6640 intermittent electrical problem

[RickB]

could this be a bad diode in alternator?

Absolutely; that was my first response. Whether it makes sense to repair/replace an otherwise functional alternator solely for the purpose of extinguishing the indicator lamp has made for the rest of the discussion.

 

[jinman]

Absolutely; that was my first response. Whether it makes sense to repair/replace an otherwise functional alternator solely for the purpose of extinguishing the indicator lamp has made for the rest of the discussion.

Rick, if this is a bad diode in the alternator, shouldn't there be ripple on the output DC voltage? Instead of just looking for DC volts out of the regulator, I think I'd put a VOM set to a low AC range onto the output and see if I did not have some excessive AC ripple when the idiot light is on brightly.

Since I know nothing about the circuit, this is just speculation, but I do know a lot about rectifiers and if you get a leaky diode, you also get AC ripple. However, since the battery effectively works like a big capacitor for smoothing the ripple, you might never see the ripple with it attached. Don't know. . . .

 

[RickB]

Rick, if this is a bad diode in the alternator, shouldn't there be ripple on the output DC voltage? Instead of just looking for DC volts out of the regulator, I think I'd put a VOM set to a low AC range onto the output and see if I did not have some excessive AC ripple when the idiot light is on brightly.

Since I know nothing about the circuit, this is just speculation, but I do know a lot about rectifiers and if you get a leaky diode, you also get AC ripple. However, since the battery effectively works like a big capacitor for smoothing the ripple, you might never see the ripple with it attached. Don't know. . . .

That's beyond my level of expertise on the topic (you won't get me to admit that often). I can tell you the tachometer operates from an AC signal from the alternator, and Jack reports tach readings as stable and accurate.

 

[Jackfr]

I understand about the possibly weak or bad diode. It makes no sense to me to change the diode or the alternator because of this dim light problem as it charges ok and the tach seems to be operating ok. Rick you answered the bulb question it has to stay so the system will charge. Just was curious what could cause the flashing bright idiot light. Could this be caused by a bad diode also? Why only does it come on and flash sometimes when I first start then it will go out (go to dim) when I restart right away? Rick It sounds like the best thing I can do is the black tape over the light as you first suggested so I can't see it, use the voltmeter and run it until it stops charging if ever.

 

[Jackfr]

Rick, if this is a bad diode in the alternator, shouldn't there be ripple on the output DC voltage? Instead of just looking for DC volts out of the regulator, I think I'd put a VOM set to a low AC range onto the output and see if I did not have some excessive AC ripple when the idiot light is on brightly.

Since I know nothing about the circuit, this is just speculation, but I do know a lot about rectifiers and if you get a leaky diode, you also get AC ripple. However, since the battery effectively works like a big capacitor for smoothing the ripple, you might never see the ripple with it attached. Don't know. . . .

Jim the problem doesn happen every time and as soon as I shut down to hook something up and then restart it goes away. So unless I can wire something semi-permantly I won't be able to get any readings.

Jack

 

[supramonsta]

Hi. Glad I stumbled on this thread. I have a 7740, which seems to exhibit a lot of problems that are similar to these. Such as...intermittent flashing of battery light (weakly). hour meter not working. tacho just started jumping/not working. (died completely yesterday when battery went flat, now is intermittent after charging battery). Headlights pulsate when on, more noticable at revs?

I have just (as per manual) checked output amps at alternateor and got 0.04?? Volts were around 12.9 with freshly charged battery with engine off, and then about 12.8 with engine at 2000 revs?

But also checked batt temp sensor voltage @ alternator, and got nothing.

Now....my questions (please). Can this all be caused by failed batt temp sensor? Or is this more likely a screwed alternator? I have been using this tractor for about 4 months. Lights surging have always been aparent, engine hour guage never worked, yet i do remember when i fully charged battery the surging lights stopped.

Any help MUCH appreciated.

Thanks

 

[Jackfr]

Welcome to TBN

Sounds like the alternator. I eventually ended up replacing the alternator on our 6640 when it stopped charging. The new alternator eliminated the battery sensor and replacing it cured all my other electrical problems except the hour meter which no longer works. I added an electric hour meter to keep track of my usage for service.

 

[supramonsta]

Thanks for your reply. I am hoping this is the cause. I also forgot to mention that the PTO started playing up, and would disengage periodically. Then it wouldn't turn on unless i tried a few times. Now it won't go at all. I read somewhere that this can re related to the alternator? My only worry here is, I just fully charged the battery and still the PTO will not light/work. I think I am best to replace the alternator with one that doesn't require a battery sensor connection?? On this note, can anyone tell me what the battery temp sensor looks like? There is a two pin oval plug that is sitting redundant a few inches off the positive terminal on the battery. I am gathering this is where the sensor goes?

I just hope I am not barking up the wrong tree....so to speak.

 

[Jackfr]

There was a round disk attached to a cable that was sitting on the top of my batteries near the positive terminal that I taped up and put to the side. You should have around 13.9-14.2 volts if alternator is working ok. RickB said that the PTO along with the tack and hour meter not working was caused by alternator not working on my 6640 not sure about yours. The new alternator we installed did not have the temp sensor connection (Directions said to just tape off sensor wires which I did on both ends) but everything works fine now that I replaced it. Just make sure you order correct amperage for your model tractor.