• Spring 2024 meetup in Calgary - tentative date Saturday, April 20/2024. Other regions are also discussing meet ups. If you want one in your area get going on organizing it! discussion
  • We are having email/registration problems again. Diagnosis is underway. New users sorry if you are having trouble getting registered. We are exploring different options to get registered. Contact the forum via another member or on facebook if you're stuck. Update -> we think it is fixed. Let us know if not.
  • Spring meet up in Ontario, April 6/2024. NEW LOCATION See Post #31 Discussion NEW LOCATION

Repairing BOSCH B20CS30SNS/01 fridge

Janger

(John)
Administrator
Vendor
“By way of example, if you have a fridge with a top freezer from the 1980s with a capacity of 19.0-21.4 cubic feet, it's likely to use around 2,000 kWH per year. If you pay $.10 for electricity per kWh, that means the aging refrigerator is costing you about $.55 per day, $16.67 per month, and $200 per year.”

Reference: https://www.directenergy.com/learning-center/how-much-electricity-does-my-refrigerator-use

And we don’t pay $0.10 a kWh it’s more like $0.18 due to all the extra fees etc. an old fridge is expensive to run. Using $0.18 kWh it’s $360 a year!
 

DPittman

Ultra Member
Premium Member
“By way of example, if you have a fridge with a top freezer from the 1980s with a capacity of 19.0-21.4 cubic feet, it's likely to use around 2,000 kWH per year. If you pay $.10 for electricity per kWh, that means the aging refrigerator is costing you about $.55 per day, $16.67 per month, and $200 per year.”

Reference: https://www.directenergy.com/learning-center/how-much-electricity-does-my-refrigerator-use

And we don’t pay $0.10 a kWh it’s more like $0.18 due to all the extra fees etc. an old fridge is expensive to run. Using $0.18 kWh it’s $360 a year!
Yes I need to check again the electricity consumption of my old fridge but from what I remember it was not nearly as bad as I thought.

Old fridges may be more expensive to run in the short term but buying a new $1000-$2000 new fridges and throwing them in the junk every 5 years isn't economical or environmentally friendly either.

I started thinking about my old fridge and that there must be a date on it somewhere....sure enough 1951. 71 years old!
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
Yes I need to check again the electricity consumption of my old fridge but from what I remember it was not nearly as bad as I thought.

Old fridges may be more expensive to run in the short term but buying a new $1000-$2000 new fridges and throwing them in the junk every 5 years isn't economical or environmentally friendly either.

I started thinking about my old fridge and that there must be a date on it somewhere....sure enough 1951. 71 years old!

The only two fridges in my life that never had to be replaced or repaired are also the first two I ever got. Prolly similar vintage to yours cuz they were already well used when I got them. One was a hand-me-down fridge we got when we got married.
 

jcdammeyer

John
Premium Member
Exactly. But I'd love to know what it is that your fridge is doing that involves frequency input. My mind doesn't immediately embrace the need for such an input or analysis. Which implies that there is a chance to learn something cool!

I hope not too.

But Awesome Lighting System! Does your contract include maintenance? Hopefully that doesn't mean crawling around up there......... I would die just thinking about it!
Nope. Haven't even had to provide spare or replacement parts.
John - please don't let me try your patience. It's not my intent to challenge you. I'm really only insanely curious because the information doesn't fit my current knowledge base.
No problem. There's no such thing as a dumb question. Only dumb and rude answers.
Feel free to bluntly tell me to pound salt or better yet provide a few links to explore on my own.
This fridge has what they call a "super cool" function. For both the fridge and freezer. Switches back to normal after max 6 hours. Designed to run the fridge harder to quickly cool down a large amount of stuff put into the freezer or fridge. We've never actually used it.

Anyway, I'm going to guess they increase the speed of the compressor motor to do this. Hence the need for a frequency controlled input rather than ON/OFF.

Now none of this is new in the general appliance world.
This is a piece of the data sheet for the IRAM module also used in my STMBL 3phase harmonic AC servo drive. Unfortunately this part was discontinued which caused real headaches for the STMBL designers.
The original purpose for the device was washing machine motors which run slowly up to very high spin speeds.
1667854089435.png
I bought a harmonic drive off EBAY and then these kits from Andy Pugh in the UK who had done a batch based on attending a machine tool show in the UK attended by the German designers. Luckily I was able to get the ICs before they went away and I have 3 of these modules as I was going to try them on my brushed servos too.
STMBL-4.1.jpg

What's cool about these is they are quite small and can handle step/dir or the smart serial used by the MESA boards for LinuxCNC or even 0-10V signals although I don't know how well that's been tested.

What I'm trying to say is that 3 phase motors even without encoders are all over the place although obviously they work better with encoders and then are usually called AC Servo motors.

