Power efficiency of induction heating???

A thought just struck me, though it's not my field of speciality, but...

isn't induction heating is supposed to be more energy efficient than the resistance heating used by the Reprapper?

If the brass/copper pipe in the extruder was replaced with an iron rod, wouldn't that both reduce power consumption and help improve temperature control?

Edit:

While we're at such odd ball questions, why not extrude powdered granulate an then use microwave welding?

Edited 1 time(s). Last edit at 02/02/2010 11:00AM by anton.

Um, Anton ... why is this sort of inquiry put in the Gada Prize thread?

I'm going to move this to the extruder thread.

Edited 1 time(s). Last edit at 02/02/2010 11:12AM by Forrest Higgs.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

If anything, I would expect induction heating to be less efficient than resistive heating.

Where did you think the losses for the nichrome were? I only see two significant factors - loss due to radiation or environmental cooling, and loss within the electronics (proportional to I^2, and sensitive to resistance.)

I see much greater potential for losses with induction: greater losses during the on/off transition of MOSFET drivers, radiated losses absorbed by the lamp on your desk instead of the platform, etc.

If you're looking for efficiency, the ideas proposed for a solid state heat pump make the most sense to me; assuming you can get a good enough heat sink to pump heat out of the ambient environment -- efficiencies well above 100% - 200% should be possible. (This does not breaking any physical laws; a heat pump can move more heat with a given amount of energy than could be produced with that energy alone.)

Forrest Higgs Wrote:
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> Um, Anton ... why is this sort of inquiry put in
> the Gada Prize thread?
>
> I'm going to move this to the extruder thread.


Because of the low power consumption clause of the price!!

BeagleFury Wrote:
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> Where did you think the losses for the nichrome
> were? I only see two significant factors - loss
> due to radiation or environmental cooling, and
> loss within the electronics (proportional to I^2,
> and sensitive to resistance.)

Like I said, I'm no specialist, I'm quite far away from my area of speciality, but .. induction stoves are supposed to be more energy efficient than ordinary stoves, I've heard numbers like 65% for ordinary stove, 84-90% for induction stove. In my simple minded head, the heater barrel is just like a pot on the stove, being warmed.

> efficiencies well above 100% - 200%
> should be possible. (This does not breaking any
> physical laws; a heat pump can move more heat with
> a given amount of energy than could be produced
> with that energy alone.)

OT: I know, my home is heated using a heat pump, though not solid state, with energy effeciency of approx 350% :-)

Edited 1 time(s). Last edit at 02/02/2010 11:23AM by anton.

anton Wrote:
>
> Like I said, I'm no specialist, I'm quite far away
> from my area of speciality, but .. induction
> stoves are supposed to be more energy efficient
> than ordinary stoves, I've heard numbers like 65%
> for ordinary stove, 84-90% for induction stove. In
> my simple minded head, the heater barrel is just
> like a pot on the stove, being warmed.

I'm not a specialist either, so don't take my word as gospel.

I think inductive stove tops are more efficient because they lose less heat to the environment. It's sort of hard to insulate the electric stovetop burners while still providing heat to the pan. I believe the situation may be slightly different on the extruder nozzle.

For the prize and energy usage, I think new out of box thinking is going to be needed to meet the power constraints. -- think of ways to avoid needing heat altogether... or, find a free source of heat (reprapped tin foil solar collector/concentrator; seems like you could probably do something for $30 and get close to 500-1000watts free

BeagleFury Wrote:
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> I think inductive stove tops are more efficient
> because they lose less heat to the environment.
> It's sort of hard to insulate the electric
> stovetop burners while still providing heat to the
> pan. I believe the situation may be slightly
> different on the extruder nozzle.

That's exactly why induction cook-tops are more efficient. Instead of having a large portion of the heat lost around the pan, the pan is basically turned into the heating element. With the extruder, you are losing a very small amount of heat to the environment already, since it is usually well insulated.

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For printing metals, induction heating may be a possibility. I've considered it myself. There are some issues though. Requirements for a large transformer and fairly complex control electronics unless you're going to use water-cooled HF valves and huge resonant coils. (the 4Kw one I had the pleasure of using was 7ft tall, ran off a 3-phase line and made a loud bang when the water loop breeched one of the capacitors)
Impractical to fit it all on a print head, so flexible copper coolant/current lines would be needed. Liable to catastrophic failure.

There is a handy guide to building your own induction heating system though, if you want a place to start your own trials into it anyway. Starts here: [webpages.charter.net]

I hope to build one myself at some point for vacuum melting/casting aluminium, silver, gold, etc..

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--
Peter "Sci" Turpin
London, England

Provider of practical solutions.

