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.
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Has anyone tried this? Paired with contactor.
Is it practical to use all of this four together in one build?
- Fuse
- Contactor
- Circuit breaker
- BMS
Hey man, this looks really interesting. Can you provide a link or more info on this? what sort of current can it handle?
Cheers!
Still asking their agent for the full specs of this product.
Good find if the specks are true! Just wonder, can You really get all this(including maximum continuous discharge current 200A) for 76 eur?
Still asking for the datasheet and specs. But I don’t think their agent knows what she is talking about. 
i asked “What is the purpose of the contactor coz BMS has it’s own safety features right? ” She answered “It’s for the bluetooth”.
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Heey Banjangelo,
did you end up getting the right info and/or did you buy the product,
its seems too good to be true,and if it works i would really be interested
thanks
A nice and cheap option for some uses!
The Pro’s
The contactor will have a very low internal resistance and therefore much less internal losses at high currents compared to the standard MOSFETs.
The connector load will truly be disconnected rather than “disconnected” by MOSFETs.
Cheaper than MOSFETs
The Con’s
The mechanical contactor, contact points eventually (depending on its abuse) will wear out or make pore contact after some time with unreliable connections as a result. This can lead to failing ESC’s if the connection is just bad enough especially with regenerative braking.
No precharge, if used with a capacitive load every time the relay will close a spark will form inside the relay. This eventually will result in the problem stated above or a welded contactor. In a MOSFET style BMS this won’t be possible.
Disconnection at high loads or short circuits, will definitely make some nice arcs inside the relay, and have it fail within no time.
If combined with a proper automated precharge system a lot of these problems will be solved. But I don’t think that’s inside this BMS.
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Hi, I’m going to build a 12s12p battery pack with 18650 samsung 30q. If I have a bms could I charge it directly with a power supply? What power supply should I get for a fast charge? Would a 48v 10a golf cart charger work or is it overkill?
I don’t know what type of charger is golf cart charger.
For 12s lipo you need 50.4V charger.
10A surely isn’t overkill for 30q in 12p setup.
They should be able to take 36 A charge max in 12p
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Been using the 60V 1000W for 2 years now charging up to 15A in both 12s and 14s https://www.aliexpress.com/item/1005002843829663.html
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This combination that you said, it is cheaper than a charger. I bought one charger few weeks ago and it cost me double
So for a 12S battery you hook this switching power supply up to the 60V output? And the 60V vs 50.8V on the battery isn’t an issue? I’m assuming you count on a BMS to cut the charging at the appropriate time then? If so, what BMS do you use?
Some words of caution: If BMS fails it is often failed shorted which means that it no longer will stop overcharge or discharge. Therefore BMS is not intended to be used as a normal charge control, it should basically only cut power during emergency events. If you build a charger with PSUs then make sure that max voltage out is the correct for your battery. 12s=12*4.2=50.4V max, no higher.
On the bms/no bms question:
Unfortunately the wear and ageing of cells is an unstable process. The weakest cell get loaded harder, it ages a bit more and becomes even weaker etc so even a perfectly built pack will eventually get out of balance without BMS or cycles on a balancing charger. I have done battery builds both with and without BMS and unfortunately i have killed some batteries without BMS… It’s good practice to use them (but get a better quality one)
I agree with pacificmeisters post that a BMS cutout while far away from home can be dangerous. I ride in the winter and so far -12 deg C in the air and zero in the water is my coldest. It’s better to damage your battery than yourself in a situation like that, therefore i can bypass my bms circuit without tools if i need to. My controller low voltage cutoff is also really low, at 2.5V, after this there’s very little energy left in the battery so i would gain more distance by paddling for a few minutes extra than to set it lower and kill the battery completely.
What about using a smart charger and monitor the cell voltage befor charging starts? A dying cell should warn you by having low initial voltage.
At least thats my plan for my next build…
I know that means i still have to leave 10%-20% as safety, but anyway id leave it to extend battery life
Sure, any way to continuously monitor your pack will be great, either a balancing charger or a smart BMS. Next build i’ll do i’m planning to get me something like the skyrc pc1500 charger https://www.skyrc.com/pc1500 and a 50Ah 14S battery, no BMS. With this huge battery i hope to stay away from the limits even on a longer trip.
Just chiming in on this old thread… looking into battery design and to/not-to BMS…
Does anyone use a non-BMS battery with an under-board design (FD #2 style)? I’m thinking of doing this - and using an RC plane low voltage alarm - I’ve used them on planes before, and as others have mentioned, setting the warning level a bit above the danger zone gives you a reserve tank to get home.
I’m not planning on having any above-deck components - other than remote - not sure if that can show voltage - be awesome if it could (Maytech) - hence the alarm idea.
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Not sure what esc you will use but the flipsky vesc you can set voltage limits to shutdown where you want. Also the vx3 remote has a voltage display.
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