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Backup Battery test questions — Parallax Forums

Backup Battery test questions

garyggaryg Posts: 420
edited 2015-04-24 09:59 in Propeller 1
Hi
I just finished assembling my 1st Hydroponic garden pump timer.
It uses PropMini, Parallax 4line LCD (serial), Parallax single relay boards.
I power it normally with Wall-Wart 7.5Volts.
When I unplug the Wall-Wart, a relay drops out and I use 5AA batteries to power the timer
until I once again plug in the Wall-Wart.

I'm doing a battery life test at the moment and started thinking about
how things behave as the battery voltage decays.

I'm using RadioShack 5volt regulator to power my LCD and RELAYs.
I'm using the full 7.5V battery directly to the PropMini Vin pin.

As the battery voltage starts dropping, I would imagine that the RadioShack 5volt regulator will start doing something
rather peculiar.
The PropMini should be ok until some time after the LCD and Relays quit working.

Question is: Will I damage my LCD or relays by having them operate below the specified 5Volts?

This is the 1st project of this type I've attempted.
I'm counting on being able to use this timer to control pumps in my garden over this summer.

Any comments, suggestions, etc. would be appreciated.

Thanks
Gary

Comments

  • lanternfishlanternfish Posts: 366
    edited 2015-04-23 15:59
    Hi Gary

    Without more info on the LCD and relays it is hard to say. Can you supply part #?
    Some LCD's are good at 3V while others aren't.
    Relays can vary in terms of operating and holding voltage and current.

    Cheers
  • garyggaryg Posts: 420
    edited 2015-04-23 16:08
    Hi
    The LCD is Parallax # 27979
    I like the serial LCD's that Parallax sells.
    I've use a couple of them.
    The battery life test I'm running will show what may happen.
    I'm hoping this test will not cost more than $100 in replacement parts.
    Thanks for any comments.
    Gary
  • kwinnkwinn Posts: 8,697
    edited 2015-04-23 19:31
    It sounds like you only need the timer to continue running when the power goes out so why not use a transistor to turn off power to the LCD and any other circuitry that is not needed. That way there is no risk of damage and the batteries last longer.
  • garyggaryg Posts: 420
    edited 2015-04-24 09:59
    My backup battery test is complete.
    I was able to run the timer, LCD and Relays for 20 hours before things started acting peculiar.
    When the battery voltage dropped to 6.25V the 5v regulator was outputting 4.75V.
    The PropMini was operating correctly because I'm using the unregulated battery voltage to power it.
    so the timer was still working correctly.
    The Relays were still operating correctly at 4.75 volts.
    The LCD really does need 5Volts to operate correctly.
    When battery voltage dropped to its 4.75v, the LCD display went dim and part of the display
    started to get confused.

    I'll be using this timer for sure this summer.

    kwinn: I think on the next iteration of timer building Your suggestion concerning shutting down the regulated 5v supply is
    something that I will need to seriously consider.

    Also, when I'm designing my next project, I'll need to seriously consider setting up access to all of the available pins
    on the PropMini.

    This project went well. I learned a lot and now I have a useful Prop powered device.

    Thanks to everyone who gave opinions, suggestions, comments.

    Gary
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