Charging Voltage?

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carpart67

carpart67

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I've got a 67 Barracuda 273, with what looks to be the original, or at least original style 1 wire alt. (1 wire from the regulator) Read lots of threads on trouble shooting if you're overcharging.

I don't remember, however, reading what the charging voltage should be. Can anyone help me out? Did a lot of electrical work over the winter. Think I'm overcharging now. (May have been before, didn't have a voltmeter in the car until now).

Thanks!
 
Start the car, get the battery "up" all accessories off, and the engine at a good fast idle. You should see somewhere between 13.5-14.5 Optimum is right at 13.8-14 depending on temperature. One good indicator of either battery problems or over voltage is constant "wet" battery and using lots of water. Use only pureified water in your battery.

One big problem nowadays is voltage drop across the harness, or ground link. To test this, first if you HAVE this problem, the voltage is normally OVER voltage.

Stab one meter probe directly onto the battery neg. post. Stab the other right onto the regulator mounting flange. Again, with engine running fast (simulate low-med cruise) you should see VERY low voltage, the lower the better. zero is perfect, anything over .2 (two tenths of a volt) is too much

Then check the "hot" harness side. Stab one probe right onto the battery positive post, the other as close as you can get to the regulator IGN terminal. Should be bare and accessable on a 69. Once again, zero perfect, over .2 is too much.

Either circuit being high indicates poor wiring or connections. On the ground side, try running an auxiliary ground, say at least no10 or 8, between the block and the regulator frame

On the hot side, check the path from the battery, starter relay, bulkhead connector, ammeter, ignition switch and connector, back OUT the switch and connector, back OUT the bulkhead. Somewhere in that path you have resistance causing a drop.
 
Maybe I'm alright. I haven't road tested the car yet, it's showing aprox 13-14 volts idling around the yard, but the car's not warm and may be on high idle.

I'll check the ground circuit first.

I did the ammeter bypass so the alt runs directly to the battery lug on the starter relay with an 8 gauge wire. 10 gauge wire runs current from the battery lug into the car, no connectors at the bulkhead. I also ran a new wire from the regulator to the alt because the old one was patched.

All this makes me suspect if I've got problems on the hot side it's the path from the interior of the car, through the bulkhead, to the ballast, and to the regulator. (blue wire)

Is there a "max" voltage that I shouldn't be exceeding throughout the entire RPM range?
 
Well I'd worry after I get a good voltage reading--you may be just fine

Up around 14.5 and higher is cause to start to worry. You'll get some arguement on just how much
 
15 volts at high idle.

Is it safe to run the car like this to perform testing?

I did a few tests but didn't want to run the car very long.

Additional ground to regulator does nothing. With the car off I checked resistance across the wire from the alt to the regulator, almost none. Same for the regulator to the ballast connection and for the ground terminal to the neg bat post. That's as far as I got before my voltmeter knob broke. (hooray for good luck)

The regulator is a pretty cheap looking replacement. Any way to bench test the regulator itself?
 
You cannot troubleshoot this by doing ohmeter tests, because of several reasons--often the voltage drop is caused by high current in the harness, and -- in the case of going through the bulkhead connector-- this resistance can change with current and heat.

Also, your meter cannot measure accurately enough at low resistances

Once you do the two tests I outlined, and they are OK, that is, low voltage drop, then you must assume that either the battery has an internal problem, or that the regulator is "high."

I know of no reliable way to bench test a regulator.

A couple of other things you can do to "eliminate the car" is:

As you said, you already ran an auxiliary ground to the regulator --and then recheck this with your voltmeter

and then for testing, run a temp. "hot lead" direct from the battery positive, or close as you can get it, like the starter relay stud --about a no 12 or 10-- direct to the regulator "IGN" terminal.

Obviously what you are doing there is simply running a great big power jumper from the battery to the reg. IGN terminal.

If it's still high, then replace the regulator.
 
So is it safe to run the car like this? Or should I only run the car and test in short intervals?

Thanks for the information, it's very helpful.
 
If you mean charging at 15 is not TERRIBLY out of the ballpark. I would watch the battery for "puking fluid", etc

Once you've done the checks we talked about, the regulator is about all that's left. If you read some of the old manuals, there's a procedure for actually adjusting the old mechanical regulators. I've never bothered with that. Frankly even "back then" shop rates were such that spending time to adjust a regulator as opposed to replacing it was usually throwing good money after bad.
 
Load tested the battery, it tested OK.

I tried some some tests today and got very inconsistent results. I have a brand new multimeter and brand new volt gauge and at one point I even had 2 different readings between the 2 instruments. I assume one must be a dud.

I'm pretty frustrated. I'll try again tomorrow.
 
What is a good way to test the voltage drop across the various points of the hot side?

Back probe the connectors? I don't have proper backprobes, but I've always found paperclips to work well.

Is there a better way to do it?

I got mixed results today. I'm going to start fresh tomorrow. Take readings after start up, and then again once the engine is warm and the car has been running a while.
 
Have you added anything ? Amplifiers, fans, etc., need to be turned off.
 
carpart67 said:
Back probe the connectors? I don't have proper backprobes, but I've always found paperclips to work well. .
Click to expand...

Good as any. I used to do this so much I don't even think about it. Paper clips, nails, etc, solder them to bits of wire, use clip leads, etc.

The major points are

the bulkhead connector from firewall side to interior, the ammeter, and the connector for the ignition switch. On "column lock" cars, this is the connector at the base of the column, and on "dash lock" cars, pull the switch itself out so you can get to the back of the switch.

I used to be able to reach up under the dash (battery disconnected) and connect clip leads to the ammeter just by feel. My age and arthritis have put an end to that.

(220, 221, whatever it takes)
 
RedFish said:
Have you added anything ? Amplifiers, fans, etc., need to be turned off.
Click to expand...

