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radiance88
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What exactly should you look for in a hot plate?
I'm thinking of buying mt first hotplate, being a budding science freak and all. After buying my beginner's set of electronics stuff, which I am
purchasing this weekend (multimeter, breadboard, power supply and DIY kits), next up on my list is a hotplate.
However, after scouring the internet, I'm still trying to come to a definite criteria as to what I'm looking for.
In another thread on cheap hotplates, someone mentioned that digital hotplates on the cheaper side have a tendency to not even gain an accurate
reading on the actual plate temperature itself, especially at higher temp settings - thus making the point of getting an economy-class digital
hotplate not exactly a great deal. This is considering you still have to use a sensor to actually gauge the accurate temperature and adjust likewise,
and their analog versions will always be cheaper.
I was wondering then, why can't we just use a regular kitchen hotplate and a thermo-sensor instead buying something that doesn't even work the way
it's intended to?
You also, have aluminum, ceramic tops, stirring and a bunch of other features or attributes that I'm not really sure are useful or not..
Anyway, what I'm really looking for here is a set of guidelines to help a first-time buyer like myself understand what I should be looking for, what
to avoid, and what works without spending half a year's savings on one of these things. I've searched around on the net for guides towards this thing,
but most of everything I've seen so far are geared towards hotplates for cooking.
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greenlight
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I would stay away from the cheaper digital reading hotplates on ebay as I think they wouldn't work effectively for very long and would end up breaking
or giving wrong temperature readings as you stated.
Definitely buy a hotplate with a stirrer as it helps with just about every reaction you will perform on it and is much easier than stirring with a
glass rod the whole time.
I usually just use a thermometer in the mixture I am heating to determine temperature.
I use an IEC aluminum top stirrer/hotplate combo and have had it for 5 years now and haven't had any problems with it at all. It is this one: https://www.scientrific.com.au/product.php?p=1179
I think it is worth paying the extra money for a good one and not a cheap Chinese brand and definitely get a heating/stirring combination.
Another really good brand is Corning and there's heaps of them on ebay.
[Edited on 15-1-2015 by greenlight]
[Edited on 15-1-2015 by greenlight]
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Praxichys
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It depends on the type of chemistry you will be doing.
For your first one, get the $20 cooking hotplate from Wal-Mart.
Every time you think "I wish this thing did xxxxx," write it down, and then after a year or so you will know exactly what you need.
I started with a Scholar 170, which ended up being an overpriced mistake, and works exactly like a cooking plate.
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Mailinmypocket
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I bought a nice used Corning PC-420D on eBay maybe 2.5 years ago for 230$ (plus around 40$ in effing duties, yay borders) and it still works like a
charm. On a side note; does anyone use induction hot plates for anything in the lab? They seem pretty neat but only heat certain metal vessels, maybe
useful for oil baths?..
Note to self: Tare the damned flask.
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Dr.Bob
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Induction heating works best in cast iron, will also work in some stainless pots, but not really used in labs that I have ever seen. I have even
seen IR heating (like on some ceramic cooktops) in limited uses in labs. A simple Corning hotplate/stirrer (~$100 or so on Ebay) will do most things
you need; finding an accurate temperature controlled one will up the price a lot, in most cases. I have done chemistry for 25+ years using simple
stirring hotplates, and for most of the jobs they do, a simple one is fine. They are good for heating water and other non-flammable solvents in a
beaker or erlenmeyer, heating oil baths, stirring magnetic stir bars in rbfs being heated either via a bath or a heating mantle, developing TLC
stains, and many other tasks.
I use the stirring more often than the heat, as many organic reactions simply need stirring overnight to go to completion. But without stirring,
many reactions will not go well, especially if they are heterogeneous (using solids that don't dissolve completely), which is common (K2CO3, silica
gel, resins, NaH, etc). But be careful, while you can heat some organics safely in them, like DMF, DMSO, high mw alcohols, etc, I do not use them
for OPEN containers of methanol, ether, hexane, etc, as those are very low flash point solvents, and fumes from them when hot will often ignite just
from the motor, switches, thermostat, or any source of ignition. If the solvent is in a rbf with a condenser and nitrogen bubbler, then fine, you
can heat with a bath and be safe.
