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Old 08-13-2010, 01:27 PM   #1
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Need help to power LARGE Nichrome Heat Sealer


Hi All,
Thanks for reading my post.

In its most basic form, my need is for a Heat Sealer with (3) - 60" wire elements. I'm using 18ga Nichrome wire rated at (.4219 Ohms/ft)

From research and online information, I've calculated the values required to heat the elements to 600 degrees F.
Hooking them up in Serials gives: Resistance 6.32, Amps 6.5, Volts 41.1, and Watts 267
Hooking them up in Parallel gives: Resistance .703, Amps 19.5, volts 13.7, and Watts 267

As a test I used a single 28" wire hooked to a small PC power supply..... once I touch the 2 ends together the power supply just shuts off.
I'm guessing that because the Resistance is so low, it thinks there is a short and shuts down.
From that simply test I know that I do not have the knowledge or the experience to create or purchase a power supply that can achieve what I need.

So I'm hoping the experience on this board can suggest or help pick a suitable power supply to make this work. Preferrably not one thats going to run me $100's of dollars, because I need to build 2 of these.

In a more advanced form....I'd really like to be able to selectively unplug 1 or 2 wires and still power the thing with the same Power Supply.
For 2 Wires, the values are:
Series: Resistance 4.219, Amps 6.5, Volts 27.4, and Watts 178
Parallel: Resistance 1.05, Amps 13.0, Volts 13.7, and Watts 178

For a single 60" wire, the values are:
Resistance 2.10, Amps 6.5, Volts 13.7, and Watts 90

Thanks alot for your time and help
Bill

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Old 08-13-2010, 01:34 PM   #2
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Need help to power LARGE Nichrome Heat Sealer


Quote:
Originally Posted by wdugdale View Post
once I touch the 2 ends together the power supply just shuts off.

I'd really like to be able to selectively unplug 1 or 2 wires and still power the thing with the same Power Supply*.
The power supply probably uses foldback.
http://en.wikipedia.org/wiki/Foldbac..._supply_design)

Look on Hosfelt.com for transformers and mix and match in series/parallel until you get what you need, assuming you don't need DC. You may need some small resistors to ensure equal current sharing between transformers.

*Sounds like you need some 12 vac [nominal value] transformers in parallel.

A car will give you 12.8 VDC with the engine off and ~14.4 VDC with the engine running at a fast idle.
You might want to put all 3 elements in parallel across the battery and see how the performance varies with engine off/on. If this variation is excessive you might need a variable, regulated, DC supply.

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Last edited by Yoyizit; 08-13-2010 at 02:41 PM.
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Old 08-15-2010, 09:34 AM   #3
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Need help to power LARGE Nichrome Heat Sealer


Hi Yoyizit,

Thanks for replying.
Yes the PC Power Supply probably uses foldback.

I dont think I'll be able to use a PC Power supply for this amount of Nichrome....nor a CAR to power it.. not in a location accessible.

Is AC or DC the best way to go with this project?

The " variable, regulated, DC supply" that you mention. Are you suggesting to use that with the wires in series or parallel?

Thanks
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Old 08-15-2010, 11:14 AM   #4
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Need help to power LARGE Nichrome Heat Sealer


Is AC or DC the best way to go with this project?
...That depends on how tightly the power into the wires needs to be controlled.
DC can be regulated but it is more costly. If your household AC is held within +/- 5% or 10% and this is close enough for your application then you can go with a transformer.

The " variable, regulated, DC supply" that you mention. Are you suggesting to use that with the wires in series or parallel?
...In parallel, like you wanted.

Another design question: do you want it to "plug and play" or is it OK to have to adjust the thing each time you want to use it?

Use the car voltage, 13.6 vdc +/- 6%, and other means to decide how precise the voltage into this thing needs to be.
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Old 08-15-2010, 11:15 PM   #5
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Need help to power LARGE Nichrome Heat Sealer


Thanks.
I think a variation of 5% or 10% is ok.

I'm looking for a plug and play solution.
I dont want to have to adjust the power each time that I start it.
However, If I switch from 3 wires to 2 wires, then Im willing to make adjustments to the power.

But once I find the correct power setting when using X number wires, I expect to be able to reproduce that settingimmediately.

Is there such thing as an AC variable power supply that will allow me to control the Volts and Amps being pushed thru the wire?
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Old 08-17-2010, 09:41 AM   #6
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Need help to power LARGE Nichrome Heat Sealer


Quote:
Originally Posted by wdugdale View Post
Is there such thing as an AC variable power supply that will allow me to control the Volts and Amps being pushed thru the wire?
A Variac. You should probably follow it with a step-down transformer to get your high current and low voltage levels.

Transformers come in 6.3 vac and multiples thereof. Check out Hosfelt.
If you cannot reasonably adjust your load resistance you should put enough identical transformers in series or parallel to get slightly above the required voltage at the current rating. You can always put resistors or incand. lamps or thin wire in series with the secondaries to reduce the voltage slightly.

As to risk, the lowest voltage anybody was ever electrocuted at in the US Navy was 47 volts.
Off-hook phone lines are 50 VDC, give or take, and they give me a slight tingle. The ringing voltages are higher and the frequency of the AC ringing signal is so low that it gives a very unpleasant shock.
Consult books or the Web for your risks at these voltages.

Last edited by Yoyizit; 08-17-2010 at 03:40 PM.
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Old 11-04-2011, 12:33 PM   #7
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Need help to power LARGE Nichrome Heat Sealer


I have picked up a 0-30V, 6A bench power supply.....not sure if I can use it for this project. Similar to this http://www.powersupplydepot.com/Powe...ly_9603_PS.asp

I've exhausted the extent of my knowledge and the heat seal table is still NOT finished.

I'm going to start a new Thread with much more details about where the project stands, along with pictures. I hope you, as well as other will give more advise to me.
Thanks

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