A new alternator and a new battery have not fixed the charging system problem on my '09 Cat 305CR. When I measured the new alternator's output, I get between 50V and 60V (is that even possible with a 12V alternator?). Also, the new alternator blew the 50A fuse located in the battery box. Bench test on the new alternator shows 14.5V. Any thoughts?
No sensing signal?
You have an open connection between the battery and alternator. Your alternator is putting out high voltage but your battery is still at 12.5 volts while running.
Yes they will put out this voltage when running open circuit. Don't run to long like that as can burn alt out. I assume you had battery connected to alt when bench testing? Was that test made before or after you blew 50A fusable link? The 14.5 is fine what you need to figure out why the fuse blew. Were the wires connected incorrectly at alt?
No, bench test was done at alternator shop on testing machine. Test was made after it blew the fuse. Three connections are on the alternator - battery, a two wire connector (one of which I assume is sensing wire), and a single connector which I assume is alternator warning light. They will only connect one way.
when did it blow fuse when you put wires on or when you turned ignition on
The only way the alt can blow the fuse is if it is faulty or the battery terminals on new batt are wrong way round
If it’s an SI alternator then yes one wire is sensing another is dash light.
Hi TVA, Can you explain more what you mean there please
Google “10SI alternator wiring” and see if it’s your alternator.
SI alternators use two blade spade connector one is sensing wire connects to the B+, the other goes to dash board warning light. Same alternator can have wrong “one wire” regulator in it though!
What you are saying is possible but even with that mix up does not explain how it took out the 50A fuse?
It's a Cat part. Usually one wire is sensing alternator frequency which is interpreted by the computer. A wiring diagram needs to be obtained and studied before people start putting out general information that may be wrong on fixing it. A blown fuse indicates a short to ground. That is about all that can be said without further information.
Im glad you got that out of your system john, hope your felling better.
Was a “power wire” between alternator and battery checked under load? Was it even checked for continuity? These things have a habit to rot inside, and the short that took out 50amp fuse could have burned the last remaining threads.
Got the problem resolved. I believe the high output voltage was caused by a low voltage at the battery. I had let the battery drain down to around 6 to 7V when I installed the alternator and read the output. Apparently the alternator will ramp up output when it senses such a low voltage. Today I put a charger on battery to bring it up to 12V, then started the machine and checked alternator output. It was normal. Ran the machine for 4 hrs and battery voltage checked out around 13V. Also, I believe the blown fuse may not have been caused by the alternator after all since dummy here forgot to disconnect battery before pulling alternator. I probably let the hot connection ground out after disconnecting it.
I feel better now.
Me too! Because OP solved the problem!
50V and you're blaming it on a dead battery? You still have the problem, it's just not going to show up again until a worse time.
Im hearing you Delmer, We will have to wait for the sequel to this. But is vaguely possible. The internal sense alt will limit to around 15V when open circuit but an external sense would go that high if wire was not sensing battery. If the sense wire was connected on battery side of the blown fusible link the alt would be high voltage but battery very low.