Magnetic stirrer / hot plate from scratch.

So I have been doing research for the past year, here and there, on magnetic stirrer / hot plates and have finally committed myself to getting down to business... The reason I want to build my own is simply the matter of cost. Home made is cheap and usually just as efficient.

The questions I have for you guys...

The wire I plan to use is called nichrome and consists of 60% nickel, 26% chromium, and 14% iron which can be bought at enasco.com for only $15.00 plus shipping.

1) -I know that the thinner and shorter the wire the hotter it will get but I need a way to pump up the heat but at the same time control the temperature accurately. I don't know what the parts are called but I would imagine it would be called an amperage / voltage regulator with a knob? I am a noob when it comes to this so please feel free to correct me. lol.

So with a way to amplify the electrical current and then a nother way to control this amplified current I could then use a thicker and longer wire coil. So it would go like this.

[electrical outlet - amplifier - amp/volt regulator knob - nichrome coil]

The amplifier and controller for it is probably why all of the magnetic stirrer hot plates are so expensive online. anyways onto the next question.

Once I have a way to control the heat of the coil from room temperature to 400C I need to figure out a ways to get a magnet right up underneath the heat spinning rapidly on a fan motor which already has three speeds One solution to this is to order a magnetic stirrer and modify it with the above device or I can make a totally custom one. Here is my problem.

When the coil is on there will be electricity passing through it. So I need something that doesn't conduct electricity surrounding it but at the same time I need this electrical insulator to allow a magnetic field to pass through it. A powerful magnet will most likely be used so this most likely wont be a problem. I mostly need help with my first question. Thank you for reading.

Original post restored - DO NOT DELETE YOUR POSTS - moderator.

this is a nice idea of a magnetic stirrer. I use it in labs to mix solutions, i'm also making a centrifuge and a PCR machine and off course magnetic stirrer. let me tell you that magnetic stirrer you want could be of two types. one rotating and other shivering. the rotating type is good to make, but a little costly than the shivering and ofcourse better and preferred. this works on the principle of brushless DC motor. it works on about 9-12 volts and give upto 1000rpm. you need a rod magnet to make it rotate in a beaker. take a computer fan and remove its magnet and fan. keep the non moving parts intact. it has winding on four arms. or make the arms to suit your size from thin sheets of iron. wind a 32-34 guaze wire about 30 feet on each arm. connect it suitably. now take a bar magnet about the diameter of your arms of motor windings. cover it with tape and make it oval to minimise contact with bottom surface. fill a beaker with water and place the magnet in it. keep it on the windings or make a platform on the windings with a non magnetic material. give windings the current and see the stirring. you can manipulate both size and power. i just gave you the idea how it works. for the bar magnet, the rattle snake sound making magnets are the best. Google for it. If you get them you are half done!!!

for a hotplate best is buying it. coz it just costs 3-5 $ and making costs more.
good luck and if you have to make any other lab instruments contact me. we could work together.

Unfortunately the original poster has deleted their initial post.

That's a first. Nigel restored the original message.

No, it's happened before.

Nothing is deleted, every time you edit, the previous version is saved.

I see no point in having a two week limit on editing any more because it's so easy for a moderator to restore the original version, if it's removed.

blueroomelectronics said:

That's a first. Nigel restored the original message.

Click to expand...

No, I've done it on a number of occasions - when posters trash the thread.

You can access the previous versions of your own post be clicking on the lasted edited by link.

**broken link removed**

I've just never noticed it before. I do see it when the OP is a lazy student and doesn't want their professor noticing they were ill prepared and wanted us to do their project for them.

ok guys

Lets stick to the original post mmk. I deleted it because I found a killer deal on ebay and got an old vwr vanlab magnetic stirrer hot plate for 60 bucks. I attached a picture...

I'm still interested in making my own highly precise magnetic stirrer hot plate. Here is the properties I wish it to have.

-Heats up to 550 C
-Temperature can be precisely and accurately controlled with a knob.
-Magnetic stirring up to 2000 rpms.
-Stirring can be precisely and accurately controlled with a knob.
-This will all fit into a 8x8" square box taking into consideration that the shorter the box the better.

