Frost proofing with incandescent bulb

[GoldDigger]

If incandescent bulb resistance were constant, two in series would provide half the heat of a single bulb. Since I understand the resistance significantly increases with operating temperature, two in series would provide somewhat more than half the heat of a single bulb.

Cheers, Wayne

Quite true. Far less than 1/2 the light, but we don't care in this application.

 

[mbrooke]

Quite true. Far less than 1/2 the light, but we don't care in this application.

Something like only 10% of the light, if that.

 

[hillbilly1]

Let me say this again. Heat tape. Heat tape is designed for exactly the purpose of keeping pipes unfrozen. It's not a safety hazard to run. It will not burn out in a few thousand hours. It does not require an enclosure around the dishwasher. It requires no mods to the dishwasher. I have used heat tape to keep my RV water and sewage lines unfrozen in the middle of winter in NC. It works well.

Can't really say that heat tape is not a safety hazard, there is a reason for the gfep, and its not for shock hazards. Heat tape failure is pretty common, and if the gfep isn't working, makes a nice fire!

 

[retirede]

Heat tape failure is pretty common, and if the gfep isn't working, makes a nice fire!

I don’t believe that’s true for modern, self-regulating types.

 

[hillbilly1]

Hazard

The Consumer Product Safety Commission (CPSC) says they no longer collect data on heat tape-related accidents. But in the 1990s, the agency reported the products were involved in about 2,000 fires, 10 deaths and 100 injuries every year.Dec 15, 2006
Chicago Tribune › news › ct-xpm-2...

Yet they no longer collect data on it according to this story. Why? Follow the money.........

 

[retirede]

Yet they no longer collect data on it according to this story. Why? Follow the money.........

Yeah, everything is a conspiracy.

 

[hillbilly1]

Yeah, everything is a conspiracy.

Until it is proven fact.........

 

[gadfly56]

Can't really say that heat tape is not a safety hazard, there is a reason for the gfep, and its not for shock hazards. Heat tape failure is pretty common, and if the gfep isn't working, makes a nice fire!

Self-regulating heat tapes don't fail. It's physics. Temperature goes up, resistance goes up, power consumption goes down. "Ye canna' change th' laws o' physics, Captain." There are heat tapes that are not self regulating, and these may be subject to controller failure or other failure modes leading to overheating.

 

[drcampbell]

I don’t believe [heat tape failure is pretty common] for modern, self-regulating types.

You are correct. The resistance of the semiconductive heating element goes up -- and the heat production goes down -- as its temperature goes up. Heat production is virtually zero long before the temperature reaches 451° Fahrenheit.

But the old-fashioned heat tapes are still available. (though I can't fathom why)

Self-regulating heat tapes don't fail. It's physics. ...

I'm not so sure about that. What if it were crushed, pinched, twisted, or installed with a too-tight radiator-hose clamp and the geometry of the semiconductive heating element radically changed? What if the two wires were almost in contact with each other (or the metal overbraid) and started arcing? I haven't seen it happen, but it wouldn't surprise me any.

 

[retirede]

What if the two wires were almost in contact with each other (or the metal overbraid) and started arcing? I haven't seen it happen, but it wouldn't surprise me any.

I’d guess this risk is no different than a normal appliance or lamp supply cord. Probably even lower once installed given where most are installed.

 

[kwired]

Let me say this again. Heat tape. Heat tape is designed for exactly the purpose of keeping pipes unfrozen. It's not a safety hazard to run. It will not burn out in a few thousand hours. It does not require an enclosure around the dishwasher. It requires no mods to the dishwasher. I have used heat tape to keep my RV water and sewage lines unfrozen in the middle of winter in NC. It works well.

Type you would use for this application is going to be self regulating as well, warmer the ambient the less power it will draw.

 

[hillbilly1]

I do know of a fire where the maintenance guy wadded a bunch up in a styrofoam wall to keep an opening of a conveyor tunnel from icing up. For some reason the story disappeared. I personally know it happened. Pretty sure it was the self regulating type. Industrial braided sheath on it.

 

[gadfly56]

I do know of a fire where the maintenance guy wadded a bunch up in a styrofoam wall to keep an opening of a conveyor tunnel from icing up. For some reason the story disappeared. I personally know it happened. Pretty sure it was the self regulating type. Industrial braided sheath on it.

There are power-limiting heat tapes that run at much higher temperatures. They have a conductive wire, like a toaster wire, with a positive temperature coefficient to limit heat output.

 

[GoldDigger]

There are power-limiting heat tapes that run at much higher temperatures. They have a conductive wire, like a toaster wire, with a positive temperature coefficient to limit heat output.

