Lecture 1 - Heaters and how they work

Discussion in 'General Equipment discussion' started by Zafgak, Jun 11, 2009.

  1. Zafgak

    Zafgak Old fart

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    General info important to know
    - Warm water rises
    - The heater has a control element near the top of the heater tube where the mains wire goes in and a heating element at the bottom of the tube.
    So when the heater is in the tank and it is vertical ie. 12 and 6 oclock position, the warm water rising goes straight to the control element and turns the heater off. When the heater turns off, the cold water then settles around the contriol element and the heater turns on. You know have a heater that turns on and off often and does not efficiently heat the water in the tank.
    If you put the heater in a 9 and 3 oclock or horizontal position, near the bottom of the tank, the warm water rises away from the heater and control element to the top of the tank. this drags cold water across the heater warming it and therefore most of the water is warmed before the control element turns the heater off. You now have an efficient heater.

    The efficiency decreases as your turn the heater from horizontal to vertical..

    Now comes the technical bit, you may get a bit bored :bigsmile:

    All heaters have one common element and that is the heating ELEMENT :bigsmile:
    This is one or more coils of NiChrome or similar wire, coiled to make a given wattage heater. When current passes through this type of wire the wire heats up. In theory the shorter the wire the more heat you get, therefore higher wattage heaters have less wire in the elements - BUT too short and the wire will burn. So what they do is use a different physical wire for the high wattage heaters with more coils. If the element get wet it will normally burn out at the point where the moisture is.

    Then the next thing is the control ELEMENT. There are two types, the cheap bi-metallic heaters and the expensive electronic heaters.

    Bi-Metallic heaters have in the top of the heater a controller made of two strips of different metals, normally copper and iron joined together - as in the pic ... As the metals warm up they bend at a different rate, this will make the strip curve. If you attach your power cable onto the strip and then from a contact that touches the strip, to the heating element, what will happen is : as the strip warms and curves it will eventually curve away from the contact touching it and current will then stop flowing through the heating element. As it cools and straightens the contact will touch and current flows again.
    If you make the curve just right it will connect and disconnect at approximately the correct temperature. NOTE these types of heaters are normally +- 3 degrees in accuracy, which is not too bad as the water around the heater takes time to heat and cool thus limiting the temperature change to about +- 1 or 2 degrees.
    The problem is that after a while the contacts stick together due to arcing as the power breaks and makes. When they stick, the fish will boil as current never stops flowing..


    Electronic heaters have a device to measure the temperature which is normally accurate to about +-0,1 degrees. This measured vale is compared electronically against a setpoint value.
    When higher than the setpoint the electronics stops current flow to the heating element and when lower than setpoint it allows current flow.
    The gap between on and off is electronically set to +- 0,5 degrees accuracy.
    As there are no mechanical contacts to arc there is nothing that can stick. So only if the electronics fails could you possibly overheat the tank, but the electronics is normally designed that if it fails, it will fail OFF.

    Bimetal.jpg
     
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  3. wito-zn

    wito-zn

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    what type of heater would be accurate for a 1.5m tank?
     
  4. Reafer

    Reafer

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    :bigsmile:great thread , thx for the info , i like knowing how things work:bigsmile:
     
  5. SauRoN

    SauRoN

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    Zafgak some nice points made there which we often don't think about.

    Mine is mounted vertically, for aesthetic reasons (hidden behind the down pipe) but does switch on and of constantly.

    I've though of relocating it horizontally in the dark corner at the back, but fear it might run dry when the water level drops, making it more of a worry.
     
  6. Zoom

    Zoom Retired Moderator

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    Great lesson,

    Quick question, how much wattage per liter of water is considered effective?
     
  7. rlowe

    rlowe

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    You’re forgetting one fundamental thing and that is that most of us have adequate filtration and therefore you have to ad circulation into the equation. This is the very thing that debunked the efficiency myth in modern day application. With adequate filtration\circulation you create equilibrium and your heater will not switch off until set temperature is reached.

    If you’re going to place a heater vertically in a filterless or tank with lesser circulation, it’s going to do exactly as described above and only in this type of situation will it be less efficient.

