fd alernator blowing stock main fuse
 

okay so i was hammering down the interstate doing some fuel tuning because i just got a new turbo installed today. at 7k rpms the car dies and i roll to a stop in the emergency lane. right before this though i noticed on my stock voltometer that i was at 15 volts. well i get out and pop the hood and my main fuse is blown. it's an 80 amp. from what i hear the fd uses a 100 main fuse. do i need to get a 100 main fuse for my setup or is there a larger problem i need to be looking for?

How is it wired?

I have the one wire going to the 12volt positive on the battery. the L terminal is wired into the W/B wire on the fem-01 plug. I have had the FD alternator hooked up in my car for months.

When I start my car I have to rev the engine over 3000 miles to activate the alternator.

Today I hooked up the L terminal to the W/B wire and now when I start my car the alternator is already active. I've been driving around today tuning fuel because I installed a new turbo. But now I seem to be blowing my 80 amp main fuses. I blew one tonight while tuning fuel (7k rpms in boost, yikes!). luckily ih ad a spare in my car so i replaced then, then when driving 80mphs on the way home the main fuse blew again. so i either need a higher amperage fuse or I'm guessing I need to unhook my L terminal.

I do notice that my voltage is alot higher than it usually is during night driving. it's usually around 14.2 (haltech verified) but now it's at 15volts. my guess it during the higher rpms the alternator is producing even more amperage thus blowing the main fuse. But it's weird that it didn't start doing that tonight. But earlier today i wasn't hammering on it or going over a certain rpms so I can't really be sure. I'm going to ground my car for awhile while I figure this out. IF anyone has any insight, let me know.

You don't need to upgrade the MAIN fuse when you upgrade the alternator, and nor should you. The alternator only provides whatever current the car's system are drawing. If you've added high current electrical items like amps and e-fans, they should not be going through any of the stock fuses, so upgrading them is unnecesary (and potentially damaging). Nor should you disconnect anything from the alternator.

If you're popping a fuse, look for shorts. If the voltage is higher than normal, there's most likely a problem with the voltage regulator.

Wouldn't adding a 100amp fuse where the 80amp fuse is, reduce the resistance and possibly allow current through easier and charge the batt easier?

ohms(impedance) has to do with resistance not amps.

No. It will increase the amount of amps allowed through the fuse block; which shouldn't change that much ever... You should NEVER have to change the amperages of fuses going through that fuse block or any fuse block. The wires are rated to handle amperages slightly higher than the fuses they are running behind.. So increasing the fuse amperage could likely fry your wiring if you have big-amp devices behind them.

I'm no electrician..... but. it sounds like maybe you hooked the FD alt up wrong. It uses the same S, L, and + functions as any other alt. As long as you mapped those correctly from the FD plug to the FC harness, there should be no problem.

EDIT: Another note... The S5 FC's use a 100A main fuse as well, but are only sporting an 80A alternator. Isn't the FD one 100 or 105 or something? Not that it has anything to do with the problem... just curious.

Well, technically, since we're talking about an automotive DC based system, we should only be referring to the resistance, as the impedance of the circuit should always equal the resistance. While impedance and resistance are both measured in ohms, they are not the same thing. Impedance is the overall system resistance in an AC circuit, found by adding the vectors of pure resistance, inductive reactance, and capactive reactance. With a pure DC system, using a DC rectified alternator such as in a car, there would be no reactance vectors, and impedance would equal resistance. You typically do not refer to impedance in a DC circuit.

When using an ohmeter, you can easily find a load's resistance. In an AC RLC circuit, however, the measured voltage and the measured current won't follow Ohm's law V=IR, like it does with a DC circuit. The measured current will always be lower than the calculated current. In AC circuits, the correct formula to use is V=IZ. Z can easily be calculated by the equation Z = [(XL - XC)^2 + R^2]^1/2.

More than anyone ever wanted to know about resistance. :D

Fuses do have resistance. Larger fuses always have less resistance than smaller fuses. However, the amount of resistance relative to the total system is always completely negligible. Its purely a theoretical argument. There is no measurable voltage drop across any working automotive fuse, and therefor, no considerable resistance. While upgrading to a larger fuse would give less resistance, we are talking a difference of micro-ohms. Completely moot to discuss.

If you are popping the 80 Amp fuse, you are definitely doing so through an electrical short somewhere in the car. Look towards any unfused aftermarket wiring you have, check for melted wire insulation in that circuit.

^^ OH.... Mr "Big Words" scathcart thinks he's SOOOOO coool....

:) :bowdown:

I found the problem. I had everything wired correctly. The b terminal on the alternator was arcing to the intercooler causing it to short out. Sorry, newb move. Everything is working perfectly and I'm still sporting an 80amp fuse, np.

I wouldn't exactly call the nerdish quoting of first year eng courses "cool". If anything, its exactly the opposite. It was just a little post for anyone who wanted to know about the subject.

Good to hear. Thanks for posting this for future searches.

Alternator belt too long?

Yeah, I know... It was a joke.... do I need to wrap everything in <sarcasm> quotes? :)

Besides, I did give you the :bowdown:

Sarcasm is lost on the internet. So is truth.

I have some nice charr marks on my UIM from that (+) post arcing when i was installing my FD alt. it makes for a nice show at night.

Ain't that the thruth.....

I had to get shorter alt belts when I put the RB underdrive pulley on.

Man, you are such a downer... I'm going to go slit my wrists I think. :)

how'd you fix that? i'm assuming shielding? tape or something? i'm total noob.
but i am pretty sure my alternator is going to be a constant source of problems so yeh heh.

was the 3K+ rpm thing the same problem? or did you fix that by tightening the pulley system so the alternator was actually working 100%? some guy in another recent post is having that same problem i believe he has some kind of aftermarket fan on that changed the belt system

and actually, on that note... reading the mechanics manual on how to tune the belts... wtf..?!? has anyone actually done the red marker thing w/ degree angles or whatever it says. coz im pretty sure my belts are far from where they're supposed to be

It's all about the L terminal my friend. It makes the alternator activate immediately and what fixed my 3k+ rpm problem. It also does controls the voltage regulator so I'm always making 14vdc no matter if the headlights are on or off. (Was making 15vdc with headlights off and 14vdc with headlights on)

To solve the arcing problem I put the boot over the b terminal tongue ring and electrical taped it. Then I put a few layers of duct tape on the intercooler where it was arcing for added protection. I haven't had any problems since.

Thank you for clearing that up. It was just something I heard from time to time and figured I would ask.

Thanks again.