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Dual Voltage Heaters

Why Users Should Almost Never Use Dual Voltage Heaters

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Home > Blog Archive > Category: Industrial Heating Technology > Why Users Should Almost Never Use Dual Voltage Heaters

What are Dual Voltage Heaters?

diagram of Thermal Corporation dual voltage mica band heater

Some heaters are designed to operate from more than one voltage. These are referred to as Dual Voltage heaters. One of the voltages is always twice the other voltage, such as 240 volt/480 volts. These heaters have three terminals or wires. The terminals are connected one way for 240 volts and another way for 480 volts. (Inside are two separate heaters. For the smaller voltage, the heaters are connected in parallel. For the larger voltage, the heaters are connected in series.)

What are the advantages?

These heaters offer an advantage to OEM manufacturers when building equipment. By using these heaters, the OEM can put Dual Voltage heaters on the equipment without knowing which voltage their customer will use. If they did not use Dual Voltage heaters, they would end up building the equipment for one voltage and then if their customer wants the other voltage and they would have to change all the heaters. With these heaters, the OEM just provides documentation on how to connect up the heaters for each voltage. Thus, many heaters shipped on OEM equipment are dual voltage heaters. Dual voltage heaters are more complex and cost more than single voltage heaters, but still make sense for OEM manufacturers.

Failed Heaters

When the equipment is installed at the customer’s facility, it is connected to the appropriate voltage. Eventually one of these heaters fails. Now, what should the replacement heater look like? Should it be a dual voltage heater? Usually, when then equipment is installed, the voltage very rarely changes. Now, in this case, a heater of similar configuration but operating only from a single voltage should be used. Many times, the failed heater is taken to the purchasing agent and the agent is requested to buy a heater just like this heater.

Conclusion

If a user purchases a dual voltage heater rather than a single voltage heater, the dual voltage heater will be more expensive, more non-standard, more complex and because of the complexity, have a shorter life. So for a lower cost and a more reliable heater, order a single voltage heater rather than a dual voltage heater.

Looking for a specific heater? Click one of the links below to browse our product line.

Cartridge Heaters

Mica Band Heaters

Strip Heaters

Rectangular Band Heaters

Ceramic Band Heaters

Thermocouples & RTDs

Custom Heaters

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 05.09.2018
Last Updated: 09.06.2019

photo showing a close up of the 3 phase option on a Thermal Corporation mica band heater

Why Do We Have 3 Phase Industrial Heaters?

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Home > Blog Archive > Category: Industrial Heating Technology > Why Do We Have 3 Phase Industrial Heaters?

close up image of the 3 phase option on a Thermal Corporation mica band heater
3 Phase Option on Thermal Corporation Mica Band Heater

Introduction

We have 3 Phase electric power because of economics. It is just more economical to produce electricity as 3 Phase Power. If we generated single phase electricity, the voltage changes as if follows a sine wave pattern and the power to generate the voltage would change also. This changing power or torque is not an efficient way to convert mechanical power to electricity. If we generate the power as 3 separate voltages, each voltage wave form is one third of a revolution apart (120 degrees), the power or torque to generate the electricity is constant. That is, the sum of the voltages and the torque as a function of time remains a constant. This makes the conversion of power to electricity very efficient versus having the power be required to change 60 times a second. Also, the vibration created by a varying torque, increases the wear on the bearings and other parts of the generator, a further economic savings. Just about all utility company power, grid power, is generated as 3 phase power, even all of the 120 volts power in our homes.

We have Three Phase Industrial Heaters for 2 Reasons:

  1. By carrying the power to a heater with 3 wires rather than 2 wires, each wire carries less electric current. This means you can use smaller, less expensive wire. A water analogy would be that if you are carrying less water in a pipe, you can use smaller pipes. You should only use 3 Phase power for larger heaters, say above 2000 watts and especially above 5000 watts. If you use 3 Phase Power for small heater, it will be a more expensive heater and possible a heater with lower reliability.
  2. For 3 Phase Power, the larger the currents, (as in a large non- 3 phase industrial heaters), the more heat is produced in the connections inside the heater. Connections are one of the main areas that generate failures. If a connection weakens some with time, the heat produced in the connection will be equal to the current squared times the resistance of the connection. Basically a high currents in the heater generally means a less reliable heater.

Looking for our products? Visit our Products page to view our complete product line of industrial heaters, and industrial heating equipment and accessories!


