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13 votes
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Powering a RPI board with a 22V battery pack

No and no. Neither are good ideas. Unparallel draining of your batteries will lead to issues. 2 will die sooner than the others in best case. A resistor or a resistor divider is not a good way to drop ...
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12 votes

Question about an electronic component which could be a fuse

Yes it's a controlled fuse, more precisely it's called fusible link. https://www.schott.com/en-us/products/lithium-ion-battery-protectors/product-variants Dexerials The fuse can melt, when large ...
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6 votes

Is a battery pack connected parallelly or in series?

All four cells are connected in series between B1- and B+. These will be the main connections for carrying the current. So the total voltage will be the sum of all the cells (14.8V). The maximum ...
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  • 14.7k
5 votes

I'd like to know if my own version of a cell balancer will do the job

Your proposed balancer is similar to the one you posted in your own answer. Your understanding of its function seems to be correct - the charge current is distributed to the cells depending on the ...
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  • 57.5k
4 votes

Undervoltage protection strategy for Li-ion batteries

The only proper answer to this is really how much confidence do you need to have in your solution. If this is going to be a consumer product like you say, you will probably want to go after UL listing....
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3 votes
Accepted

Identify chip on 2S BMS / Balance card

PAY is Seiko S-8242AAY-M6T2GZ battery protection IC. The last letter G is related to lot ...
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  • 1,568
3 votes

Multiple CC/CV charge controllers in parallel?

You misunderstood the purpose of this controller IC. This is just the sensor to an opto coupled LED input to a flyback primary driver that can draw up to 100mA while the flyback supply charges the ...
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3 votes

BMS charging voltage. Can I supply overvoltage?

No. 4.2V for a lithium cell is not a lower limit, it is the upper limit. For increased cell life, a lot of products will only charge to 4-4.1V and not discharge fully either. A battery charger does ...
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  • 883
3 votes
Accepted

Is an Ideal Diode necessary for BMS?

Answer is neither yes, nor no. And, it depends on how much value you consider to add to your battery pack. There is no problem, once 5P are at near the same voltage, close enough that the Over-current ...
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  • 3,661
3 votes
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BMS adjusting charge current

A BMS is not the device that decides the charging current. Neither is the power supply. It is the lithium charger that defines the charging current. The charger is the device that takes power from ...
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  • 87.2k
3 votes

BMS Two Stage OP Amp

(1) Your schematics says "LMV324" for channel 3 and 4 -- but LMV is a low voltage part, rated up to 5.5V. (2) You want to be aware of "common mode voltage" value, which is average ...
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  • 3,058
2 votes
Accepted

Why is my self built LiFePO4 battery pack not charging?

There is no detailed manual for the BMS board, so it could work as it is supposed to, but we just don't know how it is supposed to work. So this question may not be answerable - we can't know but we ...
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  • 87.2k
2 votes

How can I determine LI-ion battery charge while varying the load?

You need to measure the output current and determine what the charge is with that current. You could use a look up table with the curves you posted. You could also try to make a fit for each curve. ...
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  • 2,149
2 votes
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How to use a (cheap) BMS for discharge only

The simplest workaround to an un-activated BMS (sleep mode) is to supply it with power from it's own batteries. To achieve this, a push switch/momentary switch can be used between the P- and B- ...
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2 votes
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Different capacity lithium-ion batteries in parallel

short answer yes, it is a problem... the weaker battery will start causing damage on the better one. it will cause current flow from one to the other battery and in best case you will suffer early ...
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  • 2,488
2 votes

18650 battery pack with "dead" cells, other cells still usable?

Are my "good" cells good?: It is likely that the cells that test at 3.6-3.7V are entirely acceptable for future use. If a pack becomes severely unbalanced the more discharged cells get ...
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  • 142k
2 votes

Undervoltage protection strategy for Li-ion batteries

is it safe to rely on the built-in safety PCM of a Li-ion battery? A better question might be, "is it safe to rely on the PCM in a UN 38.3 approved lithium ion cell or a battery constructed of ...
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2 votes
Accepted

3S Lithium-Ion power solution for a project

Your 3s9p cells @ 3Ah /cell may supply 36Ah in 12h to a pack and with 27Ah capacity pack but additional soak time is required to achieve this capacity during CV mode. This is a tradeoff between ...
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2 votes

Recharging 14v battery straight from 18v supply?

There is nothing to limit the supply voltage so it will overcharge batteries. Do not connect randomly found power supplies directly to a battery, you'll end up damaging the batteries and lithium ...
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  • 87.2k
2 votes
Accepted

Can anyone help me identify this component? SMD P636

They are 18V unidirectional TVS diodes: SMBJ18A. Their marking code is LT, not P636.
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2 votes
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How does a fuse prevent battery overcharging/discharging?

A fuse doesn't protect a battery from overcharging or discharging. It also doesn't prevent a short circuit, however if a short circuit happens then hopefully the fuse will blow preventing fire or ...
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  • 159
2 votes
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Is a buck converter necessary for a 18V drill conversion? (NiCad to Li-Ion)

Both my father and I had/have (respectively) 18 V NiCd-powered drills, which took identically connectored power packs. I converted my dead NiCd pack to a 5S lithium setup, and at the just-charged ...
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  • 140k
2 votes
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Can I Charge 2 18650 with 2 TP4056 boards with single input

If I would re-draw that "hookup" and made a proper schematic, it would look like this: simulate this circuit – Schematic created using CircuitLab Note how this boils down to two ...
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  • 78.8k
2 votes
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Are parallel wired BMS controlled batteries even necessary?

If you are using a battery with a built-in BMS, unless you are willing to tear the battery apart, you don't have access to the individual cells, hence the issue of paralleling BMSs. If you are ...
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  • 1,042
2 votes
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Is it a good idea to charge multiple Li-Ion batteries using a single buck converter?

Most BMS modules do actually charge all cells in series with a single converter. They just have extra circuitry to discharge single cells that are charged too much. This can be achieved by simply ...
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  • 7,198
2 votes

Power adapter 12V for charging LiFePo4 12V battery with BMS with passive balancing

No, you can't charge a battery with a power supply, you need a battery charger. A BMS is not a charger either.
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  • 87.2k
2 votes
Accepted

2S BMS shuts down by itself

The job of the BMS is to protect the cells. At start-up, the motor draws too much current for the cells. Therefore, the BMS shuts down the battery to protect the cells from that high current. The ...
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2 votes
Accepted

Battery Management System - Fast charging

I want to implement fast charging in this system. How can I go about achieving it? This requires an external circuit to be designed that sets the charging current. The BQ76940 is not a charger ...
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  • 379k
1 vote
Accepted

Using 19v laptop charger to charge 4S 18650 battery pack

Laptop power supply is a power supply. It is not a charger for lithium batteries. It can not and must not be directly connected to batteries. Most likely what happens is that the 19V output will drop ...
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  • 87.2k
1 vote

Help identifying pneumatically activated switch with possible BMS

By the look of it, it could be an electret pressure switch. An electret microphone would serve as a differential pressure sensor if the opposite sides of the electret could be isolated.
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  • 9,737

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