Island Time 1,235 Posted May 29, 2013 Share Posted May 29, 2013 Todays technical issue. Engine is a Volvo Penta 2003T. Fitted with a Balmar 6 series Alt. The Tacho works, but reads high, and inaccurately. Does not seem to be a stable % error. Actual Revs Indicated Revs 1150 1500 1770 2200 1970 2500 2300 3000 2700 3500 2900 3750 Actual revs read with an optical Tacho.... Anyone know how these Tachos work? I understand its a pulse from the Alt. Is there any way to adjust the Tacho? Link to post Share on other sites
Jon 360 Posted May 29, 2013 Share Posted May 29, 2013 Some tachometers have dip switches on the back which you set Is this a new setup or old that's started playing up? If old could be faulty wiring between alt and tacho ( eg, dry joint, loose or broken wire) If new should have setup instructions or just adjust till correct. Link to post Share on other sites
Island Time 1,235 Posted May 29, 2013 Author Share Posted May 29, 2013 new? um, no. Original Tach, 1988!! Probably been reading low for ages. I just got an optical tachometer to check it with as the prop performance did not seem right. It wasn't as the revs were nowhere near what was indicated! I had thought the governor was faulty.... Link to post Share on other sites
Jon 360 Posted May 29, 2013 Share Posted May 29, 2013 To check governor see what the output voltage is It should be 14.8 volts near enough but maybe higher if you've got a smart thingy Then will drop off as your batteries fill up. Its possible that it was never setup correctly ? I setup one a few years back and we didn't have the instructions so just tried all the options until it matched up with the optical one, near enough anyway Link to post Share on other sites
Island Time 1,235 Posted May 29, 2013 Author Share Posted May 29, 2013 I guess you mean the Alternator voltage. Governor is Mechanical on this engine. Alt output (at alt, there is a diode splitter and smartcharging, 3 stage) is up to 15.3 v max, depending on charge state. This is reduced by the diode splitter to about 14.8 at batt terminals. Alternator and charging are working fine. Link to post Share on other sites
Jon 360 Posted May 29, 2013 Share Posted May 29, 2013 I've got your spare tacho in my shed and also your spare engine ( ideal for parts) Will have a look at the back of the tacho this arvo to see if its adjustable and report back Another thought Belt slip will put your readings out also Link to post Share on other sites
Island Time 1,235 Posted May 29, 2013 Author Share Posted May 29, 2013 Cheers Danaide, thanks for your help. Belt slip should make the Tacho read LOW, not high. I looked at the back of the Tacho, nothing obvious - but I have not removed the case (yet)! Matt Link to post Share on other sites
banaari 27 Posted May 29, 2013 Share Posted May 29, 2013 Pulley sizing issues? i.e. if alternator pulley is/was downsized, alternator will be turning faster and tacho reading higher. Link to post Share on other sites
Island Time 1,235 Posted May 29, 2013 Author Share Posted May 29, 2013 Could be (likely) but with what is there the charging works well. I'd rather not slow the alternator, but adjust the tacho! Link to post Share on other sites
banaari 27 Posted May 29, 2013 Share Posted May 29, 2013 Could be (likely) but with what is there the charging works well. I'd rather not slow the alternator, but adjust the tacho! Absolutely, but it might be the smoking gun that changed since the original install (if it ever was calibrated correctly). Link to post Share on other sites
Jon 360 Posted May 29, 2013 Share Posted May 29, 2013 Had a look at my old one and if its genuine Volvo then its not adjustable, it's the generic type that you have to setup. Maybe Banaari is onto it and its been wrong for awhile ? Has it always pulled about the same revs on the tacho ? Link to post Share on other sites
Island Time 1,235 Posted May 29, 2013 Author Share Posted May 29, 2013 ok, for anyone interested, I'll answer my own question. I went down to the boat and took the Tacho off. It is a VDO diesel Tach. It is not supposed to be serviceable, as the front (only access) is crimped on. I used a small screwdriver to undo the crimp, and took it apart. The Front comes off by twisting. Take out the O Ring, the plastic case and the 4 screws off the back, and the guts come out. There is a control pot inside that does calibration. Easy to adjust with a small (2mm) screwdriver. Did that, now tacho is with 30rpm right across the range!! All Good!! Just in case anyone finds themselves in the same situation! Thanks for your suggestions everyone, it helps to clarify one's thinking! Matt Link to post Share on other sites
Jon 360 Posted May 29, 2013 Share Posted May 29, 2013 That's great I thought it had that VDO feel about it Had the same issue on my last yacht Link to post Share on other sites
wheels 543 Posted May 29, 2013 Share Posted May 29, 2013 Sorry I came across this post just now. I would have told you that all these Alt drive tachos have a Pot for setting the correct RPM. I am surprised there is not a small hole in the back for access to that pot though. Link to post Share on other sites
Island Time 1,235 Posted May 29, 2013 Author Share Posted May 29, 2013 No prob Wheels, this is not a paid service!! There has been a feeble attempt to waterproof it, at least from the front. I guess a hole would compromise that, but still should be one! Link to post Share on other sites
wheels 543 Posted May 29, 2013 Share Posted May 29, 2013 Some have a little open hole and some can have a little rubber plug in the hole. Glad you sorted it. Link to post Share on other sites
John B 106 Posted May 29, 2013 Share Posted May 29, 2013 Robinson instruments in Onehunga are good guys. You could give em a call.Clever people. sorry. missed page 2, looks like you have it all sorted. Link to post Share on other sites
Clive 13 Posted May 29, 2013 Share Posted May 29, 2013 I think you'll find this is a tacho issue. I had the same problem years ago and had to replace them (1989 vintage). Went down the same route, belts, alternator wiring etc... New ones fitted and all was fixed. Link to post Share on other sites
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