Friday, 28 October 2016

Building Robot DIY Power Supply


Having multiple off shelf devices can make some things easier. But have a car battery of 12 volt doesn't fit on all of them. Converting 12 volt to a number of required volts:
  • +5v for IP camera's and Arduino's
  • +5v positive and -5v negative for robot arm (?linkje naar project?)
  • +7,5v for network switch
  • +12v (no conversion) for motors (shoulders, feet, neck) and used for Pico PSU for secondary computer.
  • +19 for laptop power-supply (E-Bay car adapter)
The last few devices were simple, just direct (as motor uses 12 volt) or a convertor from E-bay that uses 12 volt.
The first four did pose a challenge as they did take up Ampere! A quick count came to 8 Amp!! And overload must be avoided, specially the arms could use good part. So have a 10 and 5 schema to be sure. The motors will draw directly from the batteries.

Drawing Board

First found an 10 A negative and 10 A positive schema for converting the 12 to 5 volt. Then a simple regulator (7,5 volt) schema. All thanks to CircuitOnline, a great dutch elektro website.
The positive side
To extract positive and negative, two 12 volt batteries are required. If only one battery, you can use a volt divider but this will lower the voltage.
The negative side.
But with heavy loads you will need heavy resistors! So to use two batteries, just remember that combined gives double the current! As the robot has enough space for two batteries and the battery weight will increase stability, the choice was easy.

The additional 5 Amp
5A print

The choice was to used an older PC power-supply as case. It has a fan, lots of holes and spacey.
Everything inside
Running some tests
Ready for first test!

For details on first attempt see below. But it is fine to skip that.
After First Attempt, measuring the damage...

First Attempt

All apart again!
When using the MJ2955 or MJ3055, I forgot to use mica (isolation)...Because if using the same they can share the ground (which is the body on MJ2955). But with MJ3055 this causes short circuit!
MJ3055, which was fried 
Then by accident, forgot to wire ground first...This resulted in a lot of smoke and me order the same list...again!!!


So this cost some additional time, but also made me redesign and clean up wires.
In the end everything was fine. All measurements were in the green and the power-supply was good to go!
Here it is finished and close. Not yet install in the body.

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