Electrical Load

[Jtsky 10+ year member]

I am curious how the load on your cars electrical sytem changes depending on how you wire your amps. Lets say you have an amp that does:

250 wrms @ 4 ohm

or

400 wrms @ 1 ohm

The first thought that comes to my mind is more wattage = more load on electrical system, but for some reason I am doubting this. Can anyone help me out here? Is it true that either of these setting would have equal load?

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[hzsogood 5,000+ posts]

voltage and impedance.. The lower the impedance the more ur charging system is pushing in due to less resistance

 

[Jtsky 10+ year member]

Okay, so more wattage = more load, and an amp at 1 ohm is more draw than an amp at 4 ohms.

Thanks

 

[yacob.naif 10+ year member]

That's a good question, and while you're on the topic, i've always wondered why it's possible to set amplifier gains correctly while no speakers are connected to the amplifier.....? Especially when using a dmm to set them.

I think i understand why it works ok with an o-scope, since clipping is a function of the amplifier's pre-amp, and not the actual amplifier itself, but i don't understand how you can use a dmm to set gains with no speakers connected, if the power's going to be completely different with speakers connected.

 

[qtipextra 5,000+ posts]

That's a good question, and while you're on the topic, i've always wondered why it's possible to set amplifier gains correctly while no speakers are connected to the amplifier.....? Especially when using a dmm to set them.
I think i understand why it works ok with an o-scope, since clipping is a function of the amplifier's pre-amp, and not the actual amplifier itself, but i don't understand how you can use a dmm to set gains with no speakers connected, if the power's going to be completely different with speakers connected.

Because voltage is a constant variable in this case, and the amperage changes when the resistence decreases. So, when you set gains with a DMM, your setting at a certain voltage that will remain there. Whereas, when you add a resistence, that detirmines how much amperage. Remember, Power is an equation with all three things considered, Voltage, Amperage, and resistence.

 

[PowerNaudio 10+ year member]

the lower the impedance load the more current it will draw from your amplifier. if youre worried that your current electrical system is not up to the task. find the continues amperage of your alternator and add the fuses on the amp, if the fuse amperage exides the alternator output in amps, then its time to up grade your alternator or just rund the amp at a higher impedance load. that way you dont put too much stress on your electrical system.

i would not set the gain of an amplifier without a load, use ether a pasive load or a reactive load. for the simple fact that most amp use fedback from the amplifier output to the voltage amplifier, if you dont have a load then the adjustment made could be inacurate.

 

[Jtsky 10+ year member]

What would be the rule of thumb number, of how many watts you can run with an 80 amp alt? I know that there are many variable, but could you give an estimate.

 

[yacob.naif 10+ year member]

Pretty sure it's amperes x voltage = wattage

not sure how efficiency factors in, tho

as in, i'm not sure how to figure out how big a class d you could run vs a class a/b vs a microwave, but i guess it's a rough estimate!

 

[PowerNaudio 10+ year member]

12v x 80amps= 960watts.

remember you have other things in the vehicle ******* up juise out of that alternator as well so there is less power than that avalible for your amp.

 

[Jtsky 10+ year member]

I am confused about one more thing now. Doesn't the electrical system ussually run more like 13v?

 

[PowerNaudio 10+ year member]

true a healthy electrical system should run in aroun 14.5v

bringing the total wattage a little higher then the one i calculater earlier.

you should check your system and do the math for your vehicle.

 

[RandyJ 10+ year member]

BUT, remember that your vehicles electrical is pulling amperage as well. Your amp also will not always pull maximum amperage.

On a stock alternator of 80A, I would say devote 25-30A of it to stock electrical needs.

 

[Jtsky 10+ year member]

so

65 amps x 14.5v = 942.5 watts

and that is the most I should run if my electrical was totally healthy and putting out 14.5 volts?

 

[PowerNaudio 10+ year member]

yep!, if you run anything higher youll start getting things like head lights diming interior light diming. and on extreme cases your alternator would go out. since its powering everything in the vehicle including charging the battery, runing the ignition system and runing your stereo system.

 

[Jtsky 10+ year member]

Thanks for the help guys.