Converting Watts to Amps? Alternator Advice?

[teklein]

Im trying to convert watts to amps, so I can see what output im gonna need for a new alternator. I just want to make sure that the alternator will put out enough watts for the system I am installing.

Anyone know where I can get a high output alternator for a 1g 1.8? I think its the same alternator for a 2.0 as well.

Thanks, tim klein

 

[teklein]

Also, how would I know which optima yellow top battery to get?

Its going to run a Alpine 60x4 head unit to alpine type r speakers (4in in dash and 6x9 in back right?), and two 500w mono amps to two 10" type Rs (4ohm)

How would I hook up a 6 speaker system in the car?

Thanks again, Tim Klein

 

[BUCK]

I had my Bumper to Bumper guy look up the Highest Amp Mitsu Alternator that would fit a 1G:

- Max amperage 121 amps

- 100 amps at 3000rpm

- Max 1548 watts

- Manufacturer Ampere - Ampere P/N 21491

- Cost was about $150.00

- I run a 1 Farad Cap too with an El-Cheapo Battery that pushes a 500 Watt Sony Amp & head Unit no problems - no dimming, etc.

I put it on Car Ramps & come from underneath so no need to remove Fan - It's still a PITA...

Make sure you have NO Power Steering Fluid leaks dripping on your Alt - that will kill the Voltage Regulator in a Hearbeat & can toast your ECU...

 

[PaulPDX]

Stock alternator is fine unless you're cranking the volume and doing dB competitions.

You can get rebuilt 90 amp alternators with or without core exchange. Web search.

Optima:

Yellow - deep cycle. Juice lasts longer without the car running. Can be discharged and recharged without "memory" problems. Meaning... it will recharge back to full capacity.

Red - standard. Juice doesn't last as long without the car running.

Either one will be fine and plenty powerful for operating the car. If you have car alarm that eats a lot of juice than the standard alarm system, and don't drive the car often... you'll want the Yellow top.

Blue - marine deep cycle. You don't want. Not too good in cars. Both my friend and I have killed one of those each.

All yellow tops are basically the same. Some have two posts, some have provisions for 2 additional posts on the side.... makes adding accessories a little easier. Which one to get? Check with the Optima book at your Optima dealer, look up your car and find the appropriate part number for the battery. Just like buying spark plugs and windshield wipers.

 

[teklein]

So what your telling me is that my stock 65amp (or whatever it is) alternator that already strains and dims everything when I have my headlights, stock radio, rear defrost, and front defrost on, will handle a 60w-4 head unit and 2 500w mono amps?

My friend, Im not even that dumb.....

I will check on the 90amp alternator though. Im looking for a bigger one though...

 

[PaulPDX]

Originally posted by teklein
So what your telling me is that my stock 65amp (or whatever it is) alternator that already strains and dims everything when I have my headlights, stock radio, rear defrost, and front defrost on, will handle a 60w-4 head unit and 2 500w mono amps?

Mine works just fine. If you want help... lose the attitude.

 

[Defiant]

Originally posted by teklein
My friend, Im not even that dumb.....

As recommeded above, lose that attitude on this forum. Now.

As for your forumula, amps = watts/voltage.

 

[teklein]

I didnt have an attitude, I was grateful for the battery advice, but I think that saying the stock 65amp alternator which already strains with the factory equipped devices, will not handle a high power stereo.

and thank you for the conversion. theoretically, if i find out the amp amperage and the head unit amperage, and I make sure im near that number + stock amp specs (65amp + stereo amperage) I should be Ok?

 

[Defiant]

It's going to depend a fair bit on what the amps of the stereo system really are. I doubt the "wattage" has much to do with it, but I'm not the one to ask about it. Check with some serious stereo guys.

 

[imdrax]

As recommeded above, lose that attitude on this forum. Now.

