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Tachometer issue, erratic. Volvo Penta and VDO.

A_8

Member
Joined
28 Aug 2005
Messages
660
Location
Gothenburg
This is starting to get really annoying. I've had the issue with the starboard tachometer showing erratic readings for many years without really addressing it. Now decided to fix it for good and swapped tachometers, then replaced the cabling from the generator to the tacho, I then swapped the generators but the issue stays with the Starboard engine and tacho.....
It's usually ok for the first 30 mins or so and tend to get worse the longer we run, the starboard generator charges the starter and bow prop battery only.

I've run out of ideas and actions to correct it, any thoughts or insights out there that could help?

The engine is a KAD43 with a std Valeo 60 amp generator, I think its the same as most of the 30 and 40 series pentas, the tachometer is VDO.

I took a video of the Tacho and put it on youtube.

 

volvopaul

Well-known member
Joined
1 Apr 2007
Messages
8,021
Location
midlands
The amount the needle drops looks like either a supply problem either - or + I doubt it's to signal wire, chek the blue and red wire which is ignition supply fom the ignition switch to the tacho.
 

Elza_Skip

New member
Joined
4 Oct 2004
Messages
566
Location
Bristol, England
Hi, Paul is the expert here but I had erratic performance from the Volvo tachos on my Volvo TAMD41bs. I had them repaired/serviced by Speed Cables, however I was still experiencing problems . What it came down to was interference on the signal line, possibly from worn pick ups on the alternator. After returning the worst one to speedy cables and them not finding a fault with the unit they supplied a filter wired into the supply line that finally fixed it.

Having said all that, I would go with Paul's view and start with the supply- if you can wire up a meter to the supply line and see if that is stable it might eliminate it or prove it
 

A_8

Member
Joined
28 Aug 2005
Messages
660
Location
Gothenburg
Thanks, I will start by looking at the supply. How is this switched on and off, is it directly in the ignition or via a relay?
 

A_8

Member
Joined
28 Aug 2005
Messages
660
Location
Gothenburg
I have spent a few more hours making sure the 12 volt supply is stable and it is but there is no change. I did however find a consistent behaviour In that if I draw a lot of current from the battery and thus the generator the problem stopped and stayed away until the battery was fully charged, it then started again.
The battery set up on this engine is different to the other engine by using a diode splitter connected to the starter and bow prop battery.
It seems something happens to the tacho pulse with the generator and diode splitter combo when the generator don't have to deliver any or minimal current. I tried filtering the generator output before the splitter using a large capacitor but it did not make a difference.
Does this trigger any new insights or ideas from anyone?
I assume its the diode splitter that I should look at replacing, the generator was fine on the other engine.
 

A_8

Member
Joined
28 Aug 2005
Messages
660
Location
Gothenburg
I bypassed the diode-splitter but it did not help, still the same and if I run the anchor winch connected to this battery and generator the issue disappears until its fully charged again.
 

volvopaul

Well-known member
Joined
1 Apr 2007
Messages
8,021
Location
midlands
Try a test with the supercharger disconnected at its plug you may find its a back feed from the clutch into the loom indicating the inline diode is faulty .
 

kashurst

Well-known member
Joined
10 Oct 2003
Messages
6,894
Location
west yorkshire
it sounds like the alternator is turning itself off once there is no demand, try connecting a 10w car light bulb to the output of the alternator so that there is always a low demand on the alternator.
 
Last edited:

A_8

Member
Joined
28 Aug 2005
Messages
660
Location
Gothenburg
I'll try the supercharger plug disconnect but looking at the schematics the rpm trigger for the clutch on the 32/42/43 is a separate circuit. I've also thought about putting a load on the generator to fix it BUT I should not have this problem and as I do there should be a specific reason for it which can be fixed.
I've decided to upgrade to electronic controls, these use the signal from the generators w terminal to rpm sync the engines which won't work if the signal is messed up as soon as the starter battery is fully charged.
 

A_8

Member
Joined
28 Aug 2005
Messages
660
Location
Gothenburg
I just went through my old threads and considering all the other reports on this issue I've seen on here I wanted to report back on this. I changed the alternator (getting many more amps) as well as the tacho's to the new VDO series, problem gone.
 

SFHB

New member
Joined
19 Sep 2012
Messages
4
Hi folk

Picked up on this thread as I've a similar problem ... I can set say 3100 RPM (Volvo Penta KAD43) and the needle with indicate ok, then it will drop to zero for a few seconds then either go back to 3100 or another figure.

If I move the throttle to then say 3500 RPM it will indicate the rise in RPM then begin the fault of dropping to zero or another random figure.

Any obvious thoughts please .... New Tacho (Silly money) ... Recon/overhauled Alternator (Bearable costs) ... or just wiring.

Any help gratefully received.

John
Lowestoft / St.Helier
 
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