Resistor vs Transformer update

[Weinberger Hans]

Hello to all.
Thanks to all for your advice, it has helped us go ahead.
The step down transformer I got from your sources works well though it
measured 123V ac output instead of the 120V ac, but the alarm is
working well and the dialer function surprisingly also. I checked up
circuit and it seems neither SMPS nor a transformer , but is as Jim
Thompson had said that a capacitive reactance with relative circuitry
of Zeners , diodes and so forth is used. I
am in the act of modifying the circuit board of 1 of the modules to
which the radio signal will be transmitted in case of fire and as also
this is supposedly powered from 110V I want to change it to accomodate
the 232V my mains is delivering.
I'm replacing some of the lower voltage components with higher
voltage / power components I had some problems in differentiating
between a varistors and capacitors but it seems solved.
They used the same color , very funny I think.

My supplier sent me some higher watt resistors which are smaller then
the originals on the board ... very fishy I think. What do you say?

Hans

 

[Fred Bloggs]

Hello to all.
Thanks to all for your advice, it has helped us go ahead.
The step down transformer I got from your sources works well though it
measured 123V ac output instead of the 120V ac, but the alarm is
working well and the dialer function surprisingly also. I checked up
circuit and it seems neither SMPS nor a transformer , but is as Jim
Thompson had said that a capacitive reactance with relative circuitry
of Zeners , diodes and so forth is used. I
am in the act of modifying the circuit board of 1 of the modules to
which the radio signal will be transmitted in case of fire and as also
this is supposedly powered from 110V I want to change it to accomodate
the 232V my mains is delivering.
I'm replacing some of the lower voltage components with higher
voltage / power components I had some problems in differentiating
between a varistors and capacitors but it seems solved.
They used the same color , very funny I think.

My supplier sent me some higher watt resistors which are smaller then
the originals on the board ... very fishy I think. What do you say?

Hans

There are several power resistor manufacturing technologies in use, so
it is possible for the dimensions to be different. You should be using
the same resistor technology to preserve the intent of the original
design, especially if it calls for flameproof self-fusing metal oxide types.

 

[Roger Hamlett]

Hello to all.
Thanks to all for your advice, it has helped us go ahead.
The step down transformer I got from your sources works well though it
measured 123V ac output instead of the 120V ac, but the alarm is
working well and the dialer function surprisingly also. I checked up
circuit and it seems neither SMPS nor a transformer , but is as Jim
Thompson had said that a capacitive reactance with relative circuitry
of Zeners , diodes and so forth is used. I
am in the act of modifying the circuit board of 1 of the modules to
which the radio signal will be transmitted in case of fire and as also
this is supposedly powered from 110V I want to change it to accomodate
the 232V my mains is delivering.
I'm replacing some of the lower voltage components with higher
voltage / power components I had some problems in differentiating
between a varistors and capacitors but it seems solved.
They used the same color , very funny I think.

My supplier sent me some higher watt resistors which are smaller then
the originals on the board ... very fishy I think. What do you say?

Measured output on a transformer, will vary with load, the supply voltage
(which is not exact), and the tolerance of the part itself. 123v for a
nominal 120, is closer, than the incoming supply accuracy itself will
normally acheive...

Best Wishes

 

[John Fields]

Hello to all.
Thanks to all for your advice, it has helped us go ahead.
The step down transformer I got from your sources works well though it
measured 123V ac output instead of the 120V ac, but the alarm is
working well and the dialer function surprisingly also. I checked up
circuit and it seems neither SMPS nor a transformer , but is as Jim
Thompson had said that a capacitive reactance with relative circuitry
of Zeners , diodes and so forth is used. I
am in the act of modifying the circuit board of 1 of the modules to
which the radio signal will be transmitted in case of fire and as also
this is supposedly powered from 110V I want to change it to accomodate
the 232V my mains is delivering.
I'm replacing some of the lower voltage components with higher
voltage / power components I had some problems in differentiating
between a varistors and capacitors but it seems solved.
They used the same color , very funny I think.

My supplier sent me some higher watt resistors which are smaller then
the originals on the board ... very fishy I think. What do you say?

---
I think you're playing with fire and you should be stopped.

If the device has gone through testing by a regulatory or a UL type
of organization in order to be certified as "safe to use", then by
arbitrarily changing components internal to the device you have not
only destroyed the certification, you may also very well be making
the device dangerous to use or, at best, unreliable.

Once you connected the unit to the output of the transformer and
found that it was being supplied with 120VAC, your "design" work
should have ended.

