Dumb question - Page 1
Forum section: electronics / beginners

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 01:53:11 am
content: If I take a transformer that takes 120v in and puts 24v out and put the mains on the secondary instead, will it output 600v on the primary?Sent from my ONEPLUS A3000 using Tapatalk

author: ArthurDent
author_rank: Super Contributor
timestamp: September 25, 2018, 02:02:27 am
content: Absolutely not!!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 25, 2018, 02:25:22 am
content: Quote from: ArthurDent on September 25, 2018, 02:02:27 amTechnically the answer is yes. What you really should have done is explain why he should absolutely not do this.All other things being equal the turns ratio will end up giving about 600 volts when hooked up in reverse. BUT! The primary side of this transformer is wound to give a reasonable current when connected to the mains, and in fact to give that current with the design reflected load from the secondary. The secondary is not wound appropriately to give a reasonable current when connected to the mains, nor would the wire normally be sized appropriately for this use. What you will have created is not a high voltage transformer, but a fire starter.If you had a high impedance source (NOT THE MAINS) you could avoid the fire starter problem, but there would still be potential for dangerous problems. The primary windings have insulation designed for the mains voltage with appropriate safety margin. There is real doubt as to its adequacy of the insulation at five to six times its rated voltage. The same problems would occur in the secondary, which is design for 24 volts with some safety margin.These types of concerns are not deeply hidden dangers. It is well worth thinking through what could go wrong when using a device in a manner different than its intended application. Think about why the part is designed the way it is for it's intended usage. Then think about how your usage changes those assumptions. It isn't always wrong to use a part differently than originally designed. Sometimes it is brilliant (look into the use of a light bulb in the original Hewlett-Packard audio oscillator.)

author: Nusa
author_rank: Super Contributor
timestamp: September 25, 2018, 02:26:59 am
content: Probably not, since while the math might look good for an IDEAL transformer, such things don't exist in the real world. The turns on one side are probably adjusted slightly to allow for efficiency losses, which would mean the theoretical 5:1 winding ratio is actually a bit higher. Which would work against you in a step-up application.Also, in the real world, keep voltages on each winding within the specified ranges for safety reasons. Wire insulation that works fine at 120V may fail badly at 600V.

author: helius
author_rank: Super Contributor
timestamp: September 25, 2018, 02:29:37 am
content: To be specific, the windings are not sufficiently insulated to be safely used in that way. The primary and secondary must be insulated from each other, and insulation for 120V is not sufficient for 600V. The turns in each winding must also be insulated from one another, and the same problem exists there. Finally, the windings must be insulated from the core and chassis, and that may also be insufficient.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 02:37:35 am
content: So, while it looks good on paper, in practice probably not a good idea. I've been trying to come up with a way of stepping up voltage for inputting into a Cockroft Walton multiplier, but I don't have a 240 or 320v transformer on hand.Sent from my ONEPLUS A3000 using Tapatalk

author: Brumby
author_rank: Unknown
timestamp: September 25, 2018, 02:49:01 am
content: Quote from: GadgetBoy on September 25, 2018, 01:53:11 amAs said above - for anIDEALtransformer, the answer would be "Yes". So if this is just a question you have asked to confirm your understanding - then you are thinking in the right direction.HOWEVER - would you get this in a practical experiment? Probably not.Shouldyou try this as a practical experiment? Here's where the answers become much more clear ....NO.There a several reasons for not attempting this. First is that you will be putting 5 times the voltage on the 24V winding - so just think of the current that will flow and what that alone would do to the transformer. Then we have insulation issues with windings operating at voltages that they were not designed for - and we haven't even ventured into the magnetic field issues.As a thought experiment - onbasicprinciples - then this is quite OK to ask ... but do not try it in practice.

