Electronics Project help needed.

[Blacon]

Hi , all,
Got one of those projects that you had not planned! In this case the dehumidifier quit with a c7 code.
It's a meaco 25ltr. C7 code apparently is inferring motor issues, its sensored brushless dc motor with a wacking 340vdc rating . I used to tinker as a boy , but without cct. Diagram i,m struggling, lots of ideas but nothing conclusive. So i need help. Meaco are a waste of space, i need circuit dia and if possible some coaching.

 

[Sideways]

As it's outside warranty it isn't infant mortality (unless you don't really use it).

I'd look for signs of corrosion (they live in the damp) and overload (discoloration and smell).

Check the power supply is outputting the right voltages but "on your own head be it" because it may very well have 350VDC inside.
If you're unsure or if that's a cheap DMM, don't !
Lastly I would measure the AC voltage between the three motor wires, call them ABC.
A-B, B-C, A-C.
The only thing I'd be looking for is that they are the same within a few percent.

Does the motor spin ? Under power or turns freely by hand ?

I don't have a cct and never worked on one so these are just generic faultfinding

 

[Blacon]

As it's outside warranty it isn't infant mortality (unless you don't really use it).

I'd look for signs of corrosion (they live in the damp) and overload (discoloration and smell).

Check the power supply is outputting the right voltages but "on your own head be it" because it may very well have 350VDC inside.
If you're unsure or if that's a cheap DMM, don't !
Lastly I would measure the AC voltage between the three motor wires, call them ABC.
A-B, B-C, A-C.
The only thing I'd be looking for is that they are the same within a few percent.

Does the motor spin ? Under power or turns freely by hand ?

I don't have a cct and never worked on one so these are just generic faultfinding

Hi, was not sure anybody could help? I will try to do good photo of the board, for someone familiar it should help.
So how far have i gone? 1. I've already blown up the board with agiant FLASH and blown a pcb fuse. My logic is firstly establish voltages, as the motor code c7 i checked for 340vcc . Now, on switch on it powers up, motor runs for second compressor fires up, 2 secs later all stops and i get beeb with error code on display c7. I had this dehumidifier awhile bought second hand but never used, so i dont know what is normal and i have no manual.
i stripped motor to bits to check the windings these look ok, i fitted drill to shaft spun up the motor and monitored some voltages, albeit small ie,. 2vdc.
At the moment i think the motor is ok, getting to your points Sideways, the motor volatage at the board is there on switch on but only ifor a second as i said. So iwas thinking the fault is board side and the voltage to the relay which connects the motor supply is dropping out , but why..? Is it still the motor and its sensing a fault and shutting down?
That is enough for moment , let you mull it over while you can see photos to help

 

[Spectric]

Some of the biggest problems with repairing a lot of modern equipment is

A) It is either not designed to be repaired, ie throwaway or you just replace assemblies like a motor or PCB.

B) With the widespread use of microcontrollers at the heart of these systems then even with a circuit diagram fault finding can be difficult because you do not have access to the firmware or any logic diagrams, all you can do is check inputs and outputs but even then you require more than a simple multimeter.

The motor assembly looks to be self contained, made by Guandong Welling motor co ltd so this will be a throwaway assembly. You can see the controller for commutation is contained within the motor so that external PCB is a power supply and controller. The motor has a 340 volt Dc supply that will be switched within the motor to provide the three supplies to the windings to create the rotating magnetic field, the Yellow looks like a speed control input from 0 to 6 volts with the white being a 15 volt supply for the actual electronics. What that blue wire marked as FG does is debatable, it could be a signal back to the control board indicating some motor parameter or a fault signal to tell the power supply to shut down but here the circuit diagram would help.

At the moment i think the motor is ok,

I do not think you can say that, you need to confirm all the voltages are present including that FG wire and if they are then that could confirm the opposite, ie the motor or control electronics within have failed. To prove the motor is ok then you want one of those voltages or signals to be missing and then look at that external pcb.

