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Thread: Should a heated stir-plate base get too hot to touch, when trying to boil water?

  1. #1 Should a heated stir-plate base get too hot to touch, when trying to boil water? 
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    Hello All,
    This is my first posting to this forum.

    I tried using a very under priced no name brand lab heated stir-plate I got off of eBay (I know, I know...) and after testing the unit with about 300ml of water in a beaker to see how long it would take to boil, I waited for over an hour and the water never got above 180 degrees F. I noticed that the base of the unit was quite warm and when I touched it, it was so hot it made me pull away and I grazed the hot plate and burned my hand.
    I then tested the hot plate's temperature and it was over 450F, yet the water in the beaker never got above 180F.
    Ambient temp was about 80F.
    Does this sound normal to you?
    My hot water kettle doesn't get this hot and it boils water in less than 5 minutes.
    Should a heated stir plate get this hot when simply boiling a few hundred ml's of water?
    The thing is supposed to be set up for 2 liters and I imagine to get that to boiling temp the whole unit would turn a dull red as the metal heats up...

    Any help on this would be greatly appreciated.

    Also if you could offer suggestions of heated stir-plates that are reasonably priced that would be awesome.
    If money wasn't an object I would love to purchase an IKA, but those are sort of the Rolls Royce of heated stir-plates, I need something more in the range of a Honda Accord.

    Thank you for your help.


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    Quote Originally Posted by Chris Edward View Post
    Hello All,
    This is my first posting to this forum.
    Welcome.

    I tried using a very under priced no name brand lab heated stir-plate I got off of eBay (I know, I know...) and after testing the unit with about 300ml of water in a beaker to see how long it would take to boil, I waited for over an hour and the water never got above 180 degrees F. I noticed that the base of the unit was quite warm and when I touched it, it was so hot it made me pull away and I grazed the hot plate and burned my hand.
    I then tested the hot plate's temperature and it was over 450F, yet the water in the beaker never got above 180F.
    Ambient temp was about 80F.
    Does this sound normal to you?
    No. If the hot plate was at 450 F, unless the beaker was made out of a bloody good thermal insulator the water should have boiled. When we use them in the lab, even on a setting on 3 or 4 out of 10, water will boil in about 10 minutes. In fact we have to tell our students to be careful not to let their samples boil dry!
    Should a heated stir plate get this hot when simply boiling a few hundred ml's of water?
    Does it have a dial on the front to control the heater power? The ones we use certainly get this hot when on high power. Sometimes in the lab you just need to boil the nuts of something!
    The thing is supposed to be set up for 2 liters and I imagine to get that to boiling temp the whole unit would turn a dull red as the metal heats up...
    I've never seen a hot plate change colour on heating, but ours are normally ceramic rather than metal.


    Also if you could offer suggestions of heated stir-plates that are reasonably priced that would be awesome.
    If money wasn't an object I would love to purchase an IKA, but those are sort of the Rolls Royce of heated stir-plates, I need something more in the range of a Honda Accord.

    Thank you for your help.
    See here: https://www.timstar.co.uk/catalogsea...rrer+hot+plate in our school labs we use the "Stuart 152" series and they are pretty good.


    Last edited by PhDemon; May 16th, 2021 at 03:47 PM. Reason: Typos
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  4. #3  
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    Hello pHDemon,
    Thank you for your reply.

    To answer your question about the heat setting, the hot plate has a dial (potentiometer) with a range, but no number markings or LCD.
    The specs say it can get up to 350F, I figured once engaged at it's lowest setting that the heater would be at about 10% and with the dial set in the 90 degree (angle) position that this would be about 175F or half the heating potential, so I turned the dial to about 112 degrees (angle) or 3/4 of the way to fully on so the heating element should have gotten to about 263F, but instead it got to over 450F.
    Where I live, water boils at 206F so, I figured if anything the 262F estimated setting would be enough to get the 300ml close to boiling temp.
    I realize that the hot plate needs to be hotter than 206F (or 212F) to get the beaker to boil, but it was 300ml of water and not only was the heating plate extremely hot, but the entire unit was too hot to handle.
    That's why I made the comment about wondering how hot it would have to get to heat 2 liters.
    It just didn't feel right and it felt unsafe.
    That's why I thought I would ask and see if anyone would be kind enough to help me out, as you have done.

    Thank you again for your help
    I will look into the hot plates you suggested.

    Quote Originally Posted by PhDemon View Post
    Quote Originally Posted by Chris Edward View Post
    Hello All,
    This is my first posting to this forum.
    Welcome.

    I tried using a very under priced no name brand lab heated stir-plate I got off of eBay (I know, I know...) and after testing the unit with about 300ml of water in a beaker to see how long it would take to boil, I waited for over an hour and the water never got above 180 degrees F. I noticed that the base of the unit was quite warm and when I touched it, it was so hot it made me pull away and I grazed the hot plate and burned my hand.
    I then tested the hot plate's temperature and it was over 450F, yet the water in the beaker never got above 180F.
    Ambient temp was about 80F.
    Does this sound normal to you?
    No. If the hot plate was at 450 F, unless the beaker was made out of a bloody good thermal insulator the water should have boiled. When we use them in the lab, even on a setting on 3 or 4 out of 10, water will boil in about 10 minutes. In fact we have to tell our students to be careful not to let there samples boil dry!
    Should a heated stir plate get this hot when simply boiling a few hundred ml's of water?
    Does it have a dial on the front to control the heater power? The ones we use certainly get this hot when on high power. Sometimes in the lab you just need to boil the nuts of something!
    The thing is supposed to be set up for 2 liters and I imagine to get that to boiling temp the whole unit would turn a dull red as the metal heats up...
    I've never seen a hot plate change colour on heating, but ours are normally ceramic rather than metal.


    Also if you could offer suggestions of heated stir-plates that are reasonably priced that would be awesome.
    If money wasn't an object I would love to purchase an IKA, but those are sort of the Rolls Royce of heated stir-plates, I need something more in the range of a Honda Accord.

    Thank you for your help.
    Reply With Quote  
     

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