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High voltage via transformer from DC help

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Cicero

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Hi all, hoping you folk have some pointers for me to do this cheaply and efficiently, and simulate it first. My analogue electronics knowledge is rusty.

I need to generate a low current high voltage (150-240V) AC signal to use with flame detection.

I'm running off a 12V DC battery to start with, and am thinking of switching that at 50Hz into the secondary of this transformer https://uk.rs-online.com/web/p/pcb-transformers/1739715/

I've done a quick draft on LTSpice (attached), and I'm deliberately trying to avoid PWM techniques if I can. Not sure if I'm even headed in the right direction though so want to pass it through you guys first to make sure I'm not being stupid before I prototype it.
 

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ericgibbs

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hi C,
You could use a 555 timer for the 50Hz square wave source and say a N MOSFETs to switch the linked secondary, the transformer will be OK with a square wave input.

Do you want an example.?
E
 

Cicero

Active Member
hi C,
You could use a 555 timer for the 50Hz square wave source and say a N MOSFETs to switch the linked secondary, the transformer will be OK with a square wave input.

Do you want an example.?
E
Really, even at 50Hz? I thought I'd have to smooth out the wave to approximate sinusoidal?

Luckily I have an MCU for the FET switching, its just the transformer side I'm sceptical about.
 

ericgibbs

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hi,
Its common practice to construct 12V to Mains converters using a square wave drive.

Will the fact that the output waveform will be sort of square wave, be a problem.?

Sim it and try,
E

PS: ignore the 10:1 text, its a quick chop downed circuit, tweak the inductance to suit
 

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Cicero

Active Member
It looks great at first, but falls over when you restrict the current even a bit. Just put 10Ω in series and the nice secondary square wave changes to a spike every 10ms.
 

tcmtech

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Since I can't open your file I have no idea what you going for but for flame detection in my boiler system I just use standard optical detection via common CAD cell. Low voltage and very reliable.
 

Cicero

Active Member
Since I can't open your file I have no idea what you going for but for flame detection in my boiler system I just use standard optical detection via common CAD cell. Low voltage and very reliable.
Its an LTSpice file. Has there been an issue with the upload perhaps?

Optical isn't an option unfortunately, as it will be exposed to sunlight.
 
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alec_t

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tcmtech

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No. It works fine for me. I think tcm is LTspice-phobic :D.
For me it's that whole theory Vs reality thing. Theory comes up way too short on delivery far too often with those simulators for me to ever care to waste my time with trying to get them to tell me something I already figured out or know as is.

Optical isn't an option unfortunately, as it will be exposed to sunlight.
That would depend on what's burning regarding it's flame color spectrum and thermal values.

Pretty easy to indirectly detect something like a combustion process that gives off light and heat even in direct sunlight if you know what characteristics to look for. ;)

(^ Something LTspice won't show or tell you in a simulation.^) :p
 

alec_t

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(^ Something LTspice won't show or tell you in a simulation.^) :p
Actually, you can use LTS to model physical processes other than electronic ones. I've used it in the past for thermal modelling of a domestic heating system; also to model build-up of magma pressure leading to a volcanic eruption. :D
 

Cicero

Active Member
Fair enough. LtSpice and simulation definitely has its place, but only if you keep in mind your practical scepticism.

Like when using a calculator and it spits out a ridiculous number...you know its wrong due to intuition, its not to now say the calculator is worthless.
 

Cicero

Active Member
That would depend on what's burning regarding it's flame color spectrum and thermal values.

Pretty easy to indirectly detect something like a combustion process that gives off light and heat even in direct sunlight if you know what characteristics to look for. ;)

(^ Something LTspice won't show or tell you in a simulation.^) :p
You've got my attention, go on...

Could be any combination of, propane, butane, ethanol and diethyl ether at times.
 

tcmtech

Banned
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You've got my attention, go on...

Could be any combination of, propane, butane, ethanol and diethyl ether at times.
Without specifics most of those flames will give off enough light and heat that a properly shielded photo detector in a tube pointed at the flame will easily pick up on them.

Same with concept simple IR detection. If you can point a IR type thermometer gun at the flame and get a reading that's anywhere above worst case ambient sunlight induced thermal readings you can detect the flame that way.

Years ago I experimented with hydrogen and a hydrogen flame in broad daylight is by our visual standards invisible but its still easily detectable by a simple IR thermometer gun IR detector. :cool:

Another option if the flame is in a somewhat contained area is to use a simple thermocouple device. It's what most every furnace and portable heater uses to sense the pilot light or main burner flame. ;)
 
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