USB power passthrough to phone?

I'd like to power an Arduino off of a USB port in a car, but I don't want to take up the use of the port for phone charging. Is it possible to pass through the power to a phone for charging while splitting off enough to run the Arduino?

Car USB Port ====> Arduino ====> Phone

Just buy a cigarette lighter splitter.
I have one with 3 "ports" - one for charging my smartphone, one for my dashcam, one that is empty.

Use a small USB hub. They are usually small and inexpensive. Check ebay.

Use a small USB hub. They are usually small and inexpensive. Check ebay.

A hub is usually pretty poor at passing power.

Actually, it will work about as well as what I posted. :grinning:

Because its power circuit is what I posted. :astonished: All 5 V are connected directly together, as are grounds. There will be an additional current wastage from the hub itself.

When I posted that picture (link), I was concerned about the data connections being in parallel, but I have now realised (blush) that the charging port in a car as described by the OP probably does not have data connections anyway, certainly if it is one of those cigarette lighter adapters.

On the other hand, the actual USB port of a car radio is probably not intended for charging (read the manual) but will likely attempt to access the phone. Whether it can access via the MTP protocol instead of a Mass Storage Device however, I do not know. I will have to try it sometime. It certainly would not "talk" to the USB serial interface in the Arduino.

Thanks for the suggestions.

I don’t care about the data, it’d be going to a cig lighter power supply anyway.

I’d thought about a USB splitter or just using a multiport charger like suggested. Regarding the multiport charger, the arduino is going to be by the phone mount so running double cables just seemed inelegant. The splitter would probably work fine but I’d like the hardware to be as small as possible so I’d probably wire something like that up by hand inside the case.

I suppose I could also run the 12v from the cig lighter to my case and pass out a charging voltage for the phone and run the arduino via a voltage regulator.