Hello, i am currently designing a Battery powered Speaker.
And i wanna charge it with 5V from USB chrgers.
I will use a 3S 2P Li-ion Pack (12,6v, 5000mAh).
To charge it quite fast, i need a Boost converter that can handle 3A.
Thats not a problem i think (easy solution would be MC34063 + ext Mosfet).
But what happens if i connect it to a Phone charger that gives only 1A?
Its save to use it like this? Do cheap chargers limit properly?
Or should i build a current limiter, that limits when the charger voltage drops under 4,5V or something?
If someone has better Chips than MC34063 in mind, feel free to recomment them , thx
I hope my questions are understandable.
Greetings David.

 

If you want to use a USB source you should be aware that the maximum current available is 500Ma to 3.1A, depending on the version of USB you are using. The voltage will need to be boosted to at least 12.4V so the current available will be 5/12.4 which is about 0.4 of the input current,. The inverter will have an efficiency of around 80% so that gives 0.4 x 0.8 = 0.32 of the input current.
At the best you will only have one amp available for charging. That will not be a very fast charger! it will take about five hours!
Regards,
Keith

 

USB standards state the maximum current available for each type. If you try to draw more current than they are rated for they will go into overload protection mode and shut down. Inexpensive Chinese USB chargers may not meet the specs and could overheat and self-destruct if overloaded.
If you use a 1A USB for your source, the batteries will receive a maximum of 0.32A (see my response in post #2). That will take 15 hours to charge the pack. You will need a much higher current source than a USB outlet to charge the pack at 3A.
I think it's time to re-evaluate your project and make some changes
Regards,
Keith

 

USB standards state the maximum current available for each type. If you try to draw more current than they are rated for they will go into overload protection mode and shut down. Inexpensive Chinese USB chargers may not meet the specs and could overheat and self-destruct if overloaded.
If you use a 1A USB for your source, the batteries will receive a maximum of 0.32A (see my response in post #2). That will take 15 hours to charge the pack. You will need a much higher current source than a USB outlet to charge the pack at 3A.
I think it's time to re-evaluate your project and make some changes
Regards,
Keith

Sry i dindnt explain well.
I meant to have 3A max at the input of the Boost converter - 12,6V and approx 1A on the output.
It takes the time it needs to charge, that doesnt bother me.
My concern was, that it could be a problem if my circuit wanna draw 3A from a cheap 1A charger.
How do commercial products do it?

 

Sry i dindnt explain well.
I meant to have 3A max at the input of the Boost converter - 12,6V and approx 1A on the output.
It takes the time it needs to charge, that doesnt bother me.
My concern was, that it could be a problem if my circuit wanna draw 3A from a cheap 1A charger.
How do commercial products do it?

They have a built in current limiter. To include one, you will need more than 12.6V from the boost converter because the current limit circuit is in series and needs some voltage overhead. This, unfortunately will reduce the current available for charging.
Keith

 

Now i have time to continue with this project,
its not Dead.
But i´ve changed my mind...
At least a bit.
First i wanted to use 2*30W Drivers, but that would be a bit to much for a small speaker.
Approx 10w will be sufficient i think.
So ill use a PAM8006 at ca 12V to drive 2 Dayton CE65W-8 ohm (7W Rms 14Peak).
Bluetooth chip+DSP will be a CSR8645.

I use JLCPCB & LCSC to get my pcbs and parts,
therefore i want to use parts they can assemble. (QFN parts are not meant for diy^^).
My new idea is to use 1s battery pack because there are enough 1s Charging/Protection chips.
And then boost the voltage up to 12V.
A TPS61088 would do this job, i think, since it provides enough Power + it has a constant PWM mode