What am I looking at here nofossil

[wdc1160]

This is a graph from your controller card

(broken link removed)

Why is the oil out firing the amount and temperature we see? The graph seems odd I would have thought there would have been overlap between the firing of the wood and the oil out temp.

Why are you not heating with 130 degree water on the top of the tank?
According to some of the reading I have done you can still get some BTU's out of that right?? (broken link removed)

How do you know your sick-- when you monitoring other peoples heating cycles
just curious.

 

[Nofossil]

This is a graph from your controller card

(broken link removed)

Why is the oil out firing the amount and temperature we see? The graph seems odd I would have thought there would have been overlap between the firing of the wood and the oil out temp.

Why are you not heating with 130 degree water on the top of the tank?
According to some of the reading I have done you can still get some BTU's out of that right?? (broken link removed to http://www.heatinghelp.com/heating_howcome4.cfm)

How do you know your sick-- when you monitoring other peoples heating cycles
just curious.

The link that you posted doesn't work - this forum mangles some characters in URLs.

However, I assume that you're looking at the oil-to-wood transition last Saturday night. During the winter, I don't scavenge heat from my oil boiler to the storage tank. The reason is that I assume that there will be heat demand again soon, and I don't want to be wasting oil at that point to bring a cold boiler back up to temp. I do scavenge to heat the hot tub and overheat the domestic hot water.

The consequence is that I waste a little heat that's left in the oil boiler when I transition back to wood, but that doesn't happen often.

You're not the only person looking at my graphs. I was talking to someone who knew exactly when I had built a late-evening fire.

 

[wdc1160]

I am sorry but I cannot accept that as an answer

I included a pic.

The reason for this post is to me your graph doesn't reflect what I would have expected from you control code

This is just some random observations/misunderstandings. Please comment where you think I need corrected.
Second I have read your control code, pseudo-code and comnmentary, if you make reference to it, I believe I will understand your meaning.

1. I am surprised the oil boiler fired at all due to the temp in the top of tank-- obviously a separate issue than my main issue.

main issue

2. why did the oil out temp raise to 100 F @ 2:53, is that time or temp significant. In letter A

3. Why did it follow the pattern we see in B. I thought if demand where not being met it should look like C

4. Where I think I am confused is that I don't understand what is happending in the minutes transpiring over B.

For example. I conclude you made the fire at 5:21, demand was not being met as early as 2:50
As demand was not being met your oil out line should have risen more similar to C than it does in the actual graph

What is effecting oil out that I don't understand.

Thank you for indulging my idiocy.

 

[Nofossil]

Dang, you guys are keeping me honest!

Here's the deal: I replaced a leaking drain valve on the oil boiler, and recharged the system. That allowed water from the hot manifold to flow into the oil boiler, raising it's temperature a bit. It didn't fire.

If you'll notice, I forgot to open the isolation valve for the wood boiler after I was done with the repair. When I built a fire a bit later, it couldn't circulate and went into overtemperature.

The check boxes on the right allow you to view the digital I/O, which includes signals for the three operating modes: wood, oil, and tank. If you look at them, you'll see that it was in tank mode as you'd expect, until the wood boiler got hot. It was never in oil mode, so the oil burner couldn't fire.

 

[Eric Johnson]

I thought I was the only one who did stupid things like forgetting to open valves after maintenance.

I'm starting to think that if you hiccup, nofossil, it's going to show up on one of those graphs.

 

[wdc1160]

I am glad I asked because I would have never concluded that from a simple graph.

Actually nofossil. I have a hard time keeping up with the inputs because often the color legend indicates all black for them, so I often loose my place during my perusing your graphs.

In your spare time all of your graph groupies are requesting color legends for inputs and outputs. If and only if it doesn't downgrade your WAF.

Eric nofosil's hiccups are on a whole other page - try to keep up.

 

[Nofossil]

I realized that you asked several good questions. Here's a more complete answer.

I am sorry but I cannot accept that as an answer

I included a pic.

The reason for this post is to me your graph doesn't reflect what I would have expected from you control code

This is just some random observations/misunderstandings. Please comment where you think I need corrected.
Second I have read your control code, pseudo-code and comnmentary, if you make reference to it, I believe I will understand your meaning.

