Tachometer RPM Over-read

[Graham]

I recently replaced all my Teleflex engine instruments on my Catalina 34 Mk2 yacht (1376) with KUS Q series gauges.  The engine is Universal Westerbeke M35BC with 2,000 hours and the alternator was factory-supplied with the engine.

The new tachometer (ranges up to 4000 RPM) reads accurately with all electrical accessories switched off.  However, when I switch on any one of the refrigeration, engine blower fan or chart plotter, the tachometer over-reads especially on higher revolutions.  If I have the engine revolutions at 3,000 revs and then switch on engine blower fan, the tachometer read increases to 4,000 revs, although actual engine revolutions remain the same at 3,000 RPM.  Individual battery monitors are both reading constant 14 volt irrespective of whether refrigeration, engine blower or chart plotter is on, so I think that the alternator and positive / negative wiring is OK.

My Positive and Negative wiring for the engine panel are wired through Bus Bars which feed all engine switches and instruments.  Whilst the chart plotter and engine blower switch are located near the tachometer (on the binnacle), the refrigeration and blower fan are both located some 1 metre from the tachometer.  Also I believe the refrigeration unit wiring to be on a separate loom although all ultimately converge onto the main electrical control panel below decks.

Any ideas as to fixing this would be much appreciated.

[KWKloeber]

Have you checked w/ KUS?
I didn't know that KUS made a tach for a T input. Or are you using a pickup sensor?

[Graham]

Thank you.
Have checked with KUS and their initial response was
Quote
It sounds like you have electrical issues.
I recommend for you to consult with an electrician so they may go over your electrical system and find the cause.
Unquote
That was from their Technical Support in Florida.
They then recommended a remedy that was a cut & paste from their one-page installation instructions.  Not impressed, so went to their HO in Taiwan - am awaiting a response.

KUS tachometer sender input is from the W terminal on the alternator.

[KWKloeber]

Graham

Odd, I've never seen a "W" labeled on a Universal alt, although admittedly I've seen the one used on the B engines up close and personal only once.  Typically tach alt terminals are labeled "AC" or TAP". 
There's a couple of standards for input to tacks (like, magnetic pulse from a pickup, elec input, etc -- and AC current (a waveform) from a diesel alt.) 
KUS alts I saw seemed to be looking for an input from a pickup, not a waveform -- but again I am not versed in the different KUS alts.

[Graham]

I have a Mando alternator from when the boat was new (1997) and tachometer terminal on the alternator is marked "P".  KUS local agent confirmed the tachometer can be hooked up to alternator.

Getting my alternator repaired at present as over-charging to 15.8v at 3,000 revs with all electrical ancillaries turned on.  I believe that is the reason for the volatility on the tachometer.  Will let you know when I get alternator back and fitted.

Regards

[Ron Hill]

Graham : Isn't that Voltage problem with the Voltage regulator and not the alternator?

A thought

[KWKloeber]

Graham,

Ok Mando ("P") -- I ass/u/med you had a Moto/Prestolite ("A/C").  A nice thing about your Mando (if it gets rebuilt and not replaced) is it has external sense (S) so you could have the regulator sense V right at your battery terminal (instead of the alt output.) 

Westerbeke had like 10-12 different Alts they had available for the Universal A and B engines!!

Ron the Mando is internally regulated.

Kinda odd that that overvoltage on the regulator would affect the tach that way -- most can take 9-32 volt input signal.  and overvoltage (I wouldn't think) would double the waveform frequency (which is what fools the tach into displaying engine RPMs.)