logo
Welcome Guest! To enable all features please Login or Register.

Notification

Icon
Error
Tachometers
Options View
Previous Topic Next Topic
trontek
#1 Posted : Sunday, June 12, 2011 12:40:07 PM(UTC)
trontek

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 10/17/2008(UTC)
Posts: 340
Points: 265

Thanks: 2 times
Was thanked: 3 time(s) in 3 post(s)
Will someone 'splain to me why almost all of the tackometers I see have the needle up to about 1000rpm before the ign switch is turned on - when they drop to 0rpm....? Aren't they just a voltmeter?Brick wall
Jim

Back to top
Sponsor
Please Register : To weed out spammers, new members may not post until approved. An email is usually sent after approval. This forum is for Marinette Owners and other aluminum boat boaters who wish to share boating information. Aluminum Roamer owners are also welcome. (Do not post content you do not have the right to post and mass (robots) posters are unwelcome. We also have a marine electronics page and lots of Chrysler Engine info. State by what permission you copy content and give credit properly.) The site is now fixed with some more Chrysler information. We have space for pictures on the new location. Use shinkpic to autochange size http://www.onthegosoft.com/sp_download.htm

Great Sites - http://www.marinette.com Marinette Company

http://web.me.com/dougmrose/Doug_Roses_Website/Welcome.html

http://fastjeff.tripod.com/ Repair Tricks and Techniques for Marinettes

http://www.greatlakesmarinetteclub.com/

PLEASE post in the appropriate folder. Please, do not post your actual email address in publicly readable websites. The first rule is be a class act.
Back to top  
dougrose
#2 Posted : Sunday, June 12, 2011 4:40:03 PM(UTC)
dougrose

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member, Administration, Admin
Joined: 12/7/2007(UTC)
Posts: 1,332
Points: 1,746

Was thanked: 25 time(s) in 21 post(s)
Actually, electronic tachometers count the number of pulses per second and then translate that into volts, so they are measuring pulses, not volts. Most are pretty unaffected by battery voltage.

The circuit apparently puts out some voltage when it has no pulses to count - mine do that. When the engine starts it settles down and shows you the pulse rate.


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
Back to top
tundrarules
#4 Posted : Sunday, June 12, 2011 5:08:26 PM(UTC)
tundrarules

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 11/11/2009(UTC)
Posts: 411
Points: 413

Thanks: 22 times
Was thanked: 8 time(s) in 7 post(s)
AC dies,DC lies ...that's the old saying...at least I think that's correct. What that means is, a DC powered indicator needle will stick at the position it was in when power is removed from it.

Liar Someone back me up



.
1985 Marinette 29 Sedan bridge
Twin 318s, 660 hours
New Edelbrock 1409 carbs (working like a charm)
Original Electronic Ignition, Blaster 2 coils, 90 deg plug wire universal kit cut to fit
Raw water system
Freshwater always
Located Pickwick Lake, TN,MS,AL

RETRO BOATS ARE COOL

If the guys on this forum take their time to help you, have the courtesy to update your thread with the resolution.
Back to top
trontek
#5 Posted : Monday, June 13, 2011 11:31:31 AM(UTC)
trontek

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 10/17/2008(UTC)
Posts: 340
Points: 265

Thanks: 2 times
Was thanked: 3 time(s) in 3 post(s)
Originally Posted by: tundrarules Go to Quoted Post
AC dies,DC lies ...that's the old saying...at least I think that's correct. What that means is, a DC powered indicator needle will stick at the position it was in when power is removed from it.

Liar Someone back me up



.


Is it something to do with residual magnetism left from when pwr was last applied?? Why is it almost always 1000rpm?
Jim

Back to top
fastjeff
#6 Posted : Monday, June 13, 2011 1:16:18 PM(UTC)
fastjeff

Rank: Administration

Medals: aluminum star: For Marinette Owners Everywhere above the call of duty

Groups: Admin2, Admin2, Admin, Administration, Member
Joined: 12/5/2007(UTC)
Posts: 3,133
Points: 5,732

Was thanked: 34 time(s) in 30 post(s)
Let sleeping dogs lie!

Actually, the "Admiral" made that same comment last time we were at the boat. Thought something was wrong.

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
Back to top
jsimanella
#7 Posted : Monday, June 13, 2011 7:54:21 PM(UTC)
jsimanella

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/5/2007(UTC)
Posts: 367
Points: 637

Thanks: 12 times
Was thanked: 1 time(s) in 1 post(s)
Easy one - they stay where they were (usually idle), when you turn the ignition off.
If it bothers you, turn the key back on, for a second - they'll drop right to zero.
--
1987 32 Sedan Bridge
Twin 360s, Rebuilt 2006
Modified/Original Electronic Ignition
Raw Water Cooled
Catawba Island, Ohio
Back to top
dougrose
#8 Posted : Monday, June 13, 2011 9:38:40 PM(UTC)
dougrose

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member, Administration, Admin
Joined: 12/7/2007(UTC)
Posts: 1,332
Points: 1,746

Was thanked: 25 time(s) in 21 post(s)
Automotive gauges do not have a spring return on the needle the way lab instruments do: the "spring" is an electromagnet that pulls against the needle. I have written about this at http://web.me.com/dougmr...ses_Website/Gauges.html
When the power is removed, neither the indicating solenoid nor the return solenoid are pulling, so the needle stays where it is or flops around. A few gauges will return left by design, but most don't.


