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Discussion Starter · #1 ·
Does anyone know if a HO Alternator is available for these cars? Or if its even required when adding accessories like amps. I saw a thread on RS.org where the guys were installing aftermarket stereo amps and they're under the impression that the stock unit won't handle it. They're also running really heavy cable from the batt, like 1/0 or 2/0. Idk if the RS has the same Alt as us or not, but I thought that was overkill. I'm getting ready to install a new amp and stereo in mine and I just ran a 4ga wire for batt power. It did make me think that I should at least find out what the limits of the stock ST Alt is tho. Anyone have any thoughts or experience on this?
 

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The factory alternator is 150 amp, or at least that is what a OEM equivalent from Autozone puts out.
 
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lots of variables here. it depends on what amp, and how you will be using it...

I am about to put in a 1000W(birth test sheet shows about 1130w RMS) 5 ch amp, its full class D so its very efficient (probably close to 85-90%). I also will not be running it at 100% all of the time, nor does most of the music i listen to push the amp very hard. just ran single good quality 4ga OFC wire to the back, and to save on voltage drop due to the resistance in the wire, instead of taking the easy route and running the wire across the engine bay over to the easy to get to main harness grommet and then back across inside of the car (since I wanted my amp installed in the OEM location) I drilled a hole behind the battery box under the clutch plate in the firewall. this saved probably 5'-8' of wire alone.

now is somebody is running a true 1kw bass amp, and they are running it hard all of the time, and/or if the amp is a class A or A/B which is not as efficient then yeah, they very well may require 2ga or 1/0ga to provide enough current for the amp to be amp to receive enough current to provide the power its rated at. another consideration is the wire itself. I've had some clients bring me their own wire and the package said that it was 2ga, but really it just had a lot of insulation and was really only about 6ga... or if the wire is not good quality it may not be solid copper or silver tinned copper, it may be Copper Clad Aluminum(CCA) which while being lighter and usually more flexible, it has a higher internal resistance and require a thicker gauge of wire to deliver the same current as Oxygen Free Copper (OFC) especially over distances.

for instance, math time...

57228076ef240ed796b328a7d6387eac.jpg

lets say you ran the wire over to the pass side of the car, and used 14' of wire (I actually don't know how much I used exactly yet as I started with a 17' single piece and as soon as I mount the amp will be cutting the down the wire to fit) lets also say that you have a true 1kw bass amp and you will be pounding the streets hard with it all the time (or at least pushing it hard for a good little bit at a time) lets also say that you have a fairly efficient class D amp that is 80% efficient.

if you are getting 1kw out, then you are feeding 1250w into it, if the car is running, then the alt is putting out 14.4v which would be almost 86.7 amps of current. at that wire length, 80 amps of continuous power draw needs 4ga wire, but 90 amps need 1/0ga.

if the engine is not running then the voltage would be around 12v and the current draw would be about 104 amps...

non class D amps could be as low as 50%, therefore increasing the current requirements considerably. and its not uncommon for people to be running amps like 1500w or more (luckily, most people running "1kw+" amps are not good quality and the manufactures lie about their power and they may only be a 200-300 watt amp...)




then we get into the alternator... the question becomes, if you are running a 1kw amp at full tilt often and using 90a-100a of current, that only leaves 50a of current to run everything else like headlights, turn signals, brake lights fog lights, windshield wipers, heated seats, computers that run the car, all the dash lights, the stereo itself, power windows ignition system, ABS solenoids, power steering, charging ports, climate control blowers, fuel pump..... how long can a stock alt last for if its constantly being pushed to its limits?

while 150 may seem like a lot, there may be times when the car itself is using a whole lot of power, and especially when idling at a red light as alts don't make anywhere near full power when being spun that slow.

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Discussion Starter · #6 ·
Thanks guys. I feel better now running a 4ga wire and using the stock Alt. Hey LoudST, I was thinking of rerunning my power wire down the driver side also, more to prevent any EMI. Do you think that could be an issue? And did you find any other wire bundles running on the driver side? Appreciate your "2 cents" LOL.
 

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Doing the "Big 3" upgrade may help if you are experiencing issues with inconsistent power. (ie lots of dimming lights)
Thats running an extra FUSED wire from the alternator post to the positive terminal on the battery, running a ground from the motor to the negative battery terminal and ground from frame/body to negative battery terminal.
 
