1987 MF 375 not charging batteries

   / 1987 MF 375 not charging batteries #21  
When you get it charging, you`ve still got the problem of why a fuse blew, and the tacho not working. Good luck with that one. Unless something metal might have touched that single wire on the alternator when it was running. It might be an idea to put a bit of insulation tape or self amalgamating over that pin.
 
   / 1987 MF 375 not charging batteries
  • Thread Starter
#22  
When you get it charging, you`ve still got the problem of why a fuse blew, and the tacho not working. Good luck with that one. Unless something metal might have touched that single wire on the alternator when it was running. It might be an idea to put a bit of insulation tape or self amalgamating over that pin.
Thanks, that got it charging
 
   / 1987 MF 375 not charging batteries
  • Thread Starter
#23  
When you get it charging, you`ve still got the problem of why a fuse blew, and the tacho not working. Good luck with that one. Unless something metal might have touched that single wire on the alternator when it was running. It might be an idea to put a bit of insulation tape or self amalgamating over that pin.
What drives the tach?
 
   / 1987 MF 375 not charging batteries #24  
There are two `types` of tach. Usually the older types are run by a cable that spins like the old speedo`s. More modern types are driven by a small electric pulse. To get this pulse, sometimes a magnet is put on a crank pully and this spins past a fixed coil that sends a pulse every time it passes. Sometimes a single small wire is taken to the alternator. I don't know but at a guess this will be how yours is run. A little bit of knowledge about alternators. First inside the alternator is 3 coils, each of these coils give off a AC current, This AC current is fed through a rectifier, that converts it to DC `Direct Current`, and through a voltage regulator, where that other wire goes to, so as to control the voltage and tell the coils when the battery is full. Right, back to the Tach. Basically a single wire is taken from only one of the inner AC coils, any one will do, and that will send a pulse every time it goes round a turn to the Tacho, that is basically a pulse counter, but the dial is printed off as revolutions'. At the back of your Tacho, I guess there will be two wires going into it. One will be for the internal light, the other the pulse wire. There might be a earth [ground], but usually this is done through the case to the metal frame.
 
   / 1987 MF 375 not charging batteries
  • Thread Starter
#25  
There are two `types` of tach. Usually the older types are run by a cable that spins like the old speedo`s. More modern types are driven by a small electric pulse. To get this pulse, sometimes a magnet is put on a crank pully and this spins past a fixed coil that sends a pulse every time it passes. Sometimes a single small wire is taken to the alternator. I don't know but at a guess this will be how yours is run. A little bit of knowledge about alternators. First inside the alternator is 3 coils, each of these coils give off a AC current, This AC current is fed through a rectifier, that converts it to DC `Direct Current`, and through a voltage regulator, where that other wire goes to, so as to control the voltage and tell the coils when the battery is full. Right, back to the Tach. Basically a single wire is taken from only one of the inner AC coils, any one will do, and that will send a pulse every time it goes round a turn to the Tacho, that is basically a pulse counter, but the dial is printed off as revolutions'. At the back of your Tacho, I guess there will be two wires going into it. One will be for the internal light, the other the pulse wire. There might be a earth [ground], but usually this is done through the case to the metal frame.
The mowing is about complete for this month. So I will have a couple of weeks to straighten the wiring out hopefully. The tach is definitely electric, because I looked for a cable when it used to stop and start at random times.

Thank you for all your help.
 
   / 1987 MF 375 not charging batteries
  • Thread Starter
#26  
Using your wire technique with a bulb, is working somewhat. If I don't run the lights much it keeps the batteries strong enough to crank it up again, but it's not full charging. What do I need to do next? Try to find the tach wire?
 
   / 1987 MF 375 not charging batteries
  • Thread Starter
#27  
Anyone know where I can buy a new wiring harness?
 
   / 1987 MF 375 not charging batteries #28  
When I take the connector off the alternator, all three prongs show 14 volts. When I put the connector back on the alternator and test the back if the spade connectors, they show 12 volts while idling and 11 when I throttle up. Both batteries are down to 11 volts.

The tach stopped working a couple days ago as well. This tractor has just under 2100 hours.

Please give me an idea where to go!

Thanks
Did you find your problem. I have the same tractor doing the same thing
 
   / 1987 MF 375 not charging batteries #29  
Hi, the wire (green) seems to be your exciter wire to get your field coil (rotor) magnetized to get the charging started. This wire is in series with the charge light on the dash.
On some applications, there will also be a resistor in parallel with the bulb in case the bulb burns so that you can still excite alt field with the key switch.
It looks like this circuit is not being powered up. Look for a fuse marked instruments or for an open in the circuit between key and alt.
Once alt starts charging fld current will come from the regulator or a diode trio within alt. Tach runs on an a/c sine wave and will work when alt works.

lots of luck
 
 
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