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Amps guage on one wire alt

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amxmachine View Drop Down
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Post Options Post Options   Thanks (2) Thanks(2)   Quote amxmachine Quote  Post ReplyReply Direct Link To This Post Posted: Dec/08/2017 at 12:14am
Originally posted by FSJunkie FSJunkie wrote:

Matt's keys to getting along with people in the classic car world (I often have to rims myself of these):

  1. Present your opinion/advice as what has worked best for you, not as the universal truth for everybody and all cars.
  2. Listen politely and think about what somebody is saying when they are presenting you with their opinion/advice. You are not obligated to do/follow what they are saying, but you are obligated to be polite.
  3. If you disagree with somebody, it is best to not say anything. Avoid an argument. Just leave the conversation and continue living your life in a way that disagrees with theirs. 
  4. If you choose to openly disagree with somebody and open an argument, make sure to argue point-to-point using concrete evidence or examples. Remain impersonal. Preferably do not quote them or even mention their name.
  5. NEVER attack that person's age, experience, education, or credibility. Nobody cares about those things. They care about the facts and evidence. Personal attacks are a sign of somebody who knows they are losing an argument and is reaching for whatever they can to stay on top. Don't be that guy.
  6. When somebody disagrees with you on a topic or method, they probably do not mean it as a personal insult or attack even if it sounds like one to you. Ripping off their head because you feel insulted only makes you look like the bigger jerk. 
  7. If somebody attacks you personally or you otherwise feel offended for whatever reason, refrain from counter-attacking. Taking another person's negative attitude upon yourself only makes you into what you hate and slowly turns you into an insecure person like them. Only insecure people feel the need to beat down the people around them. 
  8. Stop caring what other people think of you, your opinions, or your car. What they think doesn't matter. Put a big friggin' rooster comb on the roof of your Chevette if it makes you happy. People will call you nuckin' futs, but don't care. Don't let other people ruin your happiness. They are not important enough to have that kind of power over you. 

Seriously. Topics on cars and politics are so much more pleasant if you keep those in mind. 


I present to you my impersonal opinions and evidence:

Ammeters with a +/0/- scale don't splice into the alternator output wire to measure alternator output current. They splice into the main power feed wire off the battery to measure current either going into or out of the battery from the entire vehicle electrical system. The alternator will keep up with all electrical loads in the vehicle up to the alternator's current rating. The only current going through the ammeter is either going into the battery to charge it (+ reading) or current leaving the battery to power electrical loads the alternator doesn't have sufficient output to handle (- reading). Unless the battery is severely discharged, extreme electrical loads are encountered, or the alternator fails, ammeters will rarely have more than 15A flowing through them. 

Ammeters are hold-overs from the days when cars had third-brush generators that did not regulate themselves. Drivers had to adjust the third brush as needed to provide proper battery charging depending on what electrical loads were switched on and the engine RPM. The easy to read ammeter provided early motorists with a simple "charging or discharging and how fast" indicator for the battery so they could set their generator brush as needed. Ammeters cannot show battery condition or voltage regulator operation however. Because of their potential for carrying high current, ammeters should always be wired with heavy gauge wire and solid connections. 

Voltmeters work fine and provide more information on battery condition and voltage regulator setting than an ammeter can. Unfortunately that makes reading them a little more complex. Failing or defective batteries can cause very strange voltmeter readings as can faulty voltmeter installation. The voltmeter should take its reading as directly off the battery as possible because current flowing through the vehicle's wiring causes IR voltage drop and you don't want the voltmeter to be biased by that. 

Whether you have an ammeter or a voltmeter, a warning light is always a good idea if your charging system has provision for one. A warning light will catch your attention faster than a gauge reading outside of normal would. The light exists to catch your attention with "something is wrong", but the gauge exists to tell you "this is what is wrong". 

Matt should practice what he preaches. On another thread he called people who dressed out thier cars idiots and wierdos. And whats all this useless psyco babble have to do with me wiring an amps guage. You are preaching to people who are at least 60 and older on how to behave. GET A LIFEGeek
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billd View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Dec/08/2017 at 7:26am
Originally posted by bigbad69 bigbad69 wrote:

I think a +/- ammeter is more useful than a voltmeter. An ammeter will tell you something is wrong now. A voltmeter will tell you something went wrong some time ago and now you're battery is discharged. It's kind of like an oil light vs oil gauge. The light tells you you lost pressure, the gauge tells you the pressure is dropping - big difference. However, the shunt style ammeter is definitely safer than the full current type.

