Using DS10a with CRMagnetics current switch

[SteveQ]

1.) Use the split core CR9380, otherwise you will have to disconnect a wire from the water heater and feed it through the core of the CR9321.

Steve Q

Which do you guys recommend? Digikey has three listed:
CR9380-ACA
CR9380-NPN
CR9380-PNP

It appears the NPN and PNP versions work with 120 volts. The ACA version is 240 Vac? Can someone confirm this, I don't want to post false info and cause someone problems

Yes, I believe the CR9380-ACA is the right one, although I have not actually used it. I intend to order 1 or 2 in the next few weeks.

Steve Q

 

[SteveQ]

I think your approach will work fine, but I would suggest:

1.) Use the split core CR9380, otherwise you will have to disconnect a wire from the water heater and feed it through the core of the CR9321.

2.) If you don't have a wireless receiver, you could use the X10 powerflash module in place of the DS10A to "put the X10 signal on the powerline". (also, you cannot use a standard X10 wireless receiver with the DS10A - it uses a different frequency; you need a special receiver such as the W800)

I am not familiar with the ELK so I can't comment on how to program it.

Steve Q

Can you use something like this EZIO8SA Input/Output Interface Module to monior 7 CR9380 devices?

It looks like it would work (using the one-wire port), but I have no experience in this area. Will it work with your home automation software ?

Steve Q

 

[SteveQ]

SteveQ said, "I intend to use this on my water heater."

If this data is to be used to calculate energy consumption, I think it will require two monitors; one for the upper and another for the lower heating element.

Thanks for the idea, Steve. For as long as we've been married, one of us asks the other if we checked to see if the electric range is off as soon as we are well out of town. Your idea connected to my Elk-to-be look to me like the solution. The checklist by the back door sure didn't work. I thought I would be working on an infra-red sensor to report the answer, but your idea just seems so right.

Yes, my intention is to calculate energy consumption.

I did not think about the issue of 2 heating elements! I have the CR3110 across the main feed to the water heater controller board. So if either element comes on it should trigger the DS10A. I don't really know if the heating elements are controlled individually or if they both come on together. The voltage out of the CR3110 when the water heater is ON is approx 13VAC. If this is one element, I suppose the voltage could go up to 26 if both elements kick in. This might fry the 2N3904 transistor. I guess I'll wait and see what happens! To your point about calculating energy useage, your right, to do it right, both elements should be monitored. But in my water heater, there is no room to get a CR3110 around the individual element feeds. I think I will see if I can detect a pattern. Perhaps I can have the software factor up the KWHr when the water heater is ON for more than 15 minutes. Any ideas would be appreciated!

If I really knew what I was doing, I would redesign the CR3110 /DS10A circuit to have 2 outputs for 2 DS10s one that switched at 13VAC (element 1) and one that switched at 20VAC (both element 1 and 2). That would be pretty slick!

Steve Q

 

[SteveQ]

I'd be in for a group buy...

Me too! But I am on the X10 mailing list ( I send it to my SPAM collector) which I check once in a while for special offers. They frequently bundle 4 DS10s with a motion sensor and keychain remote for around $30. So thats $7.50 each - not bad!

Steve Q

 

[WayneW]

I don't really know if the heating elements are controlled individually or if they both come on together. The voltage out of the CR3110 when the water heater is ON is approx 13VAC. If this is one element, I suppose the voltage could go up to 26 if both elements kick in.

Look at the electric name plate of your water heater. It should give 3 wattage or amperage numbers - upper, lower and max. If you have the same number for all three fields, then you have two identical elements and that they are sequential. If they were parallel (both on at once), the max number would be the sum of the two elements. AFAIK, most residential heaters are sequential (one at a time - lower first, then upper to try and maintain usable water).

 

[SteveQ]

Look at the electric name plate of your water heater. It should give 3 wattage or amperage numbers - upper, lower and max. If you have the same number for all three fields, then you have two identical elements and that they are sequential. If they were parallel (both on at once), the max number would be the sum of the two elements. AFAIK, most residential heaters are sequential (one at a time - lower first, then upper to try and maintain usable water).

Wayne, Thanks, the label has 3380W for all 3 values. This is good because it means the elements are the same and sequential. Therefore to calculate the energy consumption of the water heater, I just multiply the time the heater is ON by 3380W. It does not matter which element is heating. So my original plan was correct! Usually I'm not that lucky!

Steve Q

 

[Photon]

I learn something from this site every day! Thanks, Wayne.

 

[SethP]

Very cool...I'm using a few CR3110s connected to DS2406s and a DS2450 on my 1-wire network to monitor furnaces & heat zones. Thigs would be simplified with the transistor built in.

Question: How are you getting data into a database with the x-10 devices? I wrote my own plugin for Homeseer, and it saves on durations & times to my sql server.

Thanks!

Seth

 

[SteveQ]

I use Homeseer with a W800 and the ACRF2 plug-in to monitor data from the DS10A. When the DS10A changes state I use a script to write the date, time, ON/OFF state to a simple text file. The file is a simple list of the data. I then use Microsoft Excel to analyze the data. Once a week or once a month, I run the Excel spreadsheet which automatically imports the data and does all the calculations. Using the Excel "Pivot Table" tool, it is really simple to create a table that shows the number of times the water heater turns on each day and the time of day. I have built macros into Excel so the whole process is totally automated. Just click on the spreadsheet icon.

