Weird electrical puzzler - breaker pops, the PT1850 runs better until it's shut off

[LD1]

That's what I would do. I wouldn't trust the dash meter to measure accurate. The 13.2 could actually just be 12.4 static and the meter is 0.8v out of calibration.

 

[Soundguy]

And if so, the static bat measurement could mean a bad cell.

 

[ponytug]

Mike, This is my point. Alternators require batteries to set the field polarity correctly. If you remove that DC of even a nearly flat (1V) battery, the alternator fields are no longer constrained and can, and do, flip polarity. Once your breaker pops, you are running the risk of running current the wrong way. Not that this matter to most items, but your alternator diodes care- a lot. They'll fry.

Just my $0.02...

All the best,

Peter

Pulled the yellow wire off the ignition switch:

- Dash instruments go dead... Oh, they're fed by that circuit. OK -- meter on the battery
- Tractor starts
- Tractor runs indefinitely without popping the breaker
- Battery voltage declines just a bit (rather than going up to charging voltage)

Seems like the alternator is indeed backfeeding through the accessory side -- wish I'd remembered to do this yesterday, but there you go. When the accessory circuit is removed, the alternator does NOT charge the battery. I can't quite figure out what the *correct* path for the alternator to go to the battery is. If the only path is yellow back to the ignition switch then I'd think the open breaker would block it.

 

[ponytug]

These voltages are normal. They are indicative of a load on the alternator (i.e. the battery).The voltage is being measured at the battery, i.e. over some amount of resistance in the wires. The alternator is setting the voltage at the alternator, so there is a small difference, but that difference will be larger the bigger the load is on the alternator, or rather the resistance of the wires to the load. I'd bet you could raise the 11.8 to a higher number with the engine speed up a few hundred rpms. Once the breaker pops, the alternator voltage regulator is able to keep it at the normal levels.
All the best,
Peter

But but but... With everything hooked up the battery voltage jumps up from around 11.8 with the breaker set, to 13.2 when the breaker is blown. Doesn't that imply that the battery is being charged? Or is there some other way to get the voltage that high? UPDATE The battery at rest is sitting around 12.4 volts. /UPDATE

 

[MikeOConnor]

I woke up this morning thinking about just doing the alternator swap. Spent the morning discovering that I don't have the right tools, so tomorrow I'll go back to the process of isolating the circuit. Is there any way that all this could be caused by something failing in the alternator? Like fried diodes?

 

[MossRoad]

I haven't seen if you did it yet or not, but someone suggested taking the suspect alternator to Autozone for free testing before you open the box with the new one from PT.

 

[MikeOConnor]

Yeah... Unfortunately I got frustrated and took the new alternator out of the box before realizing that I need a Torx box wrench to remove the shrouds. So I own it now, no matter whether it's the culprit or not. ;-)

 

[Coyote machine]

Yeah... Unfortunately I got frustrated and took the new alternator out of the box before realizing that I need a Torx box wrench to remove the shrouds. So I own it now, no matter whether it's the culprit or not. ;-)

I wouldn't hook up the new alt, even though you own it. Figure out the circuit that is tripping the breaker first, otherwise you could fry the new alt too, if the current alt is getting fried diodes as a result of the faulty circuit.

 

[MikeOConnor]

Wildly different behavior this morning.

I mounted the new fan (the old one was burned out by getting a stick jammed in it, which started this saga). But, and this is key, I didn't connect the new fan. The old one was disconnected, this one is disconnected. Therefore, I don't think this made any difference.

I reattached the V-belt between the motor and the alternator (I'd pulled it yesterday before I realized that I needed a new wrench to get the shrouds off in order to replace the alternator). Put it back at the same tension it's been all along. Again, I don't think this is a change.

No other changes.

Started up the tractor to pop the breaker and start tracing the yellow/accessory circuits.

The breaker popped, voltage jumped much higher than before (14.8 volts instead of the 13.3-ish I've been seeing up 'til now). Ran that way for about 20 seconds and then the tractor quit. Fuel solenoid would be my guess.​

Reset the breaker.

Started it up again. Repeated this several times -- each time:

• The breaker never popped
• The voltage immediately jumped up to the new 14.8 voltage level (formerly I'd see voltage get dragged down until the breaker went, only seeing higher-than-battery voltage after it popped), and
• The tractor ran without blowing the breaker (at that nearly-pegging-the-meter 14.8 volts) until I would chicken out and shut it off (30+ seconds, fire extinguisher close at hand).

In this configuration the only changes to normal are that I've bypassed the seat dead-man switch and disconnected the thermostat and fan. I don't ever recall seeing charging voltage as high as I'm seeing now (but I'm getting a little befuddled by all this).

Summary of battery voltages: 12.4 when I started this morning with the battery disconnected, 12.4 with the battery connected, 12.1 with the key on, 14.8 when the tractor was running, 12.6 after running for a while and shutting things off, drifting down towards 12.5 the last time I checked.

All this has me leaning back towards a wonky alternator. I'm a little edgy about running the tractor now, since it seems like the voltage regulators in the alternator may have failed. Since I can't get the breaker to pop any more, it's hard to isolate stuff on the accessory circuit.

Next step? Try running it without the alternator? My inclination is to put the new alternator in.

 

[Coyote machine]

I wouldn't disconnect the alternator. 14.8 is a little high, BUT your battery may be requiring that output to be charged. 14.25-14.5 Volts would be normal regulated voltage output back to the battery if there were loads on the battery, or if it were weak and needed to be fully recharged. Are you taking those readings from the tractor gauge or a VOM at the battery posts?
Try seeing what Voltage output is when you turn on the high beam headlights. Report back. Also un-bypass the seat switch and see what happens to the breaker and voltage. Everything you do now requires a voltage reading at the battery posts. If need be attach your leads in the clamp(s) at the cables so the leads are touching the battery posts securely. Refresh the collective memory- what is the condition of the in use battery? New? Old?
Report back results.
14.8 won't blow up the battery, but IF you start seeing over 15 volts it's time to be cautious about battery off gassing/explosive vapors etc. Wear goggles and gloves until this thing is sorted out.