Trying to get Clarification on 4500 supIV power consumption

[jrhofman]

I'm trying to get the AMP draw of the Supervisor IV and am having some trouble. IF I go to the Cisco Power Calculator it says the SupIV draws 12.08 amps. If I look at the data sheet (hard to find) it says 1.61 amps. You need to search on "supervisor IV power consumption" to find a data sheet.

Anyone have any insights into this discrepancy. I'm trying to calculate power and HVAC for a customer and want to make sure I'm accurate. Cisco Pre-sales was not much help......

If you do the same thing for a sup32/6500 the data sheet and the power calculator match up.

[ougryphon]

The current draw listed on the power calculator is the current draw from the PSU at 12 VDC. The current draw on the data sheet is at 120 VAC (or 240 or 90). Using Power = current x voltage, a voltage 1/10th of 120 VAC would use approximately 10 times the current. Hope that helps.

[jrhofman]

I guess I'm not tracking....

In the calculator I selected a 4503 SupIV with 100-120AC input. At the bottom of the calculator output (configuration details) it shows 12.08A output for the sup IV module. I don't see anything about 12 VDC.

[ougryphon]

Yeah, they don't actually list PSU output voltage - you have to calculate it from the output power and the output current. I've already closed that window, but the calculator shows used power and used current. PSU output Voltage is power divided by current and equals exactly 12 volts.

If the SupIV card really drew 12.08 A at 120 VAC, it would be drawing 1.5 kW of power.

[jrhofman]

Thamks for your feed back. I'm not much of an electrical engineer on this power stuff. So do you feel that the power calculator is accurate at 12.08 or the data sheet a 1.62 amps.

The 6500 supervisors are at 6.x amps for the sup 720 and 3.x for the sup32. Seems like a big spread between the 4500 sups and the 6500 supervisors.

[ougryphon]

I would say both figures are accurate. If you are calculating current drawn from a power supply, you would use the 12.08 Amp number. Since the power calculator is used for sizing power supplies, this is the figure it gives you.

If you are calculating current drawn "from the wall" you would use the 1.61 Amp number from the data sheet. It appears that this number takes into account the inefficiency of the power supply. Since you are trying to spec the mains circuit, you would use the 1.61 Amp number.

One of the pages also listed heat dissipation which would be good for your HVAC calculations. But in the future if you don't have that number, all you have to do if multiply voltage times the current to get the power the device is using. For example, 1.61 A times 120 VAC = 193 Watts. Most of a device's power is dissipated as heat, therefore you will have a fairly accurate measure of heat dissipation.

I hope this clears things up a bit.

-Patrick

[jrhofman]

I does help and I appreciate you're feed back.....

[ougryphon]

No problem. I'm actually a EE who has been thrown into the role of network engineer, so this power stuff is right up my ally. I hope I solved your problem, but if you have any other questions, don't hesitate to ask.

-Patrick