Application for 100W panel

[solardreamer]

This is what I used, sourced from ebay12 volt radiator fan.jpg Says push/pull by removing and flipping the fan. They come in a variety of sizes something like 7" to 16"

That's what I ended up using after the 20W fan burned out. I use it as a pusher to be consistent with all the attic fans I have seen. Just wondering if anyone tried it as a puller in attic.

[littleharbor]

This is what I used, sourced from ebay12 volt radiator fan.jpg Says push/pull by removing and flipping the fan. They come in a variety of sizes something like 7" to 16"

[solardreamer]

Using two fans was the key to my speed control. A single fan rated at 80 watts was just screaming with a 65 watt panel.

Glad it worked out well for you. I think we may be using similar 80W 12V radiator fan. Are you fans pusher or puller fans?

I had thought about using 2 fans but I didn't really have the room and even the 1 fan was already loud enough since it's my house attic so I decided not to use 2 fans. Instead, as I mentioned earlier poss, I am using a DC-DC converter with battery and it has worked well for almost 2 years now. In general, peak attic temperature lags peak sun so I have found my setup gets the attic cooler faster than only direct connection from fan to panel which tends to slow down too much when attic temperature is still very high.

[littleharbor]

Using two fans was the key to my speed control. A single fan rated at 80 watts was just screaming with a 65 watt panel.

[SunEagle]

I guess I just got lucky in my situation after listening to all this debate. As I said it has worked flawlessly for 2 1/2 years now. When The sun is bright and especially directly overhead it runs the fastest and moves the most hot air.

I am glad you have a working system.

Moving the fastest when the sun it overhead make sense. The problem comes if the fan speed exceeds it's mechanical design. That is all I want to convey to anyone that try's this out.

[sdold]

It might be a interesting experiment to see just how a couple seriesed brushless DC fans act. They might find a way to sync
themselves together so the pulses line up. These are pretty low audio frequencies, so an RFI filter won't help. Bruce Roe

Maybe, but if the panel Isc is less than what one motor draws in normal operation, I think you'd be OK even if such a thing occurred.

[littleharbor]

I guess I just got lucky in my situation after listening to all this debate. As I said it has worked flawlessly for 2 1/2 years now. When The sun is bright and especially directly overhead it runs the fastest and moves the most hot air.

[bcroe]

Bruce, there is probably DC input filtering that is required for RFI suppression that takes care of that situation you described.

It might be a interesting experiment to see just how a couple seriesed brushless DC fans act. They might find a way to sync
themselves together so the pulses line up. These are pretty low audio frequencies, so an RFI filter won't help. Bruce Roe

[solardreamer]

... you don't know what it is until you try it ...

This is the inconvenient part as it's dependent on the specific fan and weather condition to verify. I did this and it was tedious. So, Voc would be more convenient albeit conservative spec to verify even though the panel voltage under load will never actually get that high.

[sdold]

The panel's max voltage is its open circuit voltage, but the voltage on the motor can never be that if the motor is connected and drawing current, it will be something less than that, and you don't know what it is until you try it. If you really want to be safe you could size the panels so that the Isc is about what the motor current draw at 13-14V is. Bruce, there is probably DC input filtering that is required for RFI suppression that takes care of that situation you described.

[solardreamer]

That's the reason for wiring the motors in series.

That's another way to ensure compatibility. The key point is one needs to make sure the fan motor max voltage is compatible with the panel max voltage one way or another.

[LETitROLL]

I've done exactly that with a pair of 12 volt radiator fans and a 65 watt 12 volt panel. This moves hot air out of my flat roofed garage in Baja. It has worked flawlessly for 2 1/2 years now. A single fan was screaming at a really high RPM but when I added the second fan it slowed down the fan motors to a reliable speed the more direct the sun's angle the faster they run so they kind of self regulate, depending on the time of day.

Solar panel and fan(s) only?, i have always wondered about the "grey zone", when going direct, my guess is it could be not a one size fits all solution, You have times with good sun when everything works at some level depending on the match and balance of the components, then you have times with not enough light, so not enough power to run the fan, system appears off, but the grey zone exists in some situations where there is enough power to turn the fan very, very, very slowwwly, and doesn't that cause a problem with heat buildup in the motor windings?
Well built high quality motors would have more than enough headroom to handle this i would think since current would be low at that point, i just have always wanted to know if every motor/fan are able to handle that "stall" situation, that may go on for an hour, or if that shortens their life, etc.?

[littleharbor]

A friend of mine ended up with a 100W panel like that and I told him to get rid of it, that it wasn't worth much at home. Well, against my advice he bought two automotive 12V radiator fans and connected them in series, I think. Lo and behold, when the sun is around mid day, the fans go like hell. He made an attic fan out of it. It was weird how the current draw worked out just about right. If it was me, I'd put in on Craigslist.

I've done exactly that with a pair of 12 volt radiator fans and a 65 watt 12 volt panel. This moves hot air out of my flat roofed garage in Baja. It has worked flawlessly for 2 1/2 years now. A single fan was screaming at a really high RPM but when I added the second fan it slowed down the fan motors to a reliable speed the more direct the sun's angle the faster they run so they kind of self regulate, depending on the time of day.

[bcroe]

I sometimes wonder what happens internally when DC motors are placed in series. Putting a couple small brush motors
in series for reduced speed has worked for me. But a brushless DC motor has electronics that draw big pulses, and those
are not going to line up time wise for 2 motors in series. Bruce Roe

[sdold]

That's the reason for wiring the motors in series.