eFoil Battery Packs

EFOIL.builders Electronics (ESC, remote, batteries)
265

4.22 volts is not ok.

I hate to keep beating this issue. But, I am concerned you still do not understand how dangerous it is to charge your pack like you did.

Do not charge that battery again like that without balance charging, unless you have a voltmeter on each cell, and you constantly monitor that no cell goes above 4.2.

You’re cells are brand new and one is already at 4.22. That is already a dangerously high voltage. If you repeatedly charge to over 4.2 the battery cell will be permanently damaged, and over 4.2 volts you risk thermal runaway and having the battery explode, or cause a fire.

You asked about the amp hour capacity of your battery, and wonder how to know if it’s charged to 42 amp hours. That’s the whole point as to why I was saying you need to test a single battery. The manufacturers claims are not to be believed. Even if these were sold as Samsung 30Q cells, you still would need to test them because they could be counterfeit cells.

Testing a cell will determine the capacity of the cell and will determine how many amps you can safely draw from the battery by measuring how hot the cell gets during the test. Some knock off cells will test at the correct 3.0A/hr at a 1.0 amp draw, but when you try to pull 10 amps from the battery they overheat, and threaten to catch fire, and only supply 1.0A/hr or way less.

So, you need to test your cells. Send me one and I’ll test it for you. Or buy a charger like the one I have. It’s called the “icharger X8”. You can test the battery with it. It will balance charge and show you how many amps have been charged also.

Good luck, and be safe. Lithium Ion batteries are not to be played with.

:call_me_hand:

3 Likes
266

So you have peaked my safety hat and ive been looking for a solution to add protection and a display too.

Any thoughts on this Battery Monitor

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It would seem to do everything and the price is right if I added the external relay for battery charging cut iff n discharging too? Cant find anyonr else using it though?!?

267

Thank you for reminding us those dangers. Are you suggesting that the 144+ cells should be tested individually to be on the safe side ? How long does a test cycle last then ? Are there any shortcuts to test multiple cells in one go like testing 12s1p instead of 12 times a cell.
To make more money, it would be tempting for a seller to mix 2/3 of genuine cells and 1/3 of counterfeit ones (up to 50/50)… :frowning_face:

268

Hi.

Sorry. I know it’s confusing. Here is what’s important…

When you buy a battery, either a pre-made battery, or a bulk order of individual cells, you need to test (as described previously) a sample cell from these to verify that the cell meets the manufacturers claims. Just testing one or two individual cells will accomplish this. If they mixed in 50/50 counterfeit cells you would be able to tell seeing the batteries side by side. Even the best knockoffs aren’t perfect. If any cells look suspicious I would test those too.

It’s always best to test a single battery. A single cell. If you have purchased a pre-made pack then you cannot test a single battery because several of them will be connected together in series, thus creating one cell made up of several batteries (one “S”, however many “P”). Without taking the battery apart, the best you can do is test one cell (one group of batteries hooked in parallel).

If you do not understand what makes up a cell, and the difference between hooking batteries together in series V.S. parallel you have a lot of reading to do before you start charging, building, or using a DIY battery, or one without a BMS.

Any group of single cell batteries where all the positive terminals are hooked together, and all the negatives are hooked together is one cell. This is a parallel group. Which is called 1s. Because it’s only one battery hooked in series. As in no batteries hooked in series. These batteries will all self balance with each other, and self regulate their voltage. For all practical purposes, they are one cell. 1s14p. This will act as one battery. No need to balance charge. They are only as good as the weakest battery within the group, so make sure they are all the same type and age (new).

Any cells or cell groups hooked together where the positive of one battery connects to the negative of another battery, this creates a series connection. As in 2s. This battery must be balance charged and individual cell voltage must be monitored.

Of the utmost importance is the understanding that batteries hooked together in series do not self regulate their state of charge, or voltage!

This is where voltage monitoring comes into play. If you have a 1s10p pack you do not need to balance charge. The parallel number doesn’t matter.

If you have a 14s10p pack you need to monitor and balance charge 14 different groups. These 14 groups will not stay at the same voltage as the other 14 in this group.

Your example of testing 12s1p is what not to do! This pack has 12 cells that need to be balance charged! A pack of 1s12p is one parallel group. This pack will self balance and regulate their voltage. This is how you would have to test a pre made battery. Because you can do this without taking the battery apart. But, it’s not as good to test this way because the pack is only going to perform as well as the worst cell. And you can not easily tell how many amps one cell can handle without getting hot.

Be safe guys. You really shouldn’t be playing with lithium cells untill you thoroughly understand these concepts.

:call_me_hand:

5 Likes
269

So Ive taken apart a pack 1S8P (edit, id the S & P wrong way around) to test a single battery and I’m getting voltage and current as per the manufactuer details. Put the pack back together and getting the manufactuer details that were on the pack so I’m happy that i have genuine cells (although they are differnt to everyone elses - I’m using the Buston Swing 5300 Cells.