 

[Weinberger Hans]

There are several power resistor manufacturing technologies in use, so
it is possible for the dimensions to be different. You should be using
the same resistor technology to preserve the intent of the original
design, especially if it calls for flameproof self-fusing metal oxide types.

Ah then the mystery is solved. Now the hard work of finding what
technology is used in the originals.

I am also having a problem in replacing the varistor. The original had
a limit at 130V , so I assume the new one should be about 250V but
my supplier also needs a resistance value. The load which is mostly
resistive has an actual power value of around 300Watts. Before I spend
hours checking on datasheets of MOVs , has anybody had a detailed
experience with this problem.


Hans

 

[Paul E. Schoen]

---
I think you're playing with fire and you should be stopped.

If the device has gone through testing by a regulatory or a UL type
of organization in order to be certified as "safe to use", then by
arbitrarily changing components internal to the device you have not
only destroyed the certification, you may also very well be making
the device dangerous to use or, at best, unreliable.

Once you connected the unit to the output of the transformer and
found that it was being supplied with 120VAC, your "design" work
should have ended.

I fully agree that the modification of the internal components is not the
solution to this problem, especially when undertaken by an amateur and for
such a critical application as a fire alarm system. A properly rated
step-down transformer is the only method that I think would be acceptable if
there were a suspected failure of the system and it was investigated for
insurance purposes. A separate 120 VAC line could be run to all the devices,
or individual transformers could be used.

An open circuit output voltage of 123 volts with 232 volt mains indicates
the transformer has a regulation of 123-116 = 7/120 or about 6%, which is
fairly typical for small transformers.

Circuit protection varistors are typically red or green in color, and
usually have markings indicating the peak voltage and the energy rating.
They will usually fail by becoming leaky and then shorting, so the circuit
needs to be protected by a suitable fuse.

A power resistor of a given wattage can be arbitrarily small if the
temperature can be arbitrarily high. The same amount of heat will be
generated. If more power will be dissipated inside the sealed enclosure due
to changed components and higher input voltage, there is a real danger of
overheating and eventual failure. Yes, this is literally "playing with fire"
in many ways.

Paul E. Schoen
www.pstech-inc.com

 

[Weinberger Hans]

On Fri, 17 Feb 2006 15:38:06 -0500, "Paul E. Schoen"

cut

Circuit protection varistors are typically red or green in color, and
usually have markings indicating the peak voltage and the energy rating.

cut

They had some strange code writing which was totally unrelated to
their voltage characteristics and were blue just like the capacitors.


Hans

 

[lemonjuice]

On Fri, 17 Feb 2006 15:38:06 -0500, "Paul E. Schoen"

cut
cut

They had some strange code writing which was totally unrelated to
their voltage characteristics and were blue just like the capacitors.

You should check on the circuit board. On capacitors usually a C
followed by a number. In the case of a varistor , you should see a VDR.

Hans

lemonjuice

 

[lemonjuice]

Varistors are voltage dependent resistors so that means their
resistance varies from a maximum value with no voltage to a minimum
value just before they blow out. He is probably refering to the
resistance before it burns . Quite easy to calculate that. FROM P =
VI => P= V^2/R . Substitute yr 300 watts and 250V and you have yr
resistance.

lemonjuice

 

[Paul E. Schoen]

Varistors are voltage dependent resistors so that means their
resistance varies from a maximum value with no voltage to a minimum
value just before they blow out. He is probably refering to the
resistance before it burns . Quite easy to calculate that. FROM P =
VI => P= V^2/R . Substitute yr 300 watts and 250V and you have yr
resistance.

lemonjuice

I think these are Metal Oxide Varistors (MOVs) which are essentially an AC
zener diode. When voltage exceeds the peak value, they conduct and dissipate
energy as heat, but also each spike degrades them a bit. They are highly
capacitive and should read near infinite resistance if good. When they go
bad, they short out, so be sure to have a properly sized fuse protecting the
PCB traces.

I'm getting a very bad feeling about the way this project is going!

Paul E. Schoen
www.pstech-inc.com

 

[Phil Allison]

"Weinberger Hans"

I am also having a problem in replacing the varistor. The original had
a limit at 130V , so I assume the new one should be about 250V but
my supplier also needs a resistance value. The load which is mostly
resistive has an actual power value of around 300Watts. Before I spend
hours checking on datasheets of MOVs , has anybody had a detailed
experience with this problem.

** Yes - find a supplier that knows the difference between a "varistor"
and a "thermistor".

Before you kill someone.




......... Phil

 

[Phil Allison]

"Weinberger Hans":

cut

They had some strange code writing which was totally unrelated to
their voltage characteristics and were blue just like the capacitors.


Hans

** It is VERY important that capacitors and varistors have matching colours.

Just tell your "parts grocer" you want blue ones.




