Test/Review of USB meter: Safety tester J7-t

EDC Gear for Flashlight Carriers USB Power Devices
1

USB meter: Safety tester J7-t









Official specifications:

  • Input Voltage: 3V - 30V

  • Input current : 0 - 5.1A

  • Cumulative capacity range: 0-999.99 Ah

  • Cumulative power range: 0-999.999 Wh

  • Timing the maximum range: 0-999 hours 59 minute 59 seconds precision: 1 second

  • Parameters that you can test: Voltage of battery. Current of battery, discharge capacity of battery,Quantity of electric charge,power of battery,timing.

  • Parameters adjusting function: Yes.


I found this unit on Aliexpress at a dealer called lucky bee.

The one I bought was called Security tested, but the one I got is Safety tester, They looks to be exactly the same.



How does it look









The button is used to select screen and holding it down will reset the Ah and Wh counters.

Holding the button down when connecting power will enter the configuration and calibration menu.







First screen is voltage, current, power and the summations Ah, Wh and time.



Next screen show voltage on both power and data pins, a calculated resistance of the load, internal temperature, time and current.



This screen is basically the same as the first, just with labels for the sums. The (1.00) show is a scale factor that can be adjusted in the configuration.
Press the button 5 times to define a maximum charge time (AO is auto off), wait to save. One press is down, double press is up.
Press the button 6 times to switch between Chinese and English.



I could break it open without any damage.





This design looks very simple. It has a voltage regulator, a R050 for current measurement, a processor, a EEPROM and some transistors for turning the output on/off. The missing 6 pin chips are probably ADC’s with better resolution.







Measurements



This device requires nearly 4 volt to work fully, this will affect the precision at low voltage including QC3 when at lowest voltage. When the voltage is 4 volt or above the precision is good.

  • The usb connector is reversibel, it is always possible to mount with display up.

  • Own current consumption is 20mA

  • Internal resistance is about 0.17ohm including connection resistance.

  • Remembers Wh and Ah when power is off

  • Voltage display is within 0.03 volt in the 4.0 to 6.0 volt range.

  • Current display is within 0.02 ampere in the 0 to 3.0 ampere range with 5 volt supply.

  • Over current turn off is at 5A (Can be configured)

  • Over voltage turn off at 30 volt (Can be configured)

  • Under voltage turn off is at 3V, actually 2.3V due to ADC error at low voltage (Can be configured)

  • USB data works fine.

  • Meter has a buzzer than sound when voltage is connected/disconnected.





M1: 51,5°C, M2: 49,5°C, M3: 42,9°C, HS1: 55,9°C



M1: 50,6°C, M2: 47,3°C, HS1: 64,5°C



Conclusion

This is a usb meter with a few extra function. For technical people the D+/D- voltage can be very interesting (Together with the table at the bottom of this page).
I do not see much idea in the disconnect function, scaled capacity or the timed charge.

The other function is just a good usb meter with Ah and Wh counters, but I could have wished for lower internal resistance.



Notes

How do I make the test
2

Thanks for telling me how it actually works :slight_smile:

3

Thanks for the review!

I just got this http://www.ebay.com/itm/282033539408

Which seems to have the exact same UI but an adjustable load and several additional inputs (micro usb, lightning, usb-c, mini usb) added to it. Also thanks for telling me the 6 click language switch trick, since mine didn’t come with any instructions.

4

A load with the same interface?
I am going to take a closer look on that load!

5

Mine also has an acrylic plate on the bottom to protect the pcb and the transistor. It also has a USB port for adding additional loads or measuring a cell phone charge for example.

Here are all the inputs

Also take a look at this:
http://www.ebay.com/itm/252370367873

It has a pc software for setting up the load and logging + graphing. Even automatically increasing the load to graph the current vs. voltage at user selectable intervals.

6

I have the software and I will probably be reviewing one of their loads in the near future (The software is a bit tricky to get).

7

Fantastic! I also ordered the load today and spent a good 30 minutes to try and download the software, but finally succeeded. For some reason the download site only worked with my browser in incognito mode.

8

I’ve got both models of that ZKETech load. Software is nice to work with.
And can run multiple loads at the same time.

Just hope you don’t get one like my first EBD-USB+ which has a short in the micro-usb connector… It immediately shits down the pc when connected.

9

We shall see :slight_smile: I noticed you had the EBD USB when I watched through many of your Youtube videos earlier today. Good stuff on your blog too!

10

Thanks man! Nice to hear :slight_smile:
Just found that first load you mentioned, but without the screen at BangGood :

They also have a very interesting converter :

11

There is also this bundle, with the smaller sibling to the load with the display, and the 5-digit sibling of the meter HJK just reviewed.

12

That is the one I have. It does have the screen, look closer on the second and third images. It has a ribbon cable coming off of it.

13

What kind of backlight is used in that meter?
I ask, because in mine after a month backlight went so weak, that it is barely visible.
Mike

14

It do not have backlight, each dot is a small organic led (OLED) and they have limited lifetime.

15

Heh, it dies after 2 months. (Just checked)
Mike

16

Is that running 24/7?
Heat do probably affect the lifetime.

I am using a OLED on my homemade QC trigger, I have been using that for all the QC chargers I have checked. I can see the dots are worn a bit, but there are still lot of life remaining in them.

17

This is way of topic and I apologise in advance. With the above comments about Oleds dying would you buy a tv with an Oled screen?

18

The first generation of TV’s with OLED did have a rather short lifetime. The current generations are much better, but the cheap OLED displays from China do not use the better technology.