Beta Marine BD722 Tach kicks in after I enable extractor fan!

[jaybeegee]

Hi all! I have had this problem for about 18 months (my last post on the subject was Dec-11) and have not got any where close to resolving it! I does bother me so I thought I will have another go!

I have a Beta Marine 20Hp Model BD722 (<400 hours) installed with a 5+1 way switch panel as you can see here:

The tach appears dead until I operate one of the switches on the panel!Switch one which is an extractor fan located behind the engine and will kick the tach to live. Based on the sound I think it is then pretty accurate for around 3000 revs during cruising .

Terminals and wiring all ok.

Battery light on ignition lights up and switches off after ignition.

Charger seems to be working as I dont connect to shore supply unless nececssary.

Recently changed fan belt and tension looks ok - same problem!

Any ideas?!
cheers
J.

[mitiempo]

Jay

The tach needs a 12 volt feed that is ignition activated. My guess is that your tach's wire is connected to the extractor fan instead of the ignition switch.

Here's your picture.

[jaybeegee]

thanks Brian - I dont think it is a wiring problem as in idle mode (or low revs) the tach works properly!

Would this behaviour evidence itself if I have the alternator belt too tight? I dont have the tension instrument but looks and feels ok with less than an inch of slack?

thanks

jay

[Rockter]

Jaybee :

It is very unlikely to have anything to do with the alternator belt tension.

[mitiempo]

Originally Posted by jaybeegee

thanks Brian - I dont think it is a wiring problem as in idle mode (or low revs) the tach works properly!

Would this behaviour evidence itself if I have the alternator belt too tight? I dont have the tension instrument but looks and feels ok with less than an inch of slack?

thanks

jay

You didn't originally say the tach works at idle. As it is an electric tach it has to be wiring - possibly corrosion of a connector.

[jaybeegee]

thanks - will do yet another pass on the electrics. thanks for taking the time.

[SaltyHog]

It's likely that the alternator is providing the (RPM) signal to the tach. If your batteries are all charged up and there is no other load on the alternator, the alternator regulator removes the field from the alternator. No field, no tach signal. As soon as you add a load, alternator is back on and the tach then works. Just a theory. Will switching on any other load make the tach operate? (Say, the fresh water pump?)

[jaybeegee]

apologies for the delay to respond to this thread which I missed! no it is just the extractor fan that seems to trigger the tach to mark the revs correctly. So if i switch on the lighting or the fridge I notice the engine rev up very slightly and a corresponding minimal increase in the tach! However with the fan if the tach is marking a wrong amount (say 500rpm when I am a cruising speed of 4knots) it will go from an incorrect reading of to a correct reading of 2500rpm! Not sure if I mentioned this earlier in the thread but this issue happens randomly!

[Stu Jackson]

If/when anything electrical happens randomly, it is 99% of the time the connections, just like Brian said. You should go check them out, because otherwise all the discussion on this topic will not be able to help you. Good luck. Oh, while you're at it, draw a wiring diagram, might help you and us understand things better.

[Opie91]

The tack wire on the BD722 is on the alternator. A similar thing happened to me. Check the connection.