Need Help with “A tach issue” - The title that keeps on giving…

[Gulfsailor]

I have searched here and have used Google searching this forum and elsewhere but I'm afraid I still need help.

Yesterday our tach stopped working (M35B) When I got back to the boat today I:

1) Checked the sender wire on the back of the alternator (original stock unit)loosening and tightening all good.

2) Tested battery level with engine and battery charger off using a multimeter.

3) Tested the voltage with the engine running at a fast idle read approximately 14 volts.

4) Volt meter at helm engine pod shows about 13 volts with engine running.

5) Removed tach from pod, turned the adjustment screw back and forth...remounted and still nothing. I did notice that the tach needle budged a little downward when energized.

Looks like a replacement on Catalina Direct is about $175.

I am leaning on buying a new tach but thought I would check the group here first for ideas.

Thanks in advance!

[Stu Jackson]

If your house bank is full the regulator will not require output. 

Do you have an internal or external regulator?

[Gulfsailor]

If your house bank is full the regulator will not require output. 

Do you have an internal or external regulator?

Not sure if it's internal or integrated.

[Stu Jackson]

If your house bank is full the regulator will not require output. 

Do you have an internal or external regulator?

Not sure if it's internal or integrated.

Look for a separate box with a bundled wire harness usually in black about 3/4" in diameter off the back of the alternator and the external regulator is often under the head sink or in the aft cabin although sometimes incorrectly in the engine compartment.  The regulator looks like this: https://balmar.net/product/mc-618-h/

If you don't have one then it's internal and on the back of the alternator.

My question about full batteries still applies.  If your batteries are full, regulators signal to the alternator that no more power is required and turn the signal to the tach off.

I recommend as the next step to turn your battery charger off and turn your fridge on for say a half hour.  This will assure some load and draw down the battery bank.  Then test again and let us know what you find out.

[Ron Hill]

If your alternator is the "stock alternator" then you have an internal Voltage regulator!!

A thought

[Gulfsailor]

I verified with the previous owner (who is the original owner) that the alternator is original.

[Noah]

STU—you said QUOTE: "If your batteries are full, regulators signal to the alternator that no more power is required and turn the signal to the tach off." What? Can you please explain? I have never heard of this nor experienced it before. Tach shuts-off when batteries are full??

[Gulfsailor]

STU—you said QUOTE: "If your batteries are full, regulators signal to the alternator that no more power is required and turn the signal to the tach off." What? Can you please explain? I have never heard of this nor experienced it before. Tach shuts-off when batteries are full??

I've never heard this either. I always kept the batteries fully charged on our last boat with a Universal M25XP engine. The tach always worked (even with the fully charged batteries).

Another thing I discovered here is someone in a previous thread said it is bad to start the engine while on shore power and that it can damage the tach. I've never heard or seen that happen before. Is it a Catalina specific issue maybe?

[Jim Hardesty]

Another thing I discovered here is someone in a previous thread said it is bad to start the engine while on shore power and that it can damage the tach.

One of the things I was told when I got my first boat was, not to start the engine with shore power battery charger on and not to turn off the engine key before shutting the engine off.  Some guys said for the starter, most said alternator.  Not one of the knowledgeable guys said to do it differently.
So that's what I do.
Jim

[Stu Jackson]

Alternators "report" a signal to a tachometer based on the changing frequency of the alternator's alternating current (which is later rectified into DC power output, the AO).

If the regulator is signalling that there is no need for alternator output (AO) then there will be no signal and the tach will not read.

Often what happens is that even though you arrive at your boat with it being plugged in and charging, thinking you have full batteries, you turn stuff on after you arrive.  When you disconnect the shorepower charger, the battery voltage drops to below the charge voltage and the regulator setpoint, so the regulator tells the alternator to output.

We often see questions in boating forums "My tach isn't working when I first start my engine, what should I do?"  Answer?  Is your charger still connected? If so, its voltage could be keeping the batteries above the regulator setpoint.  [If the charger is in float at 13.4V and the regulator setpoint is 14V, the tach will work.  The internal regulator is using the AO as a battery sense wire.  External regulators have separate battery sense wires.]  Turn on a load so the regulator sees that the bank needs a charge.  The regulator reads the battery voltage because it is connected to the battery via the AO wire.

There will be no damage to anything if you are connected to shorepower when you start your engine.  The tach reads the alternator output and is not connected to the starting circuit.

One of the poles of the key switch is connected to the regulator and it turns the regulator on and off via the wiring harness in addition to powering the start button (or key switch start function).  You can turn the key switch off with the engine running.  It will stop the tach signal, stop the AO because it turns off the regulator without interrupting the AO, and will harm nothing.  Never turn the 1-2-B switch off with the engine running UNLESS you've redone your electrical system and have the AO going directly to the house bank bypassing the switch.  If your AO goes to the house bank, you can turn your 1-2-B switch off with the engine running with no damage because the AO is not being interrupted.  Damage to the alternator occurs when interrupting the AO, and NOT the power to the regulator.

It's helpful to understand how all the bits and pieces work individually and connected together as a system.

[Noah]

STU— I assume that your statement "there is no tach signal with full batteries" does not apply if you are running an external regulator.  Or, some other wiring is set-up differently on my boat, as I have never had this issue. I run my engine with 100% SOC on batteries "all the time" and always have a tach reading.

[Noah]

https://c34.org/wiki/images/3/34/Gauge_Troubleshooting_Steps.pdf
 Gulf—Have you seen this?

[Gulfsailor]

https://c34.org/wiki/images/3/34/Gauge_Troubleshooting_Steps.pdf
 Gulf—Have you seen this?

Very helpful thanks!

[Stu Jackson]

STU— I assume that your statement "there is no tach signal with full batteries" does not apply if you are running an external regulator.  Or, some other wiring is set-up differently on my boat, as I have never had this issue. I run my engine with 100% SOC on batteries "all the time" and always have a tach reading.

Doesn't make a difference of external vs. internal regulators. Battery sensing: Internal sensed via AO to bank; external via sense wire from external regulator (although IIRC the Balmar ARS5 doesn't have one, but my MC612 does).

EDIT:  Internal regulators do nothing with their battery sensing, it's only the other end of the AO.  Only external regulators with properly wired battery sensing use that battery voltage to adjust output voltages based on the programmed setting.  In all cases output current is determined by the bank itself.

Also just occurred to me:  do you use your glow plugs before you start your engine?

[Craig Illman]

RE: Starting with shore power on
You can send excessive voltage to the glow plugs with the shore power on. I managed to burn out a couple once.

Craig