Thread: Power supply calc

Those calculations are done correctly. The 'puta CPU doesn't - or rather, shouldn't - power the larger external peripherals.

Monitors, scanners, etc. should all have their own power supplies.

Speakers can be powered off the input lead, but for any volume you need 'em with in-built amp... which requires another external power supply.

The USB ports typically can only supply 500mA, which is enough for small USB devices (mouse, keyboard, etc.) but even then if you're running quite a few off, say, a 4-in-1 USB adapter, the adapter will probably need power.

This is also why many external HDDs tend to not work properly when plugged into a USB/eSATA port without a supplementary power supply.

Your right in that Skew but it is still electrical current that sends the messages that travels the connections regardless of how small it is even to speakers. All leads connected to any device even WiFi devices also need power it does all drain. The ideal way to see this is a laptop with battery running many have system built in to limit power usage for devices when getting low, screen deminishes etc

Originally Posted by Skew ChiDAMN!!

The USB ports typically can only supply 500mA, which is enough for small USB devices (mouse, keyboard, etc.) but even then if you're running quite a few off, say, a 4-in-1 USB adapter, the adapter will probably need power

They're only supposed to supply 100mA unless the device asks for more, so a 4-port unpowered hub can happily run off of a powered USB port with 4 low power devices on it.

No-one takes much notice of this though.

The hard drives get around the 500mA limit by wanting to be plugged into 2 powered ports, thus getting 1000mA.

Originally Posted by wheelinround

Your right in that Skew but it is still electrical current that sends the messages that travels the connections regardless of how small it is even to speakers.

This is true. However, you're talking about the data signals which are only very low wattage and are included in the calculations for the relevant sub-systems anyway.

eg. the signal to the monitor is generated by the Video Card and as such is included in the VidCard's allotment.

That calculator does cover USB and firewire devices, but it also says in the fine print "only tick if these devices are powered off the mobo" or something like that.

Originally Posted by Dropcat

They're only supposed to supply 100mA unless the device asks for more, so a 4-port unpowered hub can happily run off of a powered USB port with 4 low power devices on it.

No-one takes much notice of this though.

I guess I should've said that "most modern computers" will only deliver 500mA. One of the advantages of an interface being abused, as USB has, is that the mfrs make allowances.

Originally Posted by Skew ChiDAMN!!

I guess I should've said that "most modern computers" will only deliver 500mA.

Sorry, I wrote that poorly. You normally get 100mA, but if the device asks nicely (power negotiation) then you can get the full 500mA. The idea is to prevent overloads on the power supply when you start up, the hub can switch ports on 1 by 1.

Some ports don't follow the standard and hand out full power to all & sundry, which is why dumb chargers work on some PCs and not others. Others do it if the data lines are shorted (iPhone etc).

USB 3 will let you have 1000mA, I think.

That's good tool. I've used it last year when I was buying new PSU.

About USB, they consume very little power and I never take them into consideration.

CPU, graphics, HDD, ram and plus 100 watts always work for me.