1. I am surprised the oil boiler fired at all due to the temp in the top of tank-- obviously a separate issue than my main issue.

main issue

2. why did the oil out temp raise to 100 F @ 2:53, is that time or temp significant. In letter A

This is from the valve replacement and system refill described in my previous post.

3. Why did it follow the pattern we see in B. I thought if demand where not being met it should look like C

4. Where I think I am confused is that I don't understand what is happending in the minutes transpiring over B.

'B' is the classic pattern that you get when you get a shot of heat followed by no demand. The boiler got hot quickly, but the boiler circ never came on. What you're seeing is the gradual loss of boiler heat up the flue and out into the boiler room.

For example. I conclude you made the fire at 5:21, demand was not being met as early as 2:50
As demand was not being met your oil out line should have risen more similar to C than it does in the actual graph

What is effecting oil out that I don't understand.

Thank you for indulging my idiocy.

Last concept is 'demand'. I play a little game that doesn't show up in the graph. The 'demand' signal that you see is based on either of the two top floors calling for heat. When I'm heating with the boiler, that's the signal that I use. When I'm heating from the tank, I use the second stage thermostat outputs instead, which are not visible on the graph. The second stage outputs come on two degrees below the primary contacts. The result is that I heat the house just a bit warmer when I'm heating with the boiler. In tank mode, you'll see demand on the graph for some time before the second stage contacts close.

Actual house temp stayed at 70 degrees throughout.

 

[wdc1160]

Ok I went back and have done my homework. The further insight on the concept of the demand IO helped me understand a few things.

One of the things I had looked at was the effciency at the end of the burns. I know this sounds odd, but I had seen on several of the graphs what I call the "rooster tail." I think this pattern is likely caused by having more BTU than all of your system can absorb. You have said before that you think that you don't have enough storage. Coincidentally this type of rooster tail end to burns never showed in your control burn demo.

If you have no idea what I am talking about look at 1-5. Look at the last 3 hrs of burn time.

Do you consider this new or not unatural?

 

[Nofossil]

Ok I went back and have done my homework. The further insight on the concept of the demand IO helped me understand a few things.

One of the things I had looked at was the effciency at the end of the burns. I know this sounds odd, but I had seen on several of the graphs what I call the "rooster tail." I think this pattern is likely caused by having more BTU than all of your system can absorb. You have said before that you think that you don't have enough storage. Coincidentally this type of rooster tail end to burns never showed in your control burn demo.

What is 'my control burn demo'? I don't remember the reference.

If you have no idea what I am talking about look at 1-5. Look at the last 3 hrs of burn time.

Do you consider this new or not unatural?

By 1-5, do you mean today? I've attached today's graph. At about 11:00, it started heating the tank. Any time the outlet temp drops too low, it will stop heating the tank to allow the boiler to recover. That creates some fluctuations in inlet and outlet temps.

At about 12:40, it tried heating the tank one last time, but the fire had died out so much that it dropped the boiler temp to the point that the circulator shut off (not shown - I don't monitor the wood circulator. The EKO controller manages it). With the circulator off, the boiler temp climbs a bit, but not enough to get the circulator to restart.

Did you notice that I skipped yesterday?

Sometimes, when the tank is really hot, the boiler puts out more than the tank can absorb. That will cause the boiler to idle for a couple of minutes until the temperature drops. When that happens, you'll see fluctuations like what you see after 11:00, but at a higher temp.

And here I thought I was the only graph junkie. By the way, adding colors and legends to the digital I/O is not trivial. I group them with inputs above outputs, and a little space between inputs and outputs. I usually look at a maximum of four each.

 

[barnartist]

You guys sound fiesty.
For the layman, what and how are these graphs.
My WAF is napping. So are my KAF. Kids. This may let me consentrate enough to catch up.
Nofossil, still pondering how to set up.

 

[Eric Johnson]

The Boiler Room is a big tent. A rainbow coalition. You name it. We welcome diversity here--even graph junkies--monochrome and otherwise. We may not understand what you guys are talking about, but it's good to know you're doing it. And some of us like to watch.

 

[wdc1160]

I noticed the skip - Your weather has to be very different from ours in Indiana -- a skip in heating would have resulted in exploded pipes. What was your outside temp?


1st
Your whole setup is non-trivial- and I don't expect color graphs on my account. I was attempting to explain the reason for my confusion and making light, but I think your setup is second to none.

