Electronics geeks sought for brainsucking (AC fan issue)

[lowkee]

I recently bought, off CL, a Kenmore humidifier which is all automagical and adjusts the fan speed based on the current and desired humidity, but has been popping the triacs on the control panel since day one. It has 3 triacs, one for each speed (L/M/H). All three have burnt up individually (I replaced them all). Now, however, all three are working but the fans still won't kick on. When it first began burning up triacs, the fans would not turn off, then the fans would not turn on. I'm not at the latter issue.

In an attempt to just hotwire the thing to always run the fans on low or medium speed, I have tried bypassing the circuit and connecting the fans directly to 120v, but nothing seems to make the fans spin.

The fan motors themselves (there are two of them) have four wires, blue/red/white/black. How can I make these fans just spin with an on/off switch? I can't seem to get them to budge.

Now, I'm no electronics guru. I know the basics and can have fun with a 555 timer and such, but when it comes to anything 'decent' I'm normally confined to an instruction manual and a puzzled expression. So, when you explain the big secret to making these fans spin (or how a triac works), please keep my ignorance in mind.

Here are some photos for reference:

Thanks for any help. I hate throwing otherwise good items in the trash, especially $175 items.

 

[ThumbPkr]

Re: Electronics geeks sought for brainsucking (AC fan issue)

I wonder if the fan motor is a stepper motor such as is used in a printer or scanner?They are used in a lot of applications these days,lathes etc and manufacturers these days will design a driver circuit to take advantage of a motor that can be bought at a surplus price or if they happen to have such an item in their inventory for whatever reason they can incorporate it into something that they can sell to avoid a loss.
Getting a schematic would be cheating and taking the easy way out but sometimes it is time well spent.LOL.Good luck with it.Ron G

 

[joed]

Re: Electronics geeks sought for brainsucking (AC fan issue)

I would suspect the fan motor.
It could also be that the the triacs were under rated when designed. Check the current ratings of the triacs and go to a one that has a higher current next time you change them.

 

[lowkee]

Re: Electronics geeks sought for brainsucking (AC fan issue)

I don't think they can be stepper motors, since they are fed via triacs (AC current). I would think a stepper motor would be driven by MOSFETs and DC. Seems too much effort to swap them out for steppers, though, as at least I know how to make a circuit which can drive them, and at variable speed.

The orig triacs were BT134's and I installed BT136's. I would consider the fan motors except there are two of them.. both being toast at the same time seems unlikely. They still spin freely (no change from before the issue).

BTW- Some extra info. The wiring on the fans was as follows:

White - 120v common
Black - High
Blue - Med
Red - Low

Anyone know of a schematic which would drive these motors? I'm not averse to throwing together a quick circuit to test the motors out. All I want them to do is spin

 

[gonefishie]

Re: Electronics geeks sought for brainsucking (AC fan issue)

If the fan doesn't turn when connected straight to an AC source then the fan is the problem. Not sure if that motor has brushes or not, there gotta be some info on the motor that you can look up the details. Have you check the output from the triacs? If the triacs fried then chances are something/s on the power supply board had gone bad.

 

[i386]

Re: Electronics geeks sought for brainsucking (AC fan issue)

The first pic looks like two independent coils to me.



Bi Polar Stepper motor?

 

[lowkee]

Re: Electronics geeks sought for brainsucking (AC fan issue)

I have no idea if it one of those or not. I know enough to tinker, but not enough to do anything useful. I did some searches on google and found HVAC systems have a blower motor with L/M/H wires as well, and they require a capacitor in order to begin spinning. Could the same be required for these motors? I have no idea what the capacitor does in the circuit, but there is one on the circuit board for this humidifier. (I should have taken a photo of the board when I had it apart ) I realize you are kind of working in the dark. I was simply hoping someone might happen across the photo and think "Oh, that's a such and such and it wires up this way" .. long shot

 

[dolluper]

Re: Electronics geeks sought for brainsucking (AC fan issue)

The cap stores electrical charge and can put out as high as 60 cycles per second {120 volt} its used when the motor starts or speeds up .....it's possible the cap blew and the reason the motor doesn't run

 

[lowkee]

Re: Electronics geeks sought for brainsucking (AC fan issue)

Alright. I have plenty of spare capacitors sitting around. I'll swap it out and take a photo of the circuit board while I'm in there. Luckily, it is a fairly simple circuit for anyone who knows their stuff, just more complex than I can follow.

Thanks for the help. I'll post back later today with my results

 

[bruceb58]

Re: Electronics geeks sought for brainsucking (AC fan issue)

The cap stores electrical charge and can put out as high as 60 cycles per second {120 volt} its used when the motor starts or speeds up .....it's possible the cap blew and the reason the motor doesn't run

The caps purpose(if it has one and I doubt it in this case) is to allow start windings to change the phase of the field so the motor has more torque to start. If the motor isn't even humming when it tries to start, it won't be a start capacitor. By the way, start caps are very large.

The 60 Hz is the frequency of the line voltage. The cap doesn't put out 60 Hz.

 

[ThumbPkr]

Re: Electronics geeks sought for brainsucking (AC fan issue)

The start capacitor will be an AC nonpolarized capacitor as well,they are not rare but a DC capacitor will not work.It is important to know the capacity and voltage ratings of the capacitor before you replace it as the circuit is designed for the values of the one you removed.You can replace it with a higher voltage rating but capacitance should be the same as the one you took out.Ron G

 

[4JawChuck]

Re: Electronics geeks sought for brainsucking (AC fan issue)

Those are cheap AC motors running on bronze bushings with little factory lubrication to make them last. If that fan doesn't spin perfectly smoothly it won't be able to spin up.

It would explain why you lost your AC drivers from current overload, just replace the fan.