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Author Topic: Disabling local control current on a WTM75?  (Read 3217 times)

ssokolow

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Disabling local control current on a WTM75?
« on: June 19, 2015, 12:11:56 PM »

I have a light fixture behind my monitors that I use as a bias light and, when I switched from a 10W 6500K (daylight white) CFL to a 9W 2700K (warm white) CFL in concert with installing Redshift (an f.lux clone), I found that the WTM75's local control signal was enough to cause faint pulses of light. (Which can't be healthy for a non-dimmable CFL)

Even adding a second nightlight to the extension cord did nothing to stop it. so I tried swapping the WTM75 with a PAM02 I was using to control a fan to see if that fixed it. It appears to have done-so, but I want to keep my bias light on code 1 and, as the unexpected volume of this summer's sales has drained my discretionary budget dry, I can't currently justify the cost of another module.

Can anyone suggest either a URL with instructions for modding a WTM75 to remove local control (all the Google results are for other models) or a way to keep the CFL from reacting badly to the local control current?
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Brian H

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Re: Disabling local control current on a WTM75?
« Reply #1 on: June 20, 2015, 06:37:13 AM »

Adding another small incandescent bulb on the output did nothing to correct the faint pulsing?

I searched the cross reference sheets and can't find a WTM75.
Do you know if it is a TM751 Transceiver with a retail or maybe private vendor part number?

Is there a small white sticker on the WTM75 with a Date Code. I know the TM751's where redesigned and depending on the date could be different from previous hardware models. Modifications for one version may not apply to the later ones.
« Last Edit: June 20, 2015, 06:40:04 AM by Brian H »
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dave w

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Re: Disabling local control current on a WTM75?
« Reply #2 on: June 20, 2015, 12:02:23 PM »


Even adding a second nightlight to the extension cord did nothing to stop it.

Was the nightlight an LED? Make sure the nightlight is at least a 7W incandescent. You can also try a 10W "golf ball" E27 base (standard size base) incandescent.
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ssokolow

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Re: Disabling local control current on a WTM75?
« Reply #3 on: June 20, 2015, 12:36:23 PM »

Quote
Was the nightlight an LED? Make sure the nightlight is at least a 7W incandescent. You can also try a 10W "golf ball" E27 base (standard size base) incandescent.

The second was an LED specifically because it consumed more energy. The first was one of those electroluminescent/LEC night lights.

I think the only incandescent bulb anywhere in the house is in the lava lamp boxed up in the garage and I don't want to go beyond shuffling existing loads around the house (eg. trading different types of night light as I did here) because I want my energy consumption to trend down over time.

(eg. Anything without a true off-switch that doesn't need to be remote-controlled, like my TV and "1 watt idle, 3 watt playback" home theatre PC, is on one of the many switched power bars I've received with scrap computer equipment over the years.)

Quote
Do you know if it is a TM751 Transceiver with a retail or maybe private vendor part number?

It looks like a TM751 and, as I remember, it was sold to me as a TM751 back when I had my only RR501 fail and jumped to the conclusion that TM751s were more reliable.

Quote
Is there a small white sticker on the WTM75 with a Date Code.

There are two small stickers on it. The smaller round one says 01C10 and the larger rectangular one says P10485B.
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Brian H

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Re: Disabling local control current on a WTM75?
« Reply #4 on: June 20, 2015, 04:02:51 PM »

Well you will never kill all of the current on the output. Local Control Sensing maybe. Am I On or Off Sensor has to stay.
The TM751 has a small sensing current to determine if it is On or Off. As the controller does not keep track of the output status.
Kill that sensor and it will sound like a machine gun firing as it tries to see if it is On or Off.

If you didn't use a incandescent night light bulb. Then the current may not have been lowered enough to stop the CFL in question from pulsing.

Some handy folks have used a resistor on the output. 33,000 Ohm, 1 watt. When the output is On. There is a .45 watt load from the resistor.
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ssokolow

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Re: Disabling local control current on a WTM75?
« Reply #5 on: June 20, 2015, 04:08:01 PM »

Well you will never kill all of the current on the output. Local Control Sensing maybe. Am I On or Off Sensor has to stay.
The TM751 has a small sensing current to determine if it is On or Off. As the controller does not keep track of the output status.
Kill that sensor and it will sound like a machine gun firing as it tries to see if it is On or Off.

If you didn't use a incandescent night light bulb. Then the current may not have been lowered enough to stop the CFL in question from pulsing.

Some handy folks have used a resistor on the output. 33,000 Ohm, 1 watt. When the output is On. There is a .45 watt load from the resistor.


None of the resistors in my 33...Ω drawer go above 1/4 watt, so I'd have to order it, but that might be possible. Do you have any schematics or photos showing the exact modification to be made?
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Brian H

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Re: Disabling local control current on a WTM75?
« Reply #6 on: June 20, 2015, 06:27:09 PM »

Not 33 Ohms. 33,000 Ohms (33K).

Not added inside the module. Mounted in a plug and use a power tap so both the CFL and 33K resistor are on the output.

I tried two TM751 modules. Date Code 09L53 and 00D17. Both did not have local control. Only the am I on or off sensor current.
You can test yours. If you turn the WTM75 off and then toggle the local switch on the fixture or unplug and then plug back in again. If the module triggers On then you have local control. Mine did not along with two different hardware RR501's.
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ssokolow

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Re: Disabling local control current on a WTM75?
« Reply #7 on: June 20, 2015, 07:21:58 PM »

Not 33 Ohms. 33,000 Ohms (33K).

