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modify presto heat dish

Devedander 8,847 826 November 4, 2012 at 12:24 PM
So I have one of these and like to run it while sleeping but the thermostat on it works by turning the device on and off rather than regulating voltage. Every time it comes on it makes a noise.

I would like to stick a resistor in it so it can stay on low all the time rather than switching off and on....

I assume just splicing into the power line that goes to the element would do but not sure what part and would appreciate any advice!

8 Comments

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#2
Probably not the best idea, modifying it makes it likely to overheat, overheating could lead to a fire. Fire bad umkay.

If you modify a UL listed heating appliance, it's no longer UL listed. If your house goes up in flames and hey look your modified heating appliance was to blame your insurance will deny your claim! A far worse scenario than getting a little cold or the little click of a relay turning on and off. Consider a down comforter.

Look for other heating appliances especially the oil filled radiator type. Read the manuals see which ones advertise silent or triac switching.
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#3
Good point about insurance...

I have had other heater types and haven't found anything that works for me... I have a really odd problem which is that my head/sinuses get really cold easily but my body doens't... so a comforter doens't really work and in order for my head to not be cold the whole room has to be really hot... these directional dishes are great because I can point it at my face and it solves the problem... with the exception that these things seem to be on full blast or off...
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#4
If you think about it, most heaters operate on the same principal of a modulated duty cycle to control the temperature.

It's technically possible to modify it for continuous lower power output or to have quieter/silent switching (would require basically gutting and completely redesigning the electronics), but there are risks as above. You might try a warm mist humidifier or a heated CPAP machine (if you mind don't going to bed looking like darth vader and spending a bit of money). Ever try sleeping with a hat on?
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Last edited by jkee November 6, 2012 at 10:53 PM.
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#5
Quote from Devedander View Post :
I assume just splicing into the power line that goes to the element would do but not sure what part and would appreciate any advice!
NO!

The part you want is a light dimmer, only you need one rated for 2,000 watts instead of the usual 300-600 watts, but even it won't eliminate the clicking unless you turn the temperature setting of the heat dish all the way up and rely on the dimmer alone to hold down the power. The heat dish should have a built-in safety to prevent absolute catastrophe, that is, it should disconnect the power if the dish gets too hot for it (but not necessarily for the food, which could burn anyway), and it should still work even with the heavy-duty dimmer in line. OTOH if you set the dimmer voltage too high, the dish will run too hot, unless you turn down its own temperature setting, but that will just bring back the clicking of its thermostat.

You can't stick a resistor in series because it will get too hot, unless it's impractically large. For example, a 130W resistor is about 6" long and 1" diameter, and resistors at their rated power run at well over 100 Celcius and can melt plastic and burn wood or paper, as I've learned from personal experience. To prevent such dangers, resistors should be rated for at least 3 times the maximum power that will flow through them. Because resistors get so hot, light dimmers instead work like switching power supplies and turn the AC fully on and fully off rapidly by using a triac switch.
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Last edited by larrymoencurly November 6, 2012 at 08:25 PM.
#6
I was screaming no to myself too as to the resistor suggestion, but didn't include my screams in my post -- I probably should have.

A dimmer would probably work but it's a bit of a gamble as to how the design of the electronics would handle the reduced voltage. I'm not sure if the safety cut-off would be effected by reduced voltage, again it depends on it's design.
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#7
OP, did you ever figure this out? I have one of these too and the noise drives me insane. At night I put it on high and point it away from the bed and that is ok if it's very cold. Otherwise it still gets too hot. The only alternative is to try putting it on medium but the clicking noise wakes me up >.<
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#8
Quote from Devedander View Post :
I would like to stick a resistor in it so it can stay on low all the time rather than switching off and on....

I assume just splicing into the power line that goes to the element would do but not sure what part and would appreciate any advice!
A experience trained electrician would never attempt what you are talking about, plus the heater was never design for this purpose.

This below heater will run silent for under 29.99 and use the 20% off coupon too.
800 Watt/400 Watt Parabolic Heater [harborfreight.com]

I have both the Presto and CE heatdish, the CE is much better quality than the Gen 1. and Gen 2. Presto
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Last edited by FAL December 26, 2012 at 03:40 PM.
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#9
I have a presto heat dish, 2014 model and am running it with a triac controller connected between heat dish and wall plug. The presto is turned fully on and the triac controls the heat level - even heating with triac from very hot and quite cool. But there is a faint buzzing when triac is on - the buzzing is not present with heat dish only. What causes the buzzing and will it damage the heat dish control?
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Last edited by bobcdy December 12, 2014 at 12:42 PM.
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