Electronic load 35W 3A with OLed display J7-f

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Official specifications:
I bought it from ebay dealer kiss_buy

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It arrived in a small box without any documentation or accessories.

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The only paper included was the above notice.

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On this side it has many different input connectors: Mini-usb, micro-usb, usb-C, Apple, screw terminals, they are all in parallel.

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This side is the usb meter with a Oled display and a single button.

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One end has usb input and usb output, the other end has coarse and fine control.
The current regulation is a bit slow, making it difficult to set a precise current, but with the low precision of the load it is not a problem.

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The circuit board is fairly well labeled and there are a few interesting solder points on it.

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The bottom is protected with a piece of plastic, due to the screws it is not a flat surface.

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A closer look at the different connectors.

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The bottom without plastic.

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The display looks and function like a typical usb meter, it has one button.




Measurement


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The current varies with voltage. The load has a power limiter, this limiter will turn the load off for a short time if the power is too high as can be seen on the yellow, magenta and white curve.
Minimum voltage is about 4 volt.

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At low current it will vary significantly with voltage.

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I did two load tests, both at 11V, but at different currents.
At the 3A the build-in meter says: 59:01min, 2.941Ah and 31.573Wh
My power supply has delivered: 2,98546Ah, 32,840758Wh over 60:01min

At the 1A the build-in meter says: 59:01min, 0.918Ah and 10.051Wh
My power supply has delivered: 0,94121Ah, 10,353675Wh over 60:01min

Some reason for differences:
Meter on load need a few seconds to startup, but not one minute!
Some power is lost in the cable and connections.
The load do not include its own idle consumption in the calculations.
Loads current calibration was a bit low, it showed 2.94A and 0.94A (Values jumped about 0.02A up and down).

Test

The precision is not very good, some of it can be calibrated out.

Temp3657

M1: 62,8C, M2: 52,8C, M3: 54,3C, M4: 47,6C, HS1: 79,1C

Temp3658

M1: 54,8C, M2: 39,7C, HS1: 78,5C

Temp3659

M1: 61,1C, HS1: 63,3C
The plastic prevents me from getting the real temperatures on the circuit board.

Temp3660

HS1: 98,2C

Temp3661

HS1: 91,7C
Here I tried to get a direct check of the transistor.

Temp3664

HS1: 150,8C
The fan stopped working during my tests and the load got very hot.



Conclusion

This load has many input connectors, making it easy to use for just about any usb power device and also for some other stuff, but the fairly low precision and annoying current setting spoils it. That the fan quit working during my test is also a bad sign.



Notes

To test QuickChargers it is possible to use the QC2-3-MTK-PE Trigger J7-t with this load. For QC it can be used in the output connector and will not add any resistance to the circuit, with MTK-PE it must be used on the input and will add resistance.