PV powered workshop ventilation fan - ideas?

[DTJ]

I've got a brick shed with some moisture issues that I want to ventilate.
I'd like something that just runs the fan when the sun is up and the fan stops when the sun power falls.

In the junk box I've got a couple of 200W 40Voc PV panels and a decent 24Vdc to 12Vdc converter. I don't have a fan as yet.

I like the idea of a 240V (bathroom) exhaust fan - they are cheap at around $20 and move enough air.
I'm thinking DC fans will be costly, I'm not sure that even 4 x PC cooling fans in parallel would be enough, hence the exhaust fan idea.

I've toyed with the idea of a cheap 21V/240V low power can type inverter, then I've got to address the issue of 1) excessive input voltage from the PV panels and 2) also wondering how happily the inverter will be to just drop in and out as the PV voltage fluctuates.

Any crazy cheap and easy ideas?

I CBF building up too much, I'm looking for a lazy approach.

Any ideas?

[Zero999]

How about using a 12V car radiator fan?

Regarding the excess voltage: either use a LDO regulaor, or you can make a high powered shunt regulator with the TL431 and some power transistors.

[Psi]

How about using a 12V car radiator fan?

Regarding the excess voltage: either use a LDO regulaor, or you can make a high powered shunt regulator with the TL431 and some power transistors.

Or the cars internal ventilation fan. They can be even higher current than the radiator fan, like 15-20A
And come mounted in a ducted enclosure
Maybe one from a 24V truck would be better suited for 40V panels than a 12V one

[Zero999]

How about using a 12V car radiator fan?

Regarding the excess voltage: either use a LDO regulaor, or you can make a high powered shunt regulator with the TL431 and some power transistors.

Or the cars internal ventilation fan. They can be even higher current than the radiator fan, like 15-20A
And come mounted in a ducted enclosure
Maybe one from a 24V truck would be better suited for 40V panels than a 12V one

Or connect three 12V fans in series, each with a TL431 + power transistor, in parallel to make sure one doesn't over volt.

[paulca]

I have seen people do this without electricity, but it involves creating airducts painted black and employing the chinmey effect of the warm incoming air rising and out the vent grill.  They were using heavy stone/terracotta 4inch pipes and lots of black painted heavy stone as heat stores

That said it was in reference to heating and ventilating a plant growing shed which probably aligns it more for "summer" use. 

Indoor humidity (in my locality) tends to be an Autumn issue in particular.  Warm, moist "summery" air meets the cold evenings and nights at this time of year and outdoor RH can rise to 100% readily.  With interior walls temp dropping fast and the "warm moist summery air" trapped indoors, condensation is likely anywhere above about 80% RH ambient.  As  you progress into Winter itself though, the outdoor temps are far cooler than indoor temps and thus the absolute humidity is more than absorbable by the indoor air.  Interior heating is likely to be on more often and dry the air even more.  In the dead of winter, humidifiers can become useful.

As I can't automate the windows yet, I turn the heating on to raise the temp and lower the RH.  I do have an extractor in the office as it gets stuffy, I smoke and solder occasionally.  I hadn't considered forcing it on to create airflow under the same "high RH" trigger automation.

[paulca]

The "proper solar" option for such a load is fairly cheap.  You have the panels.  A 10A controller should easily handle both panels.  EPEver unit will cost you about £25?  I believe the 10A model supports up to 100V of panels and either 12V or 24V battery, but it's buck only mind.  CHECK IT!

An old car battery.  Connect both the controller to the battery and the fan to the controllers "Load" output.

Set the controller up to cut the load out when the battery dips below 12V or 11V if you care less about it.

That EPEver unit (1206AN) or similar has a schedule feature for the load based on "dawn/sunset" intended for evening lights.  That could be handy as humidity (RH) tends to be highest on the "turn of the day".

EDIT: One final comment though.  If this is a single skinned outbuilding, then the air is not your only problem.  Bricks wick water through them.  Even if you seal the room up, water will get in through the brickwork and even the concrete floor depending on how it was laid.  In winter the wall of my garage which is 1 foot away from next doors actually weeps water and has a dark stain of moisture down it.  There isn't enough air gap between the two buildings so damp air collects there and rain that gets in doesn't evaporate in any sunlight.

[Phil1977]

I've toyed with the idea of a cheap 21V/240V low power can type inverter, then I've got to address the issue of 1) excessive input voltage from the PV panels and 2) also wondering how happily the inverter will be to just drop in and out as the PV voltage fluctuates.

