Complete novice newbie that need help

Discussion in 'The Projects Forum' started by liteace, Mar 22, 2013.

  1. liteace

    Thread Starter Member

    Mar 7, 2012
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    Hi All I joined a few months ago and have done a lot of reading, now it time to post. I can solder and do know what 90% of electronic components do but as for adding the correct components to the 555 to get it to do what I need is where im lost.
    I have got here a nichrome heater wire, the idea is to heat the wire and keep it at a controlled temperature for a set length of time.
    What I need is some sort of control unit that will have a switch off time after 5 mins and when its on a 90% duty cycle, I know the heater wire will draw aprox 12amp at warm up and then drop down to 7 amps, so Im thinking maybe a 15 amps mosfet somewhere in circuit, this will all be run on a 12 volt supply
    Now the main question, is this possible and if so where do I start

    I hope I have posted in the correct section, if not sorry and please move me.
    SORRY about the title, I was a bit click quick with mouse, Ive tried to edit but cant edit title

    Thanks in advance
     
    Last edited: Mar 22, 2013
  2. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    What is the relation between the 5 minute time and the 90% duty cycle?
     
  3. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Hi Thanks for the fast reply, the 5 min time is just like auto shut down as it going to run from a battery, the 90% duty is to stop the nichrome burning out

    Thanks
     
  4. antonv

    Member

    Nov 27, 2012
    149
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    I would use a MOSFET that can handle more like 30A which should not be hard to find. Also a MOSFET driver.

    As for the control circuit a small micro controller would work but if that is too much to get into then a 555 timer for the 90% duty cycle and something like a MC14541 for the 5 minutes would work. The 555 timer could function as the clock for the MC14541.
     
  5. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0

    Thanks, I would need major help with that one as thats just gone straight over my head :confused: adding other components, Ive been reading about 555 Astables & Monostables and Im only just getting to grips with that

    Thanks
     
  6. antonv

    Member

    Nov 27, 2012
    149
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    The MC14541 with a couple of resistors and a cap can be used as a 5 minute one-shot that is triggered by a button that you press to start everything. When it is not running it keeps the 555 timer in reset so that there is no output to the nichrome wire.

    The figure below shows what I think it should look like. Does this make sense to you?
     
  7. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Thanks you very much for the info, yes it does make sense to me now, a simple block diagram makes all the difference.
    I'll have to have a read up now on the 14541 timer also what component would I be looking for as the mosfet driver and then I'll need is poss. a little help putting it all togther

    Thanks Agian
     
    Last edited: Mar 23, 2013
  8. antonv

    Member

    Nov 27, 2012
    149
    27
    A simple to use MOSFET driver is an MCP1416T. All three ICs can be powered from 12V which simplifies things.
     
  9. antonv

    Member

    Nov 27, 2012
    149
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    I should ask if you are able to use small surface mount devices or if you want to stick to thru-hole.
     
  10. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    No, no SMD's as yet just something that is going to go through the holes, maybe one day i'll start doing my own PCB's, I remember etching them many many years ago in me dad's shed, I dont even think they are done like that anymore are they

    Thanks Again
     
    Last edited: Mar 23, 2013
  11. antonv

    Member

    Nov 27, 2012
    149
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    The MOSFET driver is a tiny surface mount part. There are others that are DIP (thru-hole) parts.

    People still etch their own boards.

    Once you've looked over the data sheets let me know if you need more help.
     
  12. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Thanks, I will need a lot more help, I said in my 1st post:

    "and do know what 90% of electronic components do..........."

    I think I better change that to 40% :confused:

    I will get the MOSFET driver and see if I can mount it to the strip board and work from there

    Thanks Again
     
  13. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Would you know of a DIP equivalent for the MCP1416T as i think Im going to struggle with that

    Thanks
     
  14. antonv

    Member

    Nov 27, 2012
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    27
  15. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Will it be poss. to mount all these components on 1 strip board or am I better off using a different method

    Thanks
     
  16. antonv

    Member

    Nov 27, 2012
    149
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    Strip board should work fine. All the parts should be available as 0.1" thru-hole versions.
     
  17. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Thanks, All main chips ordered exept MAX4420 Im having a little trouble finding that. As im ording would it be poss to give me a list of what else is needed so when everything is here i can start putting it all together

    Thanks
     
  18. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Im going to get some components today to start on the 555, am I right by putting:

    46uF between gnd and pin 6\2 (555)
    3 Kohm between pin 6 and 7
    29 Kohm betwwen pin 7 and + feed

    Im going to get 91% duty cycle with high of 1 sec and a low of 100Ms ?

    Thanks
     
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