Battery Backup for HRV Programmable Timer

Discussion in 'The Projects Forum' started by Scavenger, Mar 30, 2009.

  1. Scavenger

    Thread Starter Member

    Jan 5, 2005
    12
    0
    I bought a programmable timer for my HRV. It turns out the timer doesn't have battery, so when the power goes out the programming is lost. Since the power to the timer is coming from the HRV, how would I go about adding a battery backup to the timer. There are three wires going from the HRV to the timer. A coworker said the three wires would likely be power, signal, and ground - is that true? I measured the voltage across each pair of wires, when the timer is switched off (at the timer), and got these values: A-B: 4.53V A-C: 4.78V B-C: 0.25V. When the timer was switched on, the voltages were: A-B: 4.53V A-C: 4.88V B-C: 0.36V. At that time it was running the HRV fan on low speed. What sort of circuit would I need to ensure the following:

    1. I don't lose the programming
    2. I don't fry the timer circuitry
    3. I don't fry the HRV circuitry
    4. I don't blow-up the batteries
    I'm an electornics rookie, so don't assume I know anything.

    Thanks.

    Richard
     
  2. Scavenger

    Thread Starter Member

    Jan 5, 2005
    12
    0
    It's time to fire up the HRV for the winter. Still looking for help on what I'd need to provide battery backup for the timer.

    Thx.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Are you talking about a "heat recovery ventilator"?

    Do you have a manufacturer and part number/model number for this timer you bought?
     
  4. Scavenger

    Thread Starter Member

    Jan 5, 2005
    12
    0
    Last edited: Oct 30, 2009
  5. Scavenger

    Thread Starter Member

    Jan 5, 2005
    12
    0
    Anybody willing to provide some guidance?

    TIA.
     
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