How to read an Ammeter

[PTG]

Hi Guys,

I'm wondering if someone can take a minute or two and explain how to read an ammeter. I looked for some articles online to save someone the headache of explaining, however I didn't find any related more to my application.

I have a 1942 9N 6volt front mount. Can someone point me to an article or type a quick ammeter 101 for me? I'm not doing myself or anyone else any favors by not learning this.

PTG in MN

 

[TheOldHokie]

(quoted from post at 14:41:09 03/16/10) Hi Guys,

I'm wondering if someone can take a minute or two and explain how to read an ammeter. I looked for some articles online to save someone the headache of explaining, however I didn't find any related more to my application.

I have a 1942 9N 6volt front mount. Can someone point me to an article or type a quick ammeter 101 for me? I'm not doing myself or anyone else any favors by not learning this.

PTG in MN

T'ain't hard:

• 
  [*:ac305a3555]When the meter reads + the generator is charging the battery: +5 = 5 amps charge, +10 = 10 amps charge, etc.
  [*:ac305a3555]When the meter reads - the battery is discharging to power some electrical load on the tractor. Either the load is greater than the generator can produce and the battery is supplying the difference or the generator is not working.: -5 = 5 amps battery discharge, -10 = 10 amps battery discharge, etc
  [*:ac305a3555]When the meter reads 0 the generator is supplying exactly enough current to power all the electrical loads on the tractor and the battery is neither charging or discharging
  [/list:ac305a3555]
  TOH

 

[Jubilee85 (VA)]

Ptg,

To add to what TOH mentioned, an ammeter measures induction, or strength of magnetic field. In this case the current or AMPs are flowing in one direction or the other, as the current "flows" a magnetic field is created, and the meter moves like a compass indicating the strength of the field, or the flow or electrons, amps. When the meter is pointing the other way, current is flowing "backwards" or draining the system, the magnetic field has been flipped and like a compass reflecting a backwards magnetic field. HTH

 

[PTG]

Got it.

So to get the best reading the tractor should be
running correct?

And I'm guessing with the tractor running the goal
would be 0 or ideally +?

 

[JMOR]

(quoted from post at 15:23:17 03/16/10) Got it.

So to get the best reading the tractor should be
running correct?

And I'm guessing with the tractor running the goal
would be 0 or ideally +?

If it isn't running (& there are loads drawing current) it will read negative, as battery is discharging.

To obtain meaningful indication that charging system is working, it must be running at reasonable speed & yes zero or slight Positive are good goals.

A word of caution: This post and those preceding it all assume that your ammeter is as Ford factory connected them, which was as a NET reading ammeter. Some if not all of the conversion kit diagrams that I have seen instruct installing ammeter to read alternator output only, not NET. So in such case the ammeter will not read loads, battery discharge, or battery charge and will thus never show a negative (discharge) unless the alternator has some particular failure mode. When all is well, those so connected will register total alternator output which is the sum of loads plus battery charging current.

Remember, in life nothing is simple & nothing is absolute.

 

[Dell (WA)]

PTG........you ALWAYS need to run yer tractor so the genny is charging as shown on yer amp-meter. ZERO ain't gonna keep yer batter charged. Yer 3-treminal 8N genny can produce only 20-amps MAX. Yer 1-terminal 3rd-brush 9N/2N genny can only produce 11-amps max. You manually adjust the 3rd-brush on end of 9N/2N genny for about +5-amps charge at 1/3-throttle. Yes, you haffta re-adjust iff'n you have headlites ON or OFF.

Too much charge will BOIL yer battery DRY and ruin it. Too little charge and yer battery won't start yer engine. Simple, eh? .......Dell

 

[PTG]

Simple enough Dell,

One other question then.

Based on the comment of adjusting the generator I started the tractor (With a jump) and noticed at 1/3 throttle the ammeter read -3. I looked at the end of the generator and noticed the screw with two arrows one pointing to "Low" one pointing to "high", I turned in the high direction, and no matter how many turns I was not seeing any change on the ammeter. Any thoughts on where to go from here to figure out why it's not charging?

I'm going to replace the wire that runs from the cutoff to the generator for sure. It's really old and is showing signs of exposed wire. I assume that is a good place to start. At that thought, what gauge should that wire be? Also what else should I look into to see why that ammeter reading is -3 and not changing...

Any thoughts would be helpful.

PTG

 

[HCooke]

If you don't have one you need a VOM - an analog one works much better on these old tractors than a digital one. Without the engine running, your battery should read 6.2 volts. Running, it should increase to a max of 7.4 volts accross the battery terminals; if not, your charging system is not working.

 

[Greybeard - PA]

All the advice you are getting is right on, here. One other thing you should understand about your ammeter, on a properly working system, each time you start your engine, the ammeter should register some positive charge, and continue to do so until the battery is back to full charge from the last start-up. Once this happens, the gauge will drop to near zero, because the battery is no longer calling for any further charging. So it is that the battery is the brains of the whole charging system - it even tells the regulator and generator when to go to work and when to quit. Amazing, not?

Dave Erb
New Holland, PA

 

[Hobo,NC]

(quoted from post at 23:12:58 03/16/10) If you don't have one you need a VOM - an analog one works much better on these old tractors than a digital one. Without the engine running, your battery should read 6.2 volts. Running, it should increase to a max of 7.4 volts accross the battery terminals; if not, your charging system is not working.

I agree,,, Amp gauges are useless unless you are get'n into some serious diagnostics,,, folks need to learn how to read a voltmeter... Most gurus don't

WARNING :shock: all I know I read on the Internet,,, do it enuff and you can become a guru also,,, not responsible for damages,,, I read it and just pass it along,,, proceed with caution

 

[TRS]

So with 12v system and alternator then old ammeter would basically just be pegged out if working?

 

[R Geiger]

(quoted from post at 15:35:00 06/24/23)
So with 12v system and alternator then old ammeter would basically just be pegged out if working?

No, Both of my 8n's show about +10 when first started and4then drop back to 0 when the battery is charged. amp meter does not care if it is 6 volts or 12. It is reading current flow, not voltage!

 

[Jim.ME]

(quoted from post at 17:35:00 06/24/23)
So with 12v system and alternator then old ammeter would basically just be pegged out if working?

As note by others the voltage doesn t matter

If you have a 20 - 0 - 20 ammeter, an alternator may peg it as generally alternators put out at least 35 amps and many will produce over 60 amps.

 

[HFJ]

i didn't notice the nearly 10K views until after i saw Dell posting :shock:

 

[Mad Farmer]

One other thing should be mentioned, unlike an alternator, a generator will not put out current a lows rpms. So you may see discharge until you throttle up.

 

[Eman85]

(quoted from post at 07:42:27 06/25/23)
One other thing should be mentioned, unlike an alternator, a generator will not put out current a lows rpms. So you may see discharge until you throttle up.

Put an alternator on an 8N especially a 1 wire setup and you'll most likely have to throttle up to see current.