PC fan to leisure battery

[OldKettle]

Hi,
I am planning to add a DIY exhaust fan to a greenhouse.

The greenhouse is about 12 cubic metres and I was planning to start with a PC fan like this one (12V 0.25A)

https://www.amazon.co.uk/dp/B002KTVFTE

powered from a leisure battery like this one.

https://www.amazon.co.uk/SuperBatt-Leisure-Battery-Caravan-Motorhome/dp/B00WPZFAXK

I want to just initially hook it up and see if it makes a difference to the cooling (airflow is stated at 90 cubic metres/hour).

My question is, for initial testing, can I simply attach the fan to the battery terminals? Would that work and is it safe?

Also, would the theoretical run-time be 110Ah/0.25A = 440 hours?

Any thoughts would be much appreciated.

 

[jj4091]

Run time calculation is dodgy I don't think it is as simple or logical as your calculation as the voltage will drop as the battery goes flat & if you drain down completely for any length of time you risk damaging it as far as I am aware. There is no reason why you cannot just hook it up with a couple of crocodile clips though.

 

[JohnD]

you might also consider having an air outlet near the highest point, and an air inlet near the lowest point on the shady side.

Convection will have the air gushing out faster than your little fan can shift it.

you can also use a small solar panel, no battery required, when the sun shines, the fan will run.

 

[jj4091]

If you have an opening window in your greenhouse these also work well https://www.ebay.co.uk/p/Solar-Heat...nt-Hot-ZY/18021440413?iid=153098962023&chn=ps

 

[OldKettle]

Run time calculation is dodgy I don't think it is as simple or logical as your calculation as the voltage will drop as the battery goes flat & if you drain down completely for any length of time you risk damaging it as far as I am aware. There is no reason why you cannot just hook it up with a couple of crocodile clips though.

Thanks. I planned to either link it to a solar panel, or recharge frequently with a trickle charger. Just wondered if that theoretical calc was correct.

you might also consider having an air outlet near the highest point, and an air inlet near the lowest point on the shady side.

Convection will have the air gushing out faster than your little fan can shift it.

you can also use a small solar panel, no battery required, when the sun shines, the fan will run.

Thanks. I had planned to eventually recharge the battery with a solar panel, if the initial tests showed that the fan made any difference, but had wondered whether to bypass the battery completely, as you suggest.

At the moment I have two roof vents open (each 2ft x 2ft and open to 14 inches) and the door is fully open (plus the one whole side is painted with greenhouse shading wash), but can't get the temp at floor level lower than 33c (table height is 37c) once the sun hits the greenhouse (outside air temp 25-ish), so was hoping that a fan might be able to push more than the passive convection (or, at least, make a decent contribution).

If you have an opening window in your greenhouse these also work well https://www.ebay.co.uk/p/Solar-Heat...nt-Hot-ZY/18021440413?iid=153098962023&chn=ps

Thank you. I installed two of the Bayliss ones yesterday. They are opening to 14 inches, but still struggling to manage the heat.

 

[flameport]

At the moment I have two roof vents open (each 2ft x 2ft and open to 14 inches) and the door is fully open (plus the one whole side is painted with greenhouse shading wash),

Given all that, I really can't see how a tiny little battery powered fan will make any difference.

 

[OldKettle]

Given all that, I really can't see how a tiny little battery powered fan will make any difference.

Yes, you may well be right, but I reckon it can't hurt to try.

The specs on the fan I have gone for says that it can move 176 cubic metres an hour, and the greenhouse is only 12 cubic metres, so maybe it might have an effect. I just have no idea how much is currently being lost by convection, for comparison.

https://www.amazon.co.uk/dp/B075CY123M

Rather than invest in a battery and/or solar panel, can I wire it up to a 12v 1.5A power supply, just for testing purposes?

 

[flameport]

can I wire it up to a 12v 1.5A power supply, just for testing purposes?

Definitely, no point buying anything if you already have a 12V supply.

 

[OldKettle]

Definitely, no point buying anything if you already have a 12V supply.

Thanks. The problem is that the greenhouse is over 100ft from the nearest socket, so I will use an extension cord and the 12v supply just for testing, but need something standalone on a more permanent basis.

 

[RF Lighting]

You need a fuse in between the battery and the fan. If anything goes wrong with the fan without a fuse you’ll be in a whole world of trouble.

 

[JohnD]

solar battery charging panel.

https://www.aldi.co.uk/solar-battery-maintainer/p/012551262369400

 

[ericmark]

Battery voltage 12.9 and fan max 12 volt so may need something to drop voltage, possibly a diode or 2 at 0.6 volt drop each should work OK, at least for test, but then your going to add solar panel so depending on controller looking at up to 14.8 volt.

With a standard fan I would say two in series, however a PC fan is normally polyphase there is an inverter that turns the DC to AC so the fan is brushless, so you may need more control to drop voltage. It may work as it is, but you don't know.

Could use a car USB supply and run at 5 volt and allow the USB charger to regulate, or any other voltage regulator 7809 for example would give 9 volt add diodes to common and can raise in 0.6 volt steps.

I simply used a green house window opener that opens automatic when it gets hot, think your over engineering here.

 

[OldKettle]

Battery voltage 12.9 and fan max 12 volt so may need something to drop voltage, possibly a diode or 2 at 0.6 volt drop each should work OK, at least for test, but then your going to add solar panel so depending on controller looking at up to 14.8 volt.

With a standard fan I would say two in series, however a PC fan is normally polyphase there is an inverter that turns the DC to AC so the fan is brushless, so you may need more control to drop voltage. It may work as it is, but you don't know.

Could use a car USB supply and run at 5 volt and allow the USB charger to regulate, or any other voltage regulator 7809 for example would give 9 volt add diodes to common and can raise in 0.6 volt steps.

I simply used a green house window opener that opens automatic when it gets hot, think your over engineering here.

Thank you. The fan should be coming today, so I am going to wire it to the 12V 1.5A supply that I found, just to see what effect it has.

With regards to using a car USB supply to regulate, could I just use a full 12v socket, something like this

https://www.amazon.co.uk/Cigarette-Enisina-Waterproof-Motorbike-Connection/dp/B07BPM1WLJ

 

[oldbutnotdead]

Having the door wide open is short-circuiting the ventilation- drier (less dense) air will be wafting in from the top of the doorway and out the vents, the damper air sitting in the greenhouse won't be moving
As a test, leave the door open but fix something over the doorway leaving a narrow gap (50mm) or so at the bottom, get a draught running.
By the way, your fan probably won't do much. Last year had to put an 8 inch extract fan into a tiny timber shed- the control gear was overheating with the 4 inch originally fitted.

 

[OldKettle]

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