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How much are our switches costing us?


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#1 Work2Play

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Posted 05 November 2010 - 04:14 AM

So earlier today in the chat, the topic came up of how much power our switches consume. We go into this thinking that by using these switches, the lights will be off more, and the dimmer will save us money, etc. I think people forget that having this little device sitting there listening on the powerline and that cool looking colored LED light come at a cost! I knew it used something, but this piqued my curiosity.

So - I rigged up a few of them so I could plug them into the Kill-A-Watt. Knowing that just one would probably register too low, I figured I'd get a more accurate reading if I hooked 5 up then did the math.

Here's the rig - I took 5 US1140's - 4 brand new, one a used one - and I taped them together with electrical tape side-by-side (each one individually to keep it tight and secure). I found an old PC power cord (the standard C13 power cord) to sacrifice - cut the end off and hooked up the switches to hot, neutral, ground - and taped off all the load and remote wires - and hooked it up in the kitchen to a GFCI-protected outlet just for extra safe good-measure.

Posted Image

So - some fun stats:
  • Power Factor = 0.7
  • Combined (5 US1140's) consume 3 watts; almost 4 (it jumps up when you play with the switches)
  • The power consumed jumps quite a bit when you're interacting with the switches (expected)
  • The amps consumed for all 5 sat around .4
  • I threw all 5 into setup mode and added them fresh to my network - in the process, especially during the writes, the amps jumped all over the place, including up to a little over 1 full amp.
  • Off or On didn't seem to matter, nor did color of the lights - it just jumped after being switched (most likely when transmitting status).

My power gets into the high tier (I think I'd end up there even if I unscrewed every lightbulb in the house and turned off my AC - the limit is low!) - so basically anything new added to my power bill will be at the high rate - which is $.409/kWh - an absolutely insane price to pay for power... the highest it could go in my last neighborhood was $.13

So - I plugged that into the Kill-A-Watt and let it run for a bit - and checked out the cost - it's at about $10.72 to run 5 switches for a year. I'm installing about 50-60 switches, so times that by 10 - I'll be looking at $107/year, or an extra $8.92/month just to have these switches.

The good thing though is that I use the switches to set all the lights to only turn on to 80%, and keep them dimmed quite often now, so hopefully that'll off-set any costs (means I'm not saving as much as originally hoped tho!).

I'm very new to power monitoring and caring (funny how a $700 electric bill will do that to you!) - but I'll have this rig set up until Saturday if you guys want me to test any other scenarios or get any other types of readings. I have the Kill-A-Watt-Ez (I don't know what the difference is).

#2 drozwood90

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Posted 05 November 2010 - 06:30 AM

Great write-up! I had guessed about 5W per switch, however, looks like you measured 120*.4=48W per 5 so /5 = 9.6W or so.

9.6W * 30 switches = 288W * 24h = 6.912KWH / day* 30 day / month = 207.36 KWH/ month

I think my rate (living in New York) is close to what you quoted there. So, assuming the same: $84.82 / month
At your old rate, $26.96/month (much nicer!!).

We just got our power bill, so I'll as my wife to get the real number and I'll post back.

Thanks for the information! Something I've wanted to do, but just haven't had the time. Would you be able to repeat the test, but use US2-40's? I'm curious if they are more or less then the 11-40s. It's also what I use exclusively.

--Dan


My power gets into the high tier (I think I'd end up there even if I unscrewed every lightbulb in the house and turned off my AC - the limit is low!) - so basically anything new added to my power bill will be at the high rate - which is $.409/kWh - an absolutely insane price to pay for power... the highest it could go in my last neighborhood was $.13



#3 drozwood90

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Posted 05 November 2010 - 06:34 AM

Heck, at those rates, it makes me want to consider getting 1 - 2 solar panels to supplement my "base" power use.

--Dan

#4 drozwood90

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Posted 05 November 2010 - 07:38 AM

I guess as I said in this post, on the "other power" thread:

http://www.cocoontec...p...ost&p=96548


I should just get the Omega Meter out and measure the power. Looking back at that other thread, 1.2W sounds much nicer then 9.6W.

Also, we can ignore powerfactor, as we are residential. We don't get billed by that, just by V*A.

--Dan

#5 Bauer

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Posted 05 November 2010 - 08:00 AM

I guess as I said in this post, on the "other power" thread:

http://www.cocoontec...p...ost&p=96548


I should just get the Omega Meter out and measure the power. Looking back at that other thread, 1.2W sounds much nicer then 9.6W.

