24v Bed too hot

dcfc_sandy · Post by **dcfc_sandy** » Wed Mar 23, 2016 6:59 pm

Howdy all,

I hope this is a quick one that is merely just a EEPROM setting...

I've popped in a 24v PSU (the meanwell SP-750-24 for those interested), pictures will be forthcoming once the its actually neat rather than cobbled together.

Basically if I set the bed to 60C (or any temp), it blazes away and brings a tear to my eye remembering the pain of 12v stock PSU. But then almost as if it is as eager as me, it jumps up 10C above the aimed temp.

I have done numerous PID auto tunes on 60C, and reached convergence. But the issue remains.

During PID auto tune the bed will cool and reach 60C, however, if just heated to 60C from Matter Control or the LCD it will hover around the 65C mark and refuse to go any lower...

I assume the culprit is one of: Bed Heat Manager or Bed PID drive max/min? They are 1, 255 and 80 respectively.

IMBoring25 · Post by **IMBoring25** » Wed Mar 23, 2016 7:23 pm

PID min sounds like a promising candidate. That will never let it go below about 33% power. Frankly, the one on my Mendel is set to bang-bang and I plan the same on the Rostock when the next PSU gets in. The bed has enough thermal inertia the temperature swings aren't completely out of line. As an added bonus, your SSR will run cooler and last longer with bang-bang (heat manager 0) or dead-time (heat manager 3, P setting becomes dead time in seconds) control.

dcfc_sandy · Post by **dcfc_sandy** » Wed Mar 23, 2016 7:31 pm

I changed the heat manager to use dead-time (3). And lowered the PID max drive to 140. That was better heating from 40C it got to 63C before lowering, but the bed actually did turn off around the 60C mark was as it was oscillating power before that. I'll have a few more plays with PID max/mins and the dead-time control, but promising!

My biggest issue is my office an absolute box room and the bed slams up the ambient temp thus taking ages to cool back down!

dcfc_sandy · Post by **dcfc_sandy** » Wed Mar 23, 2016 7:34 pm

Wait wait wait... If I am using dead-time, does PID drive actually do anything...?

IMBoring25 · Post by **IMBoring25** » Wed Mar 23, 2016 7:51 pm

The EEPROM parameter that is normally P is the dead time. How to determine how it should be set is discussed at http://www.repetier.com/dead-time-control/

dcfc_sandy · Post by **dcfc_sandy** » Thu Mar 24, 2016 7:16 pm

That's the article I was basing everything off

why I got 140 for the PID max value. It's defiantly better, only overshoots by 3C now which is good. Using dead-time, PID drive max/mins of 120 & 20. Dead-time roughly 5 seconds. But I'll keep playing with values and see if we can't get any better

Thankyou

3D-Print · Post by **3D-Print** » Fri Mar 25, 2016 11:18 am

I had the same trouble however the PID auto tune does not work with the Duet.

Here is a link to the thread detailing what I did and final bed settings. Hope it helps.

(http://forum.seemecnc.com/viewtopic.php ... 200#p87954)

dcfc_sandy · Post by **dcfc_sandy** » Sat Mar 26, 2016 7:40 pm

A thread I had skim read before as I'm thing the next upgrades are FSR, enclosure, dual extrusion then duet in that order. But yeah I've gone through it and again playing with the settings to just find the sweet spot. I'm at a 3C overswing currently with temps settling 60.0-60.3. Bed PID drive max/mins 100 and 10. And dead time around 12s. I'll keep tinkering and report back

Thanks again guys

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24v Bed too hot

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