Where did that come from? The volt meter reads REAL TIME. This means if you are driving along and the meter was reading 13.7 and suddenly drops to 12 it has the exact same meaning as when the ammeter goes from + to -
How can the volt meter tell of past when it's reading SYSTEM VOLTAGE, alternator output voltage, at all times?
If you don't look at it and then there's a problem and you get in the car and the meter reads 11 volts then yeah it is a past problem but to say a volt meter tells you of something that went wrong some time ago is BS, period. I've lived by volt meters for decades- and when you use them instead of ignore them they'll tell you of a problem instantly like an ammeter but with more detail.
I can give a recent real-live example - mine was reading about 14 and I turned the AC on and it dropped way down - still a bit above 12 but not at the 14 it had been. UNLIKE an ammeter that would have likely still showed a bit of a charge, I knew there was a problem before I parked the car.
Bad connection, voltage drop caused by bad connection. It's like an ammeter would not have given me that sort of information. 
If you see the voltage fluctuate, depending on conditions, you can often go right to the culprit.

So explain how a volt meter tells of problems in the past when it's giving you a constant, real-time reading of the alternator regulated voltage?
What if it was reading 14 then suddenly jumps to 15? Isn't that telling me instantly there's a regulator problem to look at? Would an ammeter tell me that or would it just show a greater amperage reading, a higher plus - that may look normal to some? Why is it that people with ammeters can miss an over-charged or dry battery but with a volt meter they know exactly what voltage is proper and when it's too high?

No way a volt meter tells of past issues when it's REAL-TIME. Drivers only need to look - if it's at correct regulated voltage, all is well. If it's lower, it's not keeping up. If it's higher, you have a connection or regulator issue. (or even a BATTERY issue, depending on how smart you are at reading volt meters!)

I've driven cars with volt meters for decades and I get more info from them than I ever have from an ammeter. And I've always been told by the volt meter of a problem AS it happens. 
But you have to glance at them now and then.

I'd still love an explanation of why a volt meter is telling of problems in the past when it's a current, real-time reading of the charging system state.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Dec/08/2017 at 8:09am
my problem with volt meters is where they are in the system.

You can buy a cheap digital meter that sticks in the cigarette lighter,
but it might read 1/2 a volt or more low compared to something wired directly in.
Even the correctly hard wired gauge would likely read low compared to a reading taken directly from the battery.

So you have to know what the voltages should be under operating conditions for that specific gauge & vehicle.

Best way without rewiring an existing gauge would be to see what the gauge tells you in comparison to an actual battery reading.

But if you hop into an unknown vehicle and the gauge reads 11.5v,
it could mean a big problem,
or a gauge connected a long way from the battery through a bunch of crappy connections.

As far as the personal nature of questions, answers and personal responses on a message board like this,
I understand that there are people who can say "good morning" and it sounds like "I hate you".

There are also people who can say "I hate you" and it sounds like "have a great day".

Add in the fact that it can be impossible at times to read intent in written words,
and the fact that most people have their own type of underlying "crazy" that I try very hard to not let any words typed by others affect my mood or mental health.

It can be very easy, or really tough depending on the circumstances,
but its always a good idea to try to insulate yourself from taking stuff on message boards personally.

The only reason to visit sites like this is to improve our hobby & lives (hopefully).
I mostly just try to keep that in mind when I see stuff that makes my eyes roll or my head twitch lol.

Smiles and well wishes to all that have read this far. Smile
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was Green/green now T/A red w/blk leather

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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Dec/08/2017 at 8:37am
Here's my "logic" behind this volt meter vs. ammeter - 
First,  it's 45 years automotive experience, specializing in electric systems. I currently live by testing, repairing, restoring electric systems, especially charging systems.
College trained, as well as factory training from GM, Ford and Chrysler. Further - training by Sun (the test equipment company) as well as others.

