batsonaMaryland
join:2004-04-17
Ellicott City, MD Reviews:
 ·Vonage
 ·Verizon FiOS
| Using a clamp-on amp-meter... I've just purchased a clamp-on amp-meter. Given how much more expensive electricity is in the balt/dc area, I thought it would be a wise investment.
I know how to use it to measure current on a 110v circuit - just clamp around the black wire (or hot side), and you have your reading. Now, about about measuring the current on a 240v ckt? (Like whole-house A/C)? In this instance, there are 'two hots' that are attached to the phase bus-bars in the panel.
Help me calculate? This is a 240 air-handler for my central A/C. I run the fan 24/7 to distribute the air in my house, to prevent hot/cold spots. The A/C is new as of July 2006, and the fan-only speed is a very slow RPM.
Phase-1 was .42A and Phase-2 was .39A. Added together, we have .81A Now, do I multiply this value against 120volts, and come up with 97.2watts, or do I multiply it against 240volts, and get 194.4watts? |
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 McSummationMmmm, Zeebas Are Tastee.Premium,MVM
join:2003-08-13
Round Rock, TX
kudos:2 | What's the current through the "common" wire?
If the blower is 240V, then there should be the same current in each leg, with 0 in the common. It sounds like you've got .03A going into the common (120V circuit) - probably a 120V step-down transformer for the thermostat. |
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batsonaMaryland
join:2004-04-17
Ellicott City, MD Reviews:
·Vonage
·Verizon FiOS
| There's no common that I can see. The cable coming in from the air-handler looks to be 14AWG, and has a single black, single white, and a bare copper lead.
The Black and White are attached to the two bus-bars (one on each), and the bare copper wire is screwed down against the neutral bar. This is the same bar as where all the other white wires from 110v ckts in the house are screwed down.
The bare copper lead has .05A on it. I just re-measured the current on the black and white, and it's showing .40A and .44A respectively. My curiosity, is given connections to two seperate phases, how much total current is being used by my air-handler?
Thanks for help me on this! |
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 SparkChaserAvatar is not a SparkPremium
join:2000-06-06
Downingtown, PA
kudos:3
·Verizon FiOS
 ·Comcast
| reply to batsona
I don't think you're wire to code. 
However the answer is, say 0.40 amps X 240 volts = 96VA. Since this is an inductive load, it doesn't necessarily translate to watts. So, 96VA might be about 85 watts.
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"Facts do not cease to exist because they are ignored." - Aldous Huxley
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McSummationMmmm, Zeebas Are Tastee.Premium,MVM
join:2003-08-13
Round Rock, TX
kudos:2 | reply to batsona
So, you're telling me that you've got a 240V circuit that is "14-2 w/ ground"? Man, that definitely is not code. In fact, that is a lethal circuit waiting on some unsuspecting electrician getting killed.
The bare copper wire should never ever have any current on it. |
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public
join:2002-01-19
Santa Clara, CA
1 edit | reply to batsona
said by batsona:The bare copper lead has .05A on it. I just re-measured the current on the black and white, and it's showing .40A and .44A respectively. My curiosity, is given connections to two seperate phases, how much total current is being used by my air-handler? The average is 0.42A. The cheap clamp on meters are not very accurate especially at lower current.
For better result wrap the wire 10x around the clamp, and the divide the reading by 10.
The bare copper wire should never ever have any current on it.
It probably does not. |
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batsonaMaryland
join:2004-04-17
Ellicott City, MD Reviews:
·Vonage
·Verizon FiOS
| I just bought my meter, which indicates, "True RMS". It cost $99.
My 240v ckt being 14/2 w/grnd has been that way since it was installed in 1988. The wiring for the A/C compressor is the same way, but it's using 10AWG. Black and white are on the bus-bars, and the bare copper is on the neutral bar.
For my info: If I wanted do the wiring to-code, I'd need a 14/3 for the air-handler, and a 10/3 for the Compressor, where:
White: Connects to Neutral
Black: Connects to bus-bar
Red: Connects to bus-bar
Bare Copper: Connects to grounding screw inside dist. panel.
