beta marine BD722 tach acting very very strange!

[jaybeegee]

dear all

I have a Beta Marine 20Hp Model BD722 (350hours) installed with a 5+1 way switch panel as you can see here:

IMG00372-20110305-1016 | Flickr - Photo Sharing!

The tach worked perfect and never missed a beat until I change the services battery (not sure if problem is actually related or pure coincidence!).

All of a sudden, with the engine in motion, 5 out of 10 times it will show no reading or an incorrect reading! And if I activate a couple of the switches on the panel (eg. switch 1 - engine extractor fan) it will come to life! Switching on another switch (switch 2 - fridge) will get it to what I think is the correct rev level plus 500! And using another switch (say switch 3 - radio + vhf) will knock it a couple hunder revs down!

Any ideas what the problem could be?

Appreciate any problem areas you think might be worth investigating.

cheers

Jay

[NCboatrx]

Did you only change the battery or was something else done at the same time? I suspect that something has been disturbed when the work was done as this is a classic symptom of a loose connection of a bad wire. The tach gets its signal from the alternator so if something has been added to the charging system it could be affecting alternator output and therefore the signal to the tach.

[jaybeegee]

thanks Stan for your reply. did not add anything and checked all the cabling and all looks ok. symptoms are really very strange. i will do another pass if thats what you think the likely source is.
cheers

[donradclife]

As the tach input is from the alternator, check to see if the alternator is charging properly--you may have messed the wiring up when you changed out the battery. It depends on how the alternator regulator is wired, but generally it will only turn on the alternator when it sees a load. If it only sees a load when you throw one of the panel switches then maybe it is not hooked to the battery.

[NCboatrx]

It is also possible that the new battery is absolutely fully charged so the alternator is not providing any output. When you switch on one of the accessories you are creating a load and this gets signaled to the alternator which starts charging and thus the tach starts working.

[jaybeegee]

thanks guys. checked the wiring once again and all looks like it was originally.

I will check whether the fanbelt is tawt - would this make any difference in case it moved slightly?

[NCboatrx]

Hello Jay,

Does your "battery charge" light come on at the panel when the key switch is on?

Please check that the bulb and internal connections are good.

Farron
Beta Marine

[jaybeegee]

Hello! Yes the bulb does come on with the ignition. I also checked the cables and also the fan belt and all look in order. I will try to connect an anolog volt meter to check the current into the tach! other than that no other ideas.