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Rpm Gauge?????

noproblemo2

Member III
TRYING TO FIND OUT IF ANYONE KNOWS WHAT IS CAUSING OUR RPM GAUGE TO BOUNCE AROUND AFTER IT GETS STARTED AND WARMED UP THIS HAS JUST RECENTLY BEGUN.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
According to your "profile" you have a 38 foot boat of some kind. Is it perchance an Ericson 38? If so, it may have a Universal diesel. I have seen mention of problems similar to this involving the alternator -- because the tach is powered by pulses from the alternator.
Since this happens "after the engine is warmed", I would tend to equate this with the charging lowering from the initial higher rate of charge when the starting battery is being pumped up after the short-but-heavy drawdown for the glowplugs.
Is the alternator still charging OK, in general? Like after you draw down the house bank and really have to recharge for an hour?
If you have the stock alternator, and *all* the wiring connections are clean and tight, .......then one of the EE's on the list will have to chime in with some real help. :rolleyes:
Please keep us posted.

Loren


ps: your caps lock key is "on".....
 

u079721

Contributing Partner
I too have seen this exact same problem on my E-38. I have hunted in vain for some loose connection, but haven't found one yet. So far the problem doesn't happen too often, and does go away, so I haven't been in a hurry to do anything drastic. If anyone does know of a particular place to look I would also appreciate it.
 

sailingdeacon

Member III
If by any chance you have a smart alternator which varies voltage, some (like my older Next Step) will cause the alternator to actually stop sending to the tack. The Next Step book says to turn on something which needs amps like a light. That usually works but not always. No other known fix.
 

Sean Engle

Your Friendly Administrator
Administrator
Founder
Sorry to say it, but...

I too have had this problem for about a year - and have not thought too much about it until this past weekend...

We were 30 miles from my slip - up in Seattle - and the RPM gauge started bouncing around - and then the alternator started smoking....

Of course, as it happened, the exhaust flange on my manifold decided to uncouple itself from the riser at the same moment - and all hell broke loose when it blew - and I ended up getting towed home for a fortune....

Anyhow - I'm thinking that the alternator makes the RPM gauge bounce around because perhaps :confused: the bearings in it are going bad - causing the unit to kind of 'stick' and 'jerk' - thus throwing off unequal levels of current? :confused:

I was going to do some tests before this latest thing occurred - now I'm calling my insurance company... :(

Comments?

//sse
 

Sean Engle

Your Friendly Administrator
Administrator
Founder
More On This...

Ok, so now I've been advised to ensure that the alternator is tight in it's mounts - and if that's not it, to pull it out and have it rebuilt for $100-$200 instead of the $400 for a new unit....

I looked up rebuilding alternators on the web (click here to see the page itself) - and - to no surprise, look what I found (even though it was for autos, I think it applies here as well):

Alternators should be considered a maintenance item. Alternator brushes and slip rings wear out and must be replaced. On older American alternators I usually replace the brushes at 100,000 miles for a few dollars and get another 100,000 miles out of the alternator. On Bosch alternators the slip rings wear out with the brushes and must be replaced also. This is not an easy DIY project. The least expensive way to have this maintenance done is to remove it and take it to your local auto electrical shop and have it rebuilt. The brushes and regulator on the Bosch alternators are one assembly and must be replaced together, and the slip rings must be replaced also, so it is more expensive to rebuild than other alternators. My local shop charged me $110 for my '88. The frequency for this maintenance is approximately 100,000
miles. I don't know if the amount of air conditioning use affects this figure but if you live in a hot climate maybe you should do it at 80,000 miles.

One of the symptoms of worn brushes and slip rings are "voltage spikes" that destroy the regulator. This sounds OK since the regulator is replaced during the rebuild anyway, but are these "voltage spikes" responsible for some of our fuel injection "brain" failures? Rebuilding the alternator may be good preventative maintenance for the fuel injection "brain" also. It may be good for your sanity as well, since it will keep you from being stranded with a dead battery when the brushes wear out. I don't have experience with the earlier Paris Rohne alternators but I would think that the 100,000 mile frequency would hold true. YMMV.

Earl Gillstrom '88 S4 5 Speed

This would seem to indicate to me that the alternator is the most likely candidate for the jumpy RPM gauge we're seeing - given the spikes of voltage coming off of it, no? :confused:

I'll let you know what happens after I have mine fixed.... :D

//sse
 

Sean Engle

Your Friendly Administrator
Administrator
Founder
Update

I ordered a nice, NEW alternator today (same size, make as that I'm replacing) from a firm in Texas - for $199.00 - and have purchased the exhaust components (including a new riser) for another $110.00. The boat should be back in operation for the July 4th weekend.... :)

I'll update again once everything is installed, etc.

