Electrical experts?

Does anyone here know if I can bench test what I am told is "an induction type ammeter" in the charging system of a tractor? This is semi-OT because it is not an IH but the guys on the other board don't seem to know. This is the gauge that tells you the genny is charging the battery and is on a 6 volt positive ground system. There are no terminals, just a cradle on the back that holds one of the wires in the circuit. I was wondering if I was to make a circuit on my bench with a 6 volt power source and a lamp would it read on the gauge? Hoping one of our electrical experts might know here.

If I understand what you are describing, I have a guage very similar. You could probably test it by holding it against the wiring loom from the alternator on your truck or car. I think those guages basically work by detecting the magnetism created whenever current is flowing through wires. Probably NOT super accurate, but still a good indicator of whether the charging system is working.

Short answer is yes.
But there are a few caveats.
The meter works by putting the coil of the meter movement within the magnetic field of the current flowing in the conductor. That flowing current then induces a small current in the meter movment to make it deflect and give a reading. I have one like it, and it works very nicely to tell the direction of current flow and approximetely how many amps are flowing. It is not a pinpoint precision device, but is reasonably accurate as long as you understand it's limitations.

Yes, you can set up a circut on the bench to test it. If it is like mine, it may take more than a lamp to draw enough current for the meter to deflect very much. I think mine is a 0 - 200 amp range, so a single lamp might not have much of a noticable effect on it. You might need to add load, such as more lamps in parallel, or something that draws more amps.

Old V-8 Fords in the 30's and 40's had this type ammeter. Don't know about test but never had one fail.

Harold H

I'm thinking Ford 8N series has this type meter. You can test this by holding it against one lead of a battery charger that is charging a battery---6 or 12 volts.

Sure you can bench test it, thats the same thing it does when its on the tractor, a wire is placed in its cradle and it senses and measures the current flow therein. That saves having two terminals, just let the wire be in the right place and BY MAGIC LOL it registers current...

Faraday's (hes long dead) principle of electromagnetic induction tells us if you pass a magnet by a coil of wire (or the wire past the magnet no difference) voltage is induced and similar, current flow in a wire produces a magnetic field around it and the greater the current the stronger the magnetic field.

Those ammeters are induction type because current flow induces a magnetic field and its that magnetic field strength that is being computed and converetd into current flow so the needle deflects

The faster the magnet passes by the wire (or wire past magnet) the more voltage induced which is why a gennys output inctreases if you spin it faster.

One problem is as the distance from the wire increases the field strength decreases so placement of the wire and its insualtion thickness etc affects the reading...

Id rig up a bench test that uses the same wire gauge and insulation as on the tractor and select voltages and resistances to get a range from 0 to 30 amps or so n see what the ammeter registers PIECE OF CAKE

Ol John T NOT any expert but Ive been around electrical things n been to a rodeo and a couple goat ropings FWIW

Dave - I’ve had one of those ammeters for many years but have not found it very useful.

While it is convenient it is NOT very accurate. Readings are highly affected by the presence of any nearby magnetic field – ie, a generator, alternator, motor, voltage regulator, etc. Even another current-carrying wire located nearby will screw up the reading. (I’ve found an operating alternator is the worst offender – just holding the meter a couple feet away from the alternator on my truck will cause it to read 60 amps or more)

So unless you can place it on a single wire several feet from any other electrical component its readings will be suspicious at best.

As for testing your meter a quick “yes no” test is to bring a small magnet near the meter housing. If the hand deflects as the magnet comes close it means the meter is working.

(quoted from post at 12:25:44 11/17/09) I'm thinking Ford 8N series has this type meter. You can test this by holding it against one lead of a battery charger that is charging a battery---6 or 12 volts.

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he old Ford loop style meters (old cars & trucks and "N" tractors requires that the current carrying wire actually pass thru the loop......it is not sufficient to simply hold it close to a current carrying wire as it is with the "hold it next to the wire" test meters. That isn't speculation. Just experience.

I have one of those meters to use for checking if there is current and the direction it's flowing, but I don't depend on it to be accurate. Mine reads 75-0-75, so it will deflect at a [u:4fd2b3cc79]fairly[/u:4fd2b3cc79] low current... much more sensitive than a 200 amp meter. Just used it to check the output on a friends M-H Pony, and it read where a 200 amp did not.

JMOR--thanks for the heads-up on the meter. After reading your post, I do remember that the Ford meters do have a sensing loop.

Sounds like one of the regular clamp on meters/testers we use for testing AC current. Just clamp it over the wire to test the current. Don't know if they work for DC current.

(quoted from post at 17:09:34 11/17/09) Sounds like one of the regular clamp on meters/testers we use for testing AC current. Just clamp it over the wire to test the current. Don't know if they work for DC current.

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AC clamp on type using a transformer will not work on DC, but those labeled AC/DC WILL work, because they use a HALL-Effect sensor instead of a transformer.

Many thanks for all the help! I got some good hits on the N board also. The meter deflected enough that I think it would work but on close inspection it was losing some of it's inner integrity...to make a long description short...so I popped for a new one. Appreciate all the responses!

So how does the old one compare with the new in their readings?

Looks the same basically but, since I cannot get either gauge to read anything yet and the old one is out of the running I guess that is one that doesn't have an answer!