Tachometer Problems

[markr]

I have been having some problems with my tachometer on my 1987 MK1 (Hull# 360). I traced the root of the problem back to bad batteries - I was at sea over memorial weekend and noticed that there was a related problem with the tach dying and the alternator not charging the batteries. Long story short, I thought it was an electrical connection problem because it was intermittent and I seemed at one point to have fixed it. It then died. I had the altenator looked at since and it turns out the wires to the diodes had come off. I have now taken the opportunity to replace the 50 amp alternator with a 90 amp one. I also had a look at all my electrical connections including the engine start panel where the tach is and thought the problem was solved. The alternator charges the batteries now.

However, on start up the tach works, and can work for a long as 15 minutes before flickering and then not reading at all. Has anyone else experienced this? I had an electrician friend look at it and he sanded down all the conections on the back of the engine panel and greatly reduced a lot of the resistance across the instruments. There does not seem to be an obvious problem - perhaps apart from age! I see that I can replace the tach with one ordered from the Catalina Fordeck store for $120. However, can I reset the engine hours or do I have to sacrifice this and start over?

Advice welcome. Thanks.

[Ron Hill]

Mark : If you get the same Teleflex tach, you will not be able to set/reset the engine hours!!  

Try this with the flickering tach.  Turn on the blower and see if the tach settles down.  If it does the problem is that the batteries are full up on amps and the alternator has stopped charging!!  The blower creates a load and the alternator starts charging again and the tach settles down to it's readings.  

If that doesn't fix your problem then you have a differant defugelity.  A thought

[Stu Jackson]

Ron's right, and we've experienced this issue before.  Many people start off with full banks.  The regulator on your alternator will NOT "put out" if the batteries are full.  Regardless of your regulator, internal more often, external usually.  If you have a fridge, turn it on, too.  Ron's idea is to place a LOAD on the battery bank, so lights, stereo, or anything will do, but a larger load is better.

[markr]

Well, I replaced the Tach and just came back from 8 days at Catalina Island. Lost the engine hours so will have to re-start and keep the old tach for proof! Everything works fine now. We were at Two Harbors for the Beneteau Rendezvous - what a great place! It's always great to see so many other C34's - at one point there were several of us in a row on the moorings. I would get about in the dinghy and chat to people more, if I did not have a two year old and one year old running about on the boat!
I saw a honda generator on the fordeck of a 34. Like the idea of that a lot! It would stop me running the engine twice a day to charge batteries and keep that TV/DVD running for the kids!

[Lance Jones]

I note a trend in alternators and Tachs.... Why don't they have a tach with a direct feed from the motor? I use the tach to set my various throttle inputs. 1K for leaving dock and no wake zone, 25 for cruise etc. If I'm being "mislead" by the alternator not needing to in put to the charger I could be trying to use the wrong throttle settings. Am I reading these responses correctly?

Lance the befuddled....

[Stu Jackson]

If I'm being "mislead" by the alternator not needing to in put to the charger I could be trying to use the wrong throttle settings. Am I reading these responses correctly?

Perhaps not.

1.  The alternator will NOT be "asked" to produce current on completely full batteries.  Makes sense, right?  So far...

2.  All you have to do is place a small load on the electrical system to kick the tach into producing.  Ron suggests the blower, most people use the fridge anyway, with us so far?

3.  Using the tach for speed is a very good idea.

4.  The Universal engines do NOT come with internal mechanical tachs, our engine use the alternator output for revs.  No sense askin' Santa for somethin' he ain't got.

So, unplug your charger and cord five minutes before you leave your dock, stop wondering why your tach doesn't work when your charger is plugged in, and simply turn your fridge on.

The wandering tach needle simply won't happen again.  There have been three or four cases of people asking about this in the last 12 years.  All of them from the same thing:  being plugged into shorepower and wondering why their tach doesn't work. (Oh, and sometimes gauges actually do break... )

[Lance Jones]

Thanks again Stu, the enlightened one!
That does make sense -- I've only had that issue when I was in the process of losing a belt. Once the belt was replaced, I've had no issues. I ALWAYS seem to have a load on the batteries when running the motor -- Fridge, Nav Inst, Accessories etc.

[Ron Hill]

Guys : The flickering tach needle is especially true if you've been on shore power and the batteries are full up and when you've been motoring for a long period (4 hrs +).  A thought

[Mike_S]

This weekend Holly and I "sailed" to Catalina.  By this I mean we motored up overnight since the wind and waves were on the nose.  It's about 12 hours for us to get there.  Tach worked fine on this trip (and on many others).  On the return trip, about an hour out the tach dropped to about 1500 rpm even though the engine RPM didn't change (no audible change, nor speed change).  If the motor was slowed down to idle, the tach dropped to about normal (just below 1,000 rpm) but on accelerating back up to "normal cruising" RPM, the tach would go up to the value (2300-2500 rpm) and then after a few seconds drop back to 1500 or so ...

The batteries should not have been fully charged at this point, as we'd just spend three days at the island and we always keep the refer running, not to mention water pump, cabin lights, instruments, etc.

Anyone else seen this behavior before?

[Ken Juul]

I'd inspect your Tach wiring.  A little corrosion or a loose connection will cause your symptoms.

[Lance Jones]

Also, check the belt tension. That was the issue on my problem.