Overall this comes down to cost of a new dehumidifier against a new motor / PCB and that assumes the rest of the machine is still good and has some years left in it. This could become one of those situations where you throw money at it but still it gets chucked out, welcome to the throwaway world.

We have an old ebac, I mean old and it is a square wooden box on wheels with a control we have never changed and it just keeps on working twenty plus years later, no fancy motor or electronics. It is really just the basic motor / compressor from a refrigeration unit with a capilary type thermostat which really shows that mass produced complexity is not progress and the old adage of KISS really is true.

 

[Blacon]

Thanks, i steaming angry at mo...... i just lost all i typed out to resond only for it to vanish

 

[Blacon]

My test equip

 

[Spectric]

A decent scope is handy to see the waveforms and a logic analyser if you want to attempt to reverse engineer a system to see how it functions or not !

 

[Blacon]

Thanks Spectric, i spent 40mins yesterday one finger typing only for it to disappear. So will try again.

The motor is the target of the self diagnosis of the humidifier, its 2 problems in one, i broke it open to get to the coil, and this checks out ok, but as you also noticed it has a control board so it coud be that. I think it is essential to have a scope for my best opportunity to learn. There are several ways to control a bdcm some i am told use the negative aspect of the waveform to triger the coils and a scope would be useful here.
What about buying a 280vdc motor? I've seen one on ebay 30 quid. Its the same dimensions and same manufacturer, i could not buy a single replacement from Ali aba , had to buy 100.
The units not high power so maybe a resistor to drop voltage or add in a regulator? To tell you the truth, and you can probably see for yourself , im out of y depth here

 

[Sideways]

I share Spectric's concern here. I fear you will spend money on this and still end up throwing it away.
To me there was no reason to break open the motor when
a) you can do a fair bit of diagnosis without doing that, and
b) there are obvious issues on the circuit board which are more likely to be the cause and should have been tackled first.

There appears to be scorching and even track burnt off around those little slots cut in the circuit board. Cuts like that in the board are there to provide electrical isolation and stop electricity tracking across the surface of the PCB. They are a pointer to the presence of high voltages on nearby components.
You will have to figure out the circuitry around there, test and replace components as needed, and repair the board safely.
I think you may be taking on too much of a challenge.

 

[Spectric]

There are several ways to control a bdcm

The actual hardware is much the same, Ac is converted to a Dc supply which is then switched to provide three signals 120° out of phase at some frequency that drives the motor. It is the software that determines the control algorithm which may or may not use positional sensors but can be very complex if using some form of vector control. The best way to approach diagnostic's is a logical approach which initially looks at the major assemblies rather than any detail as @Sideways has said, no need to take the motor apart. So you check the voltage is getting to the PCB from the mains input, check the higher voltage Dc supply is present which supplies the motor, check the 15 volt supply is available which is the power source for the motor control board within the motor but look at replacing assemblies if they can be sourced rather than thinking of component level repairs but don't throw lots of money at it.

Simple initial assesment if this was given to me to evaluate:

Cost new £300 & five year warranty therefore around a £1 a week. I would just look to get 5 years after which anything more is a bonus, goes wrong just scrap. Meaco do not list spares like the motor or PCB's and I would suggest the reason for this is

This for me screams disposable throwaway items so please just look at this as a learning exercise.

Meaco also use the term Dc motor in their sales pitch, the better term would be a digitally controled motor because Dc can only generate a magnetic field that is not changing in relation to time and therefore an electomagnetic rather than a motor !!

 

[Blacon]

Hi roy
The burn ismy doing, i had the voltage at the motor for only 2 sec. Then the relay tripped , so i used oneside off the rely switch and connected to ground there by having fixed output of 340vdc to motor to check it. I forgot to take the link out and inadvertantly shortedd to ground. This bllew the cct board fuse. Hence black pcb. So just waiting for nnew fuse then i will carry on abit more, the motor is still usable and does turn slowly on first start for 2 seconds, so

 

[TomGW]

I much prefer to repair rather than replace but sometimes it's just not practical or cost effective. This looks like one of those times to me. However, hats off to you if you can get it sorted at reasonable cost.