CAN AMP METER GO BAD?

8nsyes

Member
Hello one and all;

I have an amp meter on my 1948 Ford 8N, 6 volt that has "pegged" on the discharge side and pretty well stays that way. Never worked properly.
.Checked the generator, it puts out 6.9 amps
.Checked the battery, it puts out 6.9-7 amps
.tried polarity, made no difference.
.The gauge is a 15 amp gauge...

Any and all comments, questions and "tid bits" are appreciated....
walt
 
Well any thing man has had his hands on can and will go bad. So yes sounds like your has done gone bad
 
Old is right. If it has any moving parts it can and will go bad. I had a station wagon years ago that would intermittently charge and not charge. Problem was, the current had to go through the ammeter to charge the battery. Created some uneasy moments while driving at night! You should be able to purchase a replacement ammeter at any supply house.
 
If it doesn't return to center when the ignition and lights are off, it's bad.

You'll want to get a replacement for your model tractor though. Need to match the amps to your charging system. An automotive or late model tractor gauge will have a higher amp rating and won't read well with your generator. Also tractor gauges are more shock and weather resistant than automotive instruments.
 
Yes, replaced two different ammeters last week.

First one was one our John Deere 1952 model A.

Tractor would not start, so got out the test light and worked forward from the battery.

No current passing through the ammeter.

Second one was on one of our John Deere 1951 Model MTs.

Same problem as mentioned above.

Had a 20 amp fuse leading from each battery to the ammeter.
 
AS a past used tractor dealer and engineer, I can assure you YES ammeters, especially on tractors often exposed to rain snow sleet and ice, DO GO BAD. A good one will return to center with no current flow, and, of course, swing to + or - as current flow direction dictates. I have seen many that get mechanically stuck jammed where the needle is stuck and cant move. Place a strong magnet near its front and move it back and forth and swap sides etc to see if the needle moves??? If not its likely stuck as you already know.

John T
 
Hello John T;

When no power is on, the needle comes to the center.
I turn on the key, the needle goes "a hair" to the positive. Then with in seconds of cranking the needle goes to the negative most all times completely "pegged".

From information provided from all of you on the Forum, I believe that I shall buy a new ammeter and settle the matter.

Thanks to all!
walt
 
Based on this new info, I CANT SAY FOR SURE THE METER IS BAD. I thought it was stuck and never moved. If it stays in the center with nothing on and if a magnet will cause the needle to move both ways back and forth, I wouldnt necessarily say the ammeter is bad!!!!!!

Normally if its working and in the center but you turn on Ignition (NOT cranking, just ON) it should swing to a slight NEGATIVE DISCHARGE as the coil draws around 4 amps. If it swings to + charge that sounds like a meter that's wired backwards ORRRRRRRR the battery is reverse polarity then original. Has the battery been changed and ground reversed????? If so it wont charge right until the genny is correctly re polarized.

With your new info I suspect a charging or genny or regulator problem or the battery has been reversed!!!!!!!!!!!!!

I have a charging troubleshooting procedure but its for Class A systems yet some Fords are Class B. I don't know what your ground was original or if the battery got reversed or if you have an A or B charging system so I hesitate to say much more. Id insure the battery is at the right ground and maybe polarize the genny and see what happens.

NOTE put a voltmeter on the battery and sitting there not running it should be 6.3 volts if a 6 volt or 12.6 if a 12 volt. Then start her up and if the genny is working battery voltage should rise (6.5 to 7 if a 6 volt or 13 to 14 if a 12 volt) If it does that IT IS CHARGING.

John T
 
(quoted from post at 08:28:50 04/21/15) Hello John T;

When no power is on, the needle comes to the center.
I turn on the key, the needle goes "a hair" to the positive. Then with in seconds of cranking the needle goes to the negative most all times completely "pegged".

From information provided from all of you on the Forum, I believe that I shall buy a new ammeter and settle the matter.

