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USB power change over switch

Discussion in 'Electronics & Electrics' started by ck_psy, Sep 12, 2019.

  1. ck_psy

    ck_psy Member

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    Hi guys

    I am wondereing if anything like this exists off the shelf (of it is relatively easy to make).

    I have a few powerbanks that I alternate to run a dashcam 24/7. (20000mah @ 3.7v)
    Instead of me changing the powerbanks out every day I was thinking of connecting the dashcam to a change over switch operated by a 'phase failure' or no volt relay.

    So the dashcam plugs into this device which then has 2 powerbanks (or more) connected to it. when powerbank A turns off due to not enough power the relay device changes over to powerbank B automatically.


    that way I can just change it every 2 or 3 days.
    The power banks last around 26-30 hours.

    The powerbank seems to have some sort of inbuilt protection whereby it won't recharge and output at the same time. (i.e. if i had put the dashcam into power bank A which is simultaneously being charged from power bank B, which may then be simulatenously charged by power bank C... so in 'parallel' so to speak).


    Thanks
     
  2. merlin13

    merlin13 Member

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    Played with 12 volt stuff for this off-the-shelf, but that was a fair while ago now. Honestly not looked at anything lower voltage than that, at least up to now. And Uncle Google isn't helpful...

    Building something to handle this, relatively easy for Those In The Know - low voltage sense and/or timer circuit(s) (or even an Arduino...), low power changeover relay or two, weatherpoof box etc...

    So a few points you need to clarify up front might be helpful for your quest plz:

    - budget, ballpark or 6 Sig Figs

    - your dashcam there, is it always recording/active or has a motion/impact sense/low power mode option or trigger?

    - how long does your dashcam stay alive when power is disconnected/interrupted?

    - worth pondering a custom built or off-the-shelf battery pack that'll last longer? Might be the cheapest and easiest solve for you, or do you have site restrictions on size etc?

    - can you stick a solar panel 'n suitable regulator on site, and swap the powerbank over to one that'll charge and source at the same time?

    - and, ummm... more out of curiosity, just what are you monitoring/recording?
     
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  3. OP
    OP
    ck_psy

    ck_psy Member

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    Hello

    - budget - ideally around $50? can stretch to $100.

    - dashcam is always recording

    - i opted for a capacitor based dashcam for longevity so it just dies straight away when power is removed.

    - custom build would be okay (if i can build it).

    -Rather not a solar panel at this stage. I do have a 3.2V 200AH LiFePO4 battery I have although i always wondered how I would charge it.

    -im recording for idiots who hit my car and run off (has happened twice in the past 3 years).
    Even more so now as I am a shift worker and park my car at the station overnight often.
     
  4. pantner

    pantner Member

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    I know there are powerbanks out there that DO allow you to charge it while it is providing power. One was mentioned in one of these threads but I can't quite remember it. Something about a clock being powered.
    That might help a little (eg, while you are driving, it can charge from car's power)
     
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  5. merlin13

    merlin13 Member

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    So the cam is in the car? Eazy Peazy - give the powerbanks the flick:

    - add a decent sized 12 volt gel cell/AGM (or whatever will handle the summer interior heat), big enough to run the 'cam for as long as you want/need

    - install it in the glovebox/under the front seat/in the boot/wherever sane that it'll fit

    - charge that off the Accessories/Cigarette Lighter circuit (adding a reverse blocking diode so it doesn't keep power onto the Accessories etc), and/or ponder a small solar panel that sits on your dashboard when the car is parked to keep some charge dribbling into it. I'd also add a suitable fuse/breaker (durr...), as well as a switch to isolate it from the main power if/when required

    - add a stepdown 12 to 5 volt supply, mounted/installed somewhere suitably sane

    - power the dashcam off of that arrangement. Optional On/Off switch for that as well perhaps...

    With your 200Amp/hr Lipo battery though, a suitable 12 volt powered charger should be available, but would need some serious research and deeeeep pockets though methinks.

    Personally I'd also be more than a little (!) hesitant to have that potential incendiary grenade bolted into the car... preeeeeetty sure your insurance company wouldn't like that concept to start with, especially if something went wrong and you had to make a fire-related claim (and the 5-0, Firies and Ambos wouldn't see the funny side of attending a prang with that little surprise packet lurking in the bodywork either...).

    Next Obligatory Dumb Question though if this is all to monitor your parked car - you got both font and rear view coverage?..
     
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  6. aXis

    aXis Member

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    I agree, the simplest way would be to find a small powerbank that does let you recharge and output at the same time. You can then keep that powerbank mounted permanently, and change out a larger powerbank that recharges the small one.

    The next easiest way would be to use an OR'ing diode, so both power banks would feed via a pair of low loss (0.2V drop) schottky diodes. The final output would then use the pack with the higher voltage. You could hack this into set of USB cables fairly easily. The only issue is that due to the DC-DC converters built into them it wont be self balancing - one pack would tend to supply most of the current most of the time. Still manageable though.
     
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  7. bryn

    bryn Member

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  8. OP
    OP
    ck_psy

    ck_psy Member

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    Thanks for the info.

    I think you guys a right a powerbank that recharges and outputs is probably the easiest option..

    How do I check which powerbanks are able to do that?
     
  9. aXis

    aXis Member

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    Not sure, might have to trawl through ebay and read reviews.

    If you're willing to do a bit of soldering, you can easily buy individual modules for USB to LiPo charging and LiPo to USB output. You just need to put a 18650 or pouch cell in the middle and you'll effectively have a USB UPS.
     
    Last edited: Sep 18, 2019
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  10. bryn

    bryn Member

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  11. dimension11

    dimension11 Member

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    All the Romoss 10400mAh packs that I've purchased mostly have either died within 1-2years or have started emitting noises that I've had to throw them out for.
     
