Rev Counter not 'Counting'

[Alan de Enfield]

It was working, now it is not.

Ignition light comes on, and goes out when the engine starts

The alternator is working (output measured with clamp on meter)

Rev counter back-light is lit with ignition on

All wires on the back of the rev-counter 'tight' and wiggling does not make the rev-counter flicker or work.

All wires on the back of the alternator are tight.

 

Any suggestions ?

 

 

[Machpoint005]

Is it a Beta, or a similar engine with a multi-pin connector sitting over the gearbox (or somewhere near)? If that is working loose it may exhibit these symptoms -- I know mine did!

[Tony Brooks]

2 minutes ago, Machpoint005 said:

Is it a Beta, or a similar engine with a multi-pin connector sitting over the gearbox (or somewhere near)? If that is working loose it may exhibit these symptoms -- I know mine did!

 

Agreed - multi-plug no 1 suspect until proven innocent.

[Athy]

I was surprised to learn that, despite its name, this instrument is purely secular.

[Chewbacka]

If you have a voltmeter, set it to ac and check the voltage on the signal wire going into the Rev counter, and again on the back of the alternator.  Should be the same

[WotEver]

9 minutes ago, Chewbacka said:

If you have a voltmeter, set it to ac and check the voltage on the signal wire going into the Rev counter, and again on the back of the alternator.  Should be the same

And it should be in the region of 7 - 9V. 

[Alan de Enfield]

39 minutes ago, Machpoint005 said:

Is it a Beta, or a similar engine with a multi-pin connector sitting over the gearbox (or somewhere near)? If that is working loose it may exhibit these symptoms -- I know mine did!

It is a marinized 6.2 litre, 6 cylinder Ford Cargo truck engine.

(one of a pair - the other one is still working perfectly)

25 minutes ago, Chewbacka said:

If you have a voltmeter, set it to ac and check the voltage on the signal wire going into the Rev counter, and again on the back of the alternator.  Should be the same

 

I'll give it a try.

[Alan de Enfield]

Ok - test with engine running or just ignition turned on ?

 

Back of Rev Counter - which wire would you suggest is the signal wire ?

(with the ignition turned on all terminals are live - even the push-on blade)

 

 

[Alan de Enfield]

Found the sensor wire (Doh - its marked on the rev counter)

 

The three studs are :

Top right = battery

Centre = GND

Bottom left = Sensor

The blade = Live to back-light

 

With engine running there is 6.98 volts DC / 8.6 volts AC between Sensor and 'GND'

 

With engine OFF the rev counter does not drop back to Zero it stays were it is at around 500 RPM

 

Is it 'just' a stuck rev-counter ?

Edited August 21, 2018 by Alan de Enfield

[Chewbacka]

On my rev counter if I cut the power as the engine stops the needle stays high, if the power is left on for a couple of seconds after the engine has stopped the pointer drives itself back to zero, could it be that?

 

added - the sensor output from the alternator is half wave so a spikey dc, so on dc you will get a reading, likewise a reading on ac as well. So looks like signal into the Rev counter is ok.

Edited August 21, 2018 by Chewbacka

[WotEver]

3 hours ago, Alan de Enfield said:

With engine running there is 6.98 volts DC / 8.6 volts AC between Sensor and 'GND'

 

With engine OFF the rev counter does not drop back to Zero it stays were it is at around 500 RPM

 

Is it 'just' a stuck rev-counter ?

Sounds like it. You have two rev counters, right?  Can you jury rig the sensor feed from A to B and vice versa?  That’ll prove or otherwise a faulty gauge. 

[Alan de Enfield]

5 minutes ago, Chewbacka said:

On my rev counter if I cut the power as the engine stops the needle stays high, if the power is left on for a couple of seconds after the engine has stopped the pointer drives itself back to zero, could it be that?

Thanks for the suggestion, but I have a 'pull to stop knob', so there is always a few seconds delay between stopping and cutting power.

I might have a play swapping over the tacho's (from the other engine) and see if it works or not.

2 minutes ago, WotEver said:

Sounds like it. You have two rev counters, right?  Can you jury rig the sensor feed from A to B and vice versa?  That’ll prove or otherwise a faulty gauge. 

Great minds :

 

I actually have 4 Tacho's

2 at the outside 'top' helm station and 2 at the downstairs (inside) helm.

