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

[MikeOConnor]

Hi all, sorry to be such a fair-weather member of the forum. I only bring you puzzlers and then off I go for a while.

Anyway, here's this year's puzzler:

1. reset circuit breaker
2. Turn ignition on without starting motor -- I get the normal beeps, flashing strobe and 12.4 volts on the gauge (normal for a 12 volt battery at rest)
3. Crank and start the motor
4. Voltage drops to around 11 volts (indicating to me that something is really pulling hard, maybe a short) and stays there for about 15 to 30 seconds, then the breaker pops and the voltage jumps up to 13.2 (pretty normal alternator-charging voltage, battery seems to be getting charged up).
5. With the breaker open/popped the strobe stops flashing. But tilt seat, emergency seat switch and draft control are still operational and the tractor made it back to the barn (about a mile).
6. Use the ignition switch to shut off the engine (which is weird because the breaker is right in front of the ignition switch in the wiring diagram, so why does it still work?)
7. The ignition switch is dead *after* I shut the engine off -- no strobe, no beeps, no voltage on the gauge when I key it on.
8. Return to number 1 above

So my current theory is that I have a short (that's tomorrow's project -- see if I can figure out which circuit it's in, and where). Terry wants me to replace the alternator (I have one coming, but at $600 I'd like to avoid opening the box if I can).

Any experiences like this? Any tips?

 

[MossRoad]

Maybe your starter motor is hanging on after you release the key? Just guessing.

 

[LD1]

WHat does the breaker go to?

Post a pic or link to the wiring diagram.

 

[MikeOConnor]

Thanks for the ideas.

The breaker sees the battery upstream and the battery side of the ignition switch downstream. That's why I'm puzzled that the machine continues to run -- I would have thought that the breaker would shut the machine off.

Here's a link to a blog post I just started. I plan to use it as the scratchpad for info, ideas and (hopefully) solution. There are wiring diagrams at the bottom of the post. I'll add the one that is a GIF to this reply as an attachment.

https://www.haven2.com/index.php/archives/electrical-repair-of-power-trac-pt-1850
​

Here's the PDF that I got from Terry yesterday.

https://www.haven2.com/wp-content/uploads/2015/10/1850-Wiring-diagram-6-1-20110001-copy.pdf

And here's a GIF that I found on the 'net (probably from one of us, but I can't remember where I found it)

 

[Soundguy]

as a test, if you have access to the back of the switch, unplug all wires and make sure that the red is isolated from all when off, and when in start, that it is common to black and green, maybee yellow. and in run, green and maybee yellow, and in accy, only yellow.

if that passes, check black thru pto switch to the start solenoid... though shouldn't be an issue unless red is staying common to black when switch released.

as to why it is getting power when breaker popped, I would guess it is backfeeding on yellow.

as a test you could pull yellow and see if that kills her with breaker popped.



the fault can't be on green or yellow IMHO as if green opened , fuel control drops, and when breaker open, yellow looks to be the only power source that would be keeping green hot.

that makes me think red and black are staying common somehow when starting.. but it is not a permanent short, otherwise the starter may turn any time the bat was conencted .

post back

I may have missed something else looking at the front of the diagram off the key thru my phone.

 

[LD1]

With the key in the run position, it makes sense that it keeps running even when the breaker pops. The engine is running, alternator is making voltage. There is a connection between Acc, Bat, and Ign in the key switch. The only thing popping the breaker does in prevent the battery from charging, but everything else should work normally if the alternator is good.

Turn it off then everything goes dead makes perfect sense. With the alternator no longer running, you have to rely on the battery to power things, with the breaker popped it cannot.

Hard to correlate a schematic to the actual machine, but it is puzzling why the strobe quits. IF everything else had power AFTER the breaker pops, it tells me its being fed from the alternator, same as the strobe just from a different connection point.

Try unhooking the strobe? perhaps thats the whole issue???

