8n pulling 30 amps at 1/2 throttle no load

ToddNick · Oct 29, 2012

Guys,

I have been reading your posts for awhile to help me get my 8n 6v side mount running, but now I am needing help.

My ammeter shows 30'plus at mid throttle in neutral. I began with a neg read with lights on engine off and no amps when running. I followed the diagnostic chart and jumped the bat and arm with it running and it jumped to 30 so I replaced the vr. The new vr is now showing neg amps with lights on and engine off but showing around 10 amps at idle and 30 when mid throttle. I removed the field from the gen and it immediately dropped to zero amps when running. I jumped the filed from gen to field on vr and right back to 30. Is my gen bad? Or is my new vr playing games? I did polarize after replacing the vr.

JMOR · Oct 29, 2012

(quoted from post at 20:13:31 10/29/12) Guys,

I have been reading your posts for awhile to help me get my 8n 6v side mount running, but now I am needing help.

My ammeter shows 30'plus at mid throttle in neutral. I began with a neg read with lights on engine off and no amps when running. I followed the diagnostic chart and jumped the bat and arm with it running and it jumped to 30 so I replaced the vr. The new vr is now showing neg amps with lights on and engine off but showing around 10 amps at idle and 30 when mid throttle. I removed the field from the gen and it immediately dropped to zero amps when running. I jumped the filed from gen to field on vr and right back to 30. Is my gen bad? Or is my new vr playing games? I did polarize after replacing the vr.

en to Fld jumper should have & probably did weld the field control contacts together such that it will put out full charge all the time, & eventually boil the battery.

ToddNick · Oct 29, 2012

Fld from gen goes to fld on vr, right? So I removed them both
and used a dedicated jumper to rule out a bad wire and got the
same result.

JMOR · Oct 29, 2012

(quoted from post at 20:29:44 10/29/12) Fld from gen goes to fld on vr, right? So I removed them both
and used a dedicated jumper to rule out a bad wire and got the
same result.

K, my bad. I mis-read your sentence. Yes, gen field is a direct wire to VR field terminal. It does however sound like field contacts in VR are stuck closed, thus grounding the generator Field terminal all the time & that yields full field current & max gen output. BUT, a bad or even undercharged battery will have a low enough voltage to cause the field control to call for full charge until battery voltage rises to a level that VR senses that voltage & starts to reduce field current. Can you get a good battery voltage measurement both before starting and after/while running at 30amps?

ToddNick · Oct 29, 2012

Battery shows 6.08 standing (post to post) and climbed to 7.3
after running mid throttle for a few minutes.

JMOR · Oct 29, 2012

(quoted from post at 20:50:40 10/29/12) Battery shows 6.08 standing (post to post) and climbed to 7.3
after running mid throttle for a few minutes.

ccording to Ford spec sheet @ 20amps, 6.8v should command a reduction.
At 5amps, it can reach 7.4v before reducing output.

But you are at 30A and 7.3v & that is out of spec.

I would remove reg cover & feel to see if you can open field contacts against spring force or if they are stuck closed.

ToddNick · Oct 29, 2012

I actually did that earlier this evening. Both contacts in the VR
appeared free.

JMOR · Oct 29, 2012

(quoted from post at 21:19:38 10/29/12) I actually did that earlier this evening. Both contacts in the VR
appeared free.

f field control contacts are not opening at spec voltage, then it is possible that the shunt coil that senses the voltage & pulls them open has an open wire/winding in it. Be sure the ground wire between VR case and generator case is good.

souNdguy · Oct 30, 2012

just to recap. if the vreg field contacts are propped open with a toothpic does the charge drop?

if yes, and the field contacts are jsut ataying closed full time.. then the vreg is bad.

ZANE · Oct 30, 2012

I'm just asking, but aren't there two different VRs for the 8Ns at different serial numbers????

Which one should he have?

Zane

ToddNick · Oct 30, 2012

Yea, the voltage dropped to zero when I propped the field contact open with a toothpick. Nice trick.

I will get another new VR and see if that fixes it. Stupid question- Can the gap be set on the field contacts?

I appreciate the knowledge you folks have in regards to these old gems.

souNdguy · Oct 30, 2012

sometimes you can find an adjustable field and cutout reg.. most of the itme adjustment is by tweaking / bending.

in your case.. field ckt may actually be dead, and thus not operating the field contacts at all.. just leaving them closed..

JMOR · Oct 30, 2012

(quoted from post at 16:26:50 10/30/12) I'm just asking, but aren't there two different VRs for the 8Ns at different serial numbers????

Which one should he have?

Zane

es, Zane, but the 8N10505A is unobtainium these days, so you just have to use the 8N10505B and set the 3rd brush to limit current.
See my long answer at link, near bottom of first page of threads in modern view.
http://ytforums.ytmag.com/viewtopic.php?t=956884

8n pulling 30 amps at 1/2 throttle no load

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