It could be because I’m using a battery as a load and it’s unstable, but shouldn’t the current drop if you add resistance in series with a fixed voltage source?
I don't now man, I just mess around with meters and make videos.
Maybe someone else here knows what you're on about...
If need meter only resistent, then cheapest way, I think, are use corresponding female USB sockets
I mean if you look at HKJ’s reviews like Review of USB battery box Chuwi Q-Power USB-C power bank 10000mAh M10 a lot of them mention
“What happens if the charger drops in voltage or a long cable is used? My usual 0.5ohm resistor shows it clearly: The charger will reduce charge current to a much lower value. ”
Didn't come across that behaviour in my tests, to be honest, and I've tested quite a few cables, chargers and powerbanks.
I don't know why, maybe my testing setup doesn't trigger the protection.
Yep, that is perfectly normal.
With a lower input voltage, you get a lower overall energy transfer. That means to get the same power into the powerbank, it is going to have to pull more current.
However, it is dangerous to do that with a USB power supply, so instead, it throttles back the current so the voltage goes up and the charging can continue normally.
I hope these might be informative:
(various powerbanks charging the same Galaxy S5)
(I didn’t do very “scientifically-controlled” tests though, for some of these tests, the phone is On and might be occasionally in use, but for a few, I might have turned the phone Off or at least in Airplane Mode and tried not to use the phone as much as possible while I’m doing the monitoring. Reason being if the S5 is getting used, the charge current will go up. Also, based on my previous tests of it, when the screen is OFF, the charging current can be a max 1.74A while if the screen is ON, the max charging current is 1.15-1.16A, using a USB meter to monitor; also when the phones charge level is already around 75% or 80% full, the max charging current will also start to get lower and won’t be the 1.74A max charging current when the phone is less than 75% battery capacity, based on the phone’s battery display)
in the above case, as the powerbank’s energy level drops (voltage drops), the S5 will request a lower charging current, causing the powerbank voltage to go back up, and the process repeats itself. (it seems the S5 drops in 0.1A every time it attempts to re-negotiate the charging current)
(this powerbank was from some relative, has little power left, but I just had to test it out… when it was fully charged, it only supplied 894mAh USB-measured capacity to the smartphone)
~
similar pattern here although it occurs it’s more stable while the energy level is still high, then charging current starts to drop in steps.
(the LG HG2 here in this powerbank is not a “genuine one” but possibly a rewrapped LG HE2 or HE4 since its tested capacity on an analyzing charger is around 2500mAh only — this fully charged “HG2 ~ 2500mAh” was able to supply around 1200+mAh USB charged capacity to the smartphone)
~
in this 3rd example, a “5200mAh” powerbank was able to completely charge the S5 (the powerbank still had some capacity left)
I think I might have slightly been using the phone during the later parts of the tests, so the CC/CV charge curve at the end has “spikes” (the spike are when the phone is being used, the USB chargng current draw goes up)
It seems if you want accurate measurements, you need stable, “dumb” power supplies and loads. Can’t use one that senses long cables and increases the voltage.
You never know how a horse cable will pull until you hook him up to a heavy load.