Resistor vs transformer

LOL, that's a great application for a dangerous power supply...

--DF

The receiver units will not be placed near to the fire danger areas, well not that near. So a spark shouldn't set up an explosion. Those areas are covered by sensors which should transmit a RF signal to the receiver units in case of a fire. These things were ordered for by someone above me and its now my job to adopt them at the cheapest, fastest and most cost effective way to the circumstances. I called up the technical support of the suppliers of these units and they didn't seem to have a clue about to get the things working at

230V. So I'm stuck with the option of either sending them back (what I would prefer) and looking like a fool in my bosses eyes or looking for a solution. Hans

--
Use a transformer.  

End of story.

If these units are direct off-line devices with no transformer, they probably use the reactance of a capacitor to drop the voltage.

So use one half of the capacitor value presently there as an experimental starting point.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
      http://www.analog-innovations.com/SED/DefeatHillary.gif

--
Actually, not end of story.

You need to find out whether these devices will work with your mains
frequency, and if they will, then get a proper transformer.

If they won\'t send them back and get the right ones.

A series diode will not give you 120 VAC. It will give you a half wave 240 VAC, or one half the power will be consumed by the load. 240 * .707 = 169.68 - .7 = 168.98 VAC as the effective voltage.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Great advise! Who assumes the liability when one fails and doesn't report a fire, you or him? Can either of you afford the loss?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"not i"

LOL I haven't heard that in probably twenty-five years. At any rate, I doubt philth has found any bugs with that little self-esteem.

On Tue, 07 Feb 2006 15:41:49 +0100, Weinberger Hans wrote: ...

Then spend the bucks (or euros, or rubles, or rupees, or whatever) to get a proper, approved, warranted, step-down transfomer.

Don't scrimp on safety issues.

Good Luck! Rich

Rich, John (and others) are right. Based on information available just use an approved step down transformer.

You really want something that is safe, especially if your not too clued up electrically on how to design and retrofit these other ideas others are suggesting (just think how mad your boss would be if your solution caused a fire!)

- How many of these wireless reciever units do you need to retrofit anyway?

- How big are they (how much space do you have inside the box to make the modification, can you remove the existing 230V transformer out and drop in a stepdown one or will you need a separate enclosure to house it, etc)?

- What frequency are the wireless recievers 230V power supply and your

110V supply installation (50Hz or 60Hz).

- How much time do you have to design and install the modification?

These (among other factors) will determine if it is going to be more economical for you to try one of the other solutions (series capacitor

• resistor) over the stepdown transformer option. In the end do you really want to spend (for example) 0 of your time on a problem that could be solved by a simple solution.

to adopt them at the cheapest, fastest and most cost effective way to the circumstances.

Oh dear. Did he/she/management not bother to look at the data sheet and find out what voltage they ran on?

prefer) and looking like a fool in my bosses eyes or looking for a solution.

Looks that way.

No. Get a transformer with a dual 115V+115V primary, connect the primaries in seires, and hook your fire alarm across one of the primaries. Ignore the secondary windings.

Cost goes by size, but 6VA transformers have rotten regulation. The

2002 Farnell catalogue lists a 12VA part (stock number 159-591) whcih cost 6.58 euro and would presumably do the job, You'd have to put the transfomer in a box to protect the outside world.

Farnell have a whole range of boxes - I'd probably go for the 525-625 (which cost another 5.65 euro back in 2002), and mount the transformer on the lid. You might be able to get cute and mount the fire-detector on the other side of the same lid (leaving it outside the box).

This ought to work - the transformer will run a bit warm, but it would run warm without any load at all.

--
Bill Sloman, Nijmegen

Misusing math can be lots of fun.

The fact remains that it will deliver half the time average power to a resistive load. If the load has enough thermal mass to not care that the power is now coming in more seperated pulses, the "effective voltage" will be half.

The problem in your above calculation is that you're trying to apply the same method of voltage measurement to two very different waveforms. Your .707 (RMS) in the above is only valid for a sine wave. If you integrate the area under the new wave I think you'll find it's half the area within the original sine wave, which you took with your .707 of the peak voltage.

"Frank Bemelman"

** ROTFL !!

Now for an encore - prove to us all that chalk and cheese are exactly the same !

And while you are *on a roll* try demonstrating that shit tastes just like chocolate.

Should be a doddle for a man of your intellectual capacity.

LOL

........ Phil

** I see a man about to pleasure himself publicly by doing just that. ** So, one HALF the power it would otherwise dissipate with a 240 volt supply.

Shame this is still * DOUBLE * the power dissipated with a 120 volt supply !!

** NO - you colossal CLOT !!!

The power is halved - not the damn voltage!!

Since power is proportional to voltage squared - the condition for half power is 0.707 times voltage.

** It is valid in cases where the waveform is duty cycle divided by a factor of 2.

" Misusing math can be lots of fun."

LOL

........ Phil

Correct.

The effective voltage will be reduced by a factor of 1/sqrt(2) not 1/2 or just what Michael said. Half the effective *voltage* would give you

1/4 the power, right?

To do this rigorously, calculate the definite integral of the square of the half-wave rectified voltage v(t) = Vpk*sin(w*t) over a full cycle (0 to 2*pi radians).

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

** DA SLOW MAN " strikes again.....

** Shame it only has a single 230 volt primary:

LOL

.......... Phil

Is it too late to get a refund on your "Edumacation"? :(

You are completely lost in this subject, and you should be ashamed of yourself for your glaring ignorance. I'll give you a simple setup to prove I'm correct. Hook a 1N4007 diode in series with a 120 V lamp, then connect it across 240 VAC and watch how fast it burns out.

With the diode you get POWER half the time, for an average of 50%. That means the effective voltage has to be 70.7%, unless you know of a different Ohm's law.

BTW, some of the last tube type TV sets built in the US used a 84 volt filament string and a "Dropping Diode" and this was fed from the

120 VAC line input. If the diode dropped the effective voltage to 60 volts, tell me where did they get the other 24 volts the tubes needed to work properly?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Quite a lot of advice I'm getting here so thanks again to all. Installation of everything is delayed and should start in about 2 weeks so I still have time .

As its a large area the initial order is of 20. But we will probably need more .

I haven't considering disassemblying the suppliers case and would only do that as a last resort. If a resistor/cap option is taken I will definitely have to open it up. Otherwise a seperate transformer would be placed outside the enclosure.

All the packages will be arriving in 2 weeks time . After that a week or so to get the work done.

As long as the solution is time/safe proof and reliable thats OK for me.

I gather that this manufacturer was the only one who made units like these with all the necessary requirements/bells and whistles that the boss was looking for. The problem is the unit is made to operate only at 120V probably because the market or demand for these models is in countries that operate at those voltages.

Hans