Voltmeter vs. Ammeter

[timemachine]

Okay, this isn't as sexy as all the high performance threads, but it might be interesting to some folks. I'm in the process of getting ready to retrofit rallye gauges to my car, had bought some heavy gauge wire for the ammeter etc. when I came across a short and interesting article on the egauges site:
http://egauges.com/ATM_Tips.asp?TipP...terammeter.htm
which says voltmeters are much more useful to have than ammeters. The fellow makes some interesting points, primarily that the ammeter doesn't tell you much about the state of your charging system and battery. Voltmeters used to be more common, as on old pickups etc.
I think the value of the ammeter is to tell you if your battery is discharging in a running state, and where for example if you have the lights, defroster, wiper etc. running it might indicate a maxed out or weak charge system. A voltmeter would show a voltage drop in this case, but not whether the battery is draining. Unlike the ammeter, it does tell you if the regulator is overcharging for some reason.
Voltmeters are a much easier install, all you have to do is hook it to a power source, but I am debating the logic. They made these things with a purpose in mind, both would be best I guess but I don't want to get carried away.
Jim

[2 Fast 4 U]

If you can get hold of a Ampmeter with a inline resistor this would be safe to.
Let me explain: by putting a [low rated] resistor in the charge line of the battery you can also use small gauge wires to the ampmeter the only difference is that the ampmeter is a volt meter.
If you let a current flow thru a resistor, the resistor will create a volt signal [current I * resistor R = voltage V] this signal is linear with the in- or decrease of the current

[opelnut10]

Ampmeters are used with modern systems and voltmeters are used with generators. The voltmeter will tell you how many volts your charging system is putting out but will not give you amps.

[timemachine]

The article clearly shows the distinction between an ammeter and voltmeter, and being a former radio operator, it's clear to me already. The question is, which is more useful in a car? Inevitably, both would be, but if you had to choose one or the other.....?

I am not sure I get the discussion about an inline resistor and light gauge wire. The ammeter necessarily is wired in series with the actual charging system itself and the actual output of the alrernator/regulator goes through it.

[namba209]

Originally Posted by opelnut10 Ampmeters are used with modern systems and voltmeters are used with generators. The voltmeter will tell you how many volts your charging system is putting out but will not give you amps.

Actually you have it just the opposite and not quite exact either. The voltmenter is used in newer cars, while the ammeter was used since charging circuits were installed in cars including generators and alternators. Being old school I prefer an ammeter, I want to know how manny amps are being put out by the charging circuit and you can tell the condition of the battery, if the amps don't go down after you start the engine, you already know you've got a 12 volt system. The voltmeter will only tell you if your putting out 12 or less volts. Most voltmeters I've seen factory installed do not indicate actual volts but usually some less than nominal, or they have words in the gauge vice actual numbers. I believe the reason they were installed was because it's a lot cheaper to run a 22 gauge wire a shorter distance than a 10-12 gauge wire from the alternator to the ammeter the the battery. Because it's fairly easy to wire in a voltmeter, why not have both?

[timemachine]

Originally Posted by namba209 I want to know how manny amps are being put out by the charging circuit and you can tell the condition of the battery, if the amps don't go down after you start the engine, you already know you've got a 12 volt system. The voltmeter will only tell you if your putting out 12 or less volts. Most voltmeters I've seen factory installed do not indicate actual volts but usually some less than nominal, or they have words in the gauge vice actual numbers.

Yes and no. A dead cell in a battery usually won't draw current. The ammeter in this case would be flat, but a voltmeter would show a voltage drop. A zeroed out ammeter won't tell you if a belt is slipping, but over time, voltage will drop as the battery discharges. VDO gauges go from zero to 18 volts which will also tell you if your regulater is overcharging the usual 14 or so volts.