//sse
 

Geoff Johnson

Fellow Ericson Owner
Why not get a high output alternator (and multi-stage regulator), which is only a couple of extra boat units. I think that's going to be my main project next winter. My current OEM alternator still works, but charges at a pathetic 13.65 volts (as measured at the battery). While I don't have refrigeration, my autopilot consumes about 50-60 watts and the the 32-3 has room for only two 75 Ah batteries. Therefore, rapid charging is becoming important to me.
 

Bob

Please Contact Admin.
I too have the erratic tachometer problem but only after the engine warms up (or rather, the batteries are almost fully charged). The tachometer reads okay for awhile but then will read high (I cruise at 2100 or so and it may swing to 2500 or even 2800 with no change in engine rpm, and then eventually back to 2100). I have a high output alternator (100 amp) with a 3 stage regulator from Jack Rabbit Marine. However, it's never been serviced (same brushes as came with the unit) over the 1600 hours of engine use. I would be interested in anyone who has replaced his alternator and whether this eliminated the erratic tachometer problem.
 

Sean Engle

Your Friendly Administrator
Administrator
Founder
Sorry (again) to say it, but...

I replaced the alternator - and thought that it had solved the problem - but the jumpy tach has come back again.

I checked the output of the alternator while it's doing this - and it was 14.42 - steady.

Guess I'll have to check the input on the unit itself next....

//sse
 

Geoff Johnson

Fellow Ericson Owner
This is a little off topic, but I bought a handheld tach (1950's vintage) on eBay in anticipation of installing a Balmar this winter and having to program a new tach. I tried it out on my current 1985 OEM setup and found that the Universal tach consistently reads 200 rpm low at a range of rpm's. Of course, it could be my mechanical tach, but it is one of the high quality centrifigal types, so I tend to believe it more than the alternator tach, which, according to the moderator of the Marine Diesel forum, is inherently unreliable. There is a device called Tiny Tach (http://www.tinytach.com/diesel.html) which measures the fuel pulses at the injector. Does anyone have any reports on this?
 

Geoff Johnson

Fellow Ericson Owner
Sean, I am not an electrical expert, but I believe that if your alternator is charging at 14.4 volts at the battery and you do not have a multi-stage regulator, you are going to overcharge your batteries.
 

Sean Engle

Your Friendly Administrator
Administrator
Founder
?

There is a regulator on the unit - a voltage regulator on the back of the alternator. It's the same make/model alternator that was on the engine before - so I would think I would be ok.... From what I read as long as the output is not too high, I should be ok.... I'll have to check with the Universal guys at Marine Diesel Direct....

//sse
 

noproblemo2

Member III
RPM GAUGE

JUST THOUGHT I'D GIVE AN UPDATE ON THIS, WE DID REPLACE THE ALTERNATOR AND TO DATE THIS SEEMS TO HAVE SOLVED THE PROBLEM...
 

Bob

Please Contact Admin.
I just replaced my alternator with a new Ample 125 amp alternator along with a new Next Step regulator. I still have the variable rpm problem after about 15 or so minutes. After about another 30 minutes, it seems to settle back down to a correct reading. I'm assuming it's due to the charging state of the alternator and the affect that has on the output of the tach terminal of the alternator.
 

escapade

Inactive Member
Tachometer

I had the same problem with the tach on my 34-2. Rebuilt the alternator w/no improvement. I then removed the fiberglass cover from behind the instruments and cleaned all the electrical contacts on the back of the tach. Be careful that you note the proper location so you can put them back where they came from!!I used scotch-brite abrasive pads to clean the conections. There is also a black plastic calibration adjustment on the lower third of the tach. Carefully note the position of the slot, then insert a screw driver and turn it 1/4 turn each way from it's original position. After you have given it a couple of turns, return it to it's original position. This should fix the problem. If not then check ALL the electrical connections between the tack & the alternator.I also recomend doing the electrical system changes outlined elsewhere in this website. Good Luck! Bud
 

u079721

Contributing Partner
During my recent cruise (before I broke my clutch cable) the signal on my tach began to jump so much it was useless. I had previously tested all of the wire terminals on the alternator by tugging at them and they all felt sound, but having nothing to lose I replaced them all.

Well, that did it. The signal is now rock steady, and even after 26 straight hours of motoring home it never moved from 2350 rpm.

So while this may not be a fix for everyone's jumpy tach, it might be worth a try.
 

Geoff Johnson

Fellow Ericson Owner
Having just installed a Balmar alternator and regulator I can guarantee you that with a high output alternator the rpm's you are reading are not the rpm's you are running. Even with my original Delco OEM alternator, the tachometer would read 2200 rpm when the actual speed was 2000 rpm as measured by a handheld tachometer. Now the panel reads 3000 rpm's when the actual speed is 2350 as measured by a TinyTach (which measures fuel pulses through the injector tube.)
 
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