Sciencemadness Discussion Board

Burnt hotplate cord

Murexide - 8-10-2019 at 00:37

As many amateur chemists have experienced, I had the unfortunate experience of allowing my hotplate cord to contact the hotplate for a few seconds. After realising, I immedaitely removed the cord. Around 0.5 mm of the plastic covering to the cord was burnt off, but none of the contents were visible. I removed the small plastic deposit on the hotplate and wrapped the exposed cord with electrical wire.

The hotplate should now be fully functional and hopefully safe. Are there any obvious unforseen dangers that I am missing?

markx - 8-10-2019 at 02:06

Change the cord out for a new one that is undamaged. The conduits might not be visible, but the internal insulation might have become damaged by the heat and may cause a short after being bent or wrapped in the wrong way.

Murexide - 8-10-2019 at 02:21

The cord is attached internally and leads directly into the hotplate. Is it still possible to replace such a cord?

Ubya - 8-10-2019 at 02:49

Quote: Originally posted by Murexide  
The cord is attached internally and leads directly into the hotplate. Is it still possible to replace such a cord?

by opening the case of your hotplate, yes

wg48temp9 - 8-10-2019 at 03:32

Quote: Originally posted by Ubya  
Quote: Originally posted by Murexide  
The cord is attached internally and leads directly into the hotplate. Is it still possible to replace such a cord?

by opening the case of your hotplate, yes


and there is a good chance the power connections are push on spade connectors so you could replace the lead with one salvaged from some other equipment but make certain the conductors are the same size/large or the salvaged equipment has the same or greater power rating.

Alternatively just cut the lead at the damage point and put a plug on it and if needed use an extension cord.


Tsjerk - 8-10-2019 at 03:50

You could cut out the damaged part and reconnect the wires with something like this. Then put some tape over the connector.

Praxichys - 8-10-2019 at 05:12

If you're worried about it, just cut out the damaged part and make the cord shorter. I've done this a couple of times having accidentally cut cords with both a circular saw and an electric edger.

Cut out the damaged area, strip both ends, slide small heat shrink tube over each conductor and a large one over the whole cord, twist conductors together, solder, shrink the tubes to cover the conductors, then shrink the larger one to contain the others. For my outdoor cords I usually put some silicone caulk or dielectric grease under the heat shrink to waterproof the whole thing.

As mentioned, most strain reliefs are standardized and you can probably find a replacement cord if you're willing to open the case.

Deathunter88 - 8-10-2019 at 07:03

Honestly you're better off keeping it as is, you might just make it worse by trying to replace it. Based on your description of (a few seconds), I have no idea why people think the internals could be damaged, unless your rubber suddenly changed into a superconductor of heat.

woelen - 8-10-2019 at 07:08

I agree with Deathunter88. As long as the cord is not damaged too much, keep it as is. Wrap some tape around it, just to be sure. I myself have similarly damaged cords on some equipment, with dents in the isolation of half a mm or so. No problem at all.

If you take apart the heater, then you may introduce a bigger risk of electrical shock, if things do not fit nicely together after replacing the cord.

phlogiston - 8-10-2019 at 13:08

Hardware stores sell special heat-resistant cords for equipment that gets hot, like a clothes iron. The outer coating looks like it is some kind of fibrous ceramic material. They are inexpensive.
Seems like a better replacement than the usual rubber or PVC cords.

SWIM - 8-10-2019 at 13:48

So I'm not quite clear on what you mean by hotplate.

If You're talking about a Corning or other lab type hotplate, especially a nice brand like Corning, I might be tempted to try some of the recommended fixes above.

But if it's like the hotplate I used for many years which was just a single burner kitchen hotplate I bought for $15 (USD) Then I'd just leave it the way it is.

The damage is shallow and you taped it up. That ought to do.

My old hotplate was the kind where the stuff to be heated sat on a flat metal coil that would get red hot when turned up.
I think back on all the reactions I did that way (Even making some pretty nasty stuff) and I'm amazed that I never cracked a flask. I even used to heat RBFs on that thing, with the coil contacting maybe 2% of the flask.

Either I was very lucky, or Ace Makes some great glassware.
(Probably a bit of both)




Murexide - 8-10-2019 at 17:04

So the hotplate is a cheap ebay hotplate magnetic stirrer sold widely. Doesn't have temperature control functionality, used to be sold for about $50.

You can't find them anywhere now, they're replaced with the tempearture control variant (it says up to 100 degrees C, but I think it actually can go a lot higher -anyone have any experience with these - https://www.ebay.com.au/itm/Value-1000ml-Magnetic-Stirrer-Mi... ).

I have very little experience with electronics and as a result any modification I make will probably make the situation worse.

Here's some photos of the hotplate / damage for reference (last photo shows damage)




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Deathunter88 - 8-10-2019 at 17:53

Quote: Originally posted by Murexide  
So the hotplate is a cheap ebay hotplate magnetic stirrer sold widely. Doesn't have temperature control functionality, used to be sold for about $50.

You can't find them anywhere now, they're replaced with the tempearture control variant (it says up to 100 degrees C, but I think it actually can go a lot higher -anyone have any experience with these - https://www.ebay.com.au/itm/Value-1000ml-Magnetic-Stirrer-Mi... ).

I have very little experience with electronics and as a result any modification I make will probably make the situation worse.

Here's some photos of the hotplate / damage for reference (last photo shows damage)




You are fine.

Sulaiman - 8-10-2019 at 20:02

Based on the photograph, I would just wrap some pvc tape over the melted area and not worry about it.
As the damage was casued by a brief exposure to high temperature it is likely that the internal insulation is OK.