zuke6562

HI All......

I am trying to isolate the problem with my charging system. I did the test recommended in my shop manual. Run engine at about 1500 rpm and than remove the neg cable. The engine died immediately. The manual says its probablly tha Alternator. Took alternator had it checked and they said it was ok. So bought a regulator. Replaced both. Still no charge. During my research found a doc written by Mr Joe Fisher. Following his giude...... i found that a diode was bad. Therefore, I had the alternator rechecked at a different shop. They said it was ok also .

So my question is ..... 1. how can a diode be bad and still check out ok at two different places ?? 2. Could a bad diode be the cause of my problem ???

I would appreciate any advice..... Tx confused............

mechron

Are you confusing a generator test for an alternator test? (gen and alt will be used for brevity) An alt charged car needs bat voltage to evergize the alt. It is normal for an alt charged car to die when the battery is disconnected even with a good alt. Alts work by sending the -current to ground and + current back to the +side of the battery. the diodes control that, they are like one way valves for electricity. alts have 6 diodes, three send -current to ground and three send + current back to the +side of the battery. Listen to the guys checking out your alt/diodes. Diodes are easy to check. If one is bad five are still doing their job so the alt will still charge.

The difinative test is outlined in all the old chiltons and motors manuals and the one I have used since the 60s. Disconnect the plug on the alt, put a volt meter on the alt or bat. Use a jumper wire from the the big B+ terminal on the back of the alt, it is always hot, to the F terminal spade. Battery to field = full output. 17 to 18 volts= a good alt. 12 to 14.5 volts= a bad alt. Replace it. Anything around 17 volts or above replace the reg.

just reread your post again, does a test light come on between the B+ terminal and ground, if not it could be a broken wire.

Frankie the Fink

I do believe the car should stay running if the alternator is good with the battery disconnected but that is a bad practice to get into for checking the part. It works on our old cars but the battery acts as charging circuit 'ballast' when the motor is running and, if disconnected, this test can be very bad on solid state regulators and other fragile components in later model cars.

If it came between Joe Fisher's (plaidside on here) test for a bad alternator and some FLAPS part jockey at Autozone guess who gets my vote ??

plaidside

Please describe the test you used to determine that you have a bad diode. Did you check all your terminals at the regulator? Did you full field the alternator to see if it is working?
Joe

Ironcross

A simple test without removing the alternator is to purchase the identical plug that plugs into the back of the alternator.......it will have two wires as its a repair plug .......twist the wires together and insert into the alt and full field the alt by touching the red 12 volt hot wire....the alt should start singing and jump up to the 18 volt range if its properly working..........if it does that, its a good alt....

see plaidsides reply, its almost the same

zuke6562

HI Joe............. thank you for responding. I got your writeup at "http://temp.corvetteforum.net/classic/plaidside/Alternator.shtml" and followed it to the second page.......... where it says "Connect a voltmeter to the number 2 terminal (white wire) of the regulator connector and again jump from F to 3. You should see 8-10 volts. If not u have a bad diode." Had no voltage here. All test u mentioned above this (on your writeup) was ok. Thanks Walt

plaidside

Walt,
Have you preformed this test?
"With a voltmeter connected to the battery and the RPM at approximately 1000-1200, jump from the F terminal of the regulator plug to the 3 (orange or red wire) terminal."
If you do not get a voltage reading at lest 15v then the test you described is invalid.
Joe

zuke6562

Hi Joe............ yes I did this test and I did get 15v plus volts. After this test................... i did the test to determine the status of the diode.

Tx walt

zuke6562

HI Ironcross ... because I am grasping at straws..... i did this test also. I did get 15v plus but not 18v plus. Tx walt

zuke6562

HI Mercon....... i was following my 63 corvette shop manual and it described the test of running the motor (1200-1500) and removing the neg cable to determine if the alt is good. Did the test u described of jumping the Bat terminal to the F spade. I did not get 18v plus but did get 15v plus. BTW..... I did get my test light to work when I went from the Bat to ground on the Alt. Tx walt

Sky65

How do you know there is a charging system problem? Dead battery or no start or ? What are your symptoms?

Tom

zuke6562

HI Tom............ symptoms........... ammeter does not move off of center or register that the system is charging. Car starts fine until the battery goes out. I had the alternator checked at two different parts houses. Both said the Alt was good. Bought and installed a regulator. no change.

Testing....... Took the regulator out of the system and the alternator produces about 15+ volts. Checked at Battery and Alternator. Did a continuity test from the horn realy to the ammeter (red wire). tested ok. Did a continuity test on the black wire from the bat terminal on the starter to the ammeter. Checked out ok. Also did a continuity test from the horn relay to the alternator (red #12 wire). tested ok. Did a bunch more continuity testing to check out the wiring and so far it has all been ok. In addition..... removed the wiring block at the firewall (left side) cleaned contacts (greased lightly) on both sides. No change. Am confused............ Thanks for your interest.. walt

Sky65

Hey Walt. Sounds like you charge the battery, then the car starts and runs. At some point later it won't crank or start. When it does not crank is that after sitting or driving?

mechron

Hi, all the guys above seem to be on the same page, Ironcross says 18 volts also. plaidside in post 7 is describing the same test (bat to 3 at the reg plug = bat to field at the alt) just a different way to do the same test at the reg plug. I have also tested by that method many times with a cotter key jumped between the B+ and the 3 terminal on the reg plug. It is just faster to test at the alt, it being on top of the engine as opposed to the reg being lower down on the rad support.

"15v plus" is not enough. the charging systems on these cars are speced to produce 13.8 to 14.2 volts at the bat when runnung with all accesories on. The reg takes care of that. 15 plus volts at full field is not enough to cover that load. AMPs also have to be factored in for the draw. 55 and 62 AMP alts were normal on our cars back in the day. Now 100 AMP alts are the norm, all still producing 13.8 to 14.2 volts.

Alts and regs are cheap enough, replace both and be done with it. I run a 100 Amp alt on my 64 with no accories.It is one wire, self energises at 1500 rpm after start up.

zuke6562

HI Mechron......... Thanks for your response........ after fooling with this for a couple of days...... I am thinking about doing what u did and install a one wire Alt. I have a polished aluminum one I was saving for my 32 ford.
I did a host of continuity test and so far all wiring seem to check out ok...... Anyway thanks for your assistance. Walt

zuke6562

I have finally got 14 plus volts at the battery. Seems the problem was poor grounding on the regulator. I wired it directly to the neg post of the battery and walla..... the system started charging. However, the guage still does not work. Have to see what its problem is......

Thanks guys for all the help. In the process of tracking this down i learned a lot about the charging system.