Steve Q

 

[sda]

The voltage out of the CR3110 when the water heater is ON is approx 13VAC.

If you look at the spec sheet, 13vac is "off the chart" (at the bottom of the sheet). To quote: "High secondary turn will develop signals up to 10.0 Vac across a burden resistor." I'm by no means an expert on this, but I think you're saturating the coil because you don't have a burden resistor in the circuit. I believe I read somewhere that without a burden resistor the CT will eventually fail.

 

[SteveQ]

The voltage out of the CR3110 when the water heater is ON is approx 13VAC.

If you look at the spec sheet, 13vac is "off the chart" (at the bottom of the sheet). To quote: "High secondary turn will develop signals up to 10.0 Vac across a burden resistor." I'm by no means an expert on this, but I think you're saturating the coil because you don't have a burden resistor in the circuit. I believe I read somewhere that without a burden resistor the CT will eventually fail.

Thanks, I could easily add a resistor across the CR3110 leads. Based on the chart it looks like a 2K resistor should bring the voltage down to about 8vac. Does that sound right?

The CR3110 on my baseboard heater circuit outputs about 9vac. Do you think I should still add a burden resistor?

Steve Q

 

[sda]

Thanks, I could easily add a resistor across the CR3110 leads. Based on the chart it looks like a 2K resistor should bring the voltage down to about 8vac. Does that sound right?

Here's how I would approach it. Your water heater is 3380w at 240v. That's 14amps. Plugging that into the formula V = 14*2000/3100 = 9vac output. That should be OK since its less than spec-ed 10vac max. I would use a 1K resistor V = 14*1000/3100 = 4.5vac.

Going back a couple of weeks to your original post, the circuit has the resistor on the DC side of the bridge. I don't know if or how that's going to affect the formula and resulting voltage. I'd put the resistor on the AC side so you know exactly what's going into the bridge and therefore out of it.

The CR3110 on my baseboard heater circuit outputs about 9vac. Do you think I should still add a burden resistor?

"What happens if the burden resistor is left off or opens during operation? The output voltage will rise trying to develop current until it reaches the saturation voltage of the coil at that frequency. At that point, the voltage will cease to rise and the transformer will add no additional impedance to the driving current. Therefore, without a burden resistor, the output voltage of a current transformer will be its saturation voltage at the operating frequency."

Well, there's that.

Yes, size the burden resistor based on the amps being drawn and the required output voltage. This is a good article about CTs and burden resistors. Quote above is from that article.

http://powerelectronics.com/mag/power_expl...nt_transformer/

 

[SteveQ]

Thanks, I could easily add a resistor across the CR3110 leads. Based on the chart it looks like a 2K resistor should bring the voltage down to about 8vac. Does that sound right?

Here's how I would approach it. Your water heater is 3380w at 240v. That's 14amps. Plugging that into the formula V = 14*2000/3100 = 9vac output. That should be OK since its less than spec-ed 10vac max. I would use a 1K resistor V = 14*1000/3100 = 4.5vac.

Going back a couple of weeks to your original post, the circuit has the resistor on the DC side of the bridge. I don't know if or how that's going to affect the formula and resulting voltage. I'd put the resistor on the AC side so you know exactly what's going into the bridge and therefore out of it.

The CR3110 on my baseboard heater circuit outputs about 9vac. Do you think I should still add a burden resistor?

"What happens if the burden resistor is left off or opens during operation? The output voltage will rise trying to develop current until it reaches the saturation voltage of the coil at that frequency. At that point, the voltage will cease to rise and the transformer will add no additional impedance to the driving current. Therefore, without a burden resistor, the output voltage of a current transformer will be its saturation voltage at the operating frequency."

Well, there's that.

Yes, size the burden resistor based on the amps being drawn and the required output voltage. This is a good article about CTs and burden resistors. Quote above is from that article.

http://powerelectronics.com/mag/power_expl...nt_transformer/

Thanks for the comprehensive explanation. I have modified the water heater monitor circuit to include a 2K burden resistor. I chose this rather than your suggested 1K resistor because the DC side of the circuit contains a voltage divider to bring the voltage down from 10 to 5 volts DC. Since it's all soldered up I wanted to keep the AC voltage into the bridge rectifier around 9-10 volts.

For my baseboard heater monitors, I will use a burden resistor that will drop the voltage to around 5VAC. On the DC side of the rectifier I think I will keep the 10K resistor but tie it to the base of the 2N3904 transistor. That will limit the current it can draw. It is probably not needed but it won't hurt anything.

Steve Q

 

[SteveQ]

If anyone is interested in getting some DS10A ; X10 is selling them at 4 for the price of 1. Go to http://www.x10.com/promotions/ds10a_4f1_email.html

Steve Q

 

[Madcodger]

Thanks, Steve - THAT's a find!

I ordered 8 at that price...