The hot engine relay issue

[jdk_ii]

Short history:
When my engine fuse box melted at the alternator feeds, after diagnosis,
it became apparent that it has some design faults.

First, it feeds the alternator power post through the box.
One to supply 12V, the other to feed the battery.

Based on disassembling the fuse box, this thing probably has a "max"
of 70 amps. Add some age, it's probably average of 60 amps.

Pull anything larger, the power bus gets hot, and so do the relays.

I'm certain I was pulling the max of my 80A alternator. :D

Solution:
So, the obvious solution is to add an extra set of 4 gauge wires.
One between the alternator post and positive battery terminal (slow blow fused),
and one between the negative battery terminal and body.

Relays are still hot:
When my engine fuse box melted, all relays were hot. The battery was pulling
so hard to recharge, the internal bus was being strained.

With Alternator Upgrade
With the alternator wire upgrade, only the center Main Ignition relay gets warm. Only the IGN is on. Car is not running.

Search provided these
Some problems with overheating engine relays.
http://forums.celicasupra.com/showthread.php?t=9019&page=2&highlight=hot+relay

http://forums.celicasupra.com/showthread.php?t=1581&highlight=hot+relay

Why the heat
First, relays need X volts and Y amps to trigger. The less volts, the more amps required.

Increase any resistance to the relays, more amps are required. Hence more heat.
This increase resistance can be due to aging of wires. Also, any aging of the connections or power feeds (ie, oxidation) will increase resistance.

Suspects
Age of wiring and relays is one.

Stupid fusible links. Well, it's what they used back then. Now, they use either Maxi-Fuses or PAL catridge fuses.

Borderline capacity relays (they are rated at 22amps)

Average gauge grounding wire (Dangerous Ken and I talked about this for any audio system added).

Any other ideas?
I would be interested if anyone has investigated this and found a solution.
And if your relays don't get hot.

Side Notes
JoeB (Solo1Supra) and myself are working on sourcing some components to
migrate the fusible links to newer Maxi-Fuses / PAL cartridge setup.
Don't expect anything soon. Our real jobs take up alot of our time.
But something will appear.

[Tire Shredder]

Great to hear you got to the bottom of it. not only is this a reliability project and one ot make the car work better...but a safety issue aswell! Much like when brakes are concerned, how fast your car is really means nothing if it isn't safe to drive!

Even without a stereo upgrade I'm sure 20+ years of wear and tear is not good for these electrical parts. You and Joe have my utmost support in this and the forums in general, I am sure.

So, the first step for us...without anything you have fabricated would be for some nice new battery cables, one direct from the alt to battery (by bypassing the fuse box) to reroute the high amps the battery is trying to grab around the box....reducing heat through it. Same goes for the negative terminal...along with some good terminals?

Thanks for you dedication Jim.

[jdk_ii]

Well, some form of upgrade/retrofit will occur at some point. At least to replace the fusible link wires.

It's silly, since if you burn one in the boondocks, try finding them at a parts store. :zzzzz:

As for alternator, I'll eventually post some pictures of what I did.

What you want is 4 gauge (100a) or 6 gauge (80a) wire, from the alternator post to the positive battery terminal.
One needs a slow blow fuse (PAL, Maxi-Fuse, etc) just
BEFORE the positive terminal. The closer to the battery, the better.

Current flows in the path of least resistance. So your alternator
will be feeding your battery through the new big wire. The existing
alternator wires are supplemental, still providing voltage for existing circuits.

Which, if my suspicion is correct, this alternator wire upgrade may help reduce
the stock "dim headlight" problem at idle.

Probably won't solve the issue if using the 100watt Hella bulbs, as it
pulls power from the engine fuse box. That seriously needs a seperate power feed.

I'm opting for marine battery terminals, since they have screw on wing nuts
for adding anything (car audio amp, etc).

There are those big wide battery terminals (Stinger, etc). But I would prefer
a power distribution block, and retain some boring OEM looking boot covers. :D

[Tire Shredder]

thanks for the suggestions! I may go to an audio and parts store tomorrow and check things out! te "dim lights' is quite annoying.

[Chrisfrom1986]

The12volt.com talks about upgrading the big 3 as the first upgrade anyone should do to their car.

1. Alternator post to Battery Positive.
2. Battery Negative to Body
3. Engine to Body

They reccommend a minimum of 4 guage wire for the big three, saying anything less isnt worth it. They are one of the biggest vehicle electrical information sites around, but you need to register to see anything.

Great site for electrical diagrams for almost any car.

[Dangerous Ken]

Well Jim, you are not the first to melt a fuse box...

You got the basics covered, basically run bigger wire to the current hogging accessories.

Upgraded headlights - depends on the Current draw, not wattage, but it's a good idea to increase the wire size leading to them.

Electric Fans - this is a big one - has melted several fuse boxes. Definately needs a separate 8/10 guage line off the battery post with probably a relay to take the load off the fusebox.

Stereo Amps - look at the fuse rating on the amp(s) and realize the MkII was designed for 60A to run the entire car... Wire, Alternator, and Battery upgrade is necessary or the 'car' will lose out.

Often overlooked is the wiring to the rear window defogger...

As far as fusable links, I'd like to know the Amperage ratings of them. A simple solution (at about $0.25 plus fuse) is an ATC fuse holder with 10 guage leads. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=9739209933 Those fuses are everywhere Jim.

Ken

[Andrew]

I did some research a while ago while doing the "Big Three" and wrote a few things down in order to try to learn something as I know absolutly zero about electrical, this might be useful:

http://www.zcarcreations.com/howto/maxifuse.htm

[jdk_ii]

I'm actually going for 4, #4 being the engine to firewall.

A reasonably pragmatic choice is to get an amp wiring kit
for the alternator upgrade. They usually have enough
parts for the basic alternator wiring upgrade with some
in line fuse.

The headlights feed off the engine fuse box. The H4 60/100's
will pull more, and no sense taxing that weak fuse box.
But that's for another project. :-/

I saw the Datsun conversion in my hunt for a Maxi Fuse block.
Just researching some other fuse holders. Maybe with an extra relay socket or two. :D

I want to stick with slow blow fuses, since short power surges are acceptable.
Most motors (starter, eletric fans) can have high intial amperage draw.
Maxi-fuses are common as dirt, though availability for 80+ amp ones are a bit of a challenge.

Yeah, that defroster wiring is just wrong.