USB safety tester J7-t UK
The Missing Manual - J7-t (abridged)
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.
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The Manual
The Eversame USB Digital Power Meter aka Juwei USB Safety Tester Model J7-t
Specifications
• Input Voltage: 3V - 30V
• Input Current: 0 - 5.1A
• Accuracy: +/- 1%
Accuracy compared to calibrated Fluke 87-5 Multimeter
my J7-t reads 5.12V; my Fluke reads 5.137V
The J7-t has two USB type A connectors. The male connector is reversible so you can plug it into the power source either side up. The connector has a set of pins on each side of a thin blade that makes this possible. It won't withstand rough treatment.
The female socket on the other end of the J7-t will accept a cable from the device to be charged as long as it's terminated with a Type A male connector.
The J7-t displays one of three screens when plugged into a power source. The screen will be whichever last showed, but fresh out of the box, you should see Screen 1.
Screen 1
◦ voltage
◦ current
◦ watts
◦ elapsed charging time
◦ amp hours (cumulative)
◦ watt hours (cumulative)
[If you have mistakenly held down the button (marked KEY) on the top edge of the J7-t while plugging it into the power source, you will enter calibration mode and see a different screen. Unplug the J7-t and try again.]
The cumulative counter values are derived from the time a device has actually been charging through the J7-t. The count stops whenever charging stops and resumes when charging resumes. If the J7-t is unplugged from its power source, values are preserved and can be read when powered again. To clear the cumulative counters, hold the KEY button down until you get a beep.
A short press on the KEY button will cycle the J7-t display through three screens. The remaining two are:
Screen 2
◦ voltage of all 4 pins (v-, d+, d-, v+)
◦ resistance of the connected load
◦ timer / temperature of the J7-t
◦ elapsed charging time
◦ current
Screen 3
◦ voltage / current
◦ capacity / adjustment factor
◦ energy in watt hours / temperature of J7-t in °C
◦ elapsed charging time / timer
Key Presses
A quick press of the KEY button will do the following:
• press 1 time to cycle through the three display screens
when on Screen 3
• press 2 times to reset Cap: mAh
• press 3 times to reset Ene: Wh
• press 4 times to reset Time
• press 5 times to set the charge timer
• press 6 times to change language (English or Chinese)
(Holding the KEY button down until you get a beep will clear all counters at once.)
Charge Timer
The J7-t can be set to stop charging after a certain time, from 1 to 24 hours. By default the timer is off and shows on screens two and three as OFF. To set the timer, do five quick presses of the KEY button while on screen three. OFF will start flashing on the bottom of the screen. Continue pressing the KEY button until you reach the desired setting (AO is auto-off). After charging for the set time, the J7-t will stop charging, beep a few times, and display OFF on its screen. Pressing the KEY button brings the normal display back up.
Calibration Mode
To enter calibration mode, hold the KEY button down when you connect the J7-t to its power source. Afterwards, a single press of the KEY button will cycle through the configurable settings, showing each setting alone on its own screen.
• 0.00A a 2 amp source is required to calibrate amps
• 5.12V a 5 volt source is required to calibrate volts
• >30.0V set overvoltage cutoff
• <3.00V set undervoltage cutoff
• >5.00A set overcurrent cutoff
• X1.00 set mAh and wH adjustment factor (0.50 to 1.50)
Double click the KEY button to change a value. When changing, a single click decreases the value; a double click increases the value. After a single or double click, immediately pressing and holding the KEY button will rapidly change values.
The last screen in calibration mode shows a telephone number and website for Juwei, which is a creature of Shenzhen Ouju Technology Co., Ltd.
To exit calibration mode, disconnect power to the J7-t.
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USB Safety Tester J7-t: review and instruction manual
USB Safety Tester J7-t is a compact tester for testing and testing USB ports in various devices. The tester determines the current voltage, current consumption, displays the output power, calculates the transferred capacity in Ah and Wh. The most common use case for the J7-t tester is testing of banks, power supplies and other chargers, where the USB port is used as the output connector.
On the reverse side of the USB Safety Tester j7-t are the technical specifications and capabilities of the device, as well as the standard warning not to remove the plastic protective cover to avoid electric shock. Use USB Safety Tester j7-t is recommended indoors with standard humidity.
Technical characteristics of USB Safety Tester j7-t
Operating voltage range: 3.0-30 V
Current: 0-5.1 A
Functions: Current on USB connector, voltage, capacity, current power consumption
Compatibility with fast charging standards QC 2.0 and QC 3.0, BC 1.2 and Apple voltage range
Level of accuracy: 1 (A Level)
Operating temperature: –10 to +60 degrees Celsius
The output connector is designed as a standard USB 2.0 connector. But for convenience, the input plug is designed as a two-way solution, so the USB Safety Tester j7-t tester can be placed on the display so that it is easier to observe and take readings.
In principle, the solution is convenient, but questions raise reliability, a thin plate in the center does not look strong enough and, if it is carelessly applied, it can easily break off. At least I have that impression. Hope it is false.
