Wedge TR8 Charging Voltage at 15.9

[GBRandy]

I am doing an interior refresh on my 1980 FI TR8. I replaced the radio, speakers, heater valve & carpets. I also removed an alarm system some 26 year old kid installed 20 years ago (me).

Prior to my interior work, the voltage meter in the car was fluctuating from normal to "in the red" for the past 6 months or so. Everything ran fine so no harm no foul and I left it alone.

I fired the car up to make sure everything worked and it runs just fine. The radio had a hick-up and shut down after a minute or so. The radio runs fine for 1/2 hour or more pulling from the battery and the car not running. I checked for voltage and the voltage at the battery terminals was 15.9 volts when the car is running. It should be 14 correct?

Is this a normal symptom of a failing voltage regulator or alternator? Or do I have a deeper issue created with the electrical work I just completed? (BTW I am pretty darn sure my wiring & un-wriring were accurate and correct...but you never know).

Comments?

 

[tomgt6]

I would check the meter you used first. You shouldn't see no more then 12.5 volts or so off the meter on a battery not getting charged.

If that meter is correct then something is going. Good luck

 

[GBRandy]

Thanks....

Meter is good. Thinking the voltage regulator isn't.

 

[martx-5]

I'm not here at work right now to look up to see if this unit has a regulator with a sense wire. If it does, and the sense wire is somehow disconnected, the voltage regulator will respond by increasing the charging voltage...15.9 volts would be about what it would charge under those circumstances...or, the regulator is bad.

Do you have a wiring diagram of the car to see if it has a sense circuit?? It would be one of the smaller gauge wires (maybe 14) going back toward the Battery positive. They usually hook it into a major junction point.

 

[WedgeWorks]

The maximum operating charge in the system is 13.8 volts. Anything more means the alternator is over charging. You need to get it rebuilt or replaced before you fry things. I had it happen once years ago and was a nightmare!

 

[DNK]

 

[GBRandy]

So Don.... Is that first wire on the left a sense wire then?

 

[DNK]

The one on the left I don't thin is a sense wire ,but I am far from a person in the know.
I'm the guy that's sits in the back of the class and throws out insults to the teacher.

The one on the right goes to the ignition

 

[TR3driver]

NY would normally be the wire to the warning lamp on the dash.

 

[DNK]

As usual, I put my foot in it. It's the ign. light.
Good find R.

 

[TR3driver]

Sorry, Don, I misread the question. I believe Randy has it right, the leftmost connection to the alternator in the diagram above IS a sense wire. It's brown (N) because electrically, it is part of the same circuit, but it's function is to let the regulator 'see' closer to true battery voltage without being fooled by the voltage drop in the output wire.

And if that junction between the heavy battery cable and the smaller brown wires is anything like the one found on later TR6, then it's a common trouble spot.

Take it apart and clean things up (I've been experimenting with using Tarn-X to clean copper connections, so far it seems to work well), and make sure the quick connects fit snugly. Then if the problem persists, I'd try at least cleaning the alternator. I once had a similar problem that was caused by conductive dirt that had gotten inside the alternator housing and was upsetting the regulator.

After that, I'd say it's time for a new alternator.

 

[DNK]

Which one are you talking about Randall?

 

[TR3driver]

Maybe this will help.

 

[DNK]

So the output wire is the sense wire?

 

[Mickey Richaud]

So the output wire is the sense wire?

I believe he labeled it "Sense line".

 

[DNK]

AHA,Duh

Randy, Follow a nearly identical thread on the TR7 .com site under headers

A quote from Clay.
"The exciter wire tells the alternator the state of charge of the battery. On the TR8, it connects to the connector in the middle of the main battery run, which is located under the carpet in the passenger foot well. It has a tendency to corrode and make a bad connection. When this happens, the alternator goes to high charge as it thinks that the battery is low.

This is the main reason for alternator failure in TR8s. There was a Service Bulletin instruction that the exciter wire should be connected to the main power lug on the starter."

 

[TR3driver]

Well, technically the "exciter wire" is the one that goes to the warning lamp on the dash. It's function is to supply current to the rotor before the alternator starts to generate power at startup. No doubt he meant "sense wire" instead of "exciter".

And Mickey is quite right, I called it a sense line instead of a sense wire. My bad, but don't have the tools handy to fix it just now. Maybe tonight when I get home.

 

[GBRandy]

A quote from Clay.
"The exciter wire tells the alternator the state of charge of the battery. On the TR8, it connects to the connector in the middle of the main battery run, which is located under the carpet in the passenger foot well. It has a tendency to corrode and make a bad connection. When this happens, the alternator goes to high charge as it thinks that the battery is low.

This is the main reason for alternator failure in TR8s. There was a Service Bulletin instruction that the exciter wire should be connected to the main power lug on the starter."

Interesting in that I was tugging and pulling under there when I pulled the carpet & speaker wires out and replaced them. I know exactly where that junction block is and maybe I finished off a loose connection in the process.

I'll pull it apart and clean it first and see what I get.

I read somewhere, many moons ago, that that primary cable from the battery to the alternator would corrode and go bad and cause a similar issue. The cable looks fine....but perhaps they meant the connection from the battery to the alternator goes bad.

For the sake of experiment, and becuase it is supposed to rain most of the weekend, I'll clean the connection and try it and report back.

Love this forum.....thanks to all of you.

 

[DNK]

You got a picture of that junction block?

 

[GBRandy]

Sorry for the delay...but busy all day with car stuff & grad parties.

Well, that certainly wasn't it. I have been blessed with a very dry southern CA car that I rarely drive in the rain. The connections, wires and general condition appeared to be in working order.

I cleaned things up. Applied some Di-electric grease and closed it up and test fired...15.9 again on two different meters.

As promised pictures:

The block:

The block open - the sense wire is the one on the bottom left

Looks like I need to pull that alternator tomorrow.....