Sending PWM through a relay

[clearchris]

Re: Sending PWM through a relay

That's actually a good explanation and answered one of the questions I had yet to ask. I have had the oven make a few runs today, with different pid settings, and one run in particular had the temp locked in at +/-0.1C, except 3 degrees too high. The accumulated error certainly accounts for that. On that run, I started the run with the oven temp higher than the set point. That probably messed up things.

So, humble pie time for me, you were right CG. Looks like I am going to have to do some pid tuning. I can't have too much variance on this particular profile. My primary case for this oven is actually to do filament drying. Too much heat, and the spool will be melted together and useless. So I'm reading up on PID systems.

[eccerr0r]

Re: Sending PWM through a relay

drying... filament... of... what compound? There are other ways to do a liquid-solid separation?

[Curious.George]

Re: Sending PWM through a relay

That's actually a good explanation and answered one of the questions I had yet to ask. I have had the oven make a few runs today, with different pid settings, and one run in particular had the temp locked in at +/-0.1C, except 3 degrees too high. The accumulated error certainly accounts for that. On that run, I started the run with the oven temp higher than the set point. That probably messed up things.

So, humble pie time for me, you were right CG. Looks like I am going to have to do some pid tuning. I can't have too much variance on this particular profile. My primary case for this oven is actually to do filament drying. Too much heat, and the spool will be melted together and useless. So I'm reading up on PID systems.

Control Systems aren't trivial. There are folks who devote their careers JUST to Control System Engineering! There's a lot of fancy math involved and gobs of "theory".

Most folks deal with a particular niche of controllers and controlled systems. Within a given niche, you can develop rules-of-thumb for how to mate control to plant.

For example, if you buy an HVAC system for your home, the guy who sells it to you WON'T have a formal education in controls/systems engineering. Instead, he'll have picked up a set of rules-of-thumb that guide him in sizing the plant for your particular home in your particular climate with your particular environmental exposure, etc.

Will it be "optimal"? <shrug> Doubtful -- unless if serendipitously. But, it will likely be "good enough".

There are also "tricks" that can be applied in certain circumstances. E.g., you may find switching to infrared lights gives you better control in a certain temperature range. Or, decreasing the efficiency of your plant (like venting heat OUT, deliberately, so the heating elements TEND to be on more continuously at a particular temperature/range).

Businesses that rely on "processes" spend lots of money trying to improve on their controls and the efficiency of those processes. Hence the "specialists".

Sorry, I can't recommend anything to give you a crash course as most of the texts that I have are heavy on theory -- which quickly makes things incomprehensible ("How does this relate to MY problem?")

The easiest way to understand where your problems MAY lie is to collect data on the process in-action/under-control. E.g., if you could look at the actual temperature and see when the controller was calling for action, you might be able to figure out what it's "doing wrong" (or, suboptimally). Then, go back and think about the hooks that you have into the controller that you might be able to tweak to coax it into behaving more like YOU think it should.

(the controller/control loop/tuning software doesn't know what YOUR needs are!)

You can also look to see what "advanced features" (if any) are supported in the software and contemplate how they might help you.

For example, the integrator accumulates errors. As the actual temperature approaches the setpoint, the error term diminishes. BUT, the accumulated error still persists! So, the loop could overshoot as the accumulated error is "bled off".

Some loops include a provision to limit just how much error can accumulate ("integrator windup") so this doesn't get out of control. Others include provisions that automatically ZERO OUT the accumulated error when the actual error reaches zero (the thinking being that this will stop the loop from overshooting).

There are a shitload of /ad hoc/ solutions out there that help in some applications... but not in others. Once you SEE how your controller is actually operating, you can start hypothesizing, "Gee, if I could just stop the accumulated error from driving the temperature PAST the setpoint..."

Or, whatever.

Play. Observe. Think.

Put a brick in the oven so you don't have to worry about burning something.

Put a COLD brick in and see how things change.

Etc.

[clearchris]

Re: Sending PWM through a relay

eccerror: 3d printing filament. PLA, ABS, PETG and NYLON all absorb water, listed in order of increasingly hydroscopic filaments. PLA needs it every few months, ABS maybe once a month or two, PETG every few days, and NYLON after every single print. If you print with wet filament, it causes problems, blobs and drooling from H2O evaporating in the hot end, and it the worst cases, extreme porosity and lack of adhesion. Some people use dessicant or a light bulb in a bucket, but I like my filament really dry. If you overheat it though, it becomes brittle or stuck together, neither is desirable, so temperature control is important.

