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Forum Index : Solar : Suggested inverter for shed exhaust fan
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| greg199 Newbie  Joined: 03/11/2015 Location: AustraliaPosts: 39 |
I've re built a 240V range hood exhaust fan system to exhaust the hot air from my shed ceiling space. This is it:  It has three different speeds and draws up to 200W. I'm considering buying a solar panel of about 250W, attach it directly to a suitable (inexpensive) inverter (12V DC to 240V AC) and run the exhaust fan directly from the inverter. It would only be used when it is hot and I could simply leave it ON all the time. Whenever the sun is heating up the shed it will also run the fan. Seems simple conceptually. Three questions: (1) will it work? (2) any suggestion for an inverter that would do the job reliably (and without setting fire to the shed in my absence) ? (2) I'm guessing the inverter may lose about 10% of its input wattage in the conversion. Is this about right? |
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| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Being that they are probably induction motors, you will probably want Pure Sine Wave. 300W may do it but 600 would be safer. I've got a Projecta 600W for camping, Link, and have tried it on the freezer outside, 300l, and about 200-300 watts & it can't swing the compressor for startup; pulls the battery too low & causes an alarm state. The induction motors should have an easier start-up though. Are you intending to include a battery & some sort of charge regulator, as I'd expect the inverter will expect something like 12.2 to 14v & without a battery, current available could be all over the place. Curious about the physical sizing & flow rates. 200mm fans? Cheers Phil. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Just curious. Why not a pair of 12v dc radiator cooling fans ? Cheers, Tony. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Hmmm, They may not suit well to ducting & hose friction, but in certain situations they might be good. Did just Google a Honda Civic one that was tested at 9.5 Amps. Personally, I'm using a 200mm duct fan that uses 100W on high & moves 830m³ per hour. Phil. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I think a 12v radiator cooling fan would be a much better match for a solar panel. It might be rather interesting to do a comparison. What worries me about running an inverter and an induction motor, is that it will probably work perfectly well in a clear blue sky, but what about hot cloudy days ? The inverter must work at full frequency and output voltage, it cannot decide to run at 25Hz and 90 volts output if dc input power is very low. However, a car radiator fan should still work pretty well with low dc input voltage, just a bit slow, but it will still flow some air. Much less to go wrong too. Cheers, Tony. |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
The fan from the heating/cooling system in the car is designed to work in a ducted situation and would be quieter than a radiator type fan. Two of them in series would work well with a panel with 30V output. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Yeah, Just back from a week of camping; two folding 120W panels in use. Each panel is rated at 3.34A @25°C (2 per folder). Early in the mornings I was often seeing 12A out of the PWM controller, & once the panel temps rose I was still seeing 10A. On the few overcast days, still hot, I was often seeing 6 Amps. Would be interesting to what some of the larger, say Falcon/Commodore fans use. Guessing about 20A, but they should run slower & just use what's available. Pretty sure they could load the panels down enough to keep the voltage safe for the fans. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Both radiator fans and solar panels come in a pretty wide range of sizes. I am sure with a bit of experimentation a reasonably well matched setup might be possible. Never tried it, but a solar powered fan blowing cooler air upward under the eaves might be a handy thing to have in the warmer months. Cheers, Tony. |
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| greg199 Newbie Joined: 03/11/2015 Location: AustraliaPosts: 39 |
... because I don't have any but I did have the range hood exhaust fans. I don't have any way of measuring the air flow rate but they seemed to be pretty powerful for their size. After all, they are designed to exhaust air. No, I did not plan to attach a battery and regulator. That would just add extra (and maybe unnecessary) cost and complication. I'm keeping it real simple at the moment and wondered if any one else had tried a direct connection between solar panel, inverter and fan. It does not matter if it is not efficient since exhausting any hot air is better than nothing. If the sun isn't shining and I'm desperate then I can simply plug the fan unit into the existing mains power (as I do now). |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
There are some pretty cheap airflow meters out there. Probably crap, but might be good enough for doing some fairly rough back to back testing. http://www.ebay.com.au/itm/3-in-1-Temperatrure-Humidity-Anemometer-Wind-Flow-Air-Velocity-Meter-/172406557787?hash=item2 8243b4c5b:g:QaAAAOSw44BYJvsx It might even be possible to hook up a 12v pancake motor removed from the radiator fan, and fit it to to your existing fan blades. That should make it a lot quieter. I suspect those automotive fans are noisy mainly because the blades are very thin and narrow, and not very efficient. Something like a range hood fan has big wide blades, much nicer. There is also the possibility of twisting the blades to alter the pitch angle. That should make a difference to motor current, and how happy the motor and solar panel are together. Cheers, Tony. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I vote for the 12v fan option. All you need is a solar panel, a 12 or 24v motor, and some wire. No electronics, batteries, charge regulators or inverter. Sun comes up, motor starts turning. The brighter the sun, the faster the motor runs, the more air is removed. In the past I used a 24v scoota motor for a workshop fan, see http://www.thebackshed.com/Windmill/articles/12vFloorFan.asp. Still works to this day, and moves a lot of air. If it was me, I would look at two options. First, do you have any car wrecks that you can grab the demister/air conditioning unit from? They usually have enclosed fans that can move a lot of air reasonably quietly. Use one of them instead of you rangehood unit, that way you get to keep the rangehood for another project. Or, could you rig up a 12/24v motor to drive the fans in the rangehood? Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| M Del Senior Member  Joined: 09/04/2012 Location: AustraliaPosts: 155 |
