Stirplate

now i am dumb electric wise but last year did buy a stirplate with power adaptor. question how high to i need to set the voltage on my adaptor all the way to 12volt or less on less the adaptor gets kind of warm

It seems over here that at 5 volts the stir plate works very well, not creating a tornado in the starter…. Yes you will get some heat as the voltage is restricted, would help if they made them with a ground to dump the restricted voltage to, then heat wouldn’t be a by product… Sneezles61

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By adapter do you mean the transformer that is plugged into the wall? How I believe it works without seeing it is, there is a transformer either that either hangs from the 110V AC outlet or is inline in the cord. It converts the 110V AC to 12V DC. On the stirplate there is a dial that is a potentiaometer, (also just called a pot). It is a variable resistor or rheostat. This is what controls the voltage to the motor with a magnet attached, not the transformer. Transformers will get warm but it should not get too warm. The transformer for my notebook gets warm but not dangerously.

Some of the home made stirplates I have seen use a computer fan with a magnet attached. Those are designed for 5V DC and should not have higher voltage.

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Sorry, the electrical engineer in me needs to make a couple corrections.

  1. PC case fans are designed for 9-12V
  2. Controlling motor speed with a variable resister in serial, while it seems to work OK, is a really bad design.

Basically, you’re using all the power the circuit can draw at all times. The variable resistor just bleeds power away from the fan. The problem is that the power is still used, but only to generate heat in the resistor. It keeps the maximum current flowing which keeps that wall wort pretty hot too, and shortens the lifespan of both parts, which both tend to burn when they fail. Considering we tend to leave these things running unattended overnight while our families sleep… I don’t want to be too sensational, or overstate the probability of actually starting a fire, but just don’t risk it, it’s not worth it.

The better approach is to use a voltage regulator, and use the pot to control its output. A 12V wall wort will get warm, but not too hot, if it’s uncomfortable to hold, you’re drawing too much current.

Stir starters has about the best design. It’s a solid workhorse; effective, but still simple enough to DIY.

(I’m not affiliated)

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Now that I think about it, I replaced two fans in our RV fridge with PC fans and sure enough they were 12V. RV fridge company wanted $50 each for them Amazon $17 for four.

I don’t have a stir plate but am I wrong most of them are controlled with an old fashion pot?

Edit: Never mind. I took a look at your link and figured it out.

thanks this makes sense

It does seem to be the go-to for DIY.

I’d imagine it’s what differentiates good equipment from El Cheapo. I’m not sure about Lab-grade stir plated, but I’ve seen them display the actual RPM of the motor. I would imagine if you’re adding an RPM display, a regulator is child’s play…

The better old-school approach is a variac, which is a variable transformer. Much more efficient than a pot, although very similar in appearance. As a kid in the 70’s, my father had a train from HIS childhood in the 40’s, that used variacs to control train speed. A variac adjusts the AC voltage rather than DC, so you’d need an AC motor, or a crude ac-dc converter AFTER the variac, which still makes the regulator simpler. (And waaaaaay cheaper)

the question still remains . my stirplate has no control knop on the plate it self but on the power adapt what plugs in the wall settings from 3v to 12v if i reduce the power dial say to 4v to get less action in the flask the adap gets real hot this does not make me happy

So, operating voltage is only part of it. Somewhere on that wall-wort is either a power output rating (Watts, or milliWatts) or a current output rating (Amps, or more likely milliAmps. Can you find it? And how hot is it getting?

It may be that the thing you have is designed to handle those temps. (The regulator in the design I posted can allegedly handle 150C) My rule of thumb for power bricks is: if its getting too hot to touch, it’s a problem. Those “universal” adapters are generally junk, but that’s just one guy’s opinion.

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must say it does not make me happy now looking into a different stir plate at nb think this one you can control on the stirplate it self on my next order think i gonna buy it

Stirstarter is the one I use I think…cheaper than anything at nb.

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If you are a DIY (Do It Yourself) kind of person, then you can “build” one yourself, without having to solder anything…

I simply purchased a Pulse Width Modulation (PWM) controller on Amazon for $6.99, along with a 12 volt 500 mA power supply from eBay for $3.99. I already had a spare PC fan on which I mounted two rare-earth magnets that I salvaged from an old PC hard-drive. The last thing that I purchased was a 40mm stir bar from Amazon for around $8.00.

The four electrical connections only require a screwdriver, and I mounted everything in a box.

In layman’s terms for this application, the “Pulse Width Modulation” controller is something that quickly turns the power on and off. As you turn the dial to the right, the PWM controller simply increases the time that the power is on; as you turn the dial to the left it simply decreases the time that the power is on. In other words, you no longer have to worry about the power supply, or other electrical components, overheating…

I could have bought a cheaper stir bar, but all in all I only spent a total of $19.00 on my stir plate.

In case anyone is interested, here are links to the items that I purchased:

P.S. I am not affiliated with any of these sellers.

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Sales man… SNS is better! :grin:
Sneezles61

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