Engine tachometer 'pulsing'

[DaveNTL]

Engine tachometer \'pulsing\'

My tacho has started to pulse - by this I mean it drops to 0, say if I'm running at 2400rpm for 1 second every 9 seconds with clockwork timing.

It isn't a slipping alternator belt.

It doesn't do it all the time, only during the absorption phase of the batteries charging. You can see the DC meter shoot up as the tacho goes off and go back to zero when the tacho is working.

I've read this http://www.amplepower.com/primer/tach/index.html which is all good stuff. I have an Ample Power regulator. Still confused by it though.

Any ideas what I should look for you wise people?

 

[Pincoya]

Re: Engine tachometer \'pulsing\'

Check the field and stator connector on the back of the alternator and additionally any sensor wires attached to your charge controller. From what you describe it is possible that something is a little loose and vibrating, causing the ouput to fluctuate.

Paul

 

[DaveNTL]

Re: Engine tachometer \'pulsing\'

That sort of thing, including a slipping belt were my first thoughts too and I checked that. All tight. Thanks anyway.

 

[ianc1200]

Re: Engine tachometer \'pulsing\'

The Tacho on my Nanni doesn't work when the X Alt alternator controller gets the volts beyond about 13.7, just learned to live with it. Any chance yours similarly doesn't like the higher voltages?

IanC

 

[William_H]

Re: Engine tachometer \'pulsing\'

The tacho is failing in absorption phase which means that battery voltage is high around 15+ volts and the pulses are higher than normal voltage.
You could try getting a 12v supply to the tacho from another source. ie a seperate battery not being charged. If this solves the problem then you need to reduce the 12v supply slightly by feeding it via one or more silicon diodes (cathode with band end to the tacho) Each diode will reduce voltage by .7 volt.
It is conceivable that the volt drop from alternator to the battery via the switch panel means the voltage delivered to the tacho is higher than actually at the battery. If this is the case a heavier cable from ignition switch to battery either in positive or negative or both lines may help. The above is assuming the problem is caused by excessive 12v supply to the tacho to provide power for the electronics.

Another possible source of problem is that the power pulses from the tacho are too large because the alternator is working at high power.
If there is a bypass capacitor in the tacho to smooth out any induced spikes this could be simply building up to a point where all pulses merge into one. To reduce the pulse voltage you need to add a resistor in series with the signal line. Start with 100 ohms then try 1000 ohms then 10000 ohms or even 100000 ohms to see what difference it makes.
Choose a value in between those that will just solve the problem but not stop the tacho working in float phase.
Or you could buy a potentiometer (variable resistor) of about 50000 ohms max and connect in the signal wire centre contact and one end. This will make it easy to determine what value resistor will have the desired effect.
Resistors are very cheap at electronics store. Often for a few squid you can get a bag of 100 of various sizes or pay a few pence for each individually bought. You don't need high power rating 1/4 watt should be ok. You will need a chart or explanation of resistor colour code.
There are a few thoughts if you want to fix the problem. good luck olewill

 

[DaveNTL]

Re: Engine tachometer \'pulsing\'

Thanks very much for that and everyone else who commented. /forums/images/graemlins/smile.gif

Arcmarine - thats what it was. I have hi and low voltage alarms and 'battery full' voltage via a digital controller to the regulator and it was set at 15.75V for high alarm and 14.4V for full. I've now set the high voltage alarm at 15 max / 10.5 min which is recommended for gel batteries and a 'full' voltage of 14.2. Run out with it today and it's stopped pulsing. Much appreciated.