Author Topic: Temperature control of small 12V fan (Read 11304 times)

la7qz · « **on:** August 05, 2008, 04:50:05 PM »

Hi

I've installed the rectifiers for my wind turbine and the S4w charge booster in a box which used to be a marine battery charger.

The box already has a nice little 12V fan. I'd like the fan to start automatically when the diodes start getting hot. Any ideas? Whatever I use needs to be relatively small to fit inside the box.

I've looked at a few cheap thermostats, but they all have NC contacts rather than NO. I don't want to use any kind of electronic control which would consume power when the fan is not running. The energy consumption of the fan (and relay?) when they are needed would not be a problem. If the box is hot, that means the wind turbine must be pumping out some juice, so I can spare enough to run the fan to keep things cool.

Owen

Jeff · « **Reply #1 on:** August 05, 2008, 11:51:55 AM »

Maybe some "dumpster diving" would yield some results? Check the local junk yard & look for fans. Some models, and window models, have a tempurature control knob. I've found two of them, and since they work on any voltage, you want to make sure you don't hook them up to something that draws a lot of amps. For small 3-5 inch 12v fans like in computers, they work great! Also, most thermostat controls like the one mounted on the wall for your home heating/AC will handle those small fans too!

Good luck!

RUFUS · « **Reply #2 on:** August 05, 2008, 12:08:33 PM »

I did just what your talking about

with my turbine controller with a

heat switch from ww grainger it's on at

120 and off at 90 pn# is 2e245 snap switch

$9.00 and some change thier used in

clothes driers and stuff, when i get home

i'll put a close up shot in my photo

uploads,it works well

my 2 cents

Rufus

RUFUS · « **Reply #3 on:** August 05, 2008, 12:38:40 PM »

Ooop's

Looked at your user info,

gonna be kinda hard to swing

by a WW Grainger from your place.

Let me know if i can help

Rufus

kurt · « **Reply #4 on:** August 05, 2008, 12:49:04 PM »

well if it was me i would go to my local appliance parts dealer and ask about a snap switch for the exhaust fan in an above the range microwave it is just a little mechanical thermostat that turns the exhaust fan on if the temperature under the range hood gets over 100 deg f or so totally mechanical switch one wire in one wire out will work on any voltage i wouldn't try switching high current dc with one but it would work fine for a little 12v fan.

elt · « **Reply #5 on:** August 05, 2008, 12:54:55 PM »

Look at computer case fans, some have a thermostat connected. You might find one surplus for less than the cost of a thermostat alone.

Hope that helps,

- Ed.

CmeBREW · « **Reply #6 on:** August 05, 2008, 01:13:03 PM »

Maybe you could screw some more aluminum pieces to the side to improve the heat disipation better?? (or get more rectifiers)

Or, sometimes you can find a 12v cooling fan that has brushes and just hook it up with a diode and the cooling fan only comes on when the mill generates power.

The majority of little cooling fans are brushless and use a transistor which will not work with direct hook up like that since it blows the transistor.

la7qz · « **Reply #7 on:** August 05, 2008, 02:42:39 PM »

Looks like just the thing I need.

Now, how do I get my hands on one out here...

Owen

wooferhound · « **Reply #8 on:** August 05, 2008, 03:06:44 PM »

Install another bridge rectifier in addition to the ones that are already on there

connect a big capacitor across it's output, then connect the fan to that

The fan will be running whenever the turbine is making power . . .

tecker · « **Reply #9 on:** August 05, 2008, 03:43:41 PM »

Good one Woof a 7812 might be nessesary when the control cycles out.

wooferhound · « **Reply #10 on:** August 05, 2008, 03:48:31 PM »

I was thinking that the battery will hold the voltage down good enough ?

It is a dump load on a wind turbine isn't it, even equalizing voltage shouldn't hurt it.

RUFUS · « **Reply #11 on:** August 05, 2008, 04:11:43 PM »

Dude,

Push come to shove

E-Mail me a good address

and i'll mail you one,

I know just what it's like

to be in bum#%&* Egypt and

not be able to git the stuff

you need

Rufus

tecker · « **Reply #12 on:** August 05, 2008, 04:14:19 PM »

I can't tell if he's useing a dumper or not but the 7812 is cheap enough . Of coarse the fan needs to be under an amp. The charge voltage will ride up anyhow with a charge .

RUFUS · « **Reply #13 on:** August 05, 2008, 06:22:23 PM »

Pic's are up,

at my photo uploads

Rufus

TomW · « **Reply #14 on:** August 05, 2008, 07:26:33 PM »

RUFUS' files are over here:

http://www.fieldlines.com/user/RUFUS/files

Tom

wooferhound · « **Reply #15 on:** August 06, 2008, 07:16:03 AM »

I looked at the S4W controller

http://www.s4wsbox.com/?q=node/34

I can't see how it controls the charge on the batteries, it mentions dump somewhere in the text but I don't see it.

la7qz · « **Reply #16 on:** August 06, 2008, 07:51:30 AM »

Hi

Interesting idea. However, these 12V brushless fans seem to be very finicky about power. Also, I only really want it to run when the turbine is producing a fair bit of power, say above 5A (which is why I was looking at temperature control). I don't want to waste what little charge I am getting in light winds.

The maximum I've seen out of the turbine is 34.95A according to my Doc Watson meter. On the same day, the bicycle computer registered a max RPM of 1170.

A more typical output is around 3-5A in the winds we've been having lately. The box has good heat sinks (it used to be a 40A 12V battery charger), so I'm really only looking to cool it when the turbine is really cranking. At anything below 5A output, I would probably just be wasting power by running the fan. I'm also using twice the rectifier capacity of what the alternator was originally supplied with. It originally had two single phase bridges using both inputs from one and a single input from the other. I have installed three of the same bridges and am using all inputs.

There is no regulator connected to the turbine. Output is wired direct to the batteries. I'm in the process of installing a Tristar 60 with a 600W 12V heating element in my hot water tank, but with the light winds we've been having lately (and the fridge running 24/7), It's been a long time since I've seen peak voltages over 14V. However, I also do have a second wind turbine ready to fly (with it's own rectifier box), so that should help a bit.

Owen

la7qz · « **Reply #17 on:** August 06, 2008, 08:33:36 AM »

The S4W booster doesn't control the charge.

What it does is boost the voltage when the turbine is running below cutin.

Cutin of my turbine is at 300rpm. In other words, there is no output from the turbine at 300rpm. Once it passes that speed, it starts charging.

With the S4w booster, cutin is around 140rpm. Not much, but it IS charging. At 300rpm it is producing 1A. It breaks even at around 340 - 350A and 2A. In other words, at this speed there is no increase in output when the booster is connected.

So, what it does and was designed to do is to give some charge in light winds. It probably works best with a turbine like mine which spins very easily in light winds. My other turbine (which is not flying at the moment, but probably will be by tomorrow) takes a lot more wind to start spinning, but still produces around the same once the wind picks up. Since it doesn't do much spinning in light winds, the booster would probably not do much for this turbine.

The only disadvantage I have found to the booster so far is that it produces some RFI on my shortwave (ham) radio. I have to switch it off to copy light stations. (And remember to turn it on again after.) This will naturally be less of an issue for those who do not have ham radio or live in houses where the distance between the booster and antennas and radios can be greater.

You may say that 1A is not much, but an average 1A is still 24Ah per day that I would not be getting without the booster. That's enough to run my Stirling cycle fridge.

Owen

la7qz · « **