Alternator power drain

Splinter · Post by **Splinter** » Fri Jan 13, 2006 9:02 am

So I was just looking at what my theoretically peak power consumption will be when I finish all my mods, and its looking like if I somehow managed to bring every component to its peak of consumption at the same time, I could pull 170 amps

I realized thats a huge drain on performance... until I did the math.

170 amps @ 12 volts is ~2000W

Which is... less than 3hp?

Even accounting for massive inefficiency, its gonna be less than 5hp

So really, I guess the main performance loss is in the weight of the accessories, not the power they consume

Or did I majorly screw up my math?

vrg3 · Post by **vrg3** » Fri Jan 13, 2006 3:46 pm

Your math is fine, but there's more to the picture.

Your alternator cannot supply 170 amperes. It tops out somewhere around 85 amps, and that's somewhere around redline.

So, when the load on your electrical system gets high enough, you will start discharging the battery to supply the needed current. System voltage will be reduced from the ~14 volts it's supposed to be down to less than 12 volts as the battery is being used.

Unless you've modified your ignition system the right way, lower system voltage means a weaker spark, which may mean less torque.

And low system voltage also means lazy fuel injectors, dim lights, less effective defrosters, stuff like that.

And of course, the battery can't supply this extra current forever. Eventually it'll discharge all the way and leave you stranded.

So... High-output alternator maybe?

What are you going to be doing that's going to draw 170 amps for more than a very brief time though?

Splinter · Post by **Splinter** » Fri Jan 13, 2006 6:10 pm

Oh I am getting a 160amp alt, Ive alreayd ordered it

Fairly large stereo (65A)
Autronics SM4 (16A)
CarPC (10A)
Extra headlights (13A)
MSD DIS-2 (8A)
Inverter (15A)
Misc other power drains (defogger, dash lighting, map lights, brake lights, etc 20A)

Ive lost the last 20A. Or maybe I added it wrong the first time.

vrg3 · Post by **vrg3** » Fri Jan 13, 2006 7:14 pm

To me those look more like peak values than continuous values.

Unless we're talking about a 1500-watt stereo (are we?), your audio system isn't going to draw 65 amps continuously.

The engine management isn't going to actually draw 24 amps continuously either. And the DIS-2 will actually provide a full-strength spark all the way down to about 10 volts.

You should be okay, I think.

Splinter · Post by **Splinter** » Fri Jan 13, 2006 7:23 pm

Oh its absolutely peak amperage, I think I mentioned that.

I was just surprised at the small amount of horsepower required to generate all that amperage.

I was expecting to lose 15hp or more

vrg3 · Post by **vrg3** » Fri Jan 13, 2006 7:43 pm

Oh. Right, you did. Your numbers are a generous upper bound.

Well, the alternator's of course not 100% efficient. I don't know how efficient it is exactly, but... yeah, it's only a few horsepower.

Post by **Legacy777** » Sat Jan 14, 2006 4:02 am

You'll be fine.

Splinter · Post by **Splinter** » Sat Jan 14, 2006 6:34 am

Woo, just got an email, the new alt is working great and is almost ready to get shipped out

The guy is just retooling it so it turns on below 1400rpm

60amps at idle, 160 within the driving range

+ Optima Yellowtop = no more charing system related probs!

Splinter · Post by **Splinter** » Mon Jan 16, 2006 8:22 pm

Josh, what RPM does your alt come on?

Post by **Legacy777** » Tue Jan 17, 2006 4:30 am

1177 according to the sheet.

http://www.main.experiencetherave.com:8 ... ortest.jpg

Splinter · Post by **Splinter** » Tue Jan 17, 2006 4:35 am

Interesting

Theyre setting mine up to come on at 500rpm

subawhatsubawho · Post by **subawhatsubawho** » Tue Jan 17, 2006 5:23 am

They have exciters....gets them excited. Some before others.

I used to have a monster alt on my chevy blazer. It actually had holes drilled in the casing to help with cooling.

Splinter · Post by **Splinter** » Tue Jan 17, 2006 5:25 am

Suba, just because the same guy is making mine as making Josh's

I did specify that I wanted it to come on very early tho

subawhatsubawho · Post by **subawhatsubawho** » Tue Jan 17, 2006 6:19 am

Before I got the big ass amp on my blazer I found a website that showed you how to insert a paperclip into the back of the ALT to get it to stay on all the time. It was a stock alt...and not a good idea. I went on a road trip and had to replace it when I got to my destination because it was glowing red.

Whats it costing you guys for custom ALTs? I think Josh mentioned it once before but I forgot. I'm probably going to need one soon.

Splinter · Post by **Splinter** » Tue Jan 17, 2006 6:43 am

Around $300 USD

subawhatsubawho · Post by **subawhatsubawho** » Tue Jan 17, 2006 7:24 am

I forgot to ask where....

Splinter · Post by **Splinter** » Tue Jan 17, 2006 7:37 am

Its just some guy

If you give me your email Ill get him to give you a shout

You might wanna wait til I get mine installed tho, just so I can do a writeup on it.

Post by **Legacy777** » Tue Jan 17, 2006 7:38 pm

Splinter wrote:Interesting

Theyre setting mine up to come on at 500rpm

bastards! I am running a smaller diameter pulley on the alternator to make sure it stays on. The stock sized pullies and idle RPM hovers right around the turn on rpm. So that is why I did the pulley mod.

If I knew they could've tweaked the turn on rpm....I would've had them do it like yours.

Splinter · Post by **Splinter** » Tue Jan 17, 2006 9:09 pm

Hahaha owned

You might want to fire him an email and see if theres an easy way to change it

Splinter · Post by **Splinter** » Fri Jan 20, 2006 7:45 pm

Hey whats the deal with Optima terminals? I cant seem to get the stock rings to fit over them.

Post by **Legacy777** » Fri Jan 20, 2006 8:02 pm

Splinter wrote:Hey whats the deal with Optima terminals? I cant seem to get the stock rings to fit over them.

Too small or too big?

I think the optima terminals are little smaller....so you may need to tweak the clamp

Splinter · Post by **Splinter** » Fri Jan 20, 2006 8:03 pm

The terminals are too big, the rings wont fit over them.

Its the D34/78 type

Post by **Legacy777** » Fri Jan 20, 2006 8:13 pm

hmm....that's weird. Try expanding the rings some.

Splinter · Post by **Splinter** » Fri Jan 20, 2006 8:16 pm

I undid the screw pretty much the whole way...

it seemed only too big by maybe a mm or so, but thats still no good.

I thought battery terminals were supposed to be standard sizes?

Post by **Legacy777** » Fri Jan 20, 2006 8:16 pm

They should be standard.

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Alternator power drain

Alternator power drain