pulling power for my MS1 off of the back of the alternator. good or bad? - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


MEGAsquirt A place to collectively sort out this megasquirt gizmo

Reply
 
 
 
LinkBack Thread Tools
Old 05-02-2014, 02:16 AM   #1
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: sacramento ,ca
Posts: 402
Total Cats: 46
Default pulling power for my MS1 off of the back of the alternator. good or bad?

not a miata but i trust the feed back on here more than the other forums im on.

i need constant battery power to my passenger side floor/firewall area and was thinking of tapping into the alternator charge wire that runs directly from the battery to the back of the alternator. the wire is going to go to a fuse block that will be powering my MS1, innovative LC-1, and 1 or 2 other little things. im trying not to run a wire all the way to the battery.
fastivab6tg25mr is offline   Reply With Quote
Old 05-02-2014, 08:52 AM   #2
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,833
Total Cats: 1,786
Default

you want to wire your megasquirt to constant battery?
Braineack is offline   Reply With Quote
Old 05-02-2014, 10:11 AM   #3
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,174
Total Cats: 2,575
Default

he will likely have a switch so its not powered on 24/7
18psi is offline   Reply With Quote
Old 05-02-2014, 11:36 AM   #4
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: sacramento ,ca
Posts: 402
Total Cats: 46
Default

the power will be controlled by a relay and activated by a hidden button. but my lc1 and my knocklight/ shift light need a 12v constant. im trying to keep everything in its own "standalone" harness... just in case i pull this car in half too i can swap it to another cheap craigslist find lol
fastivab6tg25mr is offline   Reply With Quote
Old 05-02-2014, 11:48 AM   #5
Boost Pope
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Chicago (Over two miles from Wrigley Field. Fuck the Cubs. Fuck them in their smarmy goat-hole.)
Posts: 26,317
Total Cats: 1,914
Default

Quote:
Originally Posted by fastivab6tg25mr View Post
but my lc1 and my knocklight/ shift light need a 12v constant.
I'm wondering if I've misinterpreted this. Do you really intend to supply the LC1 with a constant 12v supply all the time, whether the car is being operated or not?

There seems to be a lot of superstition surrounding the LC1, particularly with regard to its apparent distaste for marginal power supplies, such as the ~9-10v supply typically available while the starter is operating. The most reliable workaround I've seen for this is simply to supply it via a circuit which is on the ACC side of the keyswitch, or via a relay (from the battery or alternator) whose coil is supplied by the ACC circuit.
Joe Perez is offline   Reply With Quote
Old 05-02-2014, 12:57 PM   #6
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: sacramento ,ca
Posts: 402
Total Cats: 46
Default

The power to all devices that require switched 12v will be controled by a relay. There will also be a constant 12v at the junction block for the devices that require a 12v to retain memory
fastivab6tg25mr is offline   Reply With Quote
Old 05-02-2014, 01:30 PM   #7
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,833
Total Cats: 1,786
Default

that's limited to your radio--pretty much.
Braineack is offline   Reply With Quote
Old 05-02-2014, 01:45 PM   #8
Boost Pope
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Chicago (Over two miles from Wrigley Field. Fuck the Cubs. Fuck them in their smarmy goat-hole.)
Posts: 26,317
Total Cats: 1,914
Default

Quote:
Originally Posted by Braineack View Post
that's limited to your radio--pretty much.
My thought as well. A typical (stock) vehicle has unswitched +12 going to the radio (to store the presets) and the ECU (to store fault codes), and that's it.

A car with a non-stock ECU shouldn't need unswitched +12 for anything other than the radio. Definitely not for accessories like a wideband O2 sensor, shift light, etc.

It makes me wonder if I'm not vastly misinterpreting the OP here.



EDIT: I am obviously ignoring things like power locks, lights, horn, etc., as the OP was specifically referring to things that need to retain settings in memory.

Last edited by Joe Perez; 05-02-2014 at 02:04 PM.
Joe Perez is offline   Reply With Quote
Old 05-02-2014, 01:56 PM   #9
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,174
Total Cats: 2,575
Default

JT you should link them to your build thread.

I think it would clear up quite a bit
18psi is offline   Reply With Quote
Old 05-02-2014, 02:15 PM   #10
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,833
Total Cats: 1,786
Default

wont help us understand why he wants to constantly drain batteries.
Braineack is offline   Reply With Quote
Old 05-02-2014, 04:54 PM   #11
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: sacramento ,ca
Posts: 402
Total Cats: 46
Default

The power I'm talking about getting from the back of the alt will be going through a relay. My concern was voltage fluctuation at the rear of the alt that would mess with the megasquirt.

Edit:
i was thinking there was a mem constant power to the lc1 i guess there is not.
fastivab6tg25mr is offline   Reply With Quote
Old 05-02-2014, 05:08 PM   #12
Boost Pope
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Chicago (Over two miles from Wrigley Field. Fuck the Cubs. Fuck them in their smarmy goat-hole.)
Posts: 26,317
Total Cats: 1,914
Default

Quote:
Originally Posted by fastivab6tg25mr View Post
The power I'm talking about getting from the back of the alt will be going through a relay. My concern was voltage fluctuation at the rear of the alt that would mess with the megasquirt.
The current flow across the battery-starter-alternator cable is sufficiently small during normal operation that the voltage will be essentially identical at all three points. Thus, the voltage should actually be more stable at the back of the alternator than at most other points in the harness.


It's really not a bug deal, and I suspect that you may be over-thinking this based on having heard some horror stories about the LC1. The thing that the LC1 doesn't like is being powered on while the starter is operating and dragging the system voltage down into the 8-10v region, thus the recommendation that ACC be used to supply or switch it.
Joe Perez is offline   Reply With Quote
Old 05-02-2014, 09:54 PM   #13
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: sacramento ,ca
Posts: 402
Total Cats: 46
Default

My lc1 has always been powered by the same circuit as my MS and have had no problems with over 2 years in my daily. I was more worried about voltage fluctuations messing with my sensor signals.
fastivab6tg25mr is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Turbo 1995 Miata Low mileage Clean Tekel Cars for sale/trade 29 02-05-2016 05:16 PM
CAS weirdness Asx MEGAsquirt 5 12-15-2015 12:14 PM
Did I fry my daughterboard? wred MEGAsquirt 20 10-16-2015 02:26 AM
Headphones PaperMate Insert BS here 32 09-25-2015 09:22 AM
WTB parts for HPDE car Voltwings WTB 5 09-11-2015 09:23 AM


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 06:41 AM.