TM751 transceiver: modifying for 277V AC, inline wiring

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toasterking:
I recently needed wireless on/off control of a fluorescent lighting circuit running on 277V AC (a single phase of commercial 480V 3-phase service) by a PC. After weighing all the options (which were very few), and considering that the PC already had a CM19A connected and I was already using X10 RF there, I decided on modifying a TM751. (There are no other PLC devices running on 277V there, so PLC "rudeness" of the TM751 isn't a concern, the RR501 is too large to fit in my enclosure, and I can live with being stuck with unit code 1.)

This procedure is based on a procedure on Ido Bar-tana's web site for modifying the RR501 for 220V:
http://www.idobartana.com/hakb/modifying_remote_control_transce.htm#Modifying%20110v%20to%20220v
I had to make some minor changes to get it reliable with 277V. I ended up with a 100Ω 7W resistor for the latching relay coil mostly as a result of trial and error since I don't have all the specs on the latching relay used in the module.

The date code on the TM751 module I modified is 9F25 (25th week of 1999 during June).

   1.   Desolder the 110V plug blades and solder insulated, stranded wires in their place. Use an appropriate wire size for the load.
   2.   Desolder the 110V socket contacts and solder an insulated, stranded wire in place of the HOT out contact. (Neutral output is already connected to the neutral input so you shouldn't need an extra lead there.)
   3.   Cut the plastic out of the inside wall of the area of the plastic case where the socket contacts were. This allows you to route the new wires out through the openings previously used for the 110V socket.
   4.   Optional: If the TM751 will be mounted in an area where the telescoping antenna would touch a metal surface or the telescoping antenna cannot be used, replace the antenna with a wire. Follow the black wire from the case's antenna to the RF daughterboard. Desolder the wire from the daughterboard and replace it with a 20-24AWG wire exactly 9 1/16" (1/4 wave) or 18 1/8" (1/2 wave) in length. Note that this poses a potential shock hazard if the module will be mounted in a place where this wire could be touched with the power on! The wire must be well-insulated because it is referenced to the mains. Add a piece of shrink tubing to the end of the wire to prevent it from shorting to other conductors. Slide the telescoping antenna out of its pocket in the case and remove the old wire and the metal plate or foil coupler.
   5.   Change the large blue capacitor (2E225) from 2.2µF/250V to 1µf/400V (Digi-Key part # EF4105-ND).
   6.   Change the smaller blue capacitor (2E224) located close to the output connector from 0.22µF/250V to 0.1µF/400V (Didi-Key part # EF4104-ND).
   7.   Check that the 330kΩ resistor, close to the big capacitor, is 1/2W. It should be physically bigger than all other standard resistors. If not change it to 330kΩ 1/2W. (Did not need to change in my TM751; already 1/2W.)
   8.   Change the 220kΩ 1/2W (in some models 1/4W) close to the output connector to 470kΩ 1/2W.
   9.   Change the 130V MOV near the space that the input plug blades formerly occupied to 281V (Digi-Key part # F4010-ND).
   10.   If there is a resistor of 330kΩ 1/4W going to the output connector, change this one to 470kΩ 1/2W. (Did not exist in my TM751.)
   11.   Add a 100Ω 7W wirewound resistor (Digi-Key part # 985-1143-1-ND fits nicely) in series with one of the wires for the coil of the cam relay. The resistor could get a little warm, so try to ensure that it does not touch any other components.

My modified TM751 has been toggling its relay 6-10 times daily for 4 weeks and no failures yet!

Edit: Correction to circuit wiring for the MOV.

Brian H:
Relay is a 56 OHM coil.
Pulsed by a SCR that hits it with a single 120 volt DC pulse. Yes it is a brief 2 amp pulse if my math is not wrong.
The small MCR100-8 SCR has a voltage rating of 800 volts. 800 ma continuous current and 10 amp nonrepetitive single pulse. So it is probably OK in your mod.
The relay coil also has a small 140 volt MOV on it but your tests seem to show it maybe OK.

There is a schematic of the TM751's Main Board on the web site where you found the 220 modifications.

toasterking:
Thanks, Brian, for the additional info!

--- Quote from: Brian H on August 03, 2015, 06:30:46 AM ---Yes it is a brief 2 amp pulse if my math is not wrong. [...] 800 ma continuous current and 10 amp nonrepetitive single pulse. So it is probably OK in your mod.

--- End quote ---
I originally was using a 100Ω 2W metal oxide film resistor. It seemed to work initially, but within about 20 activations, the resistor failed internally; not completely open but high resistance in the Megohms. I tried 2 of them with the same result. So far, the 7W wirewound resistor is holding up.

--- Quote from: Brian H on August 03, 2015, 06:30:46 AM ---The relay coil also has a small 140 volt MOV on it but your tests seem to show it maybe OK.

--- End quote ---
That may be because I replaced the MOV with a 281V one. ;)

Brian H:
I thought there where two MOVs.
Even for X10. No MOV across the incoming power pins is not typical.

toasterking:

--- Quote from: Brian H on August 03, 2015, 04:32:25 PM ---I thought there where two MOVs.
Even for X10. No MOV across the incoming power pins is not typical.

--- End quote ---
Maybe there are two MOVs in some versions of this model. Mine only has one. I do have "130V MOV in parallel with the input" in my procedure, but that part of the text was copied from the original procedure at http://www.idobartana.com. I will change it to read "130V MOV near the space that the input plug blades formerly occupied".

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