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-   -   Rockford Fosgate Power 20001 bd amplifier power rating?? (http://www.diyaudio.com/forums/car-audio/42302-rockford-fosgate-power-20001-bd-amplifier-power-rating.html)

pachoorion 9th October 2004 11:29 PM

Rockford Fosgate Power 20001 bd amplifier power rating??
 
I was looking at the specifications and it says this amp produces 2000 watts RMS x 1 at 1 ohm. But, if you go to the bottom of the page, the fuse rating is 250 amps. If the fuse rating is 250 amps, wouldn't this amp produce 2,500 watts RMS x 1 at 1 ohm??
Thanks.

http://www.crutchfield.com/S-Myx7FKN...arch=amplifier

clayton 10th October 2004 11:16 PM

It is possible that you will get 2500 watts rms out of this amp. Remember Fosgate underrates there amps. I have a 500 watt rf (model 500.2) with a 70 amp fuse. The birth cirtificate says it does 752 watts rms all channels driven.

bkoopman 11th October 2004 06:50 AM

Ah-ha, another unsuspecting victim of Rockford's tricks! I love the company, but they no longer overrate their amps. They did for a very long time, so they have a lot of people thinking they still do, and buying according to that belief... good deal for them, if I do say so myself.

Fuse size and power are related, but you really can't judge one by the other, especially with car amplifiers. You should really only expect the 2000w out of this amp. Even if the amp is drawing the full amount of current, you still have to take things like efficiency into account.

- Sara

pachoorion 11th October 2004 03:35 PM

I was talking to a friend about this and he provided me with the conversion from watts to amps and his opinion = "(Watts / 12) x 1.1 = actual DC amps. So 2000 watts would need 183.3 amps. The fosgate is rated for 250. Add ten percent (this is the normal amount concidered to be unusable in any amplifier) and your total wattage would be 2200. This equates to 201 amps. I would say it is pretty safe to assume that the extra 49 amps would be pretty clean power. That is about 450 extra watts. I would say that the amp will easily handle 2400 watts RMS." Can someone verify this??








Qtd. by MikeGett

all_about the12 15th October 2004 08:49 AM

Quote:

Originally posted by bkoopman
Ah-ha, another unsuspecting victim of Rockford's tricks! I love the company, but they no longer overrate their amps. They did for a very long time, so they have a lot of people thinking they still do, and buying according to that belief... good deal for them, if I do say so myself.
- Sara


when was the last time you bought a fosgate amp, or knew someone who bought one? mine was born ont he 30th of april 04 and its the p2002. (200 watt per chanel, 2 channel amp.) and it has a max power of 813. total rms watts at two ohs of 271 rms... and 90 at four. so when did they start giving you what you paid for, and not underestimating?

tsmith1315 22nd October 2004 04:59 AM

Quote:

I was talking to a friend about this and he provided me with the conversion from watts to amps and his opinion = "(Watts / 12) x 1.1 = actual DC amps.
Well, sort of. Power(Watts) = Voltage(V) x Current(amps). I assume the 1.1 factor is to account for 10% inefficiency. However that is power dissipation for the voltage drop across a given element or system while passing that amount of current.
Very poor wording on my part, but you can't exactly calculate an amplifier's power output from the amount of current it draws without more detailed information. You can make an estimate if you know the efficiency of the amp.

We can calculate the current through a 1ohm load dissipating 2000W. That's the square root of (power/resistance.) Which turns out to be 44.7 amps. Through the one ohm load.

The Crutchfield page listed says the amp is 75% efficient. We don't know under what conditions this 75% efficiency was measured. But that's all we have to work with, so the amp will have to draw 2667 Watts to deliver 2000 Watts to the speakers.
The output power is rated at 14.4VDC input. 2667 Watts drawn from a 14.4V supply would require (current = power/voltage) 185 amps. The extra 667 watts are dissipated by the amplifier as heat.

IF (that's a big "if") the amp would continue to increase power in a linear fashion with the current drawn from this point...
AND IF it were to need to draw 250 amps from the batteries,
AND IF the batteries/alternator could deliver it,
AND IF there were still 14.4V at the DC input on the amp,
AND IF it were still 75% efficient at this point,
AND IF it were driving a load of exactly one ohm,
AND IF we lived in a perfect world...

The power INTO the amp would be 250A x 14.4V = 3600W. 75% of that, or 2700W would be delivered to the speaker after the amp was done amplifying, and 900W would be heating up your trunk.

BUT, the fuse is for protection. The amp isn't necessarily fused at the amount of current needed for rated output at minimum load. We can only reasonably assume that it's specifed at a margin of safety:
1) above the current needed to provide 2kW output while driving the maximum 1ohm load, but
2) below the current needed to do serious damage to the amp.

I've seen amps almost melt before blowing a fuse.


Tim

MEXXX 22nd October 2004 02:11 PM

Just an FYI about fuses.... Most fuses are made to "blow" at 200% of their rating over X amount of time. So a fuse rated for 250 amps could easily handle 300 amps.

Trying to figure out an amps power output by looking at the fuse rating will be even less acurate than the power rating "stamped" on most amps.

tsmith1315 23rd October 2004 05:09 AM

Quote:

Trying to figure out an amps power output by looking at the fuse rating will be even less acurate than the power rating "stamped" on most amps.
You said that way easier than I did...

joesch1999 8th May 2011 11:49 PM

hmmm sounds like common sense to me I could build a amp put a 500 amp fuse in it and call it a 5000 watt amp rockford fosgate is not half the company they used to be, I never thought there amps were that good anyway, back when rockford was at there peak you could pick up a ADCOM car amp at the same price as rockford and get three times the sound quality out of the adcom, I know some people will say yeah but rockford bass is the best, yeah it's loud bass, question is, is it clean bass? I say no not even close to adcom.


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