As for your forumula, amps = watts/voltage.

just in case you pressed the wrong key ill correct this for anyone in the future whos needs the info
***Wattage = Amperage x Voltage***

 

[Attack Eagle]

here is a simple rule of thumb

add all the fuse ratings and / 2

then multiply by 13V

thats close enough to how many amps your system will consume at max output on music (not test tones).

my little JBL 755.6 runs just fine on what is left over from my factory 75amp alternator...
and I run an underdrive pulley ( though I might change back to the stock one for the extra .6 volts)

you will be jsut fine on a 90amp alternator based on what i know of the alpine 500w monos (assuming they are class D mrd500)... any particular reason for 2 500w amps with an 18w x4 front and rear?? the class ds are pretty efficient... 500w/ 14.4 = 70 amps AT MAXIMUM OUTPUT DURING A BASS NOTE... so you'd briefly pull 90+ amps to the amps out of the battery but as soon as the bass note was over it would recharge...

now if you run around playing testones or bassmechanics at max output you might need something bigger, but I assume you aren't planning on going deaf soon and won't be doing that.

I am assuming you have dvc 4 ohms and are going to parallel the VCs to get a 2 ohm load so each alpine is giving a solid 400-500w.

 

[DGajre777]

Old thread but here's some more info for anyone else looking for the same:

Your car's alternator ampere rating determines how powerful an amplifier you can install. Multiply the ampere rating by 40%, and you'll get a rough idea of how much reserve current capacity your car's system has. Next, you'll need to calculate the approximate current draw of the amplifier you're considering installing.

To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 2 channel amp rated at 300 watts RMS per channel would be 600 watts). Double it to account for amplifier inefficiency (600 watts X 2 = 1200 watts), then divide by the average output Voltage of an alternator, 13.8 volts (1200 divided by 13.8 = 87 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (87 amps divided by 3 = 29 amps). The result is the amplifier's approximate average current draw.

A fast-and-nasty way to ballpark an amplifier's current draw is to divide the total fuse value of the amp by two. For amplifiers with multiple fuses, the rating of all fuses provided with the amp must be added together. This will likely produce a significantly higher estimate than using the proper formula. Although inaccurate, this will err on the side of safety.

Finally, compare the amplifier's approximate current draw to your vehicle's reserve current capacity to determine if the electrical system can support the amplifier.

If all those numbers are a bit much, here's a simpler way to think about it: an alternator capable of producing 65 amperes is usually adequate for systems up to 270 X 2 watts RMS. A compact car with a 35-amp alternator can accommodate around 150 X 2 watts of power, while a Sport Utility with a 145-amp alternator can handle a 600 X 2 watt system.

If you want more power than your alternator can service, you will have to consider having your alternator rebuilt for higher output — or invest in a high-output aftermarket alternator. Installing a second battery won't help — that only allows you to play your stereo for long periods with the engine off. But, remember that any system playing at one-third volume is drawing considerably less current than the same system at three-quarter volume, and may not need a charging system upgrade if the volume levels are kept reasonable.

If your system needs more current than the alternator can supply, it starts to grab current from the battery — not a good thing for your car or your music!

Here are a couple of warning signs to look for:
your headlights dim in time to the music when you crank it up loud at night;
your bass sounds great when you first turn it on, but gets mushy and less powerful within a minute or so.

One easy, effective solution is installing a capacitor. Heavy-duty capacitors connect to the power cable (just before it reaches your amplifier) and act as a buffer zone between your amp and your car's electrical system. They store up a reservoir of power which can supply the amplifier's peak demands (like a kick drum beat) without having to pull current from the battery.

Source: www.crutchfieldadvisor.com

 

[snyper1982]

just in case you pressed the wrong key ill correct this for anyone in the future whos needs the info
***Wattage = Amperage x Voltage***

Thats great, but its not what the original poster asked. He asked how to figure out his amps using his watts. All the formulas a very closely related. If you ever need one, just do a search for Ohm's Law.