(Sometimes stellifying Jupiter IS a practical solution)

Induction heating is:

(1) Cool!
(2) Useful for bronze casting and bronze-powder sintering
(3) May be useful and economic for RepRap extruders.
(4) Cool!

Please register and create a wiki page for your idea on the RepRap wiki
[objects.reprap.org]
and then we should move this thread back to the Gada Prize forum. Email me or Forrest if we forget.

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While we're at such odd ball questions, why not extrude powdered granulate an then use microwave welding?
It may be more straightforward to powder print it using RepRap+inkjet stuff, then then microwave sinter or furnace sinter the workpiece.

...Hmmm... Bronze or Ceramic filled paste or filled plastic granule would work. Filled plastic filament would break. Probably. We'd want a fill fraction of more than 80%, maybe, and I bet the filament wouldn't hold a bend. I'd suggest making 'slugs'.

The slug would be 2cm-cm10 cm long, 1 cm wide cylinders. It would be best to make them in a mold, and use a wax binding agent.

Hi all.

The thing I'd like to point out about induction heating systems is that they can be very fiddly - they need high quality capacitors and inductors and proper tuning to operate correctly.

That being said, an advantage of this sort of technology is that you'd be able to heat the barrel from outside the insulation. The issue of getting high current leads to the extruder head can be partially solved by placing the tank capacitor right next to the coil (see page 4 of the article Sci mentioned), which helps.

However, you may have trouble controlling the temperature properly - the mag fields may stuff up your thermistor reading due to 1) induced voltages and 2) heating the innards of the thermistor itself.

Finally, a word of caution: be careful with this stuff! The resonant components can easily run up to hundreds of volts, even if you start with, say, 24V. The high frequency nature of the beastie means that your heart is fairly safe (due to skin effect [en.wikipedia.org]) but you could get some nasty burns.

Good luck with any experiments!

jbb

I did some experimentation with induction heating a while back. [forums.reprap.org]

When you heat with a resistor, heat must flow from the resistor (where it is created) to the extruder head which means that the resistor must be hotter. Since induction heating creates heat in the extruder head, I had a vision of a cool copper coil heating an extruder head by induction through insulation (as jbb remarked).

I did not achieve this. My copper coil got pretty hot!

In my opinion, there is plenty of room for experimentation with induction heating, maybe at higher frequencies.

You could easily turn off the heater for a few milliseconds every so often to take the temperature measurements if there was any interference.

fdavies

I'm interested in whether the method used by Metcal soldering equipment would work. These use a 50W RF transmitter at 28MHz to power the solder tip. The tip is made of a nickel-iron mixture and the temperature is set by its curie point. The control method though, is not like the Weller irons with their magnetic switch but by some other effect of the curie point. The irons are very precise and have a fast response to temperature changes.

There is a specific tip type that might be useful - the desoldering tips. These have an angled head to accomodate the vacuum pump. This might instead be used to guide the filament into the tip.

I've been getting my head around induction heating as well, and the one advantage I can think of (and which would make it more efficient) is that you can focus more heat energy onto a smaller surface area.

The nichrome heaters rely on heat transmission from the extruder's outside of the barrel to the inside, a part which has considerable surface area to heat/cool and which will conduct heat away from the filament at a certain rate.

When you use induction heating, you could get away with heating only the extruder tip in a contact-less fashion. This is a lot less material to heat up, and since it can be (thermally) disconnected from anything but the extruder housing and the filament, almost all of the energy would go into the filament.

It also opens up the opportunity of depositing metals by heating them directly, or use a small transformer and use the metal filament as a wire, heating it up by pumping current through it.

Overall, induction heating is going to be less efficient that resistive heating. In all the heating schemes, you have a certain loss through the insulation. Induction heating _might_ slightly reduce that by avoiding wires through the insulation, but you trade that for a MUCH larger loss in the drive system (and LOTS more complexity). Further, the coupling between the induction coil and the load is not very good. You can improve it by using a magnetic load (which also gives you the opportunity to use the Curie temperature as a fail-safe temperature control). 99% or more of the power drawn by a resistive heater goes into the resistor itself; only a tiny fraction goes into the leads to and from it.
A thermoelectric device can pump heat from the ambient to the nozzle, but it has significant limitations. The maximum temperature difference (hot side to cold side) is around 30 to 40 degrees F per TED stage. The power in to power out on the hot side is not really impressive; maybe 150%. The temperature ratings of conventional TEDs are also not high enough. Stacking TEDs means that you really need to taper them (Biggest one on the hottest side). Finally, TEDs are high current low voltage devices; the ones you see for sale that used to be in cooler/fridges are rated for something like 10 Amps at 12 Volts.

