"Upgrade" your hotplate

[stupid939]

I'm guessing that most of the guys that are serious about making explosives use quality hotplates. But what about all the other guys that use cheap hotplates from places like Wal-Mart? This is for those guys.

I was skimming through one of my many catalogs that I get from companies and I saw something labeled "Temperature Controller Kit". It is a kit (needs to be soldered together) that holds a relay (not included) closed until the temperature reaches a certain set point. When it gets to that point, the electromagnet lets loose and completes the circuit for whatever you want. The temperature is adjustable, but you would have to test it and mark where each degree changes on the variable resistor (or whatever it is).

When I saw the kit, I immediately though about using it for a cheap hotplate. I have read that many people on this forum use cheap hotplates from Wal-mart or similar stores. This would be an alternative to buying expensive hotplates, and you could "upgrade" your cheap brand for about $12 plus shipping.

I have a VWR Scientific Hotplate/stirrer, and I believe that the temperature control circuit is very similar to what this one's. It heats up, and once it reaches the set point, it turns on and off maintaining a temperature.

All that you would need to do for this hotplate is:

1) Solder the kit together
2) Add the relay
3) Splice one of the wires of your hotplate's cord
4) Connect them to the relay
5) Connect the circuit to a wall wart (dc power supply)
6) Flip it on and mark each degree

I don't know if you could get the kit somewhere else, but to cut down on shipping, I would get all of the components from the same place. The links to the different things that I found are:

Kit - http://mpja.com/directview.asp?product=5289+RB
Power supply - http://www.mpja.com/productview.asp?product=16398+PD
Relay - http://www.mpja.com/productview.asp?product=12986+RL

I do not know that the relay would work, but I'm guessing that it would if you get a power supply that is 12V or higher. The Kit says that it works from 6-15V and will sink up to 100 mA to the relay. That said, I think that the power supply would suffice, but I am not too electronically inclined (but maybe a little more than some of you guys).

Depending on how much your hotplate costs (I would guess from $10-20, but I will use $20 here), then I would say the temp. controlled hotplate would cost around $32 plus shipping and handling. That seems like a better price than a few hundred dollars.

Let me know if you guys see any flaws to my "plan", and if someone does decide to construct this, let us know how (if) it works.

Here is a link to a picture of what it could look like. I threw it together in photoshop.

http://stupid939.tripod.com/hotplate

If any of the links don't work, try to copy and paste in the address bar.

[tmp]

I used one of those coffee warming hotplates for many years. I had to
constantly monitor the temperature. This is until I found two of the
variable-rate(one a dual burner !) on eBay for a relatively low price. What
you've done is an excellent workaround if you're limited on funds and can't
afford those overpriced units from scientific supply houses. Good job !

[DonS]

The "Temperature Alarm Kit" photo seems to have two potentiometers. To me, it seems likely that those allow for adjustable hysteresis; that is, it not only controls the temperature at which the external relay opens, but also the temperature at which it closes again.

If the above is true, adjusting the unit for various hot plate temperatures might be somewhat difficult (or, at least, a bit tedious). You'd want the two "trip points" far enough apart that the relay wasn't buzzing, but not so far that you get wide temperature swings. Once you had it set, though, it would likely be very stable - much more so than hand-controlling a cheap hot plate by itself, or the device I describe below.

The electric burner I've been using (Toastmaster TTS1, $15 US) uses what appears to be either a bi-metal strip or a piece of spring steel in series with the heating element. Once this component reaches a certain temperature, it "clicks" open and begins cooling; after it has cooled enough, it clicks back, closing the circuit again. Rotating the unit's control knob moves, very slightly, one end of the strip, changing the threshold temperature(s).

This device probably isn't as accurate as the arrangement stupid939 presents, but it might be another alternative for the budget-limited.

[Hirudinea]

What about using an electric skillet or frying pan? They usually have a temperature controll and can be bought fairly cheap at Goodwill.

[jellywerker]

Exactly, but the temperature control usually isn't very accurate. This allows you to modify a cheap hotplate/skillet into a decently precise hotplate. I'm still just scanning ebay for a decent used one with a chem resistant ceramic top. I don't want to see what various acids would do to a metal hotplate (with electricity running through it, naturally) in the case of an accident. Of course using a sand bath or water bath also helps precision a bit.

[stupid939]

An electric skillet or frying pan would work, but I don't know how well they maintain the temperature. As with the hotplate I described, you would most likely want to use a water or oil bath to keep the temperature even more constant.

Most of the time the skillets or frying pans go up to around 250*C and there are not very many increments. They usually go by 20-40*C increments, and for most synths, you want to keep it in about a 5*C range. It may be hard to control this, but I cannot speak from experience.

You could also add the circuit and relay to the skillet or frying pan and hook it up the same way, and it would probably control the temperature better. Especially with a water or oil bath.

[c.Tech]

and for most synths, you want to keep it in about a 5*C range. It may be hard to control this, but I cannot speak from experience.

If you wanted to keep the temperature at 5*C you wouldn’t need a hotplate in the first place, just a cheep thermometer and an ice bath or fridge (possibly a bar fridge just for your chemicals like me. :))

[nbk2000]

c.Tech, I don't know whether to think that you're attempting a joke with the above post, or if you just don't understand what was written. :rolleyes:

[Cobalt.45]

"possibly a bar fridge..."

Enough said.;)

[deadman]

It looks like c. Tech thought he meant at 5 degrees not the increments that stupid969 meant. It was 3:29 am afterall. It happens.

Cobalt what do you mean enough said by "possibly a bar fridge...". I consider multiple fridges a necessity in houses shared with family, friends, and the your familie's friends. You need one for the keystone, one for the real stuff, and a third maybe for other reasons. I think food belongs somewhere too, but hey, what else were we given women for.

[c.Tech]

c.Tech, I don't know whether to think that you're attempting a joke with the above post, or if you just don't understand what was written. :rolleyes:

:o The second one...

Deadman thanks for the support but it was earlier than that, I was tired and had the flu though.

[Cobalt.45]

I once built a lead melter, using a road kill electric oven temp control. It was capable of handling the wattage, and was "fine tunable" enough to hold temps within 8*F range.

These are expensive new, but "dead" ranges are often left by the side of the road to be picked up with the trash. Wiring diagrams are almost always glued to the back side of the front panel. You'll also need the thermocouple.

Might this be adaptable to a hot plate to better control temps?

[CosmikDebris]

Another good place to look is a vending company; as they usually have a pile of machines outside waiting to be scraped, and are often willing to let you scavenge them for parts.