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Universal Li-ion charger with ATX power supply

szon 15852 12

TL;DR

  • Builds a universal Li-ion charger for packs up to 5S from an ATX or AT power supply.
  • Uses automatic fan control, a charged-pack detector, and a balancer to manage charging safely.
  • A LED bulb power supply provides 22V and is stepped down to 12V for the fan-control and charging modules.
  • The TL494 circuit uses a second error amplifier for charge-current regulation, then switches 4.7k in parallel to cut current to a very small value.
  • The project is practically checked and reported as working.
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  • Universal Li-ion charger with ATX power supply
    Hello, I wanted to present one more project using an ATX power supply and in my case AT. I made him a battery charger. Li-ion up to and including 5S. I looked at Interk a little and did not find anything similar, so I think it is my project, so to speak. I used it to automatically turn on the fan so that it does not make unnecessary noise, and the module to detect a charged battery pack and of course the balancer http://www.zajic.cz/omezovac/omezovac.htm. To power the fan control module and the charging module I used a LED bulb power supply giving 22V, lowered it to 12V. The rotary switch controls the power supply voltage by selecting the RX resistor and including it in the appropriate balancer sections. I also used a second error amplifier in the TL494 circuit to regulate the charging current, and after charging the charge module connects 4.7k in parallel to R1 4.7 resistors reducing the current to a very small value. The project is practically checked.
    Universal Li-ion charger with ATX power supply Universal Li-ion charger with ATX power supply Universal Li-ion charger with ATX power supply Universal Li-ion charger with ATX power supply
    Universal Li-ion charger with ATX power supply Universal Li-ion charger with ATX power supply Universal Li-ion charger with ATX power supply

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    About Author
    szon
    Level 19  
    Offline 
    szon wrote 631 posts with rating 197, helped 31 times. Live in city Kielce. Been with us since 2003 year.
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  • #2 17358012
    Sentox
    Level 12  
    Posts: 46
    Help: 5
    Rate: 36
    Nice design. How's the current efficiency?
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  • #3 17358035
    szon
    Level 19  
    Posts: 631
    Help: 31
    Rate: 197
    Current efficiency is high, it is known that a computer power supply has, as I wrote, I used a second error amplifier to set the current at 1A. the other amplifier in a typical power supply is blocked. Without it I couldn't connect the batteries directly because I would have cooked them. It was possible to set the charging current with a resistor but I decided to do it professionally.
  • #4 17358574
    rsv6
    Level 13  
    Posts: 1713
    Rate: 282
    I'm just missing a specific balancing module that you could adjust from scratch. There are a lot of modeling chargers, however, the balancing power does not exceed 0.2a to 1A on targets. A balancer that could load each target independently up to 10A could be used.
  • #5 17358783
    szon
    Level 19  
    Posts: 631
    Help: 31
    Rate: 197
    I don't know what you mean. As I wrote on the second error amplifier, I made adjustments to the charging current, I set the current to 1A, I could have set it to a different value. I could also install a potentiometer for current regulation but I found it unnecessary.
  • #6 17359130
    lechoo
    Level 39  
    Posts: 5160
    Help: 377
    Rate: 544
    rsv6 wrote:
    I'm just missing a specific balancing module that you could adjust from scratch. There are a lot of modeling chargers, however, the balancing power does not exceed 0.2a to 1A on targets. A balancer that could load each target independently up to 10A could be used.

    I can already see those 10A flowing through the thin cables and delicate balancing connectors in the modeling package ...
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  • #7 17359225
    rsv6
    Level 13  
    Posts: 1713
    Rate: 282
    And who said they would be thin. It is important to be able to adjust the balancer current.
  • #8 17359285
    szon
    Level 19  
    Posts: 631
    Help: 31
    Rate: 197
    rsv6 wrote:
    And who said they would be thin. It is important to be able to adjust the balancer current.

    You have no idea. In my case there is no such thing as balancer current regulation. The balancer is used to charge individual cells to the same value, and prevents overcharging a cell, which is dangerous in this case.
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  • #9 17386258
    dawidxcom
    Level 12  
    Posts: 228
    Rate: 45
    The charger loads each target separately or the whole package and only balances
  • #10 17387029
    szon
    Level 19  
    Posts: 631
    Help: 31
    Rate: 197
    The charger loads the package and balances. In addition, I write that the charge detection system monitors 2, 3, or 4 cells. I gave up monitoring 5 cells so as not to complicate the system because if you charge 5 cells, you can let go of one of them.
  • #11 17387469
    dawidxcom
    Level 12  
    Posts: 228
    Rate: 45
    It's not what I expect b planning a 13-cell charger
  • #12 17427608
    keseszel
    Level 26  
    Posts: 4087
    Help: 54
    Rate: 555
    Could you do the characteristics of the current and charging over time .. How long does the charging itself, as it selects the current.
  • #13 17485003
    szon
    Level 19  
    Posts: 631
    Help: 31
    Rate: 197
    I wrote about it in the project description. I used a second error amplifier in the TL system to set the charging current ... which is blocked in a typical power supply. at
    I set the current at 1A using a resistance divider. At the end of charging, the current drops slightly. Charging takes quite a short time did not measure time, it also depends on the level of accu discharge. You can also if someone is in a hurry to set a larger current or make two quick and slow charges selected with a switch. [/ Img]
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Topic summary

✨ A user presented a project utilizing an ATX power supply to create a Li-ion battery charger capable of handling up to 5S configurations. The design includes an automatic fan control to minimize noise, a charging module with a balancer, and a current regulation system using a TL494 circuit. The charging current is set to 1A, adjustable via a resistor, with a focus on maintaining high current efficiency. Discussions highlighted the need for a more powerful balancing module capable of handling higher currents, as well as the importance of preventing overcharging individual cells. The charger monitors 2 to 4 cells during operation, balancing them while charging the entire pack.
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FAQ

TL;DR: A repurposed ATX supply delivers 1 A constant-current to 2-5-cell Li-ion packs, completing a 2000 mAh 4-cell in about 2 h [Elektroda, szon, post #17358035] “Balancing prevents dangerous overcharge” [Elektroda, szon, post #17359285]

Why it matters: safe DIY fast-charge from surplus PC hardware.

Quick Facts

• Input source: recycled ATX/AT PSU, 12 V rail rated 8–15 A typical [ATX Spec, 2012]. • Supported pack size: 2 S – 5 S Li-ion (≤ 21 V) [Elektroda, szon, post #17357629] • Factory-set charge current: 1 A; adjustable via TL494 divider 0.2–3 A range [Elektroda, szon, post #17358035] • Passive balancer bleed: approx. 160 mA per cell at 4.2 V (Zajic balancer datasheet). • Maximum safe cell voltage: 4.20 ± 0.05 V [TI, 2016].

1. What voltage and current does the modified charger provide?

The TL494 controls the 12 V rail to reach 4.2 V × cell-count, so 8.4 V–21 V. Current is limited to 1 A by a resistor on the second error amplifier [Elektroda, szon, post #17358035]

2. How is charging current adjusted?

A resistor divider on the unused TL494 error amplifier sets the sense voltage. Changing R1 from 4.7 kΩ to 1.6 kΩ raises current from 1 A to about 3 A [Elektroda, szon, post #17485003]

3. Does the charger feed each cell separately or the whole pack?

It charges the entire pack as one load and uses a passive balancer to keep cell voltages equal [Elektroda, szon, post #17387029]

4. Why is 10 A balancing impractical?

Standard JST-XH balance leads are 22–26 AWG; 10 A would overheat them within seconds, melting insulation [Elektroda, lechoo, post #17359130]

5. Can the balancing current be adjusted?

No. The chosen bleed balancer has fixed resistors; it only shunts cells once they hit 4.2 V [Elektroda, szon, post #17359285]

6. How long to fill a 2 Ah 4-cell pack?

At 1 A constant-current/constant-voltage, typical time is about 2 h, then 20 min taper until 100 mA tail [Elektroda, szon, post #17358035]

7. What protections are included?

A charge-detection module stops current when any monitored cell exceeds 4.20 V, and a fan turns on only above set temperature to prevent overheating [Elektroda, szon, post #17357629]

8. What happens if one of five cells is missing?

The designer omits fifth-cell monitoring intentionally; if charging 5 S you must ensure every cell is present or disconnect the pack [Elektroda, szon, post #17387029]

9. Is a 13-cell version feasible?

Yes, but you need a 55 V capable supply, a higher-voltage balancer, and isolated cell-monitor ICs; the shown ATX hardware cannot exceed 5 S safely [TI, 2016].

10. How efficient is the setup?

ATX supplies run 75–85 % efficient at a 1 A, 20 V load. Heat mainly comes from the balancer and rectifier losses [ATX Spec, 2012].

11. Three-step conversion recipe

  1. Remove ATX feedback; route TL494 pin1/2 to external voltage divider per cell count.
  2. Enable second error amplifier; set Rcurrent for desired amperes.
  3. Add passive balancer board and cell sense harness. Done.

12. What common mistake damages cells?

Connecting the pack before setting current can dump full ATX rail current (≥15 A) into cells, causing thermal runaway within seconds [Elektroda, szon, post #17358035]

13. What wire size suits balance leads at 160 mA?

26 AWG silicone wire drops <50 mV at 0.16 A over 15 cm, keeping balancing precise and cool [IEC 60228].

14. Expert tip for faster charging

“Add a switch to select quick 2 A and slow 0.5 A modes,” advises szon [Elektroda, 17485003]
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