High volts

-
txstang84

txstang84

Well-Known Member
Joined
Oct 10, 2011
Messages
4,556
Reaction score
554
Location
Abilene, TX
Hey guys, sorry if I hit a subject that's been answered a bunch, but IPhone search gets old fast. My charging system is pushing over 15V at the battery, regulator has been checked and changed three times, alternator is obviously charging, but way too high. I checked the field wire for shorts to ground-all checked good. It used to only charge 12.8V which made for interesting driving on cold wet nights leaving work, but now it cooks batteries in about 3 weeks or so. I'm struggling to figure out what's wrong with it...any ideas??

I had thoughts about either replacing the alternator, putting a resistor inline to reduce the volts going in, or trying to upgrade to a 1 or 2 wire internal regulated version, but I'm open to ideas...
 
Check that the voltage regulator is well grounded at it mounts and that mounting surface is well grounded to the battery ( the ground strap from firewall to engine ).
Then start looking for a voltage drop in the blue wire. You're looking for very close to the same voltage as battery shows on the blue wire on the rgulator and the alrenator.
 
if it's a stock alternator it's the voltage regulator that is allowing your battery to overcharge.

however, it's not uncommon for it to charge at 15v (it has to be higher than the battery or it would not charge the battery if that makes sense)

what kind of batteries are you using? are they brand new? you could have just been trying bad batteries.

if it's a denso type alternator, with built in voltage regulator, you dont need the voltage regulator. connect the voltage sense wire to where the battery positive wire connects into your harness.
 

Where you said that several batteries have been installed, I don’t think you have a battery problem which will cause over charging.

Most often voltage drop in ignition and regulation circuits cause over charge problems. If voltage regulator is seeing low voltage in harness it will boost voltage output of alternator by the difference from normal harness voltage. In other words if VR is reading 12.5 volts, and battery is at 14v, alternator will add +1.5 volt to 13.5, and charge at 15 volts which will boil a battery dry, and kill it.

You need to check for voltage drop in ground side of ignition circuits, and plus side as well. Ground side should show no voltage drop, and plus side no more than a total of 0.3 v.

Corrosion at any connection, bad conductors, loose connections, and worn ignition switch adds resistance to circuit which causes drop in voltage. There will be a small voltage drop at each of the above that all add together to make one large resistance. You need to sniff out, and eliminate as much of this age related resistance as possible by cleaning, tightening, and replacing conductors as needed.
 
wjajr said:
Where you said that several batteries have been installed, I don’t think you have a battery problem which will cause over charging.

Most often voltage drop in ignition and regulation circuits cause over charge problems. If voltage regulator is seeing low voltage in harness it will boost voltage output of alternator by the difference from normal harness voltage. In other words if VR is reading 12.5 volts, and battery is at 14v, alternator will add +1.5 volt to 13.5, and charge at 15 volts which will boil a battery dry, and kill it.

You need to check for voltage drop in ground side of ignition circuits, and plus side as well. Ground side should show no voltage drop, and plus side no more than a total of 0.3 v.

Corrosion at any connection, bad conductors, loose connections, and worn ignition switch adds resistance to circuit which causes drop in voltage. There will be a small voltage drop at each of the above that all add together to make one large resistance. You need to sniff out, and eliminate as much of this age related resistance as possible by cleaning, tightening, and replacing conductors as needed.
Click to expand...

Well, I said several batteries have been installed, but I didn't R2 the batteries for funsies...it was because they were cooked and no longer could start the car. Needless to say, I don't fancy buying batteries...they're a little pricey. And I had to replace a total of three batteries in one week including other vehicles. My Scamp killed one, my F150 was due for replacement, and my better half cratered the one in her Bimmer.

Not that you needed or cared to know about all that ;)....anyway:

I checked the voltages at the VR (blue wire), at the alternator (blue wire, and charge wire) and at the battery.

