Resistor vs transformer

"Weinberger Hans"

At least he faintly realises the figure is doubtful.

BTW:

Where is the F****NG LAW that prohibits *absolute idiots* like this WANKER from POSTING it ?????

........ Phil

The resistor would not take up much space but as you mention the heat would have to be dissipated. Using a small dual voltage 230/110v transformer as an auto transformer (the primary windings) is another option but would be more bulky, however at 6watts it would not have to be very large in physical size and would have the advantage of covering varying current requirements.

"Rheilly Phoull"

........ Phil

For 50Hz mains a 1.3uF capacitor would do the same job as a 2k4 resistor, and not dissipate very much heat at all - you'd have to find out the ESR (equivalanet series resistance) to work out how much heat it would generate.

It isn't clear why you think that your 2k4 resistor would have to dissipate 120W - if you put it in series with your load, it should dissipate no more than 7.2W, which is easy enough. Farnell lists a range of 11W ceramic cased wire-wound resistors that would do the job for less than $1 though they run pretty hot. Fanrell also list a couple of ranges of metal-cased wire-wound resistors which are a little more expensive (around $2) which you can mount on a heat sink (which can just be a metal plate - 1.5mm thick aluminium or the like) to get a lower surface temperature.

I wouldn't use a carbon resistor for this sort of job - carbon has a negative temperature coefficient of resistance, which can lead the current running through the resistor to concentrate itself in a relatively narrow hot channel of very low resistance.

Whether this would be a good way to go depends on the nature of your load - if the 6W is the powr it always dissipates, this could be a sensible approach. If the 6W is the maximum power it can dissipate, and it normally draws much less current, your 2k4 resistor (or my 1.3uF capacitor) might not provide enough protection from the 230V source.

As usual, you need to tell us more about the application.

Probably in the same "too hard" basket as the one that would prohibit discourteous and unhelpful responses like this one.

Hello Hans, It's unlikely that a resistor would be a good choice. It's only going to dissipate 6 watts, but the voltage regulation will be poor.

Use a small 240 to 120 volt transformer. A 6-watt one will be small and cheap.

" SLOW MAN IDIOT "

You asinine, GROSSLY autistic PRICK.

......... Phil

" SLOW MAN GOOGLE F****IT "

It all depends on the application - d*****ad.

Not clear ??? ???

The OP is a Kraut moron.

What could be any clearer ???

W A R N I N G !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

.......... Phil

"Ancient_Hacker"

All depends on the application - d*****ad.

All depends on the application - d*****ad.

The OP is a Kraut * bloody idiot * - so assume NOTHING !!!

........ Phil

YAWN.....

Hi Hans, I see you have had some helpful replies ;) I take it the 120W was a typo as you just mentioned 6W and you probably meant 120V drop (230V-110V). If you do want to use a resistor instead of a transformer it is best to use a series combo of a resistor and a capacitor. But before I go any further I should state that I wouldn't recommend this approach for anything but low-power non-isolated applications. You might use this if you just needed 10 to 20ma such as in some line-powered triac circuit.

It is true that a capacitor can be used instead of a resistor but you have practically no current limiting when it comes to transients, they will just pass right through the cap and let all the magic smoke out of your components.

But I think that you probably need to detail your application a little better because it may be that a transformer solution could be better suited, but of course this depends upon your load. I sure if you provide more detail, that among the many replies you may find one you can use.

We> Hi ... I need to convert 230V to 110V. I was wondering whether a 2.4K

"Peter Jakacki"

" The 120Watt consumption of the resistor makes me uncomfortable.. "

Bit bloody hard to get around the meaning of that - isn't it ????.

BTW:

WHAT is the problem with you jerk-offs just WAITING for the OP to make a reply ??

You LIKE feeding trolls ???????

........ Phil

"Phil Allison" schreef in bericht news: snipped-for-privacy@individual.net...

Nah, we're feeding you ;) Don't mind if I laugh, now do you ;)

And you, sir, are a needle dicked bug f***er!

It's such fun jerking Phillies chain.

You are right I meant 120V . Thanks and all those who gave "useful" replies. Its a wireless receiver unit which calls the fire department in case of a fire.

Hans

You probably need to figure out how it converts 120v to whatever it needs. It may be that you could rip out its power supply and substitute one for your line voltage.

For a purely resistive load, I think a series diode might work - but for something with regulation or it's own regulator followed by a filter cap, probably not.

"Phil Allison" schreef in bericht news: snipped-for-privacy@individual.net...

Let's see. Many people think faster than they type. This explains why we sometimes forget entire words, because we can't keep in pace with our thoughts.

So, "The 120Watt consumption of the resistor makes me uncomfortable.. " should perhaps be read as: "The 120V voltage drop and 6 Watt consumption of the resistor makes me uncomfortable.. ".

....adjusting squelch to ignore channel static.....

Hans, you really need to know what type of mains supply the receiver uses. If it is a transformer then you could perhaps use a choke in series with it. If it is a SMPS then it may already be designed for 230V operation or may be able to be configured for 230V (the voltage rating of the input caps should give you a hint).

I suggest you skip the resistor/cap thing as it may fail and flame and then how would the fire department be called then? Shouldn't you be working to some safety standards and compliances for this safety critical stuff anyway?

Weinberger Hans wrote: > You are right I meant 120V . > Thanks and all those who gave "useful" replies. > Its a wireless receiver unit which calls the fire department in case > of a fire.