12v Lighter outputing ~27v

[orbitron3000]

Ok, interesting problem. The cigar lighter, which i thought usually outputted between 12 and 24v, has decided to be an overachiever and put out around 27ish volts...which has fried two chargers that I plugged into it thinking the lighter itself was dead.

Why would it suddenly put out enough volts to fry peripherals, and how can I stop it? Haven't blown the fuse by plugging things in.

[David T]

The only way you could see over 14 volts is if the alternator is badly misbehaving. That means the WHOLE electrical system is overvoltage. Your lights must be burning pretty brightly! Verify your ground point and your meter scale and measure it again.
David Teitelbaum

[orbitron3000]

The only way you could see over 14 volts is if the alternator is badly misbehaving. That means the WHOLE electrical system is overvoltage. Your lights must be burning pretty brightly! Verify your ground point and your meter scale and measure it again.
David Teitelbaum

Do you mean 24v?

For reference, when I checked, I used the ground wire for the Cigar Lighter and the two purple for the positive when I checked with the multimeter. It was consistently over 24v.

[David T]

Check the voltage right at the battery and at the alternator. Use the battery negative terminal for your ground when checking at the battery and at the lighter outlet. Any voltage over 14.5 and you are risking all of the sensitive components in the electrical system. If you have the motor running and the battery is not connected it is possible to overvoltage the system. The battery is a large "sink" or load that holds the voltage down. Without it the regulator in the alternator can't control the output of the alternator.
David Teitelbaum

[orbitron3000]

Didn't know the motor could run without the battery connected. If I do get voltage over 14.5, what could be the culprit?

Ryan
#5780

[Ron]

Like David said, connection at the battrery (intermitten?) , bad regulator or you have done something to fry the meter...

[DMC5180]

Pulling the positive off the battery was an old school way verify your alternator was working. The coil needs voltage for the engine to run. Without the battery it has to come from a working alt/gen. Btw: you would only pull battery terminal for a second or two because of potentially damaging things. Older cars did not have computers like nowadays, hence I would avoid doing this on a modern vehicle.

Check voltage at the lighter so the engine running. If you see high voltage with the engine running it is likely the regulator in the alternator is toast. Time for new alternator.

[orbitron3000]

Pulling the positive off the battery was an old school way verify your alternator was working. The coil needs voltage for the engine to run. Without the battery it has to come from a working alt/gen. Btw: you would only pull battery terminal for a second or two because of potentially damaging things. Older cars did not have computers like nowadays, hence I would avoid doing this on a modern vehicle.

Check voltage at the lighter so the engine running. If you see high voltage with the engine running it is likely the regulator in the alternator is toast. Time for new alternator.

Do you mean pulling the positive off the battery while the engine is running? I usually remove the positive terminal from the battery while the engine is off as a means of disconnecting the battery, but i've never tried to unplug the battery while the engine is running.

[Ron]

At this point I would not run the engine. Take your meter to a different good running car and see what the voltage is right off of the battery with it shut off...it should be around 12 volts. If not your meter is bad. If OK, check the D battery w/ engine off. If the voltage is around 12V start it and see if it goes above 14.2 V. If so your alternator is bad (the regulator is shot) OR you have miswired it (depending on what alternator you have it's easy to do). You can unplug some types and they will quit charging.
A loose batt cable (or pulling it off, as said) can blow the regulator.

EDIT: 14.2 might be too low of a check depending on the alternator but 16 or 17 is definitely to high.

[Bitsyncmaster]

Never disconnect the battery with the engine running.

[orbitron3000]

This may seem like a bit of a dumb question, but disconnecting only the red (positive) terminal from the battery while working with the electronics couldn't have caused this, right?

Ryan
#5780

[Ron]

This may seem like a bit of a dumb question, but disconnecting only the red (positive) terminal from the battery while working with the electronics couldn't have caused this, right?

Ryan
#5780If the key was off no problem, key on possible problem, but not likely, Engine running ASKING FOR IT!

[orbitron3000]

If the key was off no problem, key on possible problem, but not likely, Engine running ASKING FOR IT!

Good. The key was never in the on position let alone in the ignition whenever I disconnected the battery.

In other news, I used my multimeter on another car's battery and it read 28v just like the Delorean battery. Guess the meter is shot.

Ryan
#5780

[TTait]

Did you double check the meter? is it possible you had it set to AC voltage or something?

What does the meter read when you shut off the car?

What does the voltmeter in your dash show?

did you use the ~ symbol to mean approximately, or does it show up on the meter?

~ is the symbol on the meter that indicates AC voltage, not DC.

[orbitron3000]

Did you double check the meter? is it possible you had it set to AC voltage or something?

What does the meter read when you shut off the car?

What does the voltmeter in your dash show?

Definitely have it on DC (V~ on the meter) and I've recently just been testing the battery completely disconnected from the car. From what I remember from the dash's volts meter, it stays constant at 13v

Ryan
#5780

[Citizen]

Definitely could be the meter itself is bad.

At first, I couldn't believe a digital VOM could actually go bad (except for a low/dead battery), but it happened. When I was getting 18-19 volts at my fuel pump, someone on this forum said to use a second VOM to verify the first. Sure enough, the second meter should correct voltage. Threw the first one away (it was one of those cheap $5 ones from Harbor Freight).

Thomas

...

[orbitron3000]

Well I'm using a cheapo analog voltimeter from home depot...probably not helping the cause...

Ryan
#5780

[orbitron3000]

So I just got back from home depot where I was surprised to find that what I thought was the symbol for AC (~) and the symbol or DC (---)...on other multimeters...were switched. Apparently, the documentation with the $5 multimeter got AC and DC backwards...

Just tested the battery...13v

[Bitsyncmaster]

As long as the engine is not running, disconnecting the battery even with the key in and on should not cause damage. It's a better practice to have things turned off (key to off) so electronics don't see the battery wire making and breaking the connection many times. It also stops sparks around the battery.

The battery is what limits the alternator output voltage because it acts like a bit capacitor that loads the voltage when it goes higher than 12.6 volts.

With the engine running and battery disconnected I bet the electrical system is seeing a lot of voltage spikes above 20 volts.

[orbitron3000]

Well it seems that everything is in order here. Battery reads 13ish volts, and the measured the cigar lighter which also came back at about 12 volts. I'm guessing that the periphs just shorted. The lighter still works as a lighter.

Ryan
#5780

[TTait]

I thought that might be it... In the future remember that alternating current on a scope or similar looks like a sine wave (remember biorhythms - if you're that old?). That's why the symbol looks like a sine wave (~).

I'm told that the lighter is not sized exactly right for modern plugs - somebody (Farrar, Ozzie?) found this replacement that is supposed to fit and work perfectly...

http://www.gowesty.com/ec_view_details.php?id=4471&category_id=4482&category_parent_id=

and detailed here:

http://dmctalk.org/showthread.php?1739-Custom-Lighter-LEDs/page2&highlight=gowesty