority vs my outboard where it is. If it’s successful on getting me up flying then I’ll count it a success.

I guess 12S makes the battery pack cheaper to build too, and when I look at BMSs for 12S peak 350 Amp /100A continuous (more than enough once you fly) that’s damn cheap. Actually this would make the pack quite cheap vs my first estimates.

How about cooling battery packs. I’m guessing heat is a big issue here. Anyone made any nice solutions for that?

With a big pack it’s no issue, with a small it gets interesting. Heat exchange to the outside is normally enough if you use some heatsink.

There have been a number of posts recently about using “high” S count batteries. Most builds here seem to limit it to 12S (50V) for a variety of reasons - safety, weight, cost etc. There are a number of threads here that discuss the safety aspect but you are already aware of the risks.

I’m wondering why you chose a gun case design that apparently requires a lot of “Jam” to get up on foil - for obvious reasons.

If you like speed choosing a smaller more foil efficient board would let you go as fast as you dare and allow you to utilize a “safer - lighter - less expensive” drive system.

At 85kg I use a 100l Fliteboard on a 1300cm foil 65161 motor and a 75200 VESC and can hit 40kmh - a speed btw I am not comfortable at!!
I am currently using a 10S battery and don’t have any problem starting. The 40kmh might not sound “fast” but falling at that speed can sting!:grinning:

I also share @Larsb concern about this wonderful activity impacted by legislation reaction to a shock injury that hits the media.

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Also if you wonder why I got the strongest Flipsky but don’t care about top speed… I’m hoping to design this to be dual use. Mast + motor + motor mount for my rubber dinghy and then I do want to run it from my BIG 72v battery pack :slight_smile:

So I’m hoping for it to be able to be used both for foil and my C classed dinghy (sea). Running that at 9kw continous would give that a 11-12 hp equivalent outboard … Damn nice :slightly_smiling_face:

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For mains voltage / 220v and batteries there’s a fundamental difference: mains voltage can be grounded to ground but batteries can’t, the only circuit is through the other pole of the battery. This means you can get the box contaminated with water and cause a short circuit - but it will not go through you to ground.

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Well thanks for the reply! Why I selected a gun case… I’m just intrigued by the build as much as foiling to be honest if not more of the build. When I saw it, it was one of those - wow - I HAVE to build that next! Moments.

I am intrigued by the gun case itself as a starting point and want to 3D print a detachable front keel to make it more aerodynamic. There are a few design ideas I have to make it both easy to detach (if I don’t select it to be glued after all). I bet with just a little work on making it more aerodynamic it would be way easier to get going. But the challenge of fixing that and making it detachable is one of those things I’d like to iterate a design over - I like the challenge in itself. The same way I enjoyed building my outboard conversion more than driving it :wink:

I guess a 10/12S the layout allows for way more parallel cells, also reducing the heat losses. So that’s a nice bonus in itself since it’s easier to design. 20S would have made the battery build much more tricky.

Cell layout doesn’t matter for losses, only number of cells. You can see each cell as a power source, it’s not actually a current source in the sense one might think.

Of course. Thanks! If that happens then the fuse would take it (BMSs usually don’t even though people think they do).

I was thinking somewhere around 2kwh for this … So 12S16P. Is that pretty normal? By my calculations that’s jaut about a 10+ kg pack.

That’s a really large pack. I would go smaller to shed weight. It’s a toy, needs to be nimble😄

Hmm wow now this opens up for using the used 80 oieces LG MJ1s I have lying around and tested! I could easily do 22P or 23p and it would be dirt cheap and still have decent safety amp margin. With the 20S config using those LG cells would have pretty much been out of the question since they are only 10A. A bit heavy but talk about long range on the cheap.

Damn. Yeah that leaves the used LG MJ1S out I guess. Still this thread saved me $300-400 just by leaving the 20S behind when switching to 12S. Using those cheaper once would have forced me to go over 20S since they are used and only 10A rated.

Well well it’s still gonna be cheap. Much cheaper than I expected.

My wife is from China so ordering the parts directly from China, and not AliExpress, has been damn cheap. It’s gonna be interesting to see the alu mast and carbon foil quality once I get it here and let my foil colleague take a look at it. The Flipsky parts are after all just flipsky. Too bad on the BMS but I can use that in my larger dinghy pack anyways or just sell it.

I’m having trouble visualizing how this would work. Can you elaborate?:grinning:

Go 14s14p. That will give you the right balance with those cells.

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