Measure Current Drain By 6 volt RF Receiver Listening For Remote Control Press

[Amorelovensheimer]

Being bored and lazy, I got a motorized bird feeder (modified koi fish feeder) that has a 6 volt lead acid battery and a small solar panel charger built in. See https://www.sweeneyfeeders.com/product/bird-feeder-10-lb/ (yeah, way overpriced). It has a timer, but I hooked up a deer feeder remote control so I could also feed "on demand". See https://www.allseasonsfeeders.com/products/the-remote (also overpriced). Especially in cold weather, the RF receiver for the remote drains the battery over time, so I assume the solar panel is providing less charging current than the RF receiver is drawing while it is "listening" for a remote control button push.

I'm trying to figure out whether I could use the Current Ranger with a Fluke 117 DMM or an oscilloscope to figure out somewhat precisely how much current the RF receiver is using while listening, and how much current the solar panel is providing (which I realize will depend on how sunny it is). What I don't understand (likely among other things) is whether the 6 volt battery power to the receiver is too much for the Current Ranger to handle - I saw this but don't really understand it: "maximum differential of 33mV is allowed before overloading starts to occur (vBat > 3.4V)."

I'd appreciate some help. Thanks!

[Felix]

The CR measures *current* (not voltage).
However, it achieves this by generating a tiny drop in voltage from the DUT's voltage source when a current passes through and across an internal shunt (there are 3 shunts depending on the range). The reason that tiny drop should not exceed 33mV is because it is multiplied by 100x with the internal opamps, and generates a maximum 3.3v at the output, and this corresponds to 3.3Amps maximum current across the input shunt.
That also essentially means we don't care so much about what voltage your DUT is powered with, as long as you don't create current leaks/paths/ground loops through the CurrentRanger by improperly wiring it to other common grounded DMM/osciloscope/USB PC etc.

You just need to also understand this is a HIGH SIDE current measurer, and while the guide goes into more detail, this means the DUT's power source + side goes directly into the CR's input +/red terminal, and then the CR's input -/black terminal becomes the DUT's power + (so you just insert the CR between the battery/PSU + and the DUT+).

The CR can also measure negative currents, in BIAS mode - which is useful for instance if you want to detect current going from a battery into a DUT, BUT ALSO back the other way into the battery when it is charged.

If you hook up a scope at the output (vs a DMM) then you can get nice waveforms representing the DUT current in real time, you can see a sample on the product page where I sample current during radio packets transmissions. Just be careful to either power the DUT from a battery (sounds like you do already), or an isolated PSU that has no common earth/ground with the scope, no there's absolutely no chance that current from the DUT PSU flows *THROUGH the CR into the scope*.

Hoping this helps you, make sure to read the guide, isolate the CR from any potential ground loops (current being forced from your DUT's PSU source through the CR into a common earth/external ground in unpredictable ways).

Can never be too lazy when chasing electrons! 

[Amorelovensheimer]

Thank you. Yes, this helps a lot.