My Bezzera Strega has the common issue of the low-water sensor activating when it shouldn't. Currently, the machine is plumbed-in and the sense wire is grounded, which I verified and even added a ground wire from the power cable to the metal chassis the sense wire is attached to. So, a grounded wire is directly connected to the brain, with nothing else in the circuit.

I've noticed the machine's low-water sensor activates and shuts the unit down when the pump and/or heaters (either boiler heater or group heater, idk) turn on or off. I suspect the formation or collapse of EM fields in the pump or heaters when they are switched on or off is generating a surge or other electrical aberration on the unit's ground that is triggering the shutdown.

I'd like to get some suggestions for how this issue could be remedied?

P.S. Bezzera says to replace the brain and I am ordering one, it's not the Gicar unit 1st line sells so I have to get it from Italy. I also want to order it from a local shop so I can bring the unit in if required, so this has been a longer process than I could have imagined. I suspect the new brain design may be to blame and a new one won't fix anything as the machine works fine except for this issue. So in the meantime I'd like to see if it's possible to isolate the sense wire for the low-water shutdown from surges or aberrations caused when the pump/heaters turn on and off. I'm somewhat familiar with typical AC line filtering and how MOVs work but eliminating surge energy from a ground connection is something I am not sure how to go about doing.

I've noticed the machine's low-water sensor activates and shuts the unit down when the pump and/or heaters (either boiler heater or group heater, idk) turn on or off. I suspect the formation or collapse of EM fields in the pump or heaters when they are switched on or off is generating a surge or other electrical aberration on the unit's ground that is triggering the shutdown.

There is only a field collapse in an inductive circuit, not a resistive circuit. So, you can rule out the heaters in this regard, as they are purely resistive. There would be a field collapse in the pump, as it is inductive. If you happen to own a good power bar that incorporates surge protection, you might plug your machine in via that and see what happens. If it fixes the problem you could just leave it there or buy an MOV and install it inside the machine.

Thanks, but it's possible the heaters have some effect when switching on and off, as the machine sometimes turns it's self off due to the heaters switching.

Plugging the machine into a power strip won't do anything, the issue is coming from the inside the machine. The question is how to protect the grounded sense wire from electrical disturbances caused by the pump and/or heaters.

"I suspect the formation or collapse of EM fields in the pump or heaters when they are switched on or off is generating a surge or other electrical aberration"

If this machine ever worked properly the problem has nothing to do with EM fields that probably have not change in their characteristic signatures. Besides, heating elements are completely shielded within metal boilers as if inside a Faraday cage.

Your Ground should be a properly connected Earth Ground as opposed to just a Chassis Ground. Post a complete schematic of your machine's electronics beyond a simple wiring diagram; if possible, bypass the low-water auto shut-off to see what happens.

I think you're barking up the wrong tree regarding, "electrical aberration on the unit's ground". Sounds more likely a relay, if mechanical, that is no longer handling the load due to pitting or carbon build up or a defective physical shut off sensor, particularly if it's not Hall effect (magnetic in characteristic). Even a Hall effect sensor has to have a freely moving magnetic float.

Thanks BBE61!

I should have pointed out the machine never worked properly, and has a new brand of brain unit vs. what 1st line offers.

It seems like everything else works fine and the machine resets it's self after being switched off for a few minutes. Also, upon disconnecting the sense wire from ground the unit shuts down just like it's supposed to. Given this I'm considering other alternatives than a bad brain but I won't know for sure until I get a new brain from Italy. I have a feeling it will be ~$250 spent for nothing but that's what Bezzera recommends so I'll try it... but they won't say it's the brain for sure.

As far as grounding, in this case the chassis and earth ground are directly connected, the power cable's ground is bolted to the chassis. I ran a wire from this point to the sheet metal contraption that holds the water tank and the low-water sense wire is grounded to, just to make sure it's properly grounded.

In tank mode the resistance of the water is in the circuit as well, I measure about 50k ohms. In tank mode the machine stays on much longer vs plumbed-in, so I guess the resistance of the water is changing the behavior of this circuit, maybe partially isolating it from electrical issues which is another clue the issue may not be the brain but an issue with shielding the brain from electrical noise, surges, aberrations, etc...

I don't think the relay is the problem as it functions just fine after the brain resets it's self after a low water shut down. It's a mechanical relay that sits right next to the brain.

I've seen a wiring diagram and will try to find it again... but in this case the low water sensor is a simple grounded wire that goes right into the brain. If in tank mode the resistance of the water is in series. I actually just added a 10k ohm resistor in series with the sense wire just to see if the behavior of the machine changes...

I reread this thread also and coming from an industrial maintenance background and having witnessed many strange things happen over 45 years of experience due to faulty grounding, are you sure that the outlet you are plugged into has a good earth? I suspect it is probably good, but I have seen multi-million dollar packaging machines and computer controlled instrumentation that had just plain weird problems caused by lifted/floating grounds and ground loops. Make sure the power source is good before spending a lot of time internally on the machine. Sometimes the strangest problems are caused by very simple issues.

Poor grounds and/or ground loops will cause all types of improper operation that is both random and slightly different depending on many supposedly unrelated events. Conductivity type water level sensors are notoriously unreliable. Some of this unreliability is directly traceable to poor design. To add to the frustration is the fact that some of these instruments will never function correctly if grounded.

I have been involved with instrumentation since the 60s.

ira wrote:As I read this for a second or third time, I wonder, why are you convinced it's the low water sensor acting up? The symptoms fit, but is it possible that there is another reason?

Ira

It's the yellow light going out that indicates it's the low water sensor, this can also happen with the level sensor in the boiler but if that happens the heater turns off but the pump is allowed to keep running to fill the boiler, so it has to be the low water sensor for the water tank.

OldNuc wrote:Poor grounds and/or ground loops will cause all types of improper operation that is both random and slightly different depending on many supposedly unrelated events. Conductivity type water level sensors are notoriously unreliable. Some of this unreliability is directly traceable to poor design. To add to the frustration is the fact that some of these instruments will never function correctly if grounded.

I have been involved with instrumentation since the 60s.

bettysnephew wrote:I reread this thread also and coming from an industrial maintenance background and having witnessed many strange things happen over 45 years of experience due to faulty grounding, are you sure that the outlet you are plugged into has a good earth? I suspect it is probably good, but I have seen multi-million dollar packaging machines and computer controlled instrumentation that had just plain weird problems caused by lifted/floating grounds and ground loops. Make sure the power source is good before spending a lot of time internally on the machine. Sometimes the strangest problems are caused by very simple issues.

Thanks! It's plugged into the kitchen's 120V circuit, which uses GFIs, but I can use a heavy duty extension cord to plug it into a different circuit and see if there are any changes. I can also check to make sure the receptacles are wired properly.

To add to the frustration is the fact that some of these instruments will never function correctly if grounded.

This is really what I am afraid of and suspect may be the case.


I really appreciate the comments from everyone.