I agree that both is best, but in a three hole mount I'm choosing my gauges. Oil pressure is a gimme, I am contemplating a vacuum gauge too. That sounds gimmicky, but like the mileage indicators in the BMWs, a vacuum gauge offers a lot of nifty diagnostic tips on the fly with a lot more detail, see this helpful page for more: http://www.earlycuda.org/tech/vacuum2.htm It's not always as simple as shown, but I had a vac gauge on an old opel I used to own that did point out issues as they arose.
If I go that way, it leaves room for a voltmeter or ammeter. Thanks for the input. -Jim

[baz]

jim a vacuum gauge is only any use if you can see it when looking out the windshield as with saab turbos and there boost gauge mounted on the windshield "A" piller putting it down with the 2 other gauges means to use it you will be looking down and not out , never a good thing
i volt meter will let you moniter your charging system at a glance by reading the voltage as the system rebuilds the charge after starting you get a low V reading and as the system charges it gets back up to 12.8 V after the battery is recharged you will get a reading of just over 13 V as the regulator does its job (this is the way jaguar do it and this is the only wat i have seen it )
this should stay around 13 V even with the lights on
an amp meter will show that the system is charging or discharging dependent on load , so if you are using more amps than the alt can put out you have -ve amps and if all is good +ve amps

[Dmcbrass]

Actually an ammeter doesn't tell you how much current your alternator is putting out. It only tells you how much current is flowing between the battery and the alternator. Most of the components that use power in an OPEL are connected between the alternator and the ammeter. Under normal conditons (battery is fully charged), nearly all of the amps coming from the alternator flow to the headlights, radio, etc. and not through the ammeter.

[namba209]

Originally Posted by timemachine Yes and no. A dead cell in a battery usually won't draw current. The ammeter in this case would be flat, but a voltmeter would show a voltage drop. A zeroed out ammeter won't tell you if a belt is slipping, but over time, voltage will drop as the battery discharges.

True to a point, except that the ammeter will indicate it is putting out amps although not much. The voltmeter will show system volts, that is, what the alternator is putting out to bring the battery back to 12 v. Both will show an indication of trying to get the full 12 volts back, either in voltage (13.8-14.2 volts) or amps, whatever the alternator is capable of. If the ammeter does not go back to minimal charging indication after a couple of miles, you know something isn't right. If the belt is slipping the temp gage will show that. But like I said, I'm old school, so I like the ammeter over the voltmeter.

[timemachine]

Thanks for all the input guys. Anyone joining this thread should read the first post for the article referred to.

Overall, I think ammeters are good because they tell you a couple of important things. If they are in the minus zone when driving, your electricals are running at least in part off the battery and hence the battery is definitely draining at some rate. (I once drove a '68 Pontiac Tempest 150 miles with a seized alternator, there was enough juice in the battery alone to run the ignition.) It also tells you when a run-down battery is brought back to full charge. I don't buy the fire issue in the article as a threat if you do a competent job of wiring.

I think the voltmeter is good because it tells you more about the state of the electrical system than just the current flowing to the battery from the alternator. Too many volts and you know your regulator is on the fritz. Too few and you know one of SEVERAL other things is wrong, though the information might or might not come to you more slowly.

On the vacuum gauge issue Baz, I think a pillar is a good place for a boost gauge since when you're using it, you're putting your foot into the car and your eyes ought to be on the road. The vacuum gauge applies to any state, like any other gauge you glance at. BMW puts them below the speedo. The purpose of that is to show the efficiency of your driving for mileage, but a vacuum gauge that measures in inches gives you that and a lot more input on your engine, ignition and exhaust. http://www.earlycuda.org/tech/vacuum2.htm

More comments welcome, again, thanks for your thoughts everyone.
-Jim

[roadings]

ok so does anyone make an aftermarket volt meter that will fit in the space provided in a GT?

[baz]

VDO the folks who make them from new or any makers 50mm (i think )

[roadings]

i didn't expect to get such a timely reply on an old thread. as for the fire issue. believe it. that is the reason i'm looking for another GT.

