what should an ammeter read?

SleepyFarmall · Jun 6, 2020

Old garden tractor has 12v starter/generator with ammeter on the dash. Ammeter reads well above zero consistantly. Probably reads 2-3 amps all the time, even more with the head light on. Is this reading normal? I thought ammeter should read zero if all is well with the electrical system. Please advise. Michael

SVcummins · Jun 6, 2020

Ammeter is an amp meter measuring the amps your charging system is putting out

Russ from MN · Jun 6, 2020

Sounds pretty normal to me, If you really want to know what it's doing check it with a voltmeter.

jal-SD · Jun 6, 2020

Older Cub Cadet? If so, the starter/generator probably has to show a charge as current is being used through the battery. When the lights are on, it's gonna show more charge because the lights are drawing the current from the battery as it is being replaced by the generator/starter. Mine shows a "trickle" charge all the time. Mine doesn't have lights, but shows a 2-3 charge like you are seeing.

Janicholson · Jun 6, 2020

The alternators are so much higher in output that the amps to maintain charge is hidden it the width of the needle. All is well. Jim

John T · Jun 7, 2020

If its good and working an ammeter measures current flow in either direction and a few + charging amps is typical for many lawn mower set ups. Sure Id expect it to go to center/zero with no load or no charging current whatsoever, but often they are not all that accurate or well calibrated. In order for the current lights are drawing to affect the reading, that current needs to flow through the ammeter, if not the ammeter doesn't sense/register that current.

John T

4wdtom · Jun 7, 2020

If the battery isn't showing signs of over charging they and isn't running down so it won't start the engine, then you are OK.

Calvin Innes · Jun 7, 2020

If you would like to know what the ammeter should read, may I suggest the National Geographic?

John T · Jun 7, 2020

I have to agree with that. Some of those ammeters aren't all that accurate, if it aint broke don't fix it lol.

John T

Steve in IL · Jun 7, 2020

Wondering... Does it return to 0 when the key is off? Does it go slightly negative when you first turn the key on (and engine and starter are off). Does it go negative when you engage the starter?

MarkB_MI · Jun 7, 2020

Ammeters are SUPPOSED to read the net charge going to the battery, but are often wired to read the alternator output for simplicity. Since yours reads higher when the lights are on, it must be reading the alternator output rather than net charge.

No reason to over-think this; if the alternator is putting SOMETHING out it's probably OK.

SleepyFarmall · Jun 9, 2020

Yes, it returns to zero when off. Thanks to everyone for their helpful responses. Michael

BarnyardEngineering · Jun 9, 2020

(quoted from post at 09:02:27 06/07/20) Ammeters are SUPPOSED to read the net charge going to the battery, but are often wired to read the alternator output for simplicity.

That's a simple matter of which side of the ammeter you connect all the "load" wires to. Load wires such as the ignition and lights.

If they're connected to the side that runs to the battery cable, you will see alternator/generator output. If they're connected to the side that runs to the BAT post on the alternator, you will see "net charge."

One way to test is to turn the lights on with the tractor not running. If the meter does not move, it's wired for alternator output. If the meter goes negative, it's wired for net charge.

what should an ammeter read?

SleepyFarmall

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SVcummins

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Russ from MN

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jal-SD

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Janicholson

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John T

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4wdtom

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Steve in IL

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