## PSN-L Email List Message

Subject: Re: Thermal Control for Sensors
From: "Jerry Payton" gpayton880@.......
Date: Sat, 17 Nov 2007 10:15:49 -0600

```Hi Pete, Chris and Others,

I failed to mention that my goal is for three instrument covers.

IDEA:   How about an inexpensive 12v battery charger, with a sufficient max
current rating, wired to three separate 15 ohm 25w resistors mounted on an
aluminum plate for proper heat dissipation?

If my math is right, that would be about 10 watts to each cover and a total
of about 2.4 amps current demand on the charger

Jerry.

----- Original Message -----
From: Pete Rowe
To: psn-l@..............
Sent: Friday, November 16, 2007 1:53 PM
Subject: Re: Thermal Control for Sensors

Hi Jerry
Since we don't know how well your insulation works, it
is hard to define how many watts you need to dissipate
to keep the inside of the box at a certain
temperature. I doubt that you need even 10 watts if
simple experiments. You'll need a thermometer inside
the box that you can read from the outside without
opening the box. Most any inexpensive indoor/outdoor
thermometers will be fine. Be aware that most of those
thermometers are only accurate to +/- 2 degrees C. For
this measurement that is ok.
Then get a 1 amp 12 volt DC wall wart and a 150 ohm 5
or 10 watt resistor. Put the resistor in your box and
hook up the 12 volts to it. The resistor will
dissipate about 1 watt (P= Esquared/R). Let it run for
a day and see if the temperature in the box goes up
and levels off. If this temp is ok, then you're done.
If you need more watts, calculate different resistors
for 2  or 5 watts and repeat the experiment. You
should find that you don't need a thermostat if you
sneak up on a fixed power dissipation that keeps the
temperature stable. If your insulation is very poor or
the outside temperature has large swings, then you'll
need more watts and a thermostat to cycle the heater.
It is best to avoid thermostats because they always
make electrical noise.
I hope this helps.
Pete Rowe
--- Jerry Payton  wrote:

> I am searching for wiring details for using Aluminum
> Housed Wirewound Power
> Resistors used for thermal control inside an
> insulated housing for the
> seismic sensors.  It has been suggested wiring
> several such resistors in
> series to accomplish a 10-30 watts from the 110v AC
> house supply source.
> I'm a little leery about the house current for
> safety reasons and possible
> AC hum.
>
> In studying the Mouser Electronics catalog, I can
> find several possible
> configurations using one to several resistors in
> series.  The resistors
> specify their wattage capability, but have different
> resistance values to
> choose from.
>
> If anyone has done this and has specific values
> etc., I'd appreciate hearing
> from you.
>
> Light bulbs attract bugs and other unwanted
> critters!
>
> Thank you,
> Jerry
>

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Public Seismic Network Mailing List (PSN-L)

Hi Pete, Chris and Others,

I failed to mention that my goal is for three instrument =
covers.

IDEA:   How about an inexpensive 12v battery =
charger, with=20
a sufficient max current rating, wired to three separate 15 ohm 25w =

resistors mounted on an aluminum plate for proper heat =
dissipation?

If my math is right, that would be about 10 watts to each cover and =
a total=20
of about 2.4 amps current demand on the charger

Jerry.

----- Original Message -----=20
From: Pete Rowe =

To: psn-l@..............
Sent: Friday, November 16, 2007 1:53 PM
Subject: Re: Thermal Control for Sensors
Hi JerrySince we don't know how well your insulation =
works,=20
itis hard to define how many watts you need to dissipateto keep =
the=20
inside of the box at a certaintemperature. I doubt that you need =
even 10=20
experiments. You'll need a thermometer insidethe box that you can =
the outside withoutopening the box. Most any inexpensive=20
indoor/outdoorthermometers will be fine. Be aware that most of=20
thosethermometers are only accurate to +/- 2 degrees C. Forthis=20
measurement that is ok.Then get a 1 amp 12 volt DC wall wart and a =
150 ohm=20
5or 10 watt resistor. Put the resistor in your box andhook up =
the 12=20
volts to it. The resistor willdissipate about 1 watt (P=3D =
Esquared/R). Let it=20
run fora day and see if the temperature in the box goes upand =
levels=20
off. If this temp is ok, then you're done.If you need more watts, =
calculate=20
different resistorsfor 2  or 5 watts and repeat the experiment. =

Youshould find that you don't need a thermostat if yousneak up =
on a=20
fixed power dissipation that keeps thetemperature stable. If your =
insulation=20
is very poor orthe outside temperature has large swings, then =
you'llneed=20
more watts and a thermostat to cycle the heater.It is best to avoid=20
thermostats because they alwaysmake electrical noise.I hope this =

helps.Pete Rowe--- Jerry Payton <gpayton880@.......> =
wrote:> I=20
am searching for wiring details for using Aluminum> Housed =
Wirewound=20
Power > Resistors used for thermal control inside an> =
insulated=20
housing for the > seismic sensors.  It has been suggested=20
wiring> several such resistors in > series to accomplish a =
10-30=20
watts from the 110v AC> house supply source. > I'm a =
little leery=20
about the house current for> safety reasons and possible > =
AC=20
hum.> > In studying the Mouser Electronics catalog, I =
can>=20
find several possible > configurations using one to several =
resistors=20
in> series.  The resistors > specify their wattage=20
capability, but have different> resistance values to > =
choose=20
from.> > If anyone has done this and has specific =
values>=20
etc., I'd appreciate hearing > from you.> > Light =
bulbs=20
attract bugs and other unwanted> critters!> > Thank =

you,> Jerry > =
=20
_________________________________________________________________________=
___________Be=20
a better sports nut!  Let your teams follow you with Yahoo =
Mobile. Try=20
it now.  http://mobile.yahoo.com/sports;_ylt=3DAt9_qDKvtAbMuh1G1SQtBI7ntAcJ=
__________________________________________________________Pub=
lic=20
Seismic Network Mailing List (PSN-L)To leave this list email PSN-L-REQUEST@...............
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the body of the message (first line only): unsubscribeSee http://www.seismicnet.co=
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