Tachometer - Electrical Problem ......help

[Chris Reinke - CD330]

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM’s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM’s were increased. Once the AMP meter and tachometer were operating the RPM’s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM’s are increased and the alternator establishes a field. So here is the problem….

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM’s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 – Innisfail (Gaelic for “a little bit of heaven on earth”)



chris.reinke@sac.com

[Catherine Monaghan]

Chris,

Maybe it's something simple and you don't have to test? You never know, but it could just be corroded contacts???

Howard Kolsby just installed brand new engine instruments in the cockpit of his CD33. He also replaced all the hoses and wiring for the engine. After installing the new istruments the new tach didn't work. He removed the wiring for the tach and cleaned the contacts on the engine then re-installed the tach wiring. After that it worked fine.

Hope somebody can provide better suggestions.


Cathy
CD32 Realization, #3
Rahway, NJ
Raritan Bay

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM’s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM’s were increased. Once the AMP meter and tachometer were operating the RPM’s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM’s are increased and the alternator establishes a field. So here is the problem….

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM’s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 – Innisfail (Gaelic for “a little bit of heaven on earth”)

catherine_monaghanNOSPAM@merck.com

[Boyd]

Hi Chris...

Until the tech types jump in on this one... Mine does something like you describe when the alternator belt is slipping. Maybe?

Boyd

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM’s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM’s were increased. Once the AMP meter and tachometer were operating the RPM’s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM’s are increased and the alternator establishes a field. So here is the problem….

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM’s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 – Innisfail (Gaelic for “a little bit of heaven on earth”)

boyd@wbta.cc

[Chris]

Thanks for the comment. That was the first thing I checked. The belt is tight and the alternator has good output of a constant 14.2v. The Amp meter is registering the charge fine. It is just the tach gauge that does not work. The tach terminal on the alternator is clean and putting out 14.2v, which the wire is transmitting to the gauge.

I am stumped......

Hi Chris...

Until the tech types jump in on this one... Mine does something like you describe when the alternator belt is slipping. Maybe?

Boyd

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM’s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM’s were increased. Once the AMP meter and tachometer were operating the RPM’s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM’s are increased and the alternator establishes a field. So here is the problem….

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM’s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 – Innisfail (Gaelic for “a little bit of heaven on earth”)

[D. Stump, Hanalei]

Captain Reinke,

The tack sensor line is usually attached to a diode on the STATOR of an alternator. If you are reading 14+ volts DC, something is wrong. you should be looking at an alternating current! Look for a broken wire..AND wait one, cause I'm sure Larry DeMers will help with this one....

Dave Stump
s/v Hanalei CD-30C

[M. R. Bober]

A few years ago when I was replacing the prop on RESPITE, the prop shop guy (an ancient and extremely savvy river rat) had me check the engine's performance with the new prop. He cautioned me not to depend on the accuracy of my tach,if I had "one of those high output alternators." I didn't (and don't) so I paid scant attention to the why, but the what was certain.

I remember that the load imposed by the high output alternator is such that there is a delay in adding them into the cicuit until the rpms come up a bit, but I don't know how to overcome the delay.
Good Luck
Mitchell Bober
RESPITE
CD330
Annapolis, MD

[John R.]

This is a problem I have run across a couple times when a stock alternator is replaced with a high output alternator. An electronic tach runs off of alternating current supplied via a terminal from the alternator stator. Engine speed is in proportion to the frequency of the AC current. If a high output alternator is not calibrated to the engine speed when first installed you can get the problem you describe but there can be other causes as well. Did you ever calibrate your tach to that alternator? There should be a calibration port on the rear of the tach. A common way to calibrate is to mark the throttle position with the engine running at around 2000 RPM and then install the new alternator. Then run the throttle up to the marked reference position on the throttle and then check the tach readout. If its off just tweak the calibration adjuster until it is reading correctly. Some tachs don't have an adjustment so then I'm afraid if it is a calibration issue you would have to replace the tach for one with an adjuster.

There are some situations where even if the tach is calibrated correctly you still have sporadic or no reading at idle unless you do a quick engine rev first. I owned a boat that did this at idle and occassionaly at around 1200 rpm even though the tach was calibrated. With a quick increase in idle that would be enough to excite or activate the tach and the rpms would look normal and usually steady from then on but not always, suddenly the tach would become sporadic or quit, then start normal functioning again. The boat was using a Balmar alternator. Balmar techs once told me that some tachs simply respond that way with high output alternators. Over the years I've learned that to be true. I never did find the actual cause of the problem on that particular boat. I eventually replaced the tach with a new one from Teleflex and the problem was corrected. It was either a flat out faulty tach or the tach (Yanmar OEM) was just not sensitive enough to picking up the low speed pulses sent from the AC tap.

