Broken euro-st p cv lab stirrer

Thread Starter

metiz

Joined Oct 27, 2014
62
I bought a lab stirrer for basically nothing, knowing full-well it was probably broken - and it is! but I think it might be salvageable. It's a Euro-st p cv. When I turn it on, the display lights up as intended. I can control the motor speed with a knob, and the display shows the RPM settings, so that's all good. But, the motor doesn't turn. When I increase the RPM to about halfway the maximum range, The unit displays an error-4, which is an over-torque protection. turning the power off and on (and turning the knob back) resets the unit. The motor shaft spins freely so it isn't actually over-torquing. Is there something obvious that comes to mind that might be wrong? I think (and hope) it has something to do with the power-board. Off-topic: can anyone tell me why these things are so ridiculously expensive? A new unit costs like $3000. There's nothing inside that would warrant a price even one tenth of that - all standard components.
 
Last edited:

jpanhalt

Joined Jan 18, 2008
11,088
Is that a gear housing between the motor and spindle? Does that turn freely? Any short circuits between the motor leads and its case, excluding a ground lead if present?
 

Thread Starter

metiz

Joined Oct 27, 2014
62
Is that a gear housing between the motor and spindle? Does that turn freely? Any short circuits between the motor leads and its case, excluding a ground lead if present?
Thanks for your reply. Yes, there's a gear housing, and it spins freely. Gear ratio is 1 or close to it. I don't measure any shorts between the motor housing and the motor leads.

To me it's out of focus can you confirm no scale deposits on unit under side of this board
I've made some better pictures, properly focused. There is a bit of grime on this side of the board, but no corrosion or anything. The other side of this board is clean.
IMG_20201018_211038472.jpgIMG_20201018_211038472.jpgIMG_20201018_211155372.jpg
 

Attachments

jpanhalt

Joined Jan 18, 2008
11,088
What's the voltage at the motor? Do you have a DC supply simply to test the motor? Doesn't need to be 60V; maybe even 12V should be enough for a test.
 

Delta prime

Joined Nov 15, 2019
841
A sonicator if you have one 99.99% alcohol or just a brush easy and won't do any harm. And I bet you'll be surprised(I see high gunk impedance connections pin to pin). That's a real scientific term that it just made up. :)
 
Last edited:

Thread Starter

metiz

Joined Oct 27, 2014
62
What's the voltage at the motor? Do you have a DC supply simply to test the motor? Doesn't need to be 60V; maybe even 12V should be enough for a test.
I have a 30V, 2A lab power supply. That should be enough to at least turn it over. I'll give it a try tomorrow, thanks.

A sonicator if you have one 99.99% alcohol or just a brush easy and won't do any harm. And I bet you'll be surprised(I see high gunk impedance connections pin to pin). That's a real scientific term that it just made up. :)
I'm a bit skeptical about this being a likely cause, but it's easy enough to do. I'll give it a good wipe tomorrow. Thanks for the suggestion.
 

jpanhalt

Joined Jan 18, 2008
11,088
I'm a bit skeptical about this being a likely cause, but it's easy enough to do. I'll give it a good wipe tomorrow. Thanks for the suggestion.
Try the correct voltage first. Which "alcohol" would you use? I would be VERY skeptical of any such ambiguous advice.
 

Thread Starter

metiz

Joined Oct 27, 2014
62
Just tested the motor: dead. No movement, no current draw. The resistance between the leads is also infinite. *edit* I just opened the motor and it looks like one of the springs pushing one of the 2 brushes against the commutator was stuck. I'm trying to resemble it now, but the springs are a pain.
 
Last edited:

Thread Starter

metiz

Joined Oct 27, 2014
62
Ok, motor spins! I had to hold the springs off the brushes with a copper shim with a thin wire soldered to it to get the motor cap slid over the commutator. When the brushes were barely over the commutator, I yanked the shims out. Reassembling now.
 
Last edited:

Thread Starter

metiz

Joined Oct 27, 2014
62
Success! The stirrer works again :D One more issue I'm having now is that the stirrer stops randomly. Sometimes after a minute, sometimes after 3. When that happens, it becomes unresponsive to inputs and I have to power cycle it. I think it has something to do with the RPM counter. It's a perforated copper disk that spins through a sensor. It was slightly wobbly. I've bent it back in shape and have been running the unit for about 10 minutes now (still going as I write this)
 

Thread Starter

metiz

Joined Oct 27, 2014
62
Well the problem persist. I'll try clamping the disk between 2 pieces of steel and then heating it up, to try getting it perfectly straight again. *edit* still does it. Could the sensor be faulty?
 
Last edited:

jpanhalt

Joined Jan 18, 2008
11,088
I have seen some pretty flexible interrupter wheels on lab equipment (like speed controls on HPLC pumps). That flex per se didn't affect operation.

Flattening a thin piece of sheet metal that is warped can be a trying experience. Don't hammer it, unless you are an expert. That I am not. Slip rollers can help. But if you are inexperienced in their use, you may end up with a thinner or more distorted mess. My best advice is to leave it alone unless it is actually rubbing against the detector walls. Then, I would only do what is necessary by hand. Inside that case, looks don't matter, and a little rub should not make it stop working.
 

Thread Starter

metiz

Joined Oct 27, 2014
62
I have seen some pretty flexible interrupter wheels on lab equipment (like speed controls on HPLC pumps). That flex per se didn't affect operation.

Flattening a thin piece of sheet metal that is warped can be a trying experience. Don't hammer it, unless you are an expert. That I am not. Slip rollers can help. But if you are inexperienced in their use, you may end up with a thinner or more distorted mess. My best advice is to leave it alone unless it is actually rubbing against the detector walls. Then, I would only do what is necessary by hand. Inside that case, looks don't matter, and a little rub should not make it stop working.
I already flattened it, as described above. It's a copper plate. Squishing it between two flat pieces of steel and then heating it up anneals the copper and retains its shape. Unfortunately it didn't solve the problem. The unit either: 1) turns on and runs normally anywhere between 1 second and 15 minutes before just stopping, 2) turns on, shoots to a high rpm and then goes into a fault-mode, 3) does nothing. With all these problems, I can see the fault indicator LED light up for just an instant before the unit stops.
 
Top