Run ventilation fans without a battery but using dc/dc converter?

[peterdeg]

I need to get some ventilation going under the house (very damp and musty)
I could buy a solar powered fan kit but I think I could my own for about 20% of the cost!
Sure, I could run something off a power pack and timer switch but that's boring.

Systems with a battery I can understand. When you don't want to use a battey confusion sets in

My thought was to use a DC-DC converter/regulator.

I'm looking at 6 fans at 0.43A each. If I'm doing the math correctly, that's 2.58A / 30.96W total.
The panel I was looking at is max 50W / 18V / 2.78A. Open circuit 21.60V. Short circuit 2.99A.

Can I use a DC/DC Converter Regulator? On face value, one that does 24V (with input from 12V-40V) Step Down to 12V 5A 60W "sounds" appropriate. eg Like this one.

Is this reasonable or am I way off track?

Thanks

[billvon]

I'm looking at 6 fans at 0.43A each. If I'm doing the math correctly, that's 2.58A / 30.96W total.
The panel I was looking at is max 50W / 18V / 2.78A. Open circuit 21.60V. Short circuit 2.99A.

What voltage are the fans?

Cheapest solution is just to connect the panel to the fan. Most 12V fans will accept up to 16V or so without damage; you can regulate the panel to that.

Best solution is to use a linear current booster (LCB.) They are designed to run motors from panels directly and will provide much more reliable startup.

A DC/DC will not work well without an input impedance limiter. Without the limiter it will keep the panel collapsed for a long time on startup; you'd have to over-spec the panel to get that to work. You can adapt a DC/DC but it takes a few additional components.

[peterdeg]

What voltage are the fans?

Oops, missed that bit - 12V

thanks

[peterdeg]

So something like one of these http://www.solarconverters.com/ppt3.htm
Now to find someone who ships to Australia!

| A thought. I want to run the fans in 3 pairs. If I wire each pair in series then wire all the pairs in parallel, any over-voltage issues go away. Sure, the fans will run more slowly but even at 6V they still move a reasonable amount of air.

[peterdeg]

Just for completeness, I thought I'd document what I ended up doing.

The shopping list
1 x 50W 18V 2.78A mono panel $95 (ebay Australia)
1 x pair MC4 cable connectors $8 (ebay Australia)
6 x Delta 12V 0.4A 80mm 2 wire fans (48.8cfm max flow) $28 (ebay Hong Kong)
6 x 80mm fan grills $16 (ebay Australia)
1 x analog volt meter $7 (ebay Hong Kong)
1 x piece of shelf timber $9 (local hardware)
1 x switch $10
1 x small electrical junction box $4
2 x large electrical junction box $7
1 x blank plate $3
30m 2 core electrical cable $40
1 x auto fuse holder $5 (local auto shop)
Other odds'n'sods (tools needed to install, silicon, brackets to mount panel etc) - make it $260 all up

Basic layout
SolarVentilation.jpg

Controls. 15V - I think that's ok given 100% cloud cover today.
The two large junction boxes are mounted one on the other to give enough depth for the voltage gauge.
IMAG0537.jpg

Fans in situ. I removed one brick which leaves a hole slightly larger than two fans. Wiring is all behind, under the floor. Nothing like crawling into a small area and thinking "How do I get out of here?!?"
IMAG0538.jpg

The system has been running for a month now quite happily. The fans whine without spinning when voltage drops below about 4V (the other night I could hear them whining when we had a full moon). I don't know at what voltage they start spinning, they've always been going when I get up in the morning.

Pity I didn't wait a fortnight, the panels are now $20 cheaper.
Yes, I did it on the cheap. It's a bit of an experiment, so let's see how it goes.

[FunGas]

The fans whine without spinning when voltage drops below about 4V

I use a simple solution, it does however, use a bank of capacitors. You don't need such a huge bank, but you do need some for it to work.

Original post here.

My dropout Voltage is set for 4.7V and startup Voltage is 10.7V, of course, you can vary that.