Odd charging issue

[Dan]

Update - Today I replaced the regulator with an Echlin VR950 for later 8Ns with a 2 brush 20 amp generator. The tractor started and ammeter showed 10 amps at fast idle. Moving the throttle up to halfway and the ammeter smoothly went up to 18 or so amps. Took a reading at the battery and it was over 7 volts. Looked at the ammeter again and it was now jumping all over the place fast between 10 to 20 amps. Checked the voltage at the battery again and it showed 7.60 volts. Shut down and restarted the tractor again and once again ammeter smoothly went up to 18 amps then started bouncing again.

Battery is new and shows 6.4 volts after sitting several days. Should it read higher? It this wht the ammeter shows 18 amps trying to charge it?

Is it right or normal for the generator to be putting out 7.6 volts to a 6 volt battery?

Any idea why the ammeter starts bouncing and never settled on a constant reading?

 

[Mad Farmer]

Might want to check the wires/connections for shorts, and verify the ammeter is not faulty.

 

[Dan]

Might want to check the wires/connections for shorts, and verify the ammeter is not faulty.

I already verified the three wires from the VR to the genny are not shorted. I may have another ammeter kicking around I could swap, but it operates smoothly until the VR starts cutting it out so I would "think" the ammeter is not the issue(?)

 

[HCooke]

Update - Today I replaced the regulator with an Echlin VR950 for later 8Ns with a 2 brush 20 amp generator. The tractor started and ammeter showed 10 amps at fast idle. Moving the throttle up to halfway and the ammeter smoothly went up to 18 or so amps. Took a reading at the battery and it was over 7 volts. Looked at the ammeter again and it was now jumping all over the place fast between 10 to 20 amps. Checked the voltage at the battery again and it showed 7.60 volts. Shut down and restarted the tractor again and once again ammeter smoothly went up to 18 amps then started bouncing again.

Battery is new and shows 6.4 volts after sitting several days. Should it read higher? It this wht the ammeter shows 18 amps trying to charge it?

Is it right or normal for the generator to be putting out 7.6 volts to a 6 volt battery?

Any idea why the ammeter starts bouncing and never settled on a constant reading?

I think it is normal for the generator to be putting out 7.6 volts. I had a '51 where the ammeter would "jump all over the place" after initially showing it to be charging.

 

[JMOR]

It likely won't do that with a well charged battery. What you are seeing is the current limiter , which is at 20 amps, and as it tried to charge beyond that it cuts back, then it looks ok, so it cuts back in and the cycle repeats... Doing what it was designed to do.

 

[Dan]

It likely won't do that with a well charged battery. What you are seeing is the current limiter , which is at 20 amps, and as it tried to charge beyond that it cuts back, then it looks ok, so it cuts back in and the cycle repeats... Doing what it was designed to do.

That makes sense. So, if a battery is already well charged, any ideas on why the generator is putting out full output to the VR? There are no shorts to ground or other wires on the three wires between the VR and genny. The previous VR acted the same way until the cutoff activated.

Is it possible the generator field insulator inside the genny is grounding to the genny body and causing what I am seeing?

 

[JMOR]

That makes sense. So, if a battery is already well charged, any ideas on why the generator is putting out full output to the VR? There are no shorts to ground or other wires on the three wires between the VR and genny. The previous VR acted the same way until the cutoff activated.

Is it possible the generator field insulator inside the genny is grounding to the genny body and causing what I am seeing?

I'm not big on guessing, but you could test you speculative cause by disconnecting the wire to generator field terminal, that should stop charging.

 

[Dan]

Final Update - for future tractor enthusiasts who find this post on a search -

Got up early this morning to work through a few hypothesis. First I removed the Field wire from the generator and measured resistance between the Field stud on the generator to the Ground lug - it showed no resistance (which I would expect this would mean the Field insulator on that lug was shorting to ground). Same result on loose Field wire to Ground, but it was still attached on th VR side. I start the tractor up and no charging seen at the battery as would be normal. Put the Field wire back on the lug and I am back to charging over 7 volts at the battery again as also would be normal. Checked voltage at Armature stud on generator and it was 8.35v on rev. Ultimately the charge voltage at the battery was 7.60v (which seems high to me). Ammeter still bouncing wildly between 10 and 20 amps.

At this point I swapped the generator with a known good 2 brush unit off my 1948 8N trailer queen. The results were similar to above. So now I am pretty sure that the original generator is good.

Taking Mad Farmers advice, I replaced the ammeter with a brand new one I had in my parts box and start it up again. Battery still shows 7.5ish volts at a rev but now ammeter goes smoothly to 8 amps, then quickly down to 3 to 4 amps as would be normal.

So, to recap, while I had and early 1950 8N with a front mount distributor, I had a later 2 brush generator so going by just the serial number I ordered the wrong voltage regulator for the later generator and therefore the VR was cutting out too soon (and also sticking and not opening back up unless I tapped on it). Replacing this VR with a quality VR for the later model 8N fixed this issue.

Next, the ammeter while working was not showing the correct amp draw I guess so replacing it fixed this issue.

Now, since I am electrically challenged, a few questions for the more learned:

In my research I see the ideal max charge voltage is 6.9 - 7.3 on a 6 volt system. Since mine is charging at 7.6 is this a concern for a 6v battery?

Also, both the old VR and the new VR was definitely cutting out due to meeting amp draw maximum settings. However, the new ammeter only shows 4 amps now? I wouldn't think bad ammeters would DRAW amps but that was the only thing I changed(?)

 

[Jim L WA]

The ammeter doesn't draw current. It only shows what's passing through it. I'm wondering if your new ammeter has an internal shunt in it to attenuate that wild fluctuation.

 

[Dan]

The ammeter doesn't draw current. It only shows what's passing through it. I'm wondering if your new ammeter has an internal shunt in it to attenuate that wild fluctuation.

This is the one I am now using, typical ammeter like from this site. The weird thing on the old one was it would go smoothly up to the amp cutoff amps and the start the wild fluctuations. Shut off the engine and restart and it is smooth again as long as the rpms are just a fast idle. It would stay steady at say 10 amps forever, until you reved the engine and the amps got to the cutoff range. The new one stays at 4 amps from fast idle to full rev and only drops at a slow idle where the genny kicks out.

 

[Btzj02]

I am also curious about the Amp meters. Are they inductive Amp meters, wire through the loop, or shunt Amp meters, wire terminated on both sides of the Amp meter.

 

[Dan]

I am also curious about the Amp meters. Are they inductive Amp meters, wire through the loop, or shunt Amp meters, wire terminated on both sides of the Amp meter.

Mine was the wire on both sides kind, not the loop kind.