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