philipj

38 Buick Century charging rate at idle...

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Hello all,

After draining my battery down a few times due to leaving the dash light on, @$#!! I decided to check the rate of charge at idle which was about 6.35 to 6.45 volts and wonder if the voltage regulator is set up properly... By increasing the rpm I get virtually no change, maybe 6.50 volts.

Is that a normal rate of charge?

Edited by philipj (see edit history)

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How many amps are you getting? Your battery will have a resting voltage of about 6-6.5 volts and should see more than 7 volts when charging. Your ammeter should show a positive charge at anything above idel (it might show discharge at idel which is OK). As long as it shows a positive charge when your driving you should be OK. If the battery is low you should see a heavy load and then gradually lowering towards 0 as it tops off the battery. Your voltage seems a little low but I dont know if you can adjust that with the regulator which I thought was just for amperage current. The battery is the "voltage" regulator on the system so maybe it is tired? What is the voltage of the battery with everything off and disconnected? 

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Yes, key question there of battery voltage with engine off.  A good battery should be around 6.3V.  After starting and the engine above idle speed the amp gage should show charging until the battery is back to normal level.  If you have an old lead acid battery be sure to check the water level as continuous charging can cook off some of the water.

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I might need some help to move this topic to the proper location... The ammeter does show a charge above idle. I will check the resting voltage tomorrow. I wonder if I damaged the battery by leaving the instrument light on at least 3 times and running the battery to the ground...

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If the ammeter is showing that it is charging and the engine starts normally without having to jump start it, I would not be too concerned. If you run a battery totally down to zero volts a few times, it is usually time to replace the battery.

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That dash light thing is just plain crazy. (did the same thing a couple of times)

I rewired my '38's through the headlight switch so that the darned things can be left on.

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I agree with the 6.3 volts for a fully charged battery, engine off.  (theoretical 2.1 volts per cell, I believe)  But, remember, this does not indicate state of charge, which is more of a capacity thing.  Make sure the battery is fully charged before analyzing the voltage that the regulator is providing.  It could be that the battery is "sinking" a lot of current due to low charge, and 6.5V is the best your generator can provide at that current level.  Later, with a full charge, you may see a bit more voltage.

 

I also agree that with everything set correctly, you should have something around 6.8V to 7.2V (I think this is defined in the shop manual).  This is adjustable by tweaking the attachment point of the regulator spring... but it's a pretty delicate operation.

 

Jeff

 

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You indicate the rate of charge not going up much with RPM and that is plainly indicating your not charging nearly enough. Should be about 8 volts or so as you need a lot more then battery voltage for charging. A 12 volt system is normal at about 14 volts so you always need at least a couple more which is why you have a voltage regulator.

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Thank you for all your replies... A lot of good information here.  My battery shows 6.11 volts resting, after driving the car for about 45 minutes yesterday, so it may be on its way out... Still, sounds like there may be a problem with the voltage regulator not charging sufficiently...

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Have you put a load tester on the battery?

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First check the wiring and grounds.

I had a regulator problem that was finally traced to the regulator ground being bad (rust)

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I had checked all the grounds recently while trying to solve another problem (intermittent miss that ended up being the original distributor set up with the three ball bearings that never work smoothly) but I can certainly check again... I might drive the car up to Napa to do a load test and check the price of a battery at the same time. I did just notice however that the water level is about 1" under the cutout so that may be a contributing factor for the battery performance...

Edited by philipj (see edit history)

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8 minutes ago, philipj said:

might drive the car up to Napa to do a load test and check the price of a battery at the same time. I did just notice however that the water level is about 1" under the cutout so that may be a contributing factor for the battery performance...

If the plates are covered, best by a small (half-inch) margin, you're OK--don't overfill.  Suggest you charge the battery to 6.3V before driving to have the battery load tested.

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Ok, I just placed the trickle charger on the battery... It will be on at least until 11.00 or 12.pm, (for I do not like to leave it on overnight) then I will see the condition of the battery and go from there... In any case, I still would like to see at least 7 volts at high idle which I have never seen.

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I just watched an interesting video from Chrysler made in 1948 about voltage regulator adjusting. It mentions needing about 26 amps to run the car lights and radio. Here is why I think mine is out of adjustment. The time before last I run the battery down I jump started the car with my jeep on my way to get ice cream on a Sunday evening... Well, I got it going except that, shortly after turning the headlights on about 2 miles from home the car just quit! Done, dead as a doorknob; left me in the middle of an intersection with my 93-year-old mother in law (she loves the car!) sitting in the back seat !@#$! To this day I have never felt more shame or public humiliation! First time in 30 years that something like this has ever happened!

