High Voltage Transformer - Page 1
Forum section: electronics / beginners

author: Architect_1077
author_rank: Regular Contributor
timestamp: June 14, 2012, 11:06:05 pm
content: I salvaged a high voltage transformer from an old microwave oven. It's a 230V -> 1000V.I was wondering if this thing could be used for something, like a high voltage linear power supply i.e.? Or maybe something else... I just don't fancy the idea of trashing a good transformer, even if it's usefulness might be somewhat questionable.What say you?

author: IanB
author_rank: Super Contributor
timestamp: June 14, 2012, 11:10:09 pm
content: I've heard of people rewinding the secondary to suit different purposes.I also think there is something special about them (gapped core?), possibly to limit the output current and make it a self-ballasting transformer a bit like a neon sign transformer perhaps? Maybe someone else knows more?

author: caroper
author_rank: Regular Contributor
timestamp: June 14, 2012, 11:36:48 pm
content: If you were to drive it backwards you could get 230V in 60 V out to build a bench supply.Not sure about current rating, but if it was a 2kW oven then you should be able to get 500W through it in reverse configuration, so you would need some hefty regulator transistors and heat sinks.CheersChris

author: Psi
author_rank: Super Contributor
timestamp: June 14, 2012, 11:53:46 pm
content: Just be very careful with it. 1000V is many times more dangerous than 230V because it can push more current through your body.Also if the diode is still on the transformer and the output is DC it's even more dangerous, as your hand can grip on the terminal and the current through your muscles stops you from letting go.Using it in the other direction for 60V output is a good plan.I've also heard of people removing the high voltage winding and replacing it with a few turns of thick wire to make a spot welder.If you decide to try that be sure you do remove the high voltage side first. Leaving it attached is super dangerous.

author: Architect_1077
author_rank: Regular Contributor
timestamp: June 15, 2012, 12:12:02 am
content: QuoteYeah, it was a 2kW oven.You guys have interesting ideas. Running it backwards as a stepdown is a good idea too.I do have a question: when caroper mentions the (guesstimated) 500W, isn't that supposed to be the maximum the TX could handle? Or is that what it consumes regardless? I'm a bit confused (I need to read up on transformer theory)

author: Psi
author_rank: Super Contributor
timestamp: June 15, 2012, 02:28:07 am
content: Quote from: Architect_1077 on June 15, 2012, 12:12:02 amYeah, it's a max, they only draw it when you use it. (except for a little bit of inefficiency)He's de-rating it because the wire was only spec'ed to handle a set amount of current.It's a little more complicated than this but basically...2000W/230V = Primary wire is intended for up to 8.7AIf you're now using this wire for 60V you can still only safely draw up to 8.7A.So 60V * 8.7A = 522WThat said, transformers are normally pretty forgiving, you can push them more than other electrical components.Especially if you're not running them continuously.However, in this case, being from a microwave oven where it only runs for minutes at a time maybe they've already pushing it a little over spec

author: SeanB
author_rank: Super Contributor
timestamp: June 15, 2012, 04:45:04 am
content: They are run far into the non linear region, as they are force cooled with a fan to keep the temperature rise down. There are plenty of guides on YT to show how to remove the secondary windings, but really they are only meant for intermittent use or where you fan cool it. Using it to make a spot welder is probably the best use, as it will have a low duty cycle.

author: T4P
author_rank: Super Contributor
timestamp: June 15, 2012, 05:22:04 am
content: Yeah, just be careful if you want to use it normal HV style, they catch fire and shit above 1amp draw without any coolingBut using it at 500W (limitation ._.) can keep it safely cool (Compared to 2000W the duty cycle to that is 1/4 so should be fine without a fan)

author: Architect_1077
author_rank: Regular Contributor
timestamp: June 15, 2012, 02:31:23 pm
content: Still thinking about the HV power supply idea... could blow lots of stuff up with one of thoseOn a more serious note, a 60V (or thereabouts) linear lab psu would be more useful to me. In either case, you guys have convinced me to save that thing and not trash it. Although, it is one heavy mother of a tx...

author: SeanB
author_rank: Super Contributor
timestamp: June 15, 2012, 02:54:52 pm
content: Got today another 7500V 50mA neon transformer, much safer cook wise. Thinking of making a Jacobs ladder with it, or use it to light up some of my neon tubing.

author: xquercus
author_rank: Contributor
timestamp: June 15, 2012, 03:26:12 pm
content: Quote from: Architect_1077 on June 14, 2012, 11:06:05 pmI frequently see microwave oven transformers for sale at hamfests. Asking prices are in the $25-$50 range. My understanding is the people use them to make HV supplies to drive tube amps. I'm not an HV or a tube guy -- just my observation.QuoteDefinitely! Have you looked at the price of enameled copper wire or litz wire? I save even small transformers and use the wire for winding chokes and my own transformers.

