One of the most common things I check when working in automotive is wire continuity. However, the usual method of using a multimeter doesn't cut it. I have seen wires with low resistance appear to be OK, but as soon as a load is applied the resistance goes high. Likewise, I have seen +12V on a line when checking with a multimeter and as soon as a load is applied it drops to 0V.
How I check wiring is by applying +12V to one end and attaching a load to the other end to see if the circuit can support a certain current (adjusted for the size of the wire, of course). I do this so often that I've decided to build myself an all-in-one continuity checker to make this process quick and easy. I've come up with an idea on how to make an (almost) automated tester, and would appreciate any feedback on my method.
- I want to run the circuit off a 9V battery and be self contained. I don't always have access to vehicle power which is why I don't want to rely on the vehicle battery. Further, in accident vehicles with damaged harnesses the battery would be dis-connected anyway while repairs are under way.
- I need to be able to provide enough current to test larger wires so I thought of charging up a capacitor to be able to provide this current for the couple seconds the test requires.
- To test wires of different gauges I need to be able to regulate the current for each size. I thought of dumping the energy from the capacitor into a load through a transistor to vary the current.
- I plan to use a microcontroller to control everything and monitor the voltage drop across the wire while the load is applied. At the end of the test I would get a simple pass/fail.
So do you think this is a good way to check a wire, or does anyone know of any other methods?
How I check wiring is by applying +12V to one end and attaching a load to the other end to see if the circuit can support a certain current (adjusted for the size of the wire, of course). I do this so often that I've decided to build myself an all-in-one continuity checker to make this process quick and easy. I've come up with an idea on how to make an (almost) automated tester, and would appreciate any feedback on my method.
- I want to run the circuit off a 9V battery and be self contained. I don't always have access to vehicle power which is why I don't want to rely on the vehicle battery. Further, in accident vehicles with damaged harnesses the battery would be dis-connected anyway while repairs are under way.
- I need to be able to provide enough current to test larger wires so I thought of charging up a capacitor to be able to provide this current for the couple seconds the test requires.
- To test wires of different gauges I need to be able to regulate the current for each size. I thought of dumping the energy from the capacitor into a load through a transistor to vary the current.
- I plan to use a microcontroller to control everything and monitor the voltage drop across the wire while the load is applied. At the end of the test I would get a simple pass/fail.
So do you think this is a good way to check a wire, or does anyone know of any other methods?
