Volt meter vs. ammeter

I just bought a volt meter by mistake to replace the ammeter meter that doesn't work on my brush chipper. How do you hitch up the volt meter compared hitching up ammeter ? Thanks for any help.
 
They measure two different items. What system do you have. The volt meter can measure your battery voltage,but it will not measure the charging system.
 
Think of it in terms of an ammeter needs to be wired in series with the load where a voltmeter is wired across the load (parallel). The internal construction of each meter is such that if you try to substitute one for the other it usually results in a destroyed meter and possible collateral damage.
 
On the back of the amp meter, there are 2 studs with a wire attached to each stud. The current flows from one wire, across the amp meter, and back out the other wire.

The volt meter will have a single + terminal and a ground wire.

To convert to a volt meter, take the wires off the amp meter and connect them together, typically with a short screw and nut. They need to be connected very well, because a lot of current flows through them as the alternator recharges the battery. Tape them tightly, making sure they can't come in contact with any metal. I like to use rubber tape, then electric tape, then shrink tube to be sure it doesn't come unraveled with heat and age.

Then install the volt meter. Connect the + terminal to a switched source from the ignition switch. You want this to be powered only when the ignition is on. The - terminal will go to ground. Any size wire will work for this, there is minimal load on the volt meter circuit.
 
You can use a volt meter instead of an amp meter. I actually prefer the voltmeter over an amp meter. You will need to connect the two wires together that are currently connected to the two terminals of the amp meter and tape them up with electrical tape. Then to connect your volt meter, simply connect the positive lead to a switched 12 volts from the main switch, and connect the negative lead to a good ground, very near the ground connection of the battery.

The voltmeter will read the voltage your alternator/generator is putting out as opposed to the charging current the amp meter was measuring.

The main thing to remember is the current passed through the amp meter, but the volt meter measures how much voltage.

Many people explain it in terms of plumbing and water flow. The current can be related to how much water is flowing in the pipe, while the voltage would be related to the pressure of the water and not related at all to the flow. Does that make sense?
 
You use a thing called a "current Shunt". It's a large piece of material, usually brass, made large to remain at a constant temperature while carrying the current for which it is rated, and develop a very low voltage in the process. Keeping a constant temp prevents voltage errors caused by material heating and resistance changing.

The shunt has 4 terminals, 2 for the current routing and 2 for voltage measurement and the resistance of the shunt is very small and very carefully calibrated, usually stamped on the shunt out to 4 or so decimal places. Putting your volt meter across the voltage measuring terminals and applying Ohm's law, solving for A = V/R you get your number.

If you don't have a shunt and want to measure a DC current of less than 10 amps, then use the ,multimeter if it has a 10 amp DC range and jack.

I think HF has them currently on sale and you can get either a VM or a clamp on A for a song. Check them out. I already have several multimeters and an Amprobe so I didn't need nor bought either.

HTH,
Mark
 
Yes it can indirectly. It can measure the effects of the process, not the process. But with today's accurate digital meters that works out ok fine for most applications.

Just some numbers I use: At the start of a normal summer day, before things get hot, at my 600' of altitude, a fully charged lead-acid battery measures 12.75 volts across the terminals no sooner than 24 hours after any charging activity has occurred....battery has had time to stabilize.

On a fully charged battery, over 1000 rpm, 14.5 volts is a good max voltage telling me the charging circuit has done it's job. After 24 hours the battery will be back down to around 12.75 or maybe up into the 13v area just showing somewhat of a slight overcharge. If the battery is partially charged, it won't read that high at the same input but watch your meter and you can see the numbers...like 13.55, 13.56,13.57 and so on as the battery is charging.

So even though you can't monitor the amps, you can monitor the effect of the amps going into the battery.

This works for me and I don't have a hydrometer. And the clamp on Amprobe is a transformer and requires an alternating current to switch power from the input wire to the meter movement, making is useless for battery charging. Yes alternator charging is rectified AC with half sine pulses all the same polarity, but what this will do is work initially (not very long) until the core is driven to one limit and then it saturates yielding nothing to speak of for an output.

HTH,
Mark
 

One can tote a ammeter in there pocket just in-case they may need it... They will get tired of tote'N it and will find its not of much use...

Voltage is the first thing you need to know so mite as well hang it on the dash in place of a amp meter...
 
With over forty years as a generator tech. When someone ask a question as the OP did. Unless I can be there to help. I will tell them no.Not picking on the guy,it's good that he ask.But I have seen to many destroyed systems.Had one man take out six six volt batteries. Replaced them with six twelve volt batteries. Took me two days to clean up the damage.
 
Hello Steve-Maine,

The volt meter should be marked. Plus side goes to battery plus. The other side to a good ground. You should have the plus side of the meter switched on by the ignition. An amp meter tells you how much the system is charging. While the volt meter will show battery voltage, which is more important to know,
 

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