Voltage/Alt gauge

[Craigerz]

Anyone care to explain what this thing actually tells you? Is it how charged your battery is, how much the alternator is charging (and if so wtf does that mean), where should it be, why does it move at all? Not having a problem just don’t have a use for a gauge I don’t even know what does.

 

[poker4me007]

This is taken out of my owners manual:

"(Charging system gauge This gauge shows the battery voltage when the ignition key is in the ON position. If the pointer moves and stays outside of the normal range, have the vehicle’s electrical system checked as soon as safely possible.)"

I guess if it stays between H and L your all set. Which means nothing unless the idiot light comes on.

 

[imp]

Anyone care to explain what this thing actually tells you? Is it how charged your battery is, how much the alternator is charging (and if so wtf does that mean), where should it be, why does it move at all? Not having a problem just don’t have a use for a gauge I don’t even know what does.

@Craigerz
My '96 wiring diagrams show both a voltmeter and an idiot light. If the voltmeter is working, note it's position when the key is turned ON. Crank engine, it should drop during cranking, and after starting it should rest slightly higher up showing the battery is being charged to replace the energy used out of it to start the engine.

The indicator light should be out when the engine is running. If it is ON the alternator is not supplying the power to run the engine, and it is being supplied by the battery, a situation which only happens when the alternator is faulty.

Again: The battery is there for ONE PURPOSE ONLY: to start the engine. Once running, the alternator does all the electrical work.

Now, why did you ask the question? Problems? imp

 

[1998Exp]

@Craigerz
....
Again: The battery is there for ONE PURPOSE ONLY: to start the engine. Once running, the alternator does all the electrical work.
....

Close, but not completely true. Do not disconnect the battery when the engine is running.
From Wikipedia:
... As well as starting the engine, an SLI battery supplies the extra power necessary when the vehicle's electrical requirements exceed the supply from the charging system. It is also a stabilizer, evening out potentially damaging voltage spikes...

 

[imp]

Close, but not completely true. Do not disconnect the battery when the engine is running.
From Wikipedia:
... As well as starting the engine, an SLI battery supplies the extra power necessary when the vehicle's electrical requirements exceed the supply from the charging system. It is also a stabilizer, evening out potentially damaging voltage spikes...

@1998Exp

Well, I don't care to get into a pissing match, but will take issue with the second part of your quote. Look at the below quote taken from your link:
"In electrical engineering, spikes are fast, short duration electrical transients in voltage (voltage spikes), current (current spikes), or transferred energy (energy spikes) in an electrical circuit.

Fast, short duration electrical transients (overvoltages) in the electric potential of a circuit are typically caused by

• Lightning strikes
• Power outages
• Tripped circuit breakers
• Short circuits
• Power transitions in other large equipment on the same power line
• Malfunctions caused by the power company
• Electromagnetic pulses (EMP) with electromagnetic energy distributed typically up to the 100 kHz and 1 MHz frequency range.
• Inductive spikes"

Not a single one of the "overvoltages" listed can or does exist in a vehicle. Lightning strikes, pulses, spikes,...etc. Get REAL!

No, I never recommended disconnecting the battery, that's not a good idea. I meant that, to understand the battery/alternator combination's function, one must see that the alternator "runs the car" once the engine is started. The other hokum in the wiki is true in that the battery does act as a "stabilizer", though such is the case under perfect operating conditions. But, what about the "real world" everyday? Pick a ****load of vehicles parked in a parking lot. How many have perfect conditions existing between their batteries and alternators? Some have very old batteries, some are brand new, some are on their last legs. Every single example defies the wiki comparison.

Or, I'm wrong. Your call. My engine starts and runs every time. imp

 

[1998Exp]

@1998Exp

Well, I don't care to get into a pissing match, but will take issue with the second part of your quote. Look at the below quote taken from your link:
"In electrical engineering, spikes are fast, short duration electrical transients in voltage (voltage spikes), current (current spikes), or transferred energy (energy spikes) in an electrical circuit.

Fast, short duration electrical transients (overvoltages) in the electric potential of a circuit are typically caused by

• Lightning strikes
• Power outages
• Tripped circuit breakers
• Short circuits
• Power transitions in other large equipment on the same power line
• Malfunctions caused by the power company
• Electromagnetic pulses (EMP) with electromagnetic energy distributed typically up to the 100 kHz and 1 MHz frequency range.
• Inductive spikes"

Not a single one of the "overvoltages" listed can or does exist in a vehicle. Lightning strikes, pulses, spikes,...etc. Get REAL!

