problem
Never heard of a "load dump" before, so I went "alookin" This is from another forum and I always take things with a grain of salt. BTW I love google. Wayne
The OP was about a car radio going out at times.
answer was
Electrical transients in automotive systems are not uncommon. But voltage spikes where you can immediately "see" effects on instrumentation indicate a problem.
Does he just notice the radio cutting out, or is the effect visible in other areas... like the instrument cluster for example?
If it's just the radio, there might be a problem with the harness/connector to the radio. Or, a loose grounding strap/bolt that is affected by vibration.
If it's happening in other areas (e.g., instrument cluster, A/C system, interior/exterior lighting, etc.), you may have a defective alternator. Does he ever see the gauges ever flutter or dip? Or does he ever notice the interior lighting suddenly increase in intensity when this happens to the radio?
"Normal" vehicle electrical systems typically exhibit a voltage around 12.8V (battery voltage w/ ignition off) or 13.8V with ignition on and alternator up to snuff). The voltage can vary between 9V to 16V depending on the battery state-of-charge and/or condition of the alternator. These are rough numbers, but you get the idea.
Most vehicle electrical and electronics systems are designed to tolerate and function "normally" with voltages in the range of 9V to 16V, and even 19V in some cases. 19V is pretty rare, and represents a failed alternator. Electronic modules are even designed to survive to 24V for several minutes (representing a double-battery jump-start), although normal functionality is generally waived until the voltage returns to normal.
Where am I going with all this... oh yeah...
The voltage regulation these days is built into your alternator. The battery itself acts as a giant capacitor that can compensate for large transient currents, but it's the alternator that keeps the voltage steady (or, tries to, anyway).
There is a phenomenon called "load dump" which occurs when large loads are switched on and off... high current items like headlamps and A/C system, etc. Load dump can also occur if the battery experiences a sudden disconnect (via loose/faulty wiring or terminal connections). This can be as high as 40V to 60V, but is very brief. Again, most electronic modules in automotive systems are designed to withstand this kind of (typically brief) transient.
Bottom line: Check, in this order...
1) Check all cables & connectors running from the battery
2) Get the alternator checked
3) Hope the problem is not buried too deep in some other part of the electrical system
Good luck!
