Chemist1357
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Brand new hotplate won't boil water?
After spending $300 I'm furious to say the least. The window to return the product has lapsed. The brand is "Four E's Scientific" and it's rated to go
280c. I put the probe in 200ml of water and after 1 hour the hotplate won't go above 96c. I have the temperature cranked all the way up to 280c and it
still won't go above 96c. My infrared thermometer says the plate is 220c+ but the water won't get past 96c.
Is there anything I can do to fix this? I just read reviews and it seems to be a common thing. If I can't fix this can anyone recommend a good
hotplate/stirrer with a temperature control probe that is NOT made in China.
[Edited on 20-3-2023 by Chemist1357]
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blogfast25
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First and foremost, check BOTH your thermocouple and IR thermometer, the discrepancy is oddly great.
Secondly, check temperature setting on device.
Thirdly, contact vendor/manufacturer anyway, you never know...
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Rainwater
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Check the manual
https://images-na.ssl-images-amazon.com/images/I/91UOqMS+OuL...
Page 9
There is a upper tempature limit setting.
A screw next to the power switch.
"You can't do that" - challenge accepted
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blogfast25
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Well spotted!
Turns out that my own recently bought heater/stirrer also has a max temperature safety that I didn't know of! 
[Edited on 21-3-2023 by blogfast25]
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Dr.Bob
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The other main issue is how many watts does it consume at max? many good hotplates are 600+ watts, but the cheap ones tend to be 200-400 watts, and
that won;t heat much other then the top of the hotplate to a high temperature. I would go with a used Corning hotplate any day over any
"new"Chinese one. The Corning 320 or 420 models are both great, and I use them both daily, and all of mine are over 12 years old.
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BromicAcid
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Also, even though you paid a good chunk of money for it. Precision can be expensive, it might not heat as well as you want but it might be designed
to hold a specific temperature range well or to adjust fast or even interface with some external piece of equipment. When I was doing chemistry in my
back yard I had one long thermometer, as long as any other that only covered from -10°C to 0°C (I won it in a lot) and I always thought that was odd
till I got in the industry and realized that precision costs money.
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Chemist1357
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I tried that, made sure it was all the way up to 320c.
Still didn't do anything.
Looks like it's new hotplate time.
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Texium
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Quote: Originally posted by BromicAcid  | When I was doing chemistry in my back yard I had one long thermometer, as long as any other that only covered from -10°C to 0°C (I won it in a lot)
and I always thought that was odd till I got in the industry and realized that precision costs money.
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The perfect tool for when you need a very precise read on the temperature of your salted ice bath! 
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Rainwater
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If i was in your shoes, I'd rip it apart, ohm out the heating element.
Calculate total wattage. Or just read the lable and see how many amps ot pulls. But thats no fun
Determine how it's powered (pwm, triac, relay). All this can be determined with an amp probe without disassembling anything, again. No Fun
So, for every ml of water, it needs 4.19 watts of power to raise the temperature 1 degree C (without changing states)
To boil 1000ml ( 0c liquid ~ 100c liquid), you need to introduce 419000 watt of power ( watts = joules)
plus your total thermal losses.
For 30 minutes, that 233-watt heater
20 minutes, 350-watts
10 minutes, 700-watts.
All UL rated heaters have a thermal limit, which provents the device from exceding a set temperature.
Let's say your wattage is sufficient and the hotplat is reaching the maximum temperature its rated for, but your water is still not boiling.
The 3 factors I have had to fix myself are thermal losse, thermal conductivity, pid settings.
Is the bottom of the beaker perfectly flat?
Is the hotplate perfectly flat?
Is the hotplate turning off more as it approaches the set point?
Quick test for good contact. With the appratus cool, wet the bottom of an empty beaker, and place it onto the plate.
Watch the water pattern as you set the beaker down. Notice any voids, puddles, bibbles. If you see them, this is likely a problem
A few layers of aluminum foil under the beaker can fix this.
Thermal losses can be beat by using an insulated wrap that is compatability with the reagents your using.
Pid setting can be tested by repeating your above described experiment with the pt1000 sencer located laying on the table top. And at room
temperature.
This will cause the controller logic to keep applying heat.
And remember, if hitting it with a hammer doesnt fix it, hit it harder to get a new one
Good luck
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Fyndium
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Do not buy Chinese hotplates unless a specific recommendation for a specific brand or type is given. Most of them are garbage and have little to no
other than superficial heating power and the stirrer units mostly suck. They can get to 400-600C - when you measure it at the heater element, but they
are incapable of heating anything smaller than few dozens of ml at most. Hotplates are generally good for smaller volumes only anyway, but these are
next level garbage.
Yes, I paid for a lesson a decade ago and had the exact same issue. It was barely able to simmer a few hundred mL of water after an hour or two of
heating.
