10 Inexpensive Automotive USB Adapters Tested -- Are They Any Good?

[Daniel Sauvageau]

Fwiw, I will be optimistic and say I believe if you buy $15-$25 adapters, most of these problems will go away.

As much as I'd love to test $20 adapters, the cost of the adapter itself eats a large chunk of the money I'd earn from writing a page or two about it. I'll have to send a wishlist to Fritz for those. (Unless their manufacturers volunteer samples.) Or I could do picture-story style mini-roundups.

Most of the cheap adapters I bought are only rated 1A, so there won't be 2A testing for those. I skipped anything under 1A since most modern devices won't charge on a 500mA adapter - that is not even enough to stop my 2012 N7 from losing charge during use, it needs 1A for that.

 

[Faux_Grey]

I loved this read. Thanks!

 

[Onus]

I have a folding solar USB charger that claims to be 16W, but could not reliably charge my Samsung S4 even in bright sun; it would constantly beep indicating charging/not charging. My suspicion is the output current is fine, but the voltage is too low. Assuming I didn't toss it, I may see if I can crack the circuit box open and see if there's any reasonable way to adjust its output; not expecting a trimmer of any kind so much as a resistor that might be able to be de-soldered and replaced.

 

[Daniel Sauvageau]

I have a folding solar USB charger that claims to be 16W, but could not reliably charge my Samsung S4 even in bright sun; it would constantly beep indicating charging/not charging. My suspicion is the output current is fine, but the voltage is too low.

The solar adapter must be using a buck converter between the solar panel's output and the load. If the converter is unable to hold its output voltage, it is usually because the source (the solar panel) is not delivering enough power. Once the buck regulator drops out of regulation from insufficient input power/voltage, the PV voltage becomes short-circuit-limited and that's all the current you get.

What is happening with your phone?
- phone is disconnected, input voltage rises to 20V open-circuit, output voltage gets regulated to ~5V
- phone gets connected, sees 5V and begins charging with incrementally higher current, the PV may drop to 12V at 1A
- when the phone exceeds the power the panel is able to sustain, the PV output voltage collapses below 5V at something like 1.2A, the buck regulator goes to 100% duty cycle and the phone stops charging due to low voltage
- when the charge current drops, PV and regulator output voltages go back up and the cycle resumes from the second step

A proper solar system needs "power point tracking" to keep the solar array near its optimal output power and some form of intermediate energy storage to buffer loads that the solar panel may not be able to directly accommodate. Otherwise, this basically becomes an issue of powering a constant-power device (phone) from what could be considered a constant-current source (solar panel): once the source voltage drops for any reason, you no longer have enough input power to recover until the load is sufficiently reduced or removed.

 

[Onus]

While your explanation is clear and makes sense, these drops should not be happening with this panel. It is one of those tri-fold panels of the type meant to be hung on a backpack or laid out in the sun. I have two others, one 11W (this one's a bi-fold) and the other 14W that work perfectly, typically charging the phone as fast as a wall adapter. I don't recall the brand of the bad one off the top of my head.

 

[Daniel Sauvageau]

I have two others, one 11W (this one's a bi-fold) and the other 14W that work perfectly, typically charging the phone as fast as a wall adapter. I don't recall the brand of the bad one off the top of my head.

In that case, that leaves fake specs/parts, poor design/parts and failure/defect as possible options. With off-brand generics, it could be some combination of all of those.

Optimistically, the "bad panel" could simply be lacking a large enough bypass cap on the PV array to absorb quick load increases.

 

[bobcrash]

Fascinating article, combined with your usual brain bursting detail... Loved it!

Keep up the great work... ...I gotta lay down now for awhile...