Temperature Frequency and Fluctuations

[NeonRabbit221B]

Just curious about the best method to set temperature checking frequency and minimizing temperature fluctuations. Currently I have two heaters, a BRS without a thermostat and an eheim as a backup. I have a temperature probe in the sump with small fluctuations of .1 every 6 minutes that controls the eheim that hasn't run in 24 hours that I have set to check every 60 seconds. My BRS without the thermostat is controlled by a probe in the display that goes high for about 15 minutes and drops .1 for about 7 minutes and this probe is checked every 45 seconds.

I am trying to minimize the wear and tear on the relay but don't want massive fluctuations on the display temperature...

 

[Reef.]

Heaters are cheap, I would get the tank temp how you want it and not worry about the number of on/off cycles, you have two heaters and a good brand.

 

[NeonRabbit221B]

Heaters are cheap, I would get the tank temp how you want it and not worry about the number of on/off cycles, you have two heaters and a good brand.

True but its a balancing act where both components can fail which can be catastrophic. If my relay fails I think it would fail (wired it normally open) so that the heater would shut off. If the temp probe fails then it may read as low and cause the heater to have a runaway state. If the heater itself fails then I guess it would just be dead.

Not sure if additional temp checks could wear down the probe or damage the relay or if my .1 temperature swing that happen about twice an hour is something that should even register as signifigant.

 

[LeftyReefer]

The ocean fluctuates temp daily due to tides, currents, weather, etc... a slight bit of temp variation isn't a problem, so I would tend to gravitate towards allowing more temp swing, and less cycling of your heaters for longevity sake.

 

[mike550]

Assuming that neither of your heaters can fully support the tank why don’t you set the BRS one really wide and use your Eheim for fine tuning. For example if the target temp is 78, then set the BRS ON as long as the temp is below 80 and then use your Eheim for fine control at 78

You might also want to set OFF if the temp is below 60 since it could be that something is off on your temp measurement.

 

[NeonRabbit221B]

Assuming that neither of your heaters can fully support the tank why don’t you set the BRS one really wide and use your Eheim for fine tuning. For example if the target temp is 78, then set the BRS ON as long as the temp is below 80 and then use your Eheim for fine control at 78

You might also want to set OFF if the temp is below 60 since it could be that something is off on your temp measurement.

I think the 200W titanium was rated up to 75 gal and my display+sump is about 54 gal of water. I will give it a shot letting it run a bit higher (moving current set point from 78 to 78.5) and set the eheim just a tad higher at 78.75. Seems like a good idea as long as the BRS won't just keep climbing!

 

[Reef.]

True but its a balancing act where both components can fail which can be catastrophic. If my relay fails I think it would fail (wired it normally open) so that the heater would shut off. If the temp probe fails then it may read as low and cause the heater to have a runaway state. If the heater itself fails then I guess it would just be dead.

Not sure if additional temp checks could wear down the probe or damage the relay or if my .1 temperature swing that happen about twice an hour is something that should even register as signifigant.

You say “catastrophic” if they were to fail in the on position then yes but that’s what temp controllers are for, if they both fail at the same time in the off position, which is extremely unlikely, that would only mean the tank dropping over a few hours to room temp, which would give you time to sort the issue. Unlikely to be catastrophic.

I don’t think you are going to beat a .1 and definitely not if you try to reduce the on/off cycles more.

Sounds to me you have it just right as it is.

 

[robsworld78]

.1 is pushing it for the DS18B20. Each step is 0.0625 at 12 bits which you should be running. One thing I've always noticed with mine is sometimes they will all do 12 bits but usually it's only 11 bits like right now so the steps are 0.125. I could never figure out why it changes randomly but it affects them all.

Maybe .2 or .3 for hysteresis would stop the constant switching. If you do want more accurate maybe try a solid state relay.