author: Brumby
author_rank: Unknown
timestamp: September 25, 2018, 02:52:51 am
content: Quote from: GadgetBoy on September 25, 2018, 02:37:35 amChange the word "probably" to "definitely".QuoteLook for a transformer designed to work at the voltages involved. It will not only pay dividends with reliability - but with safety, too.Don't try and take short cuts when it comes to high voltages. Be careful. Be thoughtful. Do it properly. Stay safe.Maybe try something with an automotive ignition coil - but I would feed it something significantly less than 12V.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 25, 2018, 03:21:13 am
content: Quote from: GadgetBoy on September 25, 2018, 02:37:35 amSome old tube equipment uses a full wave rectifier with just two diodes.This requires a secondary with a centre tap.The beauty of this, is that, say a "200 volt per side " secondary as needed for a DC rail of around 200v, will be able to deliver 400volts ac across, the whole secondary, with the centre tap not used.In Australia, I would say, "Look for an old AM Broadcast radio", but, in North America, post WW2,those were mainly Transformerless designs, so that limits the range of things to either,veryold (1930s) radios, Tube "HiFi" amplifiers, communications receivers, test gear, etc.I wouldn't mess with the 1930s transformers, as these had quite horrendous secondary voltages, like 570 volts, & 770volts, corresponding to "285 volts a side" & "385 volts a side respectively.It is quite likely that 80 years has taken a toll on the insulation, so they may be "dead" or "not long for thisworld".As for the other stuff, it would be a sin to butcher a nice old HF radio or test instrument----I don't care about the "HiFi"!Of course, if you could get someone in Oz to find you an early tube type TV power transformer, you would be laughing, as they commonly were 300v or 350v "a side" corresponding to 600 volts & 700 volts across the whole secondary.As these were designed for a 240v primary, they would deliver you half those voltages at the secondary when used on.120 volts, & the insulation would be overkill for the job.I had one, but it ended up being dumped---sorry!Also, freight may cost too much to make it viable.

author: james_s
author_rank: Super Contributor
timestamp: September 25, 2018, 04:38:52 am
content: The winding insulation is the least of the problems, what will happen if you connect a 24V winding to 120V is the core will saturate. The output voltage will stop rising as the core reaches saturation, the waveform will get really ugly, the magnetizing current will go through the roof and the transformer will get very hot.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 06:53:24 am
content: What about something like this? A Walton Cockroft ionizer needs very little power, so I'm wondering if a mains step-up transformer is a bit overkill. I just don't know if the waveform on this will work for a WC multiplier (or if waveform even matters much).https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F252419857902Sent from my ONEPLUS A3000 using Tapatalk

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 25, 2018, 01:46:56 pm
content: The link doesn't work for me, but I don't understand your question. If you are asking if you can use a Cockcroft-Walton multiplier (commonly called a voltage multiplier) to convert mains voltage to low current 600 volt DC then the answer is yes. If you think you need 600 volts as the first step in generation of a much higher voltage then I recommend that you sit back and think some more. You should understand the basic concept, insulation, spark gaps, field concentration and a number of other concepts better than you seem to before proceeding.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 25, 2018, 04:23:44 pm
content: The explanation by james_s in reply #9 is the main reason why reversing the transformer won't work backwards and is very dangerous. However the level of understanding about basic electronics indicates you should not try anything that involves any high voltage until you gain the necessary knowledge.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 05:57:33 pm
content: Quote from: ArthurDent on September 25, 2018, 04:23:44 pmWell, aren't you an arrogant twat. I'd already assumed the answer to be no, but I like confirming my conclusions on occasion.Sent from my ONEPLUS A3000 using Tapatalk

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 06:02:06 pm
content: Quote from: CatalinaWOW on September 25, 2018, 01:46:56 pmWell, I live in Canada. North American voltage isn't high enough to make a WC ionizer work, even with an abundance of stages. I've been trying to come up with an economical way of doubling or more the mains voltage before putting it into the multiplier.I've attached a picture of the eBay thing I tried to link earlier.Sent from my ONEPLUS A3000 using Tapatalk

author: TimFox
author_rank: Super Contributor
timestamp: September 25, 2018, 06:25:53 pm
content: Remember that the voltage or emf induced in a transformer winding is the time derivative of the flux linked in the winding by the core. At a fixed frequency, the emf is (2 pi)x(f)x(peak flux). The linked flux is the cross-section area multiplied by the (flux density = B field), multiplied by the number of turns. For typical iron alloys, the B value at core saturation is about 2 Tesla. That limits the AC voltage on the winding: if the transformer is designed to handle 120 V on a primary winding (5 x N turns), it cannot handle 120 V on a winding of only N turns.I wish it were easier to enter equations here.

