Tachometer bouncing then nothing

[SV STENTATO]

Hello,
I live on a 1970 35’ Pearson powered by a Westerbeke 33 w/ a westerbeke gauge cluster. Last time we were out my tach started intermittently bouncing with no change in engine speed then after a short while would appear to be functioning normally. Last week I did an oil change and when I fired her up the tach didn’t work at all. I believe the tach gets its signal from a brown wire led to an a/c tap on the back of the alternator. The wire seems to be firmly secured at both ends (tach side/alternator side) yet I’m still getting no reading at the tach? Does anyone have any advice on how I can test whether it’s the tach itself or something else? Any advice would be much appreciated! We’re getting ready to sail about 40 miles south through the Tacoma narrows in Washington to haul out and do our bottom paint and thru hulls. I want to make sure I can accurately monitor rpms during our voyage as it may require quite a bit of motoring for us to get there.
Thanks !

[meridian28]

When your tach is not reading do you get 13+ volts at your alternator output?

[Suijin]

On some brands of alternators the post on the back can come loose and loose contact inside the case. Happened on my Balmar.

[SV STENTATO]

I will check voltage out put at the alternator as soon as my new multimeter is delivered mine just went T.U. today of course �� I ordered a new one and will report back when I can test. I will check my terminal posts on the alternator as well. Thanks!

[Wotname]

Assuming your assumption that the tach is referenced from the alternator is correct, you first need to make sure the alternator is producing an output.

Easy way is to measure the output current if you have a DC clamp ammeter however measuring the DC voltage on it's output terminal is OK - it should be higher than at least 13.2V DC and could be as high as 14+V DC.

Then you need to measure the reference signal from the alternator (brown wire on the AC tap). The alternators I familiar with will have around 7V AC on this terminal. However I understand this could be as low as 2V A and still work. Most tachs can deal with any reasonable AC volts on the reference wire so any AC volts from say 2 to say 12 V AC should indicate the alternator is producing a reference signal. Make this measurement while the alternator is connected to the tach.

Finally the tach needs it own DC supply voltage which should be the same as the battery voltage i.e. 12+ to 14 VDC.

If all these voltages are correct and all the wires are clean and tight, the tach is probably on it's way out.

[Marathon1150]

We encountered this issue for quite some time after installing a new alternator with an external smart regulator. The problem became worse after installing solar panels. However, if the batteries were down and there was no sun, the tach would usually provide a reasonable display of engine RPM. As the batteries started to fill, it was possible to hear engine speed differences but usually the tach went to zero. When the regulator asked for power from the alternator, the engine sound changed and the tach came back on. After several years however, the tach just died. Checking continuity on all circuits, alternator output and disconnecting the solar panels, revealed that all was well except for the tach which read 'zero' continuously.

Replacing the tach got us back to the intermittent RPM display and the marine technician who did the installation mentioned that this is fairly common with smart regulators in his experience.

So as the last poster suggested, if everything seems to be normal except the tach, it is probably time to get a new tach.

Good luck with this one.

[Cat36Mahalo]

If your regulator is a balmar 614 you need to pull the tach signal from the regulator, this tells the regulator to keep the field energized even if the batteries don’t need charging. Alternatively you can put magnets on your crank pulley and use a hall sensor to feed the tach.

[GordMay]

Originally Posted by Cat36Mahalo

If your regulator is a balmar 614 you need to pull the tach signal from the regulator, this tells the regulator to keep the field energized even if the batteries don’t need charging. Alternatively you can put magnets on your crank pulley and use a hall sensor to feed the tach.

When an electric tachometer is used, the alternator’s stator output will provide the electrical pulse needed to drive the tachometer. The MC-614 has been designed to provide regulated tach output when the WHITE stator wire is connected to the regulator’s Stator In (#12) terminal and the out feed wire to the electric tachometer is connected to the Tach Out terminal (#13) terminal.
*Not required for magnetic pick-up Tachs.
Balmar MC-614 ➥ http://www.balmar.net/wp-content/upl...ion-Manual.pdf

[flyingfin]

First - check all wires and connectors.
Second - run separate wire from Tach neg terminal directly to battery neg terminal
Third - borrow a known good tach from a friend
Four - buy a new electronic tach

[waterman46]

Originally Posted by GordMay

When an electric tachometer is used, the alternator’s stator output will provide the electrical pulse needed to drive the tachometer. The MC-614 has been designed to provide regulated tach output when the WHITE stator wire is connected to the regulator’s Stator In (#12) terminal and the out feed wire to the electric tachometer is connected to the Tach Out terminal (#13) terminal.
*Not required for magnetic pick-up Tachs.
Balmar MC-614 ➥ http://www.balmar.net/wp-content/upl...ion-Manual.pdf

I have used an MC614 for 20 years and didn't know about this solution to keep tach running when regulator has shut down alternator output. Got to try it, thanks!

[Peregrine1983]

Check your alternator belt, the tension, and replace if it’s worn. I had the same issue on my Westerbeke 58. It was a bad belt.

[SVTatia]

All good advices above.

I assume you have the admiral panel, if so you can check the voltage the alternator is putting out.

Keep in mind: if the tach is not working properly, neither is the hour count... and if you replace the tach, make sure you account for the engine hours.

[Marathon1150]

Originally Posted by Cat36Mahalo

If your regulator is a balmar 614 you need to pull the tach signal from the regulator, this tells the regulator to keep the field energized even if the batteries don’t need charging. Alternatively you can put magnets on your crank pulley and use a hall sensor to feed the tach.

Thank you! Two marine electricians (one of whom installed the Balmar) and one marine technician, did not know this!

I will rewire as per Balmar's instructions.

Many thanks again.

[newhaul]

Originally Posted by SV STENTATO

Hello,
I live on a 1970 35’ Pearson powered by a Westerbeke 33 w/ a westerbeke gauge cluster. Last time we were out my tach started intermittently bouncing with no change in engine speed then after a short while would appear to be functioning normally. Last week I did an oil change and when I fired her up the tach didn’t work at all. I believe the tach gets its signal from a brown wire led to an a/c tap on the back of the alternator. The wire seems to be firmly secured at both ends (tach side/alternator side) yet I’m still getting no reading at the tach? Does anyone have any advice on how I can test whether it’s the tach itself or something else? Any advice would be much appreciated! We’re getting ready to sail about 40 miles south through the Tacoma narrows in Washington to haul out and do our bottom paint and thru hulls. I want to make sure I can accurately monitor rpms during our voyage as it may require quite a bit of motoring for us to get there.
Thanks !

where are you hauling out? I'm in Tacoma

It sounds to me like a loose wire at one end or the other .check clean and tighten all electrical to alternator and gauge .

[Peterbreit]

This may not apply to you but should be helpful for Yanmar engine owners.
On my Beneteau 461 with a Yanmar engine the tachometer gets its RPM input from a simple spade connector at the flywheel housing. Not from the alternator !