Begginers Guide to Processing 18650 Cells | Cell Database


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2S bms disaster
#1
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 drill so i did.
There is enough room for a bms and a charger.
So i ordered a bms from aliexpress:
[Image: 2PCS-alot-2S-12A-7-4V-solar-BMS-PCM-li-i...40x640.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 of cells 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: -font-b-2S-b-font-5A-Li-ion-Lithium-Batt...V-font.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 Smile
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#2
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
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#3
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 Smile
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#4
(07-22-2017, 09:09 PM)Scepterr Wrote: 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

(07-23-2017, 12:31 PM)daromer Wrote: 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 Smile

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't measure anything at the outputs of the bms, Can someone explain this.

Thanks in advance.
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#5
Meassure what?
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#6
(07-26-2017, 12:22 PM)daromer Wrote: Meassure what?

Voltage! on the output terminals.
i placed a resistor on the output terminals to see if the bms got active but no result.
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#7
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.
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#8
Many of them only balance on top and only when charging. They are cheap due to a reason Smile
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#9
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't have all of the bad things that mine had. 

Thanks in advance.
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#10
It depends on your purpose and what you need?
Only balancing? When to balance? active passive? over/under volt protection ?
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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