flyingbrick Posted August 6, 2013 Share Posted August 6, 2013 Hi all. So Iv got my two blowers on my little heat exchanger and would like to vary their speed with a three position switch- off, 50% and 100% Now how do I work out what size resistor I need to use to give 50% power? Would it be easy to use a variable resistor? Are either of these going to generate heaps of heat? I see jay car does dc motor speed controllers- would I be better using one of these? Quote Link to comment Share on other sites More sharing options...
Simon Posted August 6, 2013 Share Posted August 6, 2013 The last option by far. http://jaycar.co.nz/productView.asp?ID=MP3209 Quote Link to comment Share on other sites More sharing options...
Ned Posted August 6, 2013 Share Posted August 6, 2013 I forgot what Leon did in his gem. If you want yo use the original switch to do on off and 50 you could use a 555 and a get to build your own speed controller that's either off, or 50% or 100%. Wouldn't be too difficult really. Though $27 jaycar thing sounds like the least amount of fucking around required though Quote Link to comment Share on other sites More sharing options...
Ned Posted August 6, 2013 Share Posted August 6, 2013 Should probably add that if that jaycar controller isn't completely potted (or you can hack out some bits) you can use the original 3 way car switch and a resistor or 2 to replace the pot and have the 3 settings and not have to build your own driver stuff. Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted August 8, 2013 Author Share Posted August 8, 2013 Forgot about this. I'm not using the factory dash Ned so can do anything. That jay car controller looks sweet- I'll grab one tomorrow Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted August 8, 2013 Author Share Posted August 8, 2013 Oh... So that little controller is 8A My fans are 10.32 watts ea So I need 20.6 watts for two.. And that controllers good for 96 watts.. Is that correct? Just trying to make sure it's all OK. I'm no good at maths Quote Link to comment Share on other sites More sharing options...
Ned Posted August 8, 2013 Share Posted August 8, 2013 Yup, good to go Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted August 9, 2013 Author Share Posted August 9, 2013 Thanks Ned. Now the instructions say they suggest a 500v 3a diode such as IN5404 put accross the output terminals for an inductive load like mine- what's the reason for this? Would that help full down the high frequency squeel I now have at partial speeds? What about a capacitor or something? Quote Link to comment Share on other sites More sharing options...
Ned Posted August 9, 2013 Share Posted August 9, 2013 Its for a flyback diode when the fan is furned off and the coils put out a voltage spike that could fry the internals. Needs to be a diode, and put the the right way around or you blow up your electronics as well haha Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted August 9, 2013 Author Share Posted August 9, 2013 Haha so the idea is that the diode will just short out the wires when it creates its own currents? Quote Link to comment Share on other sites More sharing options...
Ned Posted August 9, 2013 Share Posted August 9, 2013 Thats the one Quote Link to comment Share on other sites More sharing options...
Ned Posted August 9, 2013 Share Posted August 9, 2013 just get this instead of the 1N5404. It costs a little more (0.95), but is faster and has a lower voltage drop so less heat generated etc. http://www.jaycar.com.au/productView.asp?ID=ZR1048 or this one if they dont have it/want something even bigger http://www.jaycar.com.au/productView.asp?ID=ZR1029 Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted August 9, 2013 Author Share Posted August 9, 2013 Excellent. So what about smoothing out the wave it's giving? Quote Link to comment Share on other sites More sharing options...
Ned Posted August 9, 2013 Share Posted August 9, 2013 you dont want/need it to smoothen anything out. You PWM it and she'll be happy. If you smoothened it out to give a steady lower voltage supply, it will do nothing but get rid of the flyback but you will also lose power/torque or whatever. If you wanted that, you should get an adjustable current thing instead of adjustable PWM like you did. PWM is legit and i wouldnt have done it any other way really. It MAY induce some hum into audio if wired "badly" or even be audible on its own depending on the frequency of the switching, but doubt you'll hear a thing Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted August 9, 2013 Author Share Posted August 9, 2013 Thanks. I won't hear a thing through audio as Iv got none.. Just screech from motors. Thanks for your help Quote Link to comment Share on other sites More sharing options...
HighLUX Posted August 9, 2013 Share Posted August 9, 2013 Just screech from motors. Which you wont hear over the rumble of the LS Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted August 9, 2013 Author Share Posted August 9, 2013 Hahaha yeah that's true. Ned when I turn this on real low it hums but the fans don't turn. Would that fuck them? Quote Link to comment Share on other sites More sharing options...
Ned Posted August 9, 2013 Share Posted August 9, 2013 Yes Quote Link to comment Share on other sites More sharing options...
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