dbcjmc

Alternator and Voltmeter question

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Hi Folks, 

My alternator failed and left me stranded yesterday.  Oddly, the voltmeter in the dash was reading 16V and the red light didn't come on to warn me of any impending failure.

I have a 77 280Z.  The alternator currently in there includes the voltage regulator from a previous replacement / swap  - this one is about 5 years old.  

Then red light in the voltmeter is good - it lights up on start and goes out after starting.  

So I'm wondering - when I replaced the alternator the first time (and bypassed the original regulator), did I render the voltmeter useless?

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The light tells you when it's not charging, too little.  The needle tells you when it's too much.  It's kind of primitive compared to today's electronic monitoring systems.  Are you sure that it failed?  Could be that the voltage sensing circuit lost contact.

It's not clear what you mean about the VR.  You said the old one is there, then said it's bypassed.  Not sure what you mean.  Did you convert to an internally regulated system?

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10 hours ago, dbcjmc said:

Hi Folks, 

My alternator failed and left me stranded yesterday.  Oddly, the voltmeter in the dash was reading 16V and the red light didn't come on to warn me of any impending failure.

I have a 77 280Z.  The alternator currently in there includes the voltage regulator from a previous replacement / swap  - this one is about 5 years old.  

Then red light in the voltmeter is good - it lights up on start and goes out after starting.  

So I'm wondering - when I replaced the alternator the first time (and bypassed the original regulator), did I render the voltmeter useless?

a way to see if the voltmeter in the car is working is to check the gauge reading and then with a multimeter check the battery at the terminals then compare the two voltages to see if the gauge in the car is accurate.

When you say the alternator failed and left you stranded, do you mean the battery was dead? did you check the battery to confirm its status? did you check the alternator to confirm its failure? Maybe some thing as simple as corroded battery terminals.

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I'm not really sure how that voltmeter light works either. For me, it seems to come on and honk at you once voltage goes really high?

Here is a video of my '78 280z with L28ET swap after the internal regulator on my alternator blew out and the ground coming off the alternator was fried into pieces:

 

 

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15 hours ago, dbcjmc said:

Hi Folks, 

My alternator failed and left me stranded yesterday.  Oddly, the voltmeter in the dash was reading 16V and the red light didn't come on to warn me of any impending failure.

I have a 77 280Z.  The alternator currently in there includes the voltage regulator from a previous replacement / swap  - this one is about 5 years old.  

Then red light in the voltmeter is good - it lights up on start and goes out after starting.  

So I'm wondering - when I replaced the alternator the first time (and bypassed the original regulator), did I render the voltmeter useless?

To answer the wondering question, I did my internal regulated swap and the volt meter works fine. Did you double and triple check the connections?

Just to be clear, the voltage regulator in your car should not be connected once the conversion is complete. You are losing around 0.23 horsepower carting around useless weight... I'm sure that number is low, I didn't actually do the math 😛

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I had an internally regulated alternator/regulator fail once and the dash light came on dimly and got brighter with RPM.  But the voltage looked correct on the meter.  The internally regulated alternators use solid state regulators though and they can fail indifferent ways.

Here's the FSM description for the external, mechanical, regulator.  There are test procedures in the FSM.  There's even an adjustment procedure.  Kind of a shame that we all swap to the later models when it's all there in the FSM's.

image.png

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Hi Folks!

Many thanks for the replies.  

Yes, the battery lost juice and I wasn't able to start.  Yes, the battery voltage dropped to 11 and the volt meter was reading 16.  What I mean about bypassing the VR is that I upgraded the last alternator that has the regulator inside.  I ditched the original external one.  I may have been too hasty to buy a replacement - haven't checked all connections as of yet.  Perhaps that's my issue.  Will check it this weekend.  

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odd how a voltmeter can read 16v with only 11v at the battery (which is now dead and should be replaced, I would not trust one that got that low to be able to recover). Only thing can be is a defective voltmeter, unless you can take it out of the circuit and directly connect it to a known voltage source. Or is the alternator really putting out 16v  (internal VR fail) and that is what the meter is reading AND for some reason the B lead from the alternator is somehow not getting back to the battery terminal. I would start by getting a good fresh battery, hooking everything up, get a meter on the battery terminal check voltage there with the car off and the car running. Next with the car running check the voltage at the alternator B lead, compare. Not sure how its wired up but the sense lead would need to be getting the battery voltage on an internal VR so you should confirm what it sees as well.

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13 hours ago, dbcjmc said:

Hi Folks!

Many thanks for the replies.  

Yes, the battery lost juice and I wasn't able to start.  Yes, the battery voltage dropped to 11 and the volt meter was reading 16.  What I mean about bypassing the VR is that I upgraded the last alternator that has the regulator inside.  I ditched the original external one.  I may have been too hasty to buy a replacement - haven't checked all connections as of yet.  Perhaps that's my issue.  Will check it this weekend.  

The answer to the problem is probably here - http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html

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