Maple mini and RC lipo’s – how to taste the black magic smoke again

madias Tue May 17, 2016 11:52 am

Just a little warning:
While playing around with 2s RC lipos (8.4V, up to 40-80A discharge power!!!) I burnt out a maple mini (not the BAITE version) very quickly (maybe only the voltage regulator, I’ll check this later). Even with the BAITE ones (they have the “bigger” AMS1117 clone voltage regulator) I wouldn’t connect them directly to such powerful lipos: I burnt those AMS clones on other devices – they are really bad made and after they are dead, they tend to give the whole input voltage to the output.
This happend without any particular load on the mini!
As a silly and cheap workaround I use a separate LM7805 (with heatsink) to reduce the power and connected it to the “Vin” of the maple.

Replies

zoomx Wed May 18, 2016 3:45 pm

I bought from DX (was DealeXtreme) some years ago. It is like a big seller on Aliexpress, they sell the same things. The difference is that you can have all packets with tracking and tracking was free when the order was over about 5$, today is more.
I never reviewed any item but sometimes you can understand something about the quality.
DX has also a UK, USA and AU shops with much less items, never bought from there.

I agree with ray but I am not a professional, I buy items for fun. Very few devices are working on italian volcanoes doing simple tasks like moving a mirror for an instrument (an FTIR spectrometer).

Slammer Wed May 18, 2016 9:12 pm

Beware with AMS1117, it is a linear regulator and you have first of all to respect the power limit.
The typical thermal resistance of SOT-223 package soldered on PCB is about 80-90 C/W.
The power limit is calculated:

Tmax = Tambient + W * 90

Tmax = 125 by datasheet, and Tambient=40, then:

Wmax =(125-40)/90 = 0.95W

It is very easy to calculate the maximum current of device given the input voltage. Some examples:

Vin=8.5V, Vout=3.3 => Imax = 0.95 / (8.5-3.3) = 182 mA, much lower than rated current of device.
Vin=8.5V, Vout=5 => Imax = 0.95 / (8.5-5) = 270 mA
Vin=12V, Vout=5 => Imax = 0.95 / (12-7) = 190 mA
Vin=12V, Vout=3.3 => Imax = 0.95 /(12-3.3) = 109 mA

Normally, AMS1117 has internally thermal protection that switches off the output if the temperature is beyond limits, but you can not depend on this, specially with questionable quality parts.
All cheap breadboard power supplies use AMS1117 in SOT-223 package. The power limit of this device is very low, try to feed it with an external regulator with as low voltage as possible, to reduce the heating dissipation ( Vin must be greater than Vout+1 )