# Looking for information on Supermac Spectrum 24 PDQ+/PSU Ratings

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Joined: Jan 15 2012
Posts: 187

Does anyone know if the Supermac Spectrum 24 PDQ+ will work in a IIsi? I have the required PDS=>NuBus adapter (FPU )

My main concern is power consumption. I am hoping someone can help me understand the situation better. I know the IIsi has a 160W PSU. I have read varying reports on the power consumption of the PDQ+. Low End Mac says the card will work on any NuBus Mac but the power info I've found for the card is 2.5A @ 5V & 2.0A @ 12V (old AF thread actually - http://www.applefritter.com/cgi-bin/YaBB/YaBB.pl?board=other;action=print;num=1058821562)

I've never taken the time to learn what those specs really mean so the above thread is a little lost on me. I mean, I know the generally idea. Consumption must be less than PSU threshold and so forth. I guess my question is, how would one compute that so they wouldn't have to ask a forum every time they were looking to do an upgrade?

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Joined: Feb 20 2013
Posts: 20
Re: Looking for information on Supermac Spectrum 24 PDQ+/PSU ...

V = volts
A = amperes (amps)

Consider the paradigm of a water pipe -- like the plumbing in your house. The amount of water in the pipe is Volts. The amount of pressure in the pipe is Amps. More volts = more electricity. More amps = more "pressure" -- which basically translates to a faster flow rate.

W = Watts

The Watt is a measure of Power. How much electricity at what pressure.

So: V*A = W
OR: W/A = V
OR: W/V = A

Volts multiplied by Amps gives you Watts. So, natch, Watts divided by Amps gives you Volts, and Watts divided by Volts gives you Amps. Yay math.

ARmed with that, you should be able to calculate exactly half of what you need to know -- which is to say, you should be able to multiply out how many Watts at 5V and at 12V your card pulls (add those two together to get a total). What you need to find out, though, is how much "room" you have with that 160W power supply to begin with -- how many Watts are being pulled from it already by the existing circuitry?

You will need a multimeter for that (which, if you're dabbling in electronics, is something you should have to begin with anyways) -- or separate ammeter and voltmeter (much more expensive when a multimeter can do both, although not at once). When using one, the meter must be in series (in-line) with the circuit. With the other, it must be in parallel (not in-line but more like bridging). That's the part I can never ever keep straight myself! I want to say that the voltmeter is the series one, but I don't remember... all I can say is that I have yet to need an amp measurement.

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Joined: Jan 15 2012
Posts: 187
Re: Looking for information on Supermac Spectrum 24 PDQ+/PSU ...

Thanks very much! Makes sense. I will pick up a multimeter today and see what I can find out.

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