CG: I spent yesterday changing the pid values and observing. I came to the conclusion that it would be a whole lot easier to just run one of the halogen lights and use the resistive heaters as boost only for high temps. Ran a pid tune on the lower halogen heater, and ran some 10 minute cycles. The halogens overshot by 1-2C and settled pretty much solid at 1-2C over target. I'm ok with that for now. Also did some testing, opening the door, a few times, the algorithm corrected quickly, no issues. I also checked temperatures front, back, top, bottom, side to side, and it's remarkably uniform. No more than 1C variation anywhere. My meter measured 47-48C when the system showed 51C. The variation could easily be error in the thermocouples.

Otherwise, I wrote some python scripts to generate my profiles, the gcode didn't react quite the way I expected it to, so there's some long stretches of "dwell for 5 seconds", "display temp" repeat. I put it through enough cycles to have some confidence that it's not going to go completely haywire, it will perform according to expected parameters.

I also found a plugin to enhance the graphing in octoprint. Pretty nice. Pic attached.

Next steps:
I have a small spool of filament in there right now, we'll see how it works in three hours. This is the first loaded test.
After that I need to see what the power consumption is with all heaters on. I measured the resistive heaters, combined they pull 10.4A. I wasn't able to get a meaningful measurement from the halogens as the resistance changes with heat. I don't have a clamp meter, I think I'll just turn it on and cross my fingers. We'll see. According to the label, they are 1000 watts total, so at 120v, that should be 8.3A. With electronics, that shouldn't put me over 20a, but who knows if the labels are accurate.
Then see if I can get a meaningful pid tune on all heaters at 225C, and maybe just the halogens at 225C. My current thinking is the resistive heaters can help boost the temp on the ramp up, but should be cut out pretty soon and temp held with the halogens alone so the oven can ramp down quickly.
I also should make a shield for at least the lower halogen to protect it from dust, etc. I think I might miss the oven flashing and lighting up my garage behind me.
I also need to get some small zero crossing SSR on order so I can do PWM control on the fan. I have concerns that the fan just wasn't made to be run as much as I'm going to run it. PWM might help lower the load on it.

[Curious.George]

Re: Sending PWM through a relay

CG: I spent yesterday changing the pid values and observing.

Welcome to the joys of loop tuning! You will discover that it can be really frustrating as you're never sure if what you're doing is making things BETTER, or WORSE. It's ART more than SCIENCE.

Also did some testing, opening the door, a few times, the algorithm corrected quickly, no issues.

Note that, to a certain extent, you can limit the number and frequency of such "disturbances". E.g., when you bake a cake, you don't keep opening the door just to see how it looks!

Otherwise, I wrote some python scripts to generate my profiles, the gcode didn't react quite the way I expected it to, so there's some long stretches of "dwell for 5 seconds", "display temp" repeat. I put it through enough cycles to have some confidence that it's not going to go completely haywire, it will perform according to expected parameters.

If you can programmatically "watch" what's happening, you can always raise an alarm or pull the plug if your code sees something wonky.

I have a small spool of filament in there right now, we'll see how it works in three hours. This is the first loaded test.

I assume its not practical to process PORTIONS of spools? I.e., you need to have "enough dry stock" to complete a print... it's not like you can piece together shorter lengths...

After that I need to see what the power consumption is with all heaters on. I measured the resistive heaters, combined they pull 10.4A. I wasn't able to get a meaningful measurement from the halogens as the resistance changes with heat. I don't have a clamp meter, I think I'll just turn it on and cross my fingers. We'll see. According to the label, they are 1000 watts total, so at 120v, that should be 8.3A. With electronics, that shouldn't put me over 20a, but who knows if the labels are accurate.

In the US, that's a "kitchen" circuit and requires a different plug/receptacle (normal receptacles are only rated to 15A -- 1800W, underated). Instead of the parallel blades ||, it will have perpendicular blades -|. Dedicated refrigerator and furnace outlets MAY be 20A capacity. And, outdoor or garage outlets. You may find it more convenient to run TWO power cords to two different outlets (on different circuits). I wired the two (required!) kitchen "countertop outlet" circuits so that every other outlet was on the same branch. So, as long as I connected to two different -- but adjacent -- "receptacles", I was guaranteed to have two circuits available.

