TR6 TR6; Amp Gauge Not Reading Positive

[Webb]

Alright, started my car up for the first time in a week since I left for school the other night (it's been in a garage at home though) and the Amp gauge in the car wouldn't read positive, even at high(ish) revs. I drove around for a while, and let it idle for a bit, and it didn't cut off. Also, my alternator is hooked up correctly, and the gauge is hooked up correctly, so I'm thinking it's a faulty gauge. I haven't changed any of the wiring or anything since it WAS working last time I started it. What could this be?

 

[LastDeadLast]

It should read positive when your alternator output is more than what you're draining. Sounds like your alternator isn't charging.

 

[YankeeTR]

A alternator won't charge if the battery is fully charged...that's what the regulator does. I'd put a volt/amp meter on it and see for sure before I went out and bought any parts.

 

[Webb]

I know. I'll have Advance check it, but it's uncommon for alternators to just quit all at once, not to mention that this particular Bosch unit was replaced by the previous owner and my friend just 4 or 5 years ago.

 

[TR3driver]

IMO, much more common for alternators to suddenly die than ammeters. Just one transistor failure will kill an alternator, while the ammeter has no semiconductors at all.

First quick check would be to turn on the headlights with the engine off; the ammeter should show a discharge around 1/2 scale (15 amps). If it will read discharge, chances are it will read charge as well.

Next check, put a voltmeter directly across the battery with the engine at fast idle. If the alternator is working, you'll see 13.5 volts or more. Under 13 means the alternator is not working.

A cheap but adequate digital multimeter is under $10; and essential equipment for LBC ownership, IMO. I keep one in every glovebox, along with a couple of clip leads.

 

[Twosheds]

Alright, started my car up for the first time in a week since I left for school the other night

Doe "the other night" go with starting up or leaving for school? If the headlights were on, it's normal to show no charge. The ammeter only shows current flowing from the battery to the loads (discharge) or from the alternator to the battery (charge). The headlights will "steal" electrons from the charging current and this will show up on the ammeter as zero or even a discharge. Disclaimer: I am used to a TR3 with a generator.

 

[Webb]

I'll put a voltmeter across the battery. It doesn't show a charge even with everything off, and the car running at 2000+ revs. It shows discharge of about half on the ammeter scale which is what I'm used to, but no charge when I flick them off.

 

[Webb]

Put the voltmeter across the battery and got 12.04 volts. Guess it's time to replace the alternator...