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i had a rockford fosgate 2500bdcp and rockford fosgate 600a4 on 100% stock electrical. only dropped to low 13's idling.
 

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Discussion Starter · #11 ·
Doing the "Big 3" upgrade may help if you are experiencing issues with inconsistent power. (ie lots of dimming lights)
Thats running an extra FUSED wire from the alternator post to the positive terminal on the battery, running a ground from the motor to the negative battery terminal and ground from frame/body to negative battery terminal.
Have you ever done those mods? Its gotta help, I just don't know if its really required on an ST. Sounds like nobody has had any issues. I haven't. I was just wondering if anyone else needed to upgrade the Alt after installing a lot of accy's.
 

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Sounds like nobody has had any issues. I haven't.
its not so much that it will keep you from having "issues", because the amp will still function fine, it just wont make all the power it should (cant have power out without power in)...

think about it this way, you often see a lot of people running heavy power wire to their amps, and heavy ground wires from their amps to the body, but they don't upgrade the cars actually ground wires. so since power needs a complete circuit, there is still a weak link. the engines ground wire and the battery's ground wire are designed to support the car in OEM form. all of that current running through the amp is now getting bottle necked at those factory ground points.

AT A BARE MINIMUM, you should be upgrading the battery's ground wire by adding the same gauge wire that the amp is using, otherwise all of that extra current is still traveling through the battery's thinner ground wire along with all of the current that is needed to keep the car running and operating. that factory ground wire isn't designed to carry all of that extra power. it would be no different than if you grounded you amp with a much thinner gauge of wire than the power wire. the only thing that keeps it from being dangerous and risk the wire overheating and burning up is that it is so short so its internal resistance is fairly low. also since you are bottle necking the current flow, the cars required current needs are fighting with the amps to squeeze through the same wire and the symptoms of not having enough power are made worse, aka lights dimming. and if the lights are dimming because the available power is not enough, then all of the other power requiring devices are also getting starved of power, sensitive equipment like computers (PCM ect) do not like running low on power. and starving the PCM on a performance car is never a good idea...


Hey LoudST, I was thinking of rerunning my power wire down the driver side also, more to prevent any EMI. Do you think that could be an issue? And did you find any other wire bundles running on the driver side?
I wouldn't so much be worried about the magnetic field caused from high current causing a whole lot of interference in the car as most computers are designed with good shielding and are usually well protected from them being affected. now you do want to keep any signal wires away from not only high current wires but also any modules in the car as low level signals wires can be effected by the EMI that a lot of those modules can emit and then your amp will amplify those noises a lot, and I'm not just talking about "alternator whine" but also kinds of static, hisses and pops.

yes there is a harness that runs back there down the drivers side and there is also power wires that into the rear doors for the window motor, nothing super high current, but high enough to get noise. you can see the harness in a couple of these pictures as I followed it and tapped my power wire to it along the way.

IMG_20170925_141829.jpg
IMG_20170925_150423.jpg
 

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Discussion Starter · #13 ·
Wow, thanks for that post. I never thought about the signal wires being too close to certain modules. I have seen a few throughout the car too. And I guess I'll be doing the Big 3 upgrade now as well. It all makes sense and its really not that hard to do. Well at least the Batt ground isn't. Thanks again.
 

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Have you ever done those mods? Its gotta help, I just don't know if its really required on an ST. Sounds like nobody has had any issues. I haven't. I was just wondering if anyone else needed to upgrade the Alt after installing a lot of accy's.
It's not about function, it's about capacity. If you are upgrading the amplifier and going to the trouble of installing a large positive power wire from battery to amp, why would you skip the battery and alternator ground?

Power capacity is like a chain. You want all the links in that chain as large and strong as possible. At the very least, try to make all the links the same size.
 

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a bigger battery wont do a whole lot more, it will give you a little longer run time before the battery is dead if the engine is not running, but it wont fix the problem of not enough energy being created (or more accurately, being converted) in the first place. the battery's main purpose is to start the engine and to smooth out the voltage ripple created from the alternator doing its job. once the engine is running, everything is running from the higher voltage coming from the alternator and the battery is charging (if there is enough power left over)
 

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I know this is an old thread but it appears I may have finally found an ho alternator for a cars that's available now.


 
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