Reply
 
Thread Tools Display Modes
 
Old 03-24-2011, 04:49 AM   #21
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,512
RE: Alternator AC Voltage

use the DC scale

That is because you are reading pulsating DC , not AC.
__________________
Advertisement

FF is offline   Reply With Quote
Old 03-24-2011, 10:55 AM   #22
Guru
 
C lectric's Avatar
 
City: Somewhere
Country: , Canada
Vessel Name: Island Pride
Vessel Model: Palmer sedan 32'
Join Date: Oct 2007
Posts: 1,860
Alternator AC Voltage

"Even though it is an AC tap it has to be measured using the DC scale of your multimeter."

*

*

*Actually it is NOT an AC signal at the Tach terminal and I think that is what is confusing you. It is DC.

Yes, the alternator generates AC initially but that AC goes through a set of diodes or a rectifier which turns that original AC into a pulsing DC. That is the case for both the main power terminal and the tach terminal.

Once it goes through that rectifier, it is no longer AC. In the case of the Tach terminal the rectifier diodes, usually a smaller set separate from the main power set, are set up so only half of the pulses get through so the signal is a lower voltage AND highly pulsing. It is that highly pusing signal that the tach reads and converts to the rpm. The rate of pulses changes as the alternator/engine speed changes.

*So yes you read the Tach terminal with the DC scale.

The alternator guys may be correct. In your case your Dmm worked, in some cases it may not have. Even though DMMs have mostly supplanted analogue guages there are some functions that the older meters can actually do better at DEPENDING on the circuit and how sensitive it is. Also DMMs have gotten much, much better at reading things like this than they were many years ago so maybe their advice is just out of date a bit and also they KNOW the analogue meter will work without guessing about the particulars. Doesn't matter here.


-- Edited by C lectric on Thursday 24th of March 2011 10:57:33 AM
__________________

C lectric is offline   Reply With Quote
Old 03-25-2011, 06:19 AM   #23
Member
 
Join Date: Dec 2010
Posts: 10
RE: Alternator AC Voltage

The alternator rectifies AC to DC internally via a regulator for recharging batteries and also running all of the accessories on your boat.

A *tachometer* feed is normally about 7 v* AC, stays steady.* It is the frequency of that voltage ( in HZ)*that the tach uses.

Carl

*
__________________

Drifter 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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Alternator awpptdt Power Systems 2 12-15-2010 05:50 PM
Voltage spike skipperdude General Discussion 7 11-10-2010 08:24 AM
Electronics Circuitry Protection From Voltage Spikes kstage Electrical and Electronics & Navigation 16 06-02-2010 08:55 AM
Voltage/charging gremlin driving us crazy dwhatty Electrical and Electronics & Navigation 10 06-17-2009 04:18 AM
Starter Cable Sizing, voltage drop Dougcole Power Systems 7 09-27-2008 05:12 AM




All times are GMT -5. The time now is 12:42 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