charging system

[Ed Hickey]

1966 327-300 with air. When I turn the heater blower on full speed, the ammeter shows a discharge (engine running). The alternator tests good and the voltage regulator was bad and was replaced. Lights, Radio etc do not show a discharge.

The blower motor does not blow any fuses, so the current draw can not be too high. The lights do not dim when the blower is on. I am thinking the ammeter is goofy. Any ideas?

Thanks

[John H.]

Re: charging system

Ed -

You didn't mention at what rpm the engine is running when the ammeter shows a discharge - the high blower is the heaviest electrical load in the whole car, and it could overpower the alternator at idle. The alternator should pick up the load above 1500 rpm; if it doesn't but it tests OK, sounds like the regulator needs adjustment.

John

[John H.]

Re: charging system - Addendum

Ed -

Double-check the grounding for the voltage regulator - this is a chronic Corvette problem, and enables all manner of gremlins.

John

[Ed Hickey]

Re: charging system - Addendum

John,

Thanks for the suggestions. I tightened the ground at the regulator and now the ammeter shows charging after I start the engine. After a few seconds the ammeter returns to zero. It looks like I would expect it to.

I turn the headlights on and I see the needle momentarily deflect to discharge and then go back to zero. Again, this is what I would expect.

When I turn the blower on the needle moves to discharge. No matter how fast the engine runs it still shows a discharge.

I drove the car for about 1/2 hour with the blower on high and the gauge showing a discharge. It didn't seem to run the battery down at all. Any other ideas?

Ed

[Jack H.]

Re: charging system - Addendum

How was the alternator 'tested good'.... Most of the corner parts store alternator testers are 'omnibus' machines meant for go/no-go (tend to bias in favor of 'no-go') readings. Alternator is AC generator with 3-phase diode bridge. If one diode (out of six) is 'flakey' or intermittent, you won't get full design rated output from the system.

As indicated, heater blower hi-speed is one of the heaviest current draw items in the car's system. Suggest you re-test alternator at a qualified shop (pro rebuilder, AC-Delco, Etc.) where the test jig is high end and robust. Personally, I like to actually see the waveform that's being output because this tells you EVERYTHING that's going on internally and not just the gross 'kinda/sorta' current production of the alternator.

These pro test machines apply a dummy load to alternator that's variable in terms of current draw and load power factor. X amps into a purely resistive load can change appreciably when the calling load is either capacitive or inductive in nature (flyback components) with a marginal alternator diode bridge.

Last, what makes you think the problem lies in your charging system alone? What if the blower motor is well worn, has high resistance bearings, Etc. and is calling for more than it's rated supply current to spin up to spec?

[Ed Hickey]

Re: charging system - Addendum

Jack,

The alternator was tested at a place called Morton Grove Electric. They rebuild alternators for a lot of the local repair shops. The machine they tested it on was a motor driven dummy load type of machine. There was nothing that would provide a waveform.

This car is a numbers matching car. The alternator has the right number on it so I don't want to just replace it.

The blower motor could be bad. The alternator was easier to get tested. I will try getting another blower motor.

Do you know of anyplace I could get the alternator tested right?

Thanks for the help,

Ed