2S bms disaster

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Lux_Gamer

Member
Joined
Oct 11, 2016
Messages
63
Hello everyone,

I have a makita 7,2v drill with ni-cd batterys.
All the batterys made for the drill are all dead.
So i taught i could but a 2s2p 18650 pack in the drillso i did.
There is enoughroom for a bms and a charger.
So i ordered a bms from aliexpress:

image_wryuha.jpg


After i received it i wire it in the drill exactly as the diagram shown.
NOTE: i did not wired the drill on the power output of the bms it can only handle 2 amps or less.
the drill was connected directly to the pack.

But after a couple of days i checked the voltages of the groups ofcells and they where still the same.
After a couple of weeks still no balancing. So i begin thinking i had a faulty bms, So i ordered a different bms
EDIT: the voltage of the battery's where 3,87V 3,96V


image_wzxiak.jpg

This one but the same fault, Do i something wrong or was i just unlucky a second time?
Maybe someone can suggest a good bms for a 2s battery pack.


Thanks in advance,

Greetings Lux.



PS. If i will get back to my solar powerwall some people really liked the solar bitcoins :)
 

Scepterr

Member
Joined
Feb 19, 2017
Messages
226
All the cheapo BMS that do any balancing, balance at the top, usually above 4.1-4.15, so there could easily be drift below 4.0. Also the balance current is usually at most 50ma
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,659
Yeap all those cheap ones only balance at top. Some even at 4.2v and above so you need to push it.

You get what you pay for :)
 

Lux_Gamer

Member
Joined
Oct 11, 2016
Messages
63
Scepterr said:
All the cheapo BMS that do any balancing, balance at the top, usually above 4.1-4.15, so there could easily be drift below 4.0. Also the balance current is usually at most 50ma

daromer said:
Yeap all those cheap ones only balance at top. Some even at 4.2v and above so you need to push it.

You get what you pay for :)

Thanks for your help, that is why i saw no difference after a month the cells where around 3,9V.
But that doesn't explain why i couldn'tmeasure anything at the outputs of the bms, Can someone explain this.

Thanks in advance.
 

daromer

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Oct 8, 2016
Messages
5,659
Meassure what?
 

Korishan

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Joined
Jan 7, 2017
Messages
6,552
Some of those units need to have external power to engage them. So, you could take 5V or what ever it needs as input and touch the power terminals on the load side.
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,659
Many of them only balance on top and only when charging. They are cheap due to a reason :)
 

Lux_Gamer

Member
Joined
Oct 11, 2016
Messages
63
Thanks for all your answers.
Does someone now if there are 2s bms for a reasonable price that do a good job at balancing and don'thave all of the bad things that minehad.

Thanks in advance.
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,659
It depends on your purpose and what you need?
Only balancing? When to balance? active passive? over/under volt protection ?
 

Lux_Gamer

Member
Joined
Oct 11, 2016
Messages
63
daromer said:
It depends on your purpose and what you need?
Only balancing? When to balance? active passive? over/under volt protection ?

I have a old 7.2v ni-cad Makita drill that i have converted to 2s2p lithium ion 1860.
The drill pulls 10 amps under full load off the pack, So if i want the over/under voltage protection i need a bms that can handle that amount of amps pulled trough it. with the previous bms i dint wired the outputs to the drill only the balance portion.
I need a bms that balance the battery's equally to each other and cuts off the power when the pack is to low.
I don't know what you mean by active of passive?
I hope someone has a idea what for bms i can buy.

Thanks in advance

ps. i really like this forum. all the positive feedback.
 
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