I'm thinking of making a small hotplate for the purpose of heating PCB etchant, and possibly to keep the tank up to temperature while etching. At the low end of the temperature range, it should be able to maintain 50degC max. Being able to go hotter and boil stuff, etc, would be good.
Seems to me that the cheapest way to get a heater, plate and thermostat is a domestic clothes iron. I got one for 5ukp (new!) and it looks easy enough to chop up and mount upside down in a box of some sort. The thermostat control is mechanical, so some gubbins is needed to link that to a front panel control.
I've never used an iron as a hotplate, and I've never used a lab hotplate thingy either. Would an iron make a suitable base for a home brew effort, or am I missing something? How long would it likely take to heat a litre of etchant from, say, 20 to 50degC?
Thanks, but the idea is to build a hotplate for peanuts. Heating the etchant is the use that led me to consider it, but I'd like to have one in any case. It strikes me that a hotplate is something useful and I'm more likely to come up with ways of doing things if there's actually one lying around. (Melting wax, for example...)
"Melodolic" wrote in news:iE2Bg.112024$ snipped-for-privacy@text.news.blueyonder.co.uk:
How about a real lab stirrer/hotplate. I have one that's going to the dump. Your's for the shipping. (Always looking for a good home for junk I don't need.) Email me direct.
(Email bounced.) Thanks for the offer, but your ISP leaves me thinking you're in the US - I'm in the UK, so the shipping might be pricey. Still worth considering, though - could you tell me what make and model it is?
Hi, Mel. While you've got the basics for a hotplate in an iron, you've also got a couple of hangups that make the iron less than desirable as the basis for one.
An electric iron, at its most basic, is just a resistive heater thermally bonded to a flat surface (the iron flat), just like a hotplate. But the temperature control works over a much higher range. Assuming some thermal resistance between your plate and the pan, you just might be able to achieve control at the desired temp if you put the temp control very low. But probably not. Even at the lowest setting, it will probably overheat your etchant.
Second, the iron itself isn't made for insulating you from spills on the iron surface with the iron upside-down. If you tip over a pan of liquid onto the iron, you might have a very hazardous situation.
If I were interested in getting a "lowest-cost" hotplate (yes, real ones are expensive), I'd return the iron and start with a small coffeemaker. You could bypass the thermostat control, and then just use a 500W lamp dimmer to control power. With a little trial and error, that will get you pretty close. Either that, or play around with an intermediate material between the Mr. Coffee hotplate and your pan such that the etchant temp would be close to 50C with the thermostat cycling.
Standard precautions apply here, of course. Any mods you make to consumer electronics may cause hazardous conditions. If you're not experienced in dealing with line voltage, don't do this. Any mods you make should be done with safety in mind, particularly paying attention to the hazards of accidental spills causing short circuits.
An interlude of really basic physics. It takes about 4185 joules or watt-seconds to raise the temp of 1 liter of water 1 degree C, assuming no losses. So, it would take 125550 watt-seconds to raise the liter of water 30 degrees C. With a 500 watt coffeemaker hotplate, and perfect thermal transmission and insulation, that would take 251 seconds, or a little more than 4 minutes. (If it's important to you, verify any newsgroup math, at least from me! ;-)
Of course, the amount of time for a real world liter of etchant to rise from room temp to 50C will be almost entirely dependent on the shape of pan you use, and its thermal insulation, if any. Most of the heat will be lost. I used to have a basic etching setup with a Pyrex pan and a hotplate that used about a liter of FeCl3, and it usually took about a half an hour to come up to temp.
And watch for fumes. Most etchants which go over temp emit toxic fumes, which can also corrode metal and ruin electronics over time. Never walk away from this potential hazard, and always etch in a well-ventilated area, with the vent going directly to the outside.
At the very least, an electric frying pan surely has exactly what you need/want.
Note that if you want to melt wax, certainly when I made candles I put them in a tin can, and immersed the can in a cooking pan that had boiling water. I could have used the double boiler insert, but who wants to mess up something you cook food in with wax?
In essence, that is what the other poster is suggesting, a double boiler.
Sounds like you're doing this the hard way You need a non-metalic tank for the etching. That limits you to anodized aluminum or enameled iron - or glass or plastic.