But, as long as your paying me any mind an outside temp thermistor would be handy. LOL
Are they glass therms u r using??

The reason for the graph questions is I plan on starting a whole new living space heating and cooling system at a new location within the next 60 days. Currently I am getting my ducks in a row. One of my favorite resources is your nofossil.org. You along with some others have inspired me to put together my own page chronicling parts/equipment, local strategies, method efficiencies, and control equipment. I hope to appeal to people who don’t have the computer, welding, engineering, or the equipment experience you do. I am guessing that is quite a few of us. I am certain few wood burners have in depth knowledge of the Linux OS, how IO works in general, PHP, Web servers . You’re the first I have seen proof of.

I plan on trying to give back to the online community. What I had in mind was a contribution of software that would be easy for a novice to setup a control system. As you know this is difficult since a system like yours is complicated and has intricate details.
I thought some simple drive image writer and some setup scripts could go along way to making the control aspect of the boiler operation smoother. Moreover, this could be done cheaply, and with a real payback of time, maybe equipment, and wood.
I think in general the control systems are being overlooked – treated as unimportant.
And they may be unimportant for some. But most probably don’t know enough to make the decision.
An example
The new house I am buying has a boiler ran on Nat gas. I ran it 2 days full(zones in demand) out while it was –5 to 15F. The boiler ran at 200F and the return temp was cold (maybe 50 F) to the touch. The boiler (1968) is new to me, but clearly there is a problem. I don’t know how long it has run this way, but I think a 200 dollar investment and 5(max) hrs by the previous owner could have saved’em a bundle. Maybe this isn’t a good example because it is clearly not operating correctly -demand was there and the water was overheating. These systems can point out the smaller problems as well.


I’m working on control equipment now. I want to spend most of my time on making sure the logic is correct(not perfect) for my setup and for the others who want to use it.


Testing is difficult since I don't have a gasser yet or the hearth chimney insert. So I am making logic without anything to impose or test on yet. -- soon though

But, your setup is well suited to make observation and predictions on. I know it has helped a great deal already.

Nofossil, I wrote a very long diatribe about this event. However, I think that it almost certainly has to do with EKO's circ and control.

However, I still don't think this type of pattern can be the most effective. And this may warrant “tricking” the EKO.

This is what I think it should look like in a perfect world. Note: I don't know/remember how your water return is piped so ignore return temp.

In an attempt to justify why I am even bothering with this question I would explain that this happens at most burns. I admit I can’t quantify or even recognize the events cause. But, When it happens it may cost half split or in some instances maybe a whole split. If that happens 90 times a year you are out the time and energy you put into maybe a face cord. Not a problem for you, but maybe for the other people who pay 230 a face(and some do). And, I don’t want to be the guy who writes the software that costs people 200 a year in extra wood. Furthermore, even if it doesn’t cost money it may cost “tinkering” time for someone else down the road. Maybe if this trend is identified a piece of software can identify it and treat it, after all, every other person who posts is talking about “becoming more efficient with time” Maybe some of the software can identify some of the short-comings and shorten the learning curve.

This isn't limited to gasification. I think a control board for standard combustion boilers, stoves and fireplaces could give many useful pieces of information as well. Circuits that show both o2 and absolute pressure i.e. draft measurements, maintenance requirements, and could email you the “need to know stuff.” -- Like your pipes are about to freeze. Come home quick. – a ways off though

Promise to keep all my posts shorter than this. But Eric as a graph voyeur I am sure you got an eyeful.

Bill

 

[barnartist]

Thought you should know this sounds cool. Keep it up, whatever it is.

 

[Eric Johnson]

Well Bill, you've been a bit of an enigma up until now, but I think I'm getting a little better read on where you are coming from. So I'm glad you're here and certainly look forward to working with you in the future. The whole issue of controls is something I should learn more about. My limited skills are in other areas, but I need to learn more about the basics of boiler control.

 

[wdc1160]

I think that technology and wood burning were at polar ends of the spectrum at one point in time. But, now with high tech being cheap, and so many of us woodburners being frugal, it just seems to make sense.
Gassifiaction with storage -- specifcally is too complicated, precise, and time consuming for it to be practical to monitor by "hand."
That said it can be done, but it makes it more difficult to see problems.

You once before mentioned a mix/HX/zone problem you were having with repetitive inefficencies. With a trasparent controller (like nofossils) that wouldn't have been
easily possible.