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
Back to top
trontek
#10 Posted : Tuesday, June 14, 2011 12:03:54 PM(UTC)
trontek

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 10/17/2008(UTC)
Posts: 340
Points: 265

Thanks: 2 times
Was thanked: 3 time(s) in 3 post(s)
Thanks to all who answered. Thank you doug for the link. Schematics do it for me....
Jim

Back to top
trontek
#3 Posted : Saturday, June 18, 2011 5:00:32 PM(UTC)
trontek

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 10/17/2008(UTC)
Posts: 340
Points: 265

Thanks: 2 times
Was thanked: 3 time(s) in 3 post(s)
Originally Posted by: dougrose Go to Quoted Post
Actually, electronic tachometers count the number of pulses per second and then translate that into volts, so they are measuring pulses, not volts. Most are pretty unaffected by battery voltage.

The circuit apparently puts out some voltage when it has no pulses to count - mine do that. When the engine starts it settles down and shows you the pulse rate.


The old tachs (and I think the new ones also) are hooked up to the neg side of the ign coil(which is the top side of the points) and the meter showed the average voltage across the moving points. I think the new ones show the average voltage across the on-off transistor in the ign package. Appears to be a volt meter to me. Lemme know fellers....There most likely are some sophisticated tachs now that DO count pulses.Whistle
Jim

Back to top
trontek
#9 Posted : Saturday, June 18, 2011 5:34:00 PM(UTC)
trontek

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 10/17/2008(UTC)
Posts: 340
Points: 265

Thanks: 2 times
Was thanked: 3 time(s) in 3 post(s)
Originally Posted by: dougrose Go to Quoted Post
A few gauges will return left by design, but most don't.


Is this because of the bitty "hair spring" associated with the needle??Think
Jim

Back to top
dougrose
#11 Posted : Sunday, June 19, 2011 6:27:11 AM(UTC)
dougrose

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member, Administration, Admin
Joined: 12/7/2007(UTC)
Posts: 1,332
Points: 1,746

Was thanked: 25 time(s) in 21 post(s)
If you put a voltmeter across the points, what you will actually measure is dwell: if the points are open half the time, then the reading will be half of the ignition voltage. If the points are open one-third of the time, you will read one third of the ignition voltage, and so on. Tachs use a capacitor in series between the points and the meter, and a diode across the meter. When the points open, the voltage rises, and the capacitor "dumps" its charge through the meter. When the points close, the diode refills the capacitor. The more rpm, the more of these pulses from the capacitor and the higher the tachometer reading.

You are lucky to have points. My diesels have tachs running off of the alternators. This is a pain to calibrate, and if the belt slips the reading is too low - not a good thing.

Most automotive gauges will stay where they are when the ignition is turned off. But some return all the way left (below zero). I assume that these have a small spring, or the armature is weighted so that gravity brings them back. Perhaps this is so they will look "off" when there is no ignition power.


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
Back to top
Barkleydave
#12 Posted : Sunday, June 19, 2011 9:26:03 AM(UTC)
Barkleydave

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/4/2007(UTC)
Posts: 460
Points: -618

Thanks: 3 times
Was thanked: 7 time(s) in 6 post(s)
Pretty high tech for the Ole boy.

Problem with most our old tachs is they are just old! Mine are either right on or jump all over the place while running.
Lower helm was ok until this year and now they are running 1K+ on the stb. When the lowers act up it effects the uppers also.

I do not pay much attention to them anymore. My ear and experience with the boat I know where they are running. Would like to replace but on the list. Like the digitals but expensive!

Now my classic car MG runs off the transmission with cable. Very accurate but.. cables fail and other problems.

dave
None
Back to top
fastjeff
#14 Posted : Monday, June 20, 2011 5:40:02 AM(UTC)
fastjeff

Rank: Administration

Medals: aluminum star: For Marinette Owners Everywhere above the call of duty

Groups: Admin2, Admin2, Admin, Administration, Member
Joined: 12/5/2007(UTC)
Posts: 3,133
Points: 5,732

Was thanked: 34 time(s) in 30 post(s)
..."Now my classic car MG runs off the transmission with cable. Very accurate but.. cables fail and other problems."

Especially if it has Lucas electrics (the "prince of darkness"). Wanna know why the Brits drink warm beer? 'Cause Lucas makes their refrigerators!

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
Back to top
Rick100
#13 Posted : Monday, June 20, 2011 9:17:23 AM(UTC)
Rick100

Rank: Dedicated Tin Star

Groups: Member
Joined: 5/25/2009(UTC)
Posts: 75
Points: 231


Problem with most our old tachs is they are just old! Mine are either right on or jump all over the place while running.
Lower helm was ok until this year and now they are running 1K+ on the stb. When the lowers act up it effects the uppers also.

The fix for an electric tach that jumps all over the place or reads to high or low is to exercise the switch on the back that says 4-6-8 or a-b-c. Just take a small screw driver and work the switch about ten times and the problem usually goes away. Slight corrosion on the switch contacts causes this condition. Do not Spray any contact cleaner into the tach housing. Now there can of course be problems in the ignition system that will cause a slightly similar problem but try the tach switch first. Rick
When I die I hope my wife sells my stuff for more than I told her I paid for it.
Back to top
Users browsing this topic
guest
Forum Jump  
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.

Powered by YAF 1.9.5.5 | YAF © 2003-2011, Yet Another Forum.NET
This page was generated in 0.504 seconds.