[If you have an electric range or clothes dryer, you can access two separate circuits in the same (220VAC!) outlet, there. Keeping in mind that they will be out-of-phase whereas two random branch circuits may or may not be!]

I also need to get some small zero crossing SSR on order so I can do PWM control on the fan. I have concerns that the fan just wasn't made to be run as much as I'm going to run it. PWM might help lower the load on it.

You could also "outboard" the fan, tying it to the oven with rigid or flexible ductwork.

Are we having FUN yet? :>

[eccerr0r]

Re: Sending PWM through a relay

From the constraints you put, freeze or otherwise cold drying is the ideal way to get rid of the water if you don't want to deal with the desiccant...

[clearchris]

Re: Sending PWM through a relay

Welcome to the joys of loop tuning! You will discover that it can be really frustrating as you're never sure if what you're doing is making things BETTER, or WORSE. It's ART more than SCIENCE.

Heh, I feel like I just got hazed. Am I a member of the club yet?

Note that, to a certain extent, you can limit the number and frequency of such "disturbances". E.g., when you bake a cake, you don't keep opening the door just to see how it looks!

Yeah, I don't plan on ever opening the oven when it's in process. I just did it for the funsies.

I assume its not practical to process PORTIONS of spools? I.e., you need to have "enough dry stock" to complete a print... it's not like you can piece together shorter lengths...

Well, I said "small spool" I meant "almost empty spool" because I didn't want to lose a full spool if something went wrong. And I can't get my cheesy ebay $12 spools anymore, china is shut down, I have been having to get the $22 fancy spools. High rollin!

And my printer is so small, I don't go through that much plastic per print. 1kg is a LOT of plastic.

In the US, that's a "kitchen" circuit and requires a different plug/receptacle (normal receptacles are only rated to 15A -- 1800W, underated). Instead of the parallel blades ||, it will have perpendicular blades -|. Dedicated refrigerator and furnace outlets MAY be 20A capacity. And, outdoor or garage outlets. You may find it more convenient to run TWO power cords to two different outlets (on different circuits). I wired the two (required!) kitchen "countertop outlet" circuits so that every other outlet was on the same branch. So, as long as I connected to two different -- but adjacent -- "receptacles", I was guaranteed to have two circuits available.

Eh, there's wiggle room, it's not like it's going to melt down at 16a. I'd be more concerned with the wire in the wall, but if it's 12ga (it is), it's good to 20a.

[If you have an electric range or clothes dryer, you can access two separate circuits in the same (220VAC!) outlet, there. Keeping in mind that they will be out-of-phase whereas two random branch circuits may or may not be!]

I have an 60a (iirc) outlet for my welder. Don't recall if it has neutral though. Really don't feel like messing with one of those enormous plugs on the end of my oven. Plus I don't have an extension cord for that...

You could also "outboard" the fan, tying it to the oven with rigid or flexible ductwork.

Oh hell no. Aside from the crazy complication, it's a recirculation fan, that would bleed heat like crazy. Hehe.

I'm trying as hard as I can to keep this simple. The software is a bit complex, but really I haven't had to do much coding yet. Just reading the code so I can figure out what hacky configuration I can make work.

[clearchris]

Re: Sending PWM through a relay

From the constraints you put, freeze or otherwise cold drying is the ideal way to get rid of the water if you don't want to deal with the desiccant...

Never considered that, the equipment is pretty expensive, isn't it? Plus, plastic doesn't always do well with the cold.

Oh, I have desiccant too. I have what's called a "dry box" with desiccant where the filament lives when it's outside of my sealed 5 gallon buckets. My next oven profile will probably be a cycle to dry out my desiccant.

[eccerr0r]

Re: Sending PWM through a relay

Nice thing about freeze drying is that it's pretty much put in and forget, much like desiccant, except you just need to power it. "Cold" is relative, you can do it at 20°C just fine, no need to go to 0°C.

[Curious.George]

Re: Sending PWM through a relay

Heh, I feel like I just got hazed. Am I a member of the club yet?

I'm just giving you a head's up that you will likely find this to be a frustrating experience.

Eh, there's wiggle room, it's not like it's going to melt down at 16a. I'd be more concerned with the wire in the wall, but if it's 12ga (it is), it's good to 20a.

You can peek at the wire by pulling the receptacle out and looking at the connections to the fixture. Chances are, if it's fused at 15A, it's 14AWG.

