I need a 12V 3 amp regulator.....small

You might as well just use a big heatsinked resistor equal to the R of the iron, and don't put it in a plastic box, it will probably melt, dissipating that much heat

A more efficient way would be to use a switch mode psu.

But if your iron is thermostatically controlled, who knows?

martin

Realize the series (pass) regulator will dissapate the same current as the soldering iron, which will be about 30 watts! That's a lot of heat, certainly not a good 'plastic box' project. (Especially a 'small' plastic box project!)

If you have to go pass transistor series regulator, use a heatsink large enough to handle the power.

BTW, this won't be 'very small'...

Mount the pass transistor and the regulator on the same heat sink, to take advantage of the fact that regulator (should) have an internal thermal protection circuit. This doggie will definately be larger than a pack of cards, probably about the size of a thick paperback book.

If you must be small, I'd look at a switching regulator which is

*much* more efficient, should be small and won't generate a lot of heat. Better solution.

The best thing to do is make your self a little Pulse width modulated supply. a 555 Timer at 50% duty cycle driving a Logic Level power Fet. With that, it'll run cool enough to put in a plastic box..

P.S. you can most likely place a pot on the box if you would like to trim the duty cycle to adjust the heat level.

This simply type of supply is fine for a soldering iron how ever, i wouldn't use it for sensitive electronics due to the 24 Volt peaks you will be getting unless you add some regulating components to monitor the output.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

See page 13 in the datasheet at

The amperage isn't a worry with a big pass transistor, the heat is. You'll need a good heatsink in open air - the plastic box isn't going to do it for you, unless you use a big box with forced air cooling. This style regulator will have to waste ~ 30 watts when the iron uses 30 watts.

You would be far better off just buying a 24V iron.

?sc=10&category=53&it=A&id=2379 Watch for the line wrap or go here: and click on the "spare soldering iron" arrow on the left.

Ed

Just use 24V solder, much easier

martin

Goto Maplins/Radio shack and get a 24 -12 converter, min 30/40- watts. This type of thing is used for Lorries powering 12V radios and other things.

need

regulator

current

You could simply use a 24V soldering iron. Weller WTCPN, WTCPS and WTCPD soldering pencils are usually 24V and their "Magnastat" operation ensures temperature control based on the tip used.

You could also use a 24V to 12V smps step-down converter such as

with your current model 12V soldering iron. Most alternative energy supply stores will have a range of 24V to 12V adapters to suit most applications.

One way or another, even if you have the ability to build a suitable PSU yourself, it is going to mean a reasonable cost outlay whichever way you go.

Yea, Weller has a 24 VDC soldering iron. Thats' the way to go! But those three soldering irons are AC powered soldering stations! It may be that the actual pencil iron connected to it is 24VDC. Guess I need to call Weller, as a Google search hasn't turned up the P/N for this, and there isn't one for sale on eBay. thanks, Geronimo

need

The Weller part is TC201 and will set you back about USD90. You might be able to score something on Ebay.

As far as a heating elemnt is concerned it makes no difference whether it is supplied 24Vac or 24Vdc.

Except that they have a temp controlled switch inside which may not like DC.

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.

whether

like DC.

The Weller TC201 uses a magnetically controlled switch which depends on tip temperature only. As soon as the tip reaches the design temperature (eg. 700 degF) the switch opens thus allowing the tip to cool and the switch to close and the process repeats ad-infinitum.

Why would DC operation affect the tip temperature or any other function? 700F is 700F no matter what heats the tip.

The probelm wit that plan is the regulator gets as much anergy as the soldering iron, an consequentually gets as hot as it too.

For regulating a resistive load like that Pulse width modulation is ideal

Bye. Jasen

The switch will suffer more arc damage when run on DC. It may fail dramatically sooner. This is especially true if the open gap is very small, and relies on the current zero crossings to extinguish the arc.

As many have pointed out a linear, such as the LM78xx is just going to get way to hot. What I don't see an answer to for you is a better part to use. I would suggest a National Simple Switcher.

Get the adjustable flavor so you can tweak it from 12V to 14.4V. My experience with 12V soldering irons is they work better at a bit higher than 12V to force the amperage draw (and hence wattage) up a bit.

I mostly quite using 12V irons though. I use the Weller Butane soldering irons for field work with much better luck. They have two flavors. The cheap on is cheap (has the big clear tank). The solid color black one is much better IMHO.

Hawker

On 2/25/2007 4:11 PM, The digits of geronimo's hands composed the following:

not

depends

to

I would agree with you if there were some inductive component in the DC supply circuit. When the TC201 is used with a mains supply it runs directly from a 24Vac secondary so I would imagine this would tend to produce some arcing when the switch opens anyway - possibly more than with DC.

If you look at some actual switch ratings from the people who make them and know what they are talking about you will find it is not unusual for the dc current rating to be 1/40th or even 1/80th of the ac current rating at the same voltage. You may also find similar current ratings specified at a dc working voltage of 1/10th or 1/20th of the ac value.

Yeah, inductive flyback voltage really exaggerates the arching at switch contacts. So the switch may last a reasonable time. But it still doubt it lasts as long as it does with AC.

runs

to

than

Yes, I realise this is a common recommendation with switch contacts. In the case of the TC201 switch assembly there is a standard 10nF ceramic spark quench cap across the dual in-series contacts which may or not be adequate to prevent excessive arcing.

I realise that the average heater current with dc will be higher than with ac but I anticipate that this will simply cause the tip to get to operating temperature faster than when on ac. The maximum heater current will be determined by the resistance of the heater element itself and this should be the same for dc as for ac. Since there is no inductive kick-back arcing should not be excessive and pehaps less than when on ac.

I have pulled these switch asemblies apart many times and the dual in-series contacts look to me to be able to handle the maximum 1.75A (42W) current without any problems. Just to be certain I have requested technical specs from Cooper Tools on the Weller TC201 switch assembly contact ratings and an opinion as to whether dc operation will have any deleterious effects on the contacts. Will post back if and when it arrives.

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I doubt it.  With DC there will be no mains return to zero volts, so
the only way the arc will be quenched is if the cap across the
switch can drop the voltage from the 24VDC source quickly enough,
when the switch opens, to a voltage low enough to no longer be able
to sustain the arc.  Either that or the separation of the contacts
will eventually be great enough to quench the arc.