Easy to build a wood box and coat the inside with polyester/epoxy resin or fiberglass it. Fiber/resin works better -won't crack in the seams/corners with temperature changes.
Get an aquarium pump to agitate the etchent - you need that or the results won't be uniform.
An immersion heater works better than a flat iron - an aquarium heater will be inexpensive and work well - or if you are destitute or like doing it the hard way - take a test tube and incorporate a heater- resistor and thermal switch. The tricky part is making it liquid proof so it won't suck in liquid.
I use a wooden box, aquarium pump and long "air stone" with an aquarium heater. cost ~20 dUS
I'm also using sodium something or other instead of ferric oxide - lots cleaner, cheap, faster acting, and doesn't stain everything. Bought a lifetime supply - so I don't remember the chemical name.
Built a light table with some unfiltered UV lights to expose the boards too.
----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
formatting link
The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
Why underneath? That's a plastic container. heat the liquid with a liquid proof resistor (easy with epoxy and silicon tubing) down at the bottom to avoid stratification, and put a simple thermostat on the surface or mid-level.
With plastic, a thermal insulator, temperature control is iffy - or you need to insulate the heating element and liquid bath together - you don't want too much heat becasue the insulating properties of the plastic will slow the response - plastic may sag before the bath is at temperature, or it may take longer to come up to temp (if you play it safe)
A thermostat is just a thermistor (liquid proofed), comparator and relay.
Some flat irons go 700+ watts - overkill for etching.
----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
formatting link
The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
I usually just heat my etchant bottle in a container of hot water from the tap...let it set for 4-5 minutes then pour the etchant into a shallow pan and float the board on top.... works fast enough for me...10 min or less
heating a lot of etchant for some really big boards ??? why not just go out and buy a hot plate....skillet head...~:>
There's always the dual-purpose option: Take the top off your computer, pull the heatsink off your Pentium, and put the pan of etchant in its place. :)
Something I haven't done is monitor the temperature over time - worth a go, I think.
The plan is to rebox it to make it into a proper little hotplate, including an aluminium plate that fits on top of the sole of the iron, mainly to give a neat rectangular shape rather than the bendy triangle of the iron itself. The plate will be bigger than the iron and of the order of 10mm thick, so I could machine a channel in the underside, which a vertical lip in the case fits into. A gasket or seal is a possibility if I can find something that can survive the max temperature (silicone?).
I don't know how hot a coffee maker can get without risking the element burning out.
Couldn't something similar be done using the iron? Its thermostat could be set to max, and some sort of circuit could feed it, say, a PWM signal (a-la motor speed control) which determines the power going into the element. That would eliminate the cycling thermostat issue.
S'okay, done a few mains boxes before.
I'll take your word for it (for now ;-).
I was thinking of a Pyrex beaker, possibly used at a higher temperature, but I'm not sure how quickly the plate would cool down to 50C.
I'm not sure about their minimum temperature - I kinda assumed that getting stuff to simmer requires something close to 100C, given that simmering is gentle boiling. I need a minimum of no more than 50C for keeping etchant at the right temperature.
A pal of mine who makes waxy stuff for a living uses stainless steel pans (well, buckets!) on a gas flame. I'm pretty sure some of his temperatures are around 130C or so, so a double boiler might not get hot enough.
Thanks - I'm rather pleased with it. Designed on the hoof while I was out buying bits for a completely different concept (mechanical things to oscillate an etching tray).
Doesn't give me a hotplate for other things, though. Still, how high would such a liquid proof resistor be? I had considered using an aquarium heater, but they were all a bit large in diameter to be sure of getting it low in the etching bath, and I figured something like a 4x6" hotplate would give a more even spread of heat.
Yup. The plastic looks to be polypropylene, which I think is okay at etchant temperatures. The idea is to preheat the liquid in a beaker or something, pour it into the tank, and then sit everything on the hotplate running at a temperature which maintains the etchant at 50C (eg, maybe setting the plate to 70C would keep the tank and etchant at 50C).
As I say above, it's more a case of finding what hotplate temperature will hold the tank at 50C - for a couple of hours, say (the purpose is to prevent cooling during an etching session).
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.