How Long 'Till Lights Out?

[Brobrian]

How long can I run my lights on these long winter nights while the ammeter reads -10 amps?

I've been meaning to ask this question ever since the shorter days have forced me to drive with my lights on. I drive to work in the dark and notice that with the lights on my ammeter reads -10. On the way home with the lights off, it charges at about 3 or so. The car starts so quickly that I can't tell if I'm slowly draining the battery just by listening to it turn over. Heck, for all I know when the battery gets low enough the alternator will boost it's charge rate. I've seen the meter read +20 when I first turn the lights on in the morning. But only for a second, then it runs a 10 amp discharge the rest of the drive to work. That rate doesn't change much no matter the rpm.

I seem to remember with my last alternator that the car never ran at a discharge.

Oh, I'm using 6v 30 amp alternator from Snyders. And, yes, it's properly installed, as is the ammeter in the dash.

[BILL WILLIAMSON]

Bro, when it's reading -10, maybe you're not reving quite high enough for the alternator to charge? Kick in the clutch & rev it & see if it charges +
Bill W.

Dog here, Bro, we waitin' fer you to try it, so's we kin go watch a Doc Martin Movie! Buster T.

[MikeK]

A group one 6V battery has a storage capacity of about 80 amp-hours when new. After a few years that is down to ~60 amp-hours. You do not want to ever draw a battery down much below 50% charge, especially if you want it to crank reliably for a re-start.

If you discharge at a 10 amp rate x 3 hours you will use 30 amp-hours. Thus, you can safely go about 3 hours, 4 if the battery is new and fully charged. You will, of course, either need to put it on an external charger or drive at least TEN HOURS the next day with the lights off if your charge rate is 3A as you say.

[Kurt in NJ]

Is the belt tight enough so the pulley doesn't slip ---try turning the pulley by hand and see how much effort it takes to make the belt slip on the pulley.

If the belt is tight enough probably there is a problem with the alternator or the wiring, compare the voltage at the alternator to the battery voltage

[Brobrian]

Originally Posted by MikeK

A group one 6V battery has a storage capacity of about 80 amp-hours when new. After a few years that is down to ~60 amp-hours. You do not want to ever draw a battery down much below 50% charge, especially if you want it to crank reliably for a re-start.

If you discharge at a 10 amp rate x 3 hours you will use 30 amp-hours. Thus, you can safely go about 3 hours, 4 if the battery is new and fully charged. You will, of course, either need to put it on an external charger or drive at least TEN HOURS the next day with the lights off if your charge rate is 3A as you say.

Very cool! That's the kind of information that helps me understand my car better. So, now all I need to figure out is whether the alternator should be picking up the extra load and effectively zeroing out the draw in amps, or if it's still functioning properly when it allows a ten amp draw. For now, I can rest easier on my way to work knowing that the 20 min drive won't completely drain my roughly 60 amp/hr reserve of power.

[Bill Goddard]

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Isn't there some way to raise the charge net rate to about 8 or 10 amps so the discharge will not be as great? Bill G

[Wick]

You do have the small pulley on the alternator? just checking.

[Tom Wesenberg]

It sure sounds like you have a bad alternator, or a badly slipping belt. After a drive turn off the engine and feel the pulley. If it's hot then the belt must be slipping. A slipping pulley will glaze the belt and make the problem worse. Alternators with the small pulley need to run a tight belt, but generators with the stock pulley don't need to be very tight.

[Brobrian]

Well, I'll check all that again. Pretty sure the belt is tight. I believe the pulley is correct as it has to be a special one to line up with the crank pulley and water pump on this car. What I'm gathering here is that the alternator if installed correctly and working properly should comopletely compensate for the amps drawn by the lights.

Thanks guys. I'll let you know.

[eagle]

With a 30A alternator you should always show a positive charge. Best way is to use a voltmeter to check the actual battery voltage, on the battery terminals. The thing is, if your battery is not going dead, your ammeter must not be telling the real story.

[jm29henry]

it does not seem to me that you have a problem the car is getting you to work and starting to get you home now if this is a generator there would be no problem it would be totally normal.Because you have a alternater you have a concern .So my question to you is how do we know if the amp meter is working properly .My suggestion would be to get an amp metor and see what it is really putting out or take it off and have it checked by an auto parts store.And if all else fells call synders there great people to work with and I am sure if there is any problem they will work with you hope it all works out great for you Joe.

[Ted in MN]

Remove battery ground strap and scrape rust or paint off frame. Re-attach ground strap and see positive amp readings.

[H. L. Chauvin]

Hi Brobrian,

Not knowing exactly what you have electrically, maybe another prudent option would be to send your old generator to Mr. Tom Wesenberg for installation of a voltage regulator which will make your batteries last much longer.

FWIW: Replacement batteries are very expensive, dim lights are dangerous, & to make matters worse, having to experience cranking a Model A engine with a hand crank in front of a group of modern young beautiful secretaries at work could affect one's profile & make one look like the old tight Scrooge fellow at Christmas time.

[Brobrian]

Originally Posted by H. L. Chauvin

Hi Brobrian,

Not knowing exactly what you have electrically, maybe another prudent option would be to send your old generator to Mr. Tom Wesenberg for installation of a voltage regulator which will make your batteries last much longer.

Tom, is this the case?
I have my old powerhouse generator. I even got new field coils and brushes for it once, but chickend out on rebuilding it myself. Years ago I opted for an alternator instead, so I wouldn't have to monitor the charge rate by manually moving the brush each season.

I'll still check out the things suggested above. It does seem that the alternator is acting like a the old generator used to. Something ain't right.

You guys are great!

[Fred K-OR]

"I'll still check out the things suggested above. It does seem that the alternator is acting like a the old generator used to. Something ain't right."

The comments about the amp meter may be you problem.

[Brobrian]

Okay, Gentlemen.

For those of you who gave advice and counsel:

I rechecked for clean connections to the batt. all good there.

Stuck the battery on the charger just to insure that I wasn't trying to charge a bad or low battery. Came to full charge within ten minutes on 2 amps. So, again, all good.

Checked the fan belt, at first I thought it was fine, but decided to change it out anyway. Turns out the belt had been slipping. After installing the new belt, the alternator immediately began charging at over 20 amps (I only have a 20 amp ammeter). I felt the face of the ammeter and it felt warm and the charging rate hadn't dropped. Shut down the car. Felt the alternator and pulley. The whole thing was too hot to touch. Tried again a bit later same result.

Today I swapped out the alternator for one I'd bought for my p/u. Works perfectly!

Showed an initial charge of 15 amps, but within a minute or two registered zero. Turning on the lights showed a bump in the charge rate and seconds later back to zero.

So, I'm back on the road, even at night. And I'll be taking my other alternator in to a shop to see if it doesn't have the wrong diode, or whatever. Seems like it might be set up for a 12 volt battery.

Thanks again for everyone's help.

Brian