This is my first ever forum post so please be gentle with me. I'm making a fan controller with an LED bargraph display using Macromans Electrobus and either cpemmas Bargraph Display or the pointofnoreturn LED voltage monitor, but with having a limited knowledge of electronics i'm having a few problems. I've built Macromans Electrobus on a breadboard which works OK but i'm finding that when I turn the 10K pot right down the fan completely stops. Could I change either R1 or R2 to a preset to allow fine tuning? If so which one and what value preset should I use? I've yet to build the bargraph display and hope to use cpemmas design. My problem is finding a 0.47uF 16V tantalum bead capacitor. I found an old forum post which goes into this problem but the Maplin code quoted WW58N is for a 35V capacitor, will this work? (On the pointofnoreturn design they use a 0.47uF ceramic capacitor, would this do instead?) Also in cpemmas notes he states that aluminium electrolytics can be used instead of the tantalum bead capacitors but the values given are different, are these correct and if so why?
Hi, Bozzy34, welcome! macroman's components give an output range from 4.1v to about 12v (13.6v in theory, but not with only 12v going in), using the formula for the LDO controller here. Some fans won't run at 4v, but it's possible to change the resistors to give a higher minimum. Though without Carol Vordemann to help me, I'm struggling to get much higher. edit: Carol tells me R1=100k and R2=12k will give you 6.9v to 12.6v which should suit you. If you change the circuit very slightly so the pot is all on one side of pin#5, making it part of R1, it's much easier and the various resistor values shown in the table at the link will let you choose whatever range you want. (All you need do is link the pot wiper to the pot pin nearest R1 as shown at the link and take the other pot pin to the IC as shown below). The resistors shown will give you 6.9v to 12v output which should run most fans from cold. I've used noise-filter capacitors as advised by the datasheet, but you may not notice any difference without - a fan motor isn't a delicate load. The bargraph capacitor values are not critical, use them as minimums. The 35v tantalum would be OK, but Maplin's resin-dipped 0.47uF ceramic RA52G is cheaper and should be OK. Comments on extra size for aluminium electrolytics are from the NS LM3914 datasheet, I don't argue with NS. Any problems you have with stuff on my site, you can always email me direct.
Thanks cpemma for the reply, I've got a couple more quick questions, Am I right in thinking I can run two fans off this single controller and if so do I connect them in series or parallel? Regarding your reply to the capacitor problem, can I also replace the 2.2uF tantalum bead with another type? I ask because RS seems to be the only place to get them and the minimum order is 10.
If you're using the MIC29302 it will run fans to a total of 36W (3A) with a big heat sink, which is lot of fans. The MIC29152 I used is a bit cheaper and will run 18W (1.5A), 6-8 typical case fans. Fans all go in parallel. Rapid list 2u2 tantalums as do Maplin and ESR. But no problem replacing with a 10uF aluminium electrolytic.
Thanks again cpemma. Sorry, I forgot you said 35v ones would be OK Anyway time to spend some money, heat up my soldering iron and get this thing made.
