• From: Colorado Springs, CO
  • Registered: 2004-03-27
  • Posts: 3,622

Topic: General Ammeter question.....

Ok, I found an old 30-0-30 DC ammeter at a garage sale and of course I had to have it ($2). I know that an ammeter must be connected in series but I won't go into the specialty shunts, etc. that may be installed in certain models, since mine doesn't have one.

So my question is: since this is a bi-directional meter that centers on "0", does it matter which post on the ammeter would be connected to the voltage regulator (B+) and which post to the battery? (Neither of the posts are marked) And does the needle move in the direction that current is "flowing"?

So in schematic terms:
[Regulator (B+)----Ammeter----Heavy red wire to the Battery positive post]

If the needle is moving -----"0"--->>> (to the "right" of "0") does that mean the Battery is receiving the charge? And conversely if the needle is moving to the left
<<----"0"----- then the battery is discharging?

Simple questions I hope....I understand the operating principles, but when I connected to my Bug last night I found ----"0"--> at idle and <<<<----"0"--- when rpms increased to around 3000.  For some reason I thought it should be just the opposite.

Help the boy understand.

Clancy

  • From: Henderson, ky
  • Registered: 2007-01-15
  • Posts: 49

Re: General Ammeter question.....

Clancy,

Another test is with the motor not running just turn on the lights. If it is wired correctly
then the meter will show a discharge. If it doesn't then reverse the wiring of the meter.
I thought that most ammeters were marked with a +/- side of the gage.

abba

  • From: B.C.Canada
  • Registered: 2005-01-26
  • Posts: 2,610

Re: General Ammeter question.....

If you want it in the dash you must run one heavy wire (10?), same as the red/white one, from the regulator area to the meter.

Connect the red wire from the battery to this wire instead of the reg.

If you don't want to cut the large female spade connector off you can salvage a male connector from an old regulator and make this a plug in, easily reversed connection. I put a 30 amp fuse in at this point, since the VW has no protection all the way to the front.

This thing was made just to insert a fuse, not for an ammeter, so instead of the wire on the right, which would plug into the reg., connect the new wire that goes to the ammeter in the dash. It has to be taped up or mounted in a way not to short out of course.

http://i29.tinypic.com/2lc7gxx.jpg

Connect the other terminal on the ammeter to the fuse box where the wire from the regulator connects. (red/white)

Determine polarity as abba74 says.

Voltmeters and ammeters tell you a lot of the same things and voltmeters are easier to install. An ammeter gives you a better idea of your battery ability to hold a charge. It will also tell you if something is draining your battery when everything is off. It's nice to have both but I get by with just a voltmeter right now. I use my dash type ammeter as a portable test instrument so I can insert it in any particular circuit.

jim

Last edited by jamesdagg (2008-06-03 17:29:25)

'71 SB(DD only 79K(now 84K miles) & '78 FI Westy (project)
PO of '65 Beetle in '69, '70 Crewcab & '70 Ghia in '77
'71 Super inside rear vents now available
http://www.openroad.ca/volkswebbin/view … p?id=85915
  • From: Henderson, ky
  • Registered: 2007-01-15
  • Posts: 49

Re: General Ammeter question.....

In a system where everything is in good working condition then at idle
the ammeter should show a slight discharge. As you raise the rpm then
you should see a slight increase in amps and then as the battery is fully
charged then the amp gage should be at 0. The rate of charge (+) will
depend on the level of charge in the battery.


abba

  • From: Colorado Springs, CO
  • Registered: 2004-03-27
  • Posts: 3,622

Re: General Ammeter question.....

Thanks, Jim and Abba: (Take a chance, Take a chance, Take a chance on me.....) I am not installing this little baby, just was trying to use it as a test instrument, like they do in the big blue Bentley manual. What is really confusing me is that I thought on the "bi-directional" meters (e.g. 30-0-30) that the needle swung in the direction of the current flow. I'll post a picture of the little non-automotive ammeter......
http://images.thesamba.com/vw/gallery/pix/447226.jpg
http://images.thesamba.com/vw/gallery/pix/447225.jpg
http://images.thesamba.com/vw/gallery/pix/447235.jpg

Clancy

  • From: B.C.Canada
  • Registered: 2005-01-26
  • Posts: 2,610

Re: General Ammeter question.....

Well yours doesn't say + or - so it's irrelevant. An auto one shows polarity and often is red on the discharge side so it matters. But to use as a test instrument it matters so test it with a battery and a load and use a red lead for + and a brown for ground.

As Abba says you should see a "slight" increase in amps till your battery recovers from cranking. If it takes more amps after startup to return to 0 then your battery is not holding a charge. That's one thing a voltmeter won't tell you.

jim

'71 SB(DD only 79K(now 84K miles) & '78 FI Westy (project)
PO of '65 Beetle in '69, '70 Crewcab & '70 Ghia in '77
'71 Super inside rear vents now available
http://www.openroad.ca/volkswebbin/view … p?id=85915
  • From: Colorado Springs, CO
  • Registered: 2004-03-27
  • Posts: 3,622

Re: General Ammeter question.....

Continued thanks. So in my scenario, I attached the right hand 'pigtail' to the heavy red wire I disconnected from the B+ post on the regualtor. Then I attached the left pigtail to the B+ post on the regulator. At idle, the needle floats to around 5 to 10 on the right of the "0".  At higher rpms, (~3,000) the needle floats to around 15 to 20 on the left side of the scale. Intuitively, that would seem to indicate a 'charging' condition (i.e., the higher rpms are runing the generator at a higher speed and should be sending a charge to the battery) but in the case of this meter, the needle is floating away from the battery..... By the way, I tested the generator and it is producing upwards of 15 to 18 volts when disconnected from the regulator, so I'm assuming that it's ok. I need to try Abba's suggestion of having the meter hooked up, engine off and turning the headlights on....that should finalize my experiment.

Thanks, again.

Clancy

  • Registered: 2007-03-27
  • Posts: 2,422

Re: General Ammeter question.....

Big red wire << Charge wire ! Cut it in half !
2 wires out of the ammeter connect them too both the end's of the Big red charge wire where you cut it in half ! << That simple ! Your just installing it inline .
  JUst dont really cut the charge wire << As in figure somethin out similar !
Should read about 2 ta 6 amp's when reg cut's in . Pull head light's on usually trip's the reg  over to chargeing !
  A discharge condition the meter will go to one side indicateing Discharge .
                                                                                                Sean