No, I never recommended disconnecting the battery, that's not a good idea. I meant that, to understand the battery/alternator combination's function, one must see that the alternator "runs the car" once the engine is started. The other hokum in the wiki is true in that the battery does act as a "stabilizer", though such is the case under perfect operating conditions. But, what about the "real world" everyday? Pick a ****load of vehicles parked in a parking lot. How many have perfect conditions existing between their batteries and alternators? Some have very old batteries, some are brand new, some are on their last legs. Every single example defies the wiki comparison.

Or, I'm wrong. Your call. My engine starts and runs every time. imp

Wikipedia is not the Holy Grail - just what someone, perhaps not all that knowledgeable, wrote.
There is plenty of nasty transients in the automotive power system, with all manner of loads turning on, and mainly dumping stored energy when rapidly turning off.
Seems to me that because there is a lot of inductance in the armature, the regulator bandwidth is quite low, but I don't have the numbers. Perhaps more importantly, you need a cycle or two of the alternator output to see any effect of the excitation on the rectified result, so probably, at 2400 rpm (40 Hz), about 120-240 Hz (because it's a three-phase device and the alternator turns about twice as fast as the engine). Any transient significantly faster than that the alternator won't handle. Will the battery? I would think it will easily go into the 10 KHz range or more. Battery internal resistance is something on the order of 25mOhm, so it's limited mostly by the wiring - I would assume in the usec range. If, as you said, the wiring is degraded, all bets are off, but this will also affect DC and someone will probably notice that his headlights are very dim...
Oh well...

 

[koda2000]

Humph, starting to sound like a "pissing contest" to me...

Ever wonder why our "gauges" for TEMP, OIL PRESSURE and VOLTS don't have any numbers on them? It's because they are not gauges at all, they are idiot lights with needles. Let's call them displays. Real gauges have numbers. Auto manufactures use these displays because most people would freak-out if they saw how the needles in real gauges moving around under normal different operating conditions.

Under "normal" circumstances all three display needles reside in approximately in the center of their sweeps with the engine running and at normal operating temperature, though you might notice some fluctuation on the TEMP and VOLT displays if you stare at them enough. Especially the TEMP gauge if you have a cooling system problem (low coolant, malfunctioning thermostat, bad water pump).

The OIL PRESSURE display is controlled by a switch, not a sender. You either have a minimum of 5 PSI of oil pressure or you have none. If you have no oil pressure the needle doesn't come up at all and the "CHECK GAGES" light comes on. The CHECK GAGES light seems to be connected to the position of the display needle (or perhaps the pressure switch) because you can have good oil pressure and still have the display showing no oil pressure and the CHECK GAGES light on. I've found that several of my Explorers, regardless of engine, will sometimes indicate no oil pressure when I know I do have good oil pressure. This is always at cold start (when oil pressure is actually at its highest) and the needle will eventually pop up as the engine warms. I blame this on a sticking oil pressure switch, which is a bit of a PITA to replace due to its location on the engine (behind the power steering pump). Sometimes the oil pressure switch will pop the display needle up and down so quickly that it will get the needle stuck under it's peg. I've experienced this on 2 Explorers. Note: If you have a SOHC V6 engine this may indicate timing chain tensioner failure and is caused by broken pieces of plastic blocking the oil pump's pickup.

The TEMP display functions w/in a range of "normal" coolant temperature. I don't recall the exact temp range, but around 167-205 degrees will put the needle in the approx center of the display. Below 167 degrees the needle remains in the lower portion or bottom of its sweep, above 205 degrees it will go to full HOT and the "CHECK GAGES" light will come on.

The VOLT display provides an indication of the state of charge of your battery, which is also an indication of whether your alternator is charging the battery. If your alternator quits working the display's needle will indicate a LOW voltage at the battery and the "CHECK GAGES" (maybe its a BATT or CHG light?) will come on. Your engine will not run for very long on just its battery and, in my experience, our trucks don't like running on low voltage. If I want to check the performance of my charging system I use my VOM at the battery and I expect to see around 13.6-14 volts with the engine running.

