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ENV-VST-C Power Problem

We have a project that need to use this item as our thermostat but the contractor of the HVAC system said that this item is not compatible to their device this is what their email:

Dear Manoj,

This thermostat is not compatible to the two-way actuator provided at site. We have provided for Honeywell 230V On/Off two way valve & actuator for the Fan Coil units in the three proposed rooms. The proposed AMX thermostat is a 24V input thermostat and cannot action the installed valve. Attached again in the brochure of the Honeywell thermostat we are installing and it is clear that the input and output from the thermostat shall be 230V.
Kindly forward the same to the automation contractor and they will have to give a thermostat which works on the same logic.

So what solution do we need to work to make this thermostat to work with their system. can we convert the power? but they said you need to convert the in and out. but this one doesn't make sense for me as im pure programmer and do know the logic behind this HVAC system


  • Of course, as a programmer, the most you can do is to refer this back to your design engineers and project manager. You will have a difficult time explaining an HVAC (or any) contractor on site how our system actually works and how things are actually very simple if you think a bit out of the cooler-box.
    A good starting point in how a dry contact or a 24V actuator can be "transformed" to a 230V is here http://www.hager.com.sg/energy-distribution/power-interface/modular-contactors/3323.htm
  • JubalJubal Posts: 77
    if i use this. the power from FCU which is 230v can be converted to 24v for our thermostat. how about the out? 24v-230v? they said it must be converted. i will include all the email from contractor and the email from AMX ME about this matter

    Jericho, Zoran,

    AMX thermostat, ENV-VST-C, does not support 230V output. The specs are well defined in the datasheet, as well as wiring and compatible HVAC systems. Power rating of ENV-VST-C is 24VAC only.
    If you go through the "Installation and Wiring" section of the attached manual and find out that the current system can be compatible from connectivity perspective, you may manually connect the contact closures output of the ENV-VST-C to 3rd party 230VAC transformers in order to control the fans/valves, as applicable.
    The other alternatives are:
    1- to show the wiring diagrams and compatible HVAC's to the HVAC expert and let him determine work around for the system using the devices in hand.
    2- to provide clear HVAC system datasheets which allows AMX experts to advise regarding compatibility, or a workaround if possible.
    3- to request the HVAC expert to advise if they can provide any data bus and interface through which the AMX system can communicate to the HVAC system, such as Serial RS232 or RS485, KNX, LON, or BacNet.

    Let me know if you have any questions.

    Dear Jericho,
    As per the contractor had said many times that the power supply of their FCU will come from the THERMOSTAT. A stand alone power supply could not be able to do the task to trigger the FCU through THERMOSTAT as the AMX THERMOSTAT is 24VAC output and this could not be able to power up the FCU because it needs a supply of 230VAC.

    Our required controls for the FCU is a BMS type of control where it requires to have a voltage supply of 24VAC.

  • As I said, it is best to refer this back to your design engineers. The Hager contactors are a mere example of devices that could accommodate the request. Every decent electrical board components manufacturer will have something similar, but the principle was outlined:

    24v actuates the relay, which has a main feed of 230V. When 24v is present, the 230V will go through. (Latches the circuit closed)
    The reverse 230V->24V should also be in their offer. An AC actuated relay, with an input from a 24V PSU that passes through when relay latched (when 230V present).

    I would not recommend an inline voltage transformer as they normally have a lag and current is still present in the secondary coil even after supply is not present, subject to the current drawn by your end device.

    Again, if any of the above sounds confusing, it is better for somebody with electrical background to design it for you
  • JubalJubal Posts: 77
    so there's an item that can do that? or we need to customize this board to fit in the requirement? thanks for your help now it take a picture in my mind now the logic of this thing. for best and fast solution, better to find this item that have capacity to convert 230v-24v for input and 24v-230v for output
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