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ATX based power supply. Need to vary output voltage on the 12 volt line.  


GBH168
(@gbh168)
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Hi everyone.

I have built/adapted an old ATX power supply to provide a 12 volt DC supply to a foam hot wire cutter.

I have posted on the forum before about this, but some info on how to regulate the 12 volt output to varying voltages dependant on the various hot wire cutting rigs I have.

A 12 volt output on my small cutting rig gives me a to high cutting wire temperature. The wire is almost white hot. On my larger cutting rig 12 volt output is OK.

What component would I need to insert into the 12 volt DC output from the ATX unit to allow me to vary the voltage to avoid overheating the cutting wire on my small cutting rig, but still allow me to use the full 12 volt output on the larger rig?

I am not an electronics engineer so please be gentle with me.

Many thanks for any answers/info.

Gary


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jker
 jker
(@jker)
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I suspect the issue is that you're running more current (and thus power) from the atx psu than your other system. ATX supplies can put out absurd current at close to their spec'd voltage.

The two basic approaches are to plonk some resistance into the circuit, or regulate it with pwm. Another approach might tackle it from a current limiting perspective directly, but I have little experience there.

The issue with using resistance is that any power being used by the resistor is going to just turn into heat on your resistor instead of heat on your cutter. This may be the easiest option, but the details are important. If you drop a little low value quarter-watt resistor in there you will likely create a lightbulb for a brief moment. What is the resistance of your cutter setup? More or less measuring across the wires you are connecting to the psu? Using ohms law and 12V, you can determine approximately the current and power involved here.

Another way of doing this is with a pwm signal controlling a mosfet on the heater circuit. I'm rather fond of potentiometer-driven 555 IC chips driving mosfets for this sort of thing, but it's a somewhat complicated circuit in some ways. This thing ( https://www.amazon.com/dp/B084SPLDJY or https://www.amazon.com/dp/B081XQLN46) is basically a fine chinesium variant of the circuits I have built along these lines. (watch the amp limits though... do measure your resistance to figure out your current ceiling)

"A resistor makes a lightbulb and a capacitor makes an explosion when connected wrong"
"There are two types of electrical engineers, those intentionally making antennas and those accidentally doing so."


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GBH168
(@gbh168)
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jker, many thanks for the reply and info. Regrettably the link doesn't seem to work.

Gary


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Troles
(@troles)
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gbh168, Jker may know more about your situation than I, and I do not know if you have a current issue.  but, with regard to your question, I built the ATX power supply as demonstrated on this site, and I added a cheap $2 adjustable dc boost module

https://www.amazon.com/DZS-Elec-Adjustable-Converter-Regulator/dp/B07QYKLZLG/ref=sr_1_2_sspa?dchild=1&keywords=dc+boost+module&qid=1618854641&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExSzgwT1NLUEQwMVFOJmVuY3J5cHRlZElkPUEwOTIxOTY5MVNBTThCMUlQWTZSNiZlbmNyeXB0ZWRBZElkPUEwMjcyNTIwNThGVkdaUFA5WEVBJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

to mine on the 5 volt atx output so I can adjust it up (sometimes I need voltages between 5 and 12).  I suppose you could also do it with a buck converter on the 12 v to drop it.  These cheap voltage adjusters only handle low amps, but they work for the little electronic stuff I do.  I also added the volt/amp meter he discusses (I run the 5 v into the boost converter, then run that into the volt/amp meter, then out to the device).  I plan to add the INA219 volt amp meter device into my system soon when I get a chance (I am spending all my free time trying to build (unsuccessfully =( ) the joystick robot cars and now the esp32cam car).  


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jker
 jker
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@gbh168

It looks like the forum included the closing parenthesis when it linkified my text.

https://www.amazon.com/dp/B081XQLN46

 

Troles' suggestion to use a buck converter may be worth considering.  But I'm unfortunately a little bit blind here. I don't know how much current your heating wire is drawing. If we clamp it down too much with any of these methods, it won't function anymore. Without knowing the resistance of your cutter line, it's hard to give specific or safe recommendations.

"A resistor makes a lightbulb and a capacitor makes an explosion when connected wrong"
"There are two types of electrical engineers, those intentionally making antennas and those accidentally doing so."


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borkutip
(@borkutip)
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Hello, for a buck-boost converter I ordered this from Aliexpress:
https://www.aliexpress.com/item/4000766900344.html
(ZK-4KX). It works for me, connected to an old ATX power supply.

I ordered another one:
https://www.aliexpress.com/item/1005001475669496.html
But this did not stable, sometimes it did not switch on. However, same specs.

Both have current limiting.

They even show (nearly in real time) the actual current flowing through the device, which is very useful.

 

Péter

This post was modified 4 weeks ago by borkutip

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GBH168
(@gbh168)
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Joined: 1 month ago
Posts: 6
Topic starter  

Hi guys, just a quick update. I have now managed to get the ATX unit wired correctly now with a variable PWM controller to enable me to vary the voltage to my hot wire cutter. 

Please to say with the help from the Forum, it works great and does exactly what I wanted.

Many thanks to everyone for your help.

Gary


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