@ VR = 14.5V
@ alt (sense) = 14.2V~14.5V
@ alt (charge) = 15.1V~15.4V

Also checked resistance from VR to nearby chassis ground, at (-) battery terminal, and battery (-) to chassis ground. Resistance from VR to ground was < 1 ohm, VR chassis battery (-) was ~40 ohms, batttery (-) to same chassis ground was ~40 ohms.

Another item of possible interest: Before I did the Magnum engine swap, I used a Powermaster 75A alternator, with the same wiring, same regulator (same type anyway), and same battery (before it cooked) and my volts were never above 14.2V at the battery. If you're wondering why I swapped back to a standard alternator, the PM housing was too big to fit against the heads on the Magnum, and of course, you can't reclock the housing. So, that leads me to a logical question: could the alternator itself be suspect of overcharging due to wrong internal components?
 
if your Alt has a sense wire then it must have an internal regulator... thus you should not even have a mopar voltage regulator at all...
 
moparlover said:
if your Alt has a sense wire then it must have an internal regulator... thus you should not even have a mopar voltage regulator at all...
Click to expand...

Lemme amend/clarify that: What I mistakenly referred to as a "sense" wire, is the 12V input to the non-IR standard Mopar type alternator...the blue wire...better?

I couldn't think of what else to call is since there's a field, a charge, and a blue wire....
 
If your alternator is truly outputing 15+ volts it is overcharging. Should be in the 13.5 range.
 
try cleaning your bulkhead connector on both the male and female connectors. that fixed my overcharging problems.
 
63dartman said:
If your alternator is truly outputing 15+ volts it is overcharging. Should be in the 13.5 range.
Click to expand...

Yup...it is...anywhere from 15V~15.5V...cooks a battery in a matter of a couple weeks. Measured at the charge wire, and at the terminals, and shows on my voltmeter.
 
jimjimjimmy said:
try cleaning your bulkhead connector on both the male and female connectors. that fixed my overcharging problems.
Click to expand...

Thank you! I'll try that tonite after I get off work...sometimes swing shift is no bueno for working on a car. And the cold won't help much. While I'm thinking about it, how bad was yours?
 
I had he same deal last summer on my duster stock reman 76 alternator and it ended up being a bad alternator the diodes some how failed causeing the hi volts. I flip floped the field wires and it worked normal for a few miles then just quit charging at all. So yes it could be the alternator.
 
Sounds like your VR and alternator is working perfectly. I measure 14.3 V at the cigarette lighter in most of my cars when the engine is running and 12.6 V with engine off. Yours is controlling 14.4 V (relative to its case?) for the voltage it senses. It does not know the voltage at the big stud on the alternator. It just makes it higher or lower (via the field) until it gets the 14.5 V it wants at its sense lead (a proportional feedback controller). I am talking about a factory Mopar regulator, either the older 1-field wire or later 2-field wire type.

Your problem is in the connectors and harness. This is a typical problem and you can find many posts. You shouldn't have any appreciable (>0.2 V ) drops in the path from the alternator output to all loads in the cabin (measure in fuse box). There is a ~0.75 V drop across the ammeter at full scale (~50 A) in the final run to the battery. The bulkhead connector, key switch, and "fused junction" in the dash harness are the typical culprits. The 40 ohm from VR case to BATT- sounds way too high. Sometimes that is a bad touching of the probes. Better to measure the voltage drop with engine running. Verify that BATT-, frame, and engine are all well connected.

Your batteries probably weren't ruined. Over-charging just electrolyses the water into H2 and O2, so you just need to add distilled water back. Maybe if it gets too low, you can "sulfate" the plates permanently. Sorry, not a battery expert.
 
I'm not using the ammeter; I bypassed that circuit several years ago and used a 8ga wire directly from the post on the alternator to the battery side of the starter relay. I understand what you're saying about the voltage drop-I'll start looking for those when I get the chance...probably have to wait till this weekend as the weather is not nice right now.

I'll also check the connection between the battery and the chassis ground...the cable assembly is only a couple years old, so I know it's not bad; just probably gotta clean the mounting holes and use some new hardware.

