Tachometer Problem
One of the VDO tachs for my Lehman 135s seems to "skip" or "bounce." For
example, running at 1700 RPM, it will drop to zero and then immediately bounce
back up to 2000 before settling back to 1700. I thought that perhaps the belt
was loose but that does not appear to be the problem. Any suggestions from the
fertile minds of this knowledgeable group?
<<<Gary Ritzman>>> M/V Dharma Albin 40 Mercer Island WA
Does it do this very often? They will bobble if you have a fuel filter
clogging, sometimes its like a small warning before it really plugs up.
From: ritzmans@msn.com> To: trawlers-and-trawlering@lists.samurai.com> Date:
Tue, 5 Aug 2008 05:13:22 -0700> Subject: T&T: Tachometer Problem> > One of the
VDO tachs for my Lehman 135s seems to "skip" or "bounce." For> example,
running at 1700 RPM, it will drop to zero and then immediately bounce> back up
to 2000 before settling back to 1700. I thought that perhaps the belt> was
loose but that does not appear to be the problem. Any suggestions from the>
fertile minds of this knowledgeable group?> <<<Gary Ritzman>>> M/V Dharma
Albin 40 Mercer Island WA> _______________________________________________>
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GARY RITZMAN ritzmans@msn.com writes:
One of the VDO tachs for my Lehman 135s seems to "skip" or "bounce." For
example, running at 1700 RPM, it will drop to zero and then immediately
bounce
back up to 2000 before settling back to 1700. I thought that perhaps the belt
was loose but that does not appear to be the problem. Any suggestions from
the
fertile minds of this knowledgeable group?
Well, I have good and bad news.
The good news is that I know what causes this, because it also happens to me
on my VDO tach. It happens when the batteries reach full charge and the field
current on the alternator drops to such a low point that the tachometer feed
from the alternator is too weak for the tach to read.
The bad news is that I have not yet figured out what I can do about it, other
than installing a dedicated tachometer sender.
Perhaps someone else has a suggestion?
Scott Welch
FirstClass Product Manager
www.firstclass.com
Those who make no mistakes rarely make anything.
Scott H.E. Welch wrote:
The bad news is that I have not yet figured out what I can do about it, other
than installing a dedicated tachometer sender.
Perhaps someone else has a suggestion?
REPLY
The easy solution is to place a dropping resistor from alternator output
to ground. Something along the line of 20 - 30 ohms and 25 watts to
dissipate the heat.
This was a trick often suggested by Balmar to cure this tach drive issue.
Arild
Tuesday, August 5, 2008, 5:07:20 PM, Arild wrote:
AJ> Scott H.E. Welch wrote:
The bad news is that I have not yet figured out what I can do about it, other
than installing a dedicated tachometer sender.
Perhaps someone else has a suggestion?
AJ> REPLY
AJ> The easy solution is to place a dropping resistor from alternator output
AJ> to ground. Something along the line of 20 - 30 ohms and 25 watts to
AJ> dissipate the heat.
AJ> This was a trick often suggested by Balmar to cure this tach drive issue.
AJ> Arild
But make certain that that resistor (and/or the alternator output)
is disconnected from the battery when the engine is off. On my boat,
I think I'd have to add a relay to disconnect the resistor when the
engine is off (or rather connect it only when the engine is running).
--
Peter Bennett, VE7CEI Vancouver, B.C., Canada
Ennos 31 "Honeycomb"
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
Greetings all,
Just read Steve D'Antonio's newsletter article on stainless
hardware...probably the best and coherent explanation I've ever read on the
subject of stainless fasteners.
Well, I still have a question of priorities when choosing fasteners: On my
steel trawler, built in the mid '50s, I've got an aluminum pilot house
riveted to its aluminum structure. The rivet heads were all covered by
bondo for appearance, but someone had filed down some of the rivet heads so
much, in places not much was holding the plate to the structure. So we
removed most of the rivets, and replaced them with brass round-head machine
bolts. Then I thought there may be a galvanic problem with the brass vs
aluminum, so we switched out all the brass bolts with 18-8 stainless bolts.
These will again be covered by bondo to provide a smooth surface to the
pilot house exterior.
Steve mentions that stainless, when embedded in a hydroscopic (I think he
meant hygroscopic) substance, can still corrode. My question is: Would
bondo be that sort of substance? Are our 18-8 bolts fine embedded in bondo
fastening aluminum together? I'd hate to find out down the road that the
pilot house skin is not connected to the framework anymore.
And, would the brass bolts have been a better choice for this application
replacing the aluminum rivets?
Any ideas?
Mark Andrew
Holland, MI
"Black River", 56' steel, circa 1955