I have an 60a (iirc) outlet for my welder. Don't recall if it has neutral though. Really don't feel like messing with one of those enormous plugs on the end of my oven. Plus I don't have an extension cord for that...

That's why I suggested using TWO cords: e.g., one for the resistive heaters and one for the halogens. It seems a logical way to split the load.

I'm trying as hard as I can to keep this simple. The software is a bit complex, but really I haven't had to do much coding yet. Just reading the code so I can figure out what hacky configuration I can make work.

Again, control loops are often messy and the "remedies" often are kludges.

For example, in many industrial processes, you often have cascaded loops because the heating/cooling/humidification/dessicating element (e.g., in an air handler) may be distant from the "point of delivery" -- which is where you ultimately want to control at. But, using that as a SINGLE sense point means you have SECONDS of lag built into the loop as it takes the "treated air" that long to travel down the ductwork to reach the sensor. So, you add a sensor near the control element and build a loop, there. Then, superimpose another loop AROUND that using the "remote" sensor. I.e., an air handler is expensive (tens of kilobucks)

To get good control, you may have more than one air handler, each operating at different temperature/flowrate/humidity levels. And, a mechanical "vane" that acts as a valve to select between "air handler A" and "air handler B". This is easier than trying to get a single air handler to quickly switch from supplying, for example, hot/moist air to cold/dry air.

If you're moving thousands of dollars worth of "product" through the process each hour, the cost of the second air handler is "nothing", over time.

[sam_sam_sam]

Re: Sending PWM through a relay

Why not use a heat lamp and a CPU fan at very low speed

From you are saying I will probably have to do the same thing with a roll that I took out the bag and did not realize that why it was inside a sealed bag and also did not realize that bag was resealable

I glad you posted this information

[clearchris]

Re: Sending PWM through a relay

You can peek at the wire by pulling the receptacle out and looking at the connections to the fixture. Chances are, if it's fused at 15A, it's 14AWG.

Yeah, my house was built in apparently a transitional period. It's older, all 12ga wire and 20a breakers, but only recently rewired outlets have ground. I didn't know there was a period between 12ga wire adoption and three prong outlets, I always thought it happened around the same time.

That's why I suggested using TWO cords: e.g., one for the resistive heaters and one for the halogens. It seems a logical way to split the load.

Making it work is half the fun! No constraints, it's too easy.

Again, control loops are often messy and the "remedies" often are kludges.

I'm starting to believe that.

To get good control, you may have more than one air handler, each operating at different temperature/flowrate/humidity levels. And, a mechanical "vane" that acts as a valve to select between "air handler A" and "air handler B". This is easier than trying to get a single air handler to quickly switch from supplying, for example, hot/moist air to cold/dry air.

HVAC / Refrigeration can be such a pain. I took the certification test so I could do my own work, but I always need an extra cup of coffee to do it. I hate to say it, but it has been a while since I have taken the torch out (please nothing break).

A lot of really cool tools in refrigeration though. I love my ultrasonic leak detector. It has all kinds of uses.

Right now I'm running a cycle to dry out my desiccant. Working well so far, but temperature really not important so I'm running the resistive heaters. Tomorrow, I'm going to see if I can preheat a galaxy S7 so I can change out the menu button/antenna board. The screen has to come off to do it. Fun times.

At least I'm getting a lot of use out of the oven already.

[clearchris]

Re: Sending PWM through a relay

Why not use a heat lamp and a CPU fan at very low speed

From you are saying I will probably have to do the same thing with a roll that I took out the bag and did not realize that why it was inside a sealed bag and also did not realize that bag was resealable

If it's PLA, just put it back in the bag with the desiccant, you should be ok. PLA takes a while to absorb moisture. If it's super cheap ebay PLA, I'd definitely dry it. If it's a reputable brand, and the package didn't have holes and appeared to be vacuum sealed, you should be ok. When PLA swells, you will start noticing overextrusion, you will have to change your flow multiplier, etc. But it doesn't print too badly. The other filaments will act downright horrible. I literally will not print with PETG unless I have baked it in the past 48 hours. Aside from the extrusion multiplier, you probably wouldn't notice much with PLA as your printer is stock. My $160 printer has three years of mods and probably at least another $150 in it, and it prints better than most $600 printers out of the box.

