Questions about Batteries

Recently, I started making a list of parts for my first eFoil build, and I’ve just gotten to the battery, and there’s a lot more information to unpack than I expected.

First of all, I know you can buy a lipo, or build a battery with individual cells (the Samsung q30 looks to be popular and reliable)

  1. If I were to build a battery, how should I decide whether I want 12s12p or 14s14p (the two main configurations I’ve seen so far)?

  2. Would I want to split the battery into two sets of 6s12p or 7s14p? What are the benefits of doing so?

  3. At what point should I use BMS, and is BMS unnecessary if I use a low voltage alarm for during use?

  4. How do I test the individual cells before building the battery, to ensure I don’t use a faulty cell?

  5. How do I know which BMS I should purchase, if it is necessary?

  6. What kind of charger should I get for the battery (or batteries if I go for the 2 set option)?

If it makes a difference, these are some of my main components so far…

Motor: https://flipsky.net/collections/e-skateboard/products/brushless-sensored-motor-amphibious-fully-waterproof-motor-65161-120kv-6000w-for-efoil-ejet-boards-ebike?variant=33538980937863

ESC: https://flipsky.net/collections/electronic-products/products/high-current-fsesc-200a-60v-base-on-vesc6

Foil: https://www.realwatersports.com/products/liquid-force-rocket-v2-foil-kit/?utm_source=gshopping&utm_medium=cpc&utm_campaign=kiteboarding

I’ve read @Flightjunkie thread on batteries, which was really helpful, but in some ways, it left me with even more questions than when I started (probably a good thing).

Lastly, I know this was a really long post, and I don’t want to take up too much of anybody’s time, so please don’t try and answer all of my questions, just point me in the right direction and I’ll do the rest.

Thank you to everyone that bothered to read all of this, it turned out to be slightly longer than I expected, but hopefully other people will be able to benefit from this thread as well as myself.

I’m going to share one approach of many great ones detailed on here. I like to keep it simple.

Buy (2) 20Ah 6S Li-Po packs from Hobby King
Buy (1) XT90 series connector from Hobby King
Buy (2) ISDT BattGo BG-8S monitors from Amazon

You will also need a Li-Po balance charger and a wall power supply for said charger. The way this works is you balance charge each battery separately. Don’t like that? Buy another charger and PSU and cut your charge time in half. Every charge the cells are balanced. Connect the BG-8S to the balance leads of each pack. It will tell you the voltage of each cell, alarm you at low voltage and allow you to balance the cells on site.

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1- depending on weight , room , money, esc… in your case with your fesc you need 12s

2- split in two mainly in order to use classic lipo charger (6s-8s) , faster charger with a high current for balancing

3- no need for a bms, discharging : you use the safety included in your esc vesc type
charging: lipo charger will do that

4- mainly by checking voltage, lowest voltage cell in the same batch should put inside, how low? you decided
more accurate would be to test each cell internal resistance IR ( charger will give this information )

6- ISDT 8S charger or icharger X8, those are DC charger you need a 12v pc power supply, do a search on the forum

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This is all for li ion cells (30Q)

1 On the flipsky website it says it can handle 60v so either one is fine…
With the 14s14p you get longer ridetimes and because it has 14 cells in parallel you pull less amps per cell which should help preserve your battery longer.

2 If you split them in half you can use a charger that is only able to provide less power(cheaper)

3 You don’t necessarily have to use a bms ,i would use one for it’s protection features overcurrent,overvoltage ,short circuit etc.
If you are comfortable standing on a battery of that size without protection…

4 Check it with a multimeter as long as they are close (0.1-0.2 volts,at least 3.7 volt)they should be fine.

5 They have got a voltage and a max cont.current rating. I would say you need 150amps cont.current or higher… it depends on the battery the voltage rating needs to be higher or equal to number of cells in series x 4.2volts

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@calikiter made me aware of a setup involving two Lipos connected with the adapter listed below.


Can anyone give me an approximate ride time with a setup like this?

Would a low voltage alarm during use, and a balance charger for charging be enough to keep the battery in good condition?

Also, I believe the connector would connect the batteries in series (The description says it increases voltage), which I believe would give me 44.4V and 20000mAh.

The low voltage alarm is only an indicator, you need to stop discharging when it goes off. I would set it rather high as it’s easy to over discharge these packs and poof $400. Ask me how I know! I’m using the 12Ah versions now. I expect very poor range. I will learn the way the Li-Po likes to be treated before I invest again.