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  12. v81

    v81 Member

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    How often is the car on per day?
    Does it get use over the weekend?
    Assuming the cam needs about ~ 3.6 wh (my DR650s as the example, 12v input, draws ~300-330mA).
    That would translate to about 720mA for a 5v unit (this seems a bit high but run with it).
    Overall looking at 17.28 Ah per day to power it.
    Lets assume my cam is a pig for some reason and yours uses half the power mine does, your at about 9Ah per day.
    Assume you're on the road for 2 hours per day and the powerbank can take 4Ah of charge in that time (lets be generous and say that is after losses).
    You'll be running at a loss of 5Ah per day.
    It doesn't seem sustainable.
    Even if you can find a powerbank that can charge twice as fast you're still at a loss.

    The 12v Lead acid / gel battery will be able to soak up charge much faster (assuming it has a decent capacity) and can be implemented with minimal circuitry.

    If you drive 4hrs /day or more and have a powerbank that can take charge at a decent rate you might be ok.
    A USB power meter will give you an idea of how much power your gear needs.


    Last of all, an off the shelf solution.
    I think these were a bit expensive from memory, says up to 28 hrs for a single dash cam.
    Claims to charge in 40 mins of hardwired or 80 mins via cig lighter.
    Read up on this...
    https://www.blackvue.com/power-magic-ultra-battery-b-124x/

    ::edit:: Seems like the off the shelf unit is ~ $400
    For that money I'd stick with merlin13's solution
    If it were me I'd consider going DIY with a LiFePo4 battery.
    They seem to be getting cheaper.
     
    Last edited: Sep 28, 2019
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  13. Ratzz

    Ratzz Member

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    That would be me, powering an LED clock via USB through a passthrough powerbank. The clock runs via 5v USB through a TP-Link Powerbank TL-PB10000 (which DOES allow passthrough) into my clock. Google the linked battery for multiple Australian suppliers.

    The point of my system being, the clock normally runs via USB from the PC, but the mrs is a power nazi and often shuts the computers off at the wall, and the clock has been integrated into a custom case. The clock has no battery backup to save the time, and even if it did, a backup would normally not keep the display active, which was desired. Its an LED room clock at night, whether she turns the power off at night or not. Runs from USB when power is on, via passthrough from the battery, which also keeps the battery charged. When the power is off, the battery continues to provide power to the clock, recharging again when power is switched back on without interrupting power to the clock at any time.

    From memory, my clock uses about 3,500 mAh daily.

    This would work for OP, but he would need a 5v USB supply to run the battery as a passthrough supply. Cigarette lighter style USB adapter etc from an always on 12v supply would do the job, whether its a fuse from the car or even a direct connection from the car battery.

    Larger batteries of the same type exist, I've seen as much as 20,000 mAh, what you are looking for is a 5v powerbank that supports passthrough. Easily googled.

    Seems to me a better option would be to simply run the cam via a USB lighter socket which draws directly from an always on 12v supply, and not bother with the intermediate powerbank. Power draw for such devices is insignificant compared to the storage capacity of a car battery, there should be no risk of running your car battery flat.

    5v is not going to hurt your 3.7v cam, you are already supplying 5v with your current powerbank/s.

    My clock runs on 3.6v, through 3 AA batteries, or through a USB wall wart originally which was rated at 5v/1A. Problem for me was that its an either/or on my clock. The batteries or the wall wart, couldn't use both.

    Chinese shit :lol: but it performed exactly the functions I wanted, with the appearance I was looking for. I have supplanted the wall wart USB adapter with USB power from the PC instead, and used the passthrough powerbank to provide 'backup'.
     
    Last edited: Sep 30, 2019
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  14. v81

    v81 Member

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    Sorry Ratzz but I'm qualified to say this is bad information.

    Quiescent current from the car battery when the car is off is typically <50mA
    Adding a ~300mA dash cam is a bad idea (not just in theory, but from personal experience).
    Despite what many might think car batteries do not have significant capacity, they are engineered to offer high peak current instead.
    All of this depends, but chance does not favor success for most people.
    In a truck or a large vehicle / 4WDbut or with a dual battery system in a vehicle that is driven twice daily including weekends running it off the battery would probably be fine.
    But start removing some favorable conditions like morning/evening driving daily becoming weekday only or battery being less than massive then problems will arrise.

    My situation, 2013 Subaru SH Forrester (with stop/start and the larger battery that this includes) with a Blackvue DR650s installed.
    Left over a 3 day weekend would render the battery unable to start the vehicle, even a regular Sat/Sun weekend would see the car show signs of slow turning.
    Assuming the car is turned off at 7pm on a Friday and started at 7am on a Monday 300mA per hour for 60 hours, ~ 18 amps in addition to the other items in the vehicle drawing power.

    Repeat this on a lead acid battery over and over and you end up with problems fairly quickly.


    The powerbank idea is only workable if the car in running long enough per day to charge the powerbank faster then the dashcam draws from it.
    It's not like the powerbank will suck in enough power on a trip down the shops and back to compensate for 24+ hours of camera time.
    Most powerbanks charge at 2-3 amps, probably putting 2Ah of usable power into the battery in best case scenario.


    If this is a daily driver with a huge battery running from the battery might work, but only if.

    We need to know more about the type and usage pattern of the vehicle.
    Otherwise a dedicated battery with decent capacity and decent ability to recharge (this excludes powerbanks) is what is needed.
    OP mentioned a LiFepo4 battery, this would be perfect with the right electronics (CC/CV charger, over/under voltage & current disconnect, basically a simple BMS), but at 200Ah might be a bit overkill.
     
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  15. Ratzz

    Ratzz Member

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    I stand corrected :thumbup: My apologies.
     
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