The problem is, I now dry my PLA at 120F. I have ruined more than one spool of PLA. If it's too hot (140F might be too hot) it can turn brittle to where it snaps in your hands (BTDT) and it can also melt together (BTDT). Much lower than 120F and I don't know how much drying you will have. But if your temp spikes, you can easily ruin PLA. ABS, PETG and NYLON you don't have to worry much about ruining it.

Some people get away with a small incandescent light in a bucket or a food dehydrator, but I'm not convinced. Now with the oven, I can set it and walk away knowing that I can hold temp to within 1C.

You might also consider building a dry box. That way your spool stays dry when it's out of the package. I also have a few 5 gallon buckets that I store the filament in. Pic attached.

When people ask my why I have a 3d printer, I jokingly respond that I have a 3d printer so that I can print parts for the 3d printer. That's not entirely true, but sometimes it sure feels like it's true. So, get on thingiverse and find a drybox design that you like, and start looking around for a sealable container that works for you. Speaking of which, get on the ender 3 groups and ask them what parts break and what you should upgrade / print spares for. I keep a decent sized stock, and it has saved me plenty of times. The parts are dirt cheap if you order them from overseas, much more expensive if you need them in a hurry.

[Curious.George]

Re: Sending PWM through a relay

Making it work is half the fun! No constraints, it's too easy.

As long as you keep in mind that it can decide to NOT work right when you are in the middle of something that you'd EXPECTED to work. E.g., if a breaker trips because it calls for more heat than you'd previously expected, resetting the breaker will likely just cause it to trip AGAIN -- cuz now it needs all that previous heat PLUS some more.

[I don't mean to be pessimistic. Rather, its the nature of my job -- I can't come up with solutions that only work "sometimes"...]

[messy loops]

I'm starting to believe that.

Keep at it long enough and any doubts you have on the subject will evaporate! :> Just be ready to decide "this is good enough" -- for some value of "good enough". It's not like accounting where you CAN (and MUST) account for every penny in order to "get it right".

HVAC / Refrigeration can be such a pain. I took the certification test so I could do my own work, but I always need an extra cup of coffee to do it. I hate to say it, but it has been a while since I have taken the torch out (please nothing break).

What was involved in that? I've wanted to get "licensed" just to be able to repair out freezer (cuz they don't make anything similar, any more) as I don't think refrigerants are sold to "Joe User".

[dehydrator]

You may want to track how often each spool gets "baked". If, for example, you notice that the filament starts getting brittle, you might discover that three drying cycles is the limit before the medium is "compromised" -- that may help you plan your material usage (e.g., take the "last half" of the spool and "store it" so it doesn't need to get baked, repeatedly, before you need it)

At least I'm getting a lot of use out of the oven already.

Yeah, and when its not melting lead/zinc, you can always bake COOKIES!!!

Good luck! Time for lunch...

[clearchris]

Re: Sending PWM through a relay

Breaker stuff

Agree 100%. I figure I'll run it flat out a bit, and if it doesn't pop, it should be ok. I really need to get a clamp meter...

It's not like accounting where you CAN (and MUST) account for every penny in order to "get it right".

Not entirely true. Accountants use "due diligence" which is defined as: such diligence as a reasonable person under the same circumstances would use : use of reasonable but not necessarily exhaustive efforts.

What was involved in that? I've wanted to get "licensed" just to be able to repair out freezer (cuz they don't make anything similar, any more) as I don't think refrigerants are sold to "Joe User".

You need to take the EPA 608 test. Taking the test licences you to work on refrigeration and buy refrigeration products, on a federal level. On a local level, some states do allow you to work on your own equipment, some don't. Most states won't let you work on someone else's equipment without being a registered contractor, and going through hoops to get that including an apprenticeship, etc. Even if the state will allow you to work on your own equipment, it's not common to get DIY people, HVAC supply houses will often choose not to do business with those who are not contractors. I have been told to leave a few, and one even threatened to call the police on me, and I was entirely polite and not argumentative. I think he was just a generally ornery person and having a bad day on top of it. Some will try to stick you with "retail" prices, which are jobber prices times 4, or as much as they think you have in your pocket. Online buying is easy, though I have a place I like to go to in an emergency. I usually bring them donuts, I find it's really hard for people to be a jerk to someone who just stuck a donut in their mouth. You are also required to have "recovery equipment" which isn't as expensive as it was, but can still cost you a few hundred.

And you can work on refrigeration without the EPA test, you just aren't allowed to hook up gauges, braze in a new compressor, etc. Most of the things that go wrong are capacitors, fan motors, thermostats, dirty coils and somewhat more rarely compressor start relays. Most repairs I make to refrigeration I don't even touch my gauges.

