I have a Universal M25 that runs like a top, but the tach fluctuates almost all the time, usually in the general vicinity of the actual rpm (I think). The alternator and regulator appear to work well with each other and I replaced most of the main battery wiring recently with no change. The rest of the wiring could use a good going over, but would anyone have an idea where to start specific to the tach?
universal m25 tach fluctuates
- Thread starter fastfr8r
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Guessing
I know absolutely nothing about a Universal M25. However, the tachometer is probably electrically driven. Any fluctuation in the input voltage will cause the tach to fluctuate. It could be that you have a weak battery or there are excessive voltage fluctuations from the altenator or regulator. Try putting an analog voltmeter on the voltage input to the tachometer while the motor is running and see if the voltage fluctuates with the tachometer.
I know absolutely nothing about a Universal M25. However, the tachometer is probably electrically driven. Any fluctuation in the input voltage will cause the tach to fluctuate. It could be that you have a weak battery or there are excessive voltage fluctuations from the altenator or regulator. Try putting an analog voltmeter on the voltage input to the tachometer while the motor is running and see if the voltage fluctuates with the tachometer.
Check the slip ring brushes
If the alternator is over several years old the slip ring brushes and slip rings may just need cleaned/replaced. These supply the field current to the alternator (duh) field windings. While you only have 3-5 amps going through the field circuit if the brushes are dirty the alternator output will fluctuate very rapidly. This is picked up by the tack as a change in RPM. When you are putting the brushes back together note the small hole in each brush holder where you could compress the brush past and stick a paperclip to hold the brush inside. You can then reassemble the alternator and pull the paperclips. This makes the job a lot easier. Good luck.
If the alternator is over several years old the slip ring brushes and slip rings may just need cleaned/replaced. These supply the field current to the alternator (duh) field windings. While you only have 3-5 amps going through the field circuit if the brushes are dirty the alternator output will fluctuate very rapidly. This is picked up by the tack as a change in RPM. When you are putting the brushes back together note the small hole in each brush holder where you could compress the brush past and stick a paperclip to hold the brush inside. You can then reassemble the alternator and pull the paperclips. This makes the job a lot easier. Good luck.
M-25 Tach (sometimes answer is simple)
Have the M-25 on my 1983 Catalina 30; problem with a varibly reading tach was solved by re-connecting the ground wire...there is a possibility that your problem may be as easily solved...good luck and great sailing, Barry
Have the M-25 on my 1983 Catalina 30; problem with a varibly reading tach was solved by re-connecting the ground wire...there is a possibility that your problem may be as easily solved...good luck and great sailing, Barry
If your batteries have been fully charged
by keeping your shorepower plugged in all the time, the tach won't read because the alternator's regulator is not being asked to provide any power. I agree with Barry, too, check all of your wiring connections. The alternator vibrates a LOT, and unless you have lock nuts or nylocks on the studs, the wires can come loose.
by keeping your shorepower plugged in all the time, the tach won't read because the alternator's regulator is not being asked to provide any power. I agree with Barry, too, check all of your wiring connections. The alternator vibrates a LOT, and unless you have lock nuts or nylocks on the studs, the wires can come loose.
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