Amp draw and effeciency

[slim j 10+ year member]

I have a question about how to estimate amperage draw and effeciency. This thread may get bumped to competing since it is about as much about MECA as anything else.

I have minimal understanding of electronics but I think that power = voltage x current. Therefore, using a 40A inline fuse with 14.4v, the power made should be 576 watts. Well, let's say that the fuse could handle 60A for just a couple seconds, then you would have 864 watts.

Using this info, how would you determine what is the best amp to use? For instance, if I bought a 3000w amp, it wouldn't do any good because the best I could do is 576watts/864watts.

Is this line of thinking correct, or how exactly does it work?

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[slim j 10+ year member]

??

 

[prochobo 10+ year member]

It takes awhile before the fuse will blow. I had a 50 amp fuse and I was drawing well over 100 amps and it lasted over 30 seconds.

An efficient amp will do well playing on the fuse, but you aren't restricted to how much power you can use based on your fuse, to a point. You can run 3000w off of a 50 amp fuse and get a burp off for example.

 

[luvinthebass 5,000+ posts]

and most fuses can hold twice their amperage before they blow

 

[slim j 10+ year member]

An efficient amp will do well playing on the fuse, but you aren't restricted to how much power you can use based on your fuse, to a point. You can run 3000w off of a 50 amp fuse and get a burp off for example.

Put even though the amp is 3000w, isn't the power produced limited by the fuse?

 

[luvinthebass 5,000+ posts]

Put even though the amp is 3000w, isn't the power produced limited by the fuse?

Sometimes manufacturers will put a bigger fuse then needed or a smaller fuse then needed, i remember runnin a 1000 watt 45 hz test tone and had a 40 amp fuse inline to the battery and it didn't even blow until after a minute of the tone play.

 

[slim j 10+ year member]

Sometimes manufacturers will put a bigger fuse then needed or a smaller fuse then needed, i remember runnin a 1000 watt 45 hz test tone and had a 40 amp fuse inline to the battery and it didn't even blow until after a minute of the tone play.

Was the amp a 1000 watt amp or did you clamp it to see if the amp was producing 1000w?

 

[Flipx99 5,000+ posts]

I think tommyk uses a orion 2500d with that alpine. I bet he may have some good insight.

 

[luvinthebass 5,000+ posts]

Was the amp a 1000 watt amp or did you clamp it to see if the amp was producing 1000w?

it was a 1000 watt amp and i had a dmm and set the gain to hit 1000 watts at 2 ohms and the sub was playing also

 

[CBFryman2 5,000+ posts]

DMM will not tell you how much power you where producing. //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

Theoretical amp efficency of 100%, you have the voltage rail to 45v and impeadance rise to 10ohm...you are only going to be producing 202w and the amp will only be drawing ~14a with 14.4v input.

Also, Fuses are technically rated to wattage with an instantanious blow amperaged rated at three times what the voltage they are sapposed to be used for.

ie, instantanious blow amperage on a 12v fuse will be rated at 36v (in most casses). So if the fuse is rated to blow at 50a, it is likely rated at 36v. That is 150a before it will blow instantly with 12v. Above 50a will be a slow process before it blows. Or it may not blow at all as the current may be with in tollerance. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

And all that is one of the reasons why MECA = Ghey. No way to regulate it unless you make everyone use the same exact fuse...and then you will have to have a fuse with very tight tollerances for it to be "Fair." Tight tollerances on something like fuses = $$$$

dB Drag FTW.

 

[slim j 10+ year member]

So....with a 40A fuse, I will be looking at best case

120*14.4 =1728 watts if the amp was 100% effecienct. In reality most are 70% effecient. However, just because it is waisting amps, it is still drawing them. The whole thing is, I may try to compete in MECA since I may be moving to the southeast (don't know where) and there is alot of MECA shows. I was curious on what would be a good amp to get for the classes that only allow 40A fusing for 1 10. 0-500 class.

Would I want the most effecient 2000w amp, or the highest rated amp I could afford?

 

[slim j 10+ year member]

??

 

[Type699 10+ year member]

A fuse will not limit the output of an amp. Say you have a 3000w amp, that would normally use a 250 amp fuse. Put a 40 amp fuse in it, and it will not limit the power to 500 watts. You will be able to play the amp just fine. It'll just blow the fuse when the power level is high enough to pop the fuse. Most fuses I have seen will blow with double their rated power for 2 seconds, but I am sure there are variations. I've had a 100 amp fuse blow that was by the battery, but yet a 60 amp next to the amp didn't go first.

Anyways, typically amp efficiency ratings aren't published, so it'd be fairly hard to shop for an amp that way. If you simply shop for an amp w/ a 40 amp fuse, and happen to see some that are rated at 2000w, now you know that isn't possible. Power in has to be greater than power out. Amps don't create power, they use it.

I'd just buy the best amp that you can afford that'll keep you in the class you want to compete in.

 

[slim j 10+ year member]

I'd just buy the best amp that you can afford that'll keep you in the class you want to compete in.

You clarified a lot, thanks.

I guess that could be any amp. I think the rule is by the fuse.

Is there anyway to estimate at what power levels the fuse will blow?

 

[thch 10+ year member]

i've made long posts about similar topics in the past. in short, there are typically too many unknowns to "benchmark" an amp outside of a test facility.

efficiency curves for an amp will be primarily based upon class. at low power, amps are less efficient (it takes some power to keep the amp on) at high power, amps are typically more efficient.

switching amplifiers (class D and variants) offer high efficiency from low to high power outputs. sometimes arbitrarily close to ideal.

linear amplifiers (class A, B, ect...) will give higher efficiency at high power then low power, but still will be low compared to class D. a 30% efficiency @ 1/3rd power is not unheard of, with a 60% efficiency @ full power. (as you bias more towards class B, distortion increases but so does efficiency)

i've never heard of this 36V vs 12V rating scheme for fuses. its a thin peice of wire, there should be 0V across it. IIRC the relevent metric is the I2t time which gives an indication of how long a minor or major overcurrent condition can exist before the fuse opens.

class A will be especially low at any power output.