Pilot Duty Thermostats for Electric Ovens

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Anonymous Poster	Pilot Duty Thermostats for Electric Ovens 04/02/2009 7:51 AM
	I have been working on a few old electric 240v 30 to 50 amps ovens. The ovens elements are controlled by contactors. The contactors are controlled by a thermostat. I replaced the thermostats with new pilot duty ones. the contactors now chatter. On the first oven I ended up replacing the contactors. I also replaced the thermostat two times thinking that the first was bad. with no success. The second oven, I decided to look closer at the thermostat. I hooked my O-Scope to the coil of contactor. There was several 100 miliseconds of noise. I figure that maybe the arcing of the contacors. I remove the coil from the thermostat and directly wired the contactor to the control voltage. So the contactor was on all the time. I put my O-Scope on the disconnected terminal of the themostat. I found that the thermostat switching is still bouncing 100's Miliseconds even without a load. Is this common with pilot duty thermostats and is there anyway I can resolve this issue?
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Anonymous Poster	#1 Re: Commercial Applience Tech 04/02/2009 8:33 AM
	Post details of pilot duty thermostat.
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dkwarner Guru Join Date: May 2006 Location: Placerville, CA (38° 45N, 120° 47'W) Posts: 6215 Good Answers: 248	#2 Re: Pilot Duty Thermostats for Electric Ovens 04/03/2009 12:19 AM
	Post #1 was correct: we need more details. On the other hand, the name "Pilot Duty" implies that these thermostats are designed to work on a gas range or oven. The solenoid used to turn the gas on and off should use a fraction of an ampere, so these thermostats have contacts that are WAY too small to operate a 30-50 Amp electric oven. Get the correct kind of thermostat, and it will work as intended. Now I just re-read your post, and realized that the thermostat controls a contactor, so the above is probably incorrect... It might be that these thermostats are supplying AC to contactors that were designed for DC. Again, more detailed info will get an answer with greater likelihood of being correct! __________________ Teaching is a great experience, but there is no better teacher than experience.
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Haajee Guru Join Date: Feb 2006 Posts: 1758 Good Answers: 6	#5 In reply to #2 Re: Pilot Duty Thermostats for Electric Ovens 04/04/2009 12:37 AM
	Dear Sir. Electrical Thermostats are Toggle type; ON/OFF as in Electric Irons , Refridges AirConditioner etc etc These are Bi-Meatallic strips; making/ breaking itself or operating a Toggle-Mechanism to make & break instantly. In Fridge a set of multi-contacts On/Off switch is initiated by a bellow expanded or sqeezed by some liquid like [I think .. forgot but used in Clincal-thermometers sorry] having hi-Temperature Coefficient to be more sensitive. As for with an AC output I have not seen yet; but may be they may be using "Fridge a set of multi-contacts On/Off switch " Regards
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zodiac Commentator Join Date: Jan 2009 Posts: 96	#3 Re: Pilot Duty Thermostats for Electric Ovens 04/03/2009 8:48 PM
	Hi Your thermostat may be a "creep acting" type. Consider a snap acting type.
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Haajee Guru Join Date: Feb 2006 Posts: 1758 Good Answers: 6	#4 Re: Pilot Duty Thermostats for Electric Ovens 04/03/2009 11:38 PM
	Regards #1 #2 have already asked for the details of "Pilot Duty" , It seems that their out-put can handle power contactors' coils. Otherwise : I think you already have know that the output of Gas-Thermostats is very small & can only operate only special designed Gas-Solenoids. To operate Contactotors with it need a sensitive DC relay which will operate a bigger relay having contacts ratings to handle contactors Coil power. In electrical ovens thermostat "Toggles" & can handle lot of current & available in variety of Temp & current ratings Chattering is only if you are using DC Contactors on AC supply. Load has no effect on firm mating of contactors / relays. In case of overlad contacts may over-heat or melt. Introduce a Bridge Rectifier between AC supply line [for contactors] & Contactors' Coil contacts' Normally marked as A1 & A2. To add a filter Capacitor of 100 micro-F on rectified line [with proper polarity & Working voltage] is an advantage for operation of AC contactors / relays /other wound components. Have good day !
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Anonymous Poster (1); dkwarner (1); Haajee (2); zodiac (1)

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