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voltage and charging

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okay new to posting here, but recently i got a 1970 521 got it all together and running, its runs great! but problem with the charging system...

 

First off it has a brand new battery, battery cables and bosch 50amp alternator, and it was working! Drove it back and fourth to work for a week no problems always held 14.1 volts no matter the load, then drove it to the beach and on the way down there the voltage jumped up to almsot 17volts! :o (i have a sunpro guage mounted in vehicle) and after 5mins it shot down to 12 and stopped charging ever since, so i came to the fourms read up on it and came to the conclusion it was the voltage regulator! nope that wasnt it still not charging, took out the battery took it to the autoparts store and they tested it to have a cell that went out, so im assuming i burnt out the battery by overcharging, is it possibe i aslo burnt out my new alternator?? and ive looked at the wiring diagahm followd all wires, cleaned all contacted and replace all the grounds fuses everything, still nothing

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and also i stopped at orielys on the way to the beach and they siad alternator was charging... but my guage mounted in the car said diffrently.. any ideas or any possible items to check would be Greatly appreciated!

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ill get the rest of my pictures uploaded a little bit later! :D

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This is a stock system with externally mounted voltage regulator?

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Good job, a picture.

There is a simplified charge start wiring diagram for a Datsun 510.  A 521 is basically the same.  Here is the link.

https://docs.google.com/folder/d/0ByCvxnHNk90SejRibXNScEt0M28/edit?pli=1&docId=0ByCvxnHNk90SSTN4a28yQThqN1U

 

Originally, a 521 had two dedicated ground wires on the alternator.  One went from the negative battery cable, at the lifting lug behind the fuel pump down to the alternator frame.  The second dedicates ground went from the alternator frame to one of the bolts that hold the voltage regulator to the fender.  These wires must be there.  It is important that the voltage regulator has good connections to the alternator, so the voltage regulator knows what the alternator voltage is, but the regulator also has to know the electrical system voltage.

 

The positive output of the alternator goes directly to the positive battery cable on the starter.

 

 

You have a 40 year old truck.  There is a good possibility some electrical connections have some corrosion in them.  More so, if it got wet, or if in a high humidity location.

 

The battery needs to be good.   It is possible a cell on the battery went bad and the regulator is good. 

 

This is a page about checking voltage drops in electrical circuits.

http://www.vernco.com/Sparks/id606.htm

 

Check the voltage drop from the alternator frame to the negative battery terminal, and from the positive alternator terminal to the positive battery terminal.  When doing these tests, it is important to measure the voltage at the actual battery terminal, not the clamp that is on the battery terminal, because if you have a bad connection at the cable to battery terminal connection, measuring voltages at the terminal will not find it.

 

Voltage at the battery terminals should be 13.5 to 14.5.   You may want to upgrade the wires connecting the alternator to the system, because they were adequate for a stock 35 amp alternator, and a 50 amp alternator is pushing their capacity.

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Yes its the stock wiring setup nothing changed besides the componets, and mine only has 1ground wire off the alternator.. 1ground wire, 1white wire jumped to the starter and two yellow wires from a t-connector that go to the regulator

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and thanks! this diagram really helps alot, just wondering what would cuase overcharging, and then it just dying out?

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sounds like voltage regulator. If your alternator checks out...battery can be checked too..take that to Autozone.  Good luck and let us know what was the culprit.

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I thought it was the regulator racerx so I replaced it still nothing, replaced battery again still nothing, time to double check wires when I get off work this evening

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Turn the ignition key to ON.... does the red charge light light up?

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Well found the culprit, alternator went bad due to a leaking water pump pouring coolant on my alternator! xD new water pump put on and a new alternator ordered

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I found this in the Factory service manual, that you can down load from this page.

http://www.davidcmurphy.com/olddat/620tech.htm

Go down the page, and look for "Nissan L-16 L-18 series engines"

 

AltTest_zps4971a102.png

 

Lets summarize this test.   With the engine warmed up, so it does not go to a fast idle, unplug the small "T" connector from the alternator.  Connect a jumper wire from the Bat terminal on the alternator to the "F" connection on the "T".  It should be the leg of the "T" not the top.   This takes the voltage regulator out of the circuit, and forces the alternator to unregulated full output.  The voltage of the alternator is not being controlled except by the engine RPM.   DO NOT REV THE ENGINE!

With the headlights on high beam to load the alternator, and a voltmeter checking the voltage of the alternator, slowly increase the engine RPM off idle.  At around 1,100 RPM, the voltage should go above 12.5 volts.   Do not increase the RPM more to see how high the voltage will go.  You could easily burn out the headlights because the voltage of the alternator is not being regulated.  Once one headlight blows out, the voltage will spike even higher, and rapidly take out the other headlights, and any other electrical things that are on.

 

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Do the 521's require a voltage regulator or can you swap in a regular alternator from another brand of car?

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They require an external voltage regulator probably mounted on the fender near the battery.

 

You can run a later internally regulated alternator from a '78 or '79 620 that should fit. Others from cars are larger and will hit the idler arm just below it. In addition you will have to jumper two pair or wires together and disconnect the external one. If your 521 has an electric choke relay, you may need to find a new power source for it.

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