Also, we can ignore powerfactor, as we are residential. We don't get billed by that, just by V*A.

--Dan



Actually residential normally gets charged by the watts being used which is this case was 4 watts which when the math was done was about 4/5 (0.8) of a watt per switch. Remember Watts=volts * amps only for DC power not AC power.

Steve

#6 Digger

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Posted 05 November 2010 - 08:25 AM

I wonder what the difference would be for UPB which are non repeating to Zwave and Insteon which are repeating? Granted the UPB signal is much greater so maybe it is a wash but that may not be the case depending on the size of the mesh in a repeating system. That would be especially true in an Insteon setup with a lot of accesspoints or dual band devices.

In my house the laundry room uses 160 Watts for lighting and would be left on for hours or overnight. Also the garage was converted into a room using over 200 watts and the kids would go in there and leave the lights on for hours (or even days) without it being noticed. I noticed a drop in my electric bill with automation but part of the drop could be other things being done in parallel a few years ago.

#7 drozwood90

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Posted 05 November 2010 - 09:29 AM

I guess as I said in this post, on the "other power" thread:

http://www.cocoontec...p...ost&p=96548


I should just get the Omega Meter out and measure the power. Looking back at that other thread, 1.2W sounds much nicer then 9.6W.

Also, we can ignore powerfactor, as we are residential. We don't get billed by that, just by V*A.

--Dan



Actually residential normally gets charged by the watts being used which is this case was 4 watts which when the math was done was about 4/5 (0.8) of a watt per switch. Remember Watts=volts * amps only for DC power not AC power.

Steve


Steve,

I don't follow you. Can you explain a bit more?

My understanding is, apparent watts is what we are billed for. i.e. VA Maybe I have that backwards and industrial settings are being bills for VA?

I found this online:
WHAT IS POWER FACTOR?
Power factor (PF) by definition is the ratio of real to apparent power:
PF=W / VA

So:

PF*VA = W
.7*9.6VA = 6.72W ?

So, the switch is using 6.72W?

I guess I do not understand where the 4W came from (I know from the meter, but how did it get 4W from the A and V). And if it is actually 4W, isn't that already W, and not VA?

4/5 = 0.8??
(4*.7)/5 = 0.56??

So, are the switches using 0.8, or .56W?

Which, these numbers are MUCH happier!
0.8W * 30 switches = 288W * 24h / day* 30 day / month = 17.28KWH/month * 0.409 = $7.07 / mo
0.56W * 30 switches = 288W * 24h / day* 30 day / month = 12.096KWH/month * 0.409 = $4.95 / mo

--Dan

#8 sda

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Posted 05 November 2010 - 09:51 AM

My power gets into the high tier (I think I'd end up there even if I unscrewed every lightbulb in the house and turned off my AC - the limit is low!) - so basically anything new added to my power bill will be at the high rate - which is $.409/kWh - an absolutely insane price to pay for power... the highest it could go in my last neighborhood was $.13

Welcome to PG&E land.

So - I plugged that into the Kill-A-Watt and let it run for a bit - and checked out the cost - it's at about $10.72 to run 5 switches for a year. I'm installing about 50-60 switches, so times that by 10 - I'll be looking at $107/year, or an extra $8.92/month just to have these switches.

Don't eat lunch at McDonalds a couple of times a month and you've got it covered.

I'm very new to power monitoring and caring (funny how a $700 electric bill will do that to you!)

There's a lot of junk that eats power that you don't even think about. Your HVAC transformer, your doorbell transformer, your stove, your dishwasher, your coffee maker with the useless clock/timer.

#9 oberkc

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Posted 05 November 2010 - 09:58 AM

There's a lot of junk that eats power that you don't even think about. Your HVAC transformer, your doorbell transformer, your stove, your dishwasher, your coffee maker with the useless clock/timer.


...all your TVs (even when off), your computer equipment, home theater equipment (even when off).

Nice post! Thanks for this effort.

I wonder what the difference would be for UPB which are non repeating to Zwave and Insteon which are repeating?


Great question. My gut reaction is that these differences will be minimal, since these are such short transients.

#10 Work2Play

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Posted 05 November 2010 - 10:01 AM

I think you guys mis-read something (hopefully I didn't mis-state a value)...