Next thing to do is implement the over charge voltage and current. Do you think my unit above can manage this?

270

No. That device will not work.

271

Others on the forum have been happy with this BMS.

I don’t use a BMS. But, I have a hobby charger that balance charges by pack separately as two 7s batteries (icharger X8). Then I use one of those cheap voltage alarms for individual cell voltage monitoring during use. See my build for details.

:call_me_hand:

272

I agree, I almost brunt my garage down due to a crappy charger that did not stop charging but just pushed on and the battery pack overheated and then it blew up like a chines firecracker…
Fortunatly the fire blew it self out ut i needed to renovate the garage and had to throw every thing in it…
Beware of cheap products.

273

Shit. What was the redundant safety part doing at the time the charger went crazy?

274

I have a chance to make a 12s 900Wh pack versus 1200Wh 16s pack. Should I be worried about safety with 16s? Even board has a sealed compartment, ip69 connectors, and waterproof box for battery and speed controller, there is always a chance of water leak. Wondering if 16s fully charged, around 60. Volts can be a harmful electrification danger versus 14 or 12s. Are you guys aware of any marine grade regulatory specs for dc voltage for US or EU?

275

16S fully charged gives you 16*4.2 = 67.2V

Simple calculations :
30mA gives the human body respiratory paralysis (you already feel pain under 10mA)
Human body resistance is roughly something around 2000 Ohm (wet body, considering electricity breaks down human skin and therefore lowering the resistance)
Max voltage would be = 2000*0.03=60V

At 60V with 0.03A, you are probably nearly dead. Imagine 50A+ flowing through your body…

I wouldn’t go above 14S personally. I already touched 110V with a current around 20mA that flown from my hand to my feet 5years+ ago. It took me more than a whole week to recover from the pain in my elbow, and I somehow still feel the pain there today…

Beware of electricity friends, It’s all great and fun until something bad happens…

2 Likes
276

My conclusion is the same. 14s max and still there is a little risk
And that skin resistance is for dry skin which will be much lower in salty waters.
I assume 110v was AC which is the worst. in Marine standards up to 50volts seems to be considered low voltage.

277

Here is some info on HV batteries: Shocking Batteries - Electric Shocks from Batteries

2 Likes
278

Good data. Even with 50volts, wet( imagine salty water) direct touch is fatal! which is a rare possibility but still there is a risk. Most common scenario is thru salty wet skin circuit closes thru salt water to earth ground which only increases total resistance with factor of 2 not fatal but painful. Ocean water resistance is only 0.2 ohm

279

I think the largest risk is probably when unplugging the battery after use. If you were wet and created a closed circuit then there might be a issue. In a large body of water the battery will most likely just start discharging through the water.
A friend managed to get his efoil and battery underwater and still ride the foil even though the whole battery was open and submerged. I was pretty surprised that there was no real damage until everything started to corrode. No one was electrocuted either.

I’m still investigating a way to build a nice DIY waterproof pack that does not require complicated tools. Kydex is a very strong material and can be moulded with heat so might be an option.

280

At that point bms should’ve disconnected the pack from connectors. I am working in a aluminum box and smart bms with water leak detection isolated inputs. Aluminum is easy to cnc or die cast plus it will act as heatsink for cells. Unfortunately development is slow, bms remote, battery box , board itself and all with full time job and brand new baby :baby_bottle:

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281

This case would work: https://www.explorercases.com/en/products/3005/3005-be-copolymer-polypropylene-waterproof-case/
I wouldn’t go aluminium. With a good wing there is very little heat generated at the battery. I have been riding with currents as low as 18A.

2 Likes
282

It was indeed 110V AC. I only touched it for less than a second, yet my elbow is painfull till today…

I work in electricity, low and high voltage. I mean I work from the standard 110/220V AC to 380 000V AC (and also 400kV DC). I am well aware of the electricity dangers, but still managed to get hurt…

So in my day to day work, we are using special protections to protect the lines and cables that can operate a breaker in less than 50ms. Such a relay is really really expensive. I was thinking about using one for our purpose, however, as stated above, it is expensive and would make the board worth 20k€ at least I think LOL !

Ok I can’t find the price of such a relay anymore but if you’re wondering it is between 5 and 10k€. However there are cheaper alternative, that would be a world premiere for sure if we make such a protection for our purpose :heart_eyes:

1 Like
283

Same here, full time job and gotta progress on the project too. Really difficult lol.

I like your box, but if you are going CNC it will cost you more than 1000€ for both parts I think. Casting would be way cheaper if you can, or even Injection molded in PA12 is good.

I like the Phenom cell :grin:

284

Cnc will be for just proof of concept and die cast also needs high quantity to bring the price to reasonable price.