10c temperature overshoot - pump heating?

[julianf]

Ive just gone out to check on the reactor, and, whilst the PID was set for 85c, the process temp was 95c : (


Ive just fitted a JGS 110lpm pump, and this is the first process.  Ive also just re-wired my control box...however, the lights in the garage are pulsing with the PID led, so i know somthing is sucking current (but not all the time, if you see what i mean)


Foolishly, i did not look at what was going on before rebooting the PID (as in i dont know if it was still trying to heat)


My main fear is that, somehow, the pump itself is heating.  Which means i cant leave it on for long demeth, as, if the pump is heating the batch more than the losses (hard to believe!) the temp will keep going up.


What do you think?  Large PID overshoot, or pump heating?

[Head Womble]

Check the drift setting on the PID.

Mine has a function where you can choose how many ° drift above and bellow the set point that the heater will react to.

I have one of JGS's 110lpm pumps and suffer no pump heating.

[Julian]

I got heating via the pump as soon as I fitted a TAM 120.  But then I used the same venturi as I had on my Leo.

It's not really a problem, I leave it demething and dewatering for quite long periods with no ill effect.  It won't increase the temperature indefinitely, it will level out with heat losses at some point.

Personally I wouldn't worry about it, just be aware of the effect and work around it.

[julianf]

The reason im concerned right at this moment in time -

My usual process is to demeth at 85c, then turn off the heater, and leave the pump running over night, and pump out in the morning (i dont bubble at all)

I went out to turn off the heater before bed, and found the temperature 10c higher than it should be.

So im now waiting 30 mins (when i would rather be in bed) to see if the temp goes up or down, now that ive turned the heater off.

I am still using the same venturi as i was using before.

I guess i could pull some insulation off the reactor, but i would have thought the losses at 95c to be significant anyhow...

[julianf]

(basically, i dont want to go to bed and be woken by sirens!)

[Julian]

Even without the heating effect, I wouldn't leave my processor running over night ... seems like tempting fate to me!

[julianf]

I always figure that there's no way im going to watch it all the time, and, given that, if somthing goes wrong, itll go wrong so quickly anyhow, it would probably make very little difference between me being in the house, and being in the house asleep.

But, yes, i can see other people's opinions also.


Ive just got in - i went out to check again, and it had got up to 97c, so i figured i couldnt leave it unattended, and, second to that, if it had been running for hours at a higher temp than intended, it was probably well demethed anyhow.


I pump out to the settling drums via a flexible hose.  Never normally an issue at 50c ish.  Not so much fun at 97c - couldnt even hold the hose with my bare hand, and fearing significant burns if somthing went wrong.

Done now though, and no meth smell as it pumped, so im thinking itll be fine.

Will need to do somthing about the issue before next batch though.

[therecklessengineer]

PIDs need tuning. Normally the default values are good enough but you have to bear in mind that they cover the characteristics of a soldering iron to a massive oven.

There should be some sort of autotune function - but you'll have to look in the manual to find it.