Philip Pemberton escreveu: > Hi guys, > Does anyone know of any good references or rules-of-thumb for = > creepage, clearance and track width when designing = > high-voltage/high-current kit? > > With the parts I've managed to find, at least two PCBs in the = > mini-oven will need to operate at mains potential -- the power supply = > and the power-switching for the heating elements. There will be about = > half a dozen tracks on the switch board running at mains potential, and = > two on the power supply board. > > What I need to know is: > - How thick these tracks need to be to carry 1650W > = Both thickness and width are important. The track width depends on the copper thickness, maximum current (and thus of the voltage if you are speaking of power), track length, maximum allowable loss in the tracks (power/voltage drop) and the maximum allowable temperature raise of the tracks. There is a graphical table used to calculate such things. > - Same again for about 15W (the PSU uses a 6VA transformer -- "double = > it and add a bit") > - How much distance I need to have between live and either neutral or = > a switched HV track. > = There is an IEC norm that deals with this. If I recall it correctly, the tracks must be kept away 8mm for 220V and 4mm for 110V before the current passes some sort of current-limiting or protection device. > I've had a play with a few creepage/clearance calculators, which suggest = > that I need a minimum 0.1in gap between L and N at ~300V. So if I was to = > use 100mil (0.1in) tracks, those tracks would have to be placed on a = > 200mil grid (assuming they were completely straight) in order to meet = > that spec. This is based on the output from = > but other calculators seem to come up with similar results. > = I think you may need 8mm or more between mains tracks. The distance from mains to low voltage tracks may be even larger. > What I haven't managed to find yet are any guidelines on the required = > track width for carrying, say, 1650W at 240V (about 7A)... Can anyone = > suggest any rules of thumb for this? > = Get a copy of the graphical table calculator (I don't know how it is called in English :). Board manufacturers can give you some. > The PCB blanks I'm using are 1oz single-sided, FR4 laminate. If anyone = > = So you track thickness is already known and fixed. > wants to go looking up the datasheet, they're Farnell part number = > 320-4911, "FR4 composite, pre-sensitised PCB laminate, Eurocard size, = > single-sided". > > As this is a one-off, tinning the high current tracks, or soldering bits = > of wire to them to increase the thickness (and thus the track area and = > current handling capacity) is also an option, if it makes things = > significantly easier. I've seen this done in SMPSUs, if it works for = > them... *shrug* > > Thanks, > = > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com = > Version: 8.5.409 / Virus Database: 270.13.89/2359 - Release Date: 09/10/0= 9 05:50:00 > > = __________________________________________________ Fa=E7a liga=E7=F5es para outros computadores com o novo Yahoo! Messenger = http://br.beta.messenger.yahoo.com/ = -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist