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Automotive Electrical from Ewing AutomotiveEwing Automotive has the proper equipment and knowledge to check and repair your cars electrical system. We do starters, alternators and batteries as well as other automotive electrical repairs. Why you shouldn’t disconnect your cars battery while it’s running: The man from the road service thinks he’s being helpful. After he can’t jump start your car, he puts in his own known good battery and starts your car. So far so good — your battery was definitely either run down or bad, and he’s proven it. Now he decides to “test” your alternator by disconnecting the battery. After all, the car’s ignition should be able to run on just the alternator’s power alone. Wrong! The moment he disconnects either lead from your battery, it’s entirely possible he caused thousands of dollars in damage. Here’s why… Your battery does more than just provide electricity. It also shorts AC, spikes and transients to ground. Removing the battery from the circuit allows those spikes and transients to travel around, endangering every semiconductor circuit in your car. The ECU, the speed sensitive steering, the memory seat adjustments, the cruise control, and even the car’s stereo. Even if your computers and stereo remain intact, in a great many cases removing the battery burns out the diodes in the alternator, necessitating a new alternator. If disconnecting the battery interferes with the voltage regulator’s control voltage input, it’s possible for the alternator voltage to go way over the top (I’ve heard some say hundreds of volts), frying everything. Even the initial premise was wrong. If you disconnect the battery and the car conks out, you don’t know if it conked out due to insufficient alternator current, or whether the resulting transients caused your ECU (the car’s computer, which controls fuel mixture, timing, and much more) to spit out bad data, shutting down the car. No one should EVER run your engine without a battery.