Here's my two cents on extruder heating:
Old Weller soldering irons use a tubular SST heater rated for continous service at soldering temperatures! Search for "Weller HE40 Heater Assembly for SP40 Soldering Iron" and similar things. If you bought one of the old curie point sensor soldering irons you could replace the tip and the internal magnet/sensor with your extruder tube and re-use the sleeve that holds the whole thing together. Mine is 24 Volts, 42 Watts and only the last 3/4" of the heater tube actually has a heater in it. Here's the right thing at the manufacturer:
[www.cooperhandtools.com]

You can buy resistors that are made on a ceramic tube core. With one of these you could just run the extruder tube right through it (with some heat transfer goop like silicone in between). Here's two types that would be appropriate. The smallest have a hole through them that will pass a 1/8" tube and are only 0.625" long.
[www.ohmite.com]
[www.ohmite.com]
Whe you read over the specs, keep in mind that the power ratings are the FREE AIR power rating! They can handle 10 times that for short periods. The key is to keep the resistor from over heating, which you will be doing by sensing the temperature.

If you want to get really crazy you can heat the extruder barrel directly by passing a really large current through it. I built a heater that used about 4" of 1/4" copper tubing as the heating element by putting 600 Amps through it. VERY fast response. In order to do this, you need to keep the extruder barrel really thin and you need LARGE electrical connections. You can use the transformer out of an old fashioned Weller soldering gun; these are designed to put 600 Amps through the tip (measured it ;-) . I don't really think this is the right direction, but it's a thought.

On the insulation side, Silicone foam is easy to get and will survive the temperatures you are working at. It will provide MUCH more insulating value than Teflon or PEEK, but you can't use it for structural parts. You can glue pieces of it together with RTV silicone (the high temperature kind used for automotive gaskets is a good choice).

Regards,
Rod

Induction heating has advantages over resistive heating in terms of the power density that can be achieved. With resistive heating, a high resistance (5-10 ohms) is needed, otherwise the efficiency is low, as the resistance of the drive circuitry becomes comparable. Materials with resistance this high are either some ceramic, or from a coiled metal wire. In either case the temperature rating is usually not above 350 C, because at some point the insulator will break down.

Induction heating allows multiple turns of wire to be used, creating a transformer; then very high currents can be achieved in the heated element without requiring high currents in the drive circuitry. For a high frequency the skin effect will increase the effective resistance of the load. So these two things (high current and skin effect) allow something as simple as a small piece of metal to be used as the heating element. All of the power can be focused into this small piece of metal, allowing either very high temperatures to be achieved for comparably low power.

If the right frequency is chosen and the support electronics are properly designed, power transfer to the load can be very good.

I'm doing mathematical modelling work on inductive heater designs for the reprap, so I'll see how it progresses.

Each time a description of the change, there is always plenty to talk about around the world. They are not exempt. A statement usually is: "i have to change almost immediately versions, so do not expect me to date continue to attack ...

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smith

I did not know there is such a thing as induction heater, i know there are induction motor which i have been doing research and plan on putting on my car to cut down the oil. I know you can turn your motor into a very hot object, but never thinking about heating it with anything. Eventhough i am EE/Computer engineer, and never realy paying attention on the idea of the induction heater, until my friend service one of those cookware for the airport kitchen. Now that i know besides the resitive heater there is induction heater, and i am now realize that the cooking pan i have been using years ago was an induction. All these years i thought it was the resistive heater that cook my food!

I think there is a very strong point for induction heating:

You could make the hot zone very, very tiny. Right now the major part of the heat does not go to the filament but is lost from dissipation and infrared from the hot end, the heater block etc...
A induction heated hot-end could consist only of a tiny ring or mesh of iron or high permeability steel with ceramic for the rest. The plastic would be melted instantaneously which has another advantage besides efficiency: If the heat is turned off there would be only a very tiny amount of molten plastic left in the nozzle, with the potential to drastically reducing ooze.

The downside of such a system is that the heater could not rely on a thermistor for regulation because by the time it heats up there would already be too much heat. This could be circumvented by calibrating the system and tightly controlling the induction coil according to the throughput of the nozzle. A thermistor could still help but would rather function to calibrate the modulation of the heat rather than controlling it directly.

Yes there is an induction heating to replace heater band in extruders and injection machine is energy efficient and low cost have a look at [zervostassos.design.officelive.com] for any assistants contact me at pccsl4@hotmail.com

Take a look at our induction heaters quality products with the lowest prices [acrossinternational.com]

is this forum related to induction heating. i am doing induction heating as a project in university, but i am having problems with some calculations part. can anyone help?