A More Elegant Solution Needed

Discussion in 'Bob & Don's Electronics Forum' started by Kiko, Jan 25, 2015.

  1. Kiko

    Kiko Member

    Joined:
    Jul 20, 2009
    Location:
    Royal Oak, Michigan
    My parents have a Pro Com remote control gas logs fireplace. The latching solenoid that opens up to release the gas is rated for 6 volts, and the receiver box holds four AA batteries. The solenoid is sticking now, and even the freshest alkaline AA's won't actuate it.

    I soldered in a 9 volt snap connector to replace the AA's, and it works perfectly again, but looks jerry-rigged.

    I was searching for AA batteries that are greater than 1.5 volts and found AA 3.7 volt lithium ion batteries that are rechargeable. Could these work? I read somewhere that they should only be used individually, and that putting them in series could cause problems. But I don't remember what kind of problems.




    Pro Com receiver box.gif Lithium Ion Batteries -2.jpg
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Rechargeable lithium cells can be used in series. You don't want to discharge enough that either cell discharges completely. Charging in series could be a problem, but that would not be what you are doing.

    The lithium cells you are talking about are called 14500.

    I would worry that the electronics could be hurt by the higher voltage, but your 9 volt battery test says you got away with that for a while.
     
    Last edited: Jan 25, 2015
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  4. Kiko

    Kiko Member

    Joined:
    Jul 20, 2009
    Location:
    Royal Oak, Michigan
    Thanks. The manufacturer actually recommends using a 9 volt to try to unstick a sticky solenoid. But in this case it didn't work; hence the need to modify the receiver box to accept a permanent 9 volt.

    I'm a bit confused about mAh. The 3.6 volt AA lithium cells range from 1200 - 5000 mAh. The alkaline 9 volt is 570 mAh and the original AA alkalines are 2200 mAh. Why does the 9 volt have more power with less capacity than the four AA alkalines? And do I need the higher capacity Lithium cells?
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    The 9 volt has 6 little alkalines in series inside. So the 9 volt would not last as long as the 4 AAs in series.

    The 9 volts pushes more current into a given load, so the solenoid sees more power due to the higher voltage. But it will not last as long doing that.

    Power in milliwatts = volts * millamps.
     
  6. Kiko

    Kiko Member

    Joined:
    Jul 20, 2009
    Location:
    Royal Oak, Michigan
    Before I soldered in the 9 volt, I swapped out the four AA's with four AAA's and four 1.5 volt (disc) watch batteries, all in series. The output voltage registered 12 volts on my volt meter, but it didn't have enough power to open the solenoid. How can that be the case, if voltage = power.
     
  7. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Voltage is not power. Voltage * current is power.

    I suspect that at least one of your batteries was limiting the current. So if you measured the voltage to the device with your series of cells the voltage under load would have been much lower.
     
  8. Kiko

    Kiko Member

    Joined:
    Jul 20, 2009
    Location:
    Royal Oak, Michigan
    Okay, thanks.

    One last question:

    Is it okay to put lithium and alkaline AA batteries together in series? I'm thinking of using three alkalines and one lithium (or two and two) to actuate the solenoid using the least amount of voltage, so as not to fry the electronics in the receiver box.
     
  9. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
  10. Kiko

    Kiko Member

    Joined:
    Jul 20, 2009
    Location:
    Royal Oak, Michigan
    Great info, thanks again!
     

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