author: jmelson
author_rank: Super Contributor
timestamp: September 25, 2018, 06:53:54 pm
content: Quote from: GadgetBoy on September 25, 2018, 01:53:11 amNo. Transformers are made with minimal iron in them. This means that the volts/turn of any winding has an upper limit. So, the transformer you describe has 5 times as many turns on the primary as on the secondary. And, the iron was sized so that it has, at best, a 10% margin before the iron saturates. Transformers have a V*T rating, that's Volts * time. If you raise the frequency by a factor of 5, then the time is 1/5th as much per cycle, and you can get roughly 5 X more voltage before saturations starts. Core losses will increase, however. But, at the same mains frequency, you can't get more voltage.Jon

author: ArthurDent
author_rank: Super Contributor
timestamp: September 25, 2018, 06:59:22 pm
content: GadgetBoy-“Well, aren't you an arrogant twat. I'd already assumed the answer to be no, but I like confirming my conclusions on occasion.”Well I beg to differ with you on your well thought out logical retort. What I posted wasn’t a snap judgement. I have seen other threads you’ve started and there have been quite a few posters who have given you advice similar to mine. I apologize if you misinterpreted my suggesting that you should refrain from doing something that might kill you. Read back over your previous posts and you will see a pattern. One of the posts suggesting your knowledge is limited is your own. I stand behind what I posted and strongly suggest you stay away from any line or higher voltages until you really understand more.“Should you try this as a practical experiment? Here's where the answers become much more clear .... NO.”GadgetBoy-“If I put multiple schottky diodes in parallel, will their voltage rating add (i.e. put three 40v schottky diodes in parallel for 120v rating)?”GadgetBoy-“Would the capacitive dropper keep the mains side of the transformer from melting itself?”GadgetBoy-“To my knowledge (which is admittedly limited), this *should* work, but it isn't.”

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 07:32:52 pm
content: Quote from: ArthurDent on September 25, 2018, 06:59:22 pmI called you an arrogant twat, and stand by the assertion, because you've made a huge leap of logic in order to assume my level of knowledge based on a few posts.Most of my expertise is focused on CMOS logic, PLC programming, and industrial motor control. I know how to be safe around high voltage (a necessary skill when working with three phase power), it's just that in my classes, transformer saturation wasn't something that was discussed - critical gap in my knowledge for sure on THIS particular subject, but it doesn't indicate that I'm incompetent or unsafe.I also know that most enameled wire has an insulation rating of at least 600v (on paper), so I wasn't tremendously concerned about arcing. I have custom power cables with built in fuses that will break a circuit long before the breakers in the house would even start to warm up. I typically have a 250mA fuse in them unless I anticipate pulling more power than that (which is rare given my current area of experimentation).My work bench has rubber pads under the legs, and so does my wood stool. I have esd rated work boots, and if I'm feeling particularly nervous about something I'm working on, I also have insulated gloves rated for 1kV.Electronics is a HUGE field, and it is the absolute height of arrogance for you to assume that I'm incompetent or dumb because I display a lack of knowledge on a few areas. Even further, you made an assumption on my level of knowledge based on my previous posts - of course I will come here to ask questions about something I'm unsure about - why would I ask questions to something I already know the answer to?Sent from my ONEPLUS A3000 using Tapatalk

author: HB9EVI
author_rank: Frequent Contributor
timestamp: September 25, 2018, 09:13:06 pm
content: Quote from: GadgetBoy on September 25, 2018, 06:02:06 pmThis inverter is working quite well, but, like you maybe can conclude from the transformer size, its operation frequency is ~42kHz. That's no problem, if you want to feed for example a mains LED lamp or any other device, where the AC is rectified again to a DC, but you cannot use it on any device with a 50/60Hz mains transformer

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 09:27:41 pm
content: Quote from: HB9EVI on September 25, 2018, 09:13:06 pmWas hoping the output would work on a WC ionizer.Sent from my ONEPLUS A3000 using Tapatalk

author: Macbeth
author_rank: Super Contributor
timestamp: September 25, 2018, 09:40:15 pm
content: Back to back transformers, it's actually a good ol' boy way of isolating the mains without expensive isolation transformers.

author: Macbeth
author_rank: Super Contributor
timestamp: September 25, 2018, 09:44:28 pm
content: Quote from: GadgetBoy on September 25, 2018, 02:37:35 amEver heard of MOT's? (Microwave Oven Transformers) - freely available providing your local council junk yard inspector is not being an arsehole.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 25, 2018, 10:52:12 pm
content: Quote from: Macbeth on September 25, 2018, 09:44:28 pmAny time I hear of someone playing with a microwave transformer, I swear I can hear Darwin cackling with glee.Sent from my ONEPLUS A3000 using Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: September 25, 2018, 11:14:53 pm
content: Quote from: GadgetBoy on September 25, 2018, 10:52:12 pmI've been playing with them for many years, they are not any more dangerous than any number of other things people play with. Flammable materials, firearms, cars, power tools, etc. It's simply a matter of understanding the risks and using a bit of common sense. The primary side DC bus in just about any SMPS can kill you just as dead if you aren't careful.