Here is how you can approximate ride time yourself. You have 20 amp hours of capacity. If you draw 20 amps for one hour the battery will be dead. Look at builds similar to the components you are using, find a datalog, estimate the average current usage. If it’s 60A average current then 20amp*hours/60amps (notice how the amps on the top and bottom cancel each other out so your result is in unit hours) would leave you with 0.33 hours or as most would call 20 minutes!

A more complex technique involves integrating the current draw on the battery with respect to time from. Keep it simple!

One final note, each cell in a Li-Po ranges from 3.7-4.2V. The lowest the pack should ever be is 3.7 * 12=44.4V and a maximum of 4.2 * 12=50.4V. When setting the voltage alarm don’t choose 3.7 but maybe 3.8, 3.9? You will loose range but greatly extend the life of your battery. It is a good safety practice as well.

Thank you, this helps a lot. I will probably start with two of the batteries I linked above, wired in series, and later, if I think it is necessary, I can buy two more and wire them in series, and then wire the two packs in parallel, which should double the battery life, I think. For now, I’ll go with what I listed above, anything around 20min should be enough for testing my first build.

You bet! Also, you have the exact right idea on how to scale it! I’m excited for you and to hear about your results as I have yet to ride an e-foil using these packs, on an e-sk8 they pack an incredible punch.

I wouldn’t recommend those batteries. They only have a 12C discharge rate. I started with similar batteries and within a few months they had already started to puff.
I highly recommend building a 18650 pack with either Samsung 25R or 30Q cells. It won’t cost you much more and you will have safer longer lasting batteries.

Would building a battery pack really be safer? I’m sure I’d be careful, but I don’t have any experience spot welding. Also, when your batteries got puffy, were you balance charging them and not discharging any cell below 3.7 volts?

Also, if I were to build a battery, are there any specific guides that you would recommend I look at, or should I just do a general search for how to spot weld a battery pack.

Thanks for your input. I would love to get into building 18650 packs this summer. I drool over these types of projects. The restricted timeline mentioned in my build thread will shed some light on this design choice. To answer, @Malveymonster I believe Li-Po’s puff when you discharge them too quickly also known as drawing too much current. @rogjalon mentioned 12C discharge rating. He calculated 12C*12Ah=144A maximum current and he likely surpassed this value causing the puff. I am stuck with these for now but won’t complain too much as I did get these as part of a grant for the project from my university. I will report my findings. I really appreciate your safety tip from personal experience.

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Ah, that makes sense. Thank you for the clarification.

The Battery are OK.
I have this Battery 1,5 years and 320cyclen…
Its OK for this Price.
Greetings Frank

  1. On 14S you can actually get spikes higher than 60v. I’ve been investigating the Flipsky FSESC for using 14S in my build but turns out the MOSFET transistors have 60V absolute max before breakdown. 14S will most likely fry the ESC unless you have really short battery wires and extra capacitors to prevent induction spikes
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As far as my experience with lipo :

Those lipo have a max of 24C discharge for 10 sec

So do your math :

At the end , it is nice to live 20-30% in the lipo

12A x 20% x 24C = 60A Max for 10sec at the end …
That is the way I see it

We do not have this with 18650 , but the C are lower at first but constant , if heat is managed

18650 don’t burst
30Q don’t get in fire …

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I have never taken my lipo’s below 3.6 volts per cell and they still get hot. Yet my 18650 pack I drain to 3.2 volts per cell without any issues.
Spot welding with a quality spot welder is not difficult. There are plenty of YouTube video to learn from.
Ebikeschool.com has some good videos

Well worth the effort to build your own battery packs in my opinion

<hello
I also want to make my 48volt battery and around 40A / H so I thought 13S / 13P with Sony / Murata US18650VTC6 3000mAh - 30A, but I do not know which BMS to take and what peak intensity I can have with this type of battery?

What you mean ???
12Ah x 24c = 288A for 10Sec… But you not Need 288A !!!

My Set Up too time Needs 32A too foil with this Batterys , i drive with 2x 6s = 24AH and i have 40min runtime. than i Change the Battery :wink: for next drive and Charge the first.

Best regards Frank

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So would the batteries I linked earlier work, or would you recommend I get a different battery, similar to what you use?

What do I mean ?

I mean that you cannot discharge at the same max rate a 100%charged lipo and a almost empty one , what is why I think we need to live 20-30% at least inside
And you can take them lower if you respect the C rating with what is left inside and check temp