What if the A/C components only require "L1, L2, G" What if they don't require a neutral? Or, what you're saying, is that current should never be carried on the White wire, because that's assumed to always be neutral? If I wanted to do L1, L2, G, I should wire it as I indicated above, ensuring that no current is carried on the White wire, correct? |
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McSummationMmmm, Zeebas Are Tastee.Premium,MVM
join:2003-08-13
Round Rock, TX
kudos:2 | With pure 220/240V, the current is all carried by the 2 hot wires (black and red). The white should not have any current on it, neither should the ground (bare).
Sometimes, a 220/240V circuit will need to feed a 110/120V transformer (for the thermostat's 24V). In that case, you would use the black and white wires and the white (neutral) would carry current.
The problem with what you've got is that the wiring looks like a 110/120V circuit. Although it works (as you already know), it is deceptive. |
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batsonaMaryland
join:2004-04-17
Ellicott City, MD Reviews:
·Vonage
·Verizon FiOS
| reply to SparkChaser
quote:
However the answer is, say 0.40 amps X 240 volts = 96VA. Since this is an inductive load, it doesn't necessarily translate to watts. So, 96VA might be about 85 watts.
Thanks for this info; this is what I was looking for. You're assuming a PowerFactor of maybe ~.88, in order to get 85watts? I thought amps X volts = watts. Watts divided by powerFactor = VA?
Anyway, what I wanted to say, was that my new AmericanStandard air handler actually runs on DC, for power-savings - it converts AC to DC and feeds DC directly into the motor for the fan. --How does an AC to DC conversion affect powerFactor?
I wish my new meter would give me power-factor - it probably cant, since it doesn't measure in-line, it measures by clamp-on. |
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public
join:2002-01-19
Santa Clara, CA | said by batsona:Anyway, what I wanted to say, was that my new AmericanStandard air handler actually runs on DC, for power-savings - it converts AC to DC and feeds DC directly into the motor for the fan. --How does an AC to DC conversion affect powerFactor? I wish my new meter would give me power-factor - it probably cant, since it doesn't measure in-line, it measures by clamp-on. Just because you paid $99 doesn't mean the clamp is well made.
A rectifier load without power factor correction is very nonlinear and has a bad power factor.
Inductive clamp meter can measure power factor, but it needs to simultaneously measure voltage. Otherwise it can only approximate using the nonsinusoidal current waveform. |
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SparkChaserAvatar is not a SparkPremium
join:2000-06-06
Downingtown, PA
kudos:3 Reviews:
·Verizon FiOS
·Comcast
| reply to batsona
said by batsona:I thought amps X volts = watts. Watts divided by powerFactor = VA? Anyway, what I wanted to say, was that my new AmericanStandard air handler actually runs on DC, for power-savings - it converts AC to DC and feeds DC directly into the motor for the fan. --How does an AC to DC conversion affect powerFactor? Amps X Volts = Watts for DC and for AC when you have a unity PF. Otherwise it's VA*PF=Watts. As public  pointed out the AC/DC conversion can make the power waveform fairly complex. A lot of the converters now have PF correction incorporated in the circuit.
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley
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 jfgnet12 Step ProgramPremium,MVM
join:2001-02-14
Limbo | reply to batsona
Some links on Powe Factor
»www.onsemi.com/pub/Collateral/HBD853-D.PDF
»www.lmphotonics.com/pwrfact.htm
»members.tripod.com/~masterslic/FAQ-2/22.html |
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batsonaMaryland
join:2004-04-17
Ellicott City, MD Reviews:
·Vonage
·Verizon FiOS
| reply to SparkChaser
quote from Beeron:
However the answer is, say 0.40 amps X 240 volts = 96VA. Since this is an inductive load, it doesn't necessarily translate to watts. So, 96VA might be about 85 watts
Am I correct in saying the best way to measure how much a given device makes the utilty meter spin, is measuring the VA, and not the Watts or Amps alone.
For instance, a widget might soak up 50 watts, but if it had a really bad powerFactor, it might take ~80VA to run the widget. Therefore, the best way to compare the 'meter-spin' for two different widgets is to compare the VA, not just the watts, correct?