The batteries I changed out were done for...when you "boil" all the hydrogen out of the acid, it doesn't really hold voltage too well, and in my case wouldn't even turn the engine over.
 
Why not just take the alternator out of the circuit and test the output? If It is putting out 15+ volts then you know where your problem is. I am just asking why not? Does the alternator need the circuit to produce an output? Either way, good luck. I know electrical gremlins can get to you.
 
I thought about that, if I can't find a voltage drop in my harness somewhere, then I'll give it a try...the first thing I'd say for why not is simply because a new alternator isn't free, so I wanna make sure it's not the alternator before I drop more money.
 
i had about 4 volts at the coil
... polished all my bulkhead connections,coil voltage went to about 9 volts
and battery went from 15.2v to about 13.5v running
i did fry one battery before i found the problem...what a mess.
 
Thanks for the all the feedback fellas...guess I'll be cleaning some bulkhead terminals in the coming days and look for voltage loss in the ignition switch or in a couple other circuits.
 
OK, so I cleaned the bulkhead connectors and checked voltages. Lemme know if any of this sounds not quite right...

At the switch side of the ignition switch, I'm reading 14.7V steady.
At the bulkhead connector, blue/white wire 14.7V,
at the ballast resistor, 14.5V.
Voltage at the excite wire at the alternator 14.5-14.6V.
Voltage at different points in the fuse box, 14.7-15.1V

I still show 40 ohms resistance between the (-) battery terminal and any chassis ground, but I only have factory style reproduction battery cables. I might put in a bonding strap between the engine block and the firewall, but I don't know how much good that will do...worth a shot though.
 
The voltage readings sound normal to me, with the engine running. I assume "excite wire" means the +12 V terminal of your "2 field terminal" alternator, which probably means your car is ~1972+ (didn't tell us). As I said, better to measure the voltage drop from BATT- to frame w/ engine running. 40 ohm sounds high, but much harder to measure resistance accurately.

A photo of your battery cable would help. In my cars, the BATT- cable goes to the engine block and nowhere else. Another braided cable goes from the engine block to the firewall. Can never have enough ground connections and maybe run a few new ground wires from the case of the Vreg, starter relay, and such to a common ground point if you don't trust a rusty sheet metal screw like the factory did.
 
BillGrissom said:
The voltage readings sound normal to me, with the engine running. I assume "excite wire" means the +12 V terminal of your "2 field terminal" alternator, which probably means your car is ~1972+ (didn't tell us). As I said, better to measure the voltage drop from BATT- to frame w/ engine running. 40 ohm sounds high, but much harder to measure resistance accurately.

A photo of your battery cable would help. In my cars, the BATT- cable goes to the engine block and nowhere else. Another braided cable goes from the engine block to the firewall. Can never have enough ground connections and maybe run a few new ground wires from the case of the Vreg, starter relay, and such to a common ground point if you don't trust a rusty sheet metal screw like the factory did.
Click to expand...

I agree with the grounds. The regulator must have a bad ground. grab a jumper wire with alligator clips and connect directly to battery ground terminal and the regulator housing. See what you have for readings after. I would also make sure your alternator has a good ground too. Remember the alt. only grounds through the bracket. if there is any bit of corrosion between the alt. and the bracket it could cause a bad ground.
 
Yes, it's a'72, and there is a negative to chassis wire in the battery cable...the one to the starter is a 0 gage, and the chassis one looks to be a 10 gage.

I'll check the voltage from battery to chassis ground when I get home from work...wasn't thinking about that one.
 
OK, tried the following to no effect:

Replaced Alternator: still puts out 15.4V at the post still shows 14.4-14.5V at the excite wire

Attached chassis to engine ground-no change anywhere

Checked resistance from VR to chassis-2.8 ohms

Jumping VR housing to battery had no effect

Cleaned all ground connections...if anything, my voltage went up!

Any other ideas? Should I find a way to jump the alternator charge wire over to the ignition wire to induce the volts to over 14.5V?
 
You must log in or register to reply here.
-

Back
Top