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Use 5 VDC Power Bank PB to feed circuit which has no own battery.

Discussion in 'Power Electronics' started by morphingstar, Aug 5, 2021.

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  1. morphingstar


    Mar 1, 2012
    The original battery died. Replacement needed. Available are Power Banks, nothing else. Lithium falls under prohibited shipment. The choice is therefore small.
    Old battery 1+2 ADC USB outputs. 8000 mAh, does no longer accept charge.
    New Power Bank 1+2.1 ADC outputs. 12000 mAh. Charged 24h.
    Tool for checking: VDC + ADC digital indicator, shows usually 5 VDC and charge current, lowest visible 10 mA.
    Behavior of old battery while in good condition: Feeds the circuit with 1.5 A rush-in current, which drops to 0.85 immediately.
    5 LEDs indicate battery state. It will switch off automatically at low charge level.
    Load: Electronic circuit with a data display, indicates readiness immediately.

    Problem: Power Bank does not feed circuit. Switch on PB. 5 VDC, as soon load is connected the voltage goes to zero. It won't swich on with load connected.
    The outputs are not marked as to current or numbered. The result is same with both connections.
    Test PB by charging phone: This works, 1.6 ADC consumed. The phone is switched on.

    Hypothesis: PB has a voltage sensor at the output. If it can not sense 4.5 VDC (assumed value) it will switch off output, 4 LEDs going off too.
    Changing internal circuitry of PB might be impossible. The solution must come from the outside.
    Somehow feeding voltage to PB outlet using diode to isolate from load circuit? Then connect load.
    Suggestions welcome.

    The PB has other strange behavior: Kindle Fire7 charges with 0.45 A from charger while switched off. Connected to PB it "charges" with 200 ma while Fire7 is on. Power off leads to 0 charge current. Fire7 will actually discharge while fed with PB. Design logic was absent.

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Power banks are typically powered by lithium batteries inside...
    Do you mean 2 outputs, 1 × 1 A DC and 1 × 2 A DC?
    ADC is not a meaningful unit, can easily be confused with the abbreviation for Analog-Digital-Converter which makes no sense in this context.

    Your power bank might shut down due to the peak inrush current. Have you measured the actual capabilities (i.e. output voltage vs. output current) of the power bank using resistive loads? Do not trust the "technical data" of the power bank as stated by the manufacturer. These "data" are often hopelessly "optimistic" (or overrated), especially if the power bank id of the cheap type from ...
  3. morphingstar


    Mar 1, 2012
    vdc is a common "voltage direct current", in the applied situation it is CURRENT .. .
    The inrush current is known to be 1.5 ampère. Then followed by 0.85 ampère. I stated this data in my inquiry.
    The data comes from a reliable source. I do not have a scope to view. A purely resistive load has no "inrush current".
    The phone charged with 1.63 ampère (today), which is higher than the inrush.
    Analog-Digital-Converter makes no sense, right so why apply it?
    I searched for a 5 VDC batterie which is not a charger, found none so far.

    Meanwhile I made 2.5 ohm load. How to connect it without cannibalizing a USB cable is currently a mystery. Nothing untried, though the "sensor" matter described might make test impossible.
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