 

[LD1]

as a test, if you have access to the back of the switch, unplug all wires and make sure that the red is isolated from all when off, and when in start, that it is common to black and green, maybee yellow. and in run, green and maybee yellow, and in accy, only yellow.

if that passes, check black thru pto switch to the start solenoid... though shouldn't be an issue unless red is staying common to black when switch released.

as to why it is getting power when breaker popped, I would guess it is backfeeding on yellow.

as a test you could pull yellow and see if that kills her with breaker popped.



the fault can't be on green or yellow IMHO as if green opened , fuel control drops, and when breaker open, yellow looks to be the only power source that would be keeping green hot.

that makes me think red and black are staying common somehow when starting.. but it is not a permanent short, otherwise the starter may turn any time the bat was conencted .

post back

I may have missed something else looking at the front of the diagram off the key thru my phone.

BEat me to a reply. I dont think you missed anything. Looks as though red, green, and yellow are all common when the key is on. That acc has to still be in the loop otherwise I dont see how the alternator would ever charge the battery.

I agree that the issue may be in the wire going to the start solenoid. But whats got me is the strobe is the only thing that goes out when the breaker pops?

Perhaps someone could have rewired the strobe. But I dont see anywhere it could have been wired that would cause this. IF it were wired BEFORE the breaker the breaker wouldnt kill it. And even if wired AFTER the breaker anywhere it should be back-feeding from the yellow.

I guess what I am saying is with that breaker popped, EVERYTHING should still be hot. The battery side of the breaker is hot from the battery, the switch side is hot from the alternator.

 

[Soundguy]

here's what i see on the picture schematic. I can't open the pdf one and see it enough on the phone.

4 wires to switch.

red is 100% isolated once the breaker opens.

black is the pto interlocked switch to the start relay/solenoid.

green provides 'run' power to things that should be running when on.. fuel, dash lamps, etc.

yellow accy would normally feed gauges from red with machine off. with machine on and running, and red open at breaker, yellow is getting power from connector 4 - 7/alt D +. presumably.

the puzzle is that the hyd cooler fan, thru a vairable control thermostat is fed directly from 7, meaning any time the machine is running that fan should cycle based on heat, fed by the alt, even if bat is open. that SAME connector 7 seems to feed the strobe lamp. strobe SHOULD be working as that is hooked to 7/4/D+, and that eventually makes it to yellow and that is the only line that can be feeding power to the switch with red open at the breaker. green and black have no other possible power feeds other than red or yellow.

 

[Soundguy]

BEat me to a reply. I dont think you missed anything. Looks as though red, green, and yellow are all common when the key is on. That acc has to still be in the loop otherwise I dont see how the alternator would ever charge the battery.

I agree that the issue may be in the wire going to the start solenoid. But whats got me is the strobe is the only thing that goes out when the breaker pops?

Perhaps someone could have rewired the strobe. But I dont see anywhere it could have been wired that would cause this. IF it were wired BEFORE the breaker the breaker wouldnt kill it. And even if wired AFTER the breaker anywhere it should be back-feeding from the yellow.

I guess what I am saying is with that breaker popped, EVERYTHING should still be hot. The battery side of the breaker is hot from the battery, the switch side is hot from the alternator.

agreed. as per diagram.. the strobe should be common to yellow indirectly thru wiring.. and yellow must be staying hot from D+ on alt.

one thing i do not see is a amp or volt meter.

and the only charge path i can see is yellow - red, THRU the ignition switch ( wow.. I call that a POS design IMHO.. )

 

[Soundguy]

further, if you can reset the breaker and not start it and the breaker does not pop.. that means no short on that side of the switch.

hmm.

lets look at this from a charge standpoint.

starter current goes directly thru a high current contact at the starter.. then a 50a fuse, then the 20a breakr.

the 50a fuse is presumably intact, or you could not rest the breaker than restart.

perhaps the 20a breaker is thermally damaged and not taking charge current? .. but that doesn't explain low volts before pop, unless the bat is dead on one cell.. still starts but is a load on the alt. volt meter would show that. if static bat v is good.. discount that.

strobe is a puzzler...

there has to be a deviation on this diagram....