I'll warn you, repairing refrigeration gets expensive quick. There are a LOT of tools you need to do a good job, though it's surprising how little some of the old timers use. Those guys are all about rules of thumb - "beer can cold" good to go!

You may want to track how often each spool gets "baked". If, for example, you notice that the filament starts getting brittle, you might discover that three drying cycles is the limit before the medium is "compromised" -- that may help you plan your material usage (e.g., take the "last half" of the spool and "store it" so it doesn't need to get baked, repeatedly, before you need it)

I haven't noticed this to be the case, but it's a good point, I'll keep an eye on it.


If anyone wants to see the oven in action, I made a short vid: https://drive.google.com/open?id=1gC...vVBDCiA9oZlUn_

[clearchris]

Re: Sending PWM through a relay

At full blast, 2 minutes 22 sec from room temp to 200C. 190C temp rise is about 1.3C per second, straight slope, no lagging at the top either. SSR heat sink was warm, definitely not hot. No popped breaker. Looks like green light for a reflow profile.

[sam_sam_sam]

Re: Sending PWM through a relay

If anyone wants to see the oven in action, I made a short vid: https://drive.google.com/open?id=1gC...vVBDCiA9oZlUn_

Just let me say I really like your setup and you gave some ideas

The only problem that I see if you cycle the light a lot like that the bulb might not last very long just keep this in mind

I going to use this setup but I going to use a high amperage SCR controller and adjusting the amount of current to the light bulb just keep it warm and at steady temperature

And see how well I can maintain the temperature doing this way

I not saying that my concept will work or not but I going to give it a try

[Curious.George]

Re: Sending PWM through a relay

Not entirely true. Accountants use "due diligence" which is defined as: such diligence as a reasonable person under the same circumstances would use : use of reasonable but not necessarily exhaustive efforts.

Yes, but the point I was making is that currency doesn't have "tolerances". A dollar is a dollar. It's not +10, -8%.

By contrast, is that 200C really 199.9999999C? Or, 202.010101010C? There's no "absolute" that you can ever hope to achieve so you implicitly have to "settle" for something less than perfect.

(when an accountant can balance "to the penny", there's no value in any further refinement of his efforts!)

[refrigeration]

You need to take the EPA 608 test. Taking the test licences you to work on refrigeration and buy refrigeration products, on a federal level. On a local level, some states do allow you to work on your own equipment, some don't. Most states won't let you work on someone else's equipment without being a registered contractor, and going through hoops to get that including an apprenticeship, etc. Even if the state will allow you to work on your own equipment, it's not common to get DIY people, HVAC supply houses will often choose not to do business with those who are not contractors.

Understood.

A quick google leaves me with many MORE questions (different certification TYPES, classes, test fees, license RENEWAL, etc.) but I'll wait until I've done some research before pestering you (perhaps I can PM to save others the tedium of this detail?)

Some will try to stick you with "retail" prices, which are jobber prices times 4, or as much as they think you have in your pocket.

Yeah, the same with most trades. I've a lot of friends who are "big customers" of many of these types of places (e.g., electrical, plumbing, etc. supply shops) so I get recommendations from them as to which shops to visit. Then, freely drop their name with the counter staff so I have some "cred" while I'm there. It helps that I know little personal details that I can offer up to show that I know them more than superficially:

"Mike sent me.'
"Oh, OK. How's he doing?"
"Well, Kathy has been hounding him to lose weight 'for the kids' and, to his credit, he really HAS lost a shitload! If you haven't seen him recently (because he's The Boss and doesn't bother "running errands"), you will be stunned at the difference!"

(Chances are, the counter person didn't even know that Kathy was his wife OR that he had kids! But, he's the one who authorizes the payment of all the invoices submitted by their firm, so...)

Online buying is easy, though I have a place I like to go to in an emergency. I usually bring them donuts, I find it's really hard for people to be a jerk to someone who just stuck a donut in their mouth.

I use (home-)baked goods. I've a cheesecake that's good enough to be traded for sexual favors!! :> So, if I give some to a "Mike", it gives him leverage over his "Kathy"!

You are also required to have "recovery equipment" which isn't as expensive as it was, but can still cost you a few hundred.

I would opt to rent or borrow as it's not the sort of thing I plan on doing more than once or twice -- fix the freezer and possibly service the ACbrrr.

