Green / Eco-Friendly

# Idle Power Usage

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• Oct 8th, 2020 3:33 pm
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Sr. Member
Sep 14, 2003
654 posts
Toronto
Has anyone tried to calculate the actual cost of power for a 24/7 device with the ToD prices we have in Ontario? I'm probably doing the calculations wrong, so \$/kwh including the fees embedded in the "Global Adjustment." There's also only so much you can lower your bill by since there's a minimum charge per month for the privilege of being a hydro customer.

Specifically, I'm trying to figure out how long it'll take to recoup the cost of replacing an old 3Com PoE switch (Killawatt says it draws 65w!) that puts full power to each port whether needed or not, and my HP server.
May 23, 2009
2582 posts
Mississauga
videonerd wrote: Has anyone tried to calculate the actual cost of power for a 24/7 device with the ToD prices we have in Ontario? I'm probably doing the calculations wrong, so \$/kwh including the fees embedded in the "Global Adjustment." There's also only so much you can lower your bill by since there's a minimum charge per month for the privilege of being a hydro customer.

Image 7.png

Specifically, I'm trying to figure out how long it'll take to recoup the cost of replacing an old 3Com PoE switch (Killawatt says it draws 65w!) that puts full power to each port whether needed or not, and my HP server.
Your 3Com switch pulls 65w. So 65 divide by 1000 makes it 0.065kW, so 1.56kWh per 24 hours, and 46.8kWh per 30 days. There is a nice calculator here https://www.rapidtables.com/calc/electr ... lator.html

For the actual cost, OEB has the bill calculator(https://www.oeb.ca/consumer-protection/ ... calculator) but the issue is delivery and regulatory charges which are tied to your overall household consumption. Calculating usage for one appliance does not adjust so the bill estimator ends up bring inflated. TOU rates (with 50%, 25%, 25% usage) by itself is \$6.47.

Total Electricity Charges \$34.05
• Off-Peak @ 10.1 ¢/kWh \$2.36
• Mid-Peak @ 14.4 ¢/kWh \$1.68
• On-Peak @ 20.8 ¢/kWh \$2.43
• Delivery \$27.13
• Regulatory Charges \$0.44
HST \$4.43
Ontario Electricity Rebate (-\$10.83)
Total Amount \$27.65

What I personally do is forget about the TOU rates and use my average for the past 12 months; OR my average since the last time rates change.

OEB adjusted TOU rates effective Nov 1st, Alectra (Mississauga) also mentioned in my bill that there was another rate change effective Jan 1st but I cannot figure out what exactly.
Anyway to get my average I take the total cost in my bill(including HST) and divide by total kWh usage. Since the last rate change on Jan 1st my average per month for the last two months is \$0.16 per KWh.

So \$0.16 x 46.8kWh is \$7.49 in electricity per month for the 3Com switch.

Next, just do thesame calculation for the new switch and minus the difference in cost.
[OP]
Oct 9, 2010
2724 posts
Windsor
videonerd wrote: Has anyone tried to calculate the actual cost of power for a 24/7 device with the ToD prices we have in Ontario? I'm probably doing the calculations wrong, so \$/kwh including the fees embedded in the "Global Adjustment." There's also only so much you can lower your bill by since there's a minimum charge per month for the privilege of being a hydro customer.

Specifically, I'm trying to figure out how long it'll take to recoup the cost of replacing an old 3Com PoE switch (Killawatt says it draws 65w!) that puts full power to each port whether needed or not, and my HP server.
A general rule of thumb used is that power drawn = how much it costs you / year. It's not accurate from what I've observed with my power usage, so I use 1.5x. So, a 65w device costs you about \$100/year. If you wanted to do it fancier, you can adjust your kWh charges to include all of your taxes and rebates, but it's reasonably complex since each extra charge is applied differently (some are percentages of the total usage, some are totals/kWh, some are a combination of a fixed charge + usage). Also, there's varying numbers of weekdays/weekends/holidays for each billing period, meaning you the equation is quite complex. For my usage in February (350kWh; long story), my \$/kWh costs were 16.7, 21.6, and 23.1 (off/mid/peak), meaning if that continued all year (it won't), your 65w switch would cost me (for a 30 day month with 8 Saturday/Sundays) about \$103. But, with that additional consumption, all of my \$/kWh prices would be different, so \$100-ish/year.

