I've got a tankless electric water heater from eemax. that stopped
working the other day. eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? (60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. (Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

Thanks for any advice.

George H.

On Mar 1, 1:53*pm, George Herold wrote:
My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *(60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)
Does yours look like the one in the wiki article? If so, I would vote
for a value between 100K and 470K. At 100K, a half-watt resistor
would be marginal, and I would go for one rated for 1 watt. Within
this range, the value is probably not too critical.

On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold
wrote:

I've got a tankless electric water heater from eemax. that stopped
working the other day. eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? (60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. (Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

Thanks for any advice.

George H.

Assuming the neon bulb is still okay, why not measure the
break down? I'd start with perhaps 100k with your 240V. If
the breakdown is around 100V, the current will be in the area
of 1mA, which is probably safe enough. And 100mW, or so, so
you won't burn something up.

At say 2 watts, you would be talking in the area of 10k, my
guess. Not 100 ohms.

Jon

Is 100 ohms a good value as a current-limiting resistor
for a small neon lamp running off 240V AC?

It is, if you want the neon lamp to light up whitish purple for less than an
second, then explode.

You need something more in the range of 150K to 200K, possibly even larger.

On Mar 1, 5:04*pm, " wrote:
On Mar 1, 1:53*pm, George Herold wrote: My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *(60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

Does yours look like the one in the wiki article? *If so, I would vote
for a value between 100K and 470K. *At 100K, a half-watt resistor
would be marginal, and I would go for one rated for 1 watt. *Within
this range, the value is probably not too critical.

Yes the lamp looks like the picture in the wiki article. If I
believe the curve there, then I've got something like 160-200 volts
across the lamp at 20mA. So I've got (call it) 80 V to drop on the
resistor at 20mA.. I get 3 k ohm at a watt or two. Hmm maybe what
looks like brown black brown is a discolored red black red. (I always
have hated the way red and brown look almost the same on the pale blue
body of the metal film resistors.)

100k seems like it won't allow enough current through to keep the lmap
lite. (But I've never worked with neon lamps.)

George H.

George Herold wrote:
I've got a tankless electric water heater from eemax. that stopped
working the other day. eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? (60 Hz if that matters.)

Yikes! You should be looking at more like 1mA through the lamp.
Are you sure about the connections in the circuit?

I'm not sure what the I-V curve for the lamp will look like. (Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

On Mar 1, 5:11*pm, Jon Kirwan wrote:
On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold





wrote:
I've got a tankless electric water heater from eemax. that stopped
working the other day. *eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. *The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. *The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *(60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

Thanks for any advice.

George H.

Assuming the neon bulb is still okay, why not measure the
break down? *I'd start with perhaps 100k with your 240V. *If
the breakdown is around 100V, the current will be in the area
of 1mA, which is probably safe enough. *And 100mW, or so, so
you won't burn something up.

At say 2 watts, you would be talking in the area of 10k, my
guess. *Not 100 ohms.

Jon- Hide quoted text -

- Show quoted text -

Thanks Jon. This value seemed way to small to me too.

George H.

On Mar 1, 5:23*pm, D Yuniskis wrote:
George Herold wrote:
I've got a tankless electric water heater from eemax. that stopped
working the other day. *eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. *The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. *The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *(60 Hz if that matters.)

Yikes! *You should be looking at more like 1mA through the lamp.
Are you sure about the connections in the circuit?



I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp- Hide quoted text -

- Show quoted text -

Well I can see that the big (3 to 5 watt) resistor feds the neon
lamp. I don't know what else the circuit does.... I didn't bother to
try and trace the whole thing out. Perhaps I can look at it more
closely tonight and see if I can make something more out of it.

Thanks,

George H.

On Mar 1, 5:21*pm, Meat Plow wrote:
On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold
wrote:





I've got a tankless electric water heater from eemax. that stopped
working the other day. *eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. *The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. *The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *(60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

Thanks for any advice.

George H.

An NE2 needs a 22k dropper for 120 volts, do the math.- Hide quoted text -

- Show quoted text -

Thanks I'll look up an NE2 and see what I can make out of it.


George H.

In ,
George Herold wrote:
On Mar 1, 5:04*pm, " wrote:
On Mar 1, 1:53*pm, George Herold wrote: My question.
*Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *(60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

Does yours look like the one in the wiki article? *If so, I would vote
for a value between 100K and 470K. *At 100K, a half-watt resistor
would be marginal, and I would go for one rated for 1 watt. *Within
this range, the value is probably not too critical.

Yes the lamp looks like the picture in the wiki article. If I
believe the curve there, then I've got something like 160-200 volts
across the lamp at 20mA. So I've got (call it) 80 V to drop on the
resistor at 20mA.. I get 3 k ohm at a watt or two. Hmm maybe what
looks like brown black brown is a discolored red black red. (I always
have hated the way red and brown look almost the same on the pale blue
body of the metal film resistors.)

100k seems like it won't allow enough current through to keep the lmap
lite. (But I've never worked with neon lamps.)

I don't believe the voltages in that curve in Wiki - I would plan on 70
volts and peak current around 3 milliamps (peak voltage of 240 VAC is
about 340 volts).

If the glass bulb's overall length is 3/4 inch, then the neon lamp is
probably an NE-2H. I would use an 82K or 100K 2-watt resistor for an
NE-2H at 240 volts AC. I would err on the high side (100K) to maximize
life of the lamp. I suspect the toated resistor is a 100K 2 watt whose
yellow band was browned by being toasted.

- Don Klipstein )

In , William Sommerwerck wrote:

Is 100 ohms a good value as a current-limiting resistor
for a small neon lamp running off 240V AC?

It is, if you want the neon lamp to light up whitish purple for less than an
second, then explode.

You need something more in the range of 150K to 200K, possibly even larger.

100 ohms in series with a neon lamp at 240 volts AC: Not that I would
try this for the answer, but I suspect both the neon lamp and the resistor
will likely be severely damaged. Either or both may explode, and the neon
lamp may implode.

- Don Klipstein )

George Herold wrote:
I've got a tankless electric water heater from eemax. that stopped
working the other day. eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? (60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. (Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

Thanks for any advice.

George H.

100K would me more like it.. "100,000"

On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold
wrote:

I've got a tankless electric water heater from eemax. that stopped
working the other day. eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? (60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. (Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

Thanks for any advice.

George H.

Numbers more like 330K to 560K are more reasonable. Higher currents
will sputter the gas and make the thing fail sooner.

Better yet, use an LED.

John

On Mar 1, 5:48*pm, (Don Klipstein) wrote:
In ,





George Herold wrote:
On Mar 1, 5:04 pm, " wrote:
On Mar 1, 1:53 pm, George Herold wrote: My question.
Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? (60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. (Is the
one shown here OK?)

Does yours look like the one in the wiki article? If so, I would vote
for a value between 100K and 470K. At 100K, a half-watt resistor
would be marginal, and I would go for one rated for 1 watt. Within
this range, the value is probably not too critical.

Yes the lamp looks like the picture in the wiki article. * If I
believe the curve there, then I've got something like 160-200 volts
across the lamp at 20mA. *So I've got (call it) 80 V to drop on the
resistor at 20mA.. I get 3 k ohm at a watt or two. *Hmm maybe what
looks like brown black brown is a discolored red black red. *(I always
have hated the way red and brown look almost the same on the pale blue
body of the metal film resistors.)

100k seems like it won't allow enough current through to keep the lmap
lite. *(But I've never worked with neon lamps.)

* I don't believe the voltages in that curve in Wiki - I would plan on 70
volts and peak current around 3 milliamps (peak voltage of 240 VAC is
about 340 volts).

* If the glass bulb's overall length is 3/4 inch, then the neon lamp is
probably an NE-2H. I would use an 82K or 100K 2-watt resistor for an
NE-2H at 240 volts AC. I would err on the high side (100K) to maximize
life of the lamp. *I suspect the toated resistor is a 100K 2 watt whose
yellow band was browned by being toasted.

*- Don Klipstein )- Hide quoted text -

- Show quoted text -

Excellent, Thanks Don. I like the faded yellow stripe idea. The bulb
is about 1/2 that size. It's standing straight up and the tip of the
glass is 0.4" (10mm) above the circuit board.

George H.

On Mar 1, 7:32*pm, John Larkin
wrote:
On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold





wrote:
I've got a tankless electric water heater from eemax. that stopped
working the other day. *eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. *The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. *The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *(60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

Thanks for any advice.

George H.

Numbers more like 330K to 560K are more reasonable. Higher currents
will sputter the gas and make the thing fail sooner.

Better yet, use an LED.

John- Hide quoted text -

- Show quoted text -

Well somehow this must also feed power to some other part of the
circuit. There's also an LM324 and small triac Q601e3 on the pcb.

George H.

In ,
George Herold wrote:

On Mar 1, 5:48*pm, (Don Klipstein) wrote:
In ,
George Herold wrote:

SNIP to here

Yes the lamp looks like the picture in the wiki article. * If I
believe the curve there, then I've got something like 160-200 volts
across the lamp at 20mA. *So I've got (call it) 80 V to drop on the
resistor at 20mA.. I get 3 k ohm at a watt or two. *Hmm maybe what
looks like brown black brown is a discolored red black red. *(I always
have hated the way red and brown look almost the same on the pale blue
body of the metal film resistors.)

100k seems like it won't allow enough current through to keep the lmap
lite. *(But I've never worked with neon lamps.)

* I don't believe the voltages in that curve in Wiki - I would plan on 70
volts and peak current around 3 milliamps (peak voltage of 240 VAC is
about 340 volts).

* If the glass bulb's overall length is 3/4 inch, then the neon lamp is
probably an NE-2H. I would use an 82K or 100K 2-watt resistor for an
NE-2H at 240 volts AC. I would err on the high side (100K) to maximize
life of the lamp. *I suspect the toated resistor is a 100K 2 watt whose
yellow band was browned by being toasted.

Excellent, Thanks Don. I like the faded yellow stripe idea. The bulb
is about 1/2 that size. It's standing straight up and the tip of the
glass is 0.4" (10mm) above the circuit board.

That sounds just a little small for the A1B (mini NE-2) and the A1C
(mini NE-2H), so I suspect your lamp is one of those. Given the size of
the resistor, I think it's the latter.

If your neon lamp kicked the bucket along with the resistor (more likely
it survived, at least well enough to glow from 240 volts AC), Radio Shack
may still carry these (a litle incorrectly calling them NE-2H).

- Don Klipstein )

On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold
wrote:

I've got a tankless electric water heater from eemax. that stopped
working the other day. eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC?

---
No.

For a small neon lamp like an NE-2, (GE 3AD) with a recommended current
of 0.3mA and a nominal holding voltage of about 60V, peak, that's about
42VRMS, so the resistor would have to drop about 200V at 300µA:

Vs - Vne 200V
R = ---------- ~ ------- ~ 670k oms
Ine 3e-4A

and it would dissipate:

P = IE = 3e-4A * 200V ~ 0.06 watts

If that resistor were 100 ohms, then with 200V dropped across it
there'd be 200 amperes through it _and_ the neon lamp, which they'd both
hate for a little while.

OTOH, if the resistor is 100k it'll drop about 200V with a neon lamp in
series, which will let about 2mA through when the lamp fires.

That'll cause the resistor to dissipate about 0.4 watts, which doesn't
explain why it got toasted, since even into a short it would only
dissipate about:


E² 240²V
P = --- = ------- = 0.576 watts
R 1e5R

Just for grins, let's say it's a 3 watt resistor running full bore in
series with a load (like a high current neon lamp) drawing 5mA.

Then the value of the resistor would be:

E² 200²V
R = --- = ------- = 13,333 ohms ~ 13k
P 3W

and if there was some circuitry downstream from the lamp, which shorted,
then the resistor would dissipate:

E² 240²V
P = --- = ------- = 4.43 watts
R 13e3R

Not huge but, anyway, without a schematic it's all just conjecture.
---

(60 Hz if that matters.)
I'm not sure what the I-V curve for the lamp will look like. (Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

---
Only in a very general way; here's a much better one for your
application:



JF

On Mar 2, 12:23*pm, John Fields wrote:
On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold

wrote:
I've got a tankless electric water heater from eemax. that stopped
working the other day. *eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. *The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. *The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *

---
No.

For a small neon lamp like an NE-2, (GE 3AD) with a recommended current
of 0.3mA and a nominal holding voltage of about 60V, peak, that's about
42VRMS, so the resistor would have to drop about 200V at 300 A:

* * * * *Vs - Vne * * *200V
* * R = ---------- ~ ------- ~ 670k oms
* * * * * *Ine * * * *3e-4A

and it would dissipate:

* * P = IE = 3e-4A * 200V ~ 0.06 watts

If that resistor were *100 ohms, then with 200V dropped across it
there'd be 200 amperes through it _and_ the neon lamp, which they'd both
hate for a little while.

OTOH, if the resistor is 100k it'll drop about 200V with a neon lamp in
series, which will let about 2mA through when the lamp fires. *

That'll cause the resistor to dissipate about 0.4 watts, which doesn't
explain why it got toasted, since even into a short it would only
dissipate about:

* * * * *E * *240 V
* * P = --- = ------- = 0.576 watts *
* * * * *R * * 1e5R

Just for grins, let's say it's a 3 watt resistor running full bore in
series with a load (like a high current neon lamp) drawing 5mA.

Then the value of the resistor would be:

* * * * *E * *200 V
* * R = --- = ------- = 13,333 ohms ~ 13k
* * * * *P * * *3W

and if there was some circuitry downstream from the lamp, which shorted,
then the resistor would dissipate:

* * * * *E * *240 V
* * P = --- = ------- = 4.43 watts
* * * * *R * * 13e3R

Not huge but, anyway, without a schematic it's all just conjecture.
---

(60 Hz if that matters.)

I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

---
Only in a very general way; here's a much better one for your
application:



JF

Thanks John, I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) A new circuit
board is in the mail, but this won't solve the mystery. The board has
been redesigned and is no longer analog but digital. Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.


Say could you resend that link to the neon bulb I-V curve? What ever
you posted got turned into gobble-de-gook by google.

"


George H.

On Tue, 2 Mar 2010 12:34:55 -0800 (PST), George Herold
wrote:

On Mar 2, 12:23*pm, John Fields wrote:
On Mon, 1 Mar 2010 13:53:13 -0800 (PST), George Herold

wrote:
I've got a tankless electric water heater from eemax. that stopped
working the other day. *eemax won't provide any component level
support, but I've ordered a new board for $45.00.

When I opened up the unit, after switching off the circuit breaker on
the 240V AC line, I observed that a big (maybe 3-5 watt) (metal film?)
resistor was discolored and was an open circuit. *The markings look
like 100 ohms, but because of the discoloration it's hard to be sure.
I say metal film because the resistor is pale blue in color. *The
resistor feds a neon indicator bulb... (And probablly more of the
circuitry.)

My question. *Is 100 ohms a good value as a current limiting resistor
for a small neon lamp running off 240 V AC? *

---
No.

For a small neon lamp like an NE-2, (GE 3AD) with a recommended current
of 0.3mA and a nominal holding voltage of about 60V, peak, that's about
42VRMS, so the resistor would have to drop about 200V at 300 A:

* * * * *Vs - Vne * * *200V
* * R = ---------- ~ ------- ~ 670k oms
* * * * * *Ine * * * *3e-4A

and it would dissipate:

* * P = IE = 3e-4A * 200V ~ 0.06 watts

If that resistor were *100 ohms, then with 200V dropped across it
there'd be 200 amperes through it _and_ the neon lamp, which they'd both
hate for a little while.

OTOH, if the resistor is 100k it'll drop about 200V with a neon lamp in
series, which will let about 2mA through when the lamp fires. *

That'll cause the resistor to dissipate about 0.4 watts, which doesn't
explain why it got toasted, since even into a short it would only
dissipate about:

* * * * *E * *240 V
* * P = --- = ------- = 0.576 watts *
* * * * *R * * 1e5R

Just for grins, let's say it's a 3 watt resistor running full bore in
series with a load (like a high current neon lamp) drawing 5mA.

Then the value of the resistor would be:

* * * * *E * *200 V
* * R = --- = ------- = 13,333 ohms ~ 13k
* * * * *P * * *3W

and if there was some circuitry downstream from the lamp, which shorted,
then the resistor would dissipate:

* * * * *E * *240 V
* * P = --- = ------- = 4.43 watts
* * * * *R * * 13e3R

Not huge but, anyway, without a schematic it's all just conjecture.
---

(60 Hz if that matters.)

I'm not sure what the I-V curve for the lamp will look like. *(Is the
one shown here OK?)

http://en.wikipedia.org/wiki/Neon_lamp

---
Only in a very general way; here's a much better one for your
application:



JF

Thanks John, I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) A new circuit
board is in the mail, but this won't solve the mystery. The board has
been redesigned and is no longer analog but digital. Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.

Say could you resend that link to the neon bulb I-V curve? What ever
you posted got turned into gobble-de-gook by google.

"


George H.


http://www.infinitefactors.org/docs/...resistance.pdf

Jon

In ,
George Herold wrote in part:

SNIP previously quoted material

Thanks John, I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) A new circuit
board is in the mail, but this won't solve the mystery. The board has
been redesigned and is no longer analog but digital. Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.

I have seen resistors fail in ways that cause their resistance to
decrease until they get toasted and then go open circuit.

My experience has been that this happens more with carbon composition
resistors. Those tend to be cylinders with untapered ends. Many times,
the composition is exposed. The composition may absorb moisture and
experience a decrease in resistance, especially if it is operated only
intermittently. This is more likely to be a problem where there is
exposure to moisture or high humidity or salty coastal air.

And carbon's resistivity has a negative temperature coefficient.

Preferably the resistor degrades rapidly and then goes open circuit
quickly by the time it allows anything else to get overloaded to a
damaging extent.

A possible other explanation is that a severe line voltage surge caused
something in the resistor to carbonize. The resistor becomes more
conductive and hotter. The carbonization may then go into a runaway
situation, leading to sizzle-sizzle and then to *pow*, *poof* or *phut*.

- Don Klipstein )

On Tue, 2 Mar 2010 12:34:55 -0800 (PST), George Herold
wrote:


Thanks John, I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) A new circuit
board is in the mail, but this won't solve the mystery. The board has
been redesigned and is no longer analog but digital. Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.


Say could you resend that link to the neon bulb I-V curve? What ever
you posted got turned into gobble-de-gook by google.

---
Ah, Google...

Google groups doesn't support binaries so I'll email it to you.

JF

On Mar 2, 6:28*pm, (Don Klipstein) wrote:
In ,
George Herold wrote in part:

SNIP previously quoted material

Thanks John, *I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) * A new circuit
board is in the mail, but this won't solve the mystery. *The board has
been redesigned and is no longer analog but digital. *Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.

* I have seen resistors fail in ways that cause their resistance to
decrease until they get toasted and then go open circuit.

* My experience has been that this happens more with carbon composition
resistors. *Those tend to be cylinders with untapered ends. *Many times,
the composition is exposed. *The composition may absorb moisture and
experience a decrease in resistance, especially if it is operated only
intermittently. *This is more likely to be a problem where there is
exposure to moisture or high humidity or salty coastal air.

* And carbon's resistivity has a negative temperature coefficient.

* Preferably the resistor degrades rapidly and then goes open circuit
quickly by the time it allows anything else to get overloaded to a
damaging extent.

* A possible other explanation is that a severe line voltage surge caused
something in the resistor to carbonize. *The resistor becomes more
conductive and hotter. *The carbonization may then go into a runaway
situation, leading to sizzle-sizzle and then to *pow*, *poof* or *phut*.

*- Don Klipstein )

Thanks Don, This certianly wasn't a carbon composition. (Though I
was digging through a pile of 1-2 Watt 100-300k ohm carbon C's at work
today.) It doesn't seem like putting 100k in there can hurt anything,
though I don't expect it to work either... I figure something else
might have happened also.

George H.

On Mar 2, 6:53*pm, John Fields wrote:
On Tue, 2 Mar 2010 12:34:55 -0800 (PST), George Herold

wrote:
Thanks John, *I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) * A new circuit
board is in the mail, but this won't solve the mystery. *The board has
been redesigned and is no longer analog but digital. *Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.

Say could you resend that link to the neon bulb I-V curve? *What ever
you posted got turned into gobble-de-gook by google.

---
Ah, Google...

Google groups doesn't support binaries so I'll email it to you.

JF

Wow. Thanks John

On Tue, 2 Mar 2010 20:05:50 -0800 (PST), George Herold
wrote:

On Mar 2, 6:53*pm, John Fields wrote:
On Tue, 2 Mar 2010 12:34:55 -0800 (PST), George Herold

wrote:
Thanks John, *I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) * A new circuit
board is in the mail, but this won't solve the mystery. *The board has
been redesigned and is no longer analog but digital. *Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.

Say could you resend that link to the neon bulb I-V curve? *What ever
you posted got turned into gobble-de-gook by google.

---
Ah, Google...

Google groups doesn't support binaries so I'll email it to you.

JF

Wow. Thanks John

---
You're welcome. :-)

If you're interested in neon glow lamps, GE's 1965 glow lamp manual
(pretty much the Bible) is he

http://www.donsbulbs.com/cgi-bin/r/t.pl/library.html

JF

On Mar 3, 5:47*am, John Fields wrote:
On Tue, 2 Mar 2010 20:05:50 -0800 (PST), George Herold





wrote:
On Mar 2, 6:53 pm, John Fields wrote:
On Tue, 2 Mar 2010 12:34:55 -0800 (PST), George Herold

wrote:
Thanks John, I must admit it's hard to understand how a 3 watt 100k
ohm resistor across the 240 V lines would blow even if everything down
stream of it was shorted. (As your calculation shows.) A new circuit
board is in the mail, but this won't solve the mystery. The board has
been redesigned and is no longer analog but digital. Once I put the
new board in I'll look at the busted one and see if I can figure
anything out.

Say could you resend that link to the neon bulb I-V curve? What ever
you posted got turned into gobble-de-gook by google.

---
Ah, Google...

Google groups doesn't support binaries so I'll email it to you.

JF

Wow. *Thanks John

---
You're welcome. :-)

If you're interested in neon glow lamps, GE's 1965 glow lamp manual
(pretty much the Bible) is he

http://www.donsbulbs.com/cgi-bin/r/t.pl/library.html

JF- Hide quoted text -

- Show quoted text -

Excellent, lots of reading there!

George H.