how to read a volt meter charging?

[jvandyke]

I lost my ammeter for some reason, needle got stuck way out on the plus side, why I don't know, sudden amp surge and the needle physically hung up on side of the gauge maybe.
So I got a cheap volt meter instead. Looks good, seems to work fine (only thing I don't like is the lighting (due to the colored interior screens) is green. No big deal.
I left the key on for a few days (duh). Battery was flat.
I jumped it drove it a bit, it ran like crap and stalled, I parked it for more work, trickled charged the battery back up to the point where the volt meter is saying 12ish (so is my multi meter put right on the terminals).

My question is, if I'm driving down the road what should I expect the meter to read? 13-14? Start getting nervous if it falls below 12 for too long?

BTW still has a generator, rebuilt in '86 and has 4000 miles on it.

PS recent switch to - ground, polarized generator with wire to little spade run to + battery terminal for brief spark, 4 times for good measure

 

[Darwin]

The alternator or generator should put out between 13.2 and 15.2 volts depending on how the regulator is set and the current draw at the time. If you are seeing anything below 13 volt with the engine above a high idle you have an issue with the charging circuit. I have had an engine run on as little as 10 volts but if you have changed to electronic ignition things start getting weird at around 11.5 volts.

 

[jvandyke]

Okay, I'll wait til I get her fired up again and see what's what. The ignition warning light has never worked on this car. I expected it too after the re-wiring this winter but it never comes on at all. Could be the regulator is flaky. I'm getting ready to fit an XR700 AFTER I have everything squared away.
Seems like something slightly above 14 would be decent during running. I'll keep an eye on it. Maybe I'll fix the ammeter and wire it back in and have both....maybe not.

 

[Darwin]

Get ahold of a wiring diagram for your car. If you are running an alternator you must have a path through the warning light. If not the alternator will not charge. Check the bulb and see if it is good and then check for voltage along the circuit path.

 

[Darwin]

Do you have a generator or an alternator? Shoulda asked this 1st thing.

 

[jvandyke]

generator, original type, wiring is as OEM, all new harness, new bulb (though it could have blown right away of course). I haven't checked for voltage on those wires. I assume there should be some with key on but car not running yet?

 

[Darwin]

It may be as simple as re-polarizing the regulator. It is simple to do but I haven't done one in years and have forgotten how. A generator does not need the light circuit to work if I recall correctly.

 

[jvandyke]

I didn't think the regulator/control box needed any repolarizing, just the generator?

 

[Darwin]

voltage regulators on generator circuits need to be polerized for some reason. If not you will not get any charging. Been many years since I studied electronic but I'm sure you can find the reasons and how to do it on the net.
try this search:
https://www.ask.com/web?q=How+Does+a+Voltage+Regulator+Work&qsrc=6&o=0&l=dir
good starting point.

 

[jvandyke]

I don't remember any of the how-tos for positive to negative earth conversion mentioning anything about the regulator box, just the generator. If I get a chance, I'll start her up and rev it up and see what the volt meter does, I'd expect it to get near 14, if not, I'd better figure out why not.

 

[jvandyke]

Darn, started car and volt meter stays right at 12. I think I'm running on the battery and not recharging it. I'd better start looking into that, how you check the charging system....

 

[Woodie]

I have a question, I would much prefer a voltmeter in the car instead of or in addition to the red charging light. Can someone tell me where and how to wire one in please?

 

[jvandyke]

Having just put one in, Harbor Freight sells the one I got for $6, yes, that's right, $6 (at least it was last week).
perfect size (2") and face and bezel are pretty close match.
Hook up is really easy, take a hot from the ignition switch straight to the gauge, and a ground to the other side. Done. I put mine in the hole where the ammeter was. Other than the light being the wrong color, it works nice. Was accurate too when compared to my multimeter.

If you don't have a hole in the dash to fill, you can mount it hanging below too.

 

[jvandyke]

Okay, starting looking for stupid mistakes. No charging, checked the regulator, ran with cover off, saw points opening and closing with rpm. Continuity between NY's....maybe the belts loose, yep, tightened and it's putting out about 14 at speed (according to my able 8 year old assistant meter watcher)(dad was working the throttle at the carb).
Good. I thought I had belt deflection about right but I did have the generator out recently for oil adapter leak issues and probably didn't tighten up enough, well, obviously not quite enough though.
Glad I found it before I went diving into a generator swap!

 

[Woodie]

which hot did you use for the voltmeter?

 

[jvandyke]

I put a spade doubler on one of the those that come off the ignition switch's white wires, not sure if that's the right term. Female spade but with other male sticking out so you just piggy back the wires, two off of one. It runs straight to the volt meter, I read the closer to the ignition switch the more accurate it is, probably just avoiding voltage drop through connections this way. You could simply add a wire to anything switched too I guess, that's close by, any green wire should be a fused, switched hot wire.

 

[Sarastro]

I really don't think you need to polarize the regulator. I can't imagine what that would involve, or why it would be necessary.

Keep in mind that the generator won't put out enough power to knock your hat off unless you are above about 1800 RPM. Below that speed, depending on how much of an electrical load you have, the battery will have to supply the current to run the car, anything from a little to a whole lot of current. So, it certainly won't be charging.

The charging system is supposed to keep the system voltage around 13.5V. It's a really crude system, though, compared to a modern alternator, so you can expect some reasonably wide variations, mostly downward. But I'd expect it to stay reliably above about 12.5V. If it gets below 12V, something is definitely wrong.

You really should have a working ignition lamp. It leaks current into the generator's field coils so that the generator can start generating power. Without this, there may be enough residual magnetism in the coils' metal coil to get things going--or maybe not.

If the battery has gone flat, and you have a generator, it's a good idea to charge the battery completely with a good, modern battery charger. Trickle charging really won't be enough. For longest life, a battery should be charged at constant current until it's mostly charged, then constant voltage at about 14.5V until it's fully charged. Good chargers will do this.

 

[jvandyke]

I've had the battery on a tender for a week.
Ignition light works (I had it plugged into the wrong gauge, reversed with highbeam indicator...which doesn't work yet).
So anyway, I swapped those bulbs and ignition light came on with key. I haven't had a chance to run it again to know if it will go off.
It's all slowly congealing.

 

[Sarastro]

Hmmmm...I'm not sure how much current a battery tender puts out, but it probably isn't over a tenth of an amp. So, in a week, you've only put about 17 ampere-hours into the battery, which isn't much. Pprobably enough to get it started, and then eventually it will charge up on the generator, as long as the generator and regulator are OK. And, of course, keep the idle up!

Still, I recommend a good charger. A nice tool to have around--it's awfully easy to flatten a battery, and a good charger will have you up and running in an hour or two.

 

[Bayless]

The Battery Tender that most of us probably use will put out up to 3/4 amp. They also make one that doubles that amount as well as some exotic stuff with more.