Complete novice newbie that need help

Thread Starter

liteace

Joined Mar 7, 2012
136
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
 
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Thread Starter

liteace

Joined Mar 7, 2012
136
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
 

antonv

Joined Nov 27, 2012
148
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.
 

Thread Starter

liteace

Joined Mar 7, 2012
136
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.

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
 

antonv

Joined Nov 27, 2012
148
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?
 

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Thread Starter

liteace

Joined Mar 7, 2012
136
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?
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
 
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Thread Starter

liteace

Joined Mar 7, 2012
136
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
 
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antonv

Joined Nov 27, 2012
148
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.
 

Thread Starter

liteace

Joined Mar 7, 2012
136
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
 

Thread Starter

liteace

Joined Mar 7, 2012
136
Will it be poss. to mount all these components on 1 strip board or am I better off using a different method

Thanks
 

Thread Starter

liteace

Joined Mar 7, 2012
136
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
 

Thread Starter

liteace

Joined Mar 7, 2012
136
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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