All-in-all idiot lights would be just as good (probably better) than these 3 gauge-like displays. People (including me) don't monitor these displays closely and don't react to them unless the light comes on telling them to CHECK GAGES. At that point I look at the displays to see what the issue appears to be.

BTW - I was taught to never remove and replace the positive battery cable with the engine running as a means of checking the alternator. I was told that it might cause a voltage spike which might damage the vehicles electronics. Whether is is true or not IDK, but I figure better safe than sorry and I consider this a red-neck way of checking your alternator. If you want to know if your alternator/charging system is working properly use a VOM. You can buy a cheap VOM for around $10 and it's a good tool to have. I paid around $90 for mine and I use it all the time. I'd also like to have a Power Probe, but I can't justify the cost at this point in my life.

Also, your battery is not just there to start your engine, though it is its primary function. A battery is an energy storage device. Vehicles run off their battery once the engine is running, but the alternator's voltage regulator monitors battery voltage and kicks in the alternator to recharge the battery as necessary. If an alternator runs at full capacity all the time because of a bad battery it can cause the death of the alternator.

 

[poker4me007]

Koda2000 Very well said.
That's a way better explanation than my owners manual.

 

[Craigerz]

So....

If the gauge moves and my truck starts and runs it’s fine. If the gauge doesn’t move and my truck starts and runs it’s fine.

If the gauge moves and my truck doesn’t start something wrong. If the gauge doesn’t move and my truck doesn’t start something wrong.

Guess that solves that

 

[imp]

Wikipedia is not the Holy Grail - just what someone, perhaps not all that knowledgeable, wrote.
There is plenty of nasty transients in the automotive power system, with all manner of loads turning on, and mainly dumping stored energy when rapidly turning off.
Seems to me that because there is a lot of inductance in the armature, the regulator bandwidth is quite low, but I don't have the numbers. Perhaps more importantly, you need a cycle or two of the alternator output to see any effect of the excitation on the rectified result, so probably, at 2400 rpm (40 Hz), about 120-240 Hz (because it's a three-phase device and the alternator turns about twice as fast as the engine). Any transient significantly faster than that the alternator won't handle. Will the battery? I would think it will easily go into the 10 KHz range or more. Battery internal resistance is something on the order of 25mOhm, so it's limited mostly by the wiring - I would assume in the usec range. If, as you said, the wiring is degraded, all bets are off, but this will also affect DC and someone will probably notice that his headlights are very dim...
Oh well...

@1998Exp

All important points you make. Perhaps we have hopefully thrashed this to completion worthy of cancelling a pissing match!

Here's how I see things in forums concerning things quite technical. First, it's not a Physics class; few will understand or appreciate an analysis of transients in our circuitry. Transients to most folks are bums.

I like to try to approach problem solving in the simplest way I can see to present it. I think most guys see all those wires and cables as representing a nightmare. I try to get an understanding of the basic circuits out there, SERIES and PARALLEL, establish the picture in minds that everything electrical in our beloved vehicle is connected in parallel, including the battery and alternator. If thought of as voltage sources connected in parallel, with two conductors leading away from them, it seems clearer that from those two wires are all the places needing juice getting it, with switches, sensors, any variety of mysterious devices doing something with the electricity coming from those two voltage sources.

Now, the alternator presented as the main source of energy for everything except the starter, it can push current back through the battery, they're in PARALLEL with each other, at the same time "feeding" the rest of the systems demanding juice.

I liked especially your description of the battery's "internal resistance". Ever thought of doing this? Let's say during cranking, the battery is supplying 300 amperes, and it's output voltage drops to 8 volts. The imaginary internal resistance is 4 volts divided by 300 amps, or 1.3 Milliohms. Power delivered to starter is 8 X 300 = 2400 Watts. Is that a lot of power? Yes. But only for a short time, a number of seconds usually. Still, a gob of energy withdrawn from that battery; do it over and over with a dead alternator, soon the battery will also be dead. I feel these concepts help with analyzing easier than getting in real deeply.

Remember, the baseword in "analyze" is ****.........imp

 

[imp]

Humph, starting to sound like a "pissing contest" to me...