Reasoning: Just trying to reduce the meter-spin in my house. |
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public
join:2002-01-19
Santa Clara, CA | said by batsona:Am I correct in saying the best way to measure how much a given device makes the utilty meter spin, is measuring the VA, and not the Watts or Amps alone. No. The electromechanical meter measures watts within 1% for linear loads but works badly with rectifier loads with high crest factor. |
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batsonaMaryland
join:2004-04-17
Ellicott City, MD Reviews:
·Vonage
·Verizon FiOS
| I can understand this. --I thought PowerFactor was the coefficient that corrects for inductive loads, rectifiers, etc etc.
Are you saying that the electromechanical meter from the utility company does a bad job of measuring current flowing to devices that have a bad power-factor? The meter doesn't detect all the current that's flowing to a huge AC motor, for instance...?
All I'm trying to do, is determine what (if any) common measurement exists, to compare power consuption between devices, regardless of whether they're inductive or not. (I thought PowerFactor was the coefficient that corrects for this)
When you buy a UPS, they're all rated in VA. VA was the common measurement that included the PowerFactor coefficient(?) VA was to be the method to compare power consuption between a 1HP AC motor, and a 1-watt LED light soldered to a circuit board.
I'm just looking to understand this scientifically. |
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public
join:2002-01-19
Santa Clara, CA | said by batsona:Are you saying that the electromechanical meter from the utility company does a bad job of measuring current flowing to devices that have a bad power-factor? The electromechanical electric meter works well with bad power factor if the load is inductive or capacitive.
It works badly with bad power factor factor due to high crest factor such as rectifier loads. |
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SparkChaserAvatar is not a SparkPremium
join:2000-06-06
Downingtown, PA
kudos:3 Reviews:
·Verizon FiOS
·Comcast
| reply to batsona
You might take a look at these forum threads.
»Is anyone using a Power Saver 1200?
»Power Save 1200 ----Any one have experience this product?
PF for simple devices such as a motor are fairly simple. With some of the new electronics devices, it can become quite complex as public pointed out.
Worrying about power factor on 100 watt devices is usually not worth the time.
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley
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batsonaMaryland
join:2004-04-17
Ellicott City, MD Reviews:
·Vonage
·Verizon FiOS
| reply to batsona
OP here: I just made the suggested measurements. There's no appreciable voltage between the alum. braid before the lug, and the neutral bar. I measured both with normal load, and measured while my wife was turning the microwave on and off. Microwave is 1300 Watts.
However: With the microwave going on and off, I did notice a voltage drop on its phase, and an increase on the other. Both phases register ~120.5 VAC. With the microwave on, that changes to 124 VAC and 116 VAC. Turning the appliance off, puts the voltages back at about ~120.5 VAC.
That brown stuff on the neutral lug I think is soldering flux. It doesn't look like corosion; it's more brown & shiny; I haven't tried to chip away at it. |
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SparkChaserAvatar is not a SparkPremium
join:2000-06-06
Downingtown, PA
kudos:3 | reply to batsona
Problem may be at the meter. That's were mine was. |
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3 edits | reply to public
High Crest Factor With Rectifier Loads... said by public:...The electromechanical electric meter works well with bad power factor if the load is inductive or capacitive. It works badly with bad power factor factor due to high crest factor such as rectifier loads. I never heard the term "Crest Factor" before (Power Factor relationship to VA and Watts, yes - aka "Kill-A-Watt"), so I GOOGLE'd and found this 'White Paper' (for any other 'curious' LURKERS to this thread):
CREST FACTOR , POWER FACTOR, AND WAVEFORM DISTORTION
First read didn't help me much, but maybe the 2nd (or 3rd!) will...
So what's a "Rectifier Load"? AC in, DC out?
UPDATE #1:
Dan's Data: PFC decoded
Interesting LINK from jig found inside one of the Power Saver 1200 LINKs from beeron comparing a resistive load to a reactive load (water balloons and buckets -> out-of-sync?) and discussing Power Factor Correction (PFC).
UPDATE #2:
Mike Holt's NEC Newsletter: Power-Save Power Factor Correction Capacitors
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The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. --George Bernard Shaw (1856 - 1950) |
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