Alternator wiring upgrade - Again

[lee]

I was getting ready to buy the cables for the alternator wiring upgrade (having read almost all the archive posts) and decided to look through the alldata wiring diagram.

Well the archives seem to suggest no need to worry about a fuse on the line from Alt to Bat, but alldata shows the fusible link between the Alt-Bat.

Is the reason we're told not to worry because there is a 45A fuse still protecting downstream? Looks like all the link does is protect the bat from the Alt or vice versa. Or am I missing something?

[Seraph]

Originally posted by lee
I was getting ready to buy the cables for the alternator wiring upgrade (having read almost all the archive posts) and decided to look through the alldata wiring diagram.

Well the archives seem to suggest no need to worry about a fuse on the line from Alt to Bat, but alldata shows the fusible link between the Alt-Bat.

Is the reason we're told not to worry because there is a 45A fuse still protecting downstream? Looks like all the link does is protect the bat from the Alt or vice versa. Or am I missing something?

Not really. I have done that mod before on my 94. It works really well. Don't worry about the fuse. Make sure you have enough ground connection though. The gound on the SVX is really sad.

Lwin

[Aredubjay]

The fusible link is actually in the fuse box under the hood. Just follow the directions in the archive. There are many of us who've been running on this mod for 10's of thousands of miles with no problems and lots of plusses.

[Trevor]

As you have correctly ascertained the fuse link is the sole protection against a short circuit within the alternator or its wiring and there is therefore very good reason to worry about this fuse.

A solid short with the added bypass cable in place could result in extreme heat and the possibility of an engine fire. Any insurance assessor worth his salt would turn down any claim in respect of a fire in the engine bay on the basis of this modification.

I have read all the claims in respect of the so called upgrade and became doubtful that Subaru could be so stupid as some make out as well as skeptical regarding the improvements claimed. In this respect I have no desire to debate with those who have fitted a massive alternator so as to use their car as a generating plant for a public address system and claim that this produces hi ftdeltty sound. Boom boom!

A short time ago by accident I ran my battery dead flat and this provided the opportunity to take accurate measurements in respect of the complete charging circuit including the voltage drop between alternator and battery, both negative and positive, during maximum charge. As I expected all was in order and everything was as Mr. Ohm and I anticipated.

I have seen the exceptional figure of two volts quoted as a measured improvement and this could only occur if the factory system had a major fault in which case the bypass wiring would naturally improve matters. Finding and fixing the fault would have been the correct and obvious solution.

Originally posted by Seraph


The gound on the SVX is really sad.

the ground on every car is pretty sad

[Beav]

A fusible link would be advisable, even though many OEMs don't always use them on the alternator output. Not much worse than the run from the battery to the starter being unprotected. Usually the rectifier will blow before the alternator melts down. The concern would mainly be for the run from the battery to the alternator itself.

Trevor, the problem isn't so much voltage drop as it is a flow restriction. Any good electrician will tell you that 100 amps doesn't flow very well through a wire rated for 30 amps. I agree a 2 volt drop in that short of a space would indicate some serious corrosion, as even a single strand wouldn't have that much drop. Anyway, given some seat of the pants figures: headlights = 15amps, engine management=10, a/c w/hi blower=25, wipers= 20. 70 amps so far and if the factory gives you two 10ga. wires from the alternator they're only good (rated) for 60 amps.

Problems start arising when devices can't find enough clean power or a good, clear ground. I'm sure we've all seen a car with strange tailight actions, they're caused by a lamp trying to find a ground through another lamp's filament. Now imagine what happens to electronics when a similar ground problem occurs. Some days I get cars that everyone else has tried to fix, they'll have a plethora of new parts mounted (hopefully not cheap junk to add more problems to the mess) and I'll be involved in a 'crap connection' hunt for the next hour or so (and hopefully not for the next day or two. )

[Trevor]

Beav, a flow restriction as you term it in fact does equal resistance. Voltage can be termed pressure, amps volume flowing and watts power. Measuring the voltage drop and current passing through a length of a wire or cable provides a true indication of its resistance or as you put it the restriction to flow. Resistance is in fact the problem in securing maximum efficiency from any electrical circuit. By the way I have employed many Ò good electricians Ò and have instructed them in their jobs and in respect of ohms law donÕt require advice from one.

Ratings as given for wires and cables are of no use in making calculations in respect of the performance of a circuit and are only a very broad indication of capacity to pass current without becoming too warm. The rating figure is based on resistance per given length and is in no way an exact or finite figure with a host of variables to be considered when specifying for a particular application.

