Hot end and bed can't heat at same time.

[hcdbey]

I have been having considerable difficulty getting the hot end to reach the preset temperature. Now, I have noticed that if I leave the bed heater off, the hot end has no trouble reaching the preset temperature. If I then put the bed heater on, the hot end drops about ten degrees.

Does anyone have a solution? Is my power supply weak? Do I have thing wired incorrectly?

Thanks.

Hank

[mhackney]

What printer and power supply do you have? What temps are you trying to reach? Are you using PID or bang bang control on the heated bed?

Wiring is not incorrect or it would not work at all. You *might* have poor connections on the hot bed and/or RAMBo for the hot bed. But let's start with answers to the above.

[hcdbey]

"More information.
Printer: Rostock Max V2
Power Supply: VIOTEK 450W
Hot End Temp: 232 degrees
Bed Temp: 100
PID (I don't know what bang ban control is.) In EEPROM settings I see values for Bed Heat Manager [0-3], Bed PID drive max, etc.

The printer has worked reasonably well since commissioning in about 14 months ago. The usage information screen indicates 31 days of printing and 4,503 meters of filament.

Thanks for giving this consideration."

[mhackney]

I don't like throwing parts at things to fix problems but it my and many other's opinions that 100° bed is pushing the limits of the stock power supply, especially if all of the solder joints and connections are not perfect. I'd start with all the connections. Check them and resolder or tighten if needed. Certainly the new power supply SeeMeCNC offers has more than enough umph to do this.

[IMBoring25]

I also have the Viotek for the moment. Under load mine barely pushes 11V, even with the bed on its own supply. With an actual 12V supply running the bed I now have no trouble with setting any reasonable bed temperature but am still struggling with the hot end staying at temperature. That power supply's days are numbered.

[Xenocrates]

I also have the Viotek for the moment. Under load mine barely pushes 11V, even with the bed on its own supply. With an actual 12V supply running the bed I now have no trouble with setting any reasonable bed temperature but am still struggling with the hot end staying at temperature. That power supply's days are numbered.

Have you got anything on the 5V rail? Give it say, a few fans in the base running off that, and you should see the power regulation firm up some (It's a cheap and cruddy power supply, but those architectures don't handle cross loading them the way we have well at all)

[gibbonsrock]

Hi Everyone,

I have a completely stock Rostock Max V2 and I'm getting frustrated with a similar problem- the PS doesn't seem capable of heating the hotend past 235 if the bed is heating. (80 deg) My prints stick to the bed just fine, but they always have strings everywhere and nuggets of plastic hanging off the corners and walls, so I am experimenting with the printing temperature.

If I set the hotend to 240 by itself, it can get there no problem, but as soon as the bed starts heating, the hotend drops to juuuust barely 235. From a cold start, this printer takes 30-60 min to get up to 80/235. The printer is in my basement, but I've built a foam enclosure around it and using a small space heater to help it stay warm, to no avail. It seems that power supply just can't do both jobs.

Is there a workaround for this? Thanks!

[Xenocrates]

Again, the question is the power supply. If it's an older V2 (Which I can't tell by your registration date honestly), it has an ATX power supply which may have reduced power on 12V if the 5V rail is completely unloaded. If the power cord does not exit on the side (I believe it's the right side), it should be an ATX supply, and as such you likely need to open it up to install a load on 5V, say something like a couple 5V computer fans to cool the base cabinet, or a resistor (I would mount that outside if you go that route, and make sure that it can dissipate the proper amount of heat for the amperage/voltage.

There are other power supplies that do behave better under these conditions (This is usually called cross-loading, and the AX-760 I use is very good for this), usually on the higher end of the efficiency curves and also the higher end of the market, where you see things like DC-DC converters rather than multiple tap transformer/rectifier or other architectures (I am not an EE, so I don't know a whole lot beyond what I've picked up from reviews, repairs, and teardowns). These are another solution, but are likely more expensive than either loading the rail or buying a new LED power supply from Seeme.

If you do have the LED power supply (AKA cable goes to socket on side panel), and it's still failing like this, I might check to see what the voltage is at startup and under load with a multimeter. If it's dropping substantially then it's likely a defective power supply, and you may want to contact Seeme about it. If it isn't try increasing the PID drive max. However, be warned that 240C is very close to the safe limit for the V2's stock hotend, as it uses PTFE and PEEK structurally, and at highly elevated temperatures, these can melt or decompose the potentially toxic gasses (especially PTFE).

If neither of those helps sufficiently, a heater cartridge rather than a resistor may help as they usually have slightly more power, as would wrapping the hotend in an insulating tape such as Kapton or self-fusing silicon.

[gibbonsrock]

Wow, Thanks so much for the quick and in-depth answer, Xenocrates. I highly appreciate it.

I got this Rostock kit in May`16- it does have the newer power supply. I've already torn down this hot end once to re-insulate it and adjusted the PID power drive. Even building a foam enclosure around the structure and hitting it with a small space heater doesn't help- It seems to be an underpowered system. I'll contact SeeMeCNC- I'm sure they'll be thrilled to hear from me again. I've had a couple other issues with it- to the point where I gave up on it and didn't touch it again until just recently. Man, even if they give me a new power supply, the thought of the effort involved in swapping it out is daunting.

I also appreciate the reminder about the PEEK tube- I am aware of and mindful of that 247 degree melting point. Thanks again!

[Mac The Knife]

Is the powersupply like this one they currently sell on their website? https://www.seemecnc.com/collections/pa ... wer-supply

[Xenocrates]

If it was a 16 model, it's that power supply. Which means if it's dropping the hotend temperature while heating the bed, there's an issue somewhere, be it bad or off nominal resistors (Resistors have tolerance, and if the resistance is high, it won't produce as much heat as you want), failing voltage regulation of the power supply, or loss of power due to the rambo heating up under load and thus soaking slightly more power. There's also the bit where that's pretty close the the max temp the hotend and resistors are really designed for, so even with a space heater, the insulation you did should do something. Beyond that, there's not a whole lot to do. Turn up the voltage pot, replace resistors with heater cartridges, or possibly increase the wire size to the hotend (Check to see if the wires are getting warm. If they are self heating, you are losing voltage to them)

[gibbonsrock]

Yup, it's a Keling power supply. I used a similar one to power my Joe's 4x4 hybrid CNC router electronics, along with their steppers and drivers. Since it has been a while since I really dug into trying to make this machine work, I went back through my old emails with SeeMe folks and noted that JJ said I probably wouldn't have to go much higher than 235 for practical printing. It can just barely hit 80/235 with the heater and shroud in place.

There's an issue with this printer that made it a bear to calibrate- so the very idea of taking any part of it apart to do any surgery or upgrades and then having to go through that nightmare again makes me hesitant to act.

Thanks again for your insight!

[Mac The Knife]

I would connect a voltmeter to the output of the powersupply, and read the voltage while it was just on. Then I'd turn on just the hotend and read the voltage, then the bed, then both.