I'll see if I can find a general description of how these systems work.
 

jcdammeyer

John
Premium Member
“By way of example, if you have a fridge with a top freezer from the 1980s with a capacity of 19.0-21.4 cubic feet, it's likely to use around 2,000 kWH per year. If you pay $.10 for electricity per kWh, that means the aging refrigerator is costing you about $.55 per day, $16.67 per month, and $200 per year.”

Reference: https://www.directenergy.com/learning-center/how-much-electricity-does-my-refrigerator-use

And we don’t pay $0.10 a kWh it’s more like $0.18 due to all the extra fees etc. an old fridge is expensive to run. Using $0.18 kWh it’s $360 a year!
Exactly. So amortize that $4400 fridge over 12 years and add $30 per month.

Interesting day so far. Stopped in at Reliance Appliance repair and asked about a new compressor driver. The orginal part number was useless to them. As they put it: They need the fridge part # and can then look up the compressor driver. Although sometimes it's not sold separately so then you need the certified freon guy to install the new compressor and driver.

He says they order from Bosch and Bosch orders from Embraco but they can't order direct from Embraco. Oh how I wish for the right to repair legislation. But then I took Electronics 10,20 and 30 in High School and we learned how to repair things so it's in my blood.

Now I have to call Reliance with the fridge model number and apparently they don't normally stock that sort of thing anyway so it might be quite some time before I can get a repair part.
 

jcdammeyer

John
Premium Member
BTW, here's a short 18 second video of my ELS running the STMBL drive connected to my Harmonic Drive Motor. The beeps you hear are the SLEW and MOVE buttons being pressed to send stepping pulses to the STMBL

One day I really will cast the housing for this and add the face place so I can mount the collet chuck.

 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
I'll see if I can find a general description of how these systems work.

Any chance this is what they are talking about?


Still not really a frequency input but yet fits reasonably well with what you were describing and certainly fits with the need to adjust torque.
 

jcdammeyer

John
Premium Member
Any chance this is what they are talking about?


Still not really a frequency input but yet fits reasonably well with what you were describing and certainly fits with the need to adjust torque.
This is likely way too complicated but uses the series processor that is in my fridge compressor controller.

Although hard to find in the document the basic idea is that the AC from the line is turned into higher voltage DC. This is then switched on and off using what they call pulse width modulation out six pins to 3 pairs of drivers in such a way that you simulate 3 sine waves 120 degrees apart.

After that it's just a matter of what voltage and frequency are created. The natural inductance and capacitance of the motor is enough of a filter to make that ON/OFF high voltage be smoothed into something like a sine wave. Change the frequency and you get a different speed.
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
the basic idea is that the AC from the line is turned into higher voltage DC. This is then switched on and off using what they call pulse width modulation out six pins to 3 pairs of drivers in such a way that you simulate 3 sine waves 120 degrees apart.

After that it's just a matter of what voltage and frequency are created. The natural inductance and capacitance of the motor is enough of a filter to make that ON/OFF high voltage be smoothed into something like a sine wave. Change the frequency and you get a different speed.

No wonder we are having trouble communicating. You have assumed I don't know what a VFD is.....LOL! What you have just described is the basic operating principal of a VFD. If I were describing it, I'd add that VFD's are basically fancy inverters. Most are even called inverters.

Sometimes the process starts with a DC voltage like a battery. Sometimes with AC at various voltage levels. Regardless of which it is, they then create a high voltage DC which is subsequently chopped to create single or triple phase AC outputs. As you have said previously, the actual process is quite a bit more complex.

My interest is not in how a VFD works. No wonder you got leery about it. I don't think I'd want to describe how it works to most people either - especially not on a forum. But maybe over liquid refreshments or in a meeting. I only describe it generally above to give you some confidence in my knowledge level.

My interest is this case is not about how a VFD works, it is only about this weird frequency control "INPUT" that you described at the beginning of your thread. I am familiar with sensor control, sensorless vector control, direct control, etc. I'm also familiar with the way most VFD's use a 10V divider potentiometer to provide user control of output frequency.

However, I'm not familiar with any frequency input control other than feedback from the output to fine tune the control system.

The article I linked to used some terminology in it that I thought might be what you referred to from your sources. In my view, the article provides a rather confusing description because it isn't an input in the normal sense, it's more of an output.

Nonetheless, I was not aware than any of my VFD's varied their output voltage as output frequency changed. That is clearly new info to me. So I plan to do some testing to see what mine are actually doing in that respect.

I confess that it's odd that I didn't notice anything when I was assessing the output noise levels on my oscilloscope. I would have thought that would have jumped out at me as I ran up and down the frequency range watching the noise spikes.

Given that a refrigerator compressor is basically a refrigerant pump (constant high load), the required VFD output is significantly different from what is required for a lathe or a mill that usually sees very low loads - unless the operator likes 80 thou cuts like some members on here! So I can certainly see why an output voltage adjustment is appropriate as output frequency changes. But again, other than for feedback purposes, I see these as outputs not inputs.