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Mesa
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Be aware if you choose to go with the re-purposed household hotplate + variac combo, that most of these domestic style hotplates do not use spark-free
fuses. They aren't suitable for distilling flammable solvents etc.
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Zombie
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I set up a small distillation rig, and quickly found the flaws mentioned here. I also found a solution without breaking my piggy bank.
This will go hand in hand with your budding interest in electronics as well.
On line you can buy a PID controller.
http://www.ebay.com/itm/100-240V-Digital-PID-Temperature-Con...
What you do is by-pass the thermosister/temp controller on whatever hotplate you have. Just cut/splice the single wire going in, and out of that
controller
Now you can cut the power plug off the plate, and wire it direct to the PID. The plug you just cut off is now the power plug into the PID.
There are several temp probes that you can get when you place your order. They vary in length/temp ranges so figure the broadest range you will need,
and ask for something in that range.
This will make any hotplate (20 bucks) into a precision instrument. (+ or _0 .5 degrees).
The best news is if/when you graduate to a more task specific plate you still have the PID for other uses.
Incubators/freezers/hot tubs/water baths whatever.
There are loads of Utube vids on PID's so you will not fall flat on uses or info on how to wire them up.
They tried to have me "put to sleep" so I came back to return the favor.
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bismuthate
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Make sure it can reach a rather high temp. Don't buy things that only go up to around 100C for just boiling water.
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Zombie
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This will depend on what you will be using it for. I did buy a proper stirrer/hotplate (149.00 DesChem) with the thermo-coupler/stand/clamp. It does
only go to 100*c but ZI only need it for acid/base extractions, and feel safer using lower power on an open beaker.
This is just MY OPINION but for higher temps, a mantle, and boiling flasks/round bottom flasks are better suited.
Boil overs/puking are controlled, and sp=ills are less likely.
Just my opinion.
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radiance88
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One thing that I think I'd need a hotplate for is to do a lot of OTC and hardware chemical purification. I'm definitely planning on trying to distill
toluene from solvents/thinners, as well as distilling my own ethanol from sugar/yeast mash.
The thing is that chemicals really aren't available to hobbyists here, and I can't really get anything in a pure form here for experimentation - so
all of my reagents have to be purified from something else, as the legal climate here is quite harsh and dictates all the non-availability of them
towards the budding hobbyist chemist. So the thing is that any reagent that I can look to get is something I'd have to purify or repurpose from
something else. Heck the only reaction I've really observed to date is muriatic acid combined with eggshells.
So I think that I'd probably be looking for something that reaches pretty high temps, but doesn't have a predisposition for making things go boom? I'm
worried about some part of the hotplate being able to ignite volatile vapor. I also wonder if that's even a valid concern if I just work under strong
fumehood ventilation?
I'm actually very interested in the whole DIY hotplate/heating mantle idea. It's one project that in particular I'd love to do, but at the moment my
miniscule electronics knowledge is too scant for me to have enough confidence to try and pull that off just yet.
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aga
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A Stirrer is the thing you want with a Hotplate.
http://www.ebay.co.uk/itm/BUYLOWPRICE-Origin-New-hot-plate-m...
$150
All i can tell you is that it still works, and i have had it for about a year.
Mine now looks significantly different to the ebay photo, as does the area around it - in all dimensions - but that was me Learning, nothing to do
with the quality of that particular hotplate/stirrer.
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Zombie
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It sounds like distillations, and reactions requiring collection are more what you are interested in at the moment.
A hotplate really won't meet those needs. You need a mantle/stirrer.
The reason goes back to the round flask, and it's versatility. You can rig it to distill, and collect gasses. Set if for vacuum distillations to
reduce energy consumption. Set it for gas thru solvent reactions/collections.
This type set up is also less expensive in glassware, as well as being safer. The ground glass joints are more common in round glass vs. Erlenmeyer
flasks.
Prices for mantles are about the same, and you can add on different elements to vary the size of the flask.
