24V AC Digitial Temperature Controller

archibald tuttle

there is a flooded market on Ebay and Amazon of literally ten dollar digital temperature controllers. We've been discussing alternative control strategies in a strictly steam thread but my use here applies across the board. i often want a simple aquastat and the ones made for the heating industry are ridiculously priced. one understands you may need application specific stuff rated for the safety side, but i'm talking control side. And in the NFN department once it starts to come in on the control side competitive shops look at how it can be incorporated and rated in safety applications and prices drop there as well. look at the new LWCO from TACO for a quick instance.

the problems with the bulk of what i find on Ebay and Amazon readily available for project work at very reasonable dollars is that they are all designed for operating voltages of 110 AC or 12V DC. Whats a 24V AC heating tech to do with that. OK, so i can make an enclosure and run the 110 over to them and that kind of nonsense (that, i admit is one thing you get with the properitary HVAC big name aquastats is a little bit of tin with knockouts for cable restraints for connecting 110). But if these aquastats were 24 V AC . . . then its thermostat wire to the rescue. you might still have to wire 110 to it if you are switching 110 to a pump say (the switching circuit seems to be rated to 10A so the typical amp or two load of a pump ought to be well within the range even if we assume that the 10A ratings is not for inductive load. although you could just send 24V to a hockey puck SSR relay more immediately adjacent to the 110V load and higher rated, (Crydom's got 'em up to 50 amp i think)

So I do find a 24V model but they didn't think to say whether it is AC/DC or either (sometimes the case with 24V controls) and they don't mention the actual limits. Heating transformers typically deliver more like 26V. if this is intended as a 24V control its probably fine, but if 24V is the limit -- as i've seen with some controls that actually can accept a range of voltage from 10 to 24 then the slight overvoltage from the transformers could be an issue over time for the onboard power supply.

The one other less minor complaint I have about these cheaper units is, whatever mounting circumstance the manufacturers are contemplating, i can't figure it out. there is very little overhanging flange for making some kind of 'panel' mount. one guy who is making some excellent small shop made in USA differential stats thought this out and has a nice plastic housing with a couple extruded plastic flanges for back mounting and the wiring access is quite good. These are price competitive for the differential function but would be unavailing if you are looking for an inexpensive aquastat. But I gotta give him points for figuring out how people mess with this stuff in the real world. maybe all these ebay and amazon models are aimed at some 'industry' or application for which there is a simple mounting and wiring solution but i sure don't get recognize it.

trying to reach out to all you doers and dewars (well it is the holidays and i'm think if you are spending the 6th day of christmas taking a little easy or taking a thinking aid with lunch might be just the time to get you type an answer) out there to see if you have any solutions you use for 24V temperature controller. And or, I'd be interested if someone knows what mounting scenario they actually envision for some of these inexpensive manufactured ones?

thanks,

and merry 6th day of christmas.

brian

SWEI

If you want to roll your own (at least as far as enclosures go) you might check out http://www.mydtcstore.com/

icesailor

Well, as far as "Cost Effective", I keep remembering that if someone charges $60.00 Per Hour, that's $1.00 per minute. How much time do I spend trying to figure out which E-Bay item will work, and where might it have come from. And who do I call when/and/or it fails.

My friendly wholesaler stocked about everything my beating heart might desire. And If I turned LEFT when I walked in the door, there was a fully stocked electrical wholesaler that had the rest of any electrical items. Seldom was the time that I couldn't do a one stop pick-up of what I needed. Unless I forgot to put it on my shopping list.

Support your local wholesaler and they will always stock what you want and use. If they won't, find someone that will. I could never but fittings cheaper at HD or Lowes cheaper than at my local wholesaler. Don't cheap yourself out of a job.

hot_rod

Buyer beware with bargain priced electronic components. Are they listed? Tested or manufactured to any industry standard? Actual current rating? Any support or warranty?

I think most of the digital controls from Honeywell, Ranco, Johnson Controls, etc can now accept multiple input voltages, usually 24, 120, 208 and 240VAC.

BobC

I'd be leery of using this on someone else's boiler but would not hesitate one second for my own. For control it's fine I'd be more careful of using it for a safety.

