Strain on electrical vs system impedance.

[RSDXzec 10+ year member]

I've been told before that a low impedance system will cause strain on the alternator, I don't know how true that is. I know on an amp it causes more strain but does it push the alternator if the amp can handle the impedance?

My problem is I have 3 12"s with 4ohm voice coils. Right now I'm running a single sub at 300Wrms at 4 ohms off one amp, and 4 4ohm speakers at 180Wrms on another amp. I've done the big 3 upgrade with 2AWG wire on a 50A alt.

I'd like to wire up the 3 subs which would give me a 1.34ohm impedance and my current amp only goes down to 2. So I plan on buying another amp (Class D) which is 1 ohm stable and until then I'll be running 2 subs at 2 ohms with 400Wrms on my current amp (Class isn't stated in specs). When I do get around to it I'll be running 400Wrms at 1.34ohms.

So I'd like to know if at the same power draw, does the impedance of the system alter the strain on the alternator?

Cheers.

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[Imtjnotu 5,000+ posts]

running at lower impedances will draw more current then say running at 4 (by low i mean from 1 ohm and down) but in ur case running 400rms off stock electrical wont harm much really......most cant handle up to 1000rms but its always good to atleast update you battery

 

[RSDXzec 10+ year member]

running at lower impedances will draw more current then say running at 4 (by low i mean from 1 ohm and down) but in ur case running 400rms off stock electrical wont harm much really......most cant handle up to 1000rms but its always good to atleast update you battery

so if under 1 ohm is a problem, 1.34 should be fine. I'm just hesitant because it is an old car and I wouldn't push 1000rms on it.

Most cars have a 70-80 amp alt and mine's only 50 amp, granted my car has much less electrical features than most.

But because I have two amps, and they are in parallel, if one runs at 4 ohms (with 4 speakers) and the other runs at 1.3 would that mean that it's running at 1ohm all together off the electrical?

Would I be better to run the amps in series so that the resistance on the alternator is higher?

Cheers.

 

[maylar 10+ year member]

Watts is watts. The power into your amp is the power out divided by the amp's efficiency. So it's really a question of whether the efficiency of the amp is different at lower impedance, and that isn't always in the specs. So the answer to your question is, "maybe".

Switching to Class D definitely improves effieciency. You might see no additional electrical draw at all. On the other hand, a 50 amp alt is REALLY small.

 

[TitoThePirate 10+ year member]

if its only 2 ohm stable, run it at or higher than 2 ohms

 

[05fronty 5,000+ posts]

wow 50 amp alt, what kind of car?

 

[keep_hope_alive Premium Member]

So I'd like to know if at the same power draw, does the impedance of the system alter the strain on the alternator?

not really. impedance load does affect amplifier efficiency somewhat... but if your system is drawing 400W then that is all the alt cares about.

that alt is really small. that car was not designed electrically for a sound system. you should upgrade the alt to at least 80A.

 

[winkychevelle 10+ year member]

not really. impedance load does affect amplifier efficiency somewhat... but if your system is drawing 400W then that is all the alt cares about.
that alt is really small. that car was not designed electrically for a sound system. you should upgrade the alt to at least 80A.

quick question by your knowledge which amp would be more efficient

A) a 2500w @2ohm amp

or

B) a 2500w @1ohm amp

assuming that they produced exactly 2500w at that exact load on the exact same electrical

 

[keep_hope_alive Premium Member]

quick question by your knowledge which amp would be more efficientA) a 2500w @2ohm amp

or

B) a 2500w @1ohm amp

assuming that they produced exactly 2500w at that exact load on the exact same electrical

depends on amplifier topology and many other factors. assuming both were class D, both are 1 ohm stable (meaning amp A isn't operated at minimum impedance), both have equivalent thermal management designs... i would expect amp A to be slightly more efficient since current output is lower and thus wasted heat should be slightly lower.

it is generally more efficient to have higher voltage and lower current. a fundamental guideline of power transmission.

 

[winkychevelle 10+ year member]

depends on amplifier topology and many other factors. assuming both were class D, both are 1 ohm stable (meaning amp A isn't operated at minimum impedance), both have equivalent thermal management designs... i would expect amp A to be slightly more efficient since current output is lower and thus wasted heat should be slightly lower.
it is generally more efficient to have higher voltage and lower current. a fundamental guideline of power transmission.

say u are looking at a kicker 2500 and a sundown 2500 both class d both running at minimum impedance

 

[knotdrummer88 10+ year member]

what kind of car are you driving that has that itsy bitsy alternator?

 

[RSDXzec 10+ year member]

not really. impedance load does affect amplifier efficiency somewhat... but if your system is drawing 400W then that is all the alt cares about.
that alt is really small. that car was not designed electrically for a sound system. you should upgrade the alt to at least 80A.

yeah it's a pretty bad alt, but I'm making the most of it I guess. I'd like to upgrade but the cost of an alt plus all the work I'd have to put in to make the bracket would be a pain.

Watts is watts. The power into your amp is the power out divided by the amp's efficiency. So it's really a question of whether the efficiency of the amp is different at lower impedance, and that isn't always in the specs. So the answer to your question is, "maybe".
Switching to Class D definitely improves effieciency. You might see no additional electrical draw at all. On the other hand, a 50 amp alt is REALLY small.

nope the efficiency isn't in the specs, though i gather from this thread that if the amp can handle it, it should be ok. Definitely upgrading to class D for this.

what kind of car are you driving that has that itsy bitsy alternator?

It's a 30 year old holden, the equivalent of holden in the US is chevrolet I think.

 

[knotdrummer88 10+ year member]

yeah it's a pretty bad alt, but I'm making the most of it I guess. I'd like to upgrade but the cost of an alt plus all the work I'd have to put in to make the bracket would be a pain.


nope the efficiency isn't in the specs, though i gather from this thread that if the amp can handle it, it should be ok. Definitely upgrading to class D for this.

It's a 30 year old holden, the equivalent of holden in the US is chevrolet I think.

ahhhh ok, gotcha

 

[jolly_26 10+ year member]

say u are looking at a kicker 2500 and a sundown 2500 both class d both running at minimum impedance

Would be hard to say without testing, but it would likely be whichever one is running at highest impedance. There wouldn't be a huge margin in it though.

 

[winkychevelle 10+ year member]

Would be hard to say without testing, but it would likely be whichever one is running at highest impedance. There wouldn't be a huge margin in it though.

well i can say that taking amplifier efficiency out of the equation that 2500w at 2ohm and 2500w at 1ohm will draw the same amperage from the voltage supply