Portable charger voltages and cheap USB Power Monitor suggestion?

Dad’s got a ATN NV scope that can use a portable charger as an external power pack. Shortly after buying the scope he bought the ATN battery pack which is a 20000 mAh portable charger with the standard 5v 2.1a output rating.

He’s retired now and spending more time in the woods so he wants to get a couple more portable chargers for both phone chargers and more runtime on the scope. He picked up a coule of Insignia 8000 mAh chargers (also rated at 5v 2.1a output) from BestBuy, but apparently they didn’t work quite right on the scope. He sacrificed a usb cable to check voltages with a multimeter and only got 3.2v output. He returned those and got a different brand charger, it too only had 3.2v output.

FWIW he’s got a decent multi-meter and I’m pretty sure he knows how to use it, at least well enough for checking voltage.

What’s going on with this 3.2v output? Could something be causing a bad measurement or limiting voltage output?

Can you recommend a portable charger that definitely outputs 5v, but is sensible in price? Doesn’t need to be 20000 mAh, actually I think he’d rather have two in the 8-10K range.

Other subject: USB Power Monitors

This going on and reading through the forum, I realize that a Power Monitor would be a handy item to have in the tool box. For what I’d do with now it now I don’t need extreme accuracy, or need display in the thousandths.

I want order one that I can have this weekend/next week. Something decent and under $15. Seen a few on Amazon that fall in the price and estimated delivery, but really no nothing about them. Any recommendations?

If this turns out to be something I use often I’ll buy one of those YZXstudio monitors. Seems like those are the best available for the price. I’d get one now, but too many other expenses at the moment and it’d be sometime in the new year before it arrived. Also hate to spend that much on something I end up never using.

Ok, so in interest of time I’m just going to buy what ever USB meter amazon has with good reviews and at the price I want. Like I said before, if I find myself using it often I’ll get a better one.

I’d still like input on the portable charger issue though. My understanding is that USB power output is supposed to be 5v and that amperage will depend on application, most common for chargers being 1a and 2.1a.

Why would these portable chargers only be outputing 3.2v measured with multimeter? Is it something that we are doing wrong when taking the measurement or is something wring with these chargers?

I’m thinking it must be the chargers because it was the same measurement for all three, seems unlikely if we were doing something wrong. At the same time it seems unlikely that three chargers from two different brands would have the same voltage problem.


I would have expected that for amperage, but not voltage. Everything I’ve read about load sense type thing on these has been about providing additional amperage not voltage.

I knew that to check amperage I would have to actually have a load applied, didn’t think that it mattered for voltage. I’d check portable charger the one I have, but the sacrificial cable is still at dad’s house and I don’t have a spare here to cut up.

I’ll have a simple USB multimeter next week and it’ll be easy to tell if that’s what’s happening. Be nice if that’s the case, but I’m not going to hold my breath.

Agree with the above.

Some powerbanks will test having a low-voltage when not “ON”.

Depending on the powerbanks, some need a small load to wake up. I’ve actually been testing several powerbanks and using the ZKE Tech EBD-USB+ load tester (this device is powered by the PC’s USB port, so it doesn’t need to get power from the power bank which may very slightly affect result) I notice some powerbanks display something like 1.xx or 2.xx volts while “asleep” (regular USB meters that are not self-powered will not show anything; the ZY1276 meter can “operate” as low as around 2.8v based from my test — the display will be very very dim though; other USB meters typically won’t display anything at all below 3.5v and some meters display wrong results below a certain voltage threshold [eg. some cheaper stand-alone USB meters will display much lower or higher voltage if not within its operating range]).

How much load to stay awake (no load or load current lower than this will cause powerbank to automatically power off after xx seconds)? I tested some of my power banks and got these results:

APC M5 (5000mAh) powerbank:

  • will auto power off after ~20 seconds if current load is 0.08A or lower (I’m using the EBD-USB+ load tester to control the load)

Mi PLM05ZM 20000mAh powerbank:

- will auto power off ~24-25 seconds if current load is 0.025A or lower

  • there is a way to make this powerbank not auto power-off — by double-clicking the button (actually this special mode is designed for charging ‘low-power’ devices like Bluetooth earphones or smartwatches, which have a low current)

AData PV150 (10000mAh) powerbank:

  • auto powers off ~25 seconds if current load is 0.09A or lower

Pineng PN-999 (20000mAh) powerbank:

  • auto powers off ~60 seconds if current load is 0.10A or lower

generic PWB-064-M (2000mAh) powerbank:

  • auto powers off ~20-21 seconds if current load is 0.0035A(?) or lower (couldn’t test this low current with the EBD-USB+, so I’m using other informal methods)
    (I have a USB meter that consumes only 0.0035A, as tested by ZY1276 USB meter; and it will auto power off if I plug that low-power meter to this power bank; my other USB meters that consume >0.01A will be powered up indefinitely [ie. keeps powerbank awake] when plugged to this power bank)

generic 8800mAh powerbank:

  • auto powers off in ~15 seconds if current load is 0.18A or lower (this seems a bit high cut-off threshold, as when charging smartphones which are nearly full, the current load could be lower than this, so charging gets abruptly cut off once the charge rate goes below 0.18A)

as can be seen, different powerbanks have different low-current auto power-off; unless using something like the Mi PLM05ZM which has a special mode that makes it not power off (I think even when there’s no load attached) — the light indicator of the Mi PLM05ZM powerbank will blink in a special sequence to indicate it is now operating in this special mode (does not seem to power off)

Thanks guys. Got the power tester and passed it off to dad. He’s been checking everything he can get his hands on with it.

With this device he was actually able to check how much load his NV scope was using and was pleasantly surprised to see that it was drawing a lot lower amperage than he thought. I don’t think he ever tried to use it overnight with the power bank he has and was assuming that it wouldn’t last long enough. I think he’s now satisfied that his power bank will last long enough and if he decides to get a spare he’ll actually be able to check and make sure it is working properly with load.

Fortunately I think it has also saved me from having to rig up a way to use a power bank on his other NV scope. It uses AA batteries and no external power source option. He’s planning to carry it along on these hunting trips for smaller varmints and was thinking he needed more battery life. Given the low power draw of the ATN he’s not worried as much about it and I was able to convince him to just get a few more of the NIMH rechargeable that he was already using. Should be more than enough for a night and he can recharge them during the day.

Still going to get me one of those YZXstudio Monitors eventually, but I got a truck to rewire first.