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Transformerless Inverter (or at least a smaller transformer)

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cobra1

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Im looking into building a small inverter as an add-on for my project. I need to be able to heat a 100w heat bulb from a 12v battery.

If iv done my sums right then thats a current draw of about 0.5A on the hot side, on the cold side i will be pulling about 8A @12v.

Iv been looking for a fairly basic inverter circuit for a few days now, but in order to do this im looking at needing a 8A+ transformer. Currently i have a 9-0-9, 4A transformer and thats big enough as it is.

Would anyone have handy a decent schematic of a smps type inverter, i know they generally use a TL949 chip, but when looking on the net for these type inverters i always get one that needs a huge transformer.

I know its probably easier to buy an inverter and add it in but in the long run i hope that my overall project will get to market, so would like it all on 1 board.


Any help would be great.
 
Can't you get a lower voltage bulb? If it's heat you're after, the total power will always be more if you put an inverter in the way. There are plenty of 12 V bulbs around.

If you are running a bulb at 230V, you don't need the inverter bit. You can just run DC.

In fact you might be able to have a boost regulator, or several in parallel, to directly produce 230 V from 12 V
 
The bulb is a 100w, ceramic heater. It is rated at 240v.

Are you saying that i dont actually need AC to power this heater??
 
If you just need a 100 watts of heat you can go with a different heater resistance that works with 12 volts instead of 240.

A resistance of 1.44 ohms would draw 100 watts at 12 volts.
 
You can buy a 100W 115V or 230V inverter for $15.00 on sale. It has a sine-wave output and uses a tiny ferrite-core high frequency transformer.
 
I didnt want to buy an inverter, i am looking for either something i can build into my overall design, or as it has now been pointed out, run this bulb on DC.

Running it on DC doesnt sound like a bad idea to me, problem is im a little clueless as to how to go about it.

Would i just boost my 12v to 230v and that would power it up?? I assume it will still draw ~8A from the source aswell??
 
You need a power oscillator driving a transformer.
You can use a huge, heavy, expensive, low frequency transformer or a small, ferrite-core, inexpensive, high frequency transformer.
 
i dont really want to use the heavy, expensive transformer, thats why i started this thread, i also dont want to buy a ready made inverter as that defeats the object of this thread. There has to be a simple (ish) way of making a 230v bulb heat up from a 12v source
 
Hello there, If you are using a heater element that can run on DC too (most do) then you can build a boost circuit, you dont need a true inverter. A boost circuit would take the 12vdc and pump it up to 230v also DC. You dont need a transformer but you would need an inductor anyway. Also, boost ratios like that are probably better off using a transformer. You'd have to be a bit careful whatever you do as the output could be very dangerous.
 
You can buy 125 or 150 watt resistors that you can power directly from 12 Volts. This would be much easier than building an inverter to power a 240 volt heater. You need approx. 1.5 ohms to get 100 watts at 12 Volts. To dissipate 100 Watts you need to use a resistor thats rated for a higher wattage so it doesnt burn up. This way you are not actually having to make a heater, Just mount the resistor inside your device like you would an actual heater. Try Google " 1 ohm 150 watt resistor"
 
The simplest inverter method I can think of would be this. Two transistors or mosfets and two resistors with an optional output smoothing capacitor built around almost any decent ferrite HF transformer core.

Dual Transistor  Oscillator.png
 
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The 100W resistor is allowed to dissipate a max power of only 30W at an ambient of 25 degrees C with a 1cm square heatsink. Then I think its temperature is 200 degrees C which is extremely hot. It will seriously burn you and melt plastic.
 
I would suggest using several of these:-

https://docs-europe.electrocomponents.com/webdocs/01dd/0900766b801dddfa.pdf
They are obtainable from RS.

They can work with a surface temperature of 300 ºC and I think that they are much closer in construction to the heat bulb that you wanted to use.

You will need several to get to 100 W and for 12 V you want them in parallel. You will need to derate them a bit, but if you want a lot of radiated heat, you should try to run them hot so at about 75% of their rating.
 
I didnt want to buy an inverter, i am looking for either something i can build into my overall design, or as it has now been pointed out, run this bulb on DC.

Running it on DC doesnt sound like a bad idea to me, problem is im a little clueless as to how to go about it.

Would i just boost my 12v to 230v and that would power it up?? I assume it will still draw ~8A from the source aswell??

You can run the bulb on DC. It will still take 100 W and that will mean at least 8A from the 12 V supply.

A boost converter would be based on an IC like this https://datasheets.maxim-ic.com/en/ds/MAX1771.pdf

You would need a big inductor, that would have to be rated at somewhere around 12 - 15 A. It would be easier if you could get hold of 120 V versions of the lamp. I would also suggest having several boost converters. Four, each taking 2 A and producing 0.1 A at 230 V, might be a lot easier to engineer, although it would be a good idea to synchronise them if you do that.
 
Or,
use a 100 Watt, 12 volt lamp.

Such a lamp would give you 100 Watts of heat,
and would save you the trouble of making anything much,
except mounting the lamp-holder.

Such a lamp would run on AC or DC.

A car battery won't supply 8 amps for very long.

John :)
 
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