NA alternator in NB = weirdness - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


General Miata Chat A place to talk about anything Miata

Reply
 
 
 
LinkBack Thread Tools
Old 10-20-2015, 03:34 PM   #1
Senior Member
Thread Starter
 
Join Date: Dec 2007
Location: ATL
Posts: 728
Total Cats: 48
Default NA alternator in NB = weirdness

Backstory; Last year I swapped in an NA alternator in my 99 because the POS NB alternator failed and I wanted NA-simplicity. I made the necessary wiring mod and all was well. Since then I've gone through a boat-load of crap with trashing engines (all documented in my build thread) and alternator output was never on the radar.

Current situation; Now that things are working much better (knock on wood) I noticed that in the mornings my lights are semi-dim until I rev the engine beyond 2500 RPM. Looking back through morning startup logs, I can see that BATTV is 11.9(ish)V during warmup and instantly jumps to 14.9V as soon as the revs go beyond 2500. Once that happens, BATTV never drops again until the car is shut off, no matter what the RPMs go to.

Should I worry? Is this normal? If I have a defective alternator (no, it couldn't be!) would it be worthwhile to get a FD alternator with the higher output?

Thoughts?
rwyatt365 is offline   Reply With Quote
Old 10-20-2015, 04:31 PM   #2
Senior Member
iTrader: (1)
 
Join Date: Jun 2006
Location: Sweden
Posts: 1,391
Total Cats: 58
Default

Enables you to have full control at all times:
Mini DC 0 1 30V LED Panel Voltage Meter 3 Digital Display Voltmeter Motorcycle | eBay
The Alt is a little tired, that's all.
NiklasFalk is offline   Reply With Quote
Old 10-20-2015, 10:26 PM   #3
Junior Member
 
Join Date: May 2008
Location: Grants Pass, OR.
Posts: 449
Total Cats: 14
Default

Some early alts. don't kick in until over 2000 rpm on american cars, it has to do with the internal reg., I don't know about mazda but sounds like the same setup.
jmann is offline   Reply With Quote
Old 10-21-2015, 10:52 AM   #4
Elite Member
iTrader: (2)
 
fooger03's Avatar
 
Join Date: Jan 2009
Location: Columbus, OH
Posts: 4,132
Total Cats: 187
Default

sounds like an alternator on the way out. Mine would produce poor voltage at idle, but would be happy while at driving RPMs
fooger03 is offline   Reply With Quote
Old 10-21-2015, 11:04 AM   #5
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,809
Total Cats: 1,780
Default

11.9v is no charge at all.

14.9v is high as ****.


moral of story: get a new alternator.
Braineack is offline   Reply With Quote
Old 10-21-2015, 02:25 PM   #6
Senior Member
Thread Starter
 
Join Date: Dec 2007
Location: ATL
Posts: 728
Total Cats: 48
Default

Dammit!

FD alternator, here I come...
rwyatt365 is offline   Reply With Quote
Old 10-21-2015, 03:19 PM   #7
Junior Member
 
Join Date: May 2008
Location: Grants Pass, OR.
Posts: 449
Total Cats: 14
Default

Read this article: No Field Excite/Warning Light Indicator Input:
The ignition warning light indicator function is omitted with a 1-wire alternator, so your idiot light will not be operational with this setup.

For the 1-wire, self-exciting design, the field windings are not energized via the ignition switch; instead, a special circuit is built into the internal voltage regulator that senses the rotation of the alternator’s rotor. The rotor must turn at sufficient speed to trip the circuit which excites the field windings and starts the charging process. This “cut-in” speed is affected by several things and is typically higher with certain high amperage alternators. Prior to reaching the cut-in speed, the charging system is not activated and the battery will be discharging. However, once the cut-in circuit is tripped, the alternator will charge at all speeds, even very low ones, until the alternator’s rotor comes to a complete stop. At that point, the circuit will shut off and wait for the process to be repeated.

Typically, after starting the engine, the engine must be revved above 1200-2000 RPM to turn-on the 1-wire alternator.
End of article
14.9 is a little high but 14.4 to 14.6 is normal so taking into account a + or - of a few tenths I wouldn't worry about it.
jmann is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
[NC] 7.5lbs per HP build thread / xpost from M.Net albuquerquefx Build Threads 140 08-24-2017 11:39 AM
How to get AC idle up to work on an NB Dav1d MEGAsquirt 25 09-30-2016 12:20 PM
Want to build a 1.8 (check post so title isn't 3 years long) elijahmckay Meet and Greet 5 10-20-2015 01:55 PM
90' NA miata with an NA8 swap, starts then dies. reip General Miata Chat 6 10-20-2015 10:10 AM
Good Start for a 1.8 swap... Elfering Miata parts for sale/trade 0 10-19-2015 04:41 PM


Thread Tools

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 -4. The time now is 10:40 PM.