author: Architect_1077
author_rank: Regular Contributor
timestamp: June 23, 2012, 01:32:51 pm
content: I never got to update this topic with the correct specs of the HV Tx:230V - 2100V1000VAAlso has a 3.5V coilIt weighs no less than 5Kg considering it's size.

author: T4P
author_rank: Super Contributor
timestamp: June 23, 2012, 05:41:14 pm
content: Quote from: Architect_1077 on June 23, 2012, 01:32:51 pmIt's definitely a low duty transformer, normal 1kVA transformers from Schneider is about 15KGs so the maximum duty cycle it can handle is 33.3% compared to the schneiderThe lightest one is from VIGORTRONIX but that's 2x the cost

author: Zero999
author_rank: Super Contributor
timestamp: June 24, 2012, 10:30:28 am
content: Quote from: caroper on June 14, 2012, 11:36:48 pmI wouldn't recommend that.One side of the secondary is usually bonded to the iron core which would become live, if you tried that.

author: Architect_1077
author_rank: Regular Contributor
timestamp: June 24, 2012, 03:14:04 pm
content: QuoteWell, as a beginner, I have to ask the question: if that is true, then wouldn't it become live just the same regardless of how it was connected?

author: Unclegummers
author_rank: Contributor
timestamp: June 24, 2012, 07:56:45 pm
content: -Put the ground side of the output on some kind of big alligator clip, and the hot end on the end of a wooden dowel and shock the crap out of stuff?-Hook a variac the the primary side so you have an extremely wide range of AC voltages to experiment with?-Buy some HV diodes and full wave rectify the output into a dishwasher sized capacitor and make things explode?-Just keep the transformer handy if you need a decent amount of inductive ballast? (Use the impedance of the secondary side)Hopefully this was useful. Just don't waste the thing because all microwaves nowadays are "Inverter" style and you cant get these transformers out of anything else!

author: IanB
author_rank: Super Contributor
timestamp: June 24, 2012, 08:22:37 pm
content: Quote from: Architect_1077 on June 24, 2012, 03:14:04 pmIt is the secondary side that is bonded to the iron core in the normal configuration. Only the mains input is live; the secondary output is isolated by the transformer and is not live[*]. Grounding one side of the secondary to the chassis increases safety by providing a ground path for any faults in the high voltage circuitry. Such a ground path will tend to blow a fuse or trip a breaker and draw attention to the fault.*Note that "not live" does not mean "safe voltages", it just means there is no current path between the secondary side and the external mains ground. The secondary of a microwave oven transformer is stillextremelydangerous.

author: Architect_1077
author_rank: Regular Contributor
timestamp: June 25, 2012, 12:05:57 am
content: Right, gotcha. Makes sense. Is there any way to know for sure whether or not secondary is bonded to the core? Continuity test perhaps?

author: IanB
author_rank: Super Contributor
timestamp: June 25, 2012, 12:44:58 am
content: Sure, a continuity test tells all.Just make sure the transformer is detached from other circuits and is not energized.

author: T4P
author_rank: Super Contributor
timestamp: June 25, 2012, 04:01:10 am
content: And then there's also the massive eddy current field such a big transformer can produce near the transformer

author: Zero999
author_rank: Super Contributor
timestamp: June 25, 2012, 09:29:14 pm
content: The HV secondary is connected to the transformer's chassis at one end only. If the secondary is connected to the mains, the chassis will now float at mains potential because one side of the mains is connected to earth. If the neutral is connected to the side of the primary which is connected to the transformer cause, it will be slightly safer, until either the live/neutral is reversed or the neutral is disconnected before the live.

author: Architect_1077
author_rank: Regular Contributor
timestamp: June 25, 2012, 10:02:24 pm
content: Well, after a continuity check, it doesn't seem like the transformer core is in any way connected to any of the coils, primary or secondary. I wonder, though, what would be the purpose of connecting any of the windings to the core?

author: Zero999
author_rank: Super Contributor
timestamp: June 30, 2012, 09:25:54 am
content: My guess if you were measuring the primary and low voltage filament secondary, rather than the HV secondary.The HV secondary is earth bonded so it can't float at any voltage due to static and the insulation between it and the core doesn't have to be rated to 2.5kV.See links for more information:http://www.gallawa.com/microtech/xformer.htmlhttp://wiki.4hv.org/index.php/Microwave_oven_transformerhttp://www.kronjaeger.com/hv/hv/src/mot/index.html

author: Architect_1077
author_rank: Regular Contributor
timestamp: July 01, 2012, 09:36:27 pm
content: Quote from: Hero999 on June 30, 2012, 09:25:54 amNope. This tx has it's terminals properly labelled. I know I was testing the HV secondary. In any case, I'll assume improper testing on my part and look further into the matter.Thanks for links