Written by Jim Dixon
Edited by Shelby Reece
Date Published: 06.22.2014
Last Updated: 09.06.2019

temp vs heat loss in heater

Temperature vs Heat Loss In a Heater

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Home > Blog Archive > Category: Industrial Heating Technology > Temperature vs Heat Loss In a Heater

We often get questions regarding how much power (or wattage) is needed to maintain a process at a certain temperature. That is a complex question. In this article, we will discuss the general concepts that are used to determine wattage needs.

Energy Balance

First, we start with a simple energy balance: Ein = Eout

Ein is the rate of energy coming into the system. This is the wattage that is generated by the heater when an electrical current is passed through a resistance element inside the heater. Every heater is stamped with a wattage and a voltage. So, energy coming into the system is a variable that can be controlled.
Eout is the rate at which energy leaves the system. Eout is often what we want to determine because we can control Ein (the rate of energy coming in) and set it equal to this value. This consists of energy that is input into the process and leaves the system, e.g., plastic is melted, formed into a part, and then ejected from a machine. The heat that is absorbed by that plastic leaves the system. Eout also consists of power that is lost to the surroundings and is not used by the process. We call this waste heat. So, we need to determine both of those components. Power lost to the atmosphere can be approximated using heat loss graphs that are readily available online. In most cases, a wide variety of surface conditions, temperatures, and insulation thicknesses are plotted on these graphs. The end result of this calculation should yield a rate of energy loss (typically in watts per square inch) that is lost to the surroundings.

Rate of Energy Consumption

Next, we’ll look at the rate of energy consumption of the process. This is often much more complicated to determine.

For Example…

Let’s look at a process where we heat a chunk of polypropylene plastic from a temperature of 100°C to melting temperature (175°C). We are going to process one of these blocks of plastic every 15 minutes. The correct equation is:

where, E = power required in watts m = mass(kg) (25 in our example) cp = specific heat (Joules/kg°C) (1,920 in our example) = change in temperature (°C) (75 in our example) t = time in seconds (900 in our example)

Using the numbers above, we calculate that E = 4,000 which means we need 4,000 watts for this process. We can now add this 4,000W to the heat lost to the surroundings that we found on the approximate heat loss curve. That will give us a total steady-state wattage that we need to keep our process functioning.

Some Important Notes

  • Start up time is often an important consideration for selecting heaters.
    • Using the simple example above, if we wanted to heat the same mass of polypropylene from room temperature to melting temperature in the same amount of time, we would need more wattage.
  • No matter what the calculations say, it is a good idea to add 20% to this power requirement as a “safety factor” when sizing heaters. Why?
    • It is always good to allow for some error in the calculations.
    • Heater lifetime is improved if the heater does not run 100% of the time. The ideal run time, using a short cycle time, is 75% – 80%.

Written by Kyle Otte
Edited by Shelby Reece
Date Published: 04.17.2019
Last Updated: 01.29.2020

Why Higher Voltage / Lower Wattage Parameters Do NOT Make Good Industrial Heaters

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Home > Blog Archive > Category: Industrial Heating Technology > Why Higher Voltage/Lower Wattage Parameters Do NOT Make Good Industrial Heaters

The Problem

Occasionally, customers specify industrial heaters that have a higher voltage such as 480 volts in combination with a wattage of only several hundred watts. This is sometimes done because 480 volts is readily available or sometimes because it may seem that this combination would produce good heater life. In fact, this frequently produces a heater that has rather poor life.

But, Why?

The wattage of industrial heaters is the product of the voltage (E) multiplied by the current (I). Thus: W = E x I.

If for a particular heater, the voltage is on the high side, to have medium or low wattage requires that the current (I) be rather low. Now, to get a low current for a particular voltage, we need typically a higher resistance. Higher resistance is obtained either by using longer (more) element wire or by using wire that has a high amount of resistance (ohms) per foot. Usually, there is a limit on the amount of wire you can put in a heater unless it is a large heater, so in most cases we must use a wire with high ohms per foot. The higher the ohms/foot, the smaller the diameter of the element wire. Thus, most of the time we end up using wire that is very fine (small diameter). Perhaps, a wire that is finer than the hair on someone’s head.

Sometimes the wire size required is smaller than any wire we have in stock.

One of the Main Ways Industrial Heaters Fail

One of the main ways industrial heaters fail in manufacturing processes, like injection molding, is for the element (heater) wire to oxidize. As the wire oxidizes, the outside of the wire becomes a nonconductive oxide and the current is carried by the smaller diameter of unoxidized metal on the inside of the wire. All nichrome heater element wire goes through this aging process. But, if we start with a very small diameter wire, it does not take as long for the element wire to oxidize and burn into.