    If like most of us you make use of either internal or external filtration (and let’s use the external canister filter as example here) with inlet next to heater in vertical position and outlet on other side of tank, you now have current flowing over and pulling heat away from the heater. If you look at Jewel tanks or many other such examples with filter\heater corner boxes or stepping outside the glass box for a moment, Hydor inline heaters which connects inline with your canister hose or Eheim thermo filters with build in heater, you’ll find that all of these examples have one thing in common and that is that they rely on circulation i.e. if you switch off the filter they are dead in the water.

    Another thing to consider is that not all aquarium heaters are fully submersible. Even manufacturers of submersible heaters will often stress that their heaters should be mounted vertically with seal above water level to keep water from compromising the seal.

    This is a quote directly from Jäger instructions.

    "Mount thermostatic heater with double suction cup holder vertically in the aquarium, fixing it in a place where water flow is brisk."

    Once again this brings us back to adding circulation into the equation.
     
    Last edited: Jun 12, 2009
  8. butcherman

    butcherman Administrator

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    most heaters i have see recomend that they be place diagonally not stright up ot sideways.
     
  9. SauRoN

    SauRoN

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    I have a problem with my one heater not making up it's mind.

    Should I assume the thermostat is shot, and buy a new one, or is there something I can do?
     
  10. Madam

    Madam Kirsty

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    Wow, very interesting. My heater is actually vertical as well, but that's because we're nervous of this type of electricity being underwater. What are the chances of having a problem with this? (ie: electrocuting my fish / fire hazard)
     
  11. Zoom

    Zoom Retired Moderator

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    Madam,

    You would need to check with the manufacture of your heater and find out what they recommend for your heater. As mentioned, certain heaters can be submerged, others can't.

    As far as the Vertical versus horizontal debate it concerned... that is dependant on 2 factors... If the manufacture says you need the top submerged, then I would recommend going more horizontal than vertical. If you choose to stay vertical, you need to make sure you have very good circulation in the tank. When the heater is verticle, the heater heats up the water. Hot water rises, and generally speaking the thermostat is in the top part of the heater, thus the hot water will flow over the thermostat, and the heater will turn off... but the rest of the water is still cold. So good circulation will keep moving the hot water away from the heater until ALL the water is at the right temp.

    The problem often faced with having the top half of the heater above the water surface is that the thermostat is now out of the water, and will only turn the heater off when the air around the thermostat reaches the desired temp. So if you set the temp to 26 deg. the heater will turn off when the air above the water reaches 26... as you can see... you water could be sitting a lot higher.

    As far as electrocuting is concerned... I'm no electrician... but as far as I am aware, 90% of fish equipment is now double insulated, meaning there is no need to have an earth wire. Should something go faulty and cause a spark or short, it should trip either the circuit breaker or the earth leakage on your board. Your tank is not earthed, so in THEORY you shouldn't shock your fish, or yourself. But it is always SAFE PRACTISE that whenever you plan on sticking your hand into your tank you switch off and UNPLUG everything.

    This is something a lot of people neglect... they think that buy just switching off you have isolated the tank. In actual fact, all you have done is isolate the live wire... the problem comes in that you could have a faulty appliance somewhere else in your home... and this fault could still cause an electrocution in the tank even with the plug switched off. (the neutral and earth wire is not turned off when you turn a plug off!)

    Z
     
  12. Carping

    Carping MTS Victim

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    :eek: That means that I am ALWAYS going to have a cold dirty tank..... If I have to switch off my heater and filter every time I stick my hands in there LOL. I am forever busy moving, removing, or adding something to my tank
     
  13. LanceP

    LanceP

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    The way I see it, if the fish are still alive and swimming, then it's safe to stick the hands in:bigsmile:
     
  14. Gilbertr14

    Gilbertr14 Phenacogrammus

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    Oooh I love heated debates....

    My 2c is always rely on an external thermometer.

    Any heater will heat a tank, its just that a small one will take longer and finally fail.
    If common sense prevails, then you would not go this route of course.
    Get a heater that has headroom to accomodate any changes in a reasonable time.


    Also 2 x 150w instead of a 300w means that there is some redundancy if one fails, and you can heat opposite sides of the tank if you so wish.


    All of this info is useless, if you dont know the following:
    A: tank size.
    B: winter water temp unheated.
    C: required temp.

    See http://www.aquariummonsters.com.au/catalog/article_info.php/articles_id/70 for a table.
     
    Last edited: Jul 13, 2009

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