Volvo MD2030 Tachometer's Gone Bananas

[john jeffrey]

G'Day All.
We are presently sailing down the East Coast of Aust in a FP40 cat with 2 x MD2030 sail-drives. After some work was done on her in Mackay (added an inverter and an AIS plus replaced the batteries for AGM (900Ah).
All was fine until the first day out when the stb tacho went to max then died with a blinking hour meter.
After a bit of swearing we decided that we could live with 1 tacho working and one not.
Today the port tacho has maxed out and won't come back.
Any help would be appreciated as we still have a long way to run and my rev-guessing ability is not flash.
Before anybody asks the obvious, no there isn't enough wind.

Fair winds
j.j.

[colemj]

The tach runs off the alternator. Do you have the stock alternator? If aftermarket, check the wiring for the tach sender.

If the batteries are fully charged and the alternator shuts down, the tach goes. If this is the case, try turning on an electrical load (engine blowers, lights, etc) and see if it comes back.

Mark

[svcattales]

Originally Posted by john jeffrey

G'Day All.
We are presently sailing down the East Coast of Aust in a FP40 cat with 2 x MD2030 sail-drives. After some work was done on her in Mackay (added an inverter and an AIS plus replaced the batteries for AGM (900Ah).
All was fine until the first day out when the stb tacho went to max then died with a blinking hour meter.
After a bit of swearing we decided that we could live with 1 tacho working and one not.
Today the port tacho has maxed out and won't come back.
Any help would be appreciated as we still have a long way to run and my rev-guessing ability is not flash.
Before anybody asks the obvious, no there isn't enough wind.

Fair winds
j.j.

Concur with post from Colemj. When you replaced batteries did you adjust voltage regulators to different charging voltage? If your voltage regulators are shutting down your alternators due to full charge, your tachos will stop working. Do you also have solar panels or wind gen working while underway? If so, your solar/wind chargers are keeping your batteries fully charged and alternators/tachos will stay off. The cure for this is to wire in shutoff switches for solar & wind power.

If your tachos start working in the morning when batts are discharged than you will know it is a voltage regulator issue. If they still don't work when batteries are low then your tachos may have quit on you.

[john jeffrey]

Thanks for the advice however the workshop manual shows the tacho has a Hall-effect sensor on the flywheel and should be picking up pulses from the flywheel teeth. The port tacho has come back to life! The stb tacho has no backlight and the LCD hourmeter blinks about once per second. The alarm test works fine, indicating there is power to that part of the panel, at least.

[Zednotzee]

IIRC, Hall Effect sensors can be quite sensitive to spacing/gap issues. You might have a look & see if you can reduce the gap between the sensor & the flywheel. You'd better start out with the engine off, just in case the sensor actually makes contact with the flywheel!

[colemj]

Are you sure about that? In our MD2030 workshop manual, the tach wire goes to the W (phase) terminal on the alternator (and is the way it is wired on the boat). Is the alternator the stock one or has the system been changed in the past?

The lack of backlighting is probably unrelated. The small bulbs blow out easily. You can get a pack of 10 or so from Mcmaster-Carr for a couple bucks.

Mark