One thing that is mandatory is a lab rack. All your glassware needs to be supported wit a mantle but you can piece meal these rigs, and most of it can
be bought at the local hardware or just found around the house.
Be Safe!!!
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radiance88
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Wouldn't it just be possible to get a hotplate and make a sandbath of some sort on top of it instead of buying a heating mantle? So as to keep the
magnetic stirring option but spread the heat evenly like mantles do?
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Zombie
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Sand is an insulator. It will not efficiently transfer heat. In fact it will draw heat from your glass.
Mantles also come with stirrers for the same price as a hot plate.
It took me awhile to come around to the benefits of mantles. That is actually my next large purchase, and honestly I wish I bought that first.
I'm certainly not trying to talk you into something. Especially because I am as new to all this as you.
I simply see the bigger picture (for me), and I realized a mantle, is Much more versatile / safer / efficient.
Maybe try searching the forum, and the net on hotplate vs mantle.
I'm gonna give it a shot, and see myself. Hopefully someone else w/ more experience can chime in, and help us both.
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Dr.Bob
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Quote: Originally posted by Zombie  | | Sand is an insulator. It will not efficiently transfer heat. In fact it will draw heat from your glass. |
That is not quite correct. Sand is not as good a conductor as water, oil, or metals. But it does work for a bath if you are patient, I have used it
several times when having to use a large mantle for a smaller flask, or to heat odd shaped flasks in a bath that do not fit into a mantle, like a
erlenmeyer or cylindrical flask. It just requires slow heating, which is best for most reactions.
If you have a hotplate/stirrer, then you can use it to stir reactions also when using a heating mantle, so that is my favorite solution. Plus, you
need to buy several sizes of heating mantles in normal practice, plus some sort of voltage/current regulator. If you just use an oil bath, you can
heat nearly any flask (up to about 1L) on a normal lab hotplate while stirring as well. So I would agree that a stirring hotplate is one of the
first tools that an organic chemist might want to procure. But you really only need one, so that is a good purchase, and you can always add a
heating mantle to that.
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gdflp
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| Quote: Originally posted by Zombie | Sand is an insulator. It will not efficiently transfer heat. In fact it will draw heat from your glass.
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No, actually sand baths are often used for heating flasks evenly. The sand has an extremely high melting point, so it doesn't suffer the temperature
limits of water baths, but at the same time it has a large thermal mass and can keep the flask at an even temperature. Another option is using copper
or aluminum shot, as it serves a similar purpose but is more conductive. Personally I use these, since I have access to a business address, I got a free sample which contains about 150ml of beads. This is more than suitable for a bath
for a 500ml flask.
[Edited on 1-16-2015 by gdflp]
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Zombie
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I see the point. IF the sand is heated it will transfer that heat.
At the risk of distracting from Radianca's thread, Can you use a conductive material like metal in a Mantle?
Isn't that like doping metal into a toaster?
Just to clarify... This is the type mantle I am referring to. Different "sleeves" are available for 30.00 USD to work with 250/500/1000ml.
http://www.ebay.com/itm/1000ml-300W-110V-Electric-Temperatur...
Just trying to show the options, and keep the idea clear. Thank you Radianca for your indulgence.
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pepsimax
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If you want a respected heidolph plate/stirrer I have one for sale. New they are over $1700.
I'll sell it for 200gbp. Pm if interested
It has a separate control unit apart from the the temp dial that will use the readings from a probe in your solution to keep it within 1'c for as long
as you need.
It is a serious bit of kit.
[Edited on 17-1-2015 by pepsimax]
[Edited on 17-1-2015 by pepsimax]
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Zombie
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There ya go Radianca. Problem solved!
They tried to have me "put to sleep" so I came back to return the favor.
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radiance88
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I've been looking at different models. The cheaper ones are analog, while the more expensive ones tend to be digital. Is there any appreciable
difference between the two though? Or does this all boil down to just bells & whistles?
From what it seems, analogs need you to insert your own thermocouple and temp reading device, and you have to finely adjust and readjust by hand to
get the needed temperature, is this correct?
And with digital plates you can just set a temperature and be done with it?
