You can use airgaps in transformers in some cases but this design should be without one according to Ed.
I am using ferrite pot cores in some other designs where they are wound as a transformer but where the Q-value is of importance and there I use an airgap and also a trimmer through the center to adjust them for a minimum Q-value at a certain frequency. Q-value according to TDK: https://product.tdk.com/en/contact/faq/inductors-0003.html and also at Wikipedia: https://en.wikipedia.org/wiki/Q_factor This article explains airgap in inductors/transformers somewhat: https://www.linkedin.com/pulse/why-do-we-provide-air-gap-usually-inductor-designs-transformer-p So sometimes it is a choice depending on design criteria like Q-value and material used in the transformer. There are normal laminated transformers that use an airgap too, but most mains transformers do not. /Martin On Wednesday, 1 September 2021 at 15:11:31 UTC+2 Paul Andrews wrote: > Martin, > > I wonder why there should be no air gap? > > - Paul > > On Wednesday, September 1, 2021 at 1:55:30 AM UTC-4 Dekatron42 wrote: > >> Paul, >> >> I'll ask him, but a quick search at Digikey showed both some RM10 and >> ETD29 cores, but only a few. Finding Ferrite cores today is not easy, I >> have searched some for other projects and they aren't usually stocked in >> the ranges that the manufacturers make them, and if you want something >> outside what is available in stock it becomes very expensive as you'll have >> to by thousands if not more. I usually try the ones they have and have to >> live with that since I can't buy the thousands needed to get the perfect >> one. I'll ask Ed to have a look and see if any of the ones that are stocked >> will do - just remember that they will have to be the transformer type >> without an airgap between the center pieces to work in this application. >> >> /Martin >> >> On Wednesday, 1 September 2021 at 04:26:30 UTC+2 Paul Andrews wrote: >> >>> >>> Hi Martin >>> >>> I tried to find a suitable core at digikey, but their parameters don’t >>> map very well to the equation that Ed gives. Could he take a look at what >>> they have and perhaps recommend something. For simplicity’s sake I just >>> looked at toroids >>> https://www.digikey.com/en/products/filter/ferrite-cores/936?s=N4IgTCBcDaICoHsBOCCWATAhgGwAQGNkBTAZxAF0BfIA >>> >>> Thanks - Paul >>> On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote: >>> >>>> Since transformers isn't my best area, I only have basic understanding >>>> of the intricacies but I have experimented some with different >>>> transformers >>>> in different cases like when driving Trochotrons and Dekatrons I decided >>>> to >>>> ask an acquaintance who has worked with transformers. His name is Ed >>>> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio >>>> Repair and Restoration forum: https://www.vintage-radio.net/forum/), >>>> he told me you are welcome to contact him via me so that his email is >>>> somewhat protected - if you ask him anything related to the >>>> VFD-drivers it would be kind if you could post something here in this >>>> forum >>>> so we all can learn from it. >>>> >>>> This is his answer to my question on what transformer to chose for the >>>> driver in the article, it sure helped me and I hope it helps anyone who >>>> wants to experiment with this driver: >>>> >>>> "Hi Martin, as it operates about 50/100KHz virtually any ferrite should >>>> do. It should be a transformer type with no air gap. >>>> The turns are normally based on the transformer equation for square >>>> waves >>>> >>>> N= V/ 4 * F * B* Ae >>>> >>>> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a >>>> ferrite, Ae the centre pole area in M^2 >>>> >>>> The actual losses come out later on in the design process and are not >>>> part of the initial criteria >>>> >>>> Copper sizing is normally based on 3A per mm^2 of cross sectional area >>>> >>>> The turns figure he gives looks about right for something like an RM10 >>>> core, or you could try an EE25 or an ETD29 core in sat F44 materials >>>> ETD's are the core of choice for this type of application and should be >>>> readily available. >>>> >>>> The more turns that are used the lower the iron losses and the cooler >>>> the core runs, but the copper losses increase unless fatter copper is used. >>>> Skin effect will be of minor importance at your frequency >>>> >>>> It would also work on a normal laminated core at 50Hz which should not >>>> be too big as you can run that at up to 1.5T flux density. >>>> Regulation could be a normal type of regulator set for constant current. >>>> >>>> Always many choices in Engineering >>>> >>>> Cheers, Ed >>>> >>>> Ed Dinning Retired Engineer" >>>> >>>> /Martin >>>> >>>> On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote: >>>> >>>>> When I have time, I will try the driver at the link Martin gave ( >>>>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), >>>>> but without the transformer initially. As far as I can tell, the >>>>> transformer is just to make the VFD drive isolated so you can pull it up >>>>> above ground. >>>>> >>>> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/8943cc8d-1219-44d0-9f19-62357cdf4951n%40googlegroups.com.
