amp efficiency

[bigjsurdaddy]

when i did my calculations i did it for 70% and gave my self room for like 10% less effeincy. so i think i will still be good.

[IH8PunkRok]

i dont get how that works... *note* im not saying anyone is wrong

but why does it become less efficient with less resistance? makes no sense to me

[bigjsurdaddy]

they did another clamp test on smd a while back. those were the first 1500d's. i think they got a little better over the last 3 years. he's the link.

http://www.stevemeadedesigns.com/board/ind...showtopic=50753

[skittlesRgood]

they did another clamp test on smd a while back. those were the first 1500d's. i think they got a little better over the last 3 years. he's the link.

http://www.stevemeadedesigns.com/board/ind...showtopic=50753

ya i know, but they dont say efficiency on that test. i just wanted to show you efficiency numbers.

[bigjsurdaddy]

ya i know, but they dont say efficiency on that test. i just wanted to show you efficiency numbers.

and that does help. but i think i left enough head room for what i'm doing for the effiency to drop to about 59 or 60%.

[kirill007]

The amp efficiency depends on the amp used, but usually( in general) the amps efficiency drops if the impedance drops.

[finkster]

HEAT people HEAT....

[Decaf]

i dont get how that works... *note* im not saying anyone is wrong

but why does it become less efficient with less resistance? makes no sense to me

transfering heat in mosfets

diodes

transformers

all have resistance/an affect on efficiency

Edited December 31, 2009 by Decaf

[cqtama]

yes im sorry didnt mean to mislead, was just trying to explain some basics.the amp puts at more power at lower ohm loads but will have more of a draw. so you need to up the electical system (batteries ans alternators) a little bit more

[Boon]

Amps are less efficient at lower ohm loads. They make more power but they take even more power to do so.

For example, completely made up but hey...

At 4 ohms, an amp might make 1000w and require 100A of input current to do it.

At 2 ohms it might make 1800w and require 200A to make it

Then at 1 ohm you might see 2400w but you will see close to 300A being pulled.

This, as mentioned above, is mostly due to inefficiency in the MOSFETs/Transistors and transformers used in the amp.

If you look at the specification RDS(on) for a MOSFET - this is the Resistance Drain - Source for a FET. It presents an in-line resistive load to the electricity in the amp.

Say we have 20A drain - source and the FET has an RDS of 5 milli-ohms.

The FET will drop 0.1v across it.

If we increase the current across the part to 60A we are losing 0.3v instead.

This effect is most pronounced in the power supply section where the parts are carrying heavy current at the supply voltage (12.x or whatever) so a loss of 0.3v equates to a loss of approximately 2% power.

This doesn't seem like much but it doesn't allow for the increase in temperature either. As the junction temperature rises the RDS increase as well, sometimes by a factor of 2 or even more. So suddenly you're losing 5% of your power just in heat going through the power supply section, and you see how it starts to add up.