And you can work on refrigeration without the EPA test, you just aren't allowed to hook up gauges, braze in a new compressor, etc. Most of the things that go wrong are capacitors, fan motors, thermostats, dirty coils and somewhat more rarely compressor start relays. Most repairs I make to refrigeration I don't even touch my gauges.

Yeah, I've already done those sorts of things (blower motor in the furnace, cap for the condenser's fan, etc.). Where I'm at the contractor's mercy is once you try to crack open any of the "plumbing". I figure this isn't rocket science so...

I'll warn you, repairing refrigeration gets expensive quick. There are a LOT of tools you need to do a good job, though it's surprising how little some of the old timers use. Those guys are all about rules of thumb - "beer can cold" good to go!

Hence the idea of borrowing or renting. Trading my TIME for that of a contractor's (who represents a crapshoot when it comes to quality of workmanship).

[We had all sorts of headaches getting the ACbrr installed here. One contractor actually (was stupid enough) to say that our house was "built wrong". I guess he assumed I hadn't already located all of the other houses with nearly identical floor plans, built at the same time by the same builder THAT HAD AC UNITS. Oooops!]

I haven't noticed this to be the case, but it's a good point, I'll keep an eye on it.

You will now be drying the medium with a different process than before. So, what might NOT have been a problem in the past might BECOME a problem going forward. The time it takes to make a note as to "dried again on 5/3/2020" could pay off down the road if you encounter problems ("data" costs very little to accumulate BEFORE you need it)

[clearchris]

Re: Sending PWM through a relay

A quick google leaves me with many MORE questions (different certification TYPES, classes, test fees, license RENEWAL, etc.) but I'll wait until I've done some research before pestering you (perhaps I can PM to save others the tedium of this detail?)

No worries, it is quite cryptic. I'm certified type I (small refrigeration), II (hvac splits and the like) and III (chillers, industrial process) because, why not? It doesn't cost any more and the stuff you have to remember to do type III isn't that much more even though I'm not certain I have ever even seen a chiller. Type 609 is automotive, I didn't take the test for that, you don't need any license in my state to work on your own car, and you can buy the refrigerant at the store.

I use (home-)baked goods. I've a cheesecake that's good enough to be traded for sexual favors!! :> So, if I give some to a "Mike", it gives him leverage over his "Kathy"!

Lol, I don't think any of my stuff has lasted long enough to be taken home.

I would opt to rent or borrow as it's not the sort of thing I plan on doing more than once or twice -- fix the freezer and possibly service the ACbrrr.

Maybe you can, but I don't think you can. It's not something that the average person would rent, and if you were licensed (at least in my state) you are required to list the address where your recovery equipment lives. Plus, if they were rented out, people would rent them out to do burn-outs, really nasty recoveries, and they would be completely tainted. I could be wrong though.

Yeah, I've already done those sorts of things (blower motor in the furnace, cap for the condenser's fan, etc.). Where I'm at the contractor's mercy is once you try to crack open any of the "plumbing". I figure this isn't rocket science so...

Honestly, HVAC can be very subtle. It's not rocket science, but you need to be on point to 1) notice ALL the clues (and know what a clue is) and 2) interpret them properly. I too have some rules of thumb, including replace all the caps, etc., before I even start to troubleshoot.

Trading my TIME for that of a contractor's (who represents a crapshoot when it comes to quality of workmanship).

That's the truth right there. There is ONE guy in town who I trust to work on my equipment. Most techs are fresh out of a two week hvac course and want to charge $1600 to replace a condenser fan (no joke, real story).

[sam_sam_sam]

Re: Sending PWM through a relay

The air conditioning and refrigeration service supply you have to have a journeyman license and the EPA license in this county to buy any supply’s

The price that is charged can vary greatly depending who you call
I know a case where someone got bill for changing a capacitor of $200.00

Now when I do this repair I would charge 25% more than what I paid for the part plus $60.00 this is on low end of this scale

I will let you all know I have a journeyman license and the EPA license I can buy from the supply house but only because I have done this for the company that I work for

Other wise I would not be able to buy these parts other wise

But there are ways around this restriction

If you are working on a air dryer unit and it take R134A refrigerate which is the same exact thing that is used in your car as long as you use it with out any oil or leak detector add

I have done this before when I do not want to buy a 25 pound tank and at the most I need 2 pounds maybe