I for one know I cannot keep track of storage, zones, dhw, solar, and keep track of weather, then determine I am using 20 percent more wood than normal.

I am away from the house to much to know most of this.

Sorry no graphs Eric

 

[Nofossil]

I noticed the skip - Your weather has to be very different from ours in Indiana -- a skip in heating would have resulted in exploded pipes. What was your outside temp?

Started out around 0 but warmed up to mid twenties during the day.

1st
Your whole setup is non-trivial- and I don't expect color graphs on my account. I was attempting to explain the reason for my confusion and making light, but I think your setup is second to none.

But, as long as your paying me any mind an outside temp thermistor would be handy. LOL
Are they glass therms u r using??

I'm adding another set of 8 analog inputs. Outside temp will probably be one of them. I'm using glass-encapsulated thermistors - US Sensor, from Digi-Key.

The reason for the graph questions is I plan on starting a whole new living space heating and cooling system at a new location within the next 60 days. Currently I am getting my ducks in a row. One of my favorite resources is your nofossil.org. You along with some others have inspired me to put together my own page chronicling parts/equipment, local strategies, method efficiencies, and control equipment. I hope to appeal to people who don’t have the computer, welding, engineering, or the equipment experience you do. I am guessing that is quite a few of us. I am certain few wood burners have in depth knowledge of the Linux OS, how IO works in general, PHP, Web servers . You’re the first I have seen proof of.

I plan on trying to give back to the online community. What I had in mind was a contribution of software that would be easy for a novice to setup a control system. As you know this is difficult since a system like yours is complicated and has intricate details.

Thanks for the kind words. I'm trying to do the same thing.

I’m working on control equipment now. I want to spend most of my time on making sure the logic is correct(not perfect) for my setup and for the others who want to use it.


Testing is difficult since I don't have a gasser yet or the hearth chimney insert. So I am making logic without anything to impose or test on yet. -- soon though

But, your setup is well suited to make observation and predictions on. I know it has helped a great deal already.

Thanks again. I've found that having the data available is a tremendous help, and it allows detailed analysis if you're so inclined.

Nofossil, I wrote a very long diatribe about this event. However, I think that it almost certainly has to do with EKO's circ and control.

However, I still don't think this type of pattern can be the most effective. And this may warrant “tricking” the EKO.

This is what I think it should look like in a perfect world. Note: I don't know/remember how your water return is piped so ignore return temp.

I trick the EKO and oil controllers all the time. In addition to the additional analog inputs, I'm also adding some digital I/O to allow me to override the EKO controller, specifically the fan and circulator.

Upgrades on the list:

Analog:
- secondary combustion temp
- flue temp
- oxygen ratio

Digital out:
- wood circ force on
- fan disable
- alarm
- wood circ speed select

In an attempt to justify why I am even bothering with this question I would explain that this happens at most burns. I admit I can’t quantify or even recognize the events cause. But, When it happens it may cost half split or in some instances maybe a whole split. If that happens 90 times a year you are out the time and energy you put into maybe a face cord. Not a problem for you, but maybe for the other people who pay 230 a face(and some do). And, I don’t want to be the guy who writes the software that costs people 200 a year in extra wood. Furthermore, even if it doesn’t cost money it may cost “tinkering” time for someone else down the road. Maybe if this trend is identified a piece of software can identify it and treat it, after all, every other person who posts is talking about “becoming more efficient with time” Maybe some of the software can identify some of the short-comings and shorten the learning curve.

Bill

My entire purpose in setting up the nofossil site was to share what I had learned in setting up my system. Well, maybe to show off a little bit, too ;-)

I'm always tinkering with the control hardware and software. My next areas of concentration are optimizing primary and secondary air throughout the burn cycle, and recovering wood boiler heat more effectively when the fire is out. I'm also adding audible alarms for stack overtemp (350 degrees or above) and 'needs wood'. Finally, I'm getting turbulators.

Always a work in progress. I'm anxious to learn as much as I can from others.

If you haven't found it already, here's a link to an overview of my control log.

 

[wdc1160]

Started out around 0 but warmed up to mid twenties during the day.

Well then, I was mistaken, not that much different at all. Why had you not been skipping earlier in the season then?

I’m using glass-encapsulated thermistors - US Sensor, from Digi-Key.

