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John Deere Tractors Discussion Forum
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M charging circuit problem

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Ken WI

05-14-2005 11:32:21




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Clooney,

Have a charging problem w/ M (+ Gnd.) that I just got running > resto. This tractor was not running when I got it so I have no history. I checked everything out per your previous posts to Tom. The wiring seems OK and charging/cut-out test w/ bat charger all looks correct. Generator appears to be reverse pol. & efforts to repolarize do not change anything. When bring RPMs up, C.O. closes and amp shows ~ 15 amp discharge. The motoring Check out of the Gen. shows that it motors CW (fwd) w/ + gnd & -6v applied to A. but when I lift the F post Gnd wire the direction reserses (CCW). I took it to a local rebuild shop & they said that they could not see anything wrong. I took the gen apart again & looked real close & again looking for grounds but found none. Generator internal wiring has A to the third (adjustable) brush & field wire to main brush which is opposite the gnd brush. Any further wisdom would be appreciated. I thought that your previous posts on this sub. were excellent. Ken B

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Ken WI

05-15-2005 19:24:47




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 Re: M charging circuit problem in reply to Ken WI, 05-14-2005 11:32:21  
OK, If you all are still following this...
I finally met some success today.
Talked to my bro. who is a Ford/Merc tech.
He suggested flashing the field in the opposite polarity. I had my old TVOM zero centered when I did this & it was quit a dramatic thing for me to observe. I flashed it using a battery charger & it just flipped polarity and started charging ~ 10 amps. Now only problem is that the resistor for low/normal charge seems to be overheating i.e. it smokes. I need to pull that out to see whats wrong. Thanks to all who posted responses. It helps to have ideas from other tractor guys. Ken B

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Ken WI

05-14-2005 14:06:17




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 Re: M charging circuit problem in reply to Ken WI, 05-14-2005 11:32:21  
I don't think so!
When measuring at A w/ reference to ground, as I bring the RPMs up the voltage is Pos. (this should not be) When it gets to ~6.5 v the C.O. closes. Then my meter drops to a very low value and AMP reads ~ - 20 amps. My idea is that the current is very high because the gen. is charging against the battery. I believe that my AMP is wired correct because all other current loads show the proper Neg. deflection.

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Bob

05-15-2005 10:20:25




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 Re: M charging circuit problem in reply to Ken WI, 05-14-2005 14:06:17  
I wish I could get "hands-on" with this tractor!

I DOES sound weird. If it begins charging backwards at startup, once the cutout points close, the direct connection between the battery and the generator will generally overload the generator, and "flip" it's charging polarity to match that of the battery, welding the cutout points in the process. Then, at shutdown, the points remain welded closed, draining the battery, and likely letting some smoke out of the cutout, wires, and generator.

That is what usually happens, yet you're not seeing that, and 15 or 20 amp discharge is NOT much, if the polarities are not matching up.

On thing you could try, if you are sure this is what's happening, is to disconnect the 2 field coil leads from the brushholders they're connected to, and swap them if lead length allows, and then re-polarize before startup.

Something else comes to mind... probably NOT likely, but you say you don't know any history on the unit... the armature might be miss-matched to the "belly" of the generator. If you have it apart again, measure it ID of the pole shoes, and the OD of the armature, and see if they are only, maybe .015" to .020" different in diameter.

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Bob

05-14-2005 12:09:12




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 Re: M charging circuit problem in reply to Ken WI, 05-14-2005 11:32:21  
Check the voltage output of the generator while the ammeter is showing the 15 Amp discharge. It sounds to me like you have the wires swapped from side to side on the ammeter.



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LarryD

05-14-2005 12:39:23




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 Re: M charging circuit problem in reply to Bob, 05-14-2005 12:09:12  
I tend to agree with BOB, on this.. I think swaping the Wires on the AMP Meter will put You in Business.Larry



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John T

05-15-2005 07:38:20




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 Re: M charging circuit problem in reply to LarryD, 05-14-2005 12:39:23  
Larry n Bob, For whats its worth (nuttin its just another opinion) and with all due respect and for discussion purposes, Im kinda thinking maybe the ammeter is wired correct???? If Im understanding what hes saying correctly, it swings to discharge when loads (lights or ignition I assume) are turned on, and that tells me the ammeters BAT input side and the load side are, therefore, wired correct. Next, his Gens output (via the cutout relay) should be wired to the ammeters load side. If it were wired over on the incorrect BAT input side, the ammeter wouldnt be reading/monitoring any of its inputs or outputs to the battery and none of that current flow (regardless of into or out of battery) would be registered by the meter. HOWEVER I reckon if the Gen circuit was adversely affecting the batterys voltage (maybe badly shorted n dragging its voltage way down) then that could indeed affect the current going to the light n ignition loads, thereby still affectign the ammeters readings EVEN IF THE GEN WAS WIRED TO THE INCORRECT BAT INPUT SIDE OF THE AMMETER EH????? ?????

Any cussin or discussin from you good gents???

Next, it seems like the cutout relay is working. Its supposed to be normally open and then to close when the gens output voltage exceeds that of the battery, and he says it closes at higher RPM when the voltage is 6.5 (higher than the batterys 6.3).

That leaves in my thinking EITHER a Generator or a Battery problem. Im wondering if his Gen is wired correct internally and/or theres a shorted field winding or a bad armature????? ?

Ken,,,, I aint seen the good Clooney man, but in case your interested to hear other thoughts, read below.

Ken,,,,,if the armature is removed, there should be low resistance continuity between the field brush wire over to the Gens Field post BUT AN OPEN CIRCUIT TO FRAME/CASE or else the Fields grounded (suspect where fields wire together). ALSO there should be no shorts from any of the commutators segments to the steel shaft or else the armatures shorted. BOTH the field brush and the Arm brush are on that one side, while the grounded brush is the only brush over on that opposite side.

Ken,,,,, did you polarize by first dead grounding the Gens Field post to its frame/case/ground,,,,, ,,then momentarily flash jump a wire from the starter (a hot ungrounded battery feed) to the Gens ARM post and did you get a spark????? ??

Ken,,,, Is the ammeters BAT input side wired to the starter and theres ONLY ONE WIRE THERE??? While over on the ammeters load terminal the wire from the cutout relay PLUS the wire to the switch is located???

Ken,,,,, Once Polarized as above, when running at RPM if you dead ground the gens Field post DOES SHE CHARGE OKAY THEN??? If so then BUT NOT OTHERWISE, I suspect EITHER the light switch is bad,, or the light switch isnt well grounded,, or the wires bad/open from the Gens Field post up to the light switch. The light switch supplies a dead groud to the Gens Field for high charge (lights on) or a resistive field for low chage lights off)

Ken,,,Next with the Field dead grounded and at RPM I know you say the cutout closes BUTTTTT to be sure, jump around the relay by temporarily shorting its BAT and GEN terminals together n see how she acts then????? If alls well then BUT NOT OTHERWISE, I wonder about the relay.

God Bless all of you

Ol John T

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