Before going into further technicalities I make the point that I fully agree with you in respect of the chance of a short within the alternator being unlikely. Diodes usually go open and so fail safe and the rest of the machine is fairly robust from an electrical point of view.

However in the case of a frontal collision mechanical factors are involved and the chances of a high current short and fire are very much on the cards.. Any insurance company would invoke their fine print.. The Òupgrade?Ó could cause such a fire and even if it was not the cause it provides the insurer with a watertight out. I agree that the direct connection to the starter motor is a hazard but this is accepted as a risk by the insurer being OEM.

Looking at the crimped end I would say the alternator positive connection is the equivalent of your US 14 gauge. Let us say that this is 800 mm in length and therefore has a resistance of approx. 0.0072 ohms going by published tables. Allowing for a small resistance in the negative ground return and the fuse link and connections a total of 0.008 ohms would be a reasonable estimated maximum for a system in good condition.

I have made measurements as follows using two high class digital instruments in parallel as a check on accuracy of calibration.

1. Voltage dropped alternator + to battery + . Dead flat battery and all lights and accessories drawing current, engine at 4500 rpm. --- 0.5 volts.

2. As above but with a fully charged battery (measured at 12.6 volts no load), --- 0.4 volts.

3. As 2 but with only engine electrics drawing current. -- 0.2 volts



4. As 1 above but alternator frame to battery negative --- 0.13 volts

5. As 2 above but alternator frame to battery negative --- 0.11 volts

6. As 3 above but alternator frame to battery negative --- 0.08 volts

From the above the total voltage drop in the alternator to battery circuit can be summarized as ---

a, Conditions as 1 above --- 0.63 volts

b. Conditions as 2 above --- 0.51 volts

c. Conditions as 3 above --- o.28 volts

Charging current based on the above can be calculated as follows ---

a. 0.63v / 0,008 = 78 Amps

b. 0.51v / 0,008 = 63 Amps

c. 0.28v / 0.008 = 35 Amps

I regard the above measurements as indicating that the charging system on my car i.e. OEM is working perfectly and this is born out by two trouble free years in my hands plus no indication of any repairs while in the hands of Japanese owners. It goes without saying that I will not be messing with it. If I do have trouble in the future I will be looking for the cause rather than bypassing a fault. Surely this is not the way to fix Ò crap connections Ò in the charging system.

There is an advantage in having a small resistance between the alternator and the battery as this can be a form of over current protection for the alternator. My typing is too slow and arduous to explain this in detail but it is in fact illustrated within the above figures. It could be that Subaru designers had this in mind as I can not accept that they were trying to save on a few strands of copper or were ignorant in respect of basic Ohms law.

Beav, I post the above with some trepidation as I hold you in high regard and in most instances I am in more than full agreement with your views. Please do not regard the above as anything other than a technical analysis hopefully of interest to all.

Regards, Trevor.

[Beav]

Considering the variety of experience at this site, I was counting on someone piping up with a formal explanation. I was, as I hit the 'send' button, expecting a response from someone better versed than myself.

My experience relies on, well, experiences. I don't repair poor connections by running extra wires, that would be ludicrous. However I still feel that many OEMs employ under-rated wiring for some high demand circuits. You can only force so much water through a hose, no matter how high the pressure (point of no return). If you limit the pressure the only way to increase the flow is to enlarge the hose.

[Trevor]

Beav. On the basis of your various postings I have been sure that you have a sound knowledge in respect of things electrical. As you say things line up in a broad sense with hydraulics but there is no point of no return if you mean a point were flow stops unless you refer to a complete blockage which in the case of an electrical can not exist.

Flow or current will always continue to increase with pressure or volts however power will be dissipated in the form of heat in accordance with the resistance and the connected load comes very much into the equation. All I am doing I am sure is putting in print what you already know from experience and must be pissing you off. However our exchanged comments may be of assistance to some others.

Why did US car makers persist so long with a six volt system? One learned very quickly about resistance when trying to squeeze full lighting volts from an old flat head V8 Ford. When talking about overload protection and fires etc. I recall that many Ford products lacked fuses and I believe Henry's comment was that they cause trouble and are a nuisance. No doubt cost was a factor which he failed to mention. Cooked wiring looms were common. Now those thoughts take one back a few years.

Once again special regards, Trevor.