Voltage req to heat small amt of water

[darrins]

Any water heating experts here?

I have a flexible heating element that is wrapped around an aluminum cylinder that contains water. It contains about 12 oz of water at room temperature. I want to heat the water to around 100 degrees Fahrenheit from an initial temperature of about 74 degrees Fahrenheit. I want to heat the water slowly, say during a 30 sec to 1 minute interval.

My question is: How much voltage should I apply?

From some quick and dirty calculations, I think this requires about 700 to 1000 watts of energy.

I've tried hooking my heating element directly to an AC outlet and it gets HOT FAST! AND results in uneven heating.

I'd also like to know if AC is more efficient when it comes to heating elements than DC. Something tells me that AC would be better, but I don't have anything to back that up.

Also, I'd like to make a simple bang-bang controller that applies this voltage when the water temp falls below some value, say 95 deg and turns off this voltage when water temp rises above some value, say 105 deg.

Can someone point me in the right direction?

Thanks.

Darrin

 

[ante1]

Darrin,

How about a triac regulator for the AC power. This can be controlled by a feedback from a NTC.

Ante :

 

[hotwaterwizard2]

How about a water heater thermostat.

http://www.homedepot.com/prel80/HDUS/EN_US/diy_main/pg_diy.jsp?prod_id=206930&cm_ven=hd_over&cm_cat=Search&cm_ite=26-10-10-water_heater_thermostat-PR-5-206930

 

[MP1]

My question is: How much voltage should I apply?

From some quick and dirty calculations, I think this requires about 700 to 1000 watts of energy.

Darrins,
The correspondence between electric power and heat is indicated by the
fact that 1 W used during the time 1 s is equivalent to 0.24 calorie of heat energy. The electric energy converted to heat is considered to be
dissipated or used up.
Hope it is a helpful start.

MP