Solar sunroof intermittent now not working

[HPsauce]

Probably the same place as last time it's out of the way and shaded; there seem to be loads of cheap simple mechanical thermostats available.
Some even have the temperature sensor on a lead up to a metre long which might give more options and better results.
It's a really neat idea and with the right type effectively gives the on/off function too, but better.
Just need to get the right sort, typically described as "blue button" that closes at high temperature, usually for fans/aircon etc.

BUT first I need a working sunroof!

[HPsauce]

So my Buck Converter arrived this evening from China.
No instructions of course but I quickly found this handy video of almost that exact model (9A vs my 10A):
It's a few mm thicker than the Steca original so may not fit in the original locations, but it doesn't need to be there of course, though probably safest.

It has adjustments for both maximum voltage and current, so I'll start off setting it to 12V and something less than 10A (the max on my multimeter) and see what the blower fan does when I connect it up.
I don't know what the output of the panel is capable of doing, or what the blower motor needs to operate gently but I'll work it out.
Does anyone have any thoughts on what limits to set on Voltage and Current? Given the information I've had from Sean (old model panel) I suspect they were set around 9V and the later model at 12V or slightly less.

IIRC the main blower fuse is 40A, though obviously the solar panel isn't going to get anywhere near that - it's almost 500W!
The panel is actually about 400*800mm so 0.3 sqm, which given the suns maximum power of at most 1000W/sqm and likely panel efficiency under 20% is just 60W, i.e. 5A at 12V. Research suggests 14AWG wiring (around 2sqmm) would be more than adequate and probably thinner would be fine.
Normal UK ring main cable is actually thicker at 2.5sqmm, lighting cable at 1.5sqmm would probably be fine.

[HPsauce]

Does anyone have any thoughts on what limits to set on Voltage and Current?

Interestingly when I asked AI it came up with some fairly low numbers, I think for the original version, with efficiency only about 10% in peak sunlight.
These were only around 12W, regulated to a mere 3.5V and up to 4A.

[MikkiJayne]

I would suggest at the minimum use stranded copper wire of the same thickness as the factory used. 14AWG does sound about right.

[HPsauce]

Thanks MJ. I've done a little bench test using a multi-voltage PSU designed for laptops that can do 12v-24v in steps and over 6A at any setting.
Seems to do what it says set to 10V and 5A with only minor variations at lower input voltages.
Intriguingly it has green and red LEDs, the green one comes on when there's input voltage and when testing output voltage; the red one when drawing significant current. No explanation I've seen of what they signify, but I guess green means ready and red working with a load.

Next step is to connect it to the solar panel and see what output that generates. If it looks sensible I'll try the blower connections briefly.

Incidentally the multimeter I used has rather thin (replacement, not original) leads and they did noticeably warm up with 5A through them, the actual unit itself not really much at all. I've changed it down to 6V/5A for initial testing in the car. That's limiting it to 30W of the theoretical (unobtainable) 60W maximum.

[HPsauce]

Grey day, definitely no sun, output is 6V/0.66A = 4W.
No idea if that will turn the fan at all though, I need to make up some appropriate connections/leads.
I'll see what happens set back at 10V.

Interesting, happy to run at both 10V and 12V so the panel is putting out something higher without sun.
Getting almost 0.8A on both so 9W which isn't bad at all. Just need to make up some connecting leads now, maybe after lunch.

[HPsauce]

Hmm, not looking so good now. Connected up fully the panel voltage input to the unit drops to 3V and the output to the fan is minimal though there's a sort of small clunk/thump from that area when completing the circuit.
I've tried different voltage settings, down to 3V BUT the unit still gets warm, suggesting the OEM version is maybe a bit cleverer?
I'll see what happens if we get any sun another day.

[MikkiJayne]

Normal for a solar panel I think, higher voltage until you put a load on it then the voltage collapses.

[HPsauce]

Normal for a solar panel I think

Indeed, I was thinking the same.
Going onto the back burner for a while given the lack of sunny days forecast for when I have some spare time.
I might just pop the failed controller back in to tidy up the loose cables. Sod's law says it will then work!

[HPsauce]

Sod's law says it will then work!

And it does!
Who knows, bad contact somewhere, dry joint remade by being disturbed? Fan is humming quietly in partial sun.

It doesn't make much sense as I thought I tested everything at every stage...
BUT, thinking carefully I ONLY tested the voltages in the sunroof with the control unit in place, i.e. using the contacts on the sunroof itself and on the wiring at the sliding contacts, NOT on the blade terminals on the unit.
SO it could just be a bad contact on one of the blade terminals (no obvious corrosion though) and sliding them off, then back on again just now, has cleaned/corrected that. Or disturbed/remade a flaky solder joint.

Whatever the cause I've only spent a few quid, far too much time, but now understand how it fits together and have it working.

If anyone else wants to dive in there a couple of key access points are:
1. Open the sunroof slightly and push the clips apart at the outer front edge of the trim to slide it back. You'll see two black metal posts they clip back onto. You can then push it well back to reveal all the wiring.
2. With it partly open undo the Philips screws at the front end of the two support bars to drop them down slightly and release the control unit. Refit the screws immediately or you risk wrecking something if the sunroof moves! And insulate and tape up loose the wiring to avoid shorts.
3. Refitting the trim is a bit awkward, ideally (with sunroof slightly open) get someone with thin strong fingers to pull it forwards until it clips in place.