Ok, I didn't know if the switch over had been done.

I trick the EKO and oil controllers all the time. In addition to the additional analog inputs, I’m also adding some digital I/O to allow me to override the EKO controller, specifically the fan and circ.

Upgrades on the list:

Analog:
- secondary combustion temp
- flue temp
- oxygen ratio

Digital out:
- wood circ force on
- fan disable
- alarm
- wood circ speed select

Yah, I agree getting your controller mits on the fan and circ are going a long way toward making those graphs look any way you like.

Why an alarm for temps above 350, are u worried about a fire, or efficiently loss?

We will have to trade ideas on O2 regulation. I think that things really complicated, but with a payoff.

Did you pick hardware for the O2 circuit. Are u going to even use a circuit or something I have never heard of?


I had never seen at what pressure you run your setup at? Do you bump up past 15lbs?

Does the EKO have a preference, or do you??
Also wood out temp? I wouldn't know how to adjust or if it is too dangerous, but I do know in most other types of gassers and standard combust
folks say the sweet spot is higher than 180, that coupled with higher press is supposedly the holy grail.

This is not relevant, but I run my wood fired boiler 200F at 30 PSI. The manufacturer tests for one week @ 60.

BarnArtist told me a story that has convinced me that EKO's can take some heat and pressure thats why I ask.

My entire purpose in setting up the nofossil site was to share what I had learned in setting up my system. Well, maybe to show off a little bit, too

If you need any hardware, technical help in either the programming or the hardware I would offer either.

I have a piles of boards, drives and cabling that I couldn't use if I lived to be 1000 years old.

Thanks for all of your help.

 

[Eric Johnson]

What's your pressure relief valve set to open at, Bill?

I had a Marathon wood-fired boiler once that I ran at 210-220 whenever possible, trying to achieve secondary burn. I doubt if it ever did. It had a huge old riveted pressure tank which I kept in service when we tore out the old coal burner, since I figured it worked and was sized to the system. But when the temps got up above 200, the gauge would start to creep up towards 30. That was a totally gravity-feed system in an old house with cast iron rads and huge (like 2 1/2-inch) piping in the basement. The air supply on the boiler was an Ammark bimetal controller, so the whole thing ran with no electricity. That was up in the Adirondack Park where the power goes out all the time and it gets down to -50 from time to time. I'd get ten cords of wood in my basement by the end of October and hunker down for the winter. Bring it on.

The EKOs are designed to be run at atmospheric pressure in Europe. For some reason. I run mine at 15 psi. The controllers on the EKOs nofossil and I have max out at 80 degrees Centigrade. I guess that's just over 175. The new controllers ($250) allow you to go up past 190, I believe. If I can scrape up the coin I may upgrade because I like running closer to 190, but really don't have any stomach for trying to trick the existing controller by shielding the probe. I don't want to screw it up and blow out my pex.

 

[wdc1160]

What’s your pressure relief valve set to open at, Bill?

about 35, If I get the boiler to fire up hard and fast, I can get the release to drip.

I had a Marathon wood-fired boiler once that I ran at 210-220 whenever possible, trying to achieve secondary burn. I doubt if it ever did. It had a huge old riveted pressure tank which I kept in service when we tore out the old coal burner, since I figured it worked and was sized to the system. But when the temps got up above 200, the gauge would start to creep up towards 30. That was a totally gravity-feed system in an old house with cast iron rads and huge (like 2 1/2-inch) piping in the basement. The air supply on the boiler was an Ammark bimet controller, so the whole thing ran with no electricity. That was up in the Adirondack Park where the power goes out all the time and it gets down to -50 from time to time. I’d get ten cords of wood in my basement by the end of October and hunker down for the winter. Bring it on.

I like the Adirondack's , but not at -50.
I have not had the need or the cojenes to run the boiler at that temp. Eric that is a steam engine not a boiler. Lol
I always worried about running temps over 212, then decompression happening rapidly resulting in irreparably broken equipment, from experience I think that is the excpetion and not the rule.
If you have a fitting pull loose it doesn't make the system blow up, just turns the house or cabin into a steam room. I think that I will aim higher this time around.