Thus, in most cases, the combination of higher voltage and lower wattage results in a heater that has a rather short life. Sometimes, we may try to improve industrial heater life by lowering the watt density or lowering the wattage, where the real problem is that the element wire is just too small. In general, if the wattage is lower than the voltage you are probably getting into an area where the heater life is being compromised.

So, What is the Alternative?

Usually, the best alternative is to locate a lower voltage such as 240 volts or 120 volts. Sometimes, this can be achieved by putting two heaters in series, such as two 240 heaters of equal wattage across 480 volts. Sometime with 480 volts, 277 volts is also available or with 240 volts, 138 volts may be available. (Line-to-neutral voltage from a 3 phase line-to-line supply voltage).

Written by Jennifer Taylor
Edited by Shelby Reece
Date Published: 06.09.2014
Last Updated: 09.06.2019

208 volt 3 phase

Why Do We Have 208 Volt-3 Phase Power?

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Home > Blog Archive > Category: Thermal Corp Vlog > Why Do We Have 208 Volt-3 Phase Power?


The Purpose of 208 Volt-3 Phase Power

In this video, our engineer, Kyle Otte, explains why we have 208 Volt – 3 phase power. Check out our blog post on why 208 volts is a “weird” voltage and where it came from for even more information on this topic!



Looking for our products?

Visit the Products page for a list of the industrial heating products we offer, such as cartridge heaters, mica band heaters, ceramic band heaters, strip heaters, temperature sensors, and much more!


Written by Kyle Otte
Filmed & Edited by Shelby Reece
Date Published: 12.26.2019
Last Updated: 01.10.2020

oxide coating

Case Study #001: The Low Wattage-High Voltage Problem

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Home > Blog Archive > Category: Case Studies > Case Study #001: The Low Wattage-High Voltage Problem

Case Study #001

This case study was the first of many to come, recorded on May 24, 1996, by Thermal Corporation engineer, Jim Dixon. Over the last fifty years, the great team of Thermal Corporation employees has helped many countless customers with heating applications. One of the byproducts of being an established company is having an extensive library of past solutions to lean on.

A customer sent in the following quote for a cartridge heater:

Diameter: 1/4″
Length: 1-1/2″
Lead Length: 20″
Watts: 75W
Volts: 208V

When we entered the quote into our tech sheet program, the program was unable to choose an internal resistance wire for these specific cartridge heater values. This caused us to ask three questions:

  1. Why is this a problem?
  2. If the program could pick a wire, why would this probably not be a good heater?
  3. What would we recommend?

Think About the Formula for Wattage

To begin, think about the formula for wattage.

Wattage = Current x Voltage

Heaters that have low wattage and relatively high voltage are typically a problem. If wattage is low and voltage is high, then what is the current? The current would be very low. How do you make a current very low?

I (Current) = E (Voltage) / R (Resistance)
OR
R = E / I

If the current is low and the voltage is high, what does R need to be? R needs to be very high. How do you make the resistance high? Think of electricity as water flowing through a heater. What diameter water hose has high resistance to the flow of water? A very small diameter hose will resist the flow of water. Thus, we have to use a very small wire and a LOT of it. In this case, we did not have any wire on hand that was small enough to make this particular case work.

Why Would This Not Be a Good Heater?

This leads into our second question: if we did have a small enough wire, why would this not be a good heater?

Remember that as heaters age, an oxide coating builds up on the surface. Temperature cycling accelerates this. Under a certain set of circumstances, the nickel-oxide will build up a constant rate. At some point, the oxide coating cuts off the path for electricity to flow- just like cholesterol clogging up an artery.

diagram of a large diameter wire and small diameter wire with oxide coating

The oxide coating on each wire is the same thickness. So, which size do you think would fail first? If you thought the small wire, then you are correct.

What Would We Recommend?

Now, to address the question of what should be recommended. First of all, to cause the wire size to increase, what needs to be changed and how? The answer is the resistance must decrease.

W = E 2 / R

If W does not change, and R goes down, what happens to E? E must also go down, as well. This means the customer must go to a lower voltage.

208 Volts, 3 phase power, is common in small industrial plants.

diagram representing 208 volts 3 phase power

If 208V is a voltage from one hot-line to another hot-line, what is the voltage from a hot-line to the ground?

Line to Ground Voltage = Line to Line Voltage / √3 = 120V

Therefore, wherever there is 208V there is probably 120V, also. If we recommend 120 volts, how much does it help the resistance?

