Overcharging Battery ?

[Platonic Solid]

Since I’m still working on the car, I take it out around the neighborhood once in a while to keep everything functional. Sometimes I just let it run in the driveway for 5-10 minutes. Lately I’ve had to charge the battery to get it to start. The other day I tried starting it and absolutely nothing worked when I turned the key. I put the battery on the charger and it would not take a charge, so I went to NAPA and purchased a new battery.

After installing the new battery, I put it on the charger just to make sure it was fully charged, and to my surprise it wasn’t. I started the car and pulled it outside (as I had other garage projects that needed doing) and let it run 5-10 minutes. When I went to pull it back in (8 hours later), absolutely nothing worked again when I turned the key. So I charged the new battery enough to get it started and pull it into the garage.

I disconnected the positive cable and charged the battery overnight. I checked the voltage this morning and it had charged to 13.6V (though the chargers “charge-complete light” never came on), which settled to 13.1V after sitting for 2 hours (charger removed and positive cable still disconnected.

I connected the positive cable and the voltage dropped from 13.1V to 12.75V in 1/2 hour. 2 hours later the voltage seems to have settled at 12.7V. I started the car to check the charging voltage and it’s charging at 18.12V!

Is 18.12V excessive or damaging to the battery? I do see one connection on the alternator that looks like it could use to be re-spliced (I can see tiny sparks from a couple frayed wires when I wiggle it). I’ll repair the wire, but I don’t suspect that will change anything. Assuming 18.12V is a bad thing, where should I start trouble-shooting?

 

[67coupe351w]

Voltage Regulator?

I'ts not very accurate to check the voltage of a battery with a multimeter, if thats how you were testing it. It needs to be load tested for an accurate reading.

 

[66Runt]

18V is a little on the high side!

You are right, 18V is too high. Your regulator should shut off current flow to the field windings at about 15V.

Also like that you are going to fix the wiring first. That is a very good move.

As suggested above, a load test or a capacitence test would be a really good idea as well.

If after repairing the wiring and checking the battery you still find it charging at above 15V, I would suggest inspecting and/or replacing the regulator.

Scott

 

[pabear89]

Is 18.12V excessive or damaging to the battery? I do see one connection on the alternator that looks like it could use to be re-spliced (I can see tiny sparks from a couple frayed wires when I wiggle it). I’ll repair the wire, but I don’t suspect that will change anything. Assuming 18.12V is a bad thing, where should I start trouble-shooting?

You just did,

The poor connection is prob the one that controls the output of the alt.
and could be the drain on the batt.

PB

 

[D.Hearne]

Those old external voltage regulators were famous for sticking and overchaging the battery. Go to your local parts house and buy a new solid state regulator.

 

[Platonic Solid]

Those old external voltage regulators were famous for sticking and overchaging the battery. Go to your local parts house and buy a new solid state regulator.

Are the typical regulators offered by classic Mustang part resellers "solid state" or should I be looking at later model Ford regulators?

 

[Max Power]

14.2 is what both my classic Fords read at the battery while running. Even 15v sounds a little high.

Regulators are cheap. Fix the wires, buy a solid state one and you will probably be good to go.

 

[Edbert]

I thought an alternator would only put out as much power as was "requested" (wrong term I know, that's why I quoted it), as opposed to a generator that has a pretty constant output.

So it is the voltage regulator responsible for this request? Are the one-wire alternators able to otherwise sense the load?

 

[Max Power]

"Requested" is an interesting way to think of it, but I do not think it is true. Alernator output varies with rpm, and the regulator flat out limits it so as not to cook the battery. The regulator makes sure that the same alternator that charges adequately at idle also won't overcharge at speed.

One wire alternators simply have the regulator built into or inside the alternator.

 

[Tim65GT]

Are the typical regulators offered by classic Mustang part resellers "solid state" or should I be looking at later model Ford regulators?

There are two basic types. The original early type has mechanical contacts and is taller. I'm not sure what year Ford stopped using these. The replacement type is smaller and is solid state It has no moving parts to stick or wear out. Although, like anything it can still go bad.

