alternator check - The 1947 - Present Chevrolet & GMC Truck Message Board Network

marvxyz1 · 11-23-2007, 09:04 PM

I would normally check a altenator by disconnecting the hot bat. cable while the engine is running. Does anyone know if this action would cause damage to the alternator?? Thanks in advance for any input marvxyz1

shadetree · 11-24-2007, 12:59 AM

That "test" is not a valid one, IMO. Borrow or get a VOM & just read the output voltage. The gauge inside the truck should indicate weather or not the alternator is working, also.

piecesparts · 11-24-2007, 08:55 PM

We all have ways to do things. I usually just put a piece of metal against the back of the alternator (center shaft cover) and see if there is a magnetic field being generated. My pocket knife works well for this. That tells you if your alternator is making an electrical field. Second, use the VOM to check for voltage to the battery and see what you are getting. The voltage should be around 13.5 volts or more.

BLE 'BURBAN · 11-25-2007, 07:23 PM

Disconnecting the battery cable while the engine is running can,will & does cause a voltage spike for just a milisecond (18v - 36k volts) as witnessed by the tell-tale "spark". On older, precomputer controlled vehicles this isn't a real big problem. But on the newer vehicles it can fry out your PCM. I wouldn't recommend doing it on any vehicle regardless of age just for safe practice.

marvxyz1 · 11-25-2007, 08:14 PM

Turns out, that the vehicle in question problem was slightly untightened pos. cable clamp and the clamps were a little corroded. This was the no-start reason. I do thank you all for the onfo., which I wasn't sure of..
marvxyz1

Curly86 · 11-25-2007, 08:31 PM

I do it the lazy way I take mine to the local auto part store and have them put their meter on it to check it and the battery

Duro5341 · 11-27-2007, 11:57 AM

Quote:

Originally Posted by marvxyz1

I would normally check a altenator by disconnecting the hot bat. cable while the engine is running. Does anyone know if this action would cause damage to the alternator?? Thanks in advance for any input marvxyz1

My question to you is.................

Why are you checking the alternator?

Did you have a not start situation?
Is it not charging?
Is it cranking slowly?
Did you add anything aftermarket to it?

There are many different ways to check an alternator, some are more accurate than others.....

First I would check the output voltage, by checking the voltage across the battery terminals, this should be anywhere from 13.5v-14.5v for a normal alternator, with radio, headlights, turnsignal, and heater on high.

There are about 4-5 steps to accuratly check a charging system

Just my 2 cents
Duro

Duro5341 · 11-27-2007, 11:58 AM

Quote:

Originally Posted by marvxyz1

Turns out, that the vehicle in question problem was slightly untightened pos. cable clamp and the clamps were a little corroded. This was the no-start reason. I do thank you all for the onfo., which I wasn't sure of..
marvxyz1

Sorry I just read this after I posted............I was just skimming over the post

Duro

11-23-2007, 09:04 PM	#1
marvxyz1 Registered User Join Date: Oct 2005 Location: Pittsburgh, Pa Posts: 106	alternator check I would normally check a altenator by disconnecting the hot bat. cable while the engine is running. Does anyone know if this action would cause damage to the alternator?? Thanks in advance for any input marvxyz1

11-24-2007, 12:59 AM	#2
shadetree Senior Member Join Date: Dec 1999 Location: Knightstown, in, usa Posts: 2,525	Re: alternator check That "test" is not a valid one, IMO. Borrow or get a VOM & just read the output voltage. The gauge inside the truck should indicate weather or not the alternator is working, also. __________________ 1970 long fleet, 355 4 speed, primer, walnut goodies

11-24-2007, 08:55 PM	#3
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: alternator check We all have ways to do things. I usually just put a piece of metal against the back of the alternator (center shaft cover) and see if there is a magnetic field being generated. My pocket knife works well for this. That tells you if your alternator is making an electrical field. Second, use the VOM to check for voltage to the battery and see what you are getting. The voltage should be around 13.5 volts or more. Last edited by piecesparts; 11-24-2007 at 08:55 PM.

11-25-2007, 07:23 PM	#4
BLE 'BURBAN In the Forgotten far North. Join Date: Jul 2007 Location: Anchorage, Alaska Posts: 2,627	Re: alternator check Disconnecting the battery cable while the engine is running can,will & does cause a voltage spike for just a milisecond (18v - 36k volts) as witnessed by the tell-tale "spark". On older, precomputer controlled vehicles this isn't a real big problem. But on the newer vehicles it can fry out your PCM. I wouldn't recommend doing it on any vehicle regardless of age just for safe practice. __________________ 1987 R3500 CREW CAB DUALLY (BIG RED)Acquired 06/12/2015 1990 chevy suburban V2500 5.7L My cluster Mods-Nov 2007 overhead console Stereo install Round 2 Aug 2009 Heated/turn signal mirror upgrade Last edited by BLE 'BURBAN; 11-25-2007 at 07:24 PM.

11-25-2007, 08:14 PM	#5
marvxyz1 Registered User Join Date: Oct 2005 Location: Pittsburgh, Pa Posts: 106	Re: alternator check Turns out, that the vehicle in question problem was slightly untightened pos. cable clamp and the clamps were a little corroded. This was the no-start reason. I do thank you all for the onfo., which I wasn't sure of.. marvxyz1

11-25-2007, 08:31 PM	#6
Curly86 You want it there when??? Join Date: Oct 2006 Location: Lewisburg Ky Posts: 393	Re: alternator check I do it the lazy way I take mine to the local auto part store and have them put their meter on it to check it and the battery __________________ 1986 Silverado Flatbed 400 SB with 350 turbo 1997 Ford Explorer with 302 mydrive to work ride 1978 Gmc Midas RV 21ft with 46,000 actual miles 2003 Chevy Avalanche 5.3 327 and Tweety Bird Yellow Big Sandy Survivor 09 Trucks in the Blue Grass Survivor 09 TNCTC Streetcruzin Last edited by Curly86; 11-25-2007 at 08:31 PM.



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