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    Scarenius's Avatar
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    Judging an amp by its fuse rating

    Ok, this has been gone over again and again, so I spent a lot of time thinking about this at work, and here is what I believe.

    While it isn't a 100% effective way of determing an amps power, it IS a good way of getting a general idea of the RMS power an amp can do before the fuse blows. Volts * amps = watts.

    Example:
    Power Acoustik Gothic OV2 1200
    270.2 @ 4Ω RMS
    300.2 @ 2Ω RMS
    600.1 @ 4Ω RMS bridged

    Assumption:
    My Power Acoustik has two 30 amp fuses. Assuming I have only 12 volts, and this amp is at 100% efficiency, and doing 1Ω, I will have 12*60 = 720 watts power bridged. Divide that in half and you get 360 watts per channels constantly going out of the amp before those fuses gives out.

    Prediction (2 channels):
    This isn't the case, instead it's a 2Ω load per channel, I have 14.4 volts, and being at full gain, I'm going to call it 85% efficiency for example.
    14.4*30 = 432 / 2 = 216 * .85 = 183.6 watts constant per channel.

    Prediction (Bridged in series):
    Now, let's bridge it. I have 60 amps, 14.4 volts, 85% efficiency, and a 4Ω load.
    14.4 * 60 = 864 / 4 = 216 * .85 = 183.6 watts.
    Okay, now my amp is REALLY over-rated. What the hell? That is not right.

    So, where does this amp stand? If I can, I will get it benched. It's a long drive to somewhere that can accurately do that, so it could take a while. The only place close attaches them to a 25 amp power supply, and wonders why they never get far past 300 watts.

    Example 2: Mobile Authority (lesser MA Audio) Rockbox.
    25x2 @ 4Ω
    Bridgable? Some say yes, some don't, I don't know if I want to try.

    It has a 5 amp fuse.
    at 100% efficiency, 12volts, and 4 ohms, I should get 15 watts / channel out of it.
    at 85% (full gain), 14.4volts, and 4 ohms, I should get 15.3 watts, RMS.

    My only conclusion is they are assuming roughly 100% efficiency, 14.4 volts, and the lowest impedance possible.

    My other conclusion, although I can't really back this up, is that multiplying the fuse rating by 6 will give a decent RMS rating at impedance.
    30*6 = 180 / channel, or the wattage of my Power Acoustik at 2 ohms.
    5*6 = 30 (15 / channel), or the wattage of my Rockbox.

    This is my thoughts regarding fuse ratings of amplifiers with UNREGULATED POWER SUPPLIES. Amps with DC/DC converters can work at far higher voltages, and this would drastically change how this system works.

    My usual 2 cents.

    UPDATE: I was not able to bench my amp. Building a sub box is first priority. That's a different story. Edited for coherency.
    Last edited by Scarenius; 11-07-2004 at 12:00 PM.



    Current Setup
    "Power is probably the least efficient way of increasing SPL."
    - Jmac




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    Sleeklsc's Avatar
    Sleeklsc is offline CarAudio.com Veteran



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    Re: Judging an amp by its fuse rating

    im way to drunk to even begin to even comprehend what you just posted...i'll try it again tommarow.



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    Moe Lester's Avatar
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    Re: Judging an amp by its fuse rating

    #1, 2 30 amp fuses and 12v is 720w @ 1 ohm, 100% efficiency, not 360

    full gain or not, you arent getting 85% efficiency. Since you are talking about bridging, im guessing its a class A/B 2 channel?




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    Scarenius's Avatar
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    Re: Judging an amp by its fuse rating

    Yeah, I didn't quite make that clear enough. Editing over, since I did that at 2 am in the morning.



    Current Setup
    "Power is probably the least efficient way of increasing SPL."
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