LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently July 19, 2018, 3:32 pm

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 6 posts ] 
Author Message
PostPosted: August 24, 2016, 12:00 pm 
Offline
User avatar

Joined: October 27, 2006, 3:29 pm
Posts: 414
Location: Indiana
I have a race car application with a stand alone ECM & engine harness custom made from Enginewiring.com for my GM Ecotec motor. I have no lights, wipers or anything a street car would have. The wiring guy stripped down the engine harness to cover just what I need to run the motor with the factory ECM. He added a fuel pump relay and fan relay with a single power connection wire coming from the harness. I'm used to separate fuses for everything but this all now runs through the new harness. Is it a simple as it looks with a single fuse for everything? What do you recommend for a fuse block set-up a fuse size?

_________________
Building a whole car from scratch is a 1,000 little tasks, done 1 task at a time, while thinking 10 tasks ahead, then redoing it anyway.
South Bend Region SCCA D-Modifed Class Autocross & Track-Day/TT. Chevrolet 1.4 L Turbo Ecotec Power


Link to my build log:
http://www.locostusa.com/forums/viewtopic.php?f=35&t=3356


Top
 Profile  
Reply with quote  
PostPosted: August 24, 2016, 12:19 pm 
Offline
User avatar

Joined: October 19, 2012, 9:25 pm
Posts: 2701
Location: Summerville, SC
On mine I did 5 fuses and 4 relays.
Relay for fuel pump, ECU main, run/start/charge/ ECU backup power circuit, and fan
The 5th fuse is 15 amp 12v switched power to the datalogger.
I have 3 open fuses I can wire; 2 battery hot and 1 switched if I want to expand.

_________________
Too much week, not enough weekend.

OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216


Top
 Profile  
Reply with quote  
PostPosted: August 24, 2016, 12:26 pm 
Offline
User avatar

Joined: June 8, 2010, 8:02 pm
Posts: 539
Location: White Rock, BC, Canada
The problem with a single fuse is that some PCM circuits/components will not be properly protected, or may blow fuses. There is a reason PCMs have multiple fuses and, while I am not an electrical engineer, I can only assume it's to separate the big stuff from the little stuff and/or to keep clean power for sensors. Things like injector drivers shouldn't be on the same fuse as things like MAF sensors.

http://www.12voltplanet.co.uk/fuses-guide-uses.html

Cheers.

_________________
Build log: viewtopic.php?t=9291


Top
 Profile  
Reply with quote  
PostPosted: August 24, 2016, 2:42 pm 
Offline

Joined: July 6, 2008, 11:15 am
Posts: 1049
Location: Cave Creek, AZ
Fuses are used to limit the maximum current that can go down a wire to a device. Typically the fuse is sized to protect the wire from overheating and not so much to protect the end device from overheating. If your total draw is 50 amps and you put in a 50 amp fuse, the first time you get a short to ground in any of the little wires that are on that circuit, you are going to release all of the smoke that was installed in that wire at the factory, and probably some of the factory flameage too.

So you CAN use a single 50 amp fuse, but all wires that it feeds power to will have to be 6 guage wire.

Tom

_________________
Sometimes, I'm as confused as a baby in a topless bar.

My short term memory is absolutely horrible and so is my short term memory.

https://www.youtube.com/watch?v=sG16m2e4O6I


Top
 Profile  
Reply with quote  
PostPosted: August 24, 2016, 3:10 pm 
Offline
Mid-Engined Maniac

Joined: April 23, 2006, 8:26 pm
Posts: 5873
Location: SoCal
To be blunt, most people are idiots when it comes to fuses, regularly replacing "bad ones." A fuse blows in order to protect the wires and is an indication that there's something wrong downstream. Replacing it doesn't fix the problem.

_________________
Midlana book: Build this mid-engine Locost!, http://www.midlana.com/
Kimini book: Designing mid-engine cars using FWD drivetrains, http://www.kimini.com/book_info/


Top
 Profile  
Reply with quote  
PostPosted: August 24, 2016, 10:18 pm 
Offline
User avatar

Joined: June 8, 2010, 8:02 pm
Posts: 539
Location: White Rock, BC, Canada
I was in a hurry earlier. At the very least you should have these fused separate from the little sensor wires:
-Injectors
-02 heaters
-MAF
-coils
-? I may be forgetting something.

Is it possible these are fused with inline fuses hidden in the harness somewhere?


If not, I would be inclined to check your PCM wiring diagram and then add fuses to it as per OEM ratings. This still has potential to allow excess current to hit some things, but less likely, and less current than only one fuse. To do it right at this point you need to measure full expected load on each circuit, and then fuse accordingly. I forget how much you are supposed to go up in fuse size from typical load, but I want to say 15-20%(?) is typical. If you post the PCM wiring diagram, we should be able to help further.


Cheers.

_________________
Build log: viewtopic.php?t=9291


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
POWERED_BY