 

Luckily for me, she never said a word, but in my head and to this day, all I see is a cotton ball puff of hair through the front and rear glass as I push the car with my brother in law off the road; flustered with embarrassment as to what she might be thinking! I had the car loaded with 5 people for a fun Sunday ride that never happened...;(

 

And I still feel there is a problem that won't solve itself... First, the battery must be at full charge, then I need to figure out if the regulator needs adjusting and which one of the three coils within the regulator I need to change to increase the rate to about 7 volts or 20 amps minimum?... But how do I measure the amperage from the regulator? I may be overthinking the whole thing... Maybe I just should try to bring the charging rate up to 7 volts at least?

 

If anyone has any other basic suggestions it would be great, before I get ahead of myself and think that the regulator really needs cleaning or adjusting...

Edited by philipj (see edit history)

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Make sure the water level is correct in the battery. Charge the battery fully with a battery charger. Have the battery load tested at a parts store. They can probably also test the generator for you. Replace the battery if bad. Do the same with the voltage regulator if bad. Drive the car. Don't leave stuff on to kill the battery while parked. If the battery is charging and not leaving you stranded, you are probably OK. You can have the Generator rebuilt if needed.

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The battery is about 2 years old, It was discharged overnight or maybe 2 days to about 4 volts, at least 3 times within the last 2 months... I will have them do a load test tomorrow. Going through the car's paperwork I see that the generator was repaired in 2006 by Yesteryear Antique Auto Parts (Fl) with no specific information. I need a big fat note regarding the dash lights for the foreseeable future unless I am to disconnect it and run it through the headlight switch as suggested by Don M.  

Edited by philipj (see edit history)

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26 amps for lights and radio seems like alot. Most early generators dont put out much more than that, leaving not much room for reserve. I still think you have a weak battery thats going bad. Sometimes they just go bad. Some sooner then others. I would start there. Pull it out and take it to the store and let them load test it even tho thats not 100% proof either way. Give it a good charge overnite if you think that will help. If the ammeter is showing a charge at 20 MPH then the generator is working. You can ground one of the posts on top of the generator to make it go to full charge and that will show you the generator is working. If the battery is weak the regulator should run the generator at almost wide open full charge to top it off and maybe for a long time if the battery is very low. I had one car where I thought the regulator was bad because it showed a strong charge all the time but it was just the battery going flat and not being charged up all the way and it was trying to charge it up and I just didnt give it enuf time. Dont be afraid to leave a battery on a trickle charger overnight. If your really worried put it outside on an extension cord or something but battery expolsions from trickle chargers are rare. Get it 100% charged and then test. A bad battery might even show it is 100% charged but it wont be. 

 

There is an easy fix not a hard one. But now I see we are going to go down the rabbit hole again like we always do and try to make it some complicated weird uncommon problem when the most likely explanation is that you're battery is low it has never charged up all the way and it is now weak and your generator is working overtime to top it off. If anything you're regulator might be set too low but you can adjust that if you have problems later. But I will bet 5 bucks its just a bad battery that went flat one times to many. Dont make it to complicated. Charge up the battery and do a load test. Or just buy a new one and see if the problem goes away. A battery is only $100 bucks and it never hurts to have a spare around charged up and ready to go.

 

Battery. Then everything else. Dont overthink. Dont let too much info distract you. Simple machine simple solution.

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You are absolutely right my friend, unfortunately, I tend to overthink things sometimes, forgetting that these are simple systems. I will certainly start with the battery and let it charge overnight... Thank you for the sound advice.

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If you have a shop manual and / or a Motors Repair manual it can help you with adjusting your regulator should that be necessary.  The battery load test can be a great help in deciding what your next step should be.

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When I purchased my 39 Roadmaster a few years ago, it had one of those screw-down cutoff things on the negative battery post. I always experienced slow turnover when starting the car, especially so on hot days.  I first thought it was simply starter drag with the big 320 engine, or a bad battery.  The battery was fine.  I cleaned the posts and cutoff hardware with no change.  One day, the car died at an intersection.  How embarrassing! (It ran so quietly that I didn't know that it had died.)

 

Shortly, I removed the battery cutoff hardware.  No more drag and no more dead car.  The 320 engine now spins about as fast as my 49 Super with the 248 engine!  My wiring harness is new on the Roadmaster.  I have no concerns about leaving it live between uses without a cutoff. I have no discharge issues.

 

 

 

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I had easy access to a tune up specification book last night so I looked up Buick charging rates.  The book only goes back to 1946 but the 6 volt systems listed had charging rates of about 7.3 volts.  No engine speed was listed for this voltage but at least it gives you a ballpark idea of typical charging volts.

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Here is the skinny regarding the battery condition as of this morning after a full charge overnight...6.26 volts at rest. Shortly after starting the car it went to 6.34 and as it warmed up it went to 6.82 for a short time... After the vehicle was warm it went anywhere from 6.34 at idle to 6.48 about 900-1000 rpm...

Before checking it with the meter I tested the specific gravity and I got "Average" on all three cells. It seems that my battery might be on its way out, unless I can charge it more than 12 hrs and see what happens...

 

Now, given the battery condition, does it interfere with the ability of the regulator to allow a charge higher than 6.82 volts, or should I be looking elsewhere?

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