Need electrical advice.

[Soundguy]

You've done half the work so far in getting the battery tested.. now test the alternator.

Use your vom.. test the battery before starting.. should be 12-12.5 or so. Start the tractor. If the alt is charging you should see 13+ volts.. as high as 14.7 depending on the make of the alternator and battery charge state.

If it isn't charging when the light is on.. do your restart and if the light comes on and it charges. you know there is a problem. Might be in the key switch or the circuit that excites the alt's field, if it uses external excitation.. like a gm 10-si alternator. ( on those.. P1 is external excite.. and gm ran it thru a dash light.. "idiot' light.. and then to the ignition key switch. So when the ifnition was on.. powewr was supplied to the field thru the light.. and of course it glowed while the ignition was on, but engine not running. after starting, the light went out as the field was also producing back power. The light served as a good means to semi isolate the ignition circuit from the back feed from the field, so you could turn your truck off. P2 was the sensing line and can be tied right to the output stud.. or the positive of the battery, and is essentially there for the regulator to determine voltage drop and charge rates. )

Perhaps your tractor uses the popular idiot light scheme.. and something in the circuit isn't working.. even the internal regulator itself.

Also..are you sure you'r belt isn't slipping?

good luck

Soundguy

 

[GrayBeard]

Good info.
I'll do some more checking but the alt. belt seems tight enough.
I don't think the instrument panel is the old style, cluster of idiot lights that are "hard wired" by conventional means.
I think it's one (or more) printed circut boards.
I know the dash panel costs about 800.00 to replace. /forums/images/graemlins/shocked.gif
The tractor also must have an internal voltage regulator; I see nothing on the exterior that looks like what I know as a regulator.
All good ideas, none the less.
Thanks, GrayBeard

 

[Soundguy]

Just because it is an instrument cluster doesn't mean they didn't include the idiot light as part of the cluster.

See what you can find out and report back.

Soundguy

 

[Keoke]

Graybeard,
All charge lamps have a "proof" circuit that lights bulb when you turn ignition on by providing a ground to the backside of the bulb, front side voltage (pos) comes from key sw.
This circuit is needed to "prove" that the chg lamp circuit is ok by bulb coming on with engine off.
You may want to try, with key on, dis-connecting light gauge wires going to alt/reg one at time until lamp goes out. This will tell which circuit is providing the needed gnd. If, with all wires off, lamp is still on, then it is possible that the gnd used by bulb is between it's self and the wiring to alt/reg units.
Of course, you want to do the above testing ONLY if the alternator proves ok with Soundguy's voltage output check.

Soundguy, on the GM10si alternator circuits. The chg lamp is put out by a half wave rectifier (dode trio) applying B+ to it's backside. This trio of diodes, seprate from the other 6, also provide all alt field current once alt is running.
Also, the chg lamp on GM units have a 10/15 ohm resistor wired in parallel with lamp as back up bridge for inital exciter current to fld in case chg bulb opens the circuit by burning out.

hope this helps guys,

 

[Soundguy]

</font><font color="blue" class="small">( Soundguy, on the GM10si alternator circuits. The chg lamp is put out by a half wave rectifier (dode trio) applying B+ to it's backside. This trio of diodes, seprate from the other 6, also provide all alt field current once alt is running.
)</font>
Yes.. and what that gives you is an ignition that won't shut off if you don't have the lamp or an isolation switch in the circuit. Lotsa tractor guys try the 10si because it is cheap.. and they excite it with their ignition switch.. without a diode, or a lamp, once charging, if you kill the ignition switch, p1 powers the ignition coil.

It's common over on the yt board to have to answer the questions of electrical newbies that have just converted to 12v and now their tractor won't shut off.


And that proof check .. I can tell you from experience.. ( the 2n and naa in my barn ) that the bulb lights with the bulb in line with p1, and power on one side of the bulb via the ignition switch... hundreds ( thousands?) of old tractors are running like that with a '3 wire' setup. Still more are running with the 10si setup as '1wire' self exciter jobs... course they have to throttle up to about 1800 rpm to get it to excite.. etc.

Soundguy

 

[GrayBeard]

I may have mis-spoke about "instrument " panel; the only instrument(so to speak) is an LED read hour meter.
The rest are lights only. (re; temp, brake , alt. ,glow plug, etc)
Someone did mention about the alt. light coming on when the switch is in the on mode prior to start to prove the circuit.
I don't think mine does and not sure if it ever did ???
I've got to go check.
The alt. light comes on while she's crankin' ,as I recall.
I'll verify.
GrayBeard

 

[Keoke]

Soundguy, I hear you on using the 10si on 6 to 12 v conversions and the backfow to ignition circuit from diode trio.

On terminal P2, the battery sensor terminal, best to wire this to the pos battery post instead of a short loop to the alt output terminal. It always best if the internal regulator sees the lowest battery circuit availible (bat post) instead of the highest circuit voltage found at the alt output terminal.
This lower bat voltage will force alt into higher chg rate.
At a high current rate the voltage difference between the alt output terminal and the downstream battery can be considerable.
Bottom line, sensing bat strength at the alt terminal will falsely tell the regulator that the battery is stronger then it really is, consequently you will get a lower charge rate.

Graybeard, if you alt proof circuit comes on only when cranking starter then it is most likely put out by a relay that is in turn triggered by a working charging system.
Also, this is a longshot, but check for a instrument lamp fuse to see it it is open.

cheers,

 

[GrayBeard]

I did some more evaluating last nite.
I found 3 of my ac testers but couldn'd locate the dc tester for love nor money. I'm going to buy another one today.
On with the observations; all the wiring is tight and not degraded in any way at the connections. I did not take the dash apart yet(it's got a back plate on it.)
A closer look at what the alt. light is actually doing on the "first start";
With the key in the on position ready to start, no alt. light.
While cranking the engine over , no light. When she fires, the light comes on and stays.
Second start; Key on prior to start the light is on for about 5 seconds, it cancels out and is fine for any subsequent starts.
I'll pick a tester today.
Thanks for everyones help.
GrayBeard

 

[GrayBeard]

Did some testing last nite.
Before start, the battery tested 12.67 volts.
After start, (while running with the alt. light on) 14.49 volts.
'Don't know what to do now.
I still think there's a malfunction in the dash panel itself ?
I'm not clear on the testing of exciters and such.
I've not pulled the dash out and dismantled it and 'not sure I want to tackle it.
GrayBeard

 

[Soundguy]

</font><font color="blue" class="small">( On terminal P2, the battery sensor terminal, best to wire this to the pos battery post instead of a short loop to the alt output terminal. It always best if the internal regulator sees the lowest battery circuit availible (bat post) instead of the highest circuit voltage found at the alt output terminal.
)</font>

Technically yes.. but practicaly.. it doesn't matter much when you have a 1950's antique tractor that has a set of headlights, a starter and that's it. The output wire from the alternator usually gets wired directly to the hot side of the starter relay, depending on whether or not they have an ammeter.

For a tractor that had lots of electrics, wiring the sense wire to the battery would be a good idea.. but on many of the older units.. you are onlyt talking about maybee a set of lamps and the starter as the sole electrical system, and looping p2 to the output stud accomplishes the job and saves 2' of wire. Besides, if the charge wire from the alt to the battery is of sufficient gauge size to not drop any voltage over it's length, then electrically, the battery positive will be the same potential as the alternator output stud anyway.

And that only applies to the 3 wire jobs. The 1 wire jobs require the alternator's internal VR to sense voltage at the output stud anyway.

Soundguy