View attachment 506872

View attachment 506873

Both are available from a typical Mustang parts supplier, but you only want the big mechanical original type if you want to keep everything original. If you want dependability go with the smaller solid state.

12.8 Volts is the normal reading of a fully charged battery. It will read higher right after being charged, but that is just a surface charge. If you crank the motor a tad without starting it, that usually gets rid of the surface charge.

A normal alternator output should be between 13.5 and 14 volts give or take a half of volt. It should not drop below 13 volts even with all your accessories on. If it does, you may be stranded on a cold dark rainy night in traffic. (Head lamps, blower, wipers, and brake lights) It would be best to upgrade to a higher amp output.

18 volts is definitely high. It will boil the acid out of the battery and subsequently kill the battery and corrode the metal around it if not corrected.

Definitely repair or replace all wires and connectors that look flaky.

 

[D.Hearne]

They make the solid state regualtors now that look like the older ones. If I recall correctly I bought one at the local parts house a couple years back.

 

[Platonic Solid]

OK, so the regulator that is in there must be solid-state as it is the slimmer version (thanks Tim). I haven't touched any of the wiring on this car since I purchased it, so I'll go through and clean (and replace as necessary) all the charging circuit connections. This has obviously been done several times by previous owners over the years as many of the connectors are aftermarket replacement crimp-ons. If Painless made a replacement harness for 73s, I'd go for it, but it looks like I'm on my own on this one. There seems to be quite a few more wires on this car than my 72 and 71. Plus, just to make thing even messier, there's an unknown brand of electronic ignition in there.

 

[66newbie]

"Requested" is an interesting way to think of it, but I do not think it is true. Alernator output varies with rpm, and the regulator flat out limits it so as not to cook the battery. The regulator makes sure that the same alternator that charges adequately at idle also won't overcharge at speed.

One wire alternators simply have the regulator built into or inside the alternator.

I am still learning about my car so topics like this help alot. When you say "overcharge the battery", would the battery get hot to the touch ? Or would the only symptoms be corrosion etc.

 

[Max Power]

I am still learning about my car so topics like this help alot. When you say "overcharge the battery", would the battery get hot to the touch ? Or would the only symptoms be corrosion etc.

No, when a battery is being overcharged, the elecrolite in the battery starts to boil and vaporize. After a while, there is no liquid in the battery and the plates destruct. It's not the same kind of boiling as a pot on the stove.

 

[Platonic Solid]

Anyone know where I can get a new alternator harness for a 73? Seems there are repros. available for all the years except 73

Also, I believe this item is typical of most classic Mustangs, I can't seem to find a new Voltage Regulator connector.
.

 

[Edbert]

Also, I believe this item is typical of most classic Mustangs, I can't seem to find a new Voltage Regulator connector.
.

Sounds like a good time or at least a good reason to get a 1-wire alternator (internally regulated).

 

[Platonic Solid]

Sounds like a good time or at least a good reason to get a 1-wire alternator (internally regulated).

Something like this?

 

[Edbert]

Exactly, I put a 140a Powermaster on mine, probably overkill even with all the elctrics i added though.

 

[Kriek]

A normal alternator output should be between 13.5 and 14 volts give or take a half of volt. It should not drop below 13 volts even with all your accessories on. If it does, you may be stranded on a cold dark rainy night in traffic. (Head lamps, blower, wipers, and brake lights) It would be best to upgrade to a higher amp output.

I can vouch for that. Monday night was horrible. The car died and wouldn’t crank over, just that faint clicking sound. I got the jumper cables out and managed to get a jump from my girlfriend. It was 11 PM at night, Dallas in the pouring rain, so I "thought" I couldn’t drive without my headlamps and wipers, which evidently sucked the life out of the battery.

At the next traffic stoplight, it died again. I tried to start it up, nothing. This continued, several times, same exact way. Finally I drove the rest of the way home with no headlamps, no wipers, at 20 MPH, with my girlfriend trailing behind me with her flashers running.

The battery still wont keep its charge from a jump, is the alternator even working? Is the regulator overcharging? Would you recommend a solid-state regulator or an internally regulated alternator for someone on a tight budget? Is either easier to install? I dont mean to hijack the thread, but it sounded like a very similar problem.

Thanks again,

- Jon