Keep in mind that some high output alternators won't put out anything or very little until they hit a specific rotor rpm so make sure your pulley size is correct so that the alternator is rotating fast enough. Call the tech guys at the manufaturer of your alternator and ask them for the formula to calculate the proper pulley size needed for proper rotor rotation. I have found this to be a problem on some boats affecting tach performance. I used to have that formula in my service charts and I'll post the formula if I get a chance to dig them out of storage boxes.

Last but not least is a slipping belt but usually you can hear that, especially when the engine first starts running. Test by putting some heavy current loads on the alternator and listen for slippage and/or watch your ammeter reading.

You may want to try a different tach and see if it makes a difference. You don't mention what regulator you are using. Maybe the tach output is faulty in the regulator.

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM’s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM’s were increased. Once the AMP meter and tachometer were operating the RPM’s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM’s are increased and the alternator establishes a field. So here is the problem….

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM’s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 – Innisfail (Gaelic for “a little bit of heaven on earth”)

[Larry DeMers]

John,

One of the ways to cure this (with Balmar alt's. anyway) is to put a small load on the alt. Turn on a small cabin light all the time or install a small resistor across +12v and ground on the alternator output (may want to switch this in and out of circuit as you use the engine though, or it would draw down your battery while the engine is off) to draw 100ma or so. This will keep the alterators field active, and producing the AC pulses that *some* tachometers need to run.
I would like to point out that some engines use a magnetic pickup for the tach. My MD7B apparently does just this in fact. They would not be affected then by this cutout at low output from a high-output alternator.

Larry DeMers
s/v DeLaMer

This is a problem I have run across a couple times when a stock alternator is replaced with a high output alternator. An electronic tach runs off of alternating current supplied via a terminal from the alternator stator. Engine speed is in proportion to the frequency of the AC current. If a high output alternator is not calibrated to the engine speed when first installed you can get the problem you describe but there can be other causes as well. Did you ever calibrate your tach to that alternator? There should be a calibration port on the rear of the tach. A common way to calibrate is to mark the throttle position with the engine running at around 2000 RPM and then install the new alternator. Then run the throttle up to the marked reference position on the throttle and then check the tach readout. If its off just tweak the calibration adjuster until it is reading correctly. Some tachs don't have an adjustment so then I'm afraid if it is a calibration issue you would have to replace the tach for one with an adjuster.

There are some situations where even if the tach is calibrated correctly you still have sporadic or no reading at idle unless you do a quick engine rev first. I owned a boat that did this at idle and occassionaly at around 1200 rpm even though the tach was calibrated. With a quick increase in idle that would be enough to excite or activate the tach and the rpms would look normal and usually steady from then on but not always, suddenly the tach would become sporadic or quit, then start normal functioning again. The boat was using a Balmar alternator. Balmar techs once told me that some tachs simply respond that way with high output alternators. Over the years I've learned that to be true. I never did find the actual cause of the problem on that particular boat. I eventually replaced the tach with a new one from Teleflex and the problem was corrected. It was either a flat out faulty tach or the tach (Yanmar OEM) was just not sensitive enough to picking up the low speed pulses sent from the AC tap.

Keep in mind that some high output alternators won't put out anything or very little until they hit a specific rotor rpm so make sure your pulley size is correct so that the alternator is rotating fast enough. Call the tech guys at the manufaturer of your alternator and ask them for the formula to calculate the proper pulley size needed for proper rotor rotation. I have found this to be a problem on some boats affecting tach performance. I used to have that formula in my service charts and I'll post the formula if I get a chance to dig them out of storage boxes.

Last but not least is a slipping belt but usually you can hear that, especially when the engine first starts running. Test by putting some heavy current loads on the alternator and listen for slippage and/or watch your ammeter reading.

You may want to try a different tach and see if it makes a difference. You don't mention what regulator you are using. Maybe the tach output is faulty in the regulator.

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM?s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM?s were increased. Once the AMP meter and tachometer were operating the RPM?s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM?s are increased and the alternator establishes a field. So here is the problem?.

