Author Topic: heating element  (Read 4973 times)

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blueyonder

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heating element
« on: February 20, 2008, 08:34:58 PM »
 doing a lot of reading and sum things i remember was. a guy saying that a heating element couldn't see if the power was ac or dc.

  but it got me thinking.

  if he was right then its possible to use a ac water heating element.

  the other type heating element seams to work with dc .for dump loads.

  the wire type i mean.

  maybe i should have asked the one who said it. but no one disagreed with him.

  i thought if he was wrong then sum one would comment .

   i am just understanding the difference from AC and DC. so will the water heating

element know. sorry i don't know the answer to this. maybe sum one can put me right.

 
« Last Edit: February 20, 2008, 08:34:58 PM by (unknown) »

ghurd

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Re: heating element
« Reply #1 on: February 20, 2008, 02:12:35 PM »
The element will not know the difference between AC and DC.


The Problem is the Voltage.

Check Ohm's and Watt's Laws.  A 5000W 220V heater. How many Ohms?  Then how much power will it use at 12V?

G-

« Last Edit: February 20, 2008, 02:12:35 PM by ghurd »
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wooferhound

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Re: heating element
« Reply #2 on: February 25, 2008, 09:21:26 PM »
Another thing to consider is that

You would probably need a Thermostat. That thermostat would be switching High Current connections. A normal water heating thermostat would fry after a short time.
« Last Edit: February 25, 2008, 09:21:26 PM by wooferhound »

blueyonder

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Re: heating element
« Reply #3 on: February 26, 2008, 05:48:58 AM »
 thanks ghurd and woofer .

    its just i see a lot of 12 dc heaters for sale on sum sites .

   there not cheap. old post from ghurd talked about small 12dc coffee maker type thing

  from flea markets.

  as it happens i have one at home. it will boil water from the car cigarette lighter socket  . i also got it from a flea market.

   but ghurd said about 5kw .  yes i know i cant use that on a dc system .

   it would just buckle the battery plates.

    but whare do dc heating element start and finish .also ac heating elements begin

    the coffee maker element is 140 watts. so it says .so might use 11 amps.

 ive seen 300watt heaters ac.

   there are plenty dc elemts for sale . is it just the wattage that is different.

  ive taken sum apart its just a wire inside covered in  ceramic or sumthing.

  and a outer metal jacket.

   so its the wire inside that heats up.

    so is it just a matter of watts .  lower is ok for dc and higher you need ac.


   why do i want to know. its just the dc rated are so expensive.

   while the ac rated are cheap.

   looks to me there made from the same stuff. thats what is confusing me.

  just a thicker wire inside.  it must be a special wire that don't melt .

  when i get interested in sumthing i like to understand it or how it works.

  so is it one law for dc and another for ac?

« Last Edit: February 26, 2008, 05:48:58 AM by blueyonder »

wooferhound

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Re: heating element
« Reply #4 on: February 26, 2008, 07:34:48 AM »
According to this site

http://www.familyonboard.com/car_boat_vacuums.html

a 12v coffee heater for a car is 120w which is 10a


A home coffee maker is 120v at something closer to 900w

That would be 90w at 12 volts which is 7.5a <-(i think i'm right here)


It's all about the resistance of the heating elements

They don't care if you're feeding AC or DC voltage

« Last Edit: February 26, 2008, 07:34:48 AM by wooferhound »

ghurd

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Re: heating element
« Reply #5 on: February 26, 2008, 09:51:13 AM »
The 5000W 220V heater element thing.

It would draw 22.7A at 220V. Meaning the resistance is 9.7 ohms.

At 14V the element would use 1.44A. Only about 20 watts.

G-
« Last Edit: February 26, 2008, 09:51:13 AM by ghurd »
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blueyonder

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Re: heating element
« Reply #6 on: March 06, 2008, 06:08:13 AM »
 thanks woofer and ghurd . i understand now.

                     i get there in the end
« Last Edit: March 06, 2008, 06:08:13 AM by blueyonder »

tmcmurran

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Re: heating element
« Reply #7 on: October 06, 2008, 12:26:45 PM »
But it still did not lower the price of these puppies :(  Has anyone looked into RV Service Places for these?  Just wondering if they carry the 12v versions.  Bet if they do that they would still be an arm and your first born.
« Last Edit: October 06, 2008, 12:26:45 PM by tmcmurran »

Airstream

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Re: heating element
« Reply #8 on: October 06, 2008, 01:48:24 PM »
Woof, wish it was so but it ain't.


"The 120VAC heater used for low voltages"


Using E² / R = Watts and E² / P = Ohms


 120*120 = 14400 / 900 (watts) = 16 Ohms


so...


 12*12 = 144 / 16 = 9 watts


 24*24 = 576 / 16 = 36 watts


 48*48 = 2304 / 16 = 144 watts


 72*72 = 5184 / 16 = 324 watts


 96*96 = 9216 / 16 = 576 watts


 120*120 = 14400 / 16 = 900 watts

« Last Edit: October 06, 2008, 01:48:24 PM by Airstream »

ghurd

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Re: heating element
« Reply #9 on: October 06, 2008, 02:34:38 PM »
Yup.  6 arms, 4 legs and all 3 first born.  If you can find one.

That is why many people (and me) believe small scale wind powered water heating with water heater elements is a losing battle.

A tempering tank would make a lot more $ sense.

Then put the load resistors uder it.  :-)
« Last Edit: October 06, 2008, 02:34:38 PM by ghurd »
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