After literally years of looking for a compact way to power a bluetooth speaker from the mane battery, the reason why they never worked was finally found. It wasn't the large filter capacitor or the ripple but the $1 car chargers only handling 1 Amp. When they were upgraded to 2A, the speakers started working with no changes. 1A is not enough to power a speaker, despite all the current measurements coming in below 1A.

The easiest solution was always to not hack anything but stick an original speaker in with a plane old USB cable & car charger. The hacking apart of car chargers & speakers was to make them more compact & lighter. Now the convenience of only having to charge the mane battery & transmitter battery, with no beeping after 10 miles, is finally known.

The answer is no. You can't power a bluetooth speaker from a $1 car charger. The $1 car chargers are only useful for charging because they make too much ripple. Only a very large filter capacitor can reduce the ripple enough, in which case a battery is smaller. A giant filter capacitor is still more convenient than a battery. After years of taking 3 batteries out of the vehicle for charging, it's so convenient to only have to worry about 2.

The car chargers can be tested with an 8ohm load. The ripple is affected by output capacitance & battery impedance. Newer batteries can power bluetooth speakers more easily. The Rudung creates 100mV of ripple. The 10000uF output capacitor + 1R resistor reduces it to 50mV. The 10000uF with a new battery produces no ripple. An inductor on the output makes no difference.

The $1 buck converters now go up to 2A, fixed voltage of course. Almost worth building a dummy load to see how long they really handle 2A before blowing up.

$1 car USB chargers were a good substitute for expensive voltage converters for many years. Just replace the feedback resistors with a pot & they could make any voltage at 1A.
Of course, if you didn't already have a bag of pots & caps, they would be a lot more than $1.

They were useless in their intended role as car chargers because the caps exploded in the heat.

The party ended when the Chinese finally moved to fixed voltage regulators. Any application would need to run on 5V now.

Don't plug a 4.2V speaker into 12V or it'll let out the magic smoke. Fortunately, it only blew up the amplifier chip, a HT6871. The radio & leds were still intact. It would take 1 month to order a new amplifier chip from China, so went ahead & got a new speaker. With this experience, it was decided to put in different connectors for 12V than 4.2V.

It was such a good speaker during its 3 year lifespan, the lion kingdom put in a different amplifier chip & revived it. There were some amplifier chips from a terrible speaker with the same pinout. The new speaker arrived anyway & was a better deal.

https://www.amazon.com/gp/product/B01HTH3C8S

Manely, the newest speaker turns on right when power is applied instead of requiring holding a button after applying power. It's all a matter of luck, but money buys a lot more online with the 1 week delay than locally.

The sub $25 can speakers have been the right size for robots.


The new amplifier chip uses a boost converter to make 7V. It would be simpler just to use a speaker with higher impedance or a battery with higher voltage to get the same power, but apparently it's cheaper to use higher voltage with standard speakers & a battery voltage which doesn't require a boost converter for charging.