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Volt gauge

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SteveT

Jedi Hopeful
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My volt gauge goes into the red for brief periods and then settles down to around 13. I imagine the system is being over charged, but I really have no clue what to do. Is there a way to easily test electrical components or is a particular item?

Also, went to two LBC shows this weekend, Webster St. Market in Dayton, OH (Saturday) and then the Brits at Metro, Columbus, OH (Sunday). Anyone from the forum attend any? Great times!!

Thanks - Steve
 
You could first check whether the volt gauge is reading correctly by connecting a voltmeter to the battery. If the voltmeter reading is the same as the gauge, then the gauge is reading accurately, and you can trust it.

As to why the volt gauge is reading high, it would not be unusual for the alternator to be charging the battery at 14-14.5 volts for a period of time if the battery has lost some power. Maybe you have a battery drain somewhere. Check the battery voltage for a couple of days before starting up and after shutdown - see how close to 12V it is and if you possibly have something draining the battery when the car is shut off, or whether the battery is charging fully to 12 volts when it is running.

If you suspect the battery is just not charging fully, you should take it to a garage for a simple discharge load test to see what kind of condition its in.

If the higher voltage is correct (i.e. 13V+), and the battery is good and you have no leakage, then you would want to get the alternator checked out.
 
guzzul said:
it would not be unusual for the alternator to be charging the battery at 14-14.5 volts for a period of time if the battery has lost some power.
Click to expand...

The regulated voltage depends on the temperature of the alternator, not how discharged the battery is (unless the battery will take more charge current than the alternator can supply). 14.4 is about right for a cold alternator (ie 50F), then it drops as the alternator warms up.

I would check the voltmeter at two different voltages, as there are two different adjustments on the back and either one might be wrong. One of the adjustments on my Stag was so loose it would move when I laid the gauge down on the bench.

Also, having the voltmeter read somewhat below what you measure at the battery may not indicate a bad voltmeter ... might be voltage drop in the wiring or ignition switch instead. Better to check right on the back of the voltmeter.
 
I bought an e-bay volt meter for the 71 . What is the easiest way to test it before I put it in the dash. What should I use as asupply?
 
The lucas voltage regulator could be causing the problem. Ive seen them act erratically before.
 
TR3Driver,

TR3driver said:
I would check the voltmeter at two different voltages, as there are two different adjustments on the back and either one might be wrong. One of the adjustments on my Stag was so loose it would move when I laid the gauge down on the bench.
guzzul said:
Thanks for the info. The voltmeter you refer to is the dash gauge? And if so, what are the two different adjustments you are talking about? And how would they be adjusted?

Steve
Click to expand...
Click to expand...
 
TR3driver said:
guzzul said:
it would not be unusual for the alternator to be charging the battery at 14-14.5 volts for a period of time if the battery has lost some power.
Click to expand...

The regulated voltage depends on the temperature of the alternator, not how discharged the battery is (unless the battery will take more charge current than the alternator can supply). 14.4 is about right for a cold alternator (ie 50F), then it drops as the alternator warms up.
Click to expand...
The nominal output control voltage spec on my Lucas alternator is 14-14.4V, hot, generating 34 amps. The control voltage can read a little higher when cold.

My point was that a reading of 14V may be within the range of normal operation for a short period of time. If Steven's gauge is reading in excess of 13V, it would indicate to me that the alternator is trying to charge the battery, again not unusual unless it happens all the time which would suggest the battery is not fully charging, or that there may be a significant load somewhere in the system.

All this is premised on his volt gauge being accurate, which Steven might want to check. Measuring at the voltage gauge is a good idea, because there may indeed be a voltage drop within the circuit the gauge is hooked up to. However, if that is true, then the alternator voltage at the battery is even higher than the 13V Steven is recording on the gauge, which would still indicate the alternator is trying to charge the battery. Wouldn't this still suggest the battery is not charging fully (or if it is charged fully, that the alternator is not working right)?
 
DNK said:
I bought an e-bay volt meter for the 71 . What is the easiest way to test it before I put it in the dash. What should I use as asupply?
Click to expand...
Are you getting an amp gauge or a voltage gauge? If voltage, a simple function test may be just to hook it up between your battery + terminal and a good engine ground (-). Should indicate whether the gauge is working or not. You could take a comparison measurement with a volt-ohm meter to see how accurate the reading is.

Also, you could try switching the headlights on and see if there's a deflection in the gauge.

Did the '71 TR come with a standard ammeter?
 
As I said VOLT meter. And I should have thought to test it against my digital multi meter DUH!!!
The car is not running yet so will have to test later.
The 71 does come with an amp gauge but I am changing to a volt meter.
 
guzzul said:
My point was that a reading of 14V may be within the range of normal operation for a short period of time. If Steven's gauge is reading in excess of 13V, it would indicate to me that the alternator is trying to charge the battery, again not unusual unless it happens all the time which would suggest the battery is not fully charging,
Click to expand...
And my point is that the alternator does not "know" how much current the battery is, or is not, taking. It only regulates voltage.

guzzul said:
Wouldn't this still suggest the battery is not charging fully (or if it is charged fully, that the alternator is not working right)?
Click to expand...

Nope. 13.0 volts is too low at any temperature; the regulator should take the voltage up to between 13.6 and 14.4 (Lucas specification for the 15-20 ACR); then hold it there. (Assuming the alternator can meet the demand at that voltage & engine rpm.)

The setpoint for the regulator depends only on the regulator's temperature ... any drop you see is because the regulator is heated by the engine and alternator.

This is why voltmeters tell you virtually nothing about your battery's condition (which is why I prefer ammeters).
 
Anyone know how to wire an amp meter
into Dan Master's Power Block wire harness
with a GM alternator conversion?
I could never figure it out.

Thanks,

d
 
Tinster said:
Anyone know how to wire an amp meter
into Dan Master's Power Block wire harness
with a GM alternator conversion?
Click to expand...
Not sure if the TR6 kit is the same; but on the TR2-4 kit there are two heavy yellow wires that attach to the starter solenoid (as shown in Dan's schematic). To use an ammeter, join those two yellow wires together with one wire to the ammeter, and wire the other ammeter lead to the starter solenoid.

The TR2-4 instructions actually show how to do this, but they have you run the alternator wire to the "power terminal" on Dan's power block; leaving only one wire to the ammeter. Either way will work fine.

If you want to keep the stock TR2-6 ammeter, you'll need to add a shunt across it to handle part of the increased current. I made mine by experiment, using the headlights as a load and adjusting the shunt until the ammeter read 1/2 of what it read without the shunt; effectively making a 60-0-60 ammeter out of a 30-0-30. My original shunt was several strands of steel "baling" wire (are my Missouri roots showing ?) but I later remade it using insulated 16 AWG copper.

Based on measurements I later took of some TR3A ammeters, a 50% shunt for the ammeter should have been about 3.5 inches of 16 AWG; but mine wound up more like 5" long. A similar calculation based on measurements made by a friend on his TR6 called for 8" of 16 AWG. YMMV

One last comment : IMO "best practice" is to connect a separate "sense" wire from the alternator to the starter solenoid. That way, the regulator can compensate for any voltage drop through the charge circuit (including the ammeter). Dan's method of connecting the sense line to the alternator output at the alternator will work; but won't recharge the battery as quickly, or possibly not at all if the electrical load is high.

Since my alternator conversion was originally so I wouldn't have a dead battery after driving my TR3A back and forth to work in the snow (meaning short trips, cold weather, and lots of electrical load); fast charge was important to me. If you only go to parades and car shows, it's probably a lot less important to you /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
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