Denso Alt Voltage Regulator

[Moseso]

I have a 3-wire Denso alternator set up on my TR3. A little odd behavior of the amp gauge got me thinking about gremlins, so I checked a few things.

When the ignition switch is off, there should be no load on the battery from <span style="font-style: italic">anywhere</span>. If you pull the ground cable off the battery and put a voltmeter between the battery and the cable, there should be no voltage reading -- open circuit -- no way for electrons to get from hither to yon. This is not the case on my car. I get a fine 13.26V reading. So I tried the ammeter to see how much is draining. Not much: 0.4 milliamps.

There is ONLY ONE unswitched wire in the whole dang car, and that is the large one that runs from the output terminal of the alternator to the ammeter, and from there to the battery positive terminal, via the solenoid. Sure enough, when I disconnect that wire, the mystery voltage disappears.

Enough description! The question is -- Is this normal behavior of the "solid state" internal voltage regulator on my alt, or is this an aberration requiring corrective action? Anybody here know?

(A total aside: This all serves me completely right for thinking I had banished the Lucas Electrical demons from my car through use of the Denso alt AND starter. The starter is stone dead after <50 starts, and now I am thinking the alt ain't working right either.)

 

[Moseso]

So, I drove over to the auto electric place that I bought the alt from... (Nice ride, aside from worrying about the gremlins.)

1) I was wrong about the current drain -- misread the meter (duh). It's not 0.4 milliamps, it's 0.4 amps!
2) He says, "That shouldn't be happening."

So, this is no longer a question. It's become a saga. I will take the alt off the car and give it back to him ASAP -- for repair or replacement. In the meantime, I have disconnected the charging wire. I am worried that this rogue alternator is trying to overcharge my battery. I've got plenty enough battery to get me home without being recharged -- especially seeing as how I'm not using it to start the car... :crazy:

 

[TR3driver]

Moses, I see you've already got the problem well in hand.

Some alternators do drain just a tiny bit all the time; so I wouldn't have said that 0.4 milliamps was necessarily wrong. After all, that would take some 5-10 years to drain the battery to even 1/2 charge.

But 0.4 amps is clearly wrong.

Almost certainly, the regulator inside the alternator is toast, so it might well be letting the alternator run full blast all the time (thereby overcharging the battery). Of course, if you had kept the ammeter functional, you would <span style="font-weight: bold">know </span>that

Lucas gets far more blame than they deserve, IMO. Most recurring Triumph electrical problems are the result of poor application of Lucas components (like that stupid 2-bobbin regulator instead of a proper 3-bobbin) rather than poor quality components (my 50 year old regulator is still working just like new; which is to say like a 2-bobbin regulator).