......... Phil

 

[John Fields]

I am also having a problem in replacing the varistor. The original had
a limit at 130V , so I assume the new one should be about 250V but
my supplier also needs a resistance value. The load which is mostly
resistive has an actual power value of around 300Watts. Before I spend
hours checking on datasheets of MOVs , has anybody had a detailed
experience with this problem.

Something is very wrong here.

If the units are designed for 120V in and you get that 120 from 240V
mains by using a step-down transformer, then why do you want to
change the MOV's?

That is, the unit will be working on 120V, so by changing the MOVs
to 240V units all you'll be doing is making sure that 240V
transients can get into the unit, which is _not_ a good thing.

 

[John Fields]

An open circuit output voltage of 123 volts with 232 volt mains indicates
the transformer has a regulation of 123-116 = 7/120 or about 6%, which is
fairly typical for small transformers.

 

[Phil Allison]

"John Fields"
"Paul E. Schoen"

It's impossible to determine the regulation of an unloaded
transformer,

** Complete nonsense !!!!!!!!!!

Where the *rated* primary and secondary voltages are known, the regulation
percentage follows immediately from a knowledge of the off load primary and
secondary voltages.

Duh !!!!!

but small transformers usually run about 30%, no load
to full load.

** What ignorant crapology !!!!!!!!!!!!!!!!!

Only transformers of 5 VA or less have such poor regulation.

A 50 VA tranny is normally speced at 10% and a 160 VA 6%.

John Fields
Professional Bullshit Artist

.......... Phil

 

[John Fields]

I'm getting a very bad feeling about the way this project is going!

---
What I'm amazed at is that the OP's boss (who must be technically
even less competent than the OP) has let him have such a long leash.

Essentially, a novice has been given the responsibility for making
critical technical decisions which can adversely affect human life
and the protection of property with, apparently, no technical
supervision whatever.

Pretty scary.

 

[Phil Allison]

"John Fields"
"Paul E. Schoen"

What I'm amazed at is that the OP's boss (who must be technically
even less competent than the OP) has let him have such a long leash.

Essentially, a novice has been given the responsibility for making
critical technical decisions which can adversely affect human life
and the protection of property with, apparently, no technical
supervision whatever.

Pretty scary.

** The OP is almost certainly a TROLL.

Bet he has exactly one, Asian sourced, 120 volt alarm system.

John Fields
Professional Dupe

........... Phil

 

[John Fields]

On Fri, 17 Feb 2006 15:38:06 -0500, "Paul E. Schoen"

cut
cut

They had some strange code writing which was totally unrelated to
their voltage characteristics

 

[lemonjuice]

I think these are Metal Oxide Varistors (MOVs) which are essentially an AC
zener diode. When voltage exceeds the peak value, they conduct and dissipate
energy as heat, but also each spike degrades them a bit. They are highly
capacitive and should read near infinite resistance if good. When they go
bad, they short out, so be sure to have a properly sized fuse protecting the
PCB traces.

I'm getting a very bad feeling about the way this project is going!

Paul E. Schoen
www.pstech-inc.com

Paul .
Their equivalent circuit is 2 back to back zener diodes... thats why
their behaviour is what I outlined above.
They are protective devices , so if they short at excess voltages the
whole circuit will blow up which isn't the intention why they are
used.

Don't worry too much about the guy ... remebember an expert is one who
has made every possible mistake in a very narrow field.

lemonjuice

 

[John Fields]

"John Fields"
"Paul E. Schoen"


** Complete nonsense !!!!!!!!!!

Where the *rated* primary and secondary voltages are known, the regulation
percentage follows immediately from a knowledge of the off load primary and
secondary voltages.

Duh !!!!!

---
Well, good morning, Phil!

I see being up early doesn't do much for your disposition either!

Anyway, I stand corrected, but I see you either missed or chose not
to comment on that the regulation of the transformer under question
isn't 7/120, it's 7/116. Still about 6%, but since you often like
to pick nits...

** What ignorant crapology !!!!!!!!!!!!!!!!!

Only transformers of 5 VA or less have such poor regulation.

---
Sorry, Charlie, it depends on a lot more than just how much power
(OK, Volt-Amperes) they can transfer. Check page 37 of:

http://www.belfuse.com/Data/DBObject/signalcatalog.pdf

for a clue.
---

A 50 VA tranny is normally speced at 10% and a 160 VA 6%.

---
So you think the OP's using a 160VA transformer to run his 6 watt
receiver? I don't _think_ so.

Besides, I doubt whether he even made the voltage measuremrnt
correctly, don't you?
---