Post by thread:[EE] first adventure puting an AC supply on a PCB

Just as an aside, if this is small quantities, take a look at Bias Power. They make some very small power supply modules, nearly the size of a transformer, and fairly well regulated. Nothing really special about what your doing, just keep the creepage/clearance rules in mind if your going after certification with it. Don't skimp on trace widths either, keesp the inductance down. I also assume the 2.8KVa is the isolation on the transformer --- On Mon, 10/6/08, Marc Nicholas <spam_OUTgeekythingTakeThisOuTgmail.com> wrote: {Quote hidden}> From: Marc Nicholas <.....geekythingKILLspam@spam@gmail.com> > Subject: [EE] first adventure puting an AC supply on a PCB > To: "Microcontroller discussion list - Public." <piclistKILLspammit.edu> > Date: Monday, October 6, 2008, 1:18 PM > Hi all, > > Looking for advice on any pitfalls or recommendations for > putting an > AC transformer (pretty small - 110VAC primary, 9VAC > secondary, 2.8KVA) > onto a PCB design. > > Post transformer, I'll do the classic rectifier make of > diodes > (1N4004s)/LM7805 equivalent/bypass caps. > > Any pointers appreciated! > > -marc > > > Sent from my iPhone > --

Marc, > 9VAC secondary, 2.8KVA) 2.8VA ? > Post transformer, I'll do the classic rectifier make of diodes > (1N4004s)/LM7805 equivalent/bypass caps. Although the transformer is low supply current, you might want to add a series drop element (resistor or Zener) to take a little of the sting out of the voltage drop. After the bridge, you might have 11V (if the transformer is accurately specced). Meaning the 7805 will have 6V across it. At roughly 300mA (approx capability of the transformer) load that will be 1.8W of heat to diddipate in the 7805 Not a great deal, but I think it's a consideration to be aware of If you add a resistor before the 7805, to drop say 3V at 300mA, then that's what heats up, not the regulator

LOL...I had sausage fingers today...yes, it should be 2.8VA!!!! Otherwise the 4004's would likely be the size of can of beans ;) -marc On Mon, Oct 6, 2008 at 5:32 PM, Marcel Duchamp <.....marcel.duchampKILLspam.....sbcglobal.net {Quote hidden}> wrote: > Marc Nicholas wrote: > > Hi all, > > > > Looking for advice on any pitfalls or recommendations for putting an > > AC transformer (pretty small - 110VAC primary, 9VAC secondary, 2.8KVA) > > onto a PCB design. > > > > Post transformer, I'll do the classic rectifier make of diodes > > (1N4004s)/LM7805 equivalent/bypass caps. > > > > Any pointers appreciated! > > > > -marc > > > > > > Sent from my iPhone > > 2.8KVA... as in 2800VA? with 1N4004's? > -

Marc, Even though the transformer is (apparently) small, it still is likely to be considerably heavier than anything else mounted on the pcb. Make sure it is securely mounted - preferably to the case as well as the pcb itself. Vibration etc is likely to make the pcb flex and can crack traces or delaminate the copper - or produce broken solder joints. RP 2008/10/7 Marc Nicholas <EraseMEgeekythingspam_OUTTakeThisOuTgmail.com>: {Quote hidden}> LOL...I had sausage fingers today...yes, it should be 2.8VA!!!! Otherwise > the 4004's would likely be the size of can of beans ;) > > -marc > > On Mon, Oct 6, 2008 at 5:32 PM, Marcel Duchamp <marcel.duchampspam_OUTsbcglobal.net >> wrote: > >> Marc Nicholas wrote: >> > Hi all, >> > >> > Looking for advice on any pitfalls or recommendations for putting an >> > AC transformer (pretty small - 110VAC primary, 9VAC secondary, 2.8KVA) >> > onto a PCB design. >> > >> > Post transformer, I'll do the classic rectifier make of diodes >> > (1N4004s)/LM7805 equivalent/bypass caps. >> > >> > Any pointers appreciated! >> > >> > -marc >> > >> > >> > Sent from my iPhone >> >> 2.8KVA... as in 2800VA? with 1N4004's? >> --

