Generator Output Test

In service manual, it tells you to disconnect armature wire from generator and put a jumper between field terminal and armature terminal on generator. Then measure with 2 lead ammeter between armature wire terminal and armature terminal on generator. My question is, why can't I just use a DC clamp-on ammeter and measure current directly on on red armature wire with everything connected as normal? I tried and I get zero. Tractor starts with no issue so I know battery is charging but I'd like to just test generator to make sure it's putting out the recommended 20 amps @ 1500 rpm.

(quoted from post at 16:48:06 12/30/12) In service manual, it tells you to disconnect armature wire from generator and put a jumper between field terminal and armature terminal on generator. Then measure with 2 lead ammeter between armature wire terminal and armature terminal on generator. My question is, why can't I just use a DC clamp-on ammeter and measure current directly on on red armature wire with everything connected as normal? I tried and I get zero. Tractor starts with no issue so I know battery is charging but I'd like to just test generator to make sure it's putting out the recommended 20 amps @ 1500 rpm.

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ecause, "as is" means that the regulator is controlling the amount of charge & if battery is full up, it needs no charge, reg commands gen to provide no charge. Their recommended arrangement commands gen to provide full output. From the description, it appears that you have a post 1952 (8N) tractor?

Ahhh.....Makes perfect sense. I do keep it on a 6V battery maintainer to keep charge at full. I'll have to find a different ammeter. My 2 lead is only good to 10 amps.. Tractor is a '58 861. Thanks for your help.....

Tom- You didn't say if this is a 6V or 12V system
and if the tractor is gas or diesel. Really, you
are testing the charging system as a whole,
including the regulator and there needs to be some
load on it, besides charging the battery. If the
battery is nearly new there won't be much charging
current. Some current is used for the ignition
system if it is a gas engine. You could turn on
the headlights, normally about 5A if 12V and 10A
if 6V. The best test is to look at voltage after
starting and when accessories are on, etc.
Voltage should be about 6.5V or 13V respectively
at about 1000rpm. If so, with accessories on, then
all is OK. -Will

(quoted from post at 18:06:47 12/30/12) Ahhh.....Makes perfect sense. I do keep it on a 6V battery maintainer to keep charge at full. I'll have to find a different ammeter. My 2 lead is only good to 10 amps.. Tractor is a '58 861. Thanks for your help.....

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om, your clamp on DC ammeter would still be just fine. It is the Armature to Field jumper that commands full output.

Just want to be sure before I try. Leave all connections wired "as is" and then jumper the armature and field terminals on generator to command for full load? Then use my DC clamp on red armature wire to measure current going to voltage regulator? Will also check voltage going to battery when running as mentioned in previous reply.

Just want to be sure before I try. Leave all connections wired "as is" and then jumper the armature and field terminals on generator to command for full load? Then use my DC clamp on red armature wire to measure current going to voltage regulator? Will also check voltage going to battery when running as mentioned in previous reply.

(quoted from post at 22:00:39 12/30/12) Just want to be sure before I try. Leave all connections wired "as is" and then jumper the armature and field terminals on generator to command for full load? Then use my DC clamp on red armature wire to measure current going to voltage regulator? Will also check voltage going to battery when running as mentioned in previous reply.

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ou got it right.

full field her and check amps and volts...