Does that help?
 
Last edited:

jcdammeyer

John
Premium Member
I'm just going by what I've been reading on line. There is also conflicting information about how the control is done. Hard to guess who really is an expert and who was just lucky.

Here's what I've found from the manufacturer. Some controllers say they have frequency in. Mine is one of those.

I found the main control board but without a schematic I can't tell exactly which set of wires run down to the motor driver.

One source says control should be 4V to 6V which would enable the drive at a set speed. Another one has a that test cable made by taking 120VAC through a diode and a 100K resistor into the opto-isolator. I'm about to make up that setup and then I'll scope the output side of the opto-isolator. It should be pulses at 60Hz based on how the opto-coupler works.

More when I have tried it. I will also report if I create magic smoke.
 

Attachments

  • vcc-inverter-replacement-instructions.pdf
    1.8 MB · Views: 2

PaulL

Technologist at Large
Premium Member
The other reason for the VFD is it is probably used to minimize the noise emissions, partly because of controlling speed and partly by spreading out the (mechanical) power pulses over 3 phases compared to single phase.
I'm guessing it's to avoid having a starter capacitor on a motor that's always cycling on and off. I'd be willing to believe a lot of fridge reliability problems are the starter caps.
 

jcdammeyer

John
Premium Member
More when I have tried it. I will also report if I create magic smoke.
And there was smoke. I had intended to insert a small isolation transformer so I could measure with the scope. Forgot to do that.

Touched the ground lead of the scope to what I incorrectly thought was the emitter pin of the opto isolator and zap. A flash of light from what turned out to be a 0603 size 100 Ohm resistor. I've replaced that but it no longer behaves the way it did before.

What it did when I first plugged it in with this setup:

1667874300479.png
was the motor locked for a moment. Then released. Locked and released and then that was it. Cycle power it would lock at least one for a few seconds and then release. Even tried to turn but only a half a turn before it just released.

Now this 1/3HP motor has 12 ohm windings while the fridge compressor has 6 ohm windings. They are both 220VAC motors. That's only DC so doesn't say much for number of turns and inductance. But clearly it tried to turn but maybe one of the driver channels for one phase is shot. Maybe it's the capacitors like the youtube video alluded to. The caps should be here tomorrow. But at this point...

Back at square one other than having ordered $8 worth of caps and a meter to read ESR which will come in handy for other projects.

Not sure where this saga will go next.
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
I'm just going by what I've been reading on line. There is also conflicting information about how the control is done. Hard to guess who really is an expert and who was just lucky.

Here's what I've found from the manufacturer. Some controllers say they have frequency in. Mine is one of those.

All I've been able to find is what I provided earlier plus a few other references to VF (voltage frequency) mode. All of them imply that the frequency portion is a feedback mechanism that the VFD can use to determine slip and correct for it. Nothing I find suggests that it is used for control - just feedback. But that difference could be as simple as the definitions that different people have for the terms feedback and control.

To me, control means "go to 1500 rpm". Feedback means "I'm a bit slow at 1450rpm"
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
the motor locked for a moment. Then released. Locked and released and then that was it.

My experience with that is limited. I had a similar experience when I accidentally locked a motor (hi/low clutch engaged at same time as back gear. The VFD simply detected the lock and then released till I hit the e-stop. It was one of those terrifying holy crap moments. But no harm was done - that I know of.
 

VicHobbyGuy

Ultra Member
Not sure where this saga will go next.
I have a 2.5 y.o. Bosch fridge - expensive ($4200) and a lovely thing when it works which is does..mostly. A couple of times, it has 'lost its mind' and stopped cooling ... it seemed to recover with a power down a.k.a. 'reboot'. but how can we be confident about a refrigerator like that? Delays in service calls are in the weeks nowadays. I tried getting the 'Extended Warranty' to service the machine - it took over a month before they sent somebody, and when he ran the self-test and like me got no reply from the machine brains, concluded that a new controller board was required. "I'll see about getting a board and we will contact you." 3 months later, they contacted me. Fridge has been working OK all that time so I declined. I figured the odds were 50-50 that 'service' would make things worse. Consequently, I now share my single garage shop space with a full-size 'backup fridge', which I did manage to get delivered in a couple of days after the first 'incident'..
My advice: If the saga goes toward 'new refrigerator', pick a different brand. But you probably concluded to do that a few days ago.
BTW, we have a 30+ y.o. small chest freezer in the basement which keeps stuff rock solid frozen, still. We store the expensive (isn't it all these days?) frozen food down there.
 

jcdammeyer

John
Premium Member
All I've been able to find is what I provided earlier plus a few other references to VF (voltage frequency) mode. All of them imply that the frequency portion is a feedback mechanism that the VFD can use to determine slip and correct for it. Nothing I find suggests that it is used for control - just feedback. But that difference could be as simple as the definitions that different people have for the terms feedback and control.