I set up a 10 inch radiator fan with a 40 watt panel under my whirlybird to see if it improved the cooling in my house roof cavity. Air flow is noticeable and the ceiling temp dropped another 3-4 degrees on average, however I am currently looking for a good cheap/second hand 60/80 watt panel or another 40 watter (is "watter" a word?  ).The fan draws all the current from the panel and struggles to start under 2 amps so larger panel/s should improve things a little more and improve the life of the fan motor. I extended some of the wiring and installed a switch inside the house (at the manhole) with a relay at the panel/fan to make it easier on the fan till I get a bigger panel set up. Mark |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Combining a solar powered fan and and whirlybird, now that is really clever. Cheers, Tony. |
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| M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155 |
But I can not take all the credit. I was looking at the commercial solar fans on the market and figured something could be put together for way less than the 4-500 asked at the time, plus the systems on offer seemed sort of flimsy. Then I remembered some of the dozers and off road forklifts I have worked on used external fans for AC radiators lying flat exposed to dust & rain etc so figured one should work in a roof cavity on an angle. At the time Glenn had just put his workshop fan mod up on the forum so I thought why not. A couple of questions gave me the option of using a 555 chip to control the fan but in the end the switch seemed easier. Mark |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Haven't tried that, but have a sneaking suspicion that it won't work due to the current inrush when the inverter charges it's caps at startup. Considering you already have the fan unit, I'd be thinking that about a 20A solar charge reg will be required & something basic for a battery load. Don't think it will work with just an inverter connected to a panel. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Wouldn't suggest connecting the inverter direct to the panel without a battery, I have a 600w and a 2400w both sitting on my workbench needing repairs after I blew them up doing exactly that (by mistake) Was camping, was using alligator clips to connect to the battery, had the inverter alligator clips clamped to the panel ones, people tripped over leads and pull them off the battery and bang- inverter stops working Both have the same symptoms, caps still charge when connected to battery, led comes on when turned on, internal fuses ok but no 240v I'm assuming either mosfets or driver circuits blown, haven't had time to do a full diagnostic on them yet tho This was on a pair of 250w 12v panels I use to keep car fridge running, charge laptop and a battery to run lights and such at night, obviously the 12v panels went higher than the inverters could handle on their input without the battery to limit the panel voltage |
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| greg199 Newbie Joined: 03/11/2015 Location: AustraliaPosts: 39 |
Thanks for the real world experience Boppa. My 12VDC 2500W Mishto inverter has over voltage protection of 15-16V. I thought this would mean it would shut down whenever the input voltage exceeds roughly 15 or 16V. Is this thinking incorrect? Does it really mean that the inverter will shut down ONLY if the high voltage input is between 15 and 16V and that anything over 16V may cause damage (as in your case)? |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I suspect that the overvoltage is designed to shut down and protect the inverter against slight overvolts, but my panels without a battery hit nearly 20v and I suspect that it simply wasn't designed to clamp voltages that high,most O.V. circuits are a crowbar, that will basically lower the voltage the circuitry sees, but only by a certain amount (so adding say 2v drop from 16v to 14v will still leave the circuit in safe voltage territory, but that same 2v drop from say 20v is simply still too high, letting out the magic smoke I'm still on holidays atm, so until i get back home, I cant actually open them up and see whats broken- I suspect either all the mosfets have blown or the driver circuit- the power led lights up, but that's all that happens Time to buy another tin of smoke :-( One possible solution is to use a cheap solar reg (I bought one for my cars solarpanels, cost about $60), get a `stuffed' car battery from the local garage (just to act as a load) and simply let the inverters undervolts turn the fans on and off (the fans would run for a short while on the battery in the evening until it went flat) and wouldnt turn on until the panels had put a small charge into the battery in the morning, once the battery voltage rises back up again, most of the cheap inverters will turn themselves back on, starting the fans back up Only drawback is most of these inverters have a buzzer that goes off when the undervolts goes off, so it buzzes all night until the panel brings the battery back up again (its often easy to disable the buzzer tho) Another advantage of using a small capacity `dead' battery would be that intermittently cloudy weather, the fans wouldn't cycle as much as clouds cover then uncover the sun (sorry this is so long btw, didn't mean to write a novel lol) |
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