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Topic: 3 Axis CNC Power Circuit Advice (Read 116 times) previous topic - next topic

rabn21

Nov 23, 2017, 02:04 pm Last Edit: Nov 23, 2017, 03:52 pm by rabn21
Hi, I am currently putting together a small lego CNC mill. The aim is to be able to cut some small shapes out of flower foam or balsa etc. I have tested all 3 axis seperately and now I am progressing to a test with all 3 axis moving at once and then on to adding the drill motor. The 4 aa battery pack that I was using to test this I believe is under-powered to run all 3 stepper motors at once so I am trying to look at a more stable solution.

I have a laptop power supply at home that provides 19V and 2.1A and has a centre positive barrel jack. I have got a breadboard barrel socket. The 3 stepper motors are 28byj-48 controlled using my Arduino Uno and 3 ULN2003a development boards which have a specified 5-12V input.

The 4th motor is an old motor I have from an RC helicopter. It was run off a 7.2V re-chargable battery.

Would it be possible to use this power supply and use a voltage divider to reduce the voltage from 19V down to something like 8.4V using a 2.2 kilohms and a 1 kilohm resitor?

I have a concern that the current going through the breadboard would be too much in the prototyping stage. I could possibly use some protoboard to make a small power circuit or order one of the small quadcopter style power distribution boards and use that.

Would my circuit (picture below) work in principle? I could power each stepper with its own battery or just beef up the current battery pack from 4AA to something bigger but would prefer a more long term solution.

https://imgur.com/a/M1iq7

All suggestions or comments welcome and appreciated.

Thanks,

Robert


Robin2

Would it be possible to use this power supply and use a voltage divider to reduce the voltage from 19V down to something like 8.4V using a 2.2 kilohms and a 1 kilohm resitor?
NO.

Voltage dividers are not suitable for power supplies. You need a proper electronic voltage regulator.

The simplest solutions are either
{A} buy a mains power supply that provides the voltage and current you need

or {B} make up a suitable battery pack using AA cells - re-chargeable NiMh cells can produce more current than alkaline cells. Perhaps even have separate battery packs for the different motors.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

rabn21

Hi Robyn2,

I had a suspicion it would not be that simple. Thank-you for your help. I think for what I am trying to do in version 1.0, I will go with the simpler option of separate battery packs. Once I have this working and have the software working as I want it I can look for a power supply solution.

Thanks,

Robert 

MarkT

The cheap LM2596 buck converters from eBay might be suitable for converting down from 19V, they
are adjustable, rated at about 2A, and some even display the voltage on some LED displays.  At the price
its worth getting a few
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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