Reply
 
Thread Tools Display Modes
 
Old 08-25-2013, 06:42 PM   #1
Guru
 
CaptTom's Avatar
 
City: Southern Maine
Country: USA
Vessel Name: Cygnus
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
Posts: 1,373
Old Digital Tachs are Way Off

The upper helm has two tachs that are both obviously way off. The lower helm (original analog tachs) appear correct.

They upper tachs say "Ensign Digital Tachometer / Aqua Meter" by Rule Industries, which apparently no longer makes them, or even has their own web site since being taken over by ITT some years ago.

Replacing them is on my "to do" list, along with a total re-make and re-wire of the upper helm station.

Meanwhile, I'd like to see if I could fiddle with these enough to get a rough approximation of my real RPM.

I'm running twin Perkins 3.544's with the tach signal coming from the alternators.

I don't see any set screw on the back of the tachs, anybody have a manual or diagram for this, or at least a clue as to what to look for?

Thanks!
__________________
Advertisement

CaptTom is offline   Reply With Quote
Old 08-25-2013, 08:09 PM   #2
Guru
 
BruceK's Avatar
 
Join Date: Oct 2011
Posts: 7,564
I have the a problem with an older style tacho, one of 2 on the FB reads 400rpm below its equivalent below. Could you tech guys cover those too when helping CaptTom?
__________________

__________________
BruceK
Island Gypsy 36 Europa "Doriana"
Sydney Australia
BruceK is offline   Reply With Quote
Old 08-26-2013, 10:18 PM   #3
Guru
 
River Cruiser's Avatar
 
City: UMR MM283
Country: US
Vessel Name: Northern Lights II
Vessel Model: Bayliner 3870
Join Date: Jan 2013
Posts: 1,226
CaptTom I'ld replace with Aetna digital tach, I had a set on a previous boat they worked great & guaranteed correct + or - 1 rpm. Check all connections & you may get the faulty tach working correctly, some have adjustment switches on the back so they can be calibrated. To check the accuracy of tachs you can use a photo tach to check them and then adjust them if they can be calibrated. Harbor freight has cheap photo tachs or check eBay.
__________________
Ron on Northern Lights II
I don't like making plans for the day because the word "premeditated" gets thrown around in the courtroom.
River Cruiser is offline   Reply With Quote
Old 08-26-2013, 11:28 PM   #4
TF Site Team
 
Baker's Avatar
 
City: League City, Tx
Country: Texas
Vessel Model: Carver 356
Join Date: Oct 2007
Posts: 5,630
Quote:
Originally Posted by river cruiser View Post
to check the accuracy of tachs you can use a photo tach to check them and then adjust them if they can be calibrated. Harbor freight has cheap photo tachs or check ebay.

^^^^this^^^^
Baker is offline   Reply With Quote
Old 08-27-2013, 08:00 AM   #5
Guru
 
CaptTom's Avatar
 
City: Southern Maine
Country: USA
Vessel Name: Cygnus
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
Posts: 1,373
Thanks guys, I ordered a photo tach (from Amazon) and will probably end up taking the old ones out to examine, maybe there's a set screw somewhere.

I was hoping someone knew of or had these, and maybe had a manual or at least a recollection as to where the adjustment might be.

Since they run off the alternator signal, I assume there must be a way to adjust them or they'd be useless. Not that it would be the first useless thing I've found in this boat.

They look just like this dual tach, but in my case it's two single tachs:
CaptTom is offline   Reply With Quote
Old 08-31-2013, 11:31 AM   #6
Guru
 
CaptTom's Avatar
 
City: Southern Maine
Country: USA
Vessel Name: Cygnus
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
Posts: 1,373
Here's the back of the tach in question:


Anyone know what "Threshold Adjustment" means? I turn one of them too far and the RPMs go down as the throttle goes up. I assume that's the pulse width or minimum voltage, and maybe as I rev up those values get smaller. The other seems inconsistent; the reading goes from 1040 to 1500 just with a little tweak, but then a large change in the other direction does nothing.

I don't have any manual to show what the DIP switches do.

Still looking for a manual, or any experience with similar tachs.

