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OverUnity Research > Build / Construction Tips and Ideas > Component & Circuit Recommendations > Running resistive heater on pure DC or DC chopper ?
2024-11-27, 17:36:35
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Author Topic: Running resistive heater on pure DC or DC chopper ?  (Read 6645 times)
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img  forest
Running resistive heater on pure DC or DC chopper ? « on: 2015-04-12, 15:49:36 »
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Hello

I need advice how to run resistive heater made for 230VAC/2000W on pure DC from filter capacitor. I believe I should adapt DC voltage level so the power dissipation according to Ohms law will be the same 2000W, right ? Assuming I measured 28ohm of resistance of heater element then I need to compute from P(ower)=U^2/R and find U. Is that correct ?
Now the problem is two fold :
- first what would be the advantage to create DC square wave from this DC power using chopper circuit , and how to do it ? Do you know what voltage I should have in DC capacitor to chop it at 50hz and get the same 2000W on resistive heater ?
- if I run resistive heater on pure DC how I could prevent dangers in case of heater element become broken inside heater tube and in contact with (copper) wall of heater ?

I'm building electric heater for my home , and collect important information before start.

Thanks in advance for any help
   
img  TinMan
Re: Running resistive heater on pure DC or DC chopper ? « Reply #1 on: 2015-04-12, 16:20:35 »

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Quote from: forest on 2015-04-12, 15:49:36
Hello

I need advice how to run resistive heater made for 230VAC/2000W on pure DC from filter capacitor. I believe I should adapt DC voltage level so the power dissipation according to Ohms law will be the same 2000W, right ? Assuming I measured 28ohm of resistance of heater element then I need to compute from P(ower)=U^2/R and find U. Is that correct ?
Now the problem is two fold :
- first what would be the advantage to create DC square wave from this DC power using chopper circuit , and how to do it ? Do you know what voltage I should have in DC capacitor to chop it at 50hz and get the same 2000W on resistive heater ?
- if I run resistive heater on pure DC how I could prevent dangers in case of heater element become broken inside heater tube and in contact with (copper) wall of heater ?

I'm building electric heater for my home , and collect important information before start.

Thanks in advance for any help
'Why chop the DC?,as you will only consume more power in your chopper circuit. Just go for straight DC if it's a resistive heater. You will need 236 volts at 8.5 amps if your resistance is 28 ohms across the resistor element to get 2000 watts of heat power. Do you know if the resistance value rises much when the element becomes hot?.


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img  forest
Re: Running resistive heater on pure DC or DC chopper ? « Reply #2 on: 2015-04-12, 16:59:32 »
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Posts: 472
Good point.I didn't thought about that. It's standard heater for electric kettle.
http://imgusr.tradekey.com/o-B2951058-20091030034038/sell-heating-element-for-electric-kettle-lt-ekp7.jpg

I plan to use 4 of them to get 8kW.Inside this kind of pressure cooker
http://www.garneczki.pl/media/img/products/kpbig_53fd3c74da8547a8abe11fd69c40f3.jpg
Of course water will be flowing in pipe system.

 O0

All I checked is that it works fine with 230V AC with almost continous drain of about 2000W no matter how hot is water so it's good for temperatures up to 100C.
Chopper DC circuit would allow me (I think) to use commercial protection breakers to disconnect heater in case of current leakage to ground (container will be grounded), but I don't know how to simple build on for such high voltage like 340VDC
   
img  forest
Re: Running resistive heater on pure DC or DC chopper ? « Reply #3 on: 2015-04-14, 07:13:11 »
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Posts: 472
Do you know how to make microcontroller based DC-DC converter ? The problem with my device is that I must keep pulse width constant, and change the off time only according to the voltage level on output capacitor.
This voltage must be between 311 and 345 VDC and I'd like to keep the resisitve voltage divider physically separated from the Attiny 45 board . I know I can somehow use optocupler to isolate it but did anyabody checked Analog Devices Adum series to do the same ?
   
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