There are three basic types of heat tape.
1. Series, in which the resistance heating wire runs from one end of the tape to the other. It is difficult to get a significant increase in resistance over a temperature range near room temperature and definitely below 100C. So these require a thermostat and if crossed or wadded up can produce extremely high local temperatures. And if the wire gets hot enough it will cause a locally higher resistance, leading to a far higher heat density on what is essentially a constant current circuit.
2. Wire type parallel, in which short lengths of resistance wire are run from one copper or aluminum conductor to the other. This essentially puts multiple short heating elements in parallel. This will also produce excessive temperatures when crossed or wadded. But if it gets to a high enough temperature that the resistance wire increases significantly in resistance, the local heating density will decrease.
3. The self-limiting semiconductor based heat trace in which the dielectric between the two metallic conductors has a controlled resistivity designed to produce the desired heat output per length of trace. The semiconductor has a high positive temperature coefficient which is enough to drastically reduce the heat output at the design maximum temperature. Since this is also a parallel circuit, the local power density can be made quite small. But even with this there will be higher temperatures where the trace is crossed or run in parallel with itself. Not nearly as likely to start a fire though.

 

[paulengr]

There are three basic types of heat tape.
1. Series, in which the resistance heating wire runs from one end of the tape to the other. It is difficult to get a significant increase in resistance over a temperature range near room temperature and definitely below 100C. So these require a thermostat and if crossed or wadded up can produce extremely high local temperatures. And if the wire gets hot enough it will cause a locally higher resistance, leading to a far higher heat density on what is essentially a constant current circuit.
2. Wire type parallel, in which short lengths of resistance wire are run from one copper or aluminum conductor to the other. This essentially puts multiple short heating elements in parallel. This will also produce excessive temperatures when crossed or wadded. But if it gets to a high enough temperature that the resistance wire increases significantly in resistance, the local heating density will decrease.
3. The self-limiting semiconductor based heat trace in which the dielectric between the two metallic conductors has a controlled resistivity designed to produce the desired heat output per length of trace. The semiconductor has a high positive temperature coefficient which is enough to drastically reduce the heat output at the design maximum temperature. Since this is also a parallel circuit, the local power density can be made quite small. But even with this there will be higher temperatures where the trace is crossed or run in parallel with itself. Not nearly as likely to start a fire though.

The correct term is negative coefficient...output drops with temperature increases. Positive means it runs away, like laser diodes do.

There is a temperature on the last type where the output drops to basically zero. Of the major manufacturer of the stuff the two versions go to zero at around 65 F and 150 F and the second version is pretty much for industrial uses other than frost proofing. So if you cross or parallel it your wattage per foot goes up so it heats more/faster but still goes to no output well before it starts to damage anything.

The big advantage here is imagine a typical case of heat tracing a water line from a well house outside. Do you put the thermostat on the inside and let the outside section freeze or outside and the inside overheats? And what about valves where you need a few extra wraps? See you can’t win. That’s where self regulating tape fixes all these issues. Only downside is output isn’t that great so you MUST insulate or the wind blows all the heat off. Closed cell foam keeps it from soaking up water.

 

[Barbqranch]

I have had to make a hot box for some specialized chemicals. I used an aquarium thermostat (we use those for other things also) and two 60 watt light bulbs. However, I put a diode in series with each bulb (opposite polarity) so they are running on a little over half power. They will eventually burn out, but it takes a very long time, and you have the second bulb as a backup.

 

[GoldDigger]

I have had to make a hot box for some specialized chemicals. I used an aquarium thermostat (we use those for other things also) and two 60 watt light bulbs. However, I put a diode in series with each bulb (opposite polarity) so they are running on a little over half power. They will eventually burn out, but it takes a very long time, and you have the second bulb as a backup.

Since you are giving each a 50% duty cycle and the filament temp is well below normal operating temperature, you should get more than 1/2 power.

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[winnie]

The formulas given in this wikipedia article match my recollection from when I was playing with this stuff some years back.

Lamp rerating - Wikipedia

en.wikipedia.org

Va is applied voltage, Vd is design voltage:

filament lamp current is roughly (Va/Vd)^0.55
filament lamp power is roughly (Va/Vd)^1.6

If these were fixed resistors, then current would be Va/Vd and power would be (Va/Vd)^2.

(Note: these equations are approximate, and drawn from 2 different sources, and clearly not quite consistent with each other).

-Jon

 

[jusme123]

Because we're us. Why use a simple solution when there are myriad complicated ones for us to debate?

Go with geothermal heating, he needs to get a drilling truck out there before the ground freeze$

 

[GoldDigger]

Just remember in your calculations that for a half wave duty cycle the RMS voltage is not 1/2 of the nominal voltage, it is Vnominal/sqrt(2).

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