Re: Alternator Wiring Mod

surfer63 · #1 10-29-2003, 08:34 PM

Trevor... can you explain how running another wire from your alternator to your battery unfused could be dangerous?

Later,
Matt.

Trevor · #2 10-29-2003, 08:56 PM

Quote:

Originally posted by surfer63
Trevor... can you explain how running another wire from your alternator to your battery unfused could be dangerous?

Later,
Matt.

It must also be appreciated that the alternator wiring mod by passes all alternator over current protection as is incorporated in the original set up. In the event of a front end prang and and short circuit at the alternator you could end up with an nasty engine compartment fire. This is a circuit capable of passing a very high fault current. If your insurerÕs assessors are on the ball you will be out of luck in a big way in respect of any insurance claim.

Chicane · #3 10-29-2003, 09:20 PM

What if you just put a big inline fuse on that new wire?

- Rob

Trevor · #4 10-29-2003, 09:45 PM

Quote:

Originally posted by Chicane
What if you just put a big inline fuse on that new wire?

- Rob

As I have often advocated that is exactly what should be incorporated in the instructions which have unfortunately been previously taken as gospel.
The fuse obviously should be as close to the battery as possible.

Chicane · #5 10-29-2003, 11:58 PM

But of course.

- Rob

ensteele · #6 10-30-2003, 08:54 AM

Trevor

Remember that I am still waiting for your PM about this for the How-To.

Aredubjay · #7 10-30-2003, 08:58 AM

Quote:

Originally posted by Chicane
But of course.

- Rob

Do you have any Grey Poupon?

Trevor · #8 10-30-2003, 03:16 PM

Quote:

Originally posted by ensteele
Trevor

Remember that I am still waiting for your PM about this for the How-To.

I sent the following PM some time ago. I have copied the text from my outbox. Did you not receive it ?

" Re: alt upgrade question

Hi again Earl,

I have had a look in the how to documents but have not been able to find anything on the alternator up grade thing. I was sure I had seen references to it being in there but no sign of it as far as I can see. Have a look and get back to me.

While I am at it how can one remove a document which no longer is of interest ? "

I hope something has not gone haywire with what has been such a reliable site.

ensteele · #9 10-31-2003, 07:15 PM

Thanks Trevor. I have been busy lately. If you let me know what document you want removed, I can do that for you.

Trevor · #10 10-31-2003, 08:25 PM

Hi Earl,

It is some stuff in my locker I wish to delete in actual fact. Sorry for the confusion. It covers some stuff on the shift kit which is no longer valid.

#11 11-01-2003, 07:07 AM

So what wire and fuse should i use for alt. upgrade?

also if anyone knows what voltage should i get at idle on alternator, at 2000rpms and at 4000rpms...

could be nice to check that.

cheers Sergi

Trevor · #12 11-01-2003, 04:07 PM

For a standard alternator a 125 amp fuse should be OK. Maximum output is 95 amps.

Voltage will be regulated according the level of charge in the battery and the load. You should have 13.4 volts or more at the battery when above say 1500 RPM.

#13 11-01-2003, 04:22 PM

so what kinda wire will do?
gauge 8, 4?

Trevor · #14 11-01-2003, 05:07 PM

Sergi,

Why do you think you should do it ?

For your information I repeat a previous post.

Quote. ------

Please be clear that I do not wish to be involved in an argument but if the original wiring is in good condition there should be no problem.

It must be appreciated that the alternator wiring mod as originally suggested by passes all alternator over current protection as is incorporated in the original set up for very good reason,. In the event of a front end prang and a short circuit at the alternator you could end up with an engine compartment fire as this circuit is capable of passing a very high fault current. If your insurerÕs assessors are on the ball you will be out of luck in a big way should you make a claim.

I have checked the original alternator wiring on my car and have taken measurements as follows, using two high class digital instruments in parallel, as confirmation the accuracy of calibration.

1. Voltage dropped alternator + to battery + with 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 circuits can be summarised 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 three 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 by passing a fault. Making modifications 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. What is more any such small voltage drop will not effect the alternator output voltage as the electronic regulator senses battery voltage directly via a separate pilot wire.

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 Ohm's law.

Take it or leave it, I have no further comment. I am trying to be helpful rather than controversial.

If you are running a special alternator capable of delivering increased current you are in a different ball park, but you should think very seriously about the need to incorporate suitable fuse link.
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Make up your own mind.

Wire here is metric. Use the largest cross section you think will be mechanically suitable.