My condensation management setup worked!

[jwmelvin]

The target temperature is a moving target that varies moment to moment with atmospheric conditions.

Yes, for sure. PID has no issue with a changing set point. It just does a better job of maintaining the setpoint than does bang-bang control like your're using.

Duty cycle is a real concern, and the current design is basically rolling the dice and hoping the heaters never burn out.

I'm betting you will be fine, since the metal conducts heat well and will limit the temperature of the heating element.

I thought all relays were solid state?

Definitely not. It appears the IoT Relay you are using has an electromechanical relay, aka an air-gap relay. This is good/important for safety since it fully disconnects the output when desired. A solid-state relay is a form of transistor and has some leakage voltage even when off. But SSRs can handle applications with high switching rates. For your application, I don't think it's significant, but if you were using a PID controller, you might care.

I'm hoping to walk away and spend my time making things with the equipment.

I completely understand and it's almost for sure the right choice. Thanks again for sharing. I may end up doing something similar down the road.

 

[whitmore]

They're 100 watt "oil pan heaters" straight from China. I have definite concerns about not putting a heater directly on the tables...
The base of the casting is much to narrow for the heater, which is roughly 4" square. I could put one under the base, but we'll see how it does before I throw away all the time I spent dialing in the tram.

A few thoughts:
First, there's high voltage safety concerns using AC heaters, so it might pay to get some
thermoelectric 'cooler' modules instead: you can run those off safe low voltage DC, so they
pump heat into the cast iron from a 'cold side'. Fitted with some suitable vanes, the cold
side will condense water into any convenient bucket or drain... lowering the moisture content
of the air and protecting the hand tools and loose metal around the shop, not just the lathe and mill.

Second, a good thermal scheme might be to put a variety of heat exchangers onto the tools
that take circulating water/antifreeze to a central site (over the drain) with the
heat pumping modules. One might use quick-connect fittings to keep the
fluid from leaking, but it's low enough pressure that those can be plastic.quick-disconnect example

Third, calculating the dew point is a GREAT step forward. Percent humidity was a relatively
useless metric, and it dominated the discussion for too long. There are circumstances (like
entering the eye of a cyclonic disturbance) where the air pressure changes quickly and
the dew point changes VERY FAST. Lenticular clouds routinely form in the winds over
mountaintops, for instance. So, the 'dew point' margin might be expanded for safety
in windy conditions (there's always high wind before entering the eye).

 

[FanMan]

...I have an unheated, uninsulated shop with a dirt floor, and I've been battling serious condensation problems all winter.

Not to derail the subject, and I like your solution, but the dirt floor is likely a large part of your problem. I put up a fabric garage to store my plane while I repair it (damaged during an off airport emergency landing) and everything inside was dripping from the moisture coming up through the ground. I solved it by building a raised floor: I laid down black sheet plastic over the dirt, wooden pallets over that, then covered it all with 3/8" chipboard screwed to the pallets to tie it all together. It's not perfectly level (far from it, really), but it's solid and it's now dry as a bone inside.

The picture shows it with the floor half done.

 

[dewbane]

Definitely not. It appears the IoT Relay you are using has an electromechanical relay, aka an air-gap relay.

All of that went over my head until now. I didn't know solid state relays were a thing. I went and did some reading, and I'm less ignorant now. Interesting!

Well, it's 20 out there. My equipment is fine, but my only source of serious BTUs at the moment is unvented propane. I'm sure Dewbane would kick the heaters on within moments of firing up the gas, but I would be really surprised if this rig could get the equipment up to temperature fast enough to avoid condensation.

I can think of scenarios with pre-heaters triggered from my phone, but the practical thing to do is keep that bottle of CRC 3-36 handy, and hose everything down to ride out the big sweat until the metal warms up in due course.

Have I mentioned that I really hate winter, and I can't wait for it to leave me alone?

 

[dewbane]

Not to derail the subject, and I like your solution, but the dirt floor is likely a large part of your problem.

The dirt floor definitely doesn't help, but this shop started life as my smithy, and grew equipment as I made excuses to acquire it. A dirt floor is really good for a smithy, while a wood floor is really bad. The one floor that works for both is concrete, and I can't afford that yet. Good suggestions though!

 

[dewbane]

I really wanted to work in the shop today, so I broke down and hooked up the unvented propane tank heater. The relative humidity jumped way up, and I did get minor condensation on the mill tables and lathe chuck, but it really didn't take long at all to balance out. Maybe five minutes. I was pleased.

 

[jwmelvin]

That’s awesome. Five minutes seems quite fast. It’d be easy to add a preheat button but maybe not worth it if it can recover that quickly.

 

[Brento]

Where can i sign up to buy one of these?

 

[dewbane]

Where can i sign up to buy one of these?

I have on the order of $125 in raw materials in this thing, and I doubt I could shave my costs enough to produce a product people would actually buy. I'm concerned about the liability too. It's all fun and games until something goes wrong and your shop burns down. Then you go looking for someone to sue, or your homeowner's insurance company does. My shop is my problem, but I'm not really keen to make other people's shop my problem. My wife and I had a long talk, and even though there is some interest, it's probably just not worth it in the long run. The more customers I have, the greater the chances that someone is going to play the jerk card. I got sued once for giving a guy $100 for free.

 

[dewbane]

The system seems to be up to the challenge of keeping condensation at bay when I fire up the gas on a snowy day that's a little below freezing. I worked out there longer than I ever have with the heat on, and the equipment didn't sweat much at all. The humidity skyrockets with the exhaust emissions of the propane, but the ambient air temperature helps bring the equipment temperature up. It works out reasonably well.

When I fired up my gas forge within my shop, however, I developed dramatic amounts of frosty milk on my equipment right away. The system can't handle THAT much water vapor. I don't normally run the gas forge inside the shop, but we got a deep snow, and I only had a small heat treating job to do.