RatDog

When I turn on my Vintage Air, the needle on my battery gauge moves to the right. The higher I turn the blower, the more the needle moves. On the highest blower setting, the needle goes to the right side hash mark (+20?). I can't remember if the gauge has always done this but it's been doing it for the past several months I've been paying attention to it.

With the A/C off, the needle stays just a hair to the right of center.

I use a voltmeter that plugs into my cigarette lighter. It doesn't change at all when I run the A/C and that's what has me scratching my head. Shouldn't it show a change, too?

I also have a manually-controlled SPAL fan. When I switch it on, the battery gauge needle pegs to the left and then returns to center, all in the space of about 1 second. Too fast to see on the voltmeter. That seems normal to me.

When I start the car, the needle pegs to the right and then moves to the center of the gauge after running for a short time. Voltmeter shows a drop to 9.5v, then moves up to around 13.7v before settling out at 13.3v. This also seems normal.

The SPAL fan takes power from the alternator power supply terminal. The A/C takes power from the starter terminal. I have a 100 amp alternator and a solid state VR.

Other than the deflection to the right when the A/C is on, everything else seems normal. The battery maintains 12.5-12.6 volts when parked, even for a week or so and the Voltmeter shows 13.3 volts when driving.

I know there's a scientific explanation for the behavior of the battery gauge vs. the voltmeter, but as electrically-challenged as I am, I just don't understand why the gauge needle can move to the right when the A/C is on without showing a change on the voltmeter.

My second question is, is it OK for the battery meter to run on the +20 hash mark?

Thanks,
Steve

Frankie the Fink

IMO - you're not getting a true dash gauge reading of what's happening. Try disconnecting your starter feed for the V/A and temporarily connect the V/A with a 10 gauge wire to the horn relay buss to see if that helps you out. Leave the SPAL fan off for this test.

BTW - disconnect your battery while connecting the temporary jumper.

Let us know what changes...

RatDog

Thanks, Frankie, I'll try that. It may have to wait until later in the week, though. Gotta take care of a bunch of pre-op medical stuff.

Does your VA take power from your horn relay?

-- Steve

RatDog

Frankie, you're the man! I was finally able to get some time and hooked up the temporary connnection as you suggested. I get no deflection of the battery gauge needle at all so i'm going to permanently wire it that way.

I'm trying to understand the science here. I believe the gauge measures the difference in voltage between the horn relay terminal and the starter terminal. You were correct that the gauge was not reporting correctly because the A/C needed to take it's power from the horn relay. But what about the SPAL fan? It takes its power from the alternator. Like I said, the gauge makes a 1-second deflection to the left when I turn on the fan but it returns to center. I tend to think it's OK wired the way it is because that's where Dewey Hendricks hooked it up but it seems like I could wire the fan to the horn relay as well if I wanted to. No?

As always, thanks for the help.
Steve

Frankie the Fink

I think the fan is fine. The issue with hooking accessories to the battery/starter (regardless of what the instructions say) is that you are then 'lying' to the battery gauge. Its not compensating for the voltage drop at that connection. It thinks that the system is in a constant of state of charging.

The voltage regulator senses charging requirements 'remotely' at (or very near) the horn buss. You wouldn't think it would be that big a difference but the way C2s are measuring across a shunt - a small difference in where things are sensed makes a big difference in what is indicated at the gauge...

There are pages and pages of reading about the topic on the Mad Electric web site in their tech section...

And yes, my Vintage Air is powered from the horn relay buss (you asked earlier) and has been for two years...

cardo0

Steve u need to cover that battery gauge up and drive "naked" w/o it. I think u mean ammeter and if it confuses u it cannot be helpful. If your ammeter wiring has changed from stock it will no longer be accurate but maybe indicative of current flow direction. But if ammeter wiring is still correct the ammeter will show current flow direction and magnitude. A correctly working ammeter shows current flow in the negative direction for batt discharges and flow in the positive direction for batt charging. When u start the motor or turn on your fan the batt discharges and moves in the negative direction with higher magnitude as starting current is the highest load then it lowers/tapers off as the electric motor turns at normal speed and load decreases. Once alternator/generator get up to speed the current begins to flow in the positive direction back to the batt and will be highest when batt is highly discharged then taper of as batt becomes charged again.

Hope this helped.

RatDog

Thanks for the info .

My gauge's needle moves to the positive when starting and then returns to center after running for awhile. It deflects to the negative when I turn on the fan.

What's confusing are all of the threads discussing what this meter is and what it does. Some say it's an ammeter. Some say it's "sorta like an ammeter". Some say it's a galvanometer. And some say it's a voltage meter.

I like to use a small voltmeter device that plugs into my cigarette lighter. I think it gives me a better idea of what's going on with my battery and alternator.

Take care,
Steve

Frankie the Fink

You already know what the gauge does, and, what it is...don't get dragged into the semantics wars over the label on the front of it.

There are multi-page urinary competitions on here already about that...

The only thing you were missing was knowing where the C2s 'sense' the voltage to provide a gauge indication and proper charging rate

RatDog

LOL!! You got that right! There are plenty already . . . I don't need to start another one. Maybe a discussion of ethanol would be better.

Steve

Frankie the Fink

Or Pertronix or oil or.... well you get the idea

cardo0

Well if u like simple voltmeter then a cheap batt tester for $20 would be the ticket. I own at least 2 and they tell the health of the batt and the charge of the alt/gen.

Something is wired wrong if your ammeter shows charge when starting the engine. That's why I say your better to ignore it. I repair instrumentation for a living and instrument threads interest me. Some posters get creative w/thier googled interpretations. But I won't go there as I don't want to start a riot today. Just want to warn u your indications from your meter are incorrect and most likely it wired wrong as even the wrong size wire can fail it.

I really like my hand held batt testers and usually keep one in the car. It tells me current charge voltage w/batt off and w/flip of switch I can watch the batt load in less than a minute - this all w/engine off. Now start the car and u can see alt/gen charge voltage. That covers it and all u really need.

Hope this helped.

RatDog

I need to correct myself. The gauge needle does, in fact, deflect to the left when first starting the car, just as you say it should. Then, it bounces over to the right and gradually returns to center.

I have 3 different plug-in voltmeters I like to use (photo of one of them below). I leave it plugged in when the car is parked in the garage to keep an eye on the battery. Always stays at 12.5 or 12.6.



-- Steve

Frankie the Fink

Unlike modern cars the 'parasitic' draw on a midyear, parked with engine off, key in LOCK position and battery connected and interior lights off is the mechanical clock; if you have a quartz conversion then that will only be a very few milliamps.