0
\$\begingroup\$

I'm planning to use a 4s 18650 LiPo pack to power a portable speaker and I'd like to include a charging circuit, so I don't rely on an external balance charger. I currently have it hooked up to this HX-4S-A01 protection board, which apparently lacks balancing features.

Am I fine, if i just add such a balacing module and hook it up to a 16,8V Power Supply, or do I need a different module e.g. to limit current?

Would this module alone do the job of protecting, balancing and charging the batteries?

I'm a bit lost in the different types of protection and I appreciate any help.

\$\endgroup\$
2
  • \$\begingroup\$ My browser can't display aliexpress web pages, so I can't say if that particular balancer will do the job. However if it is designed for use with Lipo or li-ion cells it should be OK. "...and hook it up to a 16,8V Power Supply" a power supply is not a charger. \$\endgroup\$ Dec 7, 2019 at 4:04
  • \$\begingroup\$ That pretty much was part of my question. Isn't the difference between a charger and a PSU that a charger stops charging when a certain voltage is reached. Doesn't the protection board do that? \$\endgroup\$
    – Regster Up
    Dec 7, 2019 at 15:24

2 Answers 2

1
\$\begingroup\$

First of all, I think these 2 videos can help you a lot:

But back to your question:

I currently have it hooked up to this HX-4S-A01 protection board, which apparently lacks balancing features

As far as I can see from the AliExpress page, your current board is based on and S-8254A IC, which has plenty of security features:

  • over-charge protection
  • over-discharge protection
  • over-current protection

However, as you said, It lacks balancing. It is mainly a protection board to avoid anything going bad but It is not recommended as your only option for charging and discharging circuit.

Am I fine, if i just add such a balacing module and hook it up to a 16,8V Power Supply, or do I need a different module e.g. to limit current?

If you use a power supply that has current limiting everything becomes much easier, you just have to set the voltage to the maximum voltage of your pack (4*4.2 = 16.8V) and the current of supply to something manageable like 1C. If you lack this feature in your supply, there should also be no much problem, as long as the S-8254A IC measure any of your cells is higher that 4.2V, it will put the boards's MOSFETs into high impedance and will disconnect it from your supply. This way, your balancing board will act alone to reduce the voltage on this cell and when It drops below a certain threshold, the S-8254A will restore connection and continue to charge the other cells. If you have a really high power supply, that would damage your cells while charging due to overcurrent, It is recommended to add a series low-value resistor such as 1~10R, but as long as you have like 2.5Ah cells and an 1A power supply, everything should be fine.

So, If you use these two boards in combination, you can achieve a balancing circuit with a simple constant voltage power supply, the only factor that is out of your control is the all cells will always be balanced at exactly 4.2V, no lower and no higher, but I think this is no bad for your application.

Would this module alone do the job of protecting, balancing and charging the batteries?

This module would have everything you want in just one board, but keep in mind that its charging/balancing process would be exactly the same as the previous 2 boards combined: all cells would charge together as long as one of them reaches the 4.2V, then the charger would be disconnected and this higher voltage cell would be discharged through a "bleeding charge resistor" (which is what your balancing board does) until it passes a certain threshold to be not considered charged anymore, and then all other cells get back to charging.

Important to emphasize again that in both cases your "balancing circuit" only works as long as the cells are charging and reaches 4.2V. So if you have cells at 3.8V, 3.7V, 3.6V and 3.5V, none of your balancing circuits will work. They will only kick-in as long as your device is charging and the first cell reaches 4.2V.

I hope I've made myself clear ;) any questions...

\$\endgroup\$
1
\$\begingroup\$

A Protection Circuit Module (PCM) is designed to provide 'last-ditch' protection which (hopefully) prevents damage if other circuitry fails. It is not supposed to be used as a substitute for a proper Lipo charger, or to turn the device off when the battery gets low.

Balancing modules are designed to equalize small capacity differences between cells, to ensure that they all get fully charged without any going over-voltage before the whole battery reaches maximum voltage. Most balancers are not powerful enough to correct large imbalance (which might be caused by mismatched cells or a faulty cell) in high capacity packs.

After adding a PCM and balancer you may get away with using a basic CVCC (Constant Voltage Constant Current) or current-limited power supply to charge the battery, if it is adjusted to the correct voltage and current and has stable output. However this doesn't protect against severe cell imbalance, low voltage, or other anomalies that the PCM can't detect.

If you decide to go this way rather than using a proper charger, it is your responsibility to make sure that the battery stays in good health. Measure cell voltages regularly to check that they are well balanced (voltages within +-0.03V). If the battery gets over-discharged then you should charge at a lower rate until the voltage gets to ~3.7V per cell. If any cell shows anomalous behavior (eg. not maintaining the same voltage as others) then it is faulty and the battery should not be used.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.