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Power supply (need schematic) — Parallax Forums

Power supply (need schematic)

computer guycomputer guy Posts: 1,113
edited 2009-11-03 14:35 in General Discussion
Hi everyone,


I am about to start work on a MDP for my HSC however for this project I need a power supply with the following ratings;

Input: 240V (AC) ~ 50Hz (Australian power outlet)
Output: 24V, 12V, 5V and 3.3V DC
(basically a computer power supply but with 24v as well)


24v for solenoids
12v and 5v for various electronics
3.3v for propeller


Does anyone have a schematic on hand or know of somewhere online that could help me with building such a powersupply.


Thank you smile.gif

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Comments

  • Cluso99Cluso99 Posts: 18,069
    edited 2009-11-02 08:46
    What current do you require at each voltage?
    Do you really need 24V solenoids?

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  • computer guycomputer guy Posts: 1,113
    edited 2009-11-02 09:15
    If I can find a 12v solenoid than yes.

    For the currents I am not sure but I can guess;

    12v - 1A
    5v - 1A
    3.3v 500ma

    I have included a diagram below to show what needs power.
    12v - valve, fan
    5v - PIR sensor, 3.3v reg at end of 10m cord for propeller
    3.3v propeller, valve control circuit

    attachment.php?attachmentid=64851


    Thank you smile.gif

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  • pacmanpacman Posts: 327
    edited 2009-11-02 10:09
    12V solenoids are _fairly_ easy to obtain. (see Automationdirect.com.au, and check out their valves such as the N701). Even Jaycar/electus sell 12V Solenoids.

    Might cost you $20 for the solenoid, but IMHO you would save that by not having to build a power supply.


    Hope that helps...

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  • computer guycomputer guy Posts: 1,113
    edited 2009-11-02 10:48
    I could always just use an ATX power supply but I think that would be overkill for a single valve, a sensor and two props.

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  • kwinnkwinn Posts: 8,697
    edited 2009-11-02 14:56
    An ATX power supply might be the least expensive way to go if the circuit draws enough power for the supply to operate. Most of these supplies have minimum current draw requirements on the 3.3 and/or 5V supplies.

    If the power requirement is low you may want to use a simple linear supply. I have attached a block diagram of what I use as a starting point for such a supply. This is not a complete schematic so you will need to add electrolytic capacitors on the outputs from the regulators and small (0.1uF) ceramic or similar caps to the input and output of the regulators.
  • sailman58sailman58 Posts: 162
    edited 2009-11-02 18:40
    There are a number of sites that show how to convert a computer power supply to a bench power supply. The general idea is to use a 10 ohm 10 watt resistor across the 5 volt wiring to keep it going. Do a web search on 'convert computer power supply' and you should find several leads. Here is the first I came up with http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply , but there were others. If you have a supply that puts out -12 volts, then you can get your 24 volts between the +12 and -12 volt connections.

    Ron
  • WBA ConsultingWBA Consulting Posts: 2,935
    edited 2009-11-02 19:35
    It's overkill and a bit pricey, but I have a Condor GPC80PG Power Supply sitting on my desk that was scavenged from a JOT conveyor system that was wired for use in the UK. It would give you everything you need except the 3.3v (which can be done with an LDO off the 5v rail). Mouser lists it at $140 under part number 675-GPC80P-G.

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  • computer guycomputer guy Posts: 1,113
    edited 2009-11-02 21:23
    kwinn,

    Would a
    9V - 24V, 60VA, 5A Multi-tapped Transofmrer be alright for that curcuit if the 24v regulator was 12v?


    Thank you smile.gif

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  • Cluso99Cluso99 Posts: 18,069
    edited 2009-11-02 21:49
    If you are not using a commercial power supply (as in PC) then wouldn't it be safer to use a power pack. Say 12-15V @2A and regulate from there. Saves all the legal and safety issues of 240V connection.

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    Links to other interesting threads:

    · Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)
    · Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm
  • mikedivmikediv Posts: 825
    edited 2009-11-02 21:49
    I would have to strongly agree with Kwinn I get ads sent to me from surplus places I subscribed to, an AT Power supply with +12V +5 volts 240Watt is only $9.00 dollars I have one I took apart and converted to bench power as sailman has suggested and now have +5 +12
    and +24 I tapped off the circuit board . I also found found a negative 9V tap but have never used it other than measured with my meter. Also I am in the USA and feed it 110V
  • kwinnkwinn Posts: 8,697
    edited 2009-11-02 23:24
    Regulating the 24V input down to 12V with a linear regulator would dissipate a lot of power, probably more than a 3 terminal chip could handle if the current was more than a few mA.

    Can you post a schematic of the transformer windings/taps?
  • dMajodMajo Posts: 855
    edited 2009-11-03 09:23
    @kwinn: (PS1.bmp) are you sure lm7812 is a 24v regulator?


    I also agree with Cluso99 legal/safety issues considerations.


    @ComputerGuy: Have also a look at www.recom-international.com·or download the catalogue


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  • computer guycomputer guy Posts: 1,113
    edited 2009-11-03 11:46
    After reading everones comments I have decided to go with an ATX power supply, this will make case design a bit more challenging but will remove the stress of having to design my own power supply and is also cheaper.

    Thank you all for your comments and suggesttion. smile.gif

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  • kwinnkwinn Posts: 8,697
    edited 2009-11-03 14:35
    @computer guy

    Good choice. I use them quite often and they work well. Designing the case to fit the power supply and your circuit is probably less work than designing a power supply.

    @dMajo

    My apologies for the error. I have been doing this so long I sometimes forget that not everyone is familiar with these generic parts.
    An LM7812 is a 12V regulator. As mentioned in the post with the diagram, it is more of a generic circuit used as a starting point for a simple linear power supply. I will use different values of components (ie 24V ct xfmr, 7805, 7812, for +5 & +12V) for different output voltages. I am so familiar with this simple supply that I do not change values on the diagram and did not notice that the output from the LM7812 was marked as +24V.
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