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UPS or 5V Battery?


Since I don't have physical access to my Kiwi I really would like to make sure it won't accidentally loose power and loose its filesystem.
The unit is currently powered by a linear power supply (220V).

My first idea is to purchase a cheap UPS unit for it but I was wondering if that would introduce noise into the system. Has anyone has any experience in this regard?

Another idea is to somehow introduce a 5V battery between the power supply and the receiver. Does anybody know of a 5V solution like that isn't based on a switching PS?



  • run it off this while charging the battery off your linear supply.

    Get one or 2 of these to monitor things
  • I have seen many devices like that battery but I am afraid they would all be switching. Wouldn't they?
  • it's just a battery
  • edited February 2019
    I tried a USB battery pack for powering SDR's (Turnigy dual USB) and it was horribly noisy, like one of the worst options tried.
    If you have experience of that Adafruit device great, but useable on paper is may actually be rubbish in use.
    The battery inside is probably a lipo (4.2-3.8V roughly) so to get 5V out they must use some sort of switcher surely?

    As the use is just for power failures I wonder if a small 12V SLA battery with a DC-DC switcher that is only energised (and connected to the Kiwi DC) when mains is down would be an option.
    Small solar trickle charger or tiny linear to keep it topped up.

    There is then the issue of fast switching and making sure the Kiwi is up fast enough that is does not lock on brownout.

    To me two supplies and relays DC side would cover most eventualities.
  • The USB pack I have seems pretty quiet.... but I suspect it varies widely...... A 6V SLA battery with a 5V LM7805 type regulator is a certain quiet way.
  • I thought the 5V 7805's needed 7V input.
  • perhaps.... let's just say a linear regulator!
  • I'm looking for UPS to keep the Kiwi's on too and to alert me if there's a power cut so I can log in and monitor the battery capacity left in the UPS.

    I would probably need pure sinewave which adds to the cost.

    Battery backup to the Kiwi's is good but need to keep power to the 4G modem too.

    I had a recent power cut that killed both Kiwi files systems.

    It would be reallyh convenient to have some kind of over the air backup of all the Kiwi settings so you wouldn't need to re-load everything every time, yes I keep forgetting to make backup over micro sd but still it would be very convenient to just load the settings from the laptop over to the Kiwi's when they are back online.
  • The UPS route, to me, seems inefficient, it has to use the DC battery to power the inverter and PSU's to convert back to DC.

    Perhaps define the ideal requirement for supply failure cover time then work back from that for how much battery is required at what efficiency.
    A UPS battery that will run a UPS inverter at no load for 40 minutes would probably cover the Kiwi and Modem for two hours or more in a mostly dc setup.

    So, as an exercise
    1. How long do you want it be able to run between charges (total, maybe multiple failures)
    2. How long can you wait for it to fully recharge?
    3. How much space do you have?
    4. What temperature range?
    5. Any source of charging power when the supply is down?
    6. how deeply can you risk discharging the battery?
    7. How much current can you provide for charging (dependant on battery charge limitations obviously)

    If you said I want two hours cover (minimum) in any 12 hour period that would probably need a 8AH battery or more with efficient DC conversions, much much more the UPS route.
    Guesstimation based on...
    Kiwi ~5W
    4G Modem ~8W (just a wild guess, depends on type path to tower etc.)
    Other monitoring hardware options 4W

    That is something like 6AH actually used so assuming you would not want to completely flatten the battery size up the SLA.
    Then with charging for max ten hours you'd need something like a minimum 1A charge source.

    I doubtless have got at least part of that wrong but am considering a similar setup myself so wanted to think it through.
    Was just looking at the various PCB's sold through Banggood/Ebay etc. for battery monitoring and switching, I bet the built bits are out there for a few pounds and bit of wiring.
  • My goal is a solution able to avoid short power interruptions under domestic circumstances and I agree that the UPS solution (although easier) seems unnecessarily expensive and potentially noisy.

    One idea I am exploring is to use something like this battery:

    Take a look at the attached file.

    The battery would be constantly charged by the 5V supply through a current limiting resistor. When power goes out, the relay would connect the kiwi to the battery. A large electrolytic capacitor would supply power for the few milliseconds that the relay would take to switch, and would also prevent bouncing effects.

    Do you think this could work?


  • on a second thought, that capacitor cannot work with the relay. :(
  • The funny thing is I have that battery in 12V form, I was going to use a DC-DC after it to cope with the voltage range 12.6-10.8V, I think the 5V one must be the two combined into one device as Li-on does not do a native 5V. I would stick to the 12V and regulate after it due to my experience with the Turnigy USB battery.
    You could use the 12V version and a Linear 5V voltage reg as long as you can dispate any heat generated and don't mind a bit of power loss.
    I was totally against switchers anywhere but have softened on that stance since playing with a few current ones. One day I'll do some noise comparisons between supplies with the Kiwi in a Faraday cage (maybe with a miniwhip), I just need to get down to it and think of a suitable process so I don't have to duplicate it too many times.

    On the LiOn battery i wanted to limit the discharge voltage too, it's better to think the Kiwi will go down cleanly rather than the battery puff destroying itself and crushing anything around it in a tight enclosure.
    I see Banggood/Ebay do loads of LiOn protection boards, must look into making a cell assembly for the Kiwi out of 18650's.
    My reluctance to actually get it built here is that any rural spot I find to put the thing will probably be open to being "recovered for recycling at the local scrap yard" by some "highly responsible" locals.

    So I'm tending towards sensible battery + charge/discharge protection.
    That still doesn't cleanly shut down the Kiwi though I suspect it is more at risk from multiple fast on/off cycles than one clean power down.
    May be someone will see the need and put something dedicated to the Kiwi on Tindie.
  • I will stick to the 5V because the circuitry internal to the battery would increase safety and also provide charging circuitry.
    In order for my discharging capacitor to do the job, I will try adding a the right combination of diodes (zener) on the relay coil line so that the main power would disconnect precisely around 4.8V. I guess never falling below that tension should be enough to keep the Kiwi running for those few milliseconds until the backup battery comes online.
  • On reflection that battery might be a two cell, 8.4-7.2 volts internally, will be interesting to hear how noisy if anything it is.
    The rated capacity is higher than the one I have in the same format so probably two, not three but larger cells.
    The Turnigy battery pack looked workable for running the Kiwi mobile until the switcher noise, it also does not not power the output while being charged and needed a button push to enable the output, the current CCTV things look a better bet.

    On the relay I can't help thinking double pole would give you more options and like the analogue engineering "precisely around 4.8V".
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