Bed heater tuning questions
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I think the heater may be a bit underpowered for that size of bed.
How much did you reduce gain by? What values were used?
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@Phaedrux The gain is at .168, the dead time I lowered to 1.5. about to run a print to see if it will hold temp.
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750W heater are commonly used on Voron with bed size of 350x350. I think 1100x1100 is too much for this poor heater...too much surface that exchange heat with cool air. If you print abs then an enclosed chamber is a must, more with that size of print area. Probably you need 3 or 4 of this 750W heater to reach 110°C in a reasonable time and mantain it during printing.
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I agree that you are underpowered. I use a 1600W heater for my 450mmx450mmx8mm Al plate with insulation and thermal breaks.
I would check to make sure that you are getting the power you expect. Make sure you are running the correct voltage for the heater as well.
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@MikeS The Bed was holding heat fine until we had a power surge in the building, had to replace the wire to the bed. The entire printer is in a popup canopy with walls to act as the enclosure, but for example, it reached 110C, has been printing for about 14 minutes now and is already dropped to 100C
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@hamel 750W was a guess, I didn't build this printer the person who built it has left the company and didn't leave any specs. after more research there are similar ones on alibaba that are around 2000W but they run on 220V. I'm working on finding the receipts to find out what it is.
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@Tpmoses said in Bed heater tuning questions:
I'm working on finding the receipts to find out what it is.
That would be the best bet. The wattage could be pretty much anything and you can't tell by looking at it.
If you're familiar with Ohms law you could measure the resistance of the heater and then figure out the current and wattage.
Can you post some photos of the bed and heater so we can get an idea of what you're dealing with? Also the SSR and wiring.
You might be able to use bang bang instead of PID tuning it, but you might still run into the problem of it not heating fast enough and causing a heater error.
Adding a thermistor to the bed plate itself might be the easiest thing to do since it will give the PID algorithm some better data to tune with.
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@Phaedrux I will as soon as I can, Bed is to hot to take it apart. Wiring wise there is not much to show, As it stands, Power comes from the wall. Ground goes to common. Neutral runs through the SSD Hot wire is connected to the bed through a DIN Block, So the only things between 120V power and the heater is the SSD and one DIN block. The Guy who built it had both the bed heater and the extruder heater as well as some powers supplies for the board and Z driver all on one 120V in. We had a power surge that toasted a length of wire to the bed, I had to rewired it also adding a ground to the bed. (kept getting shocked) I then moved bed power to the 120V in that ran the X and Y power supplies. Printed fine.
The bed started to have issues holding temp on Monday, Seemed that it was not getting enough source power, so I ran a separate 120V drop and put it in its current config.
There is an integrated thermistor in the heat mat itself.
I've never used Bang Bang mode before, I'm not as worried about the slow warm up as I am the temp starts dropping the second the printer does anything but sit still. -
@Tpmoses said in Bed heater tuning questions:
We had a power surge that toasted a length of wire to the bed,
Might be time to inspect the heater pad itself if possible.
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@Phaedrux I cut the wire to have a pigtail and tested it with my meter, still has continuity. The length of Wire that I cut out had no continuity on the live wire. but still had it on the neutral, When I replaced the wire I also added a ground to the bed that connects to common.
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@Phaedrux I have talked to my boss, he is open to me replacing the mat, and my best guess at doing that and avoiding future heartache is to replace it with 4 say 500x500mm ones. any suggestions? I'll know if I go that route I need to get 3 more SSRs but I'm not sure what type of heaters I should get that wont make my boss mad at me for spending too much money.
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I am also not sure how I would integrate that into the duet 2 wifi board
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Well the only thing that makes bosses more mad than spending money is spending good money after bad money. Buy once cry once.
Having 4 smaller zones might be beneficial if you aren't always printing full volume parts. Only heating a sector might be faster and cheaper to run. But remember you're still attached to the other sections of the bed and they will draw a lot of heat away.
There's also the added complexity. Controller 4 heaters for the bed on the Duet you'll need enough ports and still need to figure out how to tune it for all heater function.
https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater
https://duet3d.dozuki.com/Wiki/Spurious_heater_faults_and_how_to_avoid_them
https://duet3d.dozuki.com/Wiki/Tuning_the_heater_temperature_controlThat's where I would buy my heater pads from. They will do custom options too.
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@Phaedrux I am going to make another thread asking questions, I think I have found the heaters I need. The big thing I need to figure out now is how to wire them up. Thank you for all your help
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Get a custom one made. They don't cost all that much, and you can just get the exact size you need to avoid the hassles of either specing them to run in series, or dealing with multiple thermisters and heaters from the control side. I would recommend a thermal switch (manual resettable) that is just above your max temp range incase the SSR fails closed (does happen). Alternatively, you could add a contactor that will trip if a fault occurs (more industrial oriented persons will prefer that method).
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@hamel The problem is time, this machine is used to make parts that are then used to make molds for fiberglass parts. A custom replacement wouldn't be here till May.... I already checked. Four smaller ones can be here by Monday. Ultimately its not my decision to make, bosses liked the faster option.
