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How to test ammeter for good/bad?

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RobJJ

04-06-2007 08:42:18

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How can I test an ammeter to tell if it is good or bad. There is continuity across the terminals, but the needle doesn't move when hooked up...how can I know whether the ammeter is bad, or the wiring is bad?

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Kent of SWMO

04-07-2007 10:23:32

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Re: How to test ammeter for good/bad? in reply to RobJJ, 04-06-2007 08:42:18

I for one do not agee with the comment that a amp meter is a accident waiting to happen. If you use wire that is to small to catty the current the charging system is capable of generating you will have heating problems. I would much rather be WITHOUT any gauge than have a volt meter. The problem with a voltmeter to warn of a problem with an electrical system is that the meter need to read in at least the tenths of volts. Most analog meters for vehical use do not. Also on a vehical equipment after starting the meter will return to around 12 volt you will think you are doing fine but your charging system could still be weak or not functioning. On a vehical equipment with an amp meter, when you start it the amp meter will immediately show the charging system is working. As you use the equipment over a period of time the opperator will become use to seeing this happen. The first time you start the engine and the amp meter DOES NOT show the system charging after start up you will know immdiately that you have a charging system problem. The only reason the auto manufacture use a voltmeter is because it is cheap to install, one light wire with the other side of the meter grounded to the frame. They can still say there is a gauge to monitor the electrical system. In my opinion the voltmeter is note the best BUT they can claim they have a gauge.

Kent

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DouginOr

04-08-2007 12:41:55

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Re: How to test ammeter for good/bad? in reply to Kent of SWMO, 04-07-2007 10:23:32

I disagree that a voltmeter needs to read in 10th of a volt. Yes, the ideal voltage for charging a battery (12 volt battery) is 13.8 volts, but generally if an alternator or generator is working, a voltmeter will show something in the neighborhood of 14 volts. If the charging system is not working, the voltmeter will show something in the 12 volt range. Now let's look at the ammeter issue.. a generator can be delivering only 12 volts, but the ammeter may still show the generator as charging the system - providing the battery has already discharged down to about 11.5 volts. The battery will not be getting anything close to a full charge, though. To be honest, either gauge works. I would check the calibration of either against a known source.

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paul sebek

04-06-2007 11:36:31

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Re: How to test ammeter for good/bad? in reply to RobJJ, 04-06-2007 08:42:18

what kind of test meter do you have? Does it have an amp range? If it does, disconnect the wiring from the ammeter and connect your test meter(assuming digital) in. If you meter can only handle 2 amps or so(digital cheap one) then just turn the key on, don"t start the engine. You should read +/- 1-2 amps on the display if the wiring is working. The ammeter disconnected should read as 0 to 2 ohms(allowing for test leads) across the terminals. It"s possible the needle is stuck from corrosion if it tests ok. I"ve used ammeters for 30 years and never had any problems except when the ignorant use them improperly. If using a VOM watch the test meter so it doesn"t peg.
The ammeter isn"t very expensive. I don"t know if they sell them on this site but you can get one on other sites or ebay if necessary.

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Charlie free

04-06-2007 09:29:12

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Re: How to test ammeter for good/bad? in reply to RobJJ, 04-06-2007 08:42:18

Well, if you had the test equipment to read continuity through the meter, does your measurement device have an amps range? If so, set it to amps, and put it inline with the ammeter. They should be about the same give or take 10%. You can also take a spare tractor lamp and put it in series with the ammeter. Flowing current should light the lamp, the amount of current indicated by brightness. A fully charged battery might not be drawing enough to show on the tractor meter.

Charlie in NC

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BCnT

04-06-2007 09:17:18

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Re: How to test ammeter for good/bad? in reply to RobJJ, 04-06-2007 08:42:18

unless you're restoring to be judged get rid of that thing before it burns your tractor to the ground...ammeters are a accident lookin to happen...go with a voltmeter instead.

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RobJJ

04-06-2007 15:46:04

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Re: How to test ammeter for good/bad? in reply to BCnT, 04-06-2007 09:17:18

Interesting, but can you explain how/why it is? As far as a voltmeter, should I be able to find one in about the same size and do I specifically neeed to find one for 6 volt, or will these be pretty much just generic to 6 or 12 volt. Now, as far as wiring, how much will I have to change to have the voltmeter work? Will I use the same wiring setup? On the ammeter, there are three wires hooked to the one terminal and a single to the other terminal...I'll have to see where they go/come from. But, if I were to switch to the voltmeter, can you also comment on how to wire versus the ammeter. Thanks,

Rob

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BCnT

04-06-2007 21:40:50

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simple explanation on ammeters vs voltmeters... in reply to RobJJ, 04-06-2007 15:46:04

i'm sure everybody has heard the old saying that volts dont kill during an electocution...its the amps that fry ya.
ammeters carry full charging load thru a resistance coil that heats up when system is charging [sort of like the coil in a toaster oven]
sometimes the voltage regulator will stick resulting in a heavier load on the ammeter and the coil on the meter gets hotter and starts to glow...wire insulation,rats nests,bird nests,any kind of debris near ammeter catches fire and by the time you see smoke or flames its too late unless you've got an extinguisher...dont forget that fuel tank sitting rite above meter either.

voltmeter just measure voltage...no heat

to install a volt meter run 1 side of meter to ignition terminal on switch and other lead to ground [if it doesnt work or works backwards reverse leads]
hope this helps

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MikeRW

04-06-2007 09:46:06

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BCnT Please Respond in reply to BCnT, 04-06-2007 09:17:18

You commented that ampmeters are an accident looking to happen. I've never heard this before could you please expand on your comment. I have 2 tractors that i've replaced old ampmeters with newer. I have no problem switching to voltmeter if need be.

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Bob

04-06-2007 08:46:04

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Re: How to test ammeter for good/bad? in reply to RobJJ, 04-06-2007 08:42:18

An EASY way would be to connect a "known-good" unit in series with the "suspect" unit and compare readings.

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