general information on heating element

GM11
Posts: 4
Joined: 06 Nov 2013, 13:16

general information on heating element

Postby GM11 » 06 Nov 2013, 13:22

Hi, i would like to use the 70 Ohm (or any GHD element) to heat a very small drying oven (temp regulated to around 38C), could anyone tell me what voltage the elements require? and if they need AC or DC. i would like to control temp with a pic using burst mode via triac if AC or PWM if DC. But i have no idea what voltage these elements take.
thanks for any information

p.s i am a 50 year old bald bloke so have never actually seen inside any hair straighteners :lol:

gary
Site Admin
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Joined: 26 Jan 2008, 00:44

Re: general information on heating element

Postby gary » 06 Nov 2013, 13:38

Hi,

The heater element is basically a resistor. The power output by the heater is of course I^2 x R.

Therefore you can use AC or DC as long as you limit the voltage so the power dissipation is limited and don't let the heater get too hot. If you have poor thermal contact between the heater and the thing you are heating, then it will get very hot, very quickly.

I guess you'll need a decent amount of power, so AC may be easier as you'll need quite a few volts to get enough power out of a 70ohm heater.

Have you considered a low resistance, high power, power resistor? You can get some nice ones that will bolt onto a heatsink and will generate heat nicely. Then you can choose a low resistance so you can keep the voltage low and run it off a high current DC supply (which will be a lot safer to play with!)

Gary

GM11
Posts: 4
Joined: 06 Nov 2013, 13:16

Re: general information on heating element

Postby GM11 » 06 Nov 2013, 14:28

having flet the heat from a pair of straighteners i was basically just going to copy there set up I.E use the heater element and ceramic sleeve and simply cut power to it when the correct temp was reached inside the Cabinet (temp sensor is dallas 18s20). in the GHD ones what voltage do they use? and is it AC or DC? the reason for asking is i know input is obviously line voltage but i wondered if they bothered to step it down before the element.

gary
Site Admin
Posts: 1032
Joined: 26 Jan 2008, 00:44

Re: general information on heating element

Postby gary » 06 Nov 2013, 15:00

GHDs PWM mains voltage (110 or 240V) directly across the heater element.

Gary

GM11
Posts: 4
Joined: 06 Nov 2013, 13:16

Re: general information on heating element

Postby GM11 » 06 Nov 2013, 16:10

thank you Gary. i will probably go with zero cross detection and triac, maybe some kind of PID and burst mode.


regards jason

Webinfusion
Posts: 134
Joined: 20 Jan 2012, 02:13

Re: general information on heating element

Postby Webinfusion » 06 Nov 2013, 21:51

Hi,
Dont underestimate how quick they heat up, try only firing on positive cycles, you may find to achieve the temp you want you will only fire one wave form (20ms) every 4-5 seconds.

cheers
Kev

GM11
Posts: 4
Joined: 06 Nov 2013, 13:16

Re: general information on heating element

Postby GM11 » 22 Nov 2013, 21:24

have ordered some to give it a go, thanks for the tip on heating, have now decided to use a large heat sink as well see if i can get better control

Webinfusion
Posts: 134
Joined: 20 Jan 2012, 02:13

Re: general information on heating element

Postby Webinfusion » 23 Nov 2013, 22:53

Hi,
Also when mounting the heater on the heatsink make sure the heater can expand, clamping it in such a way that dosnt allow for expansion will crack the heater but possibly less noticeable at low temp control.


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