Initially:
R = E 2 / W
2082 / 75 = 577Ω

Now:
R = E 2 / W
1202 / 75 = 192Ω

Thus, resistance is decreased by a factor of 3. This is what we recommended to our customer.

Have a question about a heating application?

Contact the Thermal Corporation engineers! We can help you solve any issue or any question you may have regarding your heating application. Get in touch with us by email at engineering@thermalcorp.com, by phone at (800) 633-2962 x152, or chat with us using the instant chat feature located at the bottom of the page.

Written by Jim Dixon
Edited by Shelby Reece and Kyle Otte
Date Published: 08.23.2019
Last Updated: 08.23.2019

Should Your Heaters Be Wired in Parallel or in Series?

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Home > Blog Archive > Category: Industrial Heating Technology > Should Your Heaters Be Wired in Parallel or in Series?

Should your heaters be wired in parallel or in series?

So, should your heaters be wired in parallel or in series? This question comes up when there is more than one heater to be connected to power. Basically any number of heaters can be connected in parallel, but usually only two heaters are connected in series. Connecting more than two heaters in series becomes much more complicated. With heaters connected in series, if a heater fails it can affect the other heaters. With heaters connected in parallel, the failure of one heater usually does not affect the other heaters.

The Most Common Pairing

The most common pairing is usually a two piece heater. In this case, if the heaters are connected in series, the voltage of each heater must be equal to half the total voltage available. For example, two 240 volt heaters connected in series across a 480 volt supply. Also the wattage of each heater must be equal. (If the wattage and voltage of each heater is not equal, the heaters will not split the total voltage equally.) If the two heaters are connected is parallel, the voltage of each heater must be the same as the supply voltage.

So, Why Choose One Way Over the Other?

One reason is that some heaters may not be able to be built as reliably at one voltage. This has to do with the physical dimensions of the heater, and the watts and volts. Basically you want an optimum element wire ( the wire that gets red hot) size in the heater. In some heaters, because of close spacing, the heater may not be able to be built at 480 volts. Also, if you wire in series, the failure of one heater most likely affects the other heater.

Conclusion

Remember, in parallel, each heater has the same voltage, but in series, each heater has the same current. Basically, you only wire in series when you have two heaters of equal wattage and voltage. In most other cases, you wire in parallel.

Looking for our products? Click here to view Thermal Corporation’s complete line of industrial heaters and industrial heating accessories.

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 07.20.2014
Last Updated: 09.06.2019

heating drawing

208 Volts Is a Weird Voltage. Where Did It Come From?

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Home > Blog Archive > Category: Industrial Heating Technology > 208 Volts Is a Weird Voltage. Where Did It Come From?

Three Phase Power

Three phase power has several parts that could be classified as “weird”.

Three phase power is power that comes in on three separate lines. In each line, the voltage follows a sign wave pattern. Each wave is similar except they are out of phase. By that, we mean that the second wave begins at the point where the first wave is a third of the way through its cycle. Then, the sine wave for the third line begins at the point that the first wave is two-thirds through and the second wave is now a third of the way through its cycle. This is just like singing the song Row, Row, Row your Boat gently down the stream, in three rounds, with each part starting at a different point in time.

three phase power

Each of the three power lines is hot. A load can be place between any two of the hot line OR between one of the lines and neutral ( a return path for the current that is at “0” volts.) If you place the load between two of the hot lines, one can be a positive voltage while the other is negative. This means that the voltage between them can be greater than the voltage from one of them to neutral (volts)

3 phase 4 wire in y

208 3 Phase DELTA

FIRST IMAGE IS 3 PHASE 4 WIRE in “Y”, SECOND IS IN DELTA

208 volts 3 phase

Line-to-Line Voltage

When we talk about the voltage between two hot lines, we call it Line-to-Line Voltage. When we talk about the voltage between one of the lines and neutral we call it Line-to-Neutral Voltage. The Line-to-Line voltage is always greater. And there is a constant ratio between the two. The Line-to-Line Voltage is always 1.732 times the Line-to-Neutral Voltage. (The 1.732 is the square root of 3). Unless we specify otherwise, when we say three phase we are talking about Line-to-Line Voltage.

Conclusion

Now to get back to our question. 208 volts is Line-to-Line Voltage. This three Phase voltage is frequently used in small businesses. Why? Well, what is the Line to-Neutral Voltage for this. It is 208 volts /1.732 which is 120 volts. The power is brought is as 208 volts 3 Phase and then the Line-to-Neutral Voltage will be 120 Volts. Each of the three Line-to-Neutral line will go to a part of the plant. When the lines were installed, the plant was divided into roughly 3 equal area from a power usage standpoint, with one line going to each area. This way, these areas have 120 volts to run their equipment from.