Thanks to all!
walt

If the needle centers I wouldn't be so quick to replace it, the needle moving to Pos. when the switch is turned on sounds to me like the polarity of the system is reversed and the needle moving to full discharge when running could be indicating a proper charge but in reverse as far as the gage is concerned.

Some of them older Fords had a ammeter that the charge wire simply passed through a round loop on the back of the gage, if the wire is going through the loop in the wrong direction the polarity could be right but the meter still read backwards. If that is the case reversing the wire in the back of the gage may straighten it out.

If it is a "normal" gage the wires will be fastened directly to studs sticking out and if the battery is charged properly and hooked in correct polarity the gage can be reversed by simply moving the wires to the opposite studs.

Make sure the battery is properly charged as I have seen batteries charged backwards, Possible if the battery was COMPLETELY dead and the charger hooked up wrong.
 
You're welcome, incorrect battery polarity or the charging system may well be the problem instead of the ammeter. I think (NO warranty, ask the Ford gents) 8N are Class A Charging Systems, if so my Troubleshooting Procedure linked below can help find the problem. Id polarize the genny and see what happens. If the battery is reversed polarity re polarizing can make her charge again, but still if the ammeter is reversed she will read bass ackwards. If the meter is correct it should swing over to - discharge if you turn on the ignition just sitting there but then swing to + charge IFFFFFFF the genny is working. If turning it on makes the ammeter swing to + charge, battery or meter is at wrong polarity.

John T
Class A Charging Troubleshooting
 
Hi John T, I always find your posts to be among the best! I went to a technical school here in Nebraska through a program called Electromechanical Technology. Our lead instructor was an EE and quite a guy to listen to. The story was don't ask Mr. Reid Curtis what time it is or you'll get a lesson on how the watch works. That was 30+ years ago and I still have a very hi opinion of some of our instructors from back then. I have not read this all very thoroughly, matter of fact I kind of sped-red through it. But do you suppose this is an installation where a meter shunt was used? If the shunt were to fail, hi resistance or loose connection then all current would be forced through the meter movement. No I'm thinking it would be tough to get much current through the windings in the meter movement but I thought I'd mention it. Good Day!
 
Did you ever polarize the generator after replacing the battery? I had the starter/generator rebuilt on my IH 154 last week. I asked the man if I need to polarize the starter/ generator. He said, hook it up and start it up, if the amp gauge goes( + ) I do not need to polarize it. If it went( - )when the tractor is running, then I would have to polarize it.
 
Thanks for the kind words. Okay, here's my best recollection but no warranty as its been a longgggggggg time ago lol. Also, Im NOT a Ford man, I don't know that much about them so cut me some slack lol

I think your thinking right !!!!!!!!!!and Im thinking if the shunt were open the current would pop the galvo windings (very small wire) instantly and the meter wouldn't move at all????????????

Some ammeters, and I "think" some on old Fords, used an induction type of ammeter where the battery cable simply passed by the meter with no in and out or actual series connections. True, many ammeters are shunt type with a low resistance shunt in parallel with a high resistance galvo type of meter movement. That served as a current divider where most current passed through the low resistance shunt, while a small fraction of current had to actually flow through the small galvo assembly to deflect the needle. Id think if the low resistance shunt (whats designed to carry most of the current) was bad/open normal current would then be so great it would burn the galvo windings open instantly.

In this case it appears the needle and galvo is functioning as the needle still moves and again I think if the shunt was open the galvo winding would burn open instantly.

An "ideal" ammeter is ZERO resistance while an "ideal" voltmeter has infinite resistance. An ammeter is NOT supposed to be a load that affects the load current readings which is why its like ZERO ohms resistance which is why if I recall correctly any shunt would be very low ohms so the current divider allows most current through it with only a small fraction having to pass through the small tiny wire galvo windings

Maybe Bob or some Ford men can correct me if my memory is wrong!!!!!!!!!!!!!!!!!!!!!!

Does this help or answer your question or make any sense at all lol

John T
 
Hello John;
I did polarize the generator after I received the advise from you on the forum.
regards,
walt
 

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