> Vibration etc is likely to make the pcb flex and can crack traces or > delaminate the copper - or produce broken solder joints On a couple of designs I've seen a plastic tie to hold the transformer down. You could likely use contact adhesive too (eg Ados F2) or double-sided tape. The transformer is probably the component that expands/contracts the most and dry joints are common on PCB-mount types. More than a few things around here were originally throw-outs because of dry joints on transformers and connectors (like DC sockets) which are seldom properly anchored

part 1 928 bytes content-type:text/plain; charset="gb2312" (decoded quoted-printable) 2.8KVA? keep that board away from me. > Date: Mon, 6 Oct 2008 16:18:31 -0400> From: @spam@geekythingKILLspamgmail.com> To: KILLspampiclistKILLspammit.edu> Subject: [EE] first adventure puting an AC supply on a PCB> > Hi all,> > Looking for advice on any pitfalls or recommendations for putting an> AC transformer (pretty small - 110VAC primary, 9VAC secondary, 2.8KVA)> onto a PCB design.> > Post transformer, I'll do the classic rectifier make of diodes> (1N4004s)/LM7805 equivalent/bypass caps.> > Any pointers appreciated!> > -marc> > > Sent from my iPhone> -- > http://www.piclist.com PIC/SX FAQ & list archive> View/change your membership options at> mailman.mit.edu/mailman/listinfo/piclist _________________________________________________________________ һ�㼴�ģ�MSN�Ƴ��¹��ܡ��ң�� http://im.live.cn/click/ part 2 35 bytes content-type:text/plain; charset="us-ascii" (decoded 7bit)

I have fat traces....and I have about 1cm clearance, which I believe to be adequate. Thanks! -marc On Mon, Oct 6, 2008 at 5:17 PM, alan smith <RemoveMEmicro_eng2TakeThisOuTyahoo.com> wrote: {Quote hidden}> Just as an aside, if this is small quantities, take a look at Bias Power. > They make some very small power supply modules, nearly the size of a > transformer, and fairly well regulated. > > Nothing really special about what your doing, just keep the > creepage/clearance rules in mind if your going after certification with it. > Don't skimp on trace widths either, keesp the inductance down. > > I also assume the 2.8KVa is the isolation on the transformer > > > --- On Mon, 10/6/08, Marc Nicholas <spamBeGonegeekythingspamBeGonegmail.com> wrote: > > > From: Marc Nicholas <TakeThisOuTgeekythingEraseMEspam_OUTgmail.com> > > Subject: [EE] first adventure puting an AC supply on a PCB > > To: "Microcontroller discussion list - Public." <RemoveMEpiclistTakeThisOuTmit.edu> > > Date: Monday, October 6, 2008, 1:18 PM > > Hi all, > > > > Looking for advice on any pitfalls or recommendations for > > putting an > > AC transformer (pretty small - 110VAC primary, 9VAC > > secondary, 2.8KVA) > > onto a PCB design. > > > > Post transformer, I'll do the classic rectifier make of > > diodes > > (1N4004s)/LM7805 equivalent/bypass caps. > > > > Any pointers appreciated! > > > > -marc > > > > > > Sent from my iPhone > > --

> pcb itself. Vibration etc is likely to make the pcb flex and can > crack traces or delaminate the copper - or produce broken solder > joints. Here's a lesson - http://www.nzherald.co.nz/technology/news/article.cfm?c_id=5&objectid=10536216 A poor soldering job on one of 10,000 connections is the most likely cause of the failure that sidelined the world's largest atom smasher just days after the new collider was launched with great fanfare Only one fault in 10,000 isn't bad, "but it cost dearly", said Lyn Evans, project leader of the new Large Hadron Collider at CERN It halted operations for at least two months, which meant that the collider cannot be restarted until spring CERN specialists have already figured out that a connector between electromagnets failed and heated up, causing a magnet "quench", or shutdown. It apparently melted a hole in the tube, causing a leak that spilled about a ton of the liquid helium used to chill that section

