On Sun, 12 Dec 2004 22:56:37 -0000, (Dave Platt)
wrote:

In article ,
default wrote:

My electric stove is talking to my modem, resulting in the modem
dropping its speed back or losing the connection (dial up). I can
turn any burner on high and everything works. Turn the "infinite"
control to a midpoint heat setting and the modem goes out to lunch.

The controls are primitive types with a heater and bimetallic strip
inside them (I disassembled one to fix it). The contacts appear to be
real silver.

Seems to me that you may have either (or both) of two problems: a
brief voltage drop when the stove heating element is switched on
(perhaps enough to "brown out" the modem's power supply) or a burst of
RF noise when the contacts open and close.

I'd guess that the stove heater element is drawing a pretty hefty
surge when it's first turned on, before it heats up and its resistance
increases. This might result in a one- or two-cycle voltage-drop
brownout which affects the whole circuit and may show up in other
circuits as well... it'd depend on the quality of the house wiring and
of your electrical service connection.

If this is the case, you might be able to correct its effect on the
modem by using a UPS. Unfortunately, most consumer-type "UPS"
products are actually SPS (standby power supply) designs, and they
don't turn on their inverter and supply power to the device-under-load
until there's been a brownout or power loss for a couple of cycles.
This might not be fast enough to keep your modem happy.

If your modem uses a 12 VDC supply from its wall-wart, you might be
able to fix the problem by using a "12-volt" gel cell as a power
supply, with a well-regulated DC supply of 13.4 - 13.5 volts to keep
it charged up. If the AC voltage sags for a moment, the modem
wouldn't even notice.

Another possibility is that it's a burst of RF noise, carried in
differential mode on the power wiring, when the bimetallic switch
opens or closes. A common-mode ferrite on the wall-wart cord wouldn't
help with this, I think. You could try either of two things:

- A differential-and-common mode AC-line filter, at the modem. Some
AC power strips incorporate them, and you can get ones with better
filtering/attenuation in sealed metal cans, with either wire-lead
or push-on connectors (Corcom and others make 'em, and electronics-
surplus stores usually have some).

- A snubber, at the stove itself (the source of the problem). The
snubbers I've seen are usually caps of .1 - 1 uF in capacity,
in series with a few ohms of resistance, in a flame-resistant
plastic encapsulation. They're designed and rated for use
directly across a power line (I believe they have "X" and "Y"
rating codes).

You'd probably need to have one of these wired in across the line,
either just before or just after the bimetallic switch. Probably
the sort of thing which should be done by a licensed electrician.

A battery-powered-modem-with-float-charger-backup might also be a good
way to deal with the problem if its cause is RF noise on the phone
line. You could add additional filtering of the DC before it reaches
the battery, to keep it well out of the modem's supply.

Hmmm... another thought. You might want to check the arrangments by
which the phone lines are safety-grounded at your building's MPOE.
If your phone line's grounding system is connected to the same ground
rod as the power (which it probably is), and if there's any amount of
"ground bounce" when the stove load is turned on or off, and if
there's some amount of current leakage in the phone line protection
system (e.g. if it has old-style carbon-block spike-eaters, or if
there's a dirt-and-moisture current path) then it's perhaps
conceivable that turning the stove on and off might result in a
momentary voltage spike on the phone line due to this common-ground-path
setup.

Thanks Dave

I do have a common ground for phone and AC at the box, I figured
lifting the ground and watching with a scope as the stove cycled ruled
it out. I can lift it at the 'puter end and see what happens.

Phone has a MOV protector and it was put in 5 years ago. All wiring
looks clean and AC and Phone are outside a few feet apart with no
common path (and problem doesn't get worse with rain etc.)

You did give me two ideas I hadn't thought of. Snubbers on the stove
and a battery isolator on the modem. I think it is 12 AC but the case
comes apart easily.

Make that three - brown out, my AC line runs 106 to 108 most days. I
don't complain to the power company because I figure it probably saves
me money in the long run (power bill ~$20 month for year average but
I'm frugal too). I do have a variac and can wire a boost transformer
to the modem if need be. The three terminal regulator in the modem
runs hot so I guess I developed a blind spot about the low voltage
possibility.

Thanks again


An electrician? perish the thought. The stove is just a big metal box
with a few switches and resistors in it. Besides it can be unplugged
or switched at the breaker. (how I normally work on it)