How does it work - inductive hour meter?

[TimR]

Those inductive hour meters that you attach to your lawn mower by
wrapping the wire around the spark plug cable - how do they work?

Would they pick up other current? For example, could I use one on my
air conditioner or refrigerator by wrapping around the power leads?
Or do you need the high voltage of the spark?

I found several manufacturers, like Redington, SenDEC, etc., but none
explained the functioning.

 

[JeffM]

Those inductive hour meters...how do they work?

...could I use one on my air conditioner...
TimR news:<[email protected]>

Inductive-pickup timing lights for car ignitions work similarly.
It should be easier, hours-wise, with appliances (constant 60Hz).

It's a current transformer.
(Think: 1-winding primary, 1000-winding secondary for a 1:1000 ratio.)
You terminate it into a resistor to develop voltage
and count the zero-crossings with a digital circuit.