Vantrue JS3 Jump Starter & Air Compressor - Unboxing and First Impressions

[Hack_man]

Unless you press the boost button, the only thing the booster does is measure the car's battery voltage. It's not providing any current to charge the car's battery (boosting) until the button is pressed. Maybe I'm stating the obvious, but I was pointing out that @Julian23 did not mention that he pressed the button. The JS3 is just a voltmeter until that button is pressed.

 

[Augustus]

Unless you press the boost button, the only thing the booster does is measure the car's battery voltage. It's not providing any current to charge the car's battery (boosting) until the button is pressed. Maybe I'm stating the obvious, but I was pointing out that @Julian23 did not mention that he pressed the button. The JS3 is just a voltmeter until that button is pressed.

You don't have to press the Boost button in every instance.

This applies to all jump starters. You only have to press the Boost button when the jump starter measures the current and either displays on screen (or lights up a light on some other models), that the car battery voltage isn't enough.

Then you press the Boost button and then you can try starting the engine again.

 

[Hack_man]

You don't have to press the Boost button in every instance.

This applies to all jump starters. You only have to press the Boost button when the jump starter measures the voltage and either displays on screen (or lights up a light on some other models), that the car battery voltage isn't enough.

Then you press the Boost button and then you can try starting the engine again.

I think we are saying the same thing but:
If there was no need to press the boost button, it means the jump starter was not needed at all.

If the car starts with the jumper attached without pressing the button, it means the car's battery was able to start the car with no assistance from an outside power source. If he didn't press the boost button then the JS3 was just a heavy voltmeter with cables attached to his car battery.

 

[Augustus]

If there was no need to press the boost button, it means the jump starter was not needed at all.

If the car starts with the jumper attached without pressing the button, it means the car's battery was able to start the car with no assistance from an outside power source. I think we are saying the same thing, but if he didn't press the boost button then the JS3 was just a heavy voltmeter with cables attached to his car battery.

I've used my own Gooloo brand jump starter for a few years now, and a couple of times I've not had to press the Boost button and it started the engine. And no the engine was not starting at all until I connected the jump starter to it.

Other times I had to press the Boost button and then the engine started. So yes it needed power from the jump starter to start the engine. The Boost function just provides more voltage to the car battery.

Its not rocket science. Once you've had to jump start a few engines, it makes sense.

 

[Hack_man]

I've used my own Gooloo brand jump starter for a few years now, and a couple of times I've not had to press the Boost button and it started the engine. And no the engine was not starting at all until I connected the jump starter to it.

Other times I had to press the Boost button and then the engine started. So yes it needed power from the jump starter to start the engine. The Boost function just provides more voltage to the car battery.

Its not rocket science. Once you've had to jump start a few engines, it makes sense.

I measured the output of the JS3 and it provides no power to the cables until the button is pressed.
Perhaps other jump starters operate differently or mine has a defect.

What do you think the boost button is doing? Are you saying it's providing a higher JS3 output voltage than not pressing the boost button? From a safety standpoint I can't see how it would supply current until the user operated the switch.

 

[Augustus]

I measured the output of the JS3 and it provides no power to the cables until the button is pressed.
Perhaps other jump starters operate differently or mine has a defect.

What do you think the boost button is doing? Are you saying it's providing a higher output voltage than not pressing the boost button?

Well maybe it works differently on the JS3 then but for others like my Gooloo you connect the clamps and either the green light stays on to signify it's ready. Or flashing to signify that it needs you to press the Boost button. So it's drawing current at the very least.

Either way a jump starter is providing a surge of current to the battery, which I would presume explain why its got nothing to do with voltage.

Safety-wise well it's not completing the circuit until one starts the engine..

 

[Julian23]

Did you press the boost button during this process? The way I'm understanding it, the boost button enables a relay inside the JS3 which sends power to the jumper cables.

Also, I don't understand why the user manual says:

1. When the car voltage is less than 9V,
   BOOST+current voltage will appear on the screen+
2. At this point, press the BOOST button on the battery clamp, and the screen will change from BOOST to READY

It implies to press Boost only when the car voltage is less than 9V. But a car won't start below 12V so why do they even mention 9V? In your case it was measuring 12.0 V which would have required a boost which is enabled by pressing the button.

I did not press the button. Since the voltage was above 9V, it's not required.

Just a few hours ago I had to jump a car again. The JS3 showed a voltage of 11V. The car would not start without the jump starter. Every light went dark with the 2 attempts I did.
With the JS3 it immedialtey started.

Unless you press the boost button, the only thing the booster does is measure the car's battery voltage. It's not providing any current to charge the car's battery (boosting) until the button is pressed. Maybe I'm stating the obvious, but I was pointing out that @Julian23 did not mention that he pressed the button. The JS3 is just a voltmeter until that button is pressed.

A button press isn't needed. I just connected the clamps to the battery and then to the JS3.
The JS3 started itself and showed the following things on the display.

 

[Julian23]

What do you think the boost button is doing?

The boost button is only required if the JS3 does not detect the battery.
See the instructions on the JS3:

 

[Hack_man]

Thanks for those details!

1. I'm trying to understand at what point in the jumping process does the JS3 actually energize its cables assuming the boost button is NOT pressed?

2. It appears (like @Augustus stated), pressing the boost button simply provides a higher than normal charge voltage, but it also energizes the cables to 15.2 vdc whether or not the car is being started.

I measured zero volts on the cable ends with no load on the clamps but 15.2 V with a voltmeter with no load when the boost button is pressed.

If I hook up a 9V transistor battery to the Cables, the voltmeter and JS3 measure the no-load voltage of that battery (9.7 V). If it sensed the battery and energized the cables, I would have expected >12 V.

So evidently the JS3 is smart enough to energize the cables when the car is being started.