radio memory Battery back up

Discussion in 'Power Electronics' started by clunk7618, May 13, 2017.

  1. clunk7618

    Thread Starter New Member

    May 13, 2017
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    i have up graded the stereo in my tractor and i have a problem the safety systems with in the tractor shuts down all electrical earths 6 mins after the key is turned off so the radios memory goes blank we have tryed to put a bypass power feed from the tractors battery but the system does not accept this and wont let the safety systems shut down so this drains the battery and causes other problems .
    What i am looking to do is build a battery back up system that will switch over and save the memory but also recharge when the ignition is on so it is self supporting
    From the research i have done the radio draws between 7 and 30 mill amp and i would like to have a system that lasts as long as possible due to machine standing for extended times any help you can give me would be great
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    All you need is a 12v sla 2.6Ah battery and a diode,....you can omit D2 and resistor, beacon is your radio.



    battery_backup.jpg
     
  3. KeepItSimpleStupid

    AAC Fanatic!

    Mar 4, 2014
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    30 mA is probably too long to be good for more than a month. I'm not sure why it would shut down the earths.
    Radios usually have a +bat, a +mem and ground. Then there is a DIM input from the lights. I would suspect that mem should come direct from the battery.

    For an extended shutdown, I think I would consider a micropower comparitor like the LT6700 to turn off the backup.

    If it does indeed cut the negative power, then find a way to isolate the radio ground which is easier said than done.
     
  4. clunk7618

    Thread Starter New Member

    May 13, 2017
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    Not sure why it chops the negative side its a total pain i know the radios normally have a constant power we tryed a by pass but the tractors system sensed it and it kept all systems live and wouldn't shut down manufacturer has not been much help only help i got was one of the radio makers said to put a battery behind the radio and sent me a thing like a house brick and got no space for it
     
  5. crutschow

    Expert

    Mar 14, 2008
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    You might measure what current the radio draws when it's off.
    It might be small enough that some dry cells can maintain the memory.
     
  6. KeepItSimpleStupid

    AAC Fanatic!

    Mar 4, 2014
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    Thinking out load. To be determined if it might work or not.

    If you disconnect the radio backup will the tractor shut down?

    I'm thinking along the line of charge a super cap, and "OFF" transfers the backup to a super cap and then the radio shuts down and it gets transferred back to the vehicle battery.

    It might be a complex mess.

    So, does this work.

    Turn off radio
    remove mem+ wire
    Shut down tractor
    Attach mem wire to battery 8 minutes later.

    or does this work:
    remove power from radio
    remove mem+ wire from radio
    Shut down tractor
    Attach mem wire to battery 8 minutes later.
     
  7. clunk7618

    Thread Starter New Member

    May 13, 2017
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    memory wire is connected at all times just now soon as you switch off the ignition the radio goes dead and memory is cleared just as any radio would when it doesn't have a mem constant feed and at the moment the tractors safety systems shut down after the 6 mins if i connect the memory wire to a constant power feed from the tractors battery on the far side of the solenoid or on the solenoid that that disconnects the earths the safety systems wont shut down have tryed many work arounds just not the battery as one of the radio manufacturers told me too

    I just want it to keep the memory and re charge the battery when the ignition is on got no clue what more to do only option the tractor manufacturer is giving me is buy one of their radios with a built in e prom but they are heavily over priced and massively under spec for a machine i will be spending upwards of 100 hours a week in for the next few months nearly forgot to add their radios are £250 more expensive the one i have
     
    Last edited: May 13, 2017
  8. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Why don't you just wire the radio directly to the battery, with a fuse.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Can you measure the current the memory wire draws?
     
  10. KeepItSimpleStupid

    AAC Fanatic!

    Mar 4, 2014
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    I'm just looking at something like:
    Charge a supercapacitor and possibly a DC DC converter in the ON position to power backup lead.
    When igniton off, disconnect the 12 V source for 7 minutes.
    Then maybe put it back with an ideal diode controller.

    e.g. Start of with something like this http://cds.linear.com/docs/en/datasheet/4358fa.pdf

    just to see if it MIGHT work,

    Put a 9V battery on one input, the +12 tractor battery on the other and an input powered from the 9V source that lets one or the other sources work. e.g. Open drain buffer and open drain inverter.

    You have a switch that makes the battery backup battery or 9V. Put a capacitor on the Memory lead to ground.

    So, as I said, turn off the tractor, flip switch, wait 7 minutes, flip it back.

    In simple terms this might work.

    A 9V battery alone and a shotkey diode might work too for some time.

    ==

    if it does, then detect a power down with an LT6700 comparitor and then timeout for 7 minutes using LT's timerblox circuits.

    ==

    You might be able to make it more robust using something like this http://www.linear.com/solutions/1738 as a starting point.

    Some things would really help:

    1. How much current does memory power draw?

    2. What voltage does the memory get lost. That might be a hard number to get.

    3. What load does the tractor detect as being excessive, Grab a few resistors in 1,2 5 steps that will draw from 1 uA to 100 mA and get a guess. Turn off tractor and measure V. use that V for all other tests. Put a resistor to +12 and use a binary search type ot technique to figure out which resistor works and which doesn't.

    Say you had 11 values of resistors in decreasing values (more current). Pick the number in the table just less than 11 which is 8.

    e.g.
    1
    2
    4
    8
    16
    32


    Use resistor 8 first, Did 8 shut it down. No, pick the 1/2 way point or resistor 10. Did it shut it down? no - pick resistor 11.

    yep, it would be nice to test the extremes first. then you keep halfing the list. it's easier if the artificial "middle" is a power of 2. The number of experiments are minimized.

    You could use a potentiometer too and do t that way, Make a list of values. Set them and do the test.
    You can find the course limits and then zero in on the value.

    ==

    The 9V battery and a diode is a typical keep alive gizmo you can buy that you plug into your lighter socket wheil changing your battery, You want the diode to block 12 V to the 9V battery. Don't put it backwards.
    The back-up circuit is usually a pretty low voltage because of the drop of the electrical system when starting a "car".

    Is there a market for this thing? Whatever it might be? At what price?
     
  11. clunk7618

    Thread Starter New Member

    May 13, 2017
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