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subsecret
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Mantle vs hotplate depends on what sort of chemistry you're doing, and on what scale you're doing it. If you're using beakers or less than 250 mL
RBF's, a hotplate may be the best thing to get. If you're going bigger, than a heating mantle is the best thing to get. If possible, buy both of them
if you can find them cheaply enough. I've also seen aluminum heat transfer blocks for hotplates, which basically convert them into hemispherical
heating mantles. If you can't find any, you could pretty easily cast one out of aluminum yourself. Don't forget that an oil bath can work as a heating
method, but you have to wipe oil off your glassware.
I don't really trust the digital readout on my hotplate. There's no way for it to measure the actual temperature of the reaction, just the temperature
of something underneath the surface. It'll maintain the temperature, but it may not be what is shown on the display. So it might be good to get to
know your digital hotplate if it's like that. Of course, if you need precise regulation, a PID controller hooked up to the hotplate could to that
easily.
I bought a 500 mL "Thermowell" heating mantle first, which has a ceramic core instead of fiberglass. I later spotted a Corning PC420-D hotplate at my
local education supply store, which only cost 70 dollars, so I bought it.
Fear is what you get when caution wasn't enough.
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radiance88
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Yeah that's what I've been reading about - that even if you get a digital hotplate, the reader accuracy isn't going to be anything spectacular or
worth the extra money put into it versus what you could've gotten as analog.
But then I think that's why when getting a digital hotplate, one should definitely get the one that allow you to attach your own thermocouple that you
can drop into your solution? That would seem to be the best bet - otherwise it would seem to be a great waste of money - as I'd think the sole reasons
for going digital are the conveniences of "setting and forgetting" and pinpoint accuracy. If I can't even have those, the whole extra money spent
seems to be a moot point.
Ideally, I'm looking for a one in all solution. My plan is to get a hotplate, and then make some kind of bath or heating element that I can place on
top of it that would fit snugly around my RBF's. That way I can have full flexibility to do unorthodox stuff like distilling solvent out of hardware
chemicals cans like I've seen in youtube videos.
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Zombie
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The PID suggestion is really quite elegant. Any inexpensive stirrer/plate can easily be adapted to run thru a PID / SSR set up. You can get them on
FleaBay for 20 bucks, and loads of info for setting them up is available.
If you haven't already... Look up DesChem on FleaBay.
I bought my anolog stirrer plate thru them for 129.00 USD shipped, and it came complete w/ a stand/clamp/thermocouple.
They are running them on sale now.
100*c is the limit tho. High enough for everything I am doing ATM.
They tried to have me "put to sleep" so I came back to return the favor.
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radiance88
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Also, it would appear that there are definite pros and cons between choosing a ceramic top and aluminum.
Aluminum heats more evenly but unfortunately can be quickly tarnished due to it being a metal, and more possibly reactive to whatever might be spilled
onto it. These in general seem to have lower max temps, about 100 Celsius lower as compared to ceramic.
Ceramic top hotplate generally have higher maximum heating temperatures, but are quite sensitive to thermal shock, which isn't the case with aluminum.
So.. if you put them through a quick change in temperature they can and will crack. They are easy to clean up, but don't heat evenly nearly as much as
aluminum. It is not recommended to place metal objects on these in order to avoid potential thermal shock.
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radiance88
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So I've purchased a used Corning PC-520 today off the only person in my country on eBay who had a hotplate for sale. I got it for about a hundred
dollars, which I consider a steal considering that buying anything at all outside of the country is going to cost that much alone in terms of
shipping. I'm pretty sure he couldn't find anyone to buy it taking that into consideration as well.
Sure, it isn't digital, but I guess I'll just use the thermocouple from my multimeter and drop it into the beaker.
I can't wait to take it for a test drive when it arrives. It's a 120V appliance though, and my country uses 220V. I have a couple of power supplies
lying around, one rated for 250 watts and another for 750. The hotplate is rated for 1060 watts.
Will it be okay if I plug it into my 750 watt power supply? Or do I really need to go out and buy a power supply that goes above that 1060?
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