Battery tester is so smart I can't understand how it works...

[solarsimon]

I bought a battery tester, typically for car use. 2 x croc clips. If you don't connect both leads well enough it tells you.... but it even tells you which colour isn't mated properly. How the hell can it know which one is dodgy?

Explanations welcome!

 

[OzSolar]

I read that as it can't see the negative terminal, perhaps due to the corrosion.

But if it's like mine it won't even turn on until it can detect that it's hooked up to the battery.

Sometimes you need to rotate back and forth a few times to help the clamp get through the dirt and oxide.

 

[wpns]

There aren't two wires to each clip, are there? Or some other connection to the car's electrical system?

 

[legg]

It would be possible to get an ~ kelvin sense, if a sense lead monitored the
compression side of the crocodile's claw. It's not really possible to get milliohm
battery z measurements without it.

 

[AlpineJoe]

That's how these things work - it's a 4-wire setup, each half of the jaw is insulated from the other. It applies a load on one half of the jaw and measures the voltage on the other. The voltmeter resolution is very good and based on the drop, gives you the batteries' internal resistance value.

 

[solarsimon]

That's how these things work - it's a 4-wire setup, each half of the jaw is insulated from the other. It applies a load on one half of the jaw and measures the voltage on the other. The voltmeter resolution is very good and based on the drop, gives you the batteries' internal resistance value.

That makes so much sense. I'll have a closer look at it