Head unit is removed at this time. I do have an amp, but I assumed it would draw little current without being activated by the remote signal from the stereo. I'll remove the fuse just to be sure. Thanks. (BTW Redfish the new fuel gauge setup works, thanks!)

I'll make myself a set of backprobes today and try to get something accomplished.
 
Good morning son. Up earily aren't you? Checked my battery voltage with the other meter when I got home and you were right. The one I brought over is the dude. About 1 volt high. Battery was at 12.75 with the good meter. There are 2 regulators listed. One for 35-46 amp alternator and 1 for 60 amp alternator. Chedcked Rockland pricing and was $43.85 so Rafuse's price will probably be about $60 or more. Both regulators were same price. Probably should know what amp alternator you have before you order one. good luck.
 
I once read that there were only 2 types of the round back alternators. One made approx. 36 amps, the other 42 amps. The difference was in their armature winding and the only way to sort them is to weigh them. The aftermarket doesn't sort them so the only way to know for sure what a reman'd alternator is made of is run full field test. Totally stock charging system and everything working properly idle voltage would be 13.2 That would support the car and maintain yesterdays battery having a stored amp rating of about 300 Shelf voltage of that battery would be about 12.4
Once you start upgrading to electronic ignition and/or adding stuff like higher powered headlights and a new battery with a stored amp rating of 550 or more you will need higher idling power. Shelf voltage of that battery would be around 12.7
My brother and many others know more about how amps and voltage are relative than I know.
I can say my charging system shows 14.4 at idle. This is with square back isolated field 60 amp alternator and solid state regulator Battery labeled stored amps is 565 . Idle voltage in gear with everything possible turned on will not drop below 13.8. Slightest increase in rpm sends that back up over 14.
 
RedFish said:
I once read that there were only 2 types of the round back alternators. One made approx. 36 amps, the other 42 amps. .
Click to expand...

I can tell you this, Red. I was second owner of a 70 440sixpack RR, and one option the original owner (a friend) ordered was either a 60 or 65A alternator. It looked exactly like any other Mopar at the time, which was the old style with individual diodes and of course isolated field.

So far as we could tell, all they really did was put a smaller pulley on it to spin it faster.
 
Alrighty, I think I may be alright after all.

The voltage of the battery before the car was started and after sitting all night was 12.64 volts.

Immediately after starting the car it was charging at 14.9 volts, and wouldn't go higher than 15 with increased RPM

After the car is warm the charging voltage at idle is around 14.5 with the high RPM bringing it to 14.65-14.7 max

I did the above testing from start up without shutting the car down.

Afterwards I shut the car down, took about a 15 minute break and tested again. At that time idle voltage was around 13.5- 13.8 volts with higher RPM still in the 14.65-14.7 volt range.

If I do have a voltage drop to the regulator from what I can tell it's the bulkhead connection. I did some voltage drop testing, but I don't find my new meter to be very consistent or accurate. Considering it's price point ($60) that's agravating.

I've got a volt gauge in the car so I think I'll try a few drives and keep an eye on the gauge, as well as the top of the battery and go from there.
 
The voltages warm are just not that out of line. Most any regulator will change some with temperature.
 
RedFish said:
I once read that there were only 2 types of the round back alternators. One made approx. 36 amps, the other 42 amps. The difference was in their armature winding and the only way to sort them is to weigh them.
Click to expand...

Not true. First off, alternators do not have armatures. Also, there are three significantly different variants of the roundback alternator -- or four if you count the '60-'61 Essex-built units that have wider-spaced cooling fins and a few other physical differences. The '62-'69 grounded-brush "single field" item is the one most people bring to mind when talking about roundback alternators. There was also the '69-only insulated-brush 60A unit (see here and subsequent page), and the '70-'71 isolated-brush unit (see here), commonly referred to as a "dual field" item and completely interchangeable with the '72-up squareback alternators which are also "dual field".

Except for the '69 60A insulated-brush alternator, within each type of roundback alternator there are multiple amperage ratings, ranging from 27A to 60A. Output is contingent on the rotor and stator. Then there are multiple pulley configurations -- single or double groove, diameters ranging from 2½" to 3½". Pulley diameter was selected based on anticipated engine RPM range in a given application.

The aftermarket doesn't sort them
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It's much worse than that. The "remanufacturers" throw together any ol' rotor with any ol' stator, just whatever happens to be grabbed from the barrel. Occasionally you get a good-working set, but more often mismatched rotors and stators greatly aggravate the relatively poor low-RPM output characteristic of the Chrysler alternators we're talking about here.


idle voltage would be 13.2 That would support the car and maintain yesterdays battery having a stored amp rating of about 300 Shelf voltage of that battery would be about 12.4. Once you start upgrading to electronic ignition and/or adding stuff like higher powered headlights and a new battery with a stored amp rating of 550 or more you will need higher idling power. Shelf voltage of that battery would be around 12.7
Click to expand...

You're right that increased electrical demand calls for a higher-output alternator to keep up with the load, which in turn requires circuit upgrades (see here) but the amp-hour rating of the battery (or the cold cranking amp rating, or the cranking amp rating, or whatever you are referring to when you say the "stored amp rating") has no influence on the alternator required to keep it charged. The voltage of a fully-charged "12 volt" auto battery will be in the very close vicinity of 12.6v, regardless of its amp-hour (or any cranking) rating -- that is with the surface charge drained off by running the headlamps for 60 seconds or so with the engine off before taking a reading.

I can say my charging system shows 14.4 at idle. Idle voltage in gear with everything possible turned on will not drop below 13.8. Slightest increase in rpm sends that back up over 14.
Click to expand...

That's quite excellent; your charging system sounds to be in good shape.
 
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