author: NexusKoolaid
author_rank: Contributor
timestamp: September 25, 2018, 11:34:10 pm
content: Quote from: GadgetBoy on September 25, 2018, 07:32:52 pmWell, to be fair, you presented no indication of your level of experience or expertise, AND you posted your question in a portion of the forum intended for beginners, which you are clearly not.

author: james_s
author_rank: Super Contributor
timestamp: September 26, 2018, 12:39:41 am
content: Either way, personal attacks are expressly prohibited, and calling someone an arrogant twat is getting pretty close to a personal attack.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 26, 2018, 01:21:38 am
content: Quote from: GadgetBoy on September 25, 2018, 06:02:06 pmVoltage multipliers will happily take US 120V to several thousand volts. Back in the days of CRTs modules to do this we're widely available and inexpensive. I recall 4000 volts was one standard, which should be enough to operate many ionizers.I don't know why you have not been successful with this configuration. There are several traps, which I don't recall at the moment.I would again caution you to think carefully about working with these higher voltages. A new world again from the 600 volts of your three phase you are familiar with. Your chances of killing yourself are really pretty low, albeit higher than many are comfortable with. But the chances of a painful incident are pretty high.

author: Brumby
author_rank: Unknown
timestamp: September 26, 2018, 01:39:24 am
content: Quote from: NexusKoolaid on September 25, 2018, 11:34:10 pmThat point is one I must agree with.GadgetBoy- Please understand we get every level of skill posting on this forum - and the only way we can judge anyone's competence is by what is shared here. You could have spent 30 years in IC fabrication - but if you don't say anything, then you are not being fair if you shoot someone down for commenting about current limit of bond wires.As you will appreciate, when people start talking about 3 digit voltages and higher, most members here start treading carefully - as they should. If we don't know your background, we ARE going to be conservative and sometimes that will carry with it some strongly expressed opinion - just to make sure the significance of what is being saidhits home. We cannot look over your shoulder, so our advicehastostronglyerr on the side of safety. We would rather know you were appropriately challenged about your intentions (based on what we know of you) than make assumptions about your skills and have you die as a result.We NOW know you have sufficient knowledge to understand the risks involved ... and I ask: Ifyouwere presented with someone with the same sort of questions and lack of background as you presented tous, would you have been any less diligent in responding with a safety and knowledge oriented approach?QuoteWhat is the definition of "Beginner"?Certainly, someone who has little or no experience in electronics qualifies, but I would suggest it is just as appropriate for someone who is not well versed in a particular strand.Take me for example. The apex of my experience with RF is being able to SWR in 27MHz CB radio antennae - so if I had an RF question, I'd be considering the Beginner's section for that.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 26, 2018, 04:18:24 am
content: Quote from: Brumby on September 26, 2018, 01:39:24 amNaturally, but I would have been far less condescending.Sent from my ONEPLUS A3000 using Tapatalk

author: Brumby
author_rank: Unknown
timestamp: September 26, 2018, 04:41:06 am
content: I can appreciate that - but we have a very wide range of personalities. From grumpy old codgers to the quiet and reserved. You also have to watch out for communication issues that can arise from cultural backgrounds and non natives of the English language. This is a true global community.While people rarely set out to be offensive, sometimes a point is made quite strongly and, on occasions, it can be useful to have a thick skin.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 26, 2018, 08:31:44 am
content: A quick search for voltage multiplier modules returns dozens of inexpensive results with voltages that go far beyond anything you could want.But here, as everywhere, numbers are your friend. The can supply only tiny currents at these voltages. How much current does your io izer need? Multiply your proposed current and voltage to get the power consumption. Something tells me you are asking for a lot of power. (A lot is contextually defined, but here means more than must voltage multipliers are designed to provide)

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 26, 2018, 08:33:27 am
content: Quote from: CatalinaWOW on September 26, 2018, 08:31:44 amA CW ionizer uses micro Watts. Maybe even Nano Watts. They use insanely little power.Sent from my ONEPLUS A3000 using Tapatalk

author: macboy
author_rank: Super Contributor
timestamp: September 26, 2018, 07:46:53 pm
content: Quote from: TimFox on September 25, 2018, 06:25:53 pmYou can use LaTeX for equations\$ V=\sqrt{2}\cdot \pi\cdot f\cdot N\cdot \phi_{max} \$

author: james_s
author_rank: Super Contributor
timestamp: September 26, 2018, 08:21:45 pm
content: Years ago I took apart an ionizer. It used a CW multiplier connected directly to the 120VAC input and feeding a needle for the output. There was no transformer in it at all. Seems like it had about 15 stages but I couldn't swear to it, it's been a long time.