I was probably one of the later classes taught on tube theory, but that was back in 79, and pursued mechanical... so ...
I have a very well made rv rooftop fan. With very cheaply made (known) china circuit board!
First one had a faulty board. Or some part of circuit. Replacement has same problem.
I found out, through some investigation, if I do return till I accidentally get a good one - it'll fail, soon. Was recommended to hard wire, with an on off switch. No problem. Almost.
Cheapo board has 12VDC in (white + / black -) 6 momentary (looks like DPST, if that term is still accurate) push switches, 1 power, and 1 reversing (8 of same switch)
A 16 pin chip, and what I assume is a transistor.
Output to fan is Red, Black, Purple, Blue and Yellow.
Without pure experimentation (V in, what happens?) I do not know what wires to use to get full speed, rotating to move air out.
I would love if one of the smarter than me, could write me a three switch circuit.
1) on/off
2) fwd/reverse
3) high speed / low speed.
Any component could be soldered to to wire (assume 16ga, maybe 14ga?) and switches mounted in panel.
Is there more to it than I think, or is this doable?
Okay, you're going to have to experiment to see what does what on those fan wires. A guess is that black is "probably" common (ground) and each of the others is some particular speed... you'll have to find out yourself. I did a cheezy schematic for you, below. On/off is just that, single-pole single throw (SPST). Fwd/Rev may look confusing but is a double-pole double-throw (DPDT) switch, where when you switch it, it reverses the wires to the motor, hence the "X" in the switch wiring. The H/L switch is a single-pole double-throw (SPDT) which selects the speed. Which motor wires those are, are up to you to determine. That said, since the fan can run either direction, there won't really be a "positive" and "negative" motor wire, since to reverse direction you just reverse the wires.
Note that if you want, you could just use three DPDT switches and just use a portion of them depending upon where they're used. I'm assuming this all runs on 12VDC, though the circuit won't change if it's not. Also, it assumes that the fan frame (if metal) is not grounded to the chassis in some way. If it is, it will get briefly exciting for a moment.
In reply to kb58 :
As usual, I was over complicating that, in my head
I was thinking reversing the leads to the motor would not reverse, since main wires... but not applicable - no board, now! KISS.
This, I can do.
The cheesy "napkin" (long story. You probably get it) schematic is good to go!
p. s. Yep, 12 v dc. Unless some of the "speed" wires are stepped down, and with what ya got me thinkin', I guess not.
And no metal frame - should keep all the major smoke in.
Worst case (other than letting out smoke) is that it ends up single speed. It's possible that there's more than one winding in the motor and they do some switching to slow it down. Start by measuring the resistance between the various colors to determine what's connected to what before connecting anything to 12V.
If you have some better pictures that show the traces, and some of the component pn like U2, some of it can be mapped out.
I agree that it's likely you can get one speed on/off just by measuring the motor hookups like kb58 is saying.
Once it's working, it's best to have a fuse to protect the wiring. There's typical fuses, and then there are PTCs, sort of a solid state fuse, where if they get hot, they effectively become an open circuit until they cool down. That's mentioned because it appears there's already one there that you could use, the yellow/brownish square part near where the power comes into the board. But before all that...
Before doing anything (I should have suggested this first), is to connect it up as it was, with power applied, and flex all the wiring to see if it wakes up. If that doesn't work, try carefully flexing the board with it powered on. Both of these are cheap and free ways of finding intermittent connections.
In reply to Paul_VR6 (Forum Supporter) :
I snapped a couple of pictures, and zoomed in... no numbers on chip u2 sadly.
l did find:
I do believe that is the PTC kb58 mentioned, and that looks suspiciously like a cold solder joint to me! Be nice if that solves it. Although I'll continue to see if I can rig something up, to have with me...
Yes, that is the PTC fuse (Positive Temperature Coefficient, btw). Flexing the board with power applied will nearly always identify intermittent connections.
I've been assuming that the fan motor uses brushes. For a low-end low-cost unit, that's what would be expected. If for some crazy reason it's a brushless fan, then this whole thing becomes undoable. I only mention it because the ICs on the board wouldn't be necessary if it's as straightforward as my schematic. Curious what those parts do...
How would a jack leg like myself power a brushless fan. I really only need one speed / direction, as long as it is moving the air out!
For the six speeds, (one button for each speed) and reverseable, it's kinda hi tech, in a cheapo kinda way!
From off, touch any speed button, it turns on at that speed. Off button turns off, and use that to turn on at last known speed. If it overheats, it turns off, and comes back on when cooler. PTC, obviously. I've V drops 10.5, it shuts down completely "to not continue to run the battery down"
At least, when working. Apparently that's kinda rare 
Few things, because I find this interesting...