Some heating mantles, at least those with good reviews, seem to be better, but they aren't neither professional quality.
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PirateDocBrown
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I suspect these Chinese ones are made for any market, and when they sell to countries with 110V service, they just install a power cord for that, and
ship it. The element and controls are still for 220V.
Since you have nothing to lose, try a step up transformer, and test it on double voltage.
Phlogiston manufacturer/supplier.
For all your phlogiston needs.
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Rainwater
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Very good point. For multiple operation a 2 element design is comminly used. For 120v the heating elements should wired in parallel, 240v they will be
in series.
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Cathoderay
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| Quote: Originally posted by PirateDocBrown | I suspect these Chinese ones are made for any market, and when they sell to countries with 110V service, they just install a power cord for that, and
ship it. The element and controls are still for 220V.
Since you have nothing to lose, try a step up transformer, and test it on double voltage. |
I wouldn't do that. If your suspicion is wrong you could damage the control circuits.
If it was just the heating element then it might not be as bad.
Many times there are internal connections that are changed to accommodate the different line voltage.
It is odd that the infrared thermometer says 220 C but the water in the beaker won't boil. If the plate was that hot you should be able to put some
drops of water directly on the plate and it should boil away very fast.
As Rainwater said you might have a problem with contact or heat loss.
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Cathoderay
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Also I think that many people put too much stock in those infrared thermometers.
Among other things the emissivity setting has to be correct for accuracy.
https://www.thermoworks.com/infrared-thermometry101-limitati...
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Sulaiman
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No mention yet of the rated power of the hotplate,
which should have been a very important part of the selection process.
This and similar lower powered hotplate stirrers are only intended to keep liquids at a near constant warm temperature, and stirred.
For cost reasons, I doubt that there is a dual heating element.
As mentioned above, measuring the resistance of the heating element will give an actual power rating.
eg W = V2/R (V = supply voltage)
I've never owned a beaker with a completely flat bottom - are they common ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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Rainwater
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In my collection. No i put aluminum under everything.
Manual says 600watts 120/240v. An amp probe will reveal the accuracy of that manual
watts / volts = amps
120 = 5 amps
240 = 2.5 amps
Actually from the specs, it looks like a good one
24 month warranty.
600w heater
55mm × 10mm stirrer magnet
Only thing im not liking is the required use of an external pt1000 probe.
I would cutin a switch and install an additional sensor onto the underside of the hotplate so the external probe would be optional
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Chemist1357
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The voltage where I live is 220-240. We use the same plug as China. I did put aluminium foil underneath and it did absolutely nothing. I have a
Chinese heating mantle that blasts through heat so it just seems this one is junk.
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Sulaiman
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Have you raised this issue with the seller yet?
I would expect a full refund.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Cathoderay
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I don't have one of those Chinese hot plates, however from various sources of info I think there is a sensor in the hotplate that is selected if you
do not plug in the external probe.
From watching some NurdRage videos, some have two sensors under the plate, one controls the temperature and another is attached to the
over-temperature safety limit. NurdRage had a hotplate were the temperature sensor failed and he was able to replace it. The display would
continuously show the maximum possible temperature but the plate was not heated at all.
https://www.youtube.com/watch?v=Xa2OMNaHn_Y
I think the thermal design of those Chinese hotplates is not very good. The heating element itself may reach the correct temperature (that is where
the sensors are) but the heat does not make it to the metal plate very well.
I doubt very much the plate can be at 280 C and the water isn't boiling. You would need to have an insulating blanket between the plate and the
beaker.
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Rainwater
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The manual says do not operate with out the external sensor. If return/refund is no option, its time to go unpluged and dive deep into a crappy fake
to see if its useable. My guess would be a simple defect.
Things to look for
Missing/burnt components
Lose connections
How well the heater and hotplate are joined, is there thermal paste. Pay close attention to this part
Thermal limit sensor likely to be a pt1000 do to the external probe, (same hardware can read both)
There will be a minimum of 2 wires going to the heater connected to the board, ohm them out.
If your qualified, plug up the unit and check the voltage going to the element. Dont get killed.
And pictures, top down, text and color bands in focus.
These things are usually very easy to fix do to the unit, kinda working.
Ive gotten full refunds on a lot of equipment that hasnt worked and is to expensive to ship back
managed to fix most of it.
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Chemist1357
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I would have but I bought it months ago and never used it so it’s passed the window to return it
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Sulaiman
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I have quite a lot of free stuff from China due to claiming refunds,
sellers rarely want to pay return shipping so I get partial distillation kits, often repairable electronics etc.
I used to bargain for fair compensation with sellers
but I got so much hassle that nowadays
I test on arrival and claim in full from the seller platform if any problem.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Texium
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Thread Moved
5-12-2023 at 14:05 |
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