Thank you!!
CaptTom is offline   Reply With Quote
Old 09-01-2013, 10:00 PM   #7
Guru
 
River Cruiser's Avatar
 
City: UMR MM283
Country: US
Vessel Name: Northern Lights II
Vessel Model: Bayliner 3870
Join Date: Jan 2013
Posts: 1,226
The dip switches are set to certain positions depending on the number of cylinders. They should be set correctly if the person who did the original install followed the instructions & no one has messed with them since.
__________________
Ron on Northern Lights II
I don't like making plans for the day because the word "premeditated" gets thrown around in the courtroom.
River Cruiser is offline   Reply With Quote
Old 09-02-2013, 02:24 AM   #8
Guru
 
City: Hotel, CA
Country: Fried
Join Date: Sep 2011
Posts: 8,328
Tom, am attempting to have a motor head friend of mine who is sharper electronically than I to verify this procedure but in the meantime you can try it out and see if it works for you. A little trial and error and you may be able to calibrate it fairly accurately yourself.

Easy Method to Calibrate your tach. - ArcticChat.com - Arctic Cat Forum
__________________
Craig

It's easier to fool people than to convince them that they've been fooled - Mark Twain
CPseudonym is offline   Reply With Quote
Old 09-02-2013, 07:30 AM   #9
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,877
Quote:
Originally Posted by CPseudonym View Post
Tom, am attempting to have a motor head friend of mine who is sharper electronically than I to verify this procedure but in the meantime you can try it out and see if it works for you. A little trial and error and you may be able to calibrate it fairly accurately yourself.

Easy Method to Calibrate your tach. - ArcticChat.com - Arctic Cat Forum
Pretty slick!
psneeld is offline   Reply With Quote
Old 09-02-2013, 07:53 AM   #10
Guru
 
CaptTom's Avatar
 
City: Southern Maine
Country: USA
Vessel Name: Cygnus
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
Posts: 1,373
Very good trick Craig, thanks! But as Ron pointed out, *IF* the installer was competent, the switches should be correct. Big "if" on this boat, which has had at least one clueless PO.

I played with the two threshold adjustment screws. I think under some conditions, the signal gets noisy, which the tachs interpret as multiple sikes. This would double or triple the reading. That is consistent with what I saw. The threshold adjustment apparently helps suppress this.

Tweaking got me to a point where they're within 20 RPM of what the hand-held tach says. They're set to a 20 RPM resolution, so I think I'm on the right track.

All of this is only at the dock. It remains to be seen how noisy the signal gets underway, under load, and with the other electronics operating.
CaptTom is offline   Reply With Quote
Old 09-02-2013, 10:55 AM   #11
Guru
 
LarryM's Avatar
 
City: League City, TX
Country: USA
Vessel Name: Pelago
Vessel Model: Wellcraft 3300 Coastal
Join Date: Aug 2011
Posts: 843
Quote:
Originally Posted by CaptTom View Post
Very good trick Craig, thanks! But as Ron pointed out, *IF* the installer was competent, the switches should be correct. Big "if" on this boat, which has had at least one clueless PO.

I played with the two threshold adjustment screws. I think under some conditions, the signal gets noisy, which the tachs interpret as multiple sikes. This would double or triple the reading. That is consistent with what I saw. The threshold adjustment apparently helps suppress this.

Tweaking got me to a point where they're within 20 RPM of what the hand-held tach says. They're set to a 20 RPM resolution, so I think I'm on the right track.

All of this is only at the dock. It remains to be seen how noisy the signal gets underway, under load, and with the other electronics operating.
Sounds like you are on the right track. Not sure if this is your exact model, but I found these references over my morning coffee.

Here is the troubleshooting section from the Aquaguide 735 manual that describes the trigger threshold adjustments. The switch settings table is scrambled though

Here is a thread that has the switch settings table intact, toward the end/bottom of the thread.

Have fun!

LarryM
m/v Boomarang
LarryM is offline   Reply With Quote
Old 09-02-2013, 03:35 PM   #12
Guru
 
CaptTom's Avatar
 
City: Southern Maine
Country: USA
Vessel Name: Cygnus
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
Posts: 1,373
Thanks Larry!

I actually found those same links since my last post, sorry I didn't get back here and post the links myself. Once I pulled the tachs out of the dash and could google the exact words and abbreviations on the back, those two popped up. Unfortunately they reference a different model. Mostly they have the same settings, but my tachs have TWO adjustment screws, so I'm still sort of winging it trying to figure out what each one does. Maybe the one is threshold and the other is the normal fine adjustment.
__________________

CaptTom is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 02:38 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012