BTW - I was taught to never remove and replace the positive battery cable with the engine running as a means of checking the alternator. I was told that it might cause a voltage spike which might damage the vehicles electronics. Whether is is true or not IDK, but I figure better safe than sorry and I consider this a red-neck way of checking your alternator. If you want to know if your alternator/charging system is working properly use a VOM. You can buy a cheap VOM for around $10 and it's a good tool to have. I paid around $90 for mine and I use it all the time. I'd also like to have a Power Probe, but I can't justify the cost at this point in my life. A-OK on this one!

Also, your battery is not just there to start your engine, though it is its primary function. This could be debated. Got a gasoline-powered lawnmower, with a pull-cord? Where is it's battery? Remember those movies showing a guy struggling to crank his engine by hand, very long ago? He had no battery.

A battery is an energy storage device. Vehicles run off their battery once the engine is running, I don't buy this one either, but it's really a moot point for most everyone. The voltage regulation circuitry maintains alternator output at slightly higher voltage level than the battery's output voltage except if it's overloaded, defective, or turning too slowly. But no point in arguing the matter.....my bladder's empty!

but the alternator's voltage regulator monitors battery voltage and kicks in the alternator to recharge the battery as necessary. If an alternator runs at full capacity all the time because of a bad battery it can cause the death of the alternator.

@koda2000
Here's a quick little battery story. When I lived in very rural Missouri, the power went out very often. Bought us a generator, ran it in the back yard, had a 240-volt outlet out there for my welder, connected the generator to that outlet, therefore "back-feeding" the house circuitry through the double-pole breaker feeding that outlet. By selectively turning breakers on or off, I could run needed things, like the fridge continuously, but water heater or stove had to be used separately. Important thing was, no "transfer switch", it was imperative to disconnect at the meter out front before starting generator, by turning off the main breaker.

Once, I forgot to do that. What happened? The power company's line to the house represented a big, black, hole, like a dead battery, voltage was zero, generator tried in vain to dump it's output into that hole.........worse than a good alternator trying to recharge a sulfated old dead battery! imp

 

[1998Exp]

@1998Exp

All important points you make. Perhaps we have hopefully thrashed this to completion worthy of cancelling a pissing match!

Here's how I see things in forums concerning things quite technical. First, it's not a Physics class; few will understand or appreciate an analysis of transients in our circuitry. Transients to most folks are bums.

I like to try to approach problem solving in the simplest way I can see to present it. I think most guys see all those wires and cables as representing a nightmare. I try to get an understanding of the basic circuits out there, SERIES and PARALLEL, establish the picture in minds that everything electrical in our beloved vehicle is connected in parallel, including the battery and alternator. If thought of as voltage sources connected in parallel, with two conductors leading away from them, it seems clearer that from those two wires are all the places needing juice getting it, with switches, sensors, any variety of mysterious devices doing something with the electricity coming from those two voltage sources.

Now, the alternator presented as the main source of energy for everything except the starter, it can push current back through the battery, they're in PARALLEL with each other, at the same time "feeding" the rest of the systems demanding juice.

I liked especially your description of the battery's "internal resistance". Ever thought of doing this? Let's say during cranking, the battery is supplying 300 amperes, and it's output voltage drops to 8 volts. The imaginary internal resistance is 4 volts divided by 300 amps, or 1.3 Milliohms. Power delivered to starter is 8 X 300 = 2400 Watts. Is that a lot of power? Yes. But only for a short time, a number of seconds usually. Still, a gob of energy withdrawn from that battery; do it over and over with a dead alternator, soon the battery will also be dead. I feel these concepts help with analyzing easier than getting in real deeply.

Remember, the baseword in "analyze" is ****.........imp

Very nice! Just a minor comment: 4V at 300 Amps is 13 milliohms, not 1.3

 

[1998Exp]

@koda2000
Here's a quick little battery story. When I lived in very rural Missouri, the power went out very often. Bought us a generator, ran it in the back yard, had a 240-volt outlet out there for my welder, connected the generator to that outlet, therefore "back-feeding" the house circuitry through the double-pole breaker feeding that outlet. By selectively turning breakers on or off, I could run needed things, like the fridge continuously, but water heater or stove had to be used separately. Important thing was, no "transfer switch", it was imperative to disconnect at the meter out front before starting generator, by turning off the main breaker.
Once, I forgot to do that. What happened? The power company's line to the house represented a big, black, hole, like a dead battery, voltage was zero, generator tried in vain to dump it's output into that hole.........worse than a good alternator trying to recharge a sulfated old dead battery! imp

Nice story. And a good lesson not to hook a generator to the power line without a transfer switch. The real risk is not damaging your generator, but electrocuting a lineman who is working on a presumably a dead line. They take precautions, but I wouldn't count on those.

