Regulator gets really hot

Other Hardware General Electronics
1

I wanted to add an XBee to my Arduino based quadcoptor but after a few seconds the quad now stops working, probably because the regulator gets too hot.

So I have a XBee S1 and a MPU6050 attached to the 3.3V rail and a RC-Receiver attached to the 5V Pin of my Arduino uno. After running for a couple seconds the Arduino just turns off and the 5V regulator is really hot.

The XBee specs say that its current peaks at around 50 mA and the MPU6050 uses around 5 mA. If I add this up I get around 55 mA, the specs say that the Unos 3.3V regulator can deliver 120 mA so I'm well below the limit. The RC-Receiver uses around 70 mA on the 5V rail so it shouldn't be a problem either. As a power source I use a 11V LiPo which should be plenty.

Now my question is where I should look for the problem, could a loose connection cause this or are my calculations wrong.

This are the schematics:

                                                 Gnd
                                             +----+---+---+---+
                                             |    |   |   |   |
                                             |  +-+-+-+-+-+-+-+-+    Vcc
                                             |  | E | E | E | E +----------------------+ +
                                             |  | S | S | S | S +----------------------+ |
                                             |  | C | C | C | C |    Gnd               | |
         +--------+                          |  +-+-+-+-+-+-+-+-+                      | |
   +-----+        +------+-------------------+    |   |   |   |                        | |
   |     |MPU6050 |      |                   |Gnd |   |   |   |                        | |
   | +---+        +---------+-----------+3.3V|    |   |   |   |                        | |
   | |   +--------+      |  |           |    |    |   |   |   |            +---------+ | |
SCL| |SDA                |  |   +-------+----+----+---+---+---+-+Powerjack |         +-+ |
   | |                   |  |   |                               +----------+    LiPo |   |
   | |   +--------+      |  |   |                               +----------+    11V  +---+
   | |   |        +---------+   |   Arduino Uno                 |          |         |
   | |   |XBEE    |      |      |                               |          |         |
   | |   |        +------+      |                               |          +---------+
   | |   +--------+             |                               |
   | |       |TX|RX             +-+-+---+-+----+-+--------------+
   | |       |  |                 | |   | |    | |
   | |       |  +-----------------+ |   | | Gnd| |5V
   | |       +----------------------+   | |  +----------+
   | |                                  | |  |          |
   | +----------------------------------+ |  | RC-      |
   +--------------------------------------+  | Receiver |
                                             |          |
                                             |          |
                                             +----------+
2

Wow, drawing a schematic by hand would have been quicker.

But that max current is only valid if it can dissipate the rest of the power into heat. And that highly depends on the input voltage. If that's say 12V it has to dissipate (12V - 5V) x 100mA (lets assume some blinking leds) = 700mW. And that will get the regulator hot. Simple solution, use a DC-DC step down to give you the 5V :slight_smile: And plug that into the USB of the Uno. Into the 5V connection would be fine as well but don't connect the USB at the same time. Using the USB plug prevents that already and is really convenient because you can just use a cheap car charger :wink:

3

Don't worry i didn't make the schematic by typing it.

But thank you for your advice!

4

Measure the input current to the regulator with a multimeter, a couple of seconds to cutout implies more
current is flowing than your description suggests.

5

Really hot and shutdown is probably a wrong wiring. Check your datasheet.

6

epicepic11:
...the specs say that the Unos 3.3V regulator can deliver 120 mA so I'm well below the limit.

The RC-Receiver uses around 70 mA on the 5V rail so it shouldn't be a problem either.

As a power source I use a 11V LiPo which should be plenty.

Now my question is where I should look for the problem, could a loose connection cause this or are my calculations wrong.

  1. The datasheet of the 3.3volt chip states 150mA.

  2. What RC receiver.

  3. Voltage could be too high for a linear regulator.
    A linear regulator converts the difference between that battery voltage and 3.3 or 5volt into heat.

Let's assume your devices are using 50 + 5 + 55 + 70 = 180mA
Power (heat) in the 5volt regulator (that also supplies the 3.3volt regulator) is (11.7 - 5) * 0.18 = 1.2watt.
The regulator will be stinking hot from 1.2watt, and will shut down after a while.

Use a micro-power switching 5volt regulator to drop battery voltage to 5volt, and connect to the 5volt pin of the Arduino.

Leo..

7

1.2W won't shut it down in 2 seconds I don't think. That ought to make it too hot in about 20 to 30 seconds.