Alternator / Tachometer

[Graham]

Has anybody got any thoughts on why my tachometer displays 1000rpm more on battery 2 than battery 1.  I also have some tacho-dancing on both Batt 1 and Batt 2 but more pronounced on Batt 2.  Have done VDC test on 'P' terminal (the one wired to the alternator) and I am getting higher readings on Batt 2.  Have done all the usual checks re wiring and wired tacho direct from battery and alternator.  The only thing I can think of is battery 2 is starting to deteriorate - it holds slightly less charge 12.8 VDC v 13.0 VDC when engine shut down.  Batteries are Varta LFD180 dual purpose and only two years old.

Any thoughts most welcome.

[Stu Jackson]

Graham,

Am I correct in guessing that you have two equally sized batteries in a dual bank setup?  What ah ratings are each of your Varta LFD180s?  [We're unfamiliar with those on this side of the pond. ]

[Graham]

Hello Stu,

Got rid of the battery 2 problem creating higher tacho revs than battery 1.  Charged-up over-night.  Silly error but I thought battery 2 was fully charged.

You are correct about my batteries - both exactly the same 180AH sealed.

The problem I am left with is bouncy tacho and when I switch on ancillaries such as fridge, blower (I know you have views on the need for a blower), and navigation pod, the tacho revs increase notwithstanding engine revs remain unchanged.

Splashed-out on new alternator, new tacho (made by KUS - they sell in the US) and checked wiring by having tested individually with test cable hooked-up direct:
1) tacho to alternator,
2) tacho to negative battery, and
3) tacho to positive battery.

Still have the problem.

Charge at batteries is good at 14.5 VDC on both batteries.  Checked for stray VAC at alternator - less than 0.05 VAC.

Am now checking all wiring through to manual to see whether at some stage I have wired-up something incorrectly - current focus is on key switch and alarm buzzer - both of which I replaced.

Hope you are not suffering too much with the heat-wave I see North America is having.

Kind regards

[Stu Jackson]

Charge at batteries is good at 14.5 VDC on both batteries. 

Are you seeing this tachometer jumping around only when the batteries are full?

[Ron Hill]

Graham : Sometime the tach needle wiggles when the engine is running and the batteries are full.  Just turn ON the blower switch and the needle will go to steady  -  that's normal !!  Even a small load smooths the tach needle to steady.   

A thought

[Graham]

Hello Stu,

No, the tachometer was jumping around prior to me topping-up batteries.  As I say I have tried everything I know and I have still got the problem.  Guess, I'm just going to have to live with it.

Thanks,

Graham

[Ron Hill]

Graham :  I have a Balmar alternator and Balmar has a propriety plug of their own that connects the tach wire into the alternator. 

Anytime I have Tach problems it always seems to be in that plug.  I've had to redo that wire connection a few times!!

A thought