hot alternator wires

   / hot alternator wires #1  

elkman

New member
Joined
Jun 12, 2004
Messages
16
Location
Oregon
Tractor
Yanmar 1401d, Bobcat 825
My Yanmar 1401d 18hp had the alternator connector melt/burn until it didn't connect anymore. When I put in a new connector the wires started to get hot so I disconnected them. From someone who only has rudimentary understanding of electricity I'm at a loss for the analysis of the problem. I hooked a voltmeter to the alternator wires and nothing registered but when I touch the two wires they spark. I also thought that perhaps I got the wires reversed when I hooked them up so I tried them reversed with the same results. What's the next step?
 
   / hot alternator wires #2  
Sounds like a ground issue. You have a positive touching a negative somewhere.
 
   / hot alternator wires #3  
Did you have your meter in the AC or DC mode? Don't know if the diode bridge is internal to the alternator or external. Reading directly out of the alternator and before the diode bridge, you need to be on AC. Downstream of the diode bridge you need to be on DC.
Something is obviously causing your alternator to put out too much current. Could be a failed diode bridge, bad voltage regulator, short in the wiring. etc. I don't know anything about the Yanmar 1401d charging circuit. You will probably need a schematic of the tractor to troubleshoot it. Maybe someone on TBN will have a shop manual for one and be able to help.
 
   / hot alternator wires #4  
Hows the battery doing ? Is it charged up ? Gor water/acid in it ? Could be a bad alternator or Battery or short somewhere.
Ben
 
   / hot alternator wires
  • Thread Starter
#5  
I had the meter on DC current. I'll try on AC. Is the voltage regulator an aluminum rectangle with fins like on an air cooled engine? Can I deduce anything if it gets hot only when the key is turned on, not that I've checked yet? /forums/images/graemlins/confused.gif
 
   / hot alternator wires #6  
if it gets hot with engine not running it probley has shorted diodes. It will not put out any power if it is not hooked up or if the battery is completely dead. Larry
 
   / hot alternator wires #7  
The only reason a wire would fry on an alternator is over current (a short circuit) whereby the wire is acting like a heating element/fuse.

Turn off the tractor. Disconnect the fried wire from the alternator. Disconnect the positive side of the battery. Put the meter on Ohms. Check the intact side of the wire (away from the alternator). With the ignition off, is there a low resistance (the same sort of reading you get if you connect the meter leads together) or is it open circuit? Chances are there is a low resistance or short between the wire and the chassis, probably because of insulation failure. Basically if you have a shorted wire, you should fix it yourself.

If this isn't it, I'd suggest you bring it to a dealer, because you could cause some grief or damage fiddling around with the alternator or charging circuit. Some alternators will put out a very high voltage and fry the electrics if something goes wrong. I would do it myself and check the alternator.

It could be the alternator or regulator is bad and the wire is frying because the battery is pushing power through that circuit to ground. I doubt that would be the case because the alternator probably would have burnt up with the wire.

You have to check the alternator with the battery disconnected. If a diode has failed or if the alternator has a short, there will be a low resistance when the positive lead of the meter is one the positive lead of the alternator and the negative lead is on ground.

A lot of alternators have built in voltage regulators these days (its just a $0.10 chip anyhow).
 
   / hot alternator wires
  • Thread Starter
#8  
Thanks for the help boustany. I've checked the alternator on AC and it puts out 36v at 2000rpm. The circuit is closed when the fried wire is disconnected and the positive battery terminal is disconnectedand the key is off. I looked all over for a wire shorted/insulation worn and could not find one. I disconnected another plug going to the regulator (4 wire) and found the cuircuit (for the two alternater wires) to be closed. Does this mean that all I have to do is replace the regulator? Does it have to be the one for the tractor or will an aftermarket auto regulator work?
 
   / hot alternator wires #9  
Hmm.

I think you need the regulator connected to the battery/alternator for the output of the alternator to be regulated.

Obviously 36 volts is the wrong answer: it should be 14 ish DC, but if it measures on AC, then I'd say the diodes are likely fried, but I can't be sure. The thing is, a short circuit on the output (the big wire) could have caused the diodes to fry.

My guess is a bad diode (or two) in the alternator.

While the function of regulators is very similar, I suspect you want to replace a regulator with the same one. I guess if I were on a desert island, I'd try whatever regulator I found,. but I wouldn't do this on my tractor. Unregulated alternators can put out very high voltages which will promptly fry the electronics, lights, etc., on a tractor or car.

Honestly, I'm flying blind here, and I'm worried you are going to damage your tractor. If at all possible, I'd bring it to a dealer or a mechanic.

Failing that, most cities have places which will rebuild alternators for a reasonable cost. I would get a regulator 'just in case'

You might feel better if you check out this site:
http://members.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm . It explains some stuff pretty well.

Good luck
 
   / hot alternator wires #10  
Sounds like you need a regulator/rectifier, (it has the diodes). The 36vac is a normal reading for your alternator without the regulator hooked up. It is the item you mentioned with the heatsink, but, unfortunately, I don't believe there is an aftermarket unit available and oem's are quite pricey.
 
 
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