No I think that 210-220 could be considered safe at some pressures including 30 psi.
You and I doubled the normal atmosphere in our lines
from outside of 14.69 to 30 PSI, 2.1 BAR
that results in a boil temp of 250
I don't consider that more dangerous that 180 at 15 with boil point of 213

The EKO are designed to be run at atmospheric pressure in Europe. For some reason. I run mine at 15 psi. The controllers on the EKO nofossil and I have max out at 80 degrees Centigrade. I guess that’s just over 175. The new controllers ($250) allow you to go up past 190, I believe. If I can scrape up the coin I may upgrade because I like running closer to 190, but really don’t have any stomach for trying to trick the existing controller by shielding the probe. I don’t want to screw it up and blow out my pex.

Ask barnartist how much heat and pressure Pex can take. It is tough stuff. I think the people who make pex expect the stuff only to last about 30 years.
but during those 30 it can take a beating. Your hearing this from a guy who only has black pipe though.
Also I don't think all of the pex is equal. I think everyone on the forum agrees the Pex al is the stuff that is going to be best suited to the abuse.
Eric I think I can speak for nofossil and myself when I say:

We have no intention of buying the new controller, we both have controllers of our own that log and manipulate the equipment so it does as instructed.
My point being 190 might not be best either.
I think when I receive my EKO I will likely try burning at temps and pressures closer to what you did in the ADK Park.
I figure nofossil will beat me to this, and we will see it on a graph somewhere soon. lol

 

[Eric Johnson]

Well, if your new EKO has the new controller and you can do your modifications just as well on the old one, then maybe we can come to some sort of arrangement. My guess is that you're leaning more towards getting the boiler without a controller and building your own. But it's something to consider. Or are you buying a used one?

 

[wdc1160]

I really has to do with tricking the controller (old or new) by telling it that it is cooler than it really is or telling it that their isn't enough air.

But the real measurments of air or temp are controlled by our controlers. It is no different than blocking one nozzle for lower/slower overall output.

 

[Nofossil]

Well then, I was mistaken, not that much different at all. Why had you not been skipping earlier in the season then?

It warmed up overnight. I built too big a fire, so the tank got really hot. Even so, the house temps were a bit cool the morning after the skipped day. If it's cooler than about 20 degrees, it's marginal to try an skip with the size storage tank that I have.

Why an alarm for temps above 350, are u worried about a fire, or efficiently loss?

I'm afraid of forgetting that I started a fire and that the lower door and bypass damper are still open.

We will have to trade ideas on O2 regulation. I think that things really complicated, but with a payoff.

Did you pick hardware for the O2 circuit. Are u going to even use a circuit or something I have never heard of?

I want to experiment with an automotive wideband sensor. They won't last long, but I just want to get some baseline data and some idea of the best settings, especially for secondary air.

If you need any hardware, technical help in either the programming or the hardware I would offer either.

I have a piles of boards, drives and cabling that I couldn't use if I lived to be 1000 years old.

Thanks for all of your help.

Thanks for the offer, and I'm glad to have been of some help. Biggest area where I'm weak is electronics. I'm using relays in a ton of places where I suspect a simple transistor would be better.

 

[wdc1160]

I want to experiment with an automotive wideband sensor. They won’t last long, but I just want to get some baseline data and some idea of the best settings, especially for secondary air.

I am not sure where you would put the auto sensor?

Biggest area where I’m weak is electronics. I’m using relays in a ton of places where I suspect a simple transistor would be better.

One thing you can't do with transistors, that you can with relay or toggle switches, is put them just anywhere in a circuit and expect them to turn things on & off-- for reasons I won't go into.
I have switches used in my setup. The same effect is found in solid-state bilateral switches. Since you know in principle how a transistor works you could use these if you wanted.

They are not as widely available as auto relays, but @ .30 cents a piece if they save you ten mintues of wiring/scratching your head who cares. You could get'em at digikey I am certain.

 

[barnartist]

Thought youd like to know I left my damper open last month all night. I dont know how hot things got, but I didn't see any obvious damage. I did not relieve any water from pressure, Im set at 30-35 lbs. It did clean my upper chamber though. I dont think I even got water up to 170 either.
Don't know if this info is useful.

 

[Bartman]

Why don't you guys go with a PLC? They can be programmed to do damn near anything, on eBay you can get them relatively inexpensive. A couple of weeks ago I picked up an early TI/GE/Siemens PLC for $50. Also I picked up some digital temp controllers for about $40 with shipping and some are available with thermocouples for less than $50.