12 volt fan for polytunnel

[Bryang]

Any recommendations for a new fan for my poly? it is 20feet by 12 feet. I use a 100 watt solar panel in connection with a battery. Been looking for a replacement, but cant find anything suitable.

 

[Anduril]

Some of the allotment forums suggest car radiator fans.

https://www.allotment-garden.org/ga...nel-ventilation-solar-powered-cooling-system/

 

[Bryang]

Some of the allotment forums suggest car radiator fans.

https://www.allotment-garden.org/ga...nel-ventilation-solar-powered-cooling-system/

I have looked into them, Graham, bought one last year to vent hot air from the poly. Unfortunately they use a lot of current (amps), my storage battery is a Halfords HLB678 70Ah, which is charged by a 100 watt solar panel, the fan consumes 7.5 amps.. So if it is cloudy the battery runs low within hours.. The only other option is to acquire a lorry battery and a bigger solar panel.
PS.. I read that article and others similar, and they accept that the fan (only) works when the sun shines. I need a battery to pump water up to my drip system barrels.

 

[Anduril]

I have looked into them, Graham, bought one last year to vent hot air from the poly. Unfortunately they use a lot of current (amps), my storage battery is a Halfords HLB678 70Ah, which is charged by a 100 watt solar panel, the fan consumes 7.5 amps.. So if it is cloudy the battery runs low within hours.. The only other option is to acquire a lorry battery and a bigger solar panel.
PS.. I read that article and others similar, and they accept that the fan (only) works when the sun shines. I need a battery to pump water up to my drip system barrels.

Hi Bryan, have you tried asking the question here My father in law answers quite a few project questions. His forum name there is alec_t

 

[roche]

Figure out the power that you can afford to use, then look on the web for fans with that power rating. Decide if the air movement rating of the fan will be sufficient.

 

[Bryang]

Figure out the power that you can afford to use, then look on the web for fans with that power rating. Decide if the air movement rating of the fan will be sufficient.

Thank you roche.. I have done all the maths. My system works on a timer, and today I have been monitoring the output from the solar panel.. Looks like I'll have to buy in a higher capacity battery. The poly is in a very sheltered position so the heat builds up quickly in it, so a "blow" fan is a must also an extraction fan.. I have found a 14 inch model that uses 5.5 amps, will most probably buy it.

 

[roche]

You may find that using two extraction fans is more effective....It's a series/parallel thing. Also - go for deep cycle batteries if you can, they are better suited to the application

 

[frankenstine]

is use a 235w solar panel on 4x 80w fans wired in series on our green house 24x8 ft

i have an mppt battery charger linked on it as well but the battery is connected to the electric fence and some lights not the fans, i run on the theory more sun needs more fan. found the running fans in series worked better keeps the revs down so it quieter and the fans last longer also makes better use of the pannel

 

[Bryang]

is use a 235w solar panel on 4x 80w fans wired in series on our green house 24x8 ft

i have an mppt battery charger linked on it as well but the battery is connected to the electric fence and some lights not the fans, i run on the theory more sun needs more fan. found the running fans in series worked better keeps the revs down so it quieter and the fans last longer also makes better use of the pannel

What diameter are the fans?

 

[frankenstine]

i'll check they are 9"-10"

what i found tbh the diameter doesn't matter so much, the amount of air they move is pretty much entirely down to power, with cheep fans a lot of them are the same power over a range of diameters the smaller ones just run faster. i used 10" fans because i could fit neatly in 610x450 so just made a panel that held 2 fans and replaced 1 pane of glass. for quite a while i ran with just a pair of fans but it was 2 noisy really.

the spec of the panel I'm actually using is 210W ( the 235 is on the shed but basically the same thing )

210W Pmax
OCV 36.4
I max 8A

Vmpp 28.8
Impp 7A

with 2 fans on it was slightly overdriving them but not massively ( in automotive terms 12v actually means14.4v -15v anyway ) and in strong sun it'd float loaded at 32-33 v fans moved a lot of air but were loud. mine actually works best with 3 fans, the ocv of the panel 36v is 3x12, and 3x80w is 240 so near as dammit the panels rated power but i put 4 fans on there, reason been i had cut 2 panels to mount the fans on when i made the first one, and i had plenty of fans, running the 4 fans in series is in theory 48v i actually lost a bit of performance for doing this 4 fans move less air than 3 but are a LOT quieter and under running basic motors massively increases there life as they run from pretty much 12 hours a day albeit at varying speeds i thought increasing the life expectancy of no name Chinese clutter was probably a good idea, the toy car is the opposite way round for lightness i use small 12v fans but variable speed driven off a 24v DC-DC converter, i can get fantastic cooling moving massive amounts of air of tiny fans not weighing much, but they are LOUD when running flat out and it dosent do them any good long term

 

[Bryang]

i'll check they are 9"-10"

what i found tbh the diameter doesn't matter so much, the amount of air they move is pretty much entirely down to power, with cheep fans a lot of them are the same power over a range of diameters the smaller ones just run faster. i used 10" fans because i could fit neatly in 610x450 so just made a panel that held 2 fans and replaced 1 pane of glass. for quite a while i ran with just a pair of fans but it was 2 noisy really.

the spec of the panel I'm actually using is 210W ( the 235 is on the shed but basically the same thing )

210W Pmax
OCV 36.4
I max 8A

Vmpp 28.8
Impp 7A

with 2 fans on it was slightly overdriving them but not massively ( in automotive terms 12v actually means14.4v -15v anyway ) and in strong sun it'd float loaded at 32-33 v fans moved a lot of air but were loud. mine actually works best with 3 fans, the ocv of the panel 36v is 3x12, and 3x80w is 240 so near as dammit the panels rated power but i put 4 fans on there, reason been i had cut 2 panels to mount the fans on when i made the first one, and i had plenty of fans, running the 4 fans in series is in theory 48v i actually lost a bit of performance for doing this 4 fans move less air than 3 but are a LOT quieter and under running basic motors massively increases there life as they run from pretty much 12 hours a day albeit at varying speeds i thought increasing the life expectancy of no name Chinese clutter was probably a good idea, the toy car is the opposite way round for lightness i use small 12v fans but variable speed driven off a 24v DC-DC converter, i can get fantastic cooling moving massive amounts of air of tiny fans not weighing much, but they are LOUD when running flat out and it dosent do them any good long term

 

[frankenstine]

View attachment 20220721_190527.mp4

please excuse the really really really rough wiring its from when i was experimenting with it some time ago then alsorts of stuff happened and just ran out of round 2its

 

[Bryang]

Thank you for your reply and information.. Found it interesting . Will have to acquier a larger solar panel, and like you, will use it to drive the fans directly. Thinking about it, it would be better to have the fans running when the sun is shining.. Were the fans pre-used ones?/ Cheers Mate
Bryan