"David C. Stone" wrote in message
...
In article , Dick
wrote:

On Wed, 9 Mar 2005 20:39:19 -0500, "Bill Stock"
wrote:

I recently purchased a Won Brothers Pro Heat II aquarium digital
aquarium
heater for my 75 gallon. The old heater was too small and I plan to go
with
an auto water changer in the near future, which will only make matters
worse.

The box makes claims of +/- 1°F accuracy, which if you read carefully,
refers to the digital readout, not the actual heater. The heater has a
range of 68°F to 93°F. I currently have it set at 68°F, but the tank is
reading 72.3°F on my thermometer and 71°F on the heater LED. I thought
4°F
of error was rather crappy given the +/- 1°F claims and the fact that I
wanted to keep the tank around 70°F. I contacted the manufacturer about
the
large error, but they did not bother to respond.

[snip]

I have yet to find a heater that is calibrated. The dial markings
seem to be approximate. I have come to assume the plus and minus are
a measure of how accurately the set temperature holds.

Thus I set the dial to 78, the tank temperature settles at 76. I move
the dial to 80 and the tank settles at 78. Leaving the dial alone,
the measure temperature will vary plus or minus, there is always a
lag.

Most of the heaters I've seen cycle on and off at a rate determined by
the "temperature" setting of the control. If ambient temperature
changes by a couple of degrees, the result is a corresponding change
in water temperature since the thermostat is still adding the same
amount of heat.

I would be interested to see if your "Won Brothers Pro Heat II" actually
had a temperature controller rather than a cycling heater in it. The
former would actually measure the water temperature and adjust the
on/off cycling rate to maintain constant temperature. If any one knows
of a system that does this, I could really use one for my 120 gal. lab.
tank - the room temperature is normally pretty constant, but if the
outside temperature changes dramatically overnight, it can vary by as
much as 6 F, and I have to go adjust the thermostat.

David,

I believe the external temperature sensor is used to control the temperature
AND display it on the LEDs. The temperature is far too stable for it to be
otherwise. I have a similar (different brand) titanium heater in the pond,
but without the digital readout. It also uses the external sensor to control
the temperature. Although I'm using a custom sensor and software to control
this unit, as my temp requirements are well below the range of the
thermostat. WB makes these things up to 1000Ws, more than enough to handle
your 120 G.



Speaking of which, it's time for my daily tank check...