[hrcollinsjr]

Cut and pasted from the arcticle mentioned in the first post; "....the alternator output used to recharge the battery must first be routed through the ammeter under the dash. Which requires a heavy-gauge cable and presents a possible fire hazard. And the ammeter itself must be able to handle all this current flow, so it must have a higher current rating than the alternator's maximum rated output."

So for all those who have or are planning on installing more powerful alternators, "Does anyone know what our amp guages are rated at or are capable of handling safely?"

I've smoked an electrical system because of a misadjusted voltage regulator. We won't talk about how it got misadjusted.

Thanks,
Harold

[namba209]

Originally Posted by hrcollinsjr "Does anyone know what our amp guages are rated at or are capable of handling safely?" Harold

Harold, I don't know how many amps it would take to smoke the gage, but most ammeters have a shunt inside between the posts so that only a sampling of the actual amps is measured. Figure that when you start the engine, full amps is going through the ammeter to the starter solenoid to operate it, although I don't know how many amps that is. As I stated in another post, when I get the engine running, I'll be able to check out this question and the wiring to the alternator sensing. I'm getting close to the "Magic Smoke" test.

[jlthunder]

Here is my 0.02 a recent experience.

The amp gauge is good so you can see when your alt is going bad, you start to see it going into th (-) range when it should be charging. It can be annoying when you put the turn signal on and you can watch it move around.

My S-10 had a volt meter with actual volt indications. I knew my alt was going bad because it kept moving back and forth from 14 volts to 12 volts when I had the engine running. My mechanic confirmed this.

Moral of the story. If you can read either gauge, you can figure out what is going on with the charging/electrical system.

Jeff

[timemachine]

The leads on the old Manta gauge were braided #10 wire, heavy duty and well-jacketed stuff. The factory manual shows they run to and from the ammeter via the alternator output and starter (battery). A fusible link prevents a shorted starter from setting everything on fire. A separate, parallel circuit runs alternator output to lights and other stuff.
Since they do carry the alternator output to the battery through the firewall and back, the ammeter leads could pose a real fire hazard if chafed or something comes loose and grounds. That said, the original gauge wiring held up very well over time, I haven't been aware of any Mantas catching fire this way. (A shorted gauge won't start a fire, [after all, the meter is in series with the circuit], nor will an open circuit cause a fire. The threat arises when the circuit is GROUNDED.)
The GT electrical hazard was always in the headlight wiring, though Roadings' post has proven to me that ammeter wiring and proper regulator setting in old cars deserves a look see once in a while to make sure all is well. Ironically, a voltmeter, unlike an ammeter, would have tipped off the high output that wrecked this poor fellow's car.

For a retrofit, I think a voltmeter is a good option for the reasons I've stated above. If you decide to retrofit an ammeter, use the right materials and don't cut any corners. e-gauges, which was the source of the first entry in this thread, has lots of stuff that fits the Manta console.

[Manta Rallier]

Ammeters area throwback to older days and how electrical systems were monitored. Generators, and the old mechnaical regulators that accompanied them, did not regulate the voltage as well with variations in system current draw, so an ammeter gave more repeatable readings. Also, since generators carry higher field currents in the brushes, they were more prone to wearing out, and the use of ammeter gave one a clear indication of worn burshes. Ammeters need more interpretation to read the system health properly; for example, if you drive for an hour with the system charging the battery well, then turn on the headlights, the ammeter will typically show a slight discharge as the battery is drained down a bit due to the overall lower system voltage with the headlights on. This type of thing can be a bit baffling if you don't expect it.

With the advent of solid state regulators, the charging system voltages are much steadier with load variations. You can more reliably tell what is going on in an alternator system with a voltmenter than you could with an ammeter in a generator system. So for monitoring, a voltmeter is much better. You can tell if the atermator is working right, if the beattery is healthy, and even if you have lost a diode or 2 from indications on the VM.