It will be very unhappy as long as the PV source is not massively oversized. The voltage regulation in the converter will probably go crazy if input power fluctuates and / or the motor wants to spin up. Furthermore: Bathroom fans are often equiped with capacitor motors - they usually don't like cheap inverters.

[paulca]

Inverters efficiency is a curve.  A typically sized inverter might be at least 500VA.

If you connect a 5W fan to it, it will probably consume about 20W to run it.

When I leave my office wall lights powered, (1W) the inverter uses 7.5W but it has a 'low power' mode where it sends a rubbish sine wave with low resolution to save power under 10W.

[Seekonk]

I have a stack of 72V to 12V buck converters that only cost $8 shipped. Those two panels in series would be ideal.  I am using 24V car radiator fan ($18) on 12V panel which is ideal.  Fan runs with as little as 5V.   My garage runs on battery less inverters.  Any MSW inverter will run on any voltage put on the HV capacitor of H bridge.  Adding a little boost transformer with two panels in series gets that to a decent AC voltage.  Any buck converter is easily turned int a power point controller.  Lots of options for those comfortable with electronics.  Unfortunately, that seems to be rare on an electronics forum.

[PCB.Wiz]

In the junk box I've got a couple of 200W 40Voc PV panels and a decent 24Vdc to 12Vdc converter. I don't have a fan as yet.

I like the idea of a 240V (bathroom) exhaust fan - they are cheap at around $20 and move enough air.
I'm thinking DC fans will be costly, I'm not sure that even 4 x PC cooling fans in parallel would be enough, hence the exhaust fan idea.

Aliexpress have DC 36V 0.2A 120MM  fans, low cost, would be very simple.
https://www.aliexpress.com/item/1005004787647561.html

You can also get bilge fans, with cowling, in 24V
https://www.aliexpress.com/item/1005003637606094.html

[DTJ]

If this is a single skinned outbuilding, then the air is not your only problem.  Bricks wick water through them.  Even if you seal the room up, water will get in through the brickwork and even the concrete floor depending on how it was laid.  In winter the wall of my garage which is 1 foot away from next doors actually weeps water and has a dark stain of moisture down it.  There isn't enough air gap between the two buildings so damp air collects there and rain that gets in doesn't evaporate in any sunlight.

Yeah this is part of my problem. To minimise it I moved soil and greenery back from the outside face of the walls. I then coated the outer face of the bricks with a spray on paving sealer (clear). I really loaded it on to seal the bricks and stop further penetration.

[paulca]

If this is a single skinned outbuilding, then the air is not your only problem.  Bricks wick water through them.  Even if you seal the room up, water will get in through the brickwork and even the concrete floor depending on how it was laid.  In winter the wall of my garage which is 1 foot away from next doors actually weeps water and has a dark stain of moisture down it.  There isn't enough air gap between the two buildings so damp air collects there and rain that gets in doesn't evaporate in any sunlight.

Yeah this is part of my problem. To minimise it I moved soil and greenery back from the outside face of the walls. I then coated the outer face of the bricks with a spray on paving sealer (clear). I really loaded it on to seal the bricks and stop further penetration.

I know that sealing or coating bricks is taboo in the UK.  Supposedly bricks are meant to "breath" and if you coat them and trap moisture they are prone to cracking in winter.  There was a whole fuss as "cowboy traders" where going door to door offering "damp proofing" armed with demo bricks and spray.

The "Building code" way over here, if you were to register it as an "indoor space" would require vapour barriers with vents and drains on the wall, followed by stud/frame work to hold insulation. 

The floor will need the same.  I looked into getting my garage to a point where I could use it as a year round workshop, but you can even see daylight through the brickwork in places.  The materials alone to membraine it, foot it with treated timber, frame it, insulate it and sheet it was looking at £2500.  That wasn't going to include the new door, window seals and a new insulated/sealed garage door. 

I ended up leaving it the cob webby "junk room" it was.  Electronic devices last about 3-5 years before damp or spider nests kill them.

[Zero999]

I know that sealing or coating bricks is taboo in the UK.  Supposedly bricks are meant to "breath" and if you coat them and trap moisture they are prone to cracking in winter.

Isn't that due to freezing? The OP is in Australia where that might not be such a problem, unless they're at a high elevation.

[eTobey]

Put a black pipe as a chimney on it... no electronics, no fuzz... (add some way to let air in)