I have bought a lot of parts and electronics from ebay over the years and have only rarely been disappointed. A couple of months ago I bought a type K thermocouple meter from one supplier for $8 and 8 thermocouples from another. I put together a 8 position switch so I could monitor 8 different things with that single meter for an outlay of about $30. I used the same kind of switching arrangement back when I was profiling power supplies while doing environmental testing. That setup would have cost at least $1,000 from Omega and even more from Fluke back in the early 90's.

Bob

archibald tuttle

sorry, i forgot to star this discussion. is there a way i can set my account to automatically star any thread i have a post in -- or at least the threads i start.

appreciate all the points in response. i'm probably closer to the last in sentiment, i.e. use for control, test for repeatability and utility on your own system and roll out carefully elsewhere.

i value wholesalers after a fashion but I have to admit, if you price black nipples and fittings at supplyhouse.com formerly pexsupply.com and at your local wholesaler we're talking a 50% difference sometimes. and they offer both chinese and american options in most fittings. and i get one day shipping for free (because of where i am located - not because they give overnight shipping).

and i just do not buy that unloading $50 or these days $75 per relay box is a long term sustainable solution for those of us who like a lot of controls. While the $9 ones may leave something to be desired (i'll let you know in a couple weeks, dropping in my first one in a control circuit) look at all the SSRs out there. and like the honeywell vaporstat, the proprietary heating manufaturers are slow to change from their 60 year old line of controls -- except they madet their vaporstate worse in the industrial stampede away from mercury. And where they do engage in developing hi tech solid state stuff they push the black box side, hide the algorithms and don't give the user/installer as much access to work with the controls in any other than the narrow band of operation they conceive. and for the most part they charge a friggin pretty penny for the stuff.

now in a way this is like the drug companies. spend a lot of money investigating until you find one compound that has some upside and then lay it on in price and promote it as superior to existing medicines to make a big mark-up for a while.

some people are going to think, this is what my doc wrote me the scrip for and the drugstore has got it and all the beautiful people on the commercials get better when they take it (even if they tell me diarrhea, incontinence and death are the side effedcts) so why wouldn't i support that supply chain. others are going to wonder whether the efficacy, cost and side effects don't suggest another course of treatment.

Sometimes I think there is enough of a market and universal enough of a function set that the normative behavior of making stuff super proprietary and super expensive is overcome. I think Tacos LWCO is a good example of that. Affordable and seems to overcome the leaking and cumbersome nature of earlier attempts i had installed and IT COSTS LESS! They figure they will sell enough units to make up the R&D.

So part of the reason I ask is that maybe some manufacturer has invested in a more generic digital temperature controller and run it through the paces and simulated a million cycles and gone to UL or whatever and made a nice enclosure more aimed at established trade practices and they charge 25 or 30 bucks for it instead of 10.

If somebody has worked out the enclosure and brought something into a mainline, i'd be the first to cue up, but when I see $70 to $100 a box or more and can get the similar functionalities sometimes more addressable for an order of magnitude cheaper I do go off the reservation.

Aside from asking here, I'll be walking the aisles looking for one at AHR if we don't get a blizzard that week -- not sure why they do it in the winter except that everybody is really interested at that time even if hopelessly busy.

As to what is actually going to be stocked, there is not one local wholesaler i've found here who has the Field Controls retrofit spill switch for steam temperatures (and don't ask me why they number their lower temp spills sequentially and then number the steam control by its temperature set). So am i supposed to order it from them and wait a couple weeks to a month until they have an order together or should i just go online and get it for the same price or cheaper from someone who will have to me with a couple days.

If i'm not hurrying and the pricing is similar i will choose the local supplier, but there is some stuff they don't stock or they are really out of whack on the mark up and I tend to think supporting that is not supporting efficiencies in the market.

I agree on the $ a minute thing and as you can see from my posts i put way too much opportunity cost into thinking about stuff - but that is my personality at work. if i wasn't thinking about this i'd be thinking about something else equally retentive and intellectually squirrel holeish.

brian

RobG

Archibald, there is no offense intended but your posts are very long winded. Could you try and keep them a little shorter. I just don't have the attention span that I did when I was younger.