To me, control means "go to 1500 rpm". Feedback means "I'm a bit slow at 1450rpm"
Control is where I think you are making it too complex.

For the VFDs we use with our mills or lathes it's most often a 0-10V signal. Often created with a Pulse Width Modulation bit stream of 0V and 5V and then amplified to be 0-10V.

If I have a motor controlled with CANopen or MODBUS I can send the controller a message to tell it to run 1500 RPM. I can even tell it how fast I want it to accelerate to that. My GS-1 VFD running my lathe has both MODBUS and 0-10V or the pot on the front panel to set speed.

But it's just as reasonable that a controller receives a frequency on it's control input that tells it to turn at a specific speed. So it might get 60Hz to turn 1800 RPM which is equivalent to no speed controller at all for our line frequency. It might get 120Hz to tell it to turn 3600 RPM. or 30Hz to tell it to turn 900 RPM.

I don't know what sort of speed control is on this module when it says Frequency.
 

jcdammeyer

John
Premium Member
I have a 2.5 y.o. Bosch fridge - expensive ($4200) and a lovely thing when it works which is does..mostly. A couple of times, it has 'lost its mind' and stopped cooling ... it seemed to recover with a power down a.k.a. 'reboot'. but how can we be confident about a refrigerator like that? Delays in service calls are in the weeks nowadays. I tried getting the 'Extended Warranty' to service the machine - it took over a month before they sent somebody, and when he ran the self-test and like me got no reply from the machine brains, concluded that a new controller board was required. "I'll see about getting a board and we will contact you." 3 months later, they contacted me. Fridge has been working OK all that time so I declined. I figured the odds were 50-50 that 'service' would make things worse. Consequently, I now share my single garage shop space with a full-size 'backup fridge', which I did manage to get delivered in a couple of days after the first 'incident'..
My advice: If the saga goes toward 'new refrigerator', pick a different brand. But you probably concluded to do that a few days ago.
BTW, we have a 30+ y.o. small chest freezer in the basement which keeps stuff rock solid frozen, still. We store the expensive (isn't it all these days?) frozen food down there.
Yes. Rock and a Hard Place. This fridge has been good except for the defrost drain plugging up with dog hairs. Solution for a while is to just wait until the ice builds up and then break it out. Quite possible the buildup internally behind the plastic wall caused the compressor to run to often or too long and that overheated and blew the drive.

We've decided to expand our horizons a bit. We want something quiet and not all of them are.
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
If I have a motor controlled with CANopen or MODBUS I can send the controller a message to tell it to run 1500 RPM. I can even tell it how fast I want it to accelerate to that. My GS-1 VFD running my lathe has both MODBUS and 0-10V or the pot on the front panel to set speed.

You can set the accel and decel rates on the TECO vfds too and they will also accept external commands.


We've decided to expand our horizons a bit. We want something quiet and not all of them are.

This reads like you are giving up on it......

But it's just as reasonable that a controller receives a frequency on it's control input that tells it to turn at a specific speed. So it might get 60Hz to turn 1800 RPM which is equivalent to no speed controller at all for our line frequency. It might get 120Hz to tell it to turn 3600 RPM. or 30Hz to tell it to turn 900 RPM.

I don't know what sort of speed control is on this module when it says Frequency.

Yes, it is just as reasonable. But it's my turn to suggest that this might be making it too complicated.

The more I think about this and the more I read, the more I think the reference to frequency as a control input is incorrect (by my definition but ok by someone else's definition). I think it is simply feedback of the real speed from the motor back to the VFD so the VFD can adjust the output frequency to compensate for slip.

Compressors are basically pumps. Pumps are continuous load devices. Variable speed pumps can provide significant energy savings but being able to perform well at different speeds requires slip compensation. This is very commonly done with an encoder on the motor so the VFD can know the motors exact speed. The encoder feedback is a frequency by anyone's definition. Whether you call it an input or a control is just an arbitrary choice.

I come to this opinion because:

1. Encoder feedback is a frequency.
2. Most VFDs can be set to use motor feedback from an encoder.
3. VFDs that drive Pumps commonly use encoder feedback to adjust for slip.

It just seems too coincidental to conclude otherwise.

Unless you disagree with this assessment, my curiosity is sufficiently satisfied.

Back to your fridge..... I doubt encoder feedback (or control) is the cause of your problem. So prolly no need to think further about that possibility.

I'm sorry John, I can't think of anything to try beyond what you have done. Unless you can get better service info it may well be that your only option is part swapping (which I hate). I'd guess that swapping out the compressor is impractical though - certainly beyond what I would tackle. So that leaves you with the other boards and components. Almost like Russian roulette. :(
 
Top