Functional devices and operating modes USB Safety Tester j7-t
After the first launch of the device, the display of the USB port was displayed on the screen. This is understandable from what information this screen shows. On the left you can see 4 lines with voltages on each pin of the USB connector. On the right side additional information - resistance, temperature inside the device, operating time from the moment of reset, consumed current.
USB Safety Tester j7-t has one Key button, a single click on which changes the information on the display. The same button resets the readings. If the Key button is held down for 2 seconds, it is completely reset and the action is confirmed by a beep. There is also an incomplete reset function when only part of the data is reset. More details below.
The second screen displayed was a surprise, as it shows me with signatures in Chinese. Intuitively everything is clear, but a bit confusing.
This type of display is different data arrangement. Chinese can be changed to English by quickly pressing the button for 6 times while on the screen with Chinese inscriptions. After this, the device showed clearer signatures. Read more about the actions of the multifunction button and setting up the tester below in the section on how to operate and configure j7-t USB Tester.
Clicking on the Key button again proceeds to the third display option. Subsequent pressings cyclically in the previous versions.
In this mode, the values of voltage and current are well represented, as well as information is available on capacity and energy in Amp-hours and Watt-hours, respectively. It also displays the current power consumption and time since the full reset.
Instructions for operation and configuration of j7-t USB Tester
Since the seller did not put any instructions with the device, I had to collect information in parts from different sources and cite it further. If I missed something, write in the comments, I will add.
Key Button Actions:
one push toggles the display of information;
two presses - reset the electric charge meter in mAh;
three presses - reset the energy meter in Wh;
four presses - reset the time;
five taps - set the timer;
six taps - change the language (English or Chinese);
long press (2s) - full reset.
Pressing must be done quickly. Some of them work only on the second display mode. In the first form, they do not work at all.
Setting the timer j7-t USB Tester:
Go to the second view of the display (with the captions of the values). Press the button five times in a row. The timer value will start flashing. By default, it is turned off (OFF position). If you do not press the button for 2 seconds, the value is applied and the flashing stops.
To change the value, press the button:
1 time - to reduce;
2 times to increase the value.
Variants of values and explanations to them:
OFF - the timer is off.
AO - automatic intelligent mode. The essence of the work lies in the fact that if during the last hour of work the power consumption falls below 2W, then the tester automatically turns off charging to avoid overcharging.
1:00 - 24:00 - work time in hours with a step of 1 hour, after which the tester will disconnect the load.
System menu of the j7-t tester:
To enter the service menu, hold the button and hold it connected to the source. The service menu is loaded. Switch between views with a single button click.
1st indicator 0.00A - current, 2nd voltage. These two points are used to calibrate the readings on the reference values of 2A and 5B, respectively.
Attention! Do not make changes if you do not have a reference load and power source. Otherwise, the readings will be incorrect.
The 3rd parameter> 30.0V sets the maximum voltage at which the tester cuts off the load.
The 4th parameter sets the minimum voltage to disconnect the load.
The 5th parameter is responsible for the maximum load shedding current. When exceeded, a beep sounds.
The 6th parameter sets the ratio of measured capacity to mAh. It is displayed in parentheses on the second screen. It can be used to correct values based on the difference in nominal voltages at the USB output and battery contacts.
The 7th screen will show the manufacturer information. The screenshot is not displayed.
Changing the parameters is activated by double pressing the button. Values start flashing. If you do not perform actions on them, then after 2 seconds they are activated and stored, stop flashing. In parameters 3-6, one-click changes are made to decrease, double-click to increase the value. If, after pressing the button, the button is held down, the parameter is continuously changed until
Current and voltage calibration
Enter the service menu, the 1st parameter. Next, connect the reference load 2A. We look at the value on the screen. If it is different from 2.0A, then double-activate the change. The parameter starts flashing. After that, press twice again to set the value to 2.0A. We are waiting for 2 seconds to apply the changes. The value will stop flashing.
Calibration by voltage occurs by applying to the input of the tester a reference 5.0 V. Go to the 2nd screen. The parameter change is the same as current calibration.
Reset to factory settings
On the first screen (current calibration 0.00A) without a load, press and hold the button until a beep sounds, “RESET” is written and the device is rebooted in operating mode.
Exit the service menu by turning off the power of the device.
And what about the accuracy of USB Safety Tester j7-t measurements?
Definitely say hard for me, because there are no suitable reference devices on hand to test for accuracy. On the vise, the readings are sufficiently accurate to assess the quality of the charger or the capacity of a crib in a living environment.
Conclusions and recommendations for USB Safety Tester j7-t
In general, a good device for testing poberbankov, chargers and other devices with USB ports. It has a sufficient level of accuracy to obtain objective data. I can safely recommend to purchase
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Sources:
https://www.amazon.com/review/R3EF0QW6MAJ0VP
https://lygte-info.dk/review/USBmeter%20safety%20tester%20J7-t%20UK.html
https://igorosa.com/usb-safety-tester-j7-t-obzor-i-instrukciya-po-ekspluatacii/