So you have a problem - dim headlights, car won't crank well in the morning, that sort of thing.
You drive to a shop and explain you have troubles starting it or the headlights are dim, whatever. A good, well-trained tech comes out with a - get this - VOLT meter. He connects it to a spot close to the battery and has you start the car. He watches the voltage during cranking to see how low it drops, and when the engine starts, he looks at the reading. If it's an AMC, depending on the year, etc. (see the chart I posted showing regulators and voltage settings) and it's a 71 and he sees 14 volts he knows it's charging and the regulator is right where it should be. He'll have you turn on lights, etc. and see what happens. The voltage should stick at or around 14. If it drops - he knows there is a problem either with bad connections or the alternator can't keep up with a load (perhaps bad diode, etc. which he can also diagnose with a volt meter)
If all seems well he'll throw a load on the battery - years ago we'd wheel out the Sun tester, clip the cables on the battery and start loading it while watching the voltage. If it's a 71 AMC without AC the alternator is a 35. He'll load the battery until his meter reads close to rated alternator output - the volt meter should hang around 14. If it does there's nothing wrong with the alternator OR regulator - and he got all that from a volt meter.
If that passes........... there's another test. You've driven the car for an hour, the volt meter reads 14 while it's running, so take it home and park it.
Got out the next morning and turn the key on but don't start it. Wow, the volt meter is just 12 volts.
So what's that mean? The charging system was fine but the battery isn't holding a charge. (or you left the dome light on, etc.)
Again, volt meter diagnosed the trouble.
You are driving and the volt meter reads 14 then you turn on lights and it drops to 13 - turn on the AC and it drops to under 13. It's telling you of a problem here and now.
If it stays steady at 14, you don't have a problem. The charging system works on voltage - it's regulated by voltage. 
The battery represents a load to the system as do lights and other things. More load of course means more amperage draw but with a system regulated to 14 volts it should stay at 14. You keep the voltage constant, vary the load, the amperage will change. Simple ohm's law.
So a volt meter will tell you of the health of the charging system at all times. It won't wait until the battery is dead. Got a problem? first thing anyone here will tell you is to get a volt meter out and connect it across the battery. 
Volt meter in the car will tell you instantly of a problem or a pending problem - AS it happens, not after, because you see it at all times. 
Voltage climbs as you drive - starts out at 14 then slowly or even quickly climbs to 15, then 16 - the volt meter told you that the voltage regulator is toast. 
Voltage drops? it's telling you the charging system isn't keeping up. 
Since the system operates by sensing voltage and regulating at a set, specific voltage, a volt meter will tell you real-time if there's any problem.

As far as WHERE the volt meter is - if it's connected far from the battery and it reads low, that's handy, too as it's telling you that you have faulty connections and voltage drop!! So that's not a problem.. if it reads low, say 13 instead of 14, check with a meter AT the battery and if that's 14 but inside it's 13,, COOL, that handy volt meter in the car just told you that you need to start pulling and fixing bad connections. 
No other meter will give you that information. 

If you suspect a charging system or other electrical problem, a pro like me will first say "get your volt meter out". If you have one in the car - READ the bloody thing and it will tell you if you have a problem or if a problem is STARTING to show up. 

some love their ammeter, that's cool, that's old-school, and people love to see the wide swing of all that POWER. But for a diagnostic tool, an automotive tech trained in electrical systems will use a volt meter or ask you what your volt meter reading is.

I could list a whole list of things that will tell you how to diagnose your systems with a volt meter - I could list what every reading means and how to interpret it. I could list what a volt meter would do in several various scenarios. it's what I do....... and have for decades. 
Not opinion, but factory training and experience. 

If people really want an ammeter - GO SHUNT. I'd not install any other type these days. The early systems, as was said earlier, were lower output so the gauges went up to a whopping ten, twenty, or forty amps but not commonly higher. 
They will tell you only if the charging system is keeping up plus or minus, but not a lot more. I can tell you the condition of your BATTERY with a volt meter, the condition of your wiring, and much more. 

So volt meter or ammeter - your choice based on preference. I know what I'd do......... but if your choice is that you prefer an ammeter based on the opinions here, please consider a modern shunt type and not run that load - and yes, full load, into the cabin. If the alternator fails, you run the whole electric system (except cranking) into the car if it's not a shunt meter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/08/2017 at 8:54am
Originally posted by billd billd wrote:

So explain how a volt meter tells of problems in the past when it's giving you a constant, real-time reading of the alternator regulated voltage?
Voltmeters may give readings in real time, but batteries don't discharge instantly. When you see battery voltage drop, the alternator has not been doing its job for some time. An ammeter will let you know the moment the alternator has packed it in.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Dec/08/2017 at 9:17am
I agree. billd and I have had more instances than we both care to emntion where I have irritated him, to the degree is personal, but... for the most part a conflict of my lack to point into details, while billd is exact and leaves no room for variance until he sees reason. Not that I try to rub billd wrong by doing so. Any way I respect billd, even though to some he may be harsh with facts, but IMO he is not opinionated or condescending. Being a stickler when some are broad in views, can make for some to clash with billd. I see many here who have strong character that may be part of their business to moderate even at the lowest level.

Reminds e of my issues at times with my cousin. He has no mechanical and elctronics training, but is able to do things and get by for some time. When i tell him it would be best done differently, and ignores my advice, and is slightly irritating, but it does even more so when the issues i see that can be a problem, go on to operate for some time, and feed his careless ways.

Some can get by for many many years with a wee bit of carelessness and blame others when the facts are pointing back to themselves when the issue comes back to bite them.

I can't blame either party on the heated discussion, as points of view come from two different people and their methods from years of experience.

Edited by 304-dude - Dec/08/2017 at 9:24am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote sweatlock Quote  Post ReplyReply Direct Link To This Post Posted: Dec/08/2017 at 2:07pm
I personally like ammeters - I use a shunt-style gauge with a fusible link on my car that's equipped with a GM alternator and it's great, no problems.

Like everything else in life, do it right & everything's fine; do it wrong & bad things can happen.
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