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Swaping a voltmeter for a ampmeter

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Phlash in OK

04-10-2005 11:16:25

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I bought a voltmeter without realizing that it did not register discharge. When I wired it exactly like the ampmeter, the tractor wouldn't start. Do they make voltmeters that show charge and discharge like an ampmeter? This is a 9N on a 12 volt system that works fine.

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Sam#3

04-11-2005 07:34:29

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Re: Swaping a voltmeter for a ampmeter in reply to Phlash in OK, 04-10-2005 11:16:25

First, and most simply, An ampmeter is a series device and is used to measure AMPs, the amount of current flow. In charging circuits they are usually built to read both charge and discharge current hence the center zero. A voltmeter is a parallel device used to measure electromotive force. The most common type is a low current ampmeter in series with a dropping resistor and the meter actually reads the current flowing thru the resistor(it's all in the case). IF you want only the VM then, like someone said close the AM leads and tie one side of the VM to the joint. Howsomevever: the VM will place a constant draw on the charge lead. A better location for the tie in would be the distributor side of the ignition switch. My best guess as why the tractor doesn't start is the there is smoke in the VM case. The VM wouldn't carry the load of the ignition. Smoke isn't a good conductor.

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roger '40 9n

04-11-2005 13:35:27

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Re: Swaping a voltmeter for a ampmeter in reply to Sam#3, 04-11-2005 07:34:29

The VM in the ignition circuit would just act like a large resistance. I would not expect to see any smoke there. The only real way to "smoke" a voltmeter is by putting too many VOLTS across it -- iffn you were tyring to measure your sparkie voltage you MIGHT see smoke -- but not just by trying to measure voltage across your battery terminals.

Roger in Michigan.

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Rob

04-10-2005 16:41:34

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Re: Swaping a voltmeter for a ampmeter in reply to Phlash in OK, 04-10-2005 11:16:25

Wired it exactly like the ammeter? Did that let the smoke out of the new voltmeter?

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BigGeorge

04-10-2005 13:25:12

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Re: Swaping a voltmeter for a ampmeter in reply to Phlash in OK, 04-10-2005 11:16:25

I believe your tractor wont start because on the battery side of your starter solenoid one wire runs to your ammeter then to the terminal block on the steering colmn. Your ignition switch gets its power from the same side of the terminal block. If current doesnt get thru the ammeter or in your case you tried to put in a volt meter, you wont have any current to the terminal block. Hope I explained this correctly..... . BG

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FLAcharlie

04-10-2005 12:29:40

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Re: Swaping a voltmeter for a ampmeter in reply to Phlash in OK, 04-10-2005 11:16:25

you can't wire a voltmeter up same as an ammeter. An ammeter is meant to have the current flow through it, a voltmeter won't pass current, hence your tractor wouldn't start. If you want a voltmeter, it should be wired across the battery terminals, but it won't tell you the same kind of info really as the ammeter will, but it might identify when something is wrong with your battery or charging system.

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FLAcharlie

04-10-2005 12:56:38

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Re: Swaping a voltmeter for a ampmeter in reply to FLAcharlie, 04-10-2005 12:29:40

actually, I guess this doesn't explain whey it wouldn't start. I can see where it wouldn't CHARGE wired this way, but it oughta start.

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Dell (WA)

04-10-2005 14:56:26

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Re: Swaping a voltmeter for a ampmeter in reply to FLAcharlie, 04-10-2005 12:56:38

Charlie..... .....because the voltmeter uses micro micro amps to operate, it ain't gonnna allow the 3 amps yer sparkie coil needs to go thru it. And the same way it ain't gonnna allow the 10 amps yer genny outputs to charge the battery thru it.

The only thing incommon between voltmeters and ampmeters is them little invisable electrons. And the fact ampmeters and voltmeters look the same from the backside with 2-terminals. Different meters for different purposes, that is why they are called voltmeters and ampmeters. Understand? ..... ...respectfully, Dell former electronics calibration lab engineer

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FLAcharlie

04-10-2005 16:46:01

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Re: Swaping a voltmeter for a ampmeter in reply to Dell (WA), 04-10-2005 14:56:26

I understand that Dell, but my ammeter runs in the line from the alternator to the battery. So, if it was open, it should still start OK, it just won't charge.
Charlie, FCC licensed ham since '65.

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roger '40 9n

04-11-2005 10:33:05

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Re: Swaping a voltmeter for a ampmeter in reply to FLAcharlie, 04-10-2005 16:46:01

"So if it was open then it would still start OK."

Nope... You are using current from the battery to run your spark while starting and your volt meter does not let many amps through. Once you are started then your alternator can provide enuf amps to run your ignition. But your voltmeter will only let a few miliamps through to charge your battery.
One solution as others have mentioned is to tie both wires that were on your old ammeter together and put them on the positive (+) terminal of your voltmeter and run a wire from the negative (-) terminal to ground somewhere. That way your voltmeter is reading the voltage across your battery. (Assuming that your alternator is negative ground) Roger in Michigan.

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souNdguy

04-11-2005 06:41:17

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Re: Swaping a voltmeter for a ampmeter in reply to FLAcharlie, 04-10-2005 16:46:01

In the oem setup.. if your ammeter is gone.. no ignition power.. that's how it can measure discharge.. if the ignition is drawing off the battery... It's an electron direction thing.

In short.. the fellow need sto tie the wires together where his ammeter was, then use that point as the reference for one voltmeter leg, and then ground as the other reference. If it reads backwards.. then he can swap the leads.

Soundguy

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