Looking for info on the Alternator

[iamgnat]

Hello,
I'm curious about the Smart (fell in love with the idea when we saw them in Europe years ago) and am going for a test drive next weekend.

My current vehicle is a Ford Escape that I have done some involved modifications to (amps, speakers, 250AMP Alt, lots of sound deadener, and a computer), but it is killing me commuting to my new job (~16MPG being generous).

My problem is that with any new car I look at, i'll want to upgrade the speaker system and install a computer so that i'll enjoy spending 2 hours a day in it (otherwise i'll keep driving my Escape).

Looking at the Smart, I doubt i'll look for as much power for the stereo as I have in the Escape but i'll want an Amp that can give me a good clean sound as well as adding a 8-10" sub. Then, like in the 'scape, i'll run the computer directly through the Amp.

Since it will just be for commuting, my thought is to build a box that will take up most of the storage area that will hold the Amp, Sub, and the computer.

So my main concern is how much have they skimped on the Alternator to reduce the HP draw for better MPGs. Does anyone know A) how many AMPs the Alt puts out and B) an idea of how much is left over?

My driving habits are bad enough that I don't need adding a high output Alt to draw it down even more since the main reason to look at a Smart is for it's gas milage improvement over my Escape.

Thanks,
-dave

[doc540]

dave, if you design that sub system right you can get it to propel the Smarty and make up for any mpg losses with an alternator mod.

[iamgnat]

I'm not into that much bass. ;)

My current sub is only 6.5" (I like the factory look and didn't want to lose the storage space). All I want is something that will fill out the acoustic range and have a bit of bunch on the deep notes.

-dave

[evoluzione]

straight from the owner's manual:

alternator: 14v/90a

hope this helps.


regards,

ken

[iamgnat]

Great info thanks.

Now the big question is how many of the Amps are unused.

Thanks,
-dave

[evoluzione]

Originally Posted by iamgnat

Great info thanks.

Now the big question is how many of the Amps are unused.

Thanks,
-dave

well, when the car is running it uses them up as fast as it can make them

seriously, i don't know what the draw is but you could run some quick calculations to get a rough estimate.


regards,

ken

[24-42]

Suggestion;

Look into an "Optima" battery to replace the vehicle battery.

A 34/78 Optima will fit in the box, not only without alterations to the box but the holddown still fits. The(center) posts of the Optima are reversed but the positive cable is long enough to reach and the manf. provided another ground post (chassis) for just such a situation (even a second nut on the second stud) for the short ground cable.

Read up on the Optima, I have the "Red top",

As a "Proof is in the pudding", I found the starter spins faster and the car starts quicker.

Look at the graph for output vs time. This should answer your needs to power the 'Add-ons' with peak ability
Donald LaFavor

Donald LaFavor

[jwight]

Anybody familiar with the smaller batteries M-B put under the rear seat of their E series diesels? Very compact yet enough power to crank a diesel in the winter. Wonder if that's an alternative down the road?

[Fredvon4]

Hey Dave... the size of the Smart, the available space for big amps to drive big woofers suggest that your size and power needs to enjoy the same sound stage loudness and quality will not require more then the stock system can deliver

A 90 Amp rated alternator only can deliver that amount of amps at it's highest expected RPM and very cold temperatures. As rpm is reduced and temperature is raised the real output is DRAMATICALLY reduced in every automotive alternator ever made...

So practically speaking this is a typical system and at normal operating temp 180~200F and at cruise speed of 70mph motor rpm is 3250 and alt rpm is in the 5000~6000 range... the heat de rating means you should see about 65~70 amp max output

At night with high-beams on, heater motor or A/C blowing and all systems energized (fuel pump, black boxes etc) the engineers sized the battery and alt to have 20%~40% overhead... lets assume (becaus none of us know yet) that there is 35amps of normal operation draw from the 65~70 available

The only time amp draw exceeds system design power is starting. During starting about 100~300 amps are demanded from the battery before the alt energizes and then it must replenish the battery...

The typical voltage regulator will allow up to 14.7~8vdc to recharge the bat and should fall back to 13.8 to 14.2 most of the time.... your higher draw from the stereo amp will be sensed and the regulator should increase back to 14.7 vdc

Only you know the max constant watts or amp draw from the system you are thinking...

I personally think if you want good clean sound it can be done with low amp draw....and well within the available power...

Do you know ohms law and how to compute how many amps you need from the watts rating of your amp?

Watts (power) = volts X current (amps)
or said another way Watts / Volts = Amps

To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 4 channel amp rated at 100 watts RMS per channel would be 400 watts). Double it to account for amplifier inefficiency fo 50% (400 watts X 2 = 800 watts), then divide by the average output Voltage of an alternator, 13.8 volts (800 divided by 13.8 = 58 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (58 amps divided by 3 = 19 amps). The result is the amplifier's approximate average current draw. In short, a 400 watt class A/B amplifier draws about 19 amps when playing music!

Most people use a class D amplifier for their subwoofers, which are somewhere around 90% efficient, not the 50% figure I used for the class A/B amplifiers in the example above. So a 1000 watt class D subwoofer amplifier draws about 1100 watts at full power (rarely, if ever happens), and would draw somewhere around 27 amps while playing music. That's about 46 amps (19+27) of current draw while playing music - pretty loud. Again, since music is DYNAMIC, these numbers aren't constant, and will be lower most of the time, giving the alternator a chance to charge the battery!

Now..... if you are one of those nice young men running around town sharing only the bass thump with the rest of us two blocks away...well then I hope your alt melts down fast...really... it annoys me to not get to hear all the instruments and vocals...grin

Don't ask me about stiffinging caps... if you size the system and feed lines properly there is no need for 1, 2, or 5 Fahrad capacitors!

Here is some very good info and a great web site for car audio stuff

http://www.the12volt.com/installbay/...TID=73496&PN=1

[iamgnat]

Originally Posted by 24-42

Look into an "Optima" battery to replace the vehicle battery.

A different battery does little for you in this case. Using a deep cylce (I have a yellow top in the Escape) will let you run the battery down farther without damaging it, but if you are using more Amps than your alternator can produce the battery will discharge and you'll be SOL without a set of jumper cables ;)

The difference you notice in cranking is probably that the Red Top offers more Cold Cranking Amps that the factory battery. Therefore the starter can get more energy, spin faster, and start quicker.

-dave