Archived Alternator Fried

[RON'S RAM]

Tonight while stopped at a red light, smoke started pouring out from under the truck. I was able to get the truck off of the road, and opened the hood. Smoke had stopped and I couldn't find the problem. When I started driving away again, I noticed the voltmeter was low & the Gen light was on. So I stopped again & checked the alternator. The windings are definately burnt.

My question is, is there something else that could have caused the alternator to fry or was it just it's time to go? I've never had one burn up like that before. Just looking for some experienced advice before I install a new alternator.

Thanks,

Ron

 

[GAmes]

The ECM controls voltage. When you replace the alternator unplug your grid heaters prior to the first start. If all is well, plug them in one at a time and see if you have the huge draw caused by them being on. You can do this using the small wires attached to the side of the relays. I have had the relay fail. However, when it did the ECM kicked the alt off line until the engine was shut off and restarted. Way back when I was still in warranty my wife had the batteries both boil over because the relay failed and apparantly the ECM did not kick the alt off line.

 

[RON'S RAM]

Thanks for the advice. I did what you said after installing a brand new alternator. Tested both batteries seperately and both tested at 12. 45 volts. Started the truck and voltage was still low on the gauge. Tested voltage at batteries with engine running and still 12. 45 VDC. Tested output at big lug on alternator and am getting 30VDC there. The only codes I am getting is Bat. has been disconnected from ECM within the last 50 cycles & low voltage. Is something telling the alternator to put out maximum voltage? If it is actually putting out that voltage and I'm not reading that at the batteries, is there a fusible link in that line somwhere?

 

[GAmes]

Ron,



Tomorrow morning, when my mind is fresh I will try to trace the alt circuit in my shop manual. In the meantime, you might consider finding a factory manual for yours. It is well worth the $100 or so it will cost.

 

[RON'S RAM]

Thanks, I have a shop manual for mine and read it briefly 1/2 hour before I had to leave for work. I was just hoping that if someone else had the same problem they could save me some time. I will look more when I get home in the morning. I find more solutions on this web site than could ever be printed in any manual.

 

[JFaughn]

It sounds like the alt is full fielding [ never run an alt with the batteries disconnected for long , this tells the regulator to max out the alt ]
so the guess is that a bad connection , batteries to ECM through alt , [ I try not to use absolutes , but computers almost always control most everything through grounds ] so 2 small wires on back of alt , one ground-ECM control and the other pos -ECM-battery-reg-sensor , as the ECM see's the need for more power the ECM/reg puts more ground to alt turning on the exciter in the alt .
Thats my theory.

 

[GAmes]

If I am reading it right there are three fuses in the system. Fuse 9 in the fuse block and a 40 amp fuse #3 in of the PDC. There is also a 120 amp fuse in the PDC to check.

 

[RON'S RAM]

This morning when I got home, I looked for fuses and found the 120 amp alternator fuse. It was definately blown and not available at the local parts stores. The dealer couldn't find any info for my 1997 truck, but did find the part number for the 1996. Part # 6101756 and it list for around $8. 00 but not in stock. After he got the number, he tried the 97 again. In 97 it is called a fusible link, but in 96 it is called a fuse. (same part #) Will install tomorrow and check for shorts or stuck relays.

Thanks for any advice, I really appreciate it.

Ron

 

[Joe Mc]

Ron,

You may choose to pick up two of the $8 fuses. I would try to figure out why the fuse blew in the first place - difficult. However, if you install the fuse and it doesen't blow then all is well. If it does blow (and you pick up 2) then you have one on hand once problem is figured out.

I'd trace lines to & from alt for signs of insulation break down and ground (dead short) out somewhere first.

Hope this helps somewhat.

 

[RON'S RAM]

You are right, I should have ordered 2. I usually do, but figured this one lasted ten years. I will probably order another when I pick up the new one in the morning. I know I'll be kicking myself if there is a short & I blow the new fuse. I've been dodging rain drops getting to work on the motorcycle. It will be nice to get the truck back. I did use a piece of 12 gauge wire to jump the fuse for some testing. It doesn't seem like anything is shorted & voltage is back to around 13. 7 volts, but I'll test more tomorrow.

Thanks again,

Ron

 

[TBurow]

your alt. probably melted the insulator on the batt wire and grounded out causing the fuse to blow and tha alt to try to keep up 13. 5 volts when shortes and overheated itself untill it smoked and stopped working, look at the old one where the big pos wire goes onto the plastic is probably gone.

 

[GAmes]

120 amps is a lot of juice. I just want to reiterate the gridheater check. Other than the starter, I believe they are the biggest power draw in the system.

 

[RON'S RAM]

Yeah, thanks. I still have the grid heaters disconnected and will test them & the relays before I close the hood.

 

[RON'S RAM]

Looks like the alternator shorted out & blew the 120 amp fuse. I did not find any other problems and things seem fine now. Fuse number through dealer is 6101756. Thanks to all that replied.

Ron