We are undertaking a LED lighting project and have figured out the way circuit in motorcycle works, the AC return is through frame and the DC return (negative) is through the frame to negative ground of battery,

When both AC neutral (return) and DC negative are connected (grounded) to frame of a motorcycle how do the AC and DC waveforms interact and how do AC & DC interact with DC/AC components respectively? That is how does AC interact with DC components and how does DC interact with AC components and how is it possible to connect these circuits together through frame?

That is how circuit is connected but do not understand the laws/electronic properties that allow this to occur?

See wiring diagram below, the pertinent parts are AC generator to DC regulator rectifier and Brown (Br) wire to Ground (frame) shown. Also AC supply to AC headlights and lighting which then returns to field coil on AC generator (shown connected to ground (frame)).


  • \$\begingroup\$ Have you looked at the alternator and the rectifier? \$\endgroup\$ – Solar Mike Feb 5 '18 at 21:12
  • \$\begingroup\$ Welcome to EE.SE. Can you rotate your image and insert it into your post. You'll get better responses that way if we all don't have to follow a link to understand your question. If you haven't enough rep to insert the image then paste the link with a .png or .jpg extension and one of us will fix it for you. \$\endgroup\$ – Transistor Feb 5 '18 at 21:14
  • \$\begingroup\$ What is your question? Why there is noise in your system or why there is not? \$\endgroup\$ – Sparky256 Feb 5 '18 at 21:58
  • \$\begingroup\$ Hi, I apologise for link but it is a vector pdf and a jpg or png will not allow level of zoom or scaling to see tiny wiring numbers. My question is how is it possible to connect AC and DC return (neutral [AC] and negative [DC]) into same circuit and what are effects of AC 30-50VAC on DC components and effect of DC 12VDC on AC components? \$\endgroup\$ – Thomas Branley Feb 5 '18 at 22:27
  • In general, the frame or chassis of a vehicle is considered a very, very low resistance.
  • If you are familiar with Ohm's law it tells us that the voltage drop along the frame will be given by \$ V = IR \$. Since R is very low V will be very low too - so low that the various circuits don't interfere.
  • It might help to consider the chassis as a big sea of mobile electrons. Current can enter and leave from any point on it without the local water level rising or falling. In electrical terms all points on the chassis are at the same potential (voltage).
  • Following on with the analogy, if we put a restriction into our sea - a small channel or pipe - then feeding in a large current would cause a rise on that side of the restriction. You may find parts of your motorbike frame have poor electrical connections with other parts and might be able to measure some voltages there.

In any case, your motorbike will run on DC with the exception of inside the alternator, if there is one, which will be alternating, as the name suggests, but rectified with diodes before connection to the DC circuits. The ignition circuit may also be considered AC.


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