Testing an amp meter

[Charlie M]

I bought a used box for my BN that contains the light switch and amp meter and it came with an amp meter. Is there a way to bench test the amp meter to know if its any good or I just need to install it and see if it works.

 

[dr sportster]

feed it and add a load

 

[JMOR]

I run a known current thru one and see what it reads. Known, as from a variable power supply and another ammeter for comparison. If no equipment, use a lamp and battery. For example, my 12v headlamps are #4419, 35 Watts, which in amperes is 35/12.5v = 2.8 Amperes. Use two lamps for 5.6 Amps. Or use 4421 lamp for 100W, 100/12.5 = 8A, or two for 16Aa.

 

[BarnyardEngineering]

Definitely do NOT connect the ammeter directly to the battery. That's a good way to 100% ensure the meter is no good.

A very simple way to test, is to get any kind of 12V light bulb in a socket with wires, and wire it up like this:

battery + ----- light ---- meter ---- battery -

Polarity doesn't matter with light bulbs, and if you hook the meter up backwards it will simply read backwards. Don't worry about this "known load" stuff. All you care is if the needle moves when you pass a load through the meter.

 

[JMOR]

(quoted from post at 14:00:18 04/06/23) Definitely do NOT connect the ammeter directly to the battery. That's a good way to 100% ensure the meter is no good.

A very simple way to test, is to get any kind of 12V light bulb in a socket with wires, and wire it up like this:

battery + ----- light ---- meter ---- battery -

Polarity doesn't matter with light bulbs, and if you hook the meter up backwards it will simply read backwards. Don't worry about this "known load" stuff. All you care is if the needle moves when you pass a load through the meter.

hat's right, don't worry about it if you don't give a sheet about accuracy

 

[Russ from MN]

I think you could use a battery charger that you think has an accurate gauge. Hook the charger to a battery with the meter in series, and the 2 gauges should agree. Make sure you hook it in series, or it will be bad for sure, like someone else said!

 

[BarnyardEngineering]

(quoted from post at 11:44:15 04/06/23)

(quoted from post at 14:00:18 04/06/23) Definitely do NOT connect the ammeter directly to the battery. That's a good way to 100% ensure the meter is no good.

A very simple way to test, is to get any kind of 12V light bulb in a socket with wires, and wire it up like this:

battery + ----- light ---- meter ---- battery -

Polarity doesn't matter with light bulbs, and if you hook the meter up backwards it will simply read backwards. Don't worry about this "known load" stuff. All you care is if the needle moves when you pass a load through the meter.

hat's right, don't worry about it if you don't give a sheet about accuracy

It's an ammeter for an old tractor, not precision lab equipment being used where lives are on the line. Most of them are marked "D C" for discharge and charge. You shouldn't "give a sheet" about accuracy. If the needle moves a little toward C when it's charging a little bit, and more towards C when it's charging more, that's all you need or care to know.

Knowing exactly how many Amps are going into your battery is for people with too much time on their hands.

 

[JMOR]

(quoted from post at 15:53:50 04/06/23)

(quoted from post at 11:44:15 04/06/23)

(quoted from post at 14:00:18 04/06/23) Definitely do NOT connect the ammeter directly to the battery. That's a good way to 100% ensure the meter is no good.

A very simple way to test, is to get any kind of 12V light bulb in a socket with wires, and wire it up like this:

battery + ----- light ---- meter ---- battery -

Polarity doesn't matter with light bulbs, and if you hook the meter up backwards it will simply read backwards. Don't worry about this "known load" stuff. All you care is if the needle moves when you pass a load through the meter.

hat's right, don't worry about it if you don't give a sheet about accuracy

It's an ammeter for an old tractor, not precision lab equipment being used where lives are on the line. Most of them are marked "D C" for discharge and charge. You shouldn't "give a sheet" about accuracy. If the needle moves a little toward C when it's charging a little bit, and more towards C when it's charging more, that's all you need or care to know.

Knowing exactly how many Amps are going into your battery is for people with too much time on their hands.

k, I m beginning to see how you got the modifier, "barnyard" engineering.

 

[Geo-TH,In]

I bought this meter off Amazon under $40. It is also a clamp-on DC ammeter.

It measured 0.15 dc amps for an alternator Idiot light.
105 amps for lawn mower starter.
I haven't had the urge to compare it to other DC ammeters.
I feel it will come in handy finding a parasitic loads.

 

[Bob M]

Quick easy test: Bring a small magnet to the glass ammeter face then move it around. If the hand deflects in either direction it is not stuck. Then check continuity between the two meter posts - it should be a dead short (0 ohms).

If the ammeter passes both of the above it will HAVE to work!!

 

[sotxbill]

Yes.. do a continuity test on those 20 microamp current meters and see how many work the second time around.

 

[JMOR]

(quoted from post at 20:54:18 04/06/23) Yes.. do a continuity test on those 20 microamp current meters and see how many work the second time around.

nstead of all the BS stuff, why not just put the correct amount of current thru the meter it was designed to read and verify it? Sure you can do all kinds of "other" stuff and maybe convince yourself that it responds to something.....including , see if the needle moves when dropped from 4 feet, but when done, what do you "know"?
Yes, I know , what all need is controversy, talk, argue, confront, on & on. So , have at it!

 

[rustred]

all i do is have it in my hand , remove batt. cable then stick one terminal on cable and other terminal on battery. now the harazzing will start. its the way i check them and not nothing has blown up. its a 3 second check.

 

[JMOR]

(quoted from post at 23:08:40 04/06/23) all i do is have it in my hand , remove batt. cable then stick one terminal on cable and other terminal on battery. now the harazzing will start. its the way i check them and not nothing has blown up. its a 3 second check.

K, so that tells you is sees something, something unknown, that is. What is an ammeter supposed to do? Ans: measure current, not in pounds or ounces or liters, but in Amperes. So, the real test is does it show the correct reading for a given number of Amperes passing thru it? If that is not your particular interest, then you need a red "idiot" light.....it will tell you all you want to know.

 

[rustred]

No idea what you are talking about. But I like to see the
ammeter move to the right when tractor is running. I
dont like a red light. The guy just asked if there is a way
to see if they are good. So no idea what this off the wall
stuff is.

 

[JMOR]

(quoted from post at 00:37:02 04/07/23) No idea what you are talking about. But I like to see the
ammeter move to the right when tractor is running. I
dont like a red light. The guy just asked if there is a way
to see if they are good. So no idea what this off the wall
stuff is.

good" means it does what it was designed to do.. Pretty simple, huh? That is 'to measure Amperes".. Simple enough.

 

[John T]

As ALWAYS its fun to read all the responses to ANY electrical or legal questions... Opinions, or even feuds can develop over so very basic SIMPLE questions !! Many give an answer but its NOT an answer to the question when it comes to electrical or legal topics. Oh well lots of good people here all willing to help, it is what it is, I'm not complaining I enjoy it and glad to help anytime I can.

I recall from yearssssssssssssssssss ago how an IDEAL (none exist) AMMETER has ZERO resistance while and IDEAL VOLTMETER has INFINITE resistance. A typical cheap garden variety old car/tractor Ammeter is a passive series device. If you need an accurate test you have to supply a known accurate reference current source through the meter and see how close it corresponds to that value of current WELL DUH..Or just hook it up between the tractors battery and a known load (that yields current within meters range) and see what happens. I agree with my friend Bob M's very basic check, if a magnet causes the needle to deflect (its NOT stuck and operable) and if it shows very low resistance continuity through it, theres a good chance it will WORK while the accuracy is another thing ??????

Best wishes to all here, fun to read thread, hope this helps

John T

 

[Tim PloughNman Daley]

I don't know what a BN is nor what box you mention. Do you mean a FORD 8N tractor? If so that would be the original 30/30 A INDUCTION AMMETER also called the LOOP AMP GAUGE. It is a 30 AMP gauge, current is measured with a wire via a loop on the rear backing plate. You can test it simply by passing a magnet over the face plate and if it is good the needle will move. The first early 9N AMP GAUGE was a 20/20 AMP unit with screw terminal connections and used up thru s/n 9N-4000. Then the LOOP gauge was released and used up thru the Hundred Series models. If gauge measures backwards, that is when tractor is running and gauge shows a negative reading the wire feed direction needs to be reversed. If you have an aftermarket 30A screw terminal gauge, simply reverse the terminal connections. With tractor running at idle, AMMETER should show a POS charge. Flip the light switch ON and gauge should show a slight or NEG discharge. REV up engine and gauge should show a slight needle move to POS side. A big mistake some owners make is the failure to have a fan belt tensioning device on their GEN or ALT. Without a belt tensioner and proper fan belt tension set, you will never charge the battery. Thus they automatically assume (falsely) their AMMETER is bad. You can also test the AMMETER with the Generator on your bench. The I&T FO-4 Service Manual has a chapter on motor testing the GEN and involve the AMMETER in the circuit. You also need to heed what JMOR says. He is a highly qualified and skilled electrical engineer and knows what he is talking about.

FORD 9N-10850-A, 20/20 AMMETER w/SCREW TERMINAL CONNECTIONS, USED ONLY ON THE FIRST 4000 9N TRACTORS IN 1939:

FORD 9N-10850-B, 30/30 AMMETER w/LOOP (INDUCTION) STYLE CONNECTION, USED AFTER THE FIRST 4000 9N TRACTORS IN 1939 TIL 1957; & aftermarket screw terminal style now used:

NOTE: LOOP SHOWN ON LEFT, TERMINAL STYLE ON RIGHT.

OEM FORD 9N-10850-B LOOP AMMETER:

TESTING THE FORD TRACTOR GEN WITH THE AMMETER; from THE I&T FO-4 MANUAL:

Tim Daley(MI)

 

[Jim.ME]

A BN is a Farmall.