If we could figure out how to do this without spending over 300 bucks we would be saving money big time and getting some fun too.

this is the plate i won

still dont know if its worth the money but it's from vwr and I can modify it if I want so what evar

adamalden said:

still dont know if its worth the money but it's from vwr and I can modify it if I want so what evar

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this is a good and a big cabinet as it seems. why do you want 2000rpm? its too high. in this rpm you would spill out even 25ml from a ml beaker. mostly 500-600rpm is enough. if you want to mix at that rpm you need a centrifuge. it can mix at that rpm and 18 ml liquid. the stirrer is not a good choice. and why do you want 550 degree celcius? could you tell me what your project is? at 550 degree celcius you will lose the insulation coating on the windings of the stirrer. the heater can be used upto 100 or 125 degree celcius. still if you want to take the risk you can buy a 1000-1500 watts heating element and cover your winding with 2-3 layers of aluminium foil and the foil seperate the heating element and winding plate with a ceramic plate. also attach a foil to the plate on both sides. this might work. but now since distance to the magnet increases from the winding, you need to make the magnet even stronger. experiment a bit, but i am sure you cn do it. the heating element could be replaced with a induction heater. but at temperatures above 125 degree celcius magnets start losing magnetism. this is a major problem. so dont go for temp. above 100degree celcius. good luck.

Good point, most glassware will burst at 500C.

I haven't tried to mix anything else than food using a blender.

But it's new to me that a centrifuge can be used for mixing. I assumed that centrifuges are used for separation.

Please shed some light on it.

Thanks

Boncuk

Boncuk said:

I haven't tried to mix anything else than food using a blender.

But it's new to me that a centrifuge can be used for mixing. I assumed that centrifuges are used for separation.

Please shed some light on it.

Thanks

Boncuk

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as i have already said i am a medical biotechnologist and we people do all DNA stuff (in your language we call it recombinant DNA technology) our samples are just minute for you to be seen. 1ul and 500pl (pico litres). so to mix these for cloning them we need a homogenized solution. so what could be the way? we use 0.5ml tubes. mix the small contents in it and centrifuge it to homogenize.
here's how it works.
a simple question if you put sopa water with a single bubble in it. and centrifuge it. what happens?

the bubble is first stationary till a few RPM. then it starts moving after that to another few (higher). then it goes into the solution and swims freely (equal densities of both). then it settles at a point at the bottom. take this in case of all molecules in a solution. we spin it to a low RPM just to mix them. not seperate them.

if you understood this... ok!! otherwise google for 'principle of centrifugation'.

Anyone ever seen the internals of a fish filter impeller 'exciter' It's pretty simple, it's an electric motor, except the rotor is hermetically isolated from the actual power unit. If you drop the impeller down the hole it spins... I've had fun with them and making permanent magnets dance. Just trim the plastic around one and use an encapsulated magnet for a quick and dirty magnetic stirrer.

you don't actually need a brushless motor for a magnetic stirrer. I've seen them using a generic motor with a bar magnet attached to the end of the shaft.

Good man!

dougy83 said:

you don't actually need a brushless motor for a magnetic stirrer. I've seen them using a generic motor with a bar magnet attached to the end of the shaft.

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This is true. This dna guy doesn't know what he's talking about. Certain glasses melt at certain temperatures some higher than others. All glass will *burst* if heated to fast. The reason I was trying to get you guys in on such an awesome project is because if you look at all of the products online they don't make them this well... The best ones only go up to 450 C and stir at 1600 rpm. These cost upwards of $500. My quest here is to build something better for less. There are certain types of magnets that resist heat. This is the type the plate requires. Nichrome wire wont melt up into the 1000 C range and ALUMINUM doesn't melt until it reaches over of 600C so at most the hot plate surface would turn bright red (sounds cool to me). The 2000 RPMs could be to much for a beaker but what about a round bottom flask. What about those super thick solutions that just wont stir without the extra power? What I'm saying is this would be an awesome thing for science experiments of all types since with the extra power available so are more possibilities.. borosilicate glass starts to get soft at temperatures above 800 C. That's over 200 C more than the temperature I was shooting to achieve.

Anyways if you guys don't know how to do it I understand since this is not a common project. When my order arrives I will tinker with it and figure out all the stuff we need to make this beast. Even if you don't do chemistry experiments this would still be useful for cooking since the temperature control will be highly precise unlike gas grills or charcoal. You just wouldn't need to install the magnetic stir bar. OH and these things heat up much water than a gas or charcoal grill. Desired temperature is achieved withing seconds in some cases.

You know what! If we could do this 550C 2000RPM plate we could attempt to devise a design that reaches 1000C.

Umm... Why?!

dougy83 said:

you don't actually need a brushless motor for a magnetic stirrer. I've seen them using a generic motor with a bar magnet attached to the end of the shaft.

Click to expand...

have you ever seen a magnetic stirrer? its not magnet attached to the shaft!!! i am using these in my labs from 5 years. i said that the working is like a brushless motor.. i have also repaired a few which go bad due toguys like you not taking care of it while handling.