To BMS or not to BMS?

Hi All.

I’m building two boards based on Pacificmeister’s design. Batteries are now settled thanks to forum posts last week. Thanks to all who helped out.

This week I’m trying to figure out BMS. Seems some people do and some people don’t. I have a balance charger or two and I have low voltage alarms but I can’t decide whether I should go for BMS. I like the functionality but a couple of things. First of all, cost. As I said, I’m in this for two boards so there’s that cost. Add to it that I expect the family will want many battery packs so we can stay out for a while. So, each battery pack will add up.

Second, I don’t know what to look for. I’m not an electronics guy. I’m building 10s6P battery packs to run in parallel for each board.

Honestly, I don’t mind the extra cost. I’m already neck deep in this. So what’s some extra bucks. But, I def can’t afford the fancy BMSs that have Bluetooth and all that jazz.

Any advice appreciated. ESP, recommendations for a good bms for that battery pack.

Finally, I really appreciate all the info and community of this group. Technology is truly wonderful these days. It is enabling such cool things.

M

Hi.

What batteries did you decide on?

Personally I prefer the “no BMS, with a low voltage alarm” method.

Pro’s to no BMS:
One less thing to fail (this is huge reason for me. I have had many BMS issues on electric skateboards over the years. If the BMS thinks something is wrong it shuts off the battery. I don’t wanna swim in more often then needed.)
More reliable board (as mentioned above)
Give user more control (not having a BMS means you can decide how low you wanna run your battery, let’s you balance charge more accurately, and stop charge at lower user specified voltage so batteries last longer).
Charging battery is more accurate with hobby charger.

Con’s to not having BMS:
User can damage battery (if friends and family use board, and continue to ride below safe voltage battery will be permanently damaged.
More liability (potential fire if user error during charge). You must only charge the battery via a method that performs balance charging! This is very important.
Must have hobby charger with balance charging capability.
No BMS usually requires two separate batteries that you must manual connect in series for use, and charge separately. So, more plugs required on waterproof box.

I have removed the faulty BMS on several electric skateboards and converted them to no BMS with low voltage alarm. It is a reliable, safe system as long and user is careful not to over discharge, or over charge the batteries. And this means you must always balance charge the battery!!!

:call_me_hand:

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Thank you very much. This is most helpful.

I have a different experience with BMS. I haven’t dealt with a lot of them so I can only speak for my efoil experience but having a BMS has been great for me. I am currently using this BMS: https://m.fr.aliexpress.com/item/32827394534.html?trace=wwwdetail2mobilesitedetail&spm=a2g0o.productlist.0.0.41162bbaS8zsf9&algo_pvid=f955e98f-52e6-4f92-906e-8887cba7cdf0&algo_expid=f955e98f-52e6-4f92-906e-8887cba7cdf0-1&btsid=0ab6d69515836331292087008e052c&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_ for charging and discharging. It allows me to monitor precisely every cell from my phone and gives me the amp consumption under load. You can also set a bunch of parameters that will protect you from a lot of errors that could potentially ruin your pack. It can handle quite of bit of amps and I haven’t had any issues even when riding 1h+ continuously. It also acts as an on/off switch for your system with is great since on/off switches are still a challenge in most build. For me, the 100$ cost was well worth it. It gives me a piece of mind that my battery won’t be damaged by mistake. You gotta protect your investment!

I will be going with Samsung 30Qs

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Good choice on the cell type. That’s what I got, and that’s what I’m gonna do for my second battery here soon.

Hi! I’ve built electric cars, ATV’s boats and efoils. Some use BMS some dont. My take is: If you get HIGH quality cells AND make sure that they are charged in parallel before building your pack, you can rely on a low voltage cutoff from the ESC/controller.

With the efoil I like to test the voltage cutoff by setting it at a higher voltage and when the esc cuts off I’ll use my charge to give me a SOC reading. I’ll tune the cutoff until it gives me approx 10-15% SOC.

I would never recommend using a charger in fast mode, always do balance charge to make sure the cells are leveled.

Br

Rikard

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That’s not a bad way of doing it.

With voltage cutoff set conservatively where 10%-15% of battery capacity remaining should result in a end voltage just above 3.0v per cell. With quality cells that are properly balance charged my end voltage variation between cells is always within 0.1v.

My low voltage alarm is just added protection, as it monitors each cells voltage. But, as @Riwi says, you could get away without it.

Another great benefit of the low voltage alarm is you can set it a bit higher and it works as a “reserve fuel” indicator. On my longer rides this is nice to have. When the alarm goes off I know I have 10 minutes, or about 1.5 mile range remaining before the ESC starts to restrict power.

:call_me_hand:

1 Like