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I plan on using it mostly plugged in, batteries are there just for extra mobility and won't be used most of the time. Don't know lot about batteries so in first scheme I added a switch (pos. 1 charging, pos. 2 normal usage when plugged in) which would be on pos. 2 most of the time and I don't know if it is necessary? Anyway, I'm not sure any of those two schemes is good so please correct me or suggest a better way to do this. Thanks.

  • Link to batteries.

  • Link to charge protection board.

enter image description here

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  • \$\begingroup\$ welcome! would you mind linking the LED's so we can know the voltage rating and power draw? \$\endgroup\$ – Ryan Oct 6 '18 at 22:34
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    \$\begingroup\$ Hi, it says right there on a scheme, 12V and 2A \$\endgroup\$ – Bunnyi Oct 6 '18 at 22:35
  • \$\begingroup\$ oh i just saw that, sorry! \$\endgroup\$ – Ryan Oct 6 '18 at 22:35
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Looks mostly fine. I'm not overly familiar with this specific charging module so correct me if I'm wrong, but it looks like there is an input to charge the batteries, but no output pins, so you would have to directly draw current from the Li-ions. It should be fine for just a 2A draw, but any higher and I would make sure I have output current protection.

When your batteries drop below 4V, you wont be able to directly supply 12V any more. I would suggest a 12V regulator or some kind of LED driver to maintain constant and adequate power.

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  • \$\begingroup\$ You cannot drive a 12V load with 3 LI-ion batteries. The outputs are labeled, 4.2V, 8.4V, and 12.6V. The recommended charge current for these Panasonic NCR18650B batteries is 1625 mA. \$\endgroup\$ – Misunderstood Oct 7 '18 at 4:41
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I'm not sure any of those two schemes is good so please correct me or suggest a better way to do this.

Neither scheme is acceptable. This charger is not recommended for your application.

You must have a circuit to limit the discharge of the battery so the voltage does not drop below 3V, regulate the charge current, and maintain a full charge while charger is powered and batteries are in use.

20 Amp charging current is way too much.
See: Charging Lithium-ion


These batteries should be charged at 1625 mA.

enter image description here
Source: Panasonic NCR18650B Datasheet


Li-ion batteries are nominally 3.6V and three in series will not supply 12V very long if at all.

You could use four series batteries and a 16.8V charger rather than 12.6V then add a 12V buck step down regulator.

Better would be to use a single cell (or parallel) and charge with a 5V input (e.g. USB) and boost the the battery output to 12v.

NCR18650B Li-ion Discharge Curve
enter image description here
Source: Panasonic NCR18650B Datasheet


If you were to use this charger the input power and output to battery would be connected to the input and output of the PCB.

The input voltage is not specified by the vendor but it would be more like 19-20V input.

enter image description here


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I agree with most of what @misunderstood said except the specs. Here are my own opinions.

Charging voltage: 12.6V - 13.0V is specified by 3S,10A Protection board on vendor detail link with 10A max if ambient is cool.

  • This assumes you have a smart charger that cuts off when charge current reduces to 10% at 4.2V/cell and not a 12V 10A supply but can be made to work if adjustable with pot or drop 0.7V with one 15A power diode. Thus 11.3V/3=3.77V/cell to 3.8V max. But since you have a steady load, that wont work with a smart charger.

  • I suggest a small cooling fan for both PS and protection board with an air plenum retrofited to flow thru both rather than over the top so nothing is burning hot to touch.

  • Do you understand that most LEDstrips for white have a dim threshold just below 9V and can be operated from car voltage of 14.2 V from built in current limiting resistors , you won’t draw maximum current or radiate maximum brightness of LEDs. But if your strip is rated at 4.5A at 12V , two strips will exceed your 10A supply and rating if the supply is 14.2V.

  • So if you don’t mind a reduction of 0.7V reduction in nominal brightness at 12V, the apparent brightness will be ok but 2.3/3V rise above 9V or 77% of nominal brightness @ 12V.

  • if you can specify the LEDstrip’s actual current vs voltage then perhaps a better solution is possible like 15V @ tbd A with 4 cells.

Perhaps then drop 15V by 0.7V to achieve 14.3V (marginal hot LEDs) with one 15A to 20A power diode to reduce both the battery (4S) and 15V float charger voltage to 14.2~14.3.

There is some temporary 20% or so reduction in cell mA capacity by using 3.8V float and not charging to 4.2V/ std Li Ion cell but at least you wont accelerate the aging rate keeping it overcharged above 3.8V for long durations.

These are just my opinions.. Your mileage may vary.

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