One thing that will make a VM installtion much better is to run the + wire rigth to the alternator or battery +. If you run it from the dash, and use ignition switched power, then the electirc energy is flowing through the ignition switch, and these are notorious on many cars types for getting dirty and having the switch resitance increase with age. If you hook up you VM through switched ignition power, and see the VM flicker up and down with the blinker or with other accessories tunred on or off, you are seeing the effects of ignitions switch resistance. The VM readings are more accurtate if direct from the alternator or battery +. But, you need to arrange for the battey to be disconnected from the VM for long periods of storage.

We use nothign but VM's in our rally cars, BTW. The + wire goes to the alternator. We have the convenience of the normal battery cutoff swithc to disconnect the battery for a periods of storage.

Regards,
Mark B.

[blancojp]

Howdy guys!
Monitoring 30A does absolutely nothing for you specially if you changed your alternator to 63A or greater. Sure it is nice to see where your current is going, or not going to but the fact remains a volmeter is a more logical tool to have. Bare in mind that a a large alternator will dump the highest amount of current required to replenish the battery as quickly as it can be assimilated. If you swap your engine and you install a 90A unit per say, you would need to run a #6 wire to the gauge and the same to the fuse box.

Opels have a #10 wire which is good for about 40A max. DC rating. So if you have a big alternator installed, discharge the battery and jump start the vehicle. You will see the amp gauge peg to next week on your dash.

[namba209]

Originally Posted by blancojp So if you have a big alternator installed, discharge the battery and jump start the vehicle. You will see the amp gauge peg to next week on your dash.

You don't have to have the battery discharged for that to happen. On Willit? with the battery charger on it for a week, and just starting it, the ammeter pegged for the 5 or so seconds each time the engine was running, with the 100+ amp alternator. What will be nice is it won't stay pegged out too long. I expect to see very minor changes in needle fluctuation after about 5 minutes.

[timemachine]

Good post by Manta Rallier. I've thought about taking his tip to wire the new voltmeter directly to the alternator, but then again, wouldn't wiring it within the harness make for a good tipoff a bad ignition switch? (or relay, which is a very good upgrade to have). Would it be better to wire it to the regulator output than the alternator?

I decided to go with the classic VDO gauges for volts, oil pressure, still wavering on the vacuum gauge for reasons stated earlier. If VDO made a same-sized analog clock to fit the rallye console I'd probably go with that, but I haven't found one yet. Has anybody seen a 2 1/8 clock out there?

Jim

[jeff denton]

I can't think of any modern equipment that uses an ammeter. I'd rather know what my voltage is than how many amps are being drawn from or pushed to the battery.

[namba209]

I'm just the opposite Jeff, but it's what I grew up with, so I'm comfortable with it. You know, different strokes, etc. But when I'm charging batteries, I've got both ammeter and voltmeter in line.

[jeff denton]

I truly think that ammeters went out and voltmeters are in because most people don't know what either is showing them, but troubleshooters need to first know what the voltage is. Try being the maintenance foreman at a construction company, you wanna see how ignorant some professional drivers and operators are as to how their equipment works. If the operator can at least forward some information to the shop (besides the usual "it won't go") the shop can prepare better for the service call. I once had to describe to a truck driver over the radio whereabouts the voltmeter is, "it's on the dash next to the oil pressure gauge, what does it read at idle and what does it read at full throttle?"
Useful information, no? Ammeters help those who understand them, but don't say much when the battery is low and the engine won't crank. If somebody is paying attention to his instruments an ammeter will show a problem first, but not after the problem has developed into "all it does is click when I turn the key".
To really confuse someone try explaining what the red idiot light shaped like a battery is trying to tell him...

[GTJIM]

Originally Posted by jeff denton To really confuse someone try explaining what the red idiot light shaped like a battery is trying to tell him...

What is wrong with just having an 'idiot light' ?? Battery is charging => it is off / Alternator has stopped charging => it is on.
Suits most drivers => hence the name.....

At least it tells you the fan belt has broken.