 

[imp]

Very nice! Just a minor comment: 4V at 300 Amps is 13 milliohms, not 1.3

@1998Exp

Yeah, yer right! My caculator skipped over a decimal point! imp

 

[imp]

Nice story. And a good lesson not to hook a generator to the power line without a transfer switch. The real risk is not damaging your generator, but electrocuting a lineman who is working on a presumably a dead line. They take precautions, but I wouldn't count on those.

@1998Exp

Very good point! The linemen I've known pretty much invariably throw clamp-on jumpers from the hot conductors to ground. On the "high-lines", they wrap chain around the three legs sometimes, too. The huge transformers driving the grid are known to "ring" a long time after shutting down, putting unexpected voltage on the lines. imp

 

[CDW6212R]

@koda2000
Here's a quick little battery story. When I lived in very rural Missouri, the power went out very often. Bought us a generator, ran it in the back yard, had a 240-volt outlet out there for my welder, connected the generator to that outlet, therefore "back-feeding" the house circuitry through the double-pole breaker feeding that outlet. By selectively turning breakers on or off, I could run needed things, like the fridge continuously, but water heater or stove had to be used separately. Important thing was, no "transfer switch", it was imperative to disconnect at the meter out front before starting generator, by turning off the main breaker.

Once, I forgot to do that. What happened? The power company's line to the house represented a big, black, hole, like a dead battery, voltage was zero, generator tried in vain to dump it's output into that hole.........worse than a good alternator trying to recharge a sulfated old dead battery! imp

Interesting, and good use of a generator.

I have a kitchen next to my garage. When the power goes out and I think it might be out a while, I have an inverter I can use to power my refrigerator and microwave. The refrigerator is on the wall of the garage, and the one circuit breaker feeding it, also feeds one outlet in the garage, and the microwave, and two kitchen outlets. I can trip the one breaker, and feed the refrigerator with a car battery easily, plus cook something if needed. I'd like to move up to a real back up system run b natural gas, but that's a pipe dream right now.

 

[CDW6212R]

The instrument panel in these Explorers are among the best Ford has ever made, for displaying many things well. I like the gauge arrangement, but as noted dummy gauges are not that helpful.

I plan to eventually try to buy digital gauges(I have one water temp so far), take them apart and access the outlet circuits. If that's possible, then I'll bury the gauges in the dash, and feed small LED displays, behind existing gauge faces. I'd love to see the actual voltage, water temp, oil pressure, fuel pressure, maybe tach if it would be more accurate.

 

[imp]

Interesting, and good use of a generator.

I have a kitchen next to my garage. When the power goes out and I think it might be out a while, I have an inverter I can use to power my refrigerator and microwave. The refrigerator is on the wall of the garage, and the one circuit breaker feeding it, also feeds one outlet in the garage, and the microwave, and two kitchen outlets. I can trip the one breaker, and feed the refrigerator with a car battery easily, plus cook something if needed. I'd like to move up to a real back up system run b natural gas, but that's a pipe dream right now.

@CDW6212R
Your dilemma is guided by the frequency (no pun ) of power outages. In MO, we had one several times a month. Mainly due to the fact that we were buried in the heart of Mark Twain Nat'l Forest, 7 million acres of natural habitat. Electric Power had been run down our rural road only as recently as the '50s, the wooden poles were fragile by 1999, when we arrived. We had telephone service as well, but no internet provider. Nearest point a cell picked up signal was 15 miles away, towards town. Big deal. We lived regally, actually, relying on firewood as our chief source of energy. Each Thanksgiving, my wife pulled a perfectly roasted turkey out of our cookstove! I do miss that life of obscurity away from the rat race, but my shoulders quit being able to cut and split firewood. Today, I roam the various forums,........sometimes welcomed, sometimes scorned! imp

 

[Craigerz]

Guess that solves that. Switch will have to be hooked up Monday, my soldering gun takes the weekend off.