Fancoil.controller with current issues

[edugimeno]

Hi there! One friend called to say his fancoill (used for a main access cold Air courtain) controller caught fire, and asking if I could recover the half burnt board
He said the design was too bad as this thing was probably designed for hot water only, as the board was places right underneath the condenser radiators
I found some burnt traces and after a quick Google search for the board name (Pwr-05v-w) I could see an image of the original I was able to find where the original traces were going
The scheme seems simple, from what I understand mains gets into the while 3 lead plug closer to the side, neutral and ground are directly wire to same leads in the fan plug (white plug closer to center) but Line goes thru a switch (vertical barrel center, T3.15A slow) , main switch relay (black relay by the corner), then goes to a series of 5 cascade relays that either drive the power to the next (off position) or drive it to a faston plug at the end the last lead takes back the current to the Line lead in the fan plug

The group of 5 faston go all together to a separate toroid transforner which I believe serves as a series of loads to reduce the fan speed at 5 steps

First I wanted to warn my friend that this didn't look like a water damage.problem, more like an overxurrent problem. I asked him to see if the fan were running freely and he said they do. I checked this myself later on

Well I soldered a .95mm diameter copper wire to the missing traces and gave back to test. He said it lasted like 40 seconds, in which it all worked fine, changed speeds...but then it caught fire again

Was a ,95mm motor winding copper wire not enough?
If theres a 3.15A fuse in line how can this wire melt before such a small fuse? Would you say there's another issue outside (or inside) this board?

I removed the burnt copper wire and placed 2.5mm2 wire ibut warned the guy to be very careful when he turns it on and be present for the first minutes when he turns it on, and now he's scared to to do

What would.you say?

Thanks!!

[stj]

picture of the motor and it's spec plate/sticker would be handy.
if it can be done, i would run the motor directly for 5 minutes and have a clamp-meter over the wire to see how much current it's pulling.
i always like to test motors like that - it can give you an idea of bad windings or bearings.

[stj]

you also need to remove and replace the JST VL connector.
maybe the transformer is bad - not sure why it would even be used.
that NOT the correct way to slow a motor - they should be using PWM drive or a triac circuit with trailing cutoff.

[edugimeno]

Yes that's exactly the method I was thinking of doing next time I can go there, measure current with direct 230v drive, and then thru the board and see if the board add extra current maybe due to a internal shortcut I haven't seen

But I'm still surprised that the current was able to burn my jumper copper wire and not able to trip the 3.12A fuse... Is it right to use a motor winding copper wire for this os does it have any drawback that I didn't realize? I can't figure out how such a diameter (I believe it was 0.95mm) didn't stand a current flowing in series with a 3A fuse...

Also the toroidal transformer that provides different speeds, is this common to use it as series resistor? I believe it's outputs are in series with 230 mains from the board, not supply is different voltages by itself

Also what transformer you mena could be bad, the block one on board? The digital electronics seem to be ok as it connects with the remote panel and obeys to the start and different speeds commands

Thanks

[stj]

transformer wire is just copper wire,
i wonder if there is a temporary short to N or gronud somewhere.
as for the toroid, unless it's some type of inductor to supress noise i have no idea what it does or why
can you test the board with something else like maybe a toaster as a load?

[edugimeno]

No the transformer is used to provide a cascade of different speeds, each winding is switched by each relay
I checked continuity between N and L and there is no shortcut
Maybe the wire was damaged
The guy is now scared to test it again as it caught fire last time....

[sam_sam_sam]

I would be tempted to check this board with an incandescent light bulb ( instead of the motor ) and make sure that you do not have more than one tap on the transformer being activated at the same time because of a sticky relays or because the circuit for some reason is doing this ( do this with a volt meter or another incandescent light which would be better )

I would also check the motor directly to the main outlet power and see what the current draw is and if it what it is pulling according to motor data plate and if possible to put a load on the motor and see if it goes beyond what the data plate says

I would also recommend that like what was mention earlier that you do away with the plastic connector and hard wire it because this can cause issues if the connections are not good and tight in the connection

[sam_sam_sam]

transformer wire is just copper wire,
i wonder if there is a temporary short to N or gronud somewhere.
as for the toroid, unless it's some type of inductor to supress noise i have no idea what it does or why
can you test the board with something else like maybe a toaster as a load?

I have seen this method done before on motors but it is not common to do it this way
There was a time in the past that ceiling fans were done this way

If you plan on using this board again you need to clean the carbon off this board as good as possible because this will cause it to do this again because of the resistance that carbon has I would take a dermal tool and lightly sand it and then coated it with fingernail polish to seal it also try making the wire connections for the relays one wire if possible this would be better in the long run

[edugimeno]

I have seen this method done before on motors but it is not common to do it this way
There was a time in the past that ceiling fans were done this way

If you plan on using this board again you need to clean the carbon off this board as good as possible because this will cause it to do this again because of the resistance that carbon has I would take a dermal tool and lightly sand it and then coated it with fingernail polish to seal it also try making the wire connections for the relays one wire if possible this would be better in the long run

I didn't even think of this, carbon conductivity. After first repair I placed, as you can see, a bare copper wire on top of the board, that was charcoaled...maybe this cause a shortcut L-N...which is pretty close. Last time I've used normal household wire, with its plastic wrapping, and I didn only peel the ends. I will double check again before we plug it in tomorrow, probably measuring current with direct drive from mains, and then current while using the board, cafefully....

Thanks!

[edugimeno]

Ok, final update on this. I went to test the board. Initially I connected the 3 fans directly to mains, thru the multimeter. They started correctly (no capacitor issues) and took 2.5Amps (rated at 0,82A each), All good. Time to check the board
First I plugged only the 230 mains input. No issues, checked consumption to 8-15mA
Then I plugged the fans, with the control RJ45 plug still out (no start), and I got an arc by the mains plug in 3 seconds....turned all off and scratched the charcoaled areas of the board to remove all carbon assuming this would be it
To summarize, step by step ended up putting all cables back in, and it works fine and regulates its 5 speeds correctly, no smoke no arcs so far.

Thanks everyone involved!

[sam_sam_sam]

Like I mentioned earlier you need to make sure that you have removed all the carbon from the circuit board and I would seal the area with finger nail polish and might put several coats of it to make sure that it is sealed but also make sure that you have a very good connections in the area where the carbon was at

I would also check the electrical connection traces that had the carbon to make sure that those connections are not getting warm to touch after running for a while but please make sure that you disconnect it from the mains when checking those connections for temperature they should be at room temperature

I once had a welder controller board that this happened to I had to replace several circuit traces on this particular circuit board and after making sure that the controller was working properly I coated the circuit board traces with finger nail polish and it worked fine for several years until one of the workers managed to cut the controller connections to foot pedal and the same area burned up again but this time the circuit board was damaged beyond repair this time around

[edugimeno]

Well I left the board "as is" working fine at the client's. He really needed it there because it's a hotel and it was full this last weekend and temps were really high (100-105F) outside. I guess if he doesn't call me with new issues I will have to leave it, but if there's anything, I will do what you said
Thanks