Need a westerbeke tachometer

[SVJourney]

Hey all,

My the bezel covering my tachometer has corroded all the way through.  Found it laying on the floor of the cockpit the other day.  The tach still works, but I'm sure it won't be long for the world open to the salt like it is now. 

So.. looking for a used tach.  Hit me up either on this thread or private message if you can help me out please.

[SVJourney]

Hi All,

Still looking for this.  In fact, if someone has a whole instrument cluster I would be willing to buy that as well.  Pm here or through Dana's blog WWW.galleyWenchTales.com

A huge thanx to anyone who could come through on this.

Cheers
Wayne

[Bev & Billy on Sta-sea-dawn]

Did you find a cover....
I need to know which wire goes from the tach to the alternator.  My new alternator only has one wire labeled Tac.  My tach has a red, bronish and yellow wire running into the harness, but I can not trace it through the maze of all the PO's changes.  Where can I attach the tach wire?  Or, where can I find a diagram of the back of the tachometer....Billy

[PeteW]

Any electronic tachometer will work. Volvo, Westerbeke, and so on. One that fits in the hole is the most significant requirement. Calibrating (because of various pulley ratios)  the tachometer is another story.  There is a potentiometer on the back and you will need to borrow an optical tachometer and point it a piece of reflective tape on the crank pulley.

The tach has three wires. +12V Ignition (red) ground (blk) and stator (yellow). There may also be a lamp which goes to the same +12V that is hot when the ignition switch is on.  Stator is the connection you make to the alternator. It is literally one of the 3 phase Y connected stator leads that goes ahead of the 3  phase diode bridge inside the alternator. Its not rectified but is a sine wave voltage that represents engine speed. Its not a slip ring connection. Not all alternator have a stator wire connection. In that case you will need to take it apart on solder one on and fish it out the back.

On my Pearson I purchased a Ford Alternator that was rebuilt with 100 amp diodes. Ford is the only automobile company that uses external regulators with their alternator. All others are internally regulated and most limit you to 50 amps. I was able to purchase a Sterling programmable external regulator and set it for AGM batteries. The Sterling regulator have a sense wire which goes to the battery + terminal. In this way you can T off diode isolators from the B+ connection on the alternator to multiple  battery banks and charge to the correct programmable voltage depending upon battery chemistry you use. A similar Marine alternator setup from Bomar would have sent me back $900. This package came in at $200.

Pete  s/v Tartanic

[Bev & Billy on Sta-sea-dawn]

Thanks Pete ....that helps a lot......billy

[Bev & Billy on Sta-sea-dawn]

I am dealing with a wacky tack.....I hook up the wires and sometimes it give rpm's and some times not....it is a Motorola 7HT2007.  Is there a replacement part for it or is it still available somewhwere

[Bev & Billy on Sta-sea-dawn]

I also would like to replace panel/oil pressure gauge and water temperature gauge...any vendors for these

[SVJourney]

Billy, we've been dealing with the same problem ever since we replaced the gauge.  Dana found one at West Marine when she worked there, but its erratic.  Sometimes accurate, sometimes the needle just swings all over the place.  I thought it was bad wiring, but I just replaced ALL the engine wiring here in NZ and its still doing it.  Does anybody know if the tach senses A/c voltage?  Or frequency?  My next step is to parallel my multi meter to the AC tap to see if the alternator is being wacky, or is it the new tach.....  Might a capacitor inline be a fix? 
LOL, PeteW?  are you here?

[PeteW]

This has been a problem that I am not sure has ever been completely resolved. Here are my thoughts.

And intermittent tachometer may not actually be the fault of the tach.  The signal from the alternator is AC consisting of 1 phase of the alternator prior to rectification. It should be around 12 volts in amplitude and as such can be considered a digital pulse stream. The tachometer measures the frequency of that sine wave. That being said you can measure the amplitude of the AC signal by putting your voltmeter on AC volts. Unfortunately you need a oscilloscope or frequency counter to interrogate this signal any further.

Since its an AC signal it does require a good ground ( I suggest a dedicated twisted pair signal and ground) between the Alternator case and the tachometer ground. The voltage measured at the tach should be the same as the voltage measured at the alternator. A solid input signal at the tachometer would suggest that the problem is in the tachometer.

I don't know how your tachometer works. I suspect they are all analog frequency to voltage converter circuits. The voltage drives the meter movement.  These circuits need power, ground as well as a frequency input. So if the tach has a 12V supply connection it may be needed to power the converter circuitry in the tach. It is possible that the tach will create its supply voltage from the alternator sine wave input. In that case ground and AC input are the only connections. Although the 12V may or may not be just for the lamp.

The tachometer is by far the most complicated and failure prone link in this chain but you need to check the alternator and the wiring first.

[Bev & Billy on Sta-sea-dawn]

I could probably follow those instructions, I have an remediate need of oil and water indicator gauges.....any ideas of finding them to match holes in my Westerbeke panel holes ....thank  you for the input...Billy and Bev

[SVJourney]

PeteW
I was afraid of that.  My meter won't do frequency.  Good call on the ground though.  I checked my grounds, replaced them, but they are not grounded to the Alternator itself.  I can see how the twisted pair might reduce or replace some noise getting in from somewhere.  I have some shielded twisted pair I will do a temp run with to see if it cures the problem.

Billy,
I can only suggest the online version of the West Marine catalog.  There should be other venues with lower pricing.  The gauges are standard 2 1/4 inch and should be available pretty much anywhere as they are automotive standard.

[PeteW]

There are some 85mm dia. Tachometers on EBay in the $15 to $25 range. You will need one that is specified as a "Diesel Alternator Tachometer".  I was looking at one for $17.99 made in Taiwan. This one has an adjustment for calibration, and standard 3 wire hook up +12V, Grnd and Alternator pulse. I saw others that have adjustments for Alternator # of poles, division, and input pulse filter.

Jamestown and other marine stores all sell one by Teleflex for around $90.

Note: if your tachometer has a  +12V power connection make sure its good. A bad connection there will make the tach go squirrely.

[slokat]

Was having tach problems and my mechanic son traced it to my external voltage regulator. It was randomly telling the alternator to generate power, which randomly made the tach work...

[Bev & Billy on Sta-sea-dawn]

I am going off subject a little...but my water temperature sensors may be bad....can I check it with an ohm meter?...I seem to have 2 sensors, one in the head and one in the block.  Each have 2 tabs wired in parallel to each other and then to the gauge.
I have a new gauge but not reading temperature

[SVJourney]

Finally found our problem.

The switch for the amount of poles that was on the tach was parked halfway between one setting and another.  So it would work right, then switch to another setting.  Stupid problem, but ultimately a free fix.  LOL, rewiring the engine was just a bonus.