Electromagnetic ballast for non lighting use. - Page 1
Forum section: electronics / projects

author: davelectronic
author_rank: Frequent Contributor
timestamp: November 11, 2020, 07:37:45 pm
content: After having some good results with pairs of microwave oven transformers repurposed for power supplys run in series. I was wandering about a single transformer, and an electromagnetic ballast in series with the single MOT. My question is, does a ballast have to be the same rating as the MOT ? Or would a less powerful ballast do the same job. The transformer was from an 800 watt oven. I would be attempting to get the MOT to run on half the supply voltage, which would be 120 Volts AC as it's 240 Volts here in the UK.Thanks for looking in, any thoughts appreciated.

author: opampsmoker
author_rank: Regular Contributor
timestamp: November 11, 2020, 09:45:57 pm
content: First i am sure you know MOT's are really high voltage, and absolute utmost care is needed.I'd be worried about it flashing over to something, or to you!By "electromagnetic ballast", ...this can mean just an iron cored inductor in the case of an old fluorescent light.........or in modern times, the word" electronics ballast" refers to a high frequency, switch mode fluorescnt lamp driver, and this contains a ferrite based inductor inside it.So you would have to explain what you mean by "electromagnetic ballast"If an iron cored inductor...then really you have to look at the current rating.I dont know why you woudl want to use an iron cored inductor at the output of a MOT......the only reason fluorescent lamps used iron cored inductors was so they could interrupt the current in them, and thus cause a high voltage, high enough to ignite the gas in the fluorescent tube and start it lighting.Please be careful, ive electrocuted myslef so many times on mains by accident..........with an MOT, you aren't going to get "many times". Sorry to say, but you will be dead on the floor....i know i would be...the phone will go and distract me...and zap..

author: srb1954
author_rank: Super Contributor
timestamp: November 11, 2020, 09:48:47 pm
content: Quote from: davelectronic on November 11, 2020, 07:37:45 pmAdding a ballast in front of the transformer would very seriously degrade the output voltage regulation of the transformer, making it pretty useless for most power supply applications.

author: james_s
author_rank: Super Contributor
timestamp: November 11, 2020, 09:52:55 pm
content: What is the goal here? If you have the ballast feeding the transformer, the ballast will limit the current because that's what ballasts do. If that is what you want to do then it will work, and the wattage of lamp the ballast is meant to drive will determine the amount of current the ballast provides.

author: Zero999
author_rank: Super Contributor
timestamp: November 11, 2020, 11:04:38 pm
content: What are you trying to do? The only reason for adding a ballast is to limit the current, for example to power a Jacob's latter, or arc lamp.

author: davelectronic
author_rank: Frequent Contributor
timestamp: November 12, 2020, 03:58:40 pm
content: Thank you for your replys. I've been trying to put a power supply together using MOT transformers, I have been successful using a pair of transformers in series, both primary and secondary windings. A single MOT runs far to hot and idle consumes to much power as a single transformer.I have rewound the secondary windings (removed high voltage winding) to gain a low voltage transformer. So nothing above mains line voltage, no very high voltages etc. The question on a ballast unit is to put it in series with a single MOT to share half the mains supply voltage. In this way running as if it where two MOT's but it would be a single transformer with a series ballast wired with the primary winding.My two MOT rewind configuration has achieved 20 Volts AC and powered 300 watts of low voltage halogen lighting for testing purposes, with no problems. The ballast was to use a single MOT with the primary series ballast, as two MOT's in series run quite well. The hope is the ballast would half the supply voltage in series with one MOT. The ballast I'm referring to is the older iron / copper type fluorescent, or discharged lighting ballast etc. I have no interest in high voltage Microwave oven transformer use. Maybe that paints a clearer picture of my question about a MOT with a primary series ballast unit.Thanks for the help.

author: james_s
author_rank: Super Contributor
timestamp: November 12, 2020, 04:24:53 pm
content: Having a ballast in series will limit the current and result in a supply that sags a lot under load. If your goal is to prevent the cores from saturating then using two transformers in series is a better approach, or you can use a smaller transformer to buck the voltage feeding the MOT down.

author: drussell
author_rank: Super Contributor
timestamp: November 12, 2020, 04:45:21 pm
content: Quote from: davelectronic on November 12, 2020, 03:58:40 pmUhhh, well, yeah...A microwave oven transformer is not designed to "idle", to be connected to the line without full load being drawn from the secondary. They are intended to either be off, or supplying full B+ juice to the magnetron, not sit around with the low-inductance primary shunted across your AC line with no load. They don't have enough windings on the primary for that.

author: davelectronic
author_rank: Frequent Contributor
timestamp: November 13, 2020, 02:34:48 am
content: Something very interesting i hadn't thought of. feeding the MOT with another input transformer, the 110 Volt site transformers come to mind, but they are a bit to big to go in an enclosure. i just thought a ballast might reduce the input voltage, and address the over heating issues. The only thing with a first pre input transformer is its power rating, to realise the current output from the MOT. I do have a second pair of reclaimed MOT transformers, with the high voltage windings removed. I was hoping to find a way of using a single transformer in a project. I need the input of around 120 Volts AC with no degrading of the input current. Some head scratching, could this be achieved electronically with a reduction voltage input circuit ? Or is that idea just a non starter. So electronically doing what a step down transformer would do. I know my ideas sound a bit crazy, but i'm always the thinker.

author: james_s
author_rank: Super Contributor
timestamp: November 13, 2020, 03:43:30 am
content: You could try a triac dimmer circuit, the basic ones don't like driving inductive loads though. Do you really need the input as low as 120V? If something a bit higher would work you could try bucking down 240V with something common like a 24V transformer, that would give you around 216V. You can wire the secondary of a transformer in series but out of phase to buck voltage down, just as you can wire it in phase to boost a voltage up. You could also add more turns to the transformer core you're using and wire them in series with the primary.

author: davelectronic
author_rank: Frequent Contributor
timestamp: November 13, 2020, 03:43:52 pm
content: I had considered using a 1000 watt dimmer module, until I read they don't like inductive loads. And als read as they alter the AC wave form via rapid switching they don't really lower the voltage, but just clip the wave form down. And could overheat a transformer. Shame, as that idea would be great. Having looked at quite a few ideas, the only one that works is two MOT's in series. I would have tried increasing primary turns count, but there is little room for that, and it would eat into the area needed for the secondary. Thinking a while ago, I did wander about splitting the IE and wind enameled copper wire on a bobin. But previous splitting degraded the magnetic performance as I couldn't weld the two sections shut again. I can weld if I split the core, but would be unsure about weld penetration and possibly again degrading the magnetic circuit. I'm unsure how precise those welds need to be, mostly the weld rod material.