Edited August 21, 2018 by Alan de Enfield

[WotEver]

2 minutes ago, Alan de Enfield said:

Thanks for the suggestion, but I have a 'pull to stop knob', so there is always a few seconds delay between stopping and cutting power.

I might have a play swapping over the tacho's (from the other engine) and see if it works or not.

I actually have 4 Tacho's

2 at the outside 'top' helm station and 2 at the downstairs (inside) helm.

Well, the two that are adjacent to each other sound favourite

[Alan de Enfield]

1 minute ago, WotEver said:

Well, the two that are adjacent to each other sound favourite

Do you reckon just 'hotwire' the sensor cable or would the GND need moving as well ?
Both batteries (1 for each engine) are on a common ground.

[Chewbacka]

The grounds should all join together and all be at ground potential so should be fine.  The pos feeds if the alternator outputs are joined together should be ok, but if they are separate for example one connected to a start battery and the other to domestic batteries and there is no link eg volt sensitive relay, then the positive feed will need swapping as well.

 

added - if you have 240v ac then there should be only a single ground which all circuits eventually connect to, but if it is an old boat not following rcd regs then there is a small chance the systems are floating, but if there is no negative cable on the alternator or starter motor and they are earthed via the engine block then you will have a common earth.  Sorry i’m rambling again........

Edited August 21, 2018 by Chewbacka

[Alan de Enfield]

1 minute ago, Chewbacka said:

The grounds should all join together and all be at ground potential so should be fine.  The pos feeds if the alternator outputs are joined together should be ok, but if they are separate for example one connected to a start battery and the other to domestic batteries and there is no link eg volt sensitive relay, then the positive feed will need swapping as well.

Both alternators go thru' split charge units, each with an output to its own starter battery, via individual master switches, the other side outputs each go to a 'master switch for the leisure batteries'.

The batteries are then 'linked' across the 'battery side' of the leisure master switches.

 

So as long as both leisure master switches are 'on' the alternators are linked together.

 

The far left and far right of the master switches are now linked (not shown on sketch)

 

 

[WotEver]

26 minutes ago, Alan de Enfield said:

Do you reckon just 'hotwire' the sensor cable or would the GND need moving as well ?
Both batteries (1 for each engine) are on a common ground.

Just the sensor, assuming that both gauges have 12V power. As per previous posts the -ve will be common. 

[Alan de Enfield]

3 minutes ago, WotEver said:

Just the sensor, assuming that both gauges have 12V power. As per previous posts the -ve will be common. 

Thanks - a job for morning then.

[blackrose]

Slightly off topic, but is there any way to calibrate a rev counter or just check it's displaying something approximating reality? I don't have a strobe but I thought about using a bicycle speedo. 

[Scholar Gypsy]

14 minutes ago, blackrose said:

Slightly off topic, but is there any way to calibrate a rev counter or just check it's displaying something approximating reality? I don't have a strobe but I thought about using a bicycle speedo. 

A visiting engineer got a pretty good result using an app on an Android phone called GString. It listens to the bangs made by the exhaust and works out what musical note you are playing.

 

So for example normal cruising speed gave a frequency of 50 Hertz, that is 3,000 bangs a minute (50 x 60), which is 1500 rpm (four stroke 4 cylinder engine, so each cylinder goes bang every two revolutions). 

 

RPM = frequency x 60 x 2 / (no of cylinders)

[Alan de Enfield]

7 minutes ago, Scholar Gypsy said:

It listens to the bangs made by the exhaust and works out what musical note you are playing.

Was it waterproof - my exhaust is a couple of feet below the water line.

 

Maybe it would just quote "Handel's Water Music"

 

Glug Glub Glug Burble......

[WotEver]

 n-Track Tuner is a free iPhone app that can do this. 

[rusty69]

I just downloaded an rpm meter app. Works with proximity sensor. Now what to measure. Where's that ecofan gone? 

[Scholar Gypsy]

16 minutes ago, Alan de Enfield said:

Was it waterproof - my exhaust is a couple of feet below the water line.

 

Maybe it would just quote "Handel's Water Music"

 

Glug Glub Glug Burble......

I suspect would work just listening in the engine space..

[Horace42]

Personally, I think your fan belt might be slipping.

Tighten it and see what happens.