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[boxbiker]

I have been driving the tr since the weather cooled down and I have noticed the battery needs charging from time to time. The battery was 6 years old so I replaced it and then checked the voltage at the battery with a volt meter. Also, when I am driving it looks like the amp meter barely moves.The volt meter shows 12.4 even when I rev the motor up. I am thinking that either the generator or voltage regulator are bad.

Is there a quick and easy way to check them?

[TR3driver]

Easiest way to check, IMO, is to drive it to the nearest O'Reillys or Autozone.  They will check out both the battery and the charging system, for free.  Sears used to do it too, but last time I went there, they charged a minimal amount (like $10) which could be used as credit towards the price of a new battery.

But if you would rather do it yourself, there are some step-by-step instructions at
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B2H2NJt34OffNTc3ODkwYzAtYjRlYS00NDNmLWI0YTYtNjY5ZjQxZTA2NGFm&hl=en_US

Oh, and only 12.4 when you rev it up means that either the battery is pretty badly run down (and the ammeter should be showing roughly 20 amps charge), or the generator/control box is not working properly.  You should also be able to see 20 amps or more every time you start the engine.

OTOH, cleaning and adjusting the VR contacts may be all that is required to fix it.

[boxbiker]

I looked at the vr and it looks like it could be original to the car so I'm going to replace it and recheck.Even if it is not bad now it looks like it could go soon.

[herald948]

I wouldn't be too quick to toss the original voltage regulator. There are folks who can repair, adjust or even 'rebuild' these IF necessary...and the originals are (arguably) of better quality than the new ones. There are also folks who convert originals to a "solid-state" voltage regulator.

Just some thoughts....

[TR3driver]

I agree entirely with Andy.  The originals do require some periodic maintenance in the form of cleaning and adjusting the contacts; but they otherwise last nearly forever.  I still have what I believe is the original box and generator on my 56 TR3.

And I've heard many, many stories of new units requiring adjustment (or being flat-out defective) right out of the box.  You can't just slap it on and assume it's good.

Obvious perhaps, but worth repeating : A defective or misadjusted control box can quickly ruin a good generator.  If you install a new box, you should immediately check its no-load voltage adjustment.  Because of the 2 bobbin design, that also sets the current limit.

[bobhustead]

On a properly functioning system, the voltage when running should be 12.7 to 14.2. To check the generator, you disconnect both the battery and field wires at the gen erator and put a jumper wire across these two poles. Then connnect the negative lead of a multimeter to this jumper and the positive lead to ground. Set the meter to a high DC scale and crank the engine. The reading at 2500 RPM or so should be very high. The haynes manual says to look for 15 volts at 750 RPM, but I always check them higher. The procedure is called a runaway generator.
Bob Hustead 

[bobhustead]

PS to my last. If the voltage does spike, you problem is almost surely the regulator. If not, the generator is at fault.
Bob

[TR3driver]

The reading at 2500 RPM or so should be very high.

FWIW, Lucas warned against going higher than 20 volts.  The insulation between the wires on the armature is very thin, and letting the output go too high may cause flashover and damage an otherwise functional generator.

Besides, running it higher than 20 volts really proves nothing as far as whether it is working or not and can overheat the field windings.

I'm sure Bob will say he's always done this and never had a problem; but why take the risk?

[bobhustead]

Overheating will surely cause damage, but at any rpm the test condition is applied only long enough to read the meter. Overheating will not then be a problem.
Bob 

[TR3driver]

Not a question of overheating; but rather the voltage punching through the old enamel insulation between the wires.

Probably not very likely, but why take the chance?  Especially since if it does damage the insulation, you likely won't know it did.  The generator will just fail sometime later, rather sooner than it might have without having been run up beyond its design voltage.

[boxbiker]

What should the voltage reading be at the battery with the engine revving to 3,000 +?

I used a digital voltemeter and I get bearly 12 volts.

[TR3driver]

The correct answer is "it depends".  But unless your battery is very deeply discharged (beyond where it won't start the car), that isn't enough.

If the ammeter is showing heavy charge (like 20+ amps), then the problem is likely the battery (deeply discharged, shorted cell, etc).  Otherwise, it's the generator or control box (or wiring).

[boxbiker]

I have a new battery..never can get more than 12 volts at battery. The ampmeter looks like it bearly moves..put on brakes or headlight and the ampmeter spikes up.

[TR3driver]

Well, it seems pretty clear you've got a charging problem.  I take it the red light comes on with the key, and then goes out when the engine starts?

One quick test is to measure the voltage between the F and D terminals on the control box with the engine running at fast idle.  If you find more than 0.2 volts (with the battery voltage that low), then the voltage regulator contacts aren't making good contact.  A good cleaning and adjustment may be all that is needed.

Beyond that, either take it somewhere to be tested, or download the manual I linked to above and follow its procedure.