eFoil Battery Packs

@Hiorth, looking good.
What cells are you going to use?

Btw I built myself a 10s5p pack out of 25r cells, no bms. This pack has been strongly used in my eskateboard for more than a year now.I charge it using a regular 2amp ebike charger with an end voltage of 42 v ( 1 reason I went with 10s).
Whenever I check the cells they are evenly balaced, before and especially after charging.

So in my own personal opinion you do not need a bms if you know what you are doing. But you do need a mechanism to limit the battery amps, for example via ESC.

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@PB1 Our plan is to buy a tesla model s battery module, take it apart and use the cells. So many teslas in Norway, so it’s not that hard to get a hold of. And will give us a prise of around 3$ per cell.
the capasity of these cells are grate, but discharge is bad so not ideal.

@g.gregory8 Planning on soldering the pack with a high temp soldering Iron, and very low temp solder. I think it will give better connections than using a spot-welder. May also add Individual 10A fuses to each cell, but not yet decided.

@Flo will maybe 3d print holders to the cells. But also considering gluing them with, tek7, silicone or something similar.

nkon.nl seems to be a great cell source. I bought several different cells and testing them atm. So far so good. I will probably buy 300 Sony VTC5 for my build. 3.55€ each. Samsung 25R cost 2.55€ per cell if you buy at least 200 of them.


nkon.nl is the place where I got my cells too. Also the good quality nickel strips for welding (important!!!).
What is the spec for the vtc5? Or in other words, how many cells do we need in parallel to provide enough amps?

@Hiorth, didn’t know what sort of cells Tesla uses. According to the www they use custom Panasonic cells with a continuous discharge rate of 10A and 15A burst.
So your pack should be able to deliver around 140A and 6,2kWatts of power. Should be ok.

On the other hand, soldiering 168 cells is going to be very cumbersome and you really have to make sure that the cells don’t overheat.

Btw, I just hot glued my pack and then wrapped it in tape. The glueing didn’t warm the cells noticeably.

They are rated for 30amps but i came to the point that they get too hot then. I used several ceramic resistors in parallel to get 0.15ohm, so you have theoretically 28amps at 4.2volts. Practically you get about 20amps at around 3.6volts, because the cell voltage drops for around 0.6v under load. After 6 minutes under load i needed to cut off, because the cell reached 80° celsius. The second test was a little better. 4.2V/0.24Ω=17.5A…practically the cell voltage dropped to 3.75V with 13.5A. This time the temperature raised till 65° celsius. I can work with that.
My plan is a 20S15P pack. so we got practically 200A constant without overheating, peak current is 450A (300x3.6Vx13.5A=14.6KW). A little overkill, but its also for a surfboard, not an hydrofoil.

Btw, I am welding the cells, not directly soldering.

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I spot weld the negative pole to my cells, too. But i have to solder the fuse wire at the small metal sheet on the positive side of my cells. The fuse wire is so small that even with my overengineered spot welder i cant find the settings to reliably weld it. What’s your process for spot welding? I use nickel sheets with 0,2mm thikness. My welding process is 17V capacitor voltage and two pulses with 0,1ms and 1,7ms. I wait 0,1ms between weld pulses. This setting yields consistent welds, but I still have too thin cables for the weldcurrent.

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whats the model S battery setting you back?

Are people running anything below 40C with their lipos? Would 10C be enough?

Depends on the capacity of the pack.

A huge pack with 10c might be ok, a small pack with 10c is not ok.

Looks like you need around 1,5 kw to get foiling. Power is current times voltage. So with a 10s pack you need around 1500 watts / 37v = 40 amps
(Just theoretical as I haven’t tested)

So you need a pack that can sustain 40 amps continuou.

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Brilliant. Thanks for breaking that down to me.

just under 1000 dollars for 444 cells

I am thinking of using 12-15A fusewire on each cell for safety. Does anyone know what fuses to use? (Wire, Pico fuses etc,) , and where to get it? I will have to solder I think.