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM?s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 - Innisfail (Gaelic for ?a little bit of heaven on earth?)

demers@sgi.com

[Larry DeMers]

Mitch,

The initial delay is a built in time delay that allows the engine to warm up and the belt(s) to seat and stretch a bit before they are loaded down hard by the alternator. About 45 seconds after starting the engine, the alternator will begin to turn on slowly, ramping up to full current over a 30 sec. period. This is true with Balmar alternators at least.
The problem with the tach quitting at low rpm has to do with the alternator's regulator shutting off the alternator field current until a load is seen by the regulator. Balmar has taken care of that in their regulators with a tach drive circuit that still fires when the alt is not charging much.

Cheers,

Larry DeMers
s/v DeLaMer
CD30

A few years ago when I was replacing the prop on RESPITE, the prop shop guy (an ancient and extremely savvy river rat) had me check the engine's performance with the new prop. He cautioned me not to depend on the accuracy of my tach,if I had "one of those high output alternators." I didn't (and don't) so I paid scant attention to the why, but the what was certain.

I remember that the load imposed by the high output alternator is such that there is a delay in adding them into the cicuit until the rpms come up a bit, but I don't know how to overcome the delay.
Good Luck
Mitchell Bober
RESPITE
CD330
Annapolis, MD

demers@sgi.com

[Larry DeMers]

Dave Stump is right. The Tach works on a pulsing dc signal from the alternator, that is proportional to the RPM of the alternator. You should be seeing a pulsing DC voltage there, not a continuous dc voltage. I suspect the tach gauge is ok, but the problem is the tach output from the alt. I cannot picture what would give you a solid 14vDC though. Shorted diode would result in unrectified AC coming to the meter, which I would not expect to see show up on your voltmeter while in the DC position. So there is a DC component to the voltage, as your meter says. Is there a possible destination error for the tach wire going to the alternator? If a secondary 12vdc output were picked off instead of the alt output, then you would see that charge voltage (14.2VDC) appear at the tach.

Has anything been done to the alt since this tach last worked??

This is a strange one alright...

Larry DeMers
DeLaMer

Thanks for the comment. That was the first thing I checked. The belt is tight and the alternator has good output of a constant 14.2v. The Amp meter is registering the charge fine. It is just the tach gauge that does not work. The tach terminal on the alternator is clean and putting out 14.2v, which the wire is transmitting to the gauge.

I am stumped......

Hi Chris...

Until the tech types jump in on this one... Mine does something like you describe when the alternator belt is slipping. Maybe?

Boyd

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM?s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM?s were increased. Once the AMP meter and tachometer were operating the RPM?s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM?s are increased and the alternator establishes a field. So here is the problem?.

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM?s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 - Innisfail (Gaelic for ?a little bit of heaven on earth?)

demers@sgi.com

[D. Stump. Hanalei]

Captain DeMers,

As I understood the latest research I did about alternators, it is an AC pulse that the tack is sensing. And, that pulse comes from the stator of the alternator. DC is NOT involved at this point! Am I mis-informed??? Clarification please......

D. Stump, Hanalei

[John R.]

I dug out my old service notes this morning and I located the *pulley ratio formula* for setting up new alternators or you can use it to make sure your existing alternator pulley is correct for your engine.

Here it is:

Ideal ratio = 3:1

Minimum ratio = 2.5:1

Crankshaft pulley diameter (outside diameter) divided by alternator pulley diameter (outside diameter) equals the ratio.

Use outside diameter measurements when running V-belts
Use lower groove diameter measurements in pulleys for serpentine belts.

I have always had oddities with my tachometer, but now it does not operate at all. I replaced my alternator 3 years ago with a high output, single wire model. When I attached my tachometer wire to the terminal I found the tach would not register anything until the engine RPM’s were increased slightly above idle. I also found that the AMP meter would not register a charge until the RPM’s were increased. Once the AMP meter and tachometer were operating the RPM’s could be reduced and the gauges would continue to operate.

This season I have found that my Tachometer does not function at all. The AMP meter still has the same issues of registering once the RPM’s are increased and the alternator establishes a field. So here is the problem….

I have always been told that the tachometer operates by registering a variation in the voltage. When I test the voltage at the guage it is a constant 14.2v, regardless of engine RPM’s.

Can anyone explain to me how I can test to see if the tachometer terminal is generating the proper signal, or if the tachometer guage itself is malfunctioning?

Thanks,
Chris Reinke
CD330 – Innisfail (Gaelic for “a little bit of heaven on earth”)