I’ve discussed this somewhere here before but most VFDs are able to provide active braking by applying voltage in the reversed phase sequence. I imagine the 3 minute braking time is not limited by how quickly the motor can stop itself and the attached load but by how quickly it can do that without throwing the basket through the enclosure.
Many systems rely on a type 0 e-stop which simply cuts power to the drive and does not allow use of active braking. It sounds like this may be the case but a mechanical brake supplements the stop
imo cutting the power =/= appropriate stop sequence.
Absolutely!
I’m of the opinion that ignoring that feature, as a way to decelerate the rotating mass is NOT the right way to slow a centrifuge basket in an emergency (Jimmy climbed in…let’s just wait for it to spin down passively).
I don’t see how applying maximum allowable motor torque to the driveshaft would increase the probability of off axis forces. the drive system should be pretty specific about the vectors those forces are applied in.
if they’re just cutting the power, they’re doing in wrong. at least as far as convincing me to buy one. In all fairness, I’ve still got to set the brakes up correctly on the one I’m sitting in. at the moment I’m applying them too hard and exceeding the current limit at about 15 sec into the braking cycle. I need to spend more time with the fine manual.
Although I agree that the system shouldn’t be stopped passively in an emergency situation…
I imagine that if the vessel is full of biomass or solvent or both, that 3 minute window is greatly reduced because of the additional mass and friction generated.
once he done stuck his head in there, it was game over anyway.
I care because it effects total cycle time on my extractions. Jimmy was just a straw man I figured others might get behind.
Should have known this bunch of savages wouldn’t buy that…
@TheGratefulPhil we shouldn’t ever be at full speed with the bowl full of solvent. if we were, I’m not sure if that would be a faster or slower passive spin down. it’s testable
Biomass and solvent would speed up the slowdown process, but biomass only will increase the time it takes to stop. The greater the mass of the object spinning, the more inertia it has. More inertia means it has to fight harder to slow it down. Solvent would provide much greater friction to the spinning basket and therefore increased stopping speed when compared to the coefficient of friction provided by air.
At least that’s how it works in my head, and while I have not tracked that particular aspect of fuge work in great detail, my recollection is that it takes less time to stop when loaded with solvent and a fully loaded basket.
And @cyclopath may not have thought about trying to get a fully-loaded, solvent-filled fuge spinning full tilt, I bet he will now. That sounds like another fun R&D project (research and destruction), because everyone needs to know how hard the machines can be pushed before they say no. Testing to failure is an important part of releasing a good piece of equipment, imho.
My point could be better stated as: the slowdown rate is equal to the base slow down rate due to just air (a constant) plus some function of biomass weight and amount of solvent left in the vessel at the time of stopping.
There’s probably some mechanical engineering equation that could do it
Okay so the issue is this: the fuge will always be imbalanced to some degree. The largest force (and spindle deflection) is going to occur when the braking force is applied initially. Now, some drives definitely allow an automation curve to be applied to the braking current so you don’t get “the jerk” but its fairly rare. Drives see current and frequency, not the motor shaft getting bent like a reed in the wind lol.
On the E-stop decision, there is a reason that type 0 (immediate power isolation) is very common; electrocution is often a risk that needs to be addressed in the risk assessment. Most of my “career” I’ve worked with equipment that, like centrifuges, are a lot more likely to kill a bunch of people from something other than the proverbial fork in the socket. For something that spins a good hundred pounds of flammable solvent though, I’d think the risk assessment might consider it a good idea to be able to immediately make the lightning stop.
The best course of action IMO would be to have a safety-rated rive with a type-1 (safe stop then disconnect) e-stop but the reality is that you will pay quite a bit more for that functionality. A normally active mechanical brake might be a good compromise although 3 minutes seems like a long time. On the other hand, how long into that 3 minutes until the load is safe? I would think detecting an imbalance early would be more important than the stop time.
I have to agree about the problematic decision making tree when stopping the electrickery in an emergency that might actually benefit from fewer moving electrons.
I had not considered the possible catastrophic consequences of slamming on the brakes on an unbalanced load.
Panicking early, and cutting the power rather than hitting the brakes does look appealing for dealing with vibration (and why I wanted to retrofit a vibration sensor on that CUP15).
Guess I need to back pedal on “incorrectly programed”. And toss the concept that the panic spin down gives me any indication of min spin-up or spin-down time. Bother!
I don’t buy a 0-1500rpm time of 15sec on a rotor that size on that motor. I guess I could work the math and see. Maybe the rotor is considerably lighter than I’m used to?
Bock uses a normally ON air actuated brake. So you need air before they will rotate. Their rotor bases are massive. NSEP’s might have reduced that, but I believe the mass distribution is specifically about reducing the effects of load imbalances, based on the various machines I’ve run/torn apart.
We distribute for the same manufacturer in China that Cedarstone gets theirs from.
Good stainless, not the best but ok for china stainless.
The centrifuge is pretty nice, but the Cedarstone FFE design is flawed, and other ancillary on their systems are all off.
They requested us to help on a few projects, they had quite a lot of very unhappy customers. Some of my current clients sued them for the same exact system on A2C, they dont work at all as designed.
We declined to help them.
Parts support through them is nightmarish too.
We can service their equipment and do sell the same units from the same mfgr, if you need any parts.
lots of force ragdolling him
