Author Topic: ted off by a factor of ten?  (Read 14709 times)

bryanjabaay

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ted off by a factor of ten?
« on: July 24, 2011, 01:38:45 AM »
I just hooked up a Ted 1001 to a 220 volt appliance circuit.  The appliance is an electric 220 volt, 4500 watt water heater.  I turned up the water heater to make sure it was heating and the RDU measured .260 KW.  I watched for over an hour and the reading stayed consistent.  This is just over two amps and seems off by a factor of ten (I would imagine a reading of about 20 amps).  Anyone have an idea about either my math or my TED 1001?

GAR

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Re: ted off by a factor of ten?
« Reply #1 on: July 24, 2011, 05:38:28 AM »
110723-2111 EDT

Are your current sensors properly orientated. The red dot on the sensor on phase A must point toward the utility. The phase B sensor red dot must also point toward the utility.

I believe the two sensors are effectively connected in series to provide a composite current of the two phases, and then this is processed in combination with the voltage from one phase to calculate a short average power.

If one sensor is reversed relative to the other then the composite current is the difference. Note because phase A is 180 degrees out of phase with phase B that putting both sensors on the same wire (identical current), and both dots in the same direction and current flowing the result should be near zero. Reverse one and you will get double the power of the actual load.

If one sensor is reversed relative to how it should be connected, then one current is subtracted from the other and if these are not identical, then you would get an unbalanced reading.

A good simple test is to not put one current sensor around any cable. Thus, no current. Put the other sensor around a wire to a single 100 W incandescent bulb. This should read within a couple watts of 100. But the 1000 series only quantizes to 10 W. Reading should certainly be 90, 100, or 110.

If your problem is the correct relative sensor orientation is not correct, then the possibility in your case is that both currents are not identical and a non-zero difference results.

The 1000 and 5000 do not appear to read negative power, and thus, the primary orientation problem is the correct relationship between the two sensors.

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rotus8

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Re: ted off by a factor of ten?
« Reply #2 on: July 24, 2011, 06:18:55 PM »
The other thing to check is are the CT clamps completely closed. Even slightly open will cause a dramatic reduction in the readings.

SherlockOhms

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Re: ted off by a factor of ten?
« Reply #3 on: July 25, 2011, 11:39:16 PM »
GAR is correct, more then likely your CT's are inverted.  Simply flip one 180 degrees and it should read correct.

bryanjabaay

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Re: ted off by a factor of ten?
« Reply #4 on: July 27, 2011, 04:14:19 AM »
I've checked the ct's several times.  I've changed them from both facing one direction to both facing the other.  Always the same reading.  I just bought a klein ampmeter and found 15.3 amps on either leg of the 30 amp 240 circuit while the heater was on, so just as I surmised the TED is around a factor of ten off (actually a bit more.)
O.k., full disclosure, this  is a 3phase service with 120 volts to ground on each leg, but I am not trying to measure the service, just the branch circuit with the hot water heater.  Could this have anything to do with the low readings?  Also, this is a restaurant with a lot of equipment.  Could the rf noise be disrupting the communication between the rdu and the mtu?

rotus8

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Re: ted off by a factor of ten?
« Reply #5 on: July 27, 2011, 06:11:59 PM »
Aha, the three phase is the problem. The "two legs" are 120 degrees phase apart, not the 180 that TED expects.

bryanjabaay

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Re: ted off by a factor of ten?
« Reply #6 on: July 28, 2011, 04:55:29 AM »
I deleted the post I had put in this space for its stupidity.  I thought you were talking volts and then I saw the word "degrees".  This sounds valid. 
First question.  Are you certain of this? (In other words, I can stop looking for any other problem because you know this is the reason).
Second, If this is absolutely the problem, can you imagine that there might be a factor I could apply to KW measurement and end up getting the information I am trying to get?
« Last Edit: July 28, 2011, 06:10:29 AM by bryanjabaay »

rotus8

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Re: ted off by a factor of ten?
« Reply #7 on: July 28, 2011, 06:03:48 PM »
I am quite sure the 3-phase it the problem, but one of the TED support guys should confirm it. The TED relates the phase of the current sensed to the voltage and computes a power factor which is used to create the power consumption. Connecting to two legs of a 3-phase service will confuse the bejabbers out of it.

TEDSupport6

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Re: ted off by a factor of ten?
« Reply #8 on: July 28, 2011, 10:19:50 PM »
I am quite sure the 3-phase it the problem, but one of the TED support guys should confirm it. The TED relates the phase of the current sensed to the voltage and computes a power factor which is used to create the power consumption. Connecting to two legs of a 3-phase service will confuse the bejabbers out of it.

Rotus8 is correct. You can't use our current TED models to measure 3-phase power for this reason. We do have a 3-phase model in beta testing right now (sorry, we have no need of more testers), and we will release more information about the model as soon as it's available.

bryanjabaay

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Re: ted off by a factor of ten?
« Reply #9 on: July 29, 2011, 06:46:42 AM »
Thanks everyone for the replies.  With the measurement from my ampmeter I am making the guess that the TED is about a factor of 13 too low.  I don't know why (that is, why it is specifically a factor of thirteen) and I would love it if someone could figure out the math on that, but at least at this point I can take some of the information from the RDU and make an estimate of the energy I am using on the water heater.  Next I have to figure out how much the electric range is using.

rotus8

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Re: ted off by a factor of ten?
« Reply #10 on: July 29, 2011, 05:58:43 PM »
check out the KVA and Power Factor numbers on the Live Dashboard tab. You might find that the KVA numbers are actually pretty close for a pure resistive load. The Power Factor will be way whacked because of the phase angles are not what is expected.

GAR

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Re: ted off by a factor of ten?
« Reply #11 on: August 02, 2011, 11:33:02 PM »
110802-1515 EDT

bryanjabaay:

I think the TED discussion somewhere clearly indicates that both the 1000 and 5000 are for single phase only.

To answer your theory reason. If you subtract 0.866 (1/2 the sq-root of 3, the sine of 60 degrees) from 1 you get 0.134. You draw a vector diagram of your problem to see why.

A solution. Get a small true 2 to 1 transformer from 240 to 120 and connect the primary across the 208 input to the heater, and the secondary to the TED 120 input wires. If the transformer is not precisely 2 to 1 this can be corrected. This will work if the heater is only a resistor across the 208 line pair. Also it assumes the TED unit will work correctly at the reduced input voltage. This is 104 if the input is 208 V.

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GAR

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Re: ted off by a factor of ten?
« Reply #12 on: August 03, 2011, 05:00:59 PM »
110803-0857 EDT

Change the orientation of one, but not both, current sensors. Report back the result.

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SherlockOhms

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Re: ted off by a factor of ten?
« Reply #13 on: August 03, 2011, 07:54:47 PM »
Right,  again.... to emphasize .. flip ONE CT  not both in one direction or other... only ONE in different direction from the other.  Your measuring the difference between phases right now instead of adding them together.

HamJam

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ted 5000 - 3 phase?
« Reply #14 on: November 14, 2011, 06:15:38 PM »
I am about to set up the TED 5000 on a friends condo in the Caribbean.  As we now all understand the TED5000 does not work on 3 phase power? The local power company are not able to inform me if the power comes into the resort as 3 phase?

Question 1) If there is single phase power in the condo but the power to the condo has come initially from a 3 phase transofmer does the TED 5000 still work.  In other words the power company sends 3 phase power to the resort and then it gets transformed to single phase before entering into the condo.

Question 2)  I am not an electrician but want to know if there is anyway one can open up a breaker box and check to see if the power is coming in via a 3 phase transformer before going to the expense of setting up the TED and it not working.