Electric furnace successful melt !

[rainmaker]

If you place a SSR (solid state relay) at the proper place in your control circuit it should prevent the coil from overheating. I melted my PID controller several times befor learning, and only learned by looking at how the small tabletop kiln manufatures had their controlls set up.

SSRs are cheep and you can find them and PID controllers on E-bay along with instructions.

Rainmaker

 

[Noxx]

I was using a SSR. But the thermocouple was not installed properly and the reading temp was not the actual (I guess). But I'm trying to find a way to tune down my element to 80% of it's capacity. Do you think adding a resistor in serie will do the trick ?

Thanks

 

[Harold_V]

I was using a SSR. But the thermocouple was not installed properly and the reading temp was not the actual (I guess). But I'm trying to find a way to tune down my element to 80% of it's capacity. Do you think adding a resistor in serie will do the trick ?

Thanks

That would be some resistor, Noxx. It would likely put out as much heat as the heating element, which is also a resistor.

Harold

 

[lazersteve]

Noxx,

You want to reduce the input power to the coil so you are not melting the element. If I remember your schematic correctly, you are running it straight off of the mains power.

Perhaps a simple rheostat in line with the mains input would allow you to control the peak power getting to the element.

Another alternative would be to use a thyristor or SCR circuit to regulate the input power more precisely.

Lastly, a heavier element may survive the feed directly from the mains.

Steve

 

[Noxx]

Yes I taught about a rheostat but I can't find any cheap one which is able to handle such current.

Currently, my coil is connected to the main 120V outlet but it's controller with a PID and a SSR.

Thanks

 

[lmills148]

Noxx,

Another alternative would be to use a thyristor or SCR circuit to regulate the input power more precisely.

Lastly, a heavier element may survive the feed directly from the mains.

Steve

I would have to agree, I think ultimately the rating on the thermocouple is too low and it should probably be upgraded.

If your trying to save $ there may be another way .
Do you know how many amps it is drawing at 120v?

edited to add: I just seen your other post 13.3 amps at 120volts 1600 watts. The pot from an old hot plate would work. or range maybe crock pot etc

 

[Bernie Foley]

Hi noxx&friends,
If you look up variacs on ebay there is a company in canada that sells drills and they have variacs also. i think the 20 amp 120 volter went for about a $120.00 about as chea as one can find!! use it raise and lower the voltage going to the heating element.itself. Sorry this keyboard is skipping!
Good luck with the melter.....Bernie Foley

 

[goldsilverpro]

I have used Variacs all my working life. They are very handy for controlling heaters, stirrer speeds, etc.

 

[Bernie Foley]

Noxx&friends,
I have some good bulliten 700 relays that are 4 contacts and can be changed to no or nc.
send me a pm as i have quite a bit of stuff in that line...Trading is good...I need glass,melting dishes,erylmeyers...I'm short as hell on variacs...I can tell you who has them on ebay at good prices....I have a cnc minimill and can make simple stuff not harley
cyclinder heads.can make bullion moldsEtc...good luck Bernie

 

[Refiner232121]

Hi Everyone
I have been wanting to build an induction heater for a while.
I dont know if this is an induction heater.
If it is I would be intrested in making one


Also Gsp you said this and it would be nice if you could tell us more about that
Thanks

I have used Variacs all my working life. They are so so handy for controlling heaters, stirrer speeds, etc.

 

[goldsilverpro]

Here's a bunch of them on Ebay
http://shop.ebay.com/items/?_nkw=variac&_armrs=1&_from=&_ipg=

The simpler ones I used looked more like this one except they were usually 15-20 amps. You simply plug the 110V, AC device you want to control, into the Variac. A 15A Variac will handle most any 110V device, since the devices are most always a max of 1500 watts, or 13 amps.The Variacs are available in a myriad of sizes and, I'm sure, voltages. Some types of motors can't be controlled in this manner, but stirrers can. They are also great for heaters, hotplates, 110V furnaces, and immersion heaters. They would probably work on power supplies, but I've never tried it. The Variac will often provide much better control on these things than the controls that came with them and you can adjust them to a gnat's a**. I usually plugged in the Variac, turned the pot on the Variac to zero, turned the control on the device to max, plugged the device into the Variac, and zeroed in on the adjustments required, using the Variac pot.