According to the Kill-A-Watt, all 5 switches together were registering at 3-4 watts (it displayed 3, but would jump to 4 if I pressed a button).

so - times that by 10 for 50 switches, and we're talking about 30-40 watts total. The Kill-A-Watt Ez makes this really simple - you plug in your rate and it'll project the rates for the hour/day/week/month/year based on the average time since you last reset it so the longer you leave it connected, the more accurate the average gets. As of a couple hours after connecting it, it said the 5 switches would cost me $10.72 for a whole year. Again, times that by 10 to get to my 50 switches, and we're talking $107.20 for all 50 switches for the whole year. That's WAY better than the $84 per month that drozwood's math came back with.

I'll let it sit today and re-post all the values tonight. It does consume power just from listening on the network - you see it spike if you turn another light switch on/off - but only a little.

And lastly - I ran out of 240's, which is why my install halted - I have about 10 1140's waiting to be installed (30+ already in). Today I'm due for a shipment of four 240's and a couple more 1140's - so I'll hook up the 240's at least overnight - I hope to install them tomorrow morning.

Edit: I have a clamp on meter around here somewhere I can look for if you think it'll be that much more accurate.

#11 Bauer

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Posted 05 November 2010 - 10:15 AM

I guess as I said in this post, on the "other power" thread:

http://www.cocoontec...p...ost&p=96548


I should just get the Omega Meter out and measure the power. Looking back at that other thread, 1.2W sounds much nicer then 9.6W.

Also, we can ignore powerfactor, as we are residential. We don't get billed by that, just by V*A.

--Dan



Actually residential normally gets charged by the watts being used which is this case was 4 watts which when the math was done was about 4/5 (0.8) of a watt per switch. Remember Watts=volts * amps only for DC power not AC power.

Steve


Steve,

I don't follow you. Can you explain a bit more?

My understanding is, apparent watts is what we are billed for. i.e. VA Maybe I have that backwards and industrial settings are being bills for VA?

I found this online:
WHAT IS POWER FACTOR?
Power factor (PF) by definition is the ratio of real to apparent power:
PF=W / VA

So:

PF*VA = W
.7*9.6VA = 6.72W ?

So, the switch is using 6.72W?

I guess I do not understand where the 4W came from (I know from the meter, but how did it get 4W from the A and V). And if it is actually 4W, isn't that already W, and not VA?

4/5 = 0.8??
(4*.7)/5 = 0.56??

So, are the switches using 0.8, or .56W?

Which, these numbers are MUCH happier!
0.8W * 30 switches = 288W * 24h / day* 30 day / month = 17.28KWH/month * 0.409 = $7.07 / mo
0.56W * 30 switches = 288W * 24h / day* 30 day / month = 12.096KWH/month * 0.409 = $4.95 / mo

--Dan


This site, http://www.powerstre...om/VA-Watts.htm explains some of the simple equations for calculating watts for AC fairly well.

the things that we has to look at as well are the following (I am guessing the meter takes some of this into account as well)
1) The simple equations work for constant voltage, power factor, amperage. In real life they are not constant.
2) What is the error bounds on the meter itself. These measurements are down at the lower bounds of the meter.


The 4/5 of a watt per switch comes from the fact the meter stated it was using 4 watts (The meter calculates the watts using pf, etc. already) for the bank of 5 switches. So, then this would be 4/5 of a watt per switch.

Steve

#12 Bauer

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Posted 05 November 2010 - 10:20 AM

Another interesting point for comparison would be what are the operating costs for hard wired solutions?

Steve

#13 drozwood90

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Posted 05 November 2010 - 10:49 AM

Steve,

Thanks!

So, looks like:
0.8W * 30 switches = 288W * 24h / day* 30 day / month = 17.28KWH/month * 0.409 = $7.07 / mo

Is correct for me.

So, $84.84 for a year (assuming I am being charged the same as Work2Play).

--Dan

#14 JonW

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Posted 05 November 2010 - 10:51 AM

Great info! It would be cool to see comparisons of all the other powerline technologies. Anyone else want to throw their switches into the test?

#15 drozwood90

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Posted 05 November 2010 - 12:01 PM

Steve,

Thanks!

So, looks like:
0.8W * 30 switches = 288W * 24h / day* 30 day / month = 17.28KWH/month * 0.409 = $7.07 / mo

Is correct for me.

So, $84.84 for a year (assuming I am being charged the same as Work2Play).

--Dan


0.216/kwh for me so:
$3.74/mo
$44.88/year




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