I use tinned copper wire, you can buy those premade (i got a small amount from the uk). Now i just pull some 0.25mm wire through a tin bath and use that. I have jet to find a way to spot weld that wire, but the positive connector of a cell is actually not tightly coupled thermally to the internal components. So i solder this wire very quickly for now. Spot welding the other side with nickel sheets is easy. There is some data on the web on which size of tinned wire is necessary for a given current.

And what do you thing of this one


mentiond in an earlier link on this forum, it seems there in no welding.

I like the idea of a configurable pack. I have no experience with them but I prefer not to have clamped contacts in my high current path. They only recommend 3.5A per cell, you have to build a big battery pack if you want such a low current. The other thing is cost. Nickel plated connecting band is about 5cm or ~0.03€ per cell, and the vruzend connector is about 0.62$ per cell. So if you build a pack with less than 3.5A average current per cell, don’t mind the cost/don’t wan’t to invenst in tools and you don’t need a fuse for each cell this can be a solution. I already have the tools for welding, but if you are starting out this could be much easier :+1:

Regarding BMS.

i think this one will do the job http://www.batterysupports.com/44v-48v-504v-12s-150a-12x36v-lithium-ion-lipolymer-battery-bms-p-394.html also considering the 10s version. I will also add an independent monitoring system, at least in the beginning.

Does anyone have info/Experiences/tests with high AMP BMS?

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I am planing to build an Arduino temperature monitor into my board that will monitor the temperature of the ESC, Batteries and Motor and give warnings when too hot.

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Hey Guys,
I love this idea of knowledge sharing, you guys are visionaries. I am new to hydrofoils and have a lot to learn, but I also want to contribute. I started researching DIY E-foils and found this forum - so much good info.

So how can I help?
My company makes high end electric bikes here in Southern California. In order to keep costs down and ensure quality we have partnered with a battery factory that makes custom lithium ion batteries.
I use Samsung 18650 cells in my 48V 18amp hr removable battery packs for my bikes and have had great success. Our factory can make just about any size battery in just about any configuration. The batteries can also be made with an IP-67 waterproof rating, smart BMS and have a 1000 cycle warranty. We have injection moulding machines and 15 design engineers that can provide design to final product services.

Im an enthusiast, I’m not looking to manufacture e-foils, I just make and sell batteries. I am hoping we can work together and accelerate the process and keep the costs low so I can have my own one Foil asap.

Let me know how I can help.


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Dear Rich

I moved your post to the battery pack section.

Do you have any webpage or similar, maybe with some samle pictures of your packs? We are thinking of taking apart a Telsa module to salvage the cells and build a new battery. But it would be nicer to get a custom factory made ip67 battery (with good cells) capable of 70-80 amps.

We use the same spec batteries in our bikes that Tesla uses. It is a Samsung 18650 cell. The lithium ion battery has been around for quite some time but there have been three major problems in the past.

Firstly, the price. Most batteries are made in China and change hands and increase in price several times before they get to the consumer. Our partnership with the Turnlife factory has enabled us to have custom batteries made at way better prices. We have essentially cut out the middle man.

Secondly, lack of options. When we started building electric bikes, we were using overpriced generic hobby shop batteries that weren’t able to meet our needs. When we found something that could deliver the power we needed, it would not fit where we needed it to go.

Thirdly, the battery management system. There is very powerful chemistry inside lithium ion batteries. It has to be managed correctly or else it will cause fires and catastrophic failures. When you discharge and charge lithium batteries, they heat up. This can cause thermal run away. You have to have a very precise BMS that is designed for the charger, the battery and it’s application to prevent this from happening.

These are no longer problems for us.

I am a fireman by trade, I got into E bikes about 4 years ago with a friend after we saw one that a hobbyist had built. We loved the idea and gave it a go. We have learned and spent a lot along the way.
We knew nothing about bikes or batteries when we started our journey. I am very impressed with your guys progress and openness about your designs.

Our websites are:
www.turnlife.com and electricbikecompany.com take a look at both and we can talk more