Now, while old hardware can be pretty brutal with power, it's almost impossible that switch is dissipating 65w unless it has a very loud fan, or has impressive case cooling (both very unlikely). Think about it, how big of a CPU cooler a 65w CPU uses, and it (generally) isn't inside a tiny little case.

So, it's possible/likely the actual switch is drawing considerably less, but whatever devices are using PoE are the lion's share of that power consumption, meaning replacing the switch will have much less of an impact. You'll need to see what is using PoE, and how much power THEY use. You could get a decent estimate by unplugging those devices and seeing the difference in power consumption (there will be power conversion losses, and CPU processing that this won't account for, but it should be pretty insignificant).
One who is offended by truth, has no place among those who seek wisdom.
Deal Guru
Feb 9, 2006
11557 posts
Brampton
ChubChub wrote: A general rule of thumb used is that power drawn = how much it costs you / year. It's not accurate from what I've observed with my power usage, so I use 1.5x. So, a 65w device costs you about \$100/year. If you wanted to do it fancier, you can adjust your kWh charges to include all of your taxes and rebates, but it's reasonably complex since each extra charge is applied differently (some are percentages of the total usage, some are totals/kWh, some are a combination of a fixed charge + usage). Also, there's varying numbers of weekdays/weekends/holidays for each billing period, meaning you the equation is quite complex. For my usage in February (350kWh; long story), my \$/kWh costs were 16.7, 21.6, and 23.1 (off/mid/peak), meaning if that continued all year (it won't), your 65w switch would cost me (for a 30 day month with 8 Saturday/Sundays) about \$103. But, with that additional consumption, all of my \$/kWh prices would be different, so \$100-ish/year.

Now, while old hardware can be pretty brutal with power, it's almost impossible that switch is dissipating 65w unless it has a very loud fan, or has impressive case cooling (both very unlikely). Think about it, how big of a CPU cooler a 65w CPU uses, and it (generally) isn't inside a tiny little case.

So, it's possible/likely the actual switch is drawing considerably less, but whatever devices are using PoE are the lion's share of that power consumption, meaning replacing the switch will have much less of an impact. You'll need to see what is using PoE, and how much power THEY use. You could get a decent estimate by unplugging those devices and seeing the difference in power consumption (there will be power conversion losses, and CPU processing that this won't account for, but it should be pretty insignificant).
You've clearly never had one of these old 3Com PoE switches. I believe it's managed as well so it's got a pretty decent CPU in it, 3Com didn't make many non-managed PoE switches.
These were also rebranded Dell Switches for a while when Dell bought out 3Coms' switching div.

I had one and yes I can confirm it's a pig on power. It's always outputting full power. It actually gets worse when switching load picks up.

The Fans are IIRC 2 40x40x40MM fans so 1U cooling fans. They never ramp down. The fans themselves are like 3W.

If it wasn't for the fact that they stopped updating the firmware on them I would keep it.
[OP]
Oct 9, 2010
2724 posts
Windsor
tebore wrote: You've clearly never had one of these old 3Com PoE switches. I believe it's managed as well so it's got a pretty decent CPU in it, 3Com didn't make many non-managed PoE switches.
These were also rebranded Dell Switches for a while when Dell bought out 3Coms' switching div.

I had one and yes I can confirm it's a pig on power. It's always outputting full power. It actually gets worse when switching load picks up.

The Fans are IIRC 2 40x40x40MM fans so 1U cooling fans. They never ramp down. The fans themselves are like 3W.

If it wasn't for the fact that they stopped updating the firmware on them I would keep it.
Oh, I have, I'm just surprised anyone would still be using one today; no offense intended.

You never mentioned what the capabilities of the switch you're looking to replace it with are, but you might find that replacing it with a switch of that caliber (again: not sure what you're working with specifically), you're probably still going to have something that consumes quite a bit of power. If you're cool with a basic managed PoE switch (Netgear Prosafe type), you might save some. I have a Netgear Prosafe GS108PE that consumes 1w idle; this is quite obviously a very basic managed PoE switch.
One who is offended by truth, has no place among those who seek wisdom.
Sr. Member
Sep 14, 2003
654 posts
Toronto
I was thinking the Ubiquiti 8 port 150w as I have an AP and a 4 non-Unifi PoE cameras. But at \$300, how long until I see the ROI (and loosely on that "I"!) on the hydro bill? Even the switch management page says it's eating up 62w while only loaded with 15w.
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Member
May 6, 2003
341 posts