QuestionHi, I have a hifonics amplifer that was used and i basically got free...when the car is in acc the amp works just fine and my subs beat good. However when the engine is turned on 1 of 2 things happen it either makes a whole bunch of fast paced beats that even turning the deck off doesnt affect or the amp just goes into protect.. this amp could be defective,but why would it work fine when the car is in acc?
AnswerHi Lucas,
It sounds like your amplifier is having trouble working with your alternator's output. When the engine is running, the alternator is the vehicle's primary power source; when the engine is off, the battery is the only source of power. The question is whether your problem is with the alternator or the amplifier.
Alternator voltage will always be higher than battery voltage. A typical automotive battery, fully charged, maintains about 12.6 volts; an alternator's output usually runs up to 14.5 volts. An amplifier should be able to work with a supply voltage between 11 volts and 15 volts. Sometimes a malfunctioning alternator will produce higher voltages. If this happens, it will often trigger the amplifier's "protect" mode.
Another type of alternator defect can result in excessive AC "ripple" on the power line.
If you have a digital multimeter handy, you can test your alternator's output. Set the meter for DC volts; if it's not an auto-ranging meter, select the "20v" setting. Put the black probe on the ground terminal at the amplifier, and the red probe on the amp's power terminal. Start the engine, and watch the display. You might want to have someone rev the engine for you, as this can change the voltage level. You should not see a voltage measurement higher than 15 volts.
Keep the probes in the same position, and switch to the "AC volts" setting. In this case, the reading should be very low; you should not see an AC voltage measurement above 0.3 volts.
If you see an unusually high measurement of DC volts or AC volts, you'll want to have the alternator checked. If not, then your amplifier probably has some internal defect.
There's a small possibility that the amp's problems are related to the vibration produced when the engine is running, rather than the voltage. Check the amp's ground wire connection, both at the amp terminal and at the chassis grounding point, and make sure it isn't loose. You might also try unplugging the RCA cables from the amp, and see if the problem continues; you might have a defective RCA cable that's creating an intermittent short when the engine is running.
Good luck!
Brian