A04406 is some cheap ass SOP-8 FET main on/off maybe
U1 looks like a 5v regulator
U2 likely the speed controller
8050/8550 are likely the reversing transistors
Agreed that yellow jam looks like a polyfuse
I don't see anything here that would make me think the motor is brushless
In reply to Paul_VR6 (Forum Supporter) :
I could not have deciphered one bit of that from the board. But it all fits with my (extremely) limited knowledge.
kb58 is correct on mild bending / wiggling board and wires... tried that first with no success. Will be a bit before I can resolder that one spot. In the mean time :
and:
Assuming the R, B, P, BU, Y is common (12VDC -) at black, I assume I'd be ohming out from it to each other? I'm not sure what to think about red, black and then p, bu, y.
kb58 said:I've been assuming that the fan motor uses brushes. For a low-end low-cost unit, that's what would be expected. If for some crazy reason it's a brushless fan, then this whole thing becomes undoable. I only mention it because the ICs on the board wouldn't be necessary if it's as straightforward as my schematic. Curious what those parts do...
Was thinking the same thing, it looks like the 5-pin connector could be 2 for always-on power and 3 motor phases? Maybe an RC motor controller could work as a substitute?
Assuming you mean "speeds" not "phases" the red and black might be full speed. But to use p, bu, or y, do ya stop sending 12+ to red?
I can't come up (in my head - no hands on for a bit!) with a 6 speed scenario from the wires available.
RC controller has potential,, but my rc guy is out of state!
As long as it can be run in needed direction, I can be fine with single speed. We'll see.
kb58 said:Okay, you're going to have to experiment to see what does what on those fan wires. A guess is that black is "probably" common (ground) and each of the others is some particular speed... you'll have to find out yourself. I did a cheezy schematic for you, below. On/off is just that, single-pole single throw (SPST). Fwd/Rev may look confusing but is a double-pole double-throw (DPDT) switch, where when you switch it, it reverses the wires to the motor, hence the "X" in the switch wiring. The H/L switch is a single-pole double-throw (SPDT) which selects the speed. Which motor wires those are, are up to you to determine. That said, since the fan can run either direction, there won't really be a "positive" and "negative" motor wire, since to reverse direction you just reverse the wires.
Note that if you want, you could just use three DPDT switches and just use a portion of them depending upon where they're used. I'm assuming this all runs on 12VDC, though the circuit won't change if it's not. Also, it assumes that the fan frame (if metal) is not grounded to the chassis in some way. If it is, it will get briefly exciting for a moment.
Before you try to implement this idea check the voltage rating of the fan motor... it may not be 12 volts.
If it is a 3 phase motor an ESC (electronic speed control) from an RC might work but you'll have to get one with an analog input and come up with a variable DC input for the speed.
In reply to triumph7 :
Again, the end result only needs to be a single speed, as long as it turns in the direction to exhaust air out of the shower!
Fan itself has zero markings on it. Just the r, b, p, bu, y wires coming out.
I'm not familiar with a 3 phase in DC. I've wired single and 3 phase AC motors, and motor controllers, old school and these "newfangled" VFDs.
Are you referring to a tiny 3 phase ac motor being controlled by a circuit supplied with 12 VDC? Or am I still missing something?
In reply to 03Panther :
Yeah, it's a small module (literally 1" x 1" at least for the digitally controlled ones that we use) that has two big power wires that go to your 12 volts, 1 or 2 control wires (an analog version would, by applying a variable DC input, would give a variable speed from full one direction through stop to full the other direction) and then 3 wires go to the motor. DC is just the input voltages, the 3 phase is an AC signal.
In reply to triumph7 :
So, aside from the controller descriptions, that I don't have, and probably will not be using, do I understand:
The red is for +12 VDC
the black is -12 VDC
and the p, bu, y are 3 phase AC, and hook to a controller?
is there an analog way to make 12 VDC spin this?
or a very cheap diy controller I could build with a hobby soldering iron, and a smidgen of skill? You'd have to provide part numbers, and a schematic. Think late 70s hobbiest level.
I also have 120 VAC available in rv,but the 12 V vent is most common to buy. So what I have!
edit: I did not really understand the square box wire descriptions.
And I have 5 wires I have discribed coming out of fan motor. All small gauge. About 16 ga.
I'm familiar with pulse with modulation, to control speed, but I don't think that would have 5 wires to fan?
Normally a PWM controlled motor would just have two wires and the controller does the rest.
It is likely that you have +/- for the motor and the other ones are for turning on/off parts of the winding (hence all the resistors near U2) to control the speed and direction.
Can you see any markings on the motor? If not it would be useful to get resistance readings between the wires.
In reply to Paul_VR6 (Forum Supporter) :
That's what I was assuming on pwm, and hopefully what I have for wiring!
Thanks.
When I can, I'm going to try +/- 12 VDC to red and black to motor, bypassing the board.
for speed changes, (not entirely nesasary) would I leave that hot, and add +12 to one of the p, bu or y? Or would it need some circuitry to reduce or modify that voltage?
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