EDIT: The Variac is sort of like a high power light dimmer switch. I also kept records of the various Variac settings needed for the various devices, so I wouldn't have to play around with it each time I used it. I think you can lower the controls on some of the devices to get better sensitivity when adjusting the Variac.
http://cgi.ebay.com/Powerstat-Variac-0-140-Volt-10-Amp-Type-116B-Fused_W0QQitemZ380141343566QQcmdZViewItemQQptZBI_Circuit_Breakers_Transformers?hash=item588230934e&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1205|293%3A1|294%3A50

 

[Bernie Foley]

Hi Gsp&friends,
The metered 20 amp units like the red ones are just fine for most any project.Most even have a fuse or circuit breaker built in!
Good luck-Bernie

 

[Noxx]

I never heard of variac before... I might give it a try.

Also, do you think triacs could also work ?

 

[Refiner232121]

Hi Gsp & Friends
Thanks for your replies
I think I would have to spend at least one day to really understand this subject in debt

 

[goldsilverpro]

Bernie,

A question. The pots on the Variacs I used all went to 140 volts. I usually avoided pegging them, especially with motors. Could 140 volts damage any of the devices or cause any other problems?

 

[nicknitro]

Hi all,

I thought Variacs regulated voltage, with a constant amperage? How would this help control the output to the coils?

Sorry all you electrical engineers if this is a dumb question. LOL Hey Bernie.

Thanks,

Nick

 

[Bernie Foley]

Hi Gsp,
running 120 volt units on 140 volts usually does no harm unless overspeeding would cause something to go out of balance.
Electric motors usually run cooler at higher voltages as long as they are up to speed.Voltage allowance is 10 % so if we add
12to 120=132 which is darn close to 140volts.I always used the 208 tap on welders&power supplies to include spotwelder&
plating supplies when running on 240 volts. They just plain run better and more efficiently! Very good question!
Something like a microgram scale or a delicate measuring instrument run it exactly as told!....Have a great day!...Bernie

 

[Chumbawamba]

Hi GSP.

I'll jump in here though I may not know what I'm talking about. I don't think you want to feed anything 140V unless it's protected up to that spec. It's up to you to not send an over-voltage into your device.

Here's a good tutorial on variacs that I just found:

http://www.elect-spec.com/variac_tutorial_xref.pdf

I actually have several, and in fact just pulled one from an old dentist's x-ray controller yesterday. I'm not sure what amperage it's capable of as I haven't checked it out in detail yet. I also have a couple smaller lab variacs, along with my primary variac, which I think can handle 30A. I bought it at a ham swap years ago for something like $30 (deal of the century).

Let me know if you're interested in a trade for one of my other variacs. I'm interested in lab equipment and knowledge

 

[Bernie Foley]

Hi Nicknitro&friends,
With amperage is the result of resistance verses voltage...simply the more load the more amperage-ohms law.
one volt,one ohm=1 watt...2 volts 1 ohm=2 watts.....at half the voltage the resistance must double to equal the same wattage.
The only stupid question i know of is one that does'nt get asked!
With people that we have on the forum i don't think there is any question that can't be answered...althougt somtimes a
foolish answer is a dam good laugh!!!!.....Bernie

 

[Anonymous]

Hi Nicknitro&friends,
With amperage is the result of resistance verses voltage...simply the more load the more amperage-ohms law.
one volt,one ohm=1 watt...2 volts 1 ohm=2 watts.....at half the voltage the resistance must double to equal the same wattage.

At half the voltage, the amperage must double for the same wattage. One volt, through one ohm of resistance is one amp, do that for 1 sec and you have one watt.
If you half the voltage, and double the resistance at the same time you will get 1/4 the amperage also reducing the wattage to 1/4.

jim