Note the ellipsis. I sort my resistors by prefix. When I said my 33Ω Ohm drawer, I meant my drawer containing all resistors where the colour code begins with orange-orange.

Not added inside the module. Mounted in a plug and use a power tap so both the CFL and 33K resistor are on the output.

Is it a matter of how it responds to rapidly changing power supply? ...because the LED nightlight I switched to when the electroluminescent night light was insufficient is rated at 0.5W max. and, according to my Kill-A-Watt, is already drawing more than 0.45W.

I tried two TM751 modules. Date Code 09L53 and 00D17. Both did not have local control. Only the am I on or off sensor current.
You can test yours. If you turn the WTM75 off and then toggle the local switch on the fixture or unplug and then plug back in again. If the module triggers On then you have local control. Mine did not along with two different hardware RR501's.

Ahh. I've never had local control work for me, even on things clearly listed as having it, so I wound up assuming everything had it but it never worked. My mistake for getting my terminology muddled.
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Brian H

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Re: Disabling local control current on a WTM75?
« Reply #8 on: June 20, 2015, 08:39:58 PM »

The wattage rating is for when the light is being powered.
When it is off it maybe a high impedance circuit that can't swamp out the sensing current.
The incandescent night light bulb when off and the filament is cold. Has a much lower resistance that will swamp out the sensing current but not be too low a resistance when On. As the filaments resistance goes up as it gets hot.
I measured a 4 watt nightlight bulb and it was around 345 Ohms and a 7 watt was about 150 Ohms cold.
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ssokolow

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Re: Disabling local control current on a WTM75?
« Reply #9 on: June 20, 2015, 08:45:47 PM »

The wattage rating is for when the light is being powered.
When it is off it maybe a high impedance circuit that can't swamp out the sensing current.
The incandescent night light bulb when off and the filament is cold. Has a much lower resistance that will swamp out the sensing current but not be too low a resistance when On. As the filaments resistance goes up as it gets hot.
I measured a 4 watt nightlight bulb and it was around 345 Ohms and a 7 watt was about 150 Ohms cold.

Reminds me of how one DIY builder used a car headlamp bulb and a small cooling fan as a simple way to provide a dummy load for a "convert an ATX PSU into a bench power supply" build.

I'll have to think about how I want to do this.
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Brian H

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Re: Disabling local control current on a WTM75?
« Reply #10 on: June 21, 2015, 10:03:37 AM »

If you want to verify the 33K resistor will work. Some real touchy bulbs may still have issues.
A 33K 1/2 watt if you have one. Will test the theory. The wattage would be around .45 watts. I just don't like to push components to their full rating. So I said 1 watt.
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ssokolow

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Re: Disabling local control current on a WTM75?
« Reply #11 on: June 21, 2015, 12:04:48 PM »

If you want to verify the 33K resistor will work. Some real touchy bulbs may still have issues.
A 33K 1/2 watt if you have one. Will test the theory. The wattage would be around .45 watts. I just don't like to push components to their full rating. So I said 1 watt.


Yeah. I can confirm that the math checks out, so it's mainly a question of figuring out required heat dissipation so I don't wind up doing something like discolouring some plastic and then ordering a 1 watt resistor. (I also don't like to push components)
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dave w

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Re: Disabling local control current on a WTM75?
« Reply #12 on: June 21, 2015, 06:17:53 PM »

Yeah. I can confirm that the math checks out, so it's mainly a question of figuring out required heat dissipation so I don't wind up doing something like discolouring some plastic and then ordering a 1 watt resistor. (I also don't like to push components)

FYI
I use 33K 1W to prevent the EMF of a ceiling fan motor from tickling an Appliance Module back ON after turn-off.

I have never tried a resistor to stop CFL or LED flicker. It may only slow down the periodic flicker. Will be interested in hearing if it works for you.

http://www.ebay.com/itm/33000-ohm-33K-1-watts-1W-1-Metal-Film-Resistors-8-Pieces-/271552661775?pt=LH_DefaultDomain_0&hash=item3f39ccc90f

« Last Edit: June 22, 2015, 08:56:47 PM by dave w »
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ssokolow

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Re: Disabling local control current on a WTM75?
« Reply #13 on: June 21, 2015, 06:23:14 PM »

FYI
I use 33K 1W to prevent the EMF of a ceiling fan motor from tickling an Appliance Module back ON after turn-off.
Hmm. I think I've experienced that once or twice with my own fans so, even if it doesn't work as intended, it won't be wasted.

I have never tried a resistor to stop CFL or LED flicker. It may only slow down the periodic flicker. Will be unterested in hearing if it works for you.

http://www.ebay.com/itm/33000-ohm-33K-1-watts-1W-1-Metal-Film-Resistors-8-Pieces-/271552661775?pt=LH_DefaultDomain_0&hash=item3f39ccc90f

Doesn't sell to Canada and there's a Chinese seller that'll sell me a 5-pack for roughly 1/3rd of that price so it'll take 30-40 days before I can assemble it.
« Last Edit: June 21, 2015, 06:25:05 PM by ssokolow »
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JeffVolp

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Re: Disabling local control current on a WTM75?
« Reply #14 on: June 22, 2015, 09:00:51 AM »

Doesn't sell to Canada and there's a Chinese seller that'll sell me a 5-pack for roughly 1/3rd of that price so it'll take 30-40 days before I can assemble it.

Jeepers, resistors are easy to get.  Try a standard electronic distributor like Mouser or Digikey.

If you don't have a 33K 1W, you can connect three 100K 1/2W resistors in parallel.

Jeff
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