Looking for our product page? Click here to view Thermal Corporation’s complete product line of industrial heaters and industrial heating accessories.

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 08.07.2017
Last Updated: 11.21.2019

photo of Thermal Corporation cartridge heater

Tips for Extending the Life of Cartridge Heaters

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Home > Blog Archive > Category: Industrial Heating Technology > Tips for Extending the Life of Cartridge Heaters

Listed below are some tips for extending the life of cartridge heaters.

#1 Avoiding Contamination

photo of Thermal Corporation ease aid
  • When using a release agent, such as Thermal Corporation’s Ease-Aid, to ease heater removal from its hold, be sure to wait until agent is bone dry before inserting the heater into the hole. If the heater is inserted before the agent is dry, some of the liquid will usually be pushed towards the lead end and then will soak into the heater through the lead insulation or through the lava or ceramic plug at that end. When that happens, the heater can be expected to fail as soon as the power is applied. (Choosing the lead option of Teflon wire insulation and a Teflon plug can reduce the likelihood of water entering the heater, but this does not provide a fully hermetic seal, and the lead end of the heater must be restricted to 400°F).
  • Moisture, oil, and other liquids on the lead wires can be wicked into the heater and cause early failure.
  • Oil or other organic material on the lead end cap of the heater will carbonize at elevated temperature, causing a short from the leads to the sheath.

#2 Avoiding Over-Temperature

  • A loose fit of the cartridge heater in its hole will reduce the heater’s life time because the heat generated is not transferred efficiently to the object or material being heated, causing the heater to run at a higher temperature to transfer its energy. The higher the operating temperature, the shorter the lifetime. A rule-of-thumb for the fit is to make the hole diameter no more than .005 inches greater than the diameter of the heater.

    • Thermal Corporation cartridge heater

  • Choose the lowest wattage heater that will maintain the desired operating temperature of the part being heated and still provide a short enough start-up time. Choosing a heater with a higher wattage than required will result in the controller turning the heater on and off to maintain the desired temperature and a higher operating temperature during on-time. These conditions will shorten the heater life.
  • If used as an immersion heater, the type of fluid and its velocity passing over the heater are important factors. Ask for assistance from a Thermal Applications Engineer.

#3 Excessive Cycling

  • The way that Thermal Corporation evaluates the lifetime of their own cartridge heaters and those from competitors is to cycle the units from 150°F to 1,400°F and count the cycles to failure. Cycling reduces lifetime because the surface of the element wire oxidizes rapidly at higher temperatures; if the higher temperature is maintained, the oxide coating actually protects the wire from further oxidation, but if the wire temperature is reduced substantially, the oxide coating breaks off due to contraction and exposes fresh metal to more oxidation. With continuous cycling, the wire diameter is eventually reduced, and the resistance of the element is increased to the point that it becomes too hot. At that point, the element wire either melts and breaks open the circuit, or it causes the insulation over the wire to break down, causing a short to the sheath.

Edited by Shelby Reece
Date Published: 07.03.2018
Last Updated: 09.06.2019

wattage

Case Study #177: What Happens When Two Heaters With Different Wattage and Voltage Are Wired In Series?

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Home > Blog Archive > Category: Case Studies > Case Study #177

Case Study #177

A customer phoned in one day about an issue with two heaters. The two heaters were wired in series on a barrel. One of the heaters, however, was getting red hot and the other was not. He did not know why. Our first thoughts were that maybe the heaters were accidentally wired in parallel rather than in series. After checking with the customer, we found that the heaters were wired correctly. But, why was one of them getting so hot?

One heater was 610W at 230V. The other was 1260W at 230V. The customer applied 460V across these two heaters when they were wired in series.

Hint: to successfully wire two heaters in series, they must be equal wattage AND equal voltage, i.e. they must have equal resistance.

Now to see what happens when we calculate the resistance of each heater:

resistance equals E squared over W

Now when we apply 460V across these two heaters that are wired in series the circuit looks like this:

voltage across the 87 heater equals 310 volts, voltage across the 42 heater equals 150 volts, wattage for heater 1 equals 1,107, wattage for heater 2 equals 536 watts table showing stamped wattage versus actual wattage of the two heaters and an arrow pointing to the 1,107 watt that got red hot

Written by Jim Dixon and Shelby Reece
Edited by Kyle Otte
Date Published: 07.02.2019
Last Updated: 09.03.2019

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