Don't forget the temperatures. Since it is a small transformer the heat it generates is probably rather high even when it isn't operating at full load. This has to be considered when it is going to be put in an enclosed space, such as an ordinary enclosure. The insulation materials are rated for a certain maximum operating temperature which in turn gives a maximum operating temperature for the transformer. This can normally be around 70C. This may sound quite a lot but considering the temperature rise in an enclosed space it may mean that the operating temperature for the entire device may become as low as 40C or less. The heat generated when it is operating at worst case (short circuited or with a worst case load - power matching) may require you to put a fuse on the secondary - even if it is a so called short circuit proof transformer. It all depends on the temperatures. You also have to consider the tolerances on the input voltage. Also remember that an ordinary fuse for these purposes are considered to let through 1.7 times its rated current for ever, without blowing. Also consider the current and voltage when building a full wave bridge rectifier with filter capacitors. Sometimes it is good to use capacitors with higher ESR (or at least not use several connected in parallel) to keep the peak currents low. On the other hand low ESR decreases the temperature rise in the capacitors (higher temperature is bad for capacitor lifetime). Note that the transformer currents may need to be as high as 1.6-1.8 times the output DC current. And of course, the voltage after the bridge is close to 1.4 times the AC rms output voltage. It can be even higher for small transformers that is running on very low load. Some useful links: <http://www.powervolt.com/techan01.html> <http://www.powervolt.com/techan01.html> /Ruben {Quote hidden}> Hi all, > > Looking for advice on any pitfalls or recommendations for putting an > AC transformer (pretty small - 110VAC primary, 9VAC secondary, 2.8KVA) > onto a PCB design. > > Post transformer, I'll do the classic rectifier make of diodes > (1N4004s)/LM7805 equivalent/bypass caps. > > Any pointers appreciated! > > -marc > ============================== Ruben Jönsson AB Liros Electronic Box 9124, 200 39 Malmö, Sweden TEL INT +46 40142078 FAX INT +46 40947388 rubenEraseME.....pp.sbbs.se ==============================

alan smith wrote: > I also assume the 2.8KVa is the isolation on the transformer That doesn't make any sense considering the units are wrong. Isolation would be specified in volts. A volt-amp rating is a measure of the power the transformer can deliver, sortof. Supposedly it can deliver volts x amps up to the rating, but the weasel wording is because it doesn't guarantee they are in phase. That's why it isn't specfied in watts. Still, this is a common measurement and gives you a rough idea how "big" the transformer is. ******************************************************************** Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products (978) 742-9014. Gold level PIC consultants since 2000.

>> Or use a 10F204 to make a quick and dirty buck regulator. > > Is it really that easy? Yes. For example, see page 2 of the ReadyBoard-01 schematic, http://www.embedinc.com/products/ready01/qprot2.pdf. Nowadays I do things a little differently with a PNP transistor to sense the voltage accross the LDO, but the design shown there still works fine. ******************************************************************** Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products (978) 742-9014. Gold level PIC consultants since 2000.

Alan B. Pearce wrote: >> CERN specialists have already figured out that a connector >> between electromagnets failed and heated up, causing a magnet >> "quench", or shutdown. > > Having contracted for a company that made superconducting magnets, I can > vouch for things going 'a bit wild' as a magnet suddenly dumps boiling > helium when a quench happens. Seen it a number of times with magnets on > test. > Sounds dangerous - they must have very good ventilation in case of a spill? - Martin

>> Having contracted for a company that made superconducting magnets, I can >> vouch for things going 'a bit wild' as a magnet suddenly dumps boiling >> helium when a quench happens. Seen it a number of times with magnets on >> test. >> > >Sounds dangerous - they must have very good ventilation in case of a spill? Not dangerous exactly, the magnet has pressure release vents so that the gas that results from the liquid boiling has a safe route to exit the magnet vessel. The vent is normally connected by lagged piping to a collector tank so the gas can be recycled through the helium plant rather than being just vented to free air. but when the magnet does a 'dump' all the lagged piping suddenly frosts up - almost instantaneously it has a decent thickness of frost on it because the helium gas is so cold. I happened to be doing some cabling around a dump pipe while a magnet was under test, and suddenly had all this frost came drifting down off the pipe as the magnet 'dumped'. There was 'wasn't me Guv' sort of moment.

do proper spacing and watch for heat dissipation, ive done dozens using onboard transformers. --- On Mon, 10/27/08, Marc Nicholas <EraseMEgeekythinggmail.com> wrote: {Quote hidden}> From: Marc Nicholas <RemoveMEgeekythingEraseMEEraseMEgmail.com> > Subject: [EE] first adventure puting an AC supply on a PCB > To: "Microcontroller discussion list - Public." <RemoveMEpiclistspam_OUTKILLspammit.edu> > Date: Monday, October 27, 2008, 2:09 PM > Hi all, > > Looking for advice on any pitfalls or recommendations for > putting an > AC transf > > Sent from my iPhone > --