Thursday, June 04, 2020

Cheap high power DC power supply modification for ISDT Q8 battery charger - swap a resistor!

Disclaimer: try at your own risk! understand what you are doing.


I did not feel the need to get the 100$ ISDT T8 (42V/30A input max.) but baught the 60$ ISDT Q8 charger instead, which is limited to 34V/20A input power.

However, a DC power supply for this Lipo battery charger ISDT Q8 can not be found at a reasonnable price.
As listed below in the specs, the charger can only take a maximum of 34V. It is pretty hard to find a power supply with high power and less than 34V AND more than 30V.



ISDT Q8 Specifications: www.isdt.co

  • Charging Power: DC 500W
  • Charging Current: 0.1A-20.0A
  • Discharging Power: 15W
  • Discharging Current: 0.1A-1.5A
  • Input Voltage: DC 10-34V
  • Ouput Voltage: DC 1-34V
  • Support Battery:
    • LiFe,Lion,LiPo 1-8S
    • LiHV:1-7S
    • Pb: 1-12S
    • NiMH: 1-16S


i found this beast DC power supply for LED strips on ebay:
1000W AC 110V-240V To DC 36/48V LED Power Supply Driver Adapter With Switch

Specifications:
Wattage: 1000W
Output: DC36
Input: AC110-240V 50/60Hz
Working Temperature: 0~40℃
Storage Temperature: -20~60℃
Working Current: 27.8A
Safety Compliance: CCC/ FCC / CE  (China Export?)
Ambient Humidity: 0~95% Non-Condensation
Protections: Overload/Over voltage/Short circuit
Compatible With: 3528, 2835 ,3014, 5050, 5630 ,5730 Led strip lights

However again, the voltage of this power supply can only be adjusted in a limited range of 38 - 34.1V, which is likely to fry the ISDT Q8 charger (i chickened out and did not try).

Also, there is a safety issue on mine, i did not really understand where it comes from, the ground is not well isolated and triggers the GFCI safety fuse... 8 volts AC on the ground pin. i will have this mounted in a wooden or plastic box just in case!



The power supply is opened with 2 screws to change the AC power input, and the board can be easily removed from the box after carefully removing a few other screws hidden behind the sticker (this voids warranty - btw what warranty? on ebay, it costs 60$ : 16$ of power supply and the rest of express shipping from china, or if you got it on amazon : 16$ of board and the rest of profit for amazon).
The variablre resistor aside the green led light is connected to a 3.9 kOhm 1/4W resistor. the latter is the voltage range limiter. i replaced it with a 4.7 kOhm 1/4W resistor to obtain a voltage range of 36.0 - 30.1V ~27Amperes.

i chose to adjust the voltage to 33.0V to prevent temperature voltage drifts to go outside specifications, noxious for the charger...

this is a pretty easy modification and charger works at full power (550W)

hope it helps someone...




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