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Hello. I have a 1990 Chevrolet 1/2 ton 5.7 EFI. Can I test my alternator by unhooking the negative terminal on my battery to check if the truck keeps running? Or will this hurt any of my electronics. Thanks...
it can.... it will also damage the alternator diodes...welcome to 2011...proper testing of charging systems involve a digital volt meter..they start at 8 bucks.. you generally don't need to spend more than 20 to 25 bucks for a decent version..set digital volt meter to 20 volt DC scale...engine off.. turn on headlights for one minute.. turn off headlights...measure battery voltage..12.65 is a full charge..12.45 is a half charge..12.25 is a quarter charge...you need to have close to a full charge to properly test the charging system with a digital volt meter...start the engine.. with the battery close to fully charged... you should get over 14.1... and on a GM .. up to 15.3... usually 14.6 to 15.2... on your year and model... but anything over 14.1 shows its working...the reason to NEVER pull the battery cables to see if the alternator is working.. it ruins the alternators diodes.....how it all works... the voltage regulator looks at the charging system voltage... to make the alternator charge.. the voltage regulator pulses the circuit through the brushes to the rotor thats spinning.. the longer the pulse is on.. the bigger the magnetic field it creates... the spinning magnetic field passes through the stator windings... the outside loops of windings... there are 3 sets of windings on your alternator.. one end of the loops connected...the other ends are each connected to 2 diodes.. one positive diode and one negative diode... as the rotor spins its variable magnetic field the stator windings create electrons in an AC seine wave... all the electrons above 0 flow through the positive diode to the output terminal.. all the electrons below 0 volts goes to the alternator case and to the ground side of the battery...when you take the cable off... since the alternator on most cars is generating power.. the instant you remove the battery cable.. the output current has no place to go.. so it builds up... this is voltage... the voltage for that instant can top 120 volts... this is more than most diodes can handle... so they are weakened..as for the other systems... most can be damaged with voltages over about 16 to 18 volts.. the distance between the circuits is not great enough for that kind of voltage so the power arcs across and burns out the circuit... these are LOGIC level circuits.. not designed to handle more than a few volts.. most burn out at 14 volts.. but normally have 5 volts on them inside the computer.. these are reasons to NOT pull a battery cable...if you have ever broken an alternator output wire.. you will note that your alternator.. was good before.. is now toast... without the load.. the voltage goes so high so fast it just cooks the diodes and electronics... invest in a digital volt meter.. learn to use it.. its not hard to *** your chevy truck should also have a volt meter on the dash board.. look at it with the engine running.. should be over 14 volts..
Thanks for the info...