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Re: Ampmeter to Voltmeter
#93811 Sat Dec 10 2005 04:19 AM
Joined: Dec 2005
Posts: 20
E
Apprentice
I don't like ammeters due to the fact that they require all the electrical load to pass through them so they need to have big heavy wires,and any bad connections will lead to burning.
I find voltmeters very usefull if they are accurate,14v=healthy alternator/battery charging,less than 12v-battery depleting.

Re: Ampmeter to Voltmeter
#93812 Sat Dec 10 2005 07:09 AM
Joined: Oct 2003
Posts: 5,161
O
Cruising in the Passing Lane
I like the volt meter better because it is a diagnostic tool I understand. Amp meters tell you if the system is charging or not. I want to know more.

Watching the voltage as you start the vehicle gives you a good indication of the starting side of the system too. Voltage drops too low you have a problem.

Once running, if it says 14 volts, you are charging. Much more you've got a problem. Much less you are not charging.

If the motor is not running, you should see 12 volts, less you are in trouble, either discharged or battery is failing or maybe a short or load of some sort.

Volt meter helps me a lot more than an amp meter. But that's just me.


Its true, I really don't do anything but browse the Internet looking for trouble...
Steve@OldSub.com . www.OldSub.com . www.MaxwellGarage.com . www.OldGasTowRigs.com
'55 1st GMC Suburban . '54 GMC 250 trailer puller project. '54 GMC 250 Hydra-Matic . '54 Chevy 3100 . '47 Chevy COE . and more...
Re: Ampmeter to Voltmeter
#93813 Sat Dec 10 2005 01:57 PM
Joined: Nov 2004
Posts: 61
B
Member
Don't forget that, with the Ampmeter, when it burns out everything is lost, no start, no nothing!

As much as you need to really know, the voltmeter does that! with less heat/load involved!

By the way chevy was still putting ammeters in their truck in the 70's, I have a 71....

Re: Ampmeter to Voltmeter
#93814 Sat Dec 10 2005 07:11 PM
Joined: Dec 2003
Posts: 2,736
Shop Shark
If your using an 80 amp or above alternator then you must use a voltmeter. I'm not too sure why but all the experts agree.


1953 Chevy 5-window 3100
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Re: Ampmeter to Voltmeter
#93815 Sat Dec 10 2005 07:45 PM
Joined: Jul 2004
Posts: 5,712
A
'Bolter
I have installed several aftermarket ammeters in various cars and trucks I have owned. These were usually the Stewart Warner brand gauges with the standard two post arrangement. Power in on one side and all electrical loads on the other. If you wanted the gauge to monitor the device, it had to be hooked in series or it wouldn't affect the gauge. This meant, as pointed out many times above, that the poor old gauge had to carry the entire current load for the system.

I have various meters at work for checking current draw. They use a inductive pickup coil around the wire that senses current flow and displays it on the meter in amps.

Were any of the ammeters installed in the later model rigs of an inductive type...ones that didn't have to be wired in series and carry the full load...safer from a failure standpoint!

I personally have never had a ammeter fail, catch fire or short out, and don't believe I know anyone that has.


Stuart

Re: Ampmeter to Voltmeter
#93816 Sat Dec 10 2005 10:19 PM
Joined: Jun 2004
Posts: 8,420
W
'Bolter
The GM trucks late 60,s early 70,s used the harness itsself for a shunt. They had 2 small black wires with inline fuses fastened at 2 different places in the main feed wires. The ammeter registerred off this. I prefer a voltmeter. Once you learn to interpret it & have an idea of volts & amps, it will tell you more. I have seen many breakdowns from burned out ammeters & damaged wires but never a fire.


They say money can't buy happiness. It can buy old Chevy trucks though. Same thing.

1972 Chevy c10 Cheyenne Super
Re: Ampmeter to Voltmeter
#93817 Sat Dec 10 2005 10:53 PM
Joined: Apr 2000
Posts: 247
V
Member
You don't have to agree with me about ammeters. It's a free country, and you can use whatever you want in your truck. All I can do is to inform you of the potential safety hazards of this design.

From a systems design standpoint, they are a single point of failure - another reason they aren't good. There have been various designs like the inductive, the fused or the shunt ammeters - but they still have a basic problem that all the current has to go through the big wire feeding whatever ammeter design you have.

If there is somehow a short in this wire - anywhere along the wire, the truck dies - no matter what ammeter design it has. A short will usually melt the large feed wire going from the alternator to the ammeter. If you want to find an example of an ammeter-type design failure, all you usually have to do is look for a melted feed wire in a junkyard vehicle.

Re: Ampmeter to Voltmeter
#93818 Sat Dec 10 2005 11:03 PM
Joined: Apr 2000
Posts: 247
V
Member
And yes, I have had several ammeter-design fires that I have had to deal with. Since I usually deal with 60-66 trucks, this is the ones I have dealt with the most. Usually it just melts the wiring harness, nothing else managed to catch fire. I burned my hands pretty good trying to disconnect the underdash wiring harness before it completely self destructed. The plastic melted to my hands, which took a while to heal.

Anyway, I won't hook up ammeters in any of my trucks anymore. I ran the output of the alternator to the battery, then I set up a fused feed wire to the rest of the truck using a fuse from a later 73-87 truck (the one on the firewall), and ran it directly from the battery.

Re: Ampmeter to Voltmeter
#93819 Sun Dec 11 2005 12:36 AM
Joined: Apr 2000
Posts: 487
R
Shop Shark
GM stopped using ammeters because 90% of the people that plunked down their money for a new car didn't know squat about how a car worked. It was easier to put in an idiot light, than explain that "0" on an ammeter was a good thing. Quite frankly, I think an idiot light is just as usefull as an in-dash voltmeter.
A (in-dash)voltmeter will not tell you the condition of the battery. It will tell you what the voltage regulator is doing. Any variation in voltage is going to be more temperature variations than anything else. Any of you stovebolters here know that you adjust a voltage regulator with a thermometer and a voltmeter. You can get a jump start if you have a bad battery and that voltmeter will say 14 volts all day and all the way home. Get a jump on a car with an ammeter and that meter will read high and never go down all the way.
A (in-dash)voltmeter will not tell you the condition of the battery, other than when it's dead. Let's see. Put key in slot, turn key, nothing, I wonder if my battery is dead, I better look at the voltmeter so that I know for sure.
If you are driving down the road and say a fan belt breaks. A voltmeter, a ammeter and an idiot light will all give you an idea of what that sound was.
Only an ammeter can give you an idea of what the battery condition is before it leaves you sitting.

When these trucks were built, the symbol for Voltage was "E". If a shunt wire in a ammeter is a low resistance load then what is a straight piece of copper wire? Just thought I'd ask.
The majority of ammeter problems are at the spade connecters in the firewall bulkhead plugs. It has nothing to do with the resistance going down. On a bad connection the resistance goes up. If the resistance goes up, the voltage drop goes up and the heat goes up. SMOKE.


'67 GMC 3/4 292 4spd
Re: Ampmeter to Voltmeter
#93820 Sun Dec 11 2005 02:24 AM
Joined: Oct 2003
Posts: 5,161
O
Cruising in the Passing Lane
Given the relationhsip between voltage and current to say that one tells you nothing and that only the other is useful seems to miss the point.

If you wait to look at your voltmeter until your battery is dead its not going to tell you anything. If it reads 14 while the motor is running your charging system is working. If it reads 12 while the motor is running you have a problem.

If it drops below 8 or 9 while starting you have a problem.

If you think a volt meter is useless that's your problem.

Just like the oil pressure guage and temperature guage, waiting until you have a problem to look at the guage defeats the purpose.

Learning the correct way to use the tools might make you better prepared than 90% of GM's customers, but ignoring those tools until you have trouble sure doesn't.

In a day where it takes 100 amps plus to support all the accessories on many vehicles using an amp guage to show what is happening means some real big wire running from the alternator to the guage.

I think that is a problem. But it can be your problem if you prefer.


Its true, I really don't do anything but browse the Internet looking for trouble...
Steve@OldSub.com . www.OldSub.com . www.MaxwellGarage.com . www.OldGasTowRigs.com
'55 1st GMC Suburban . '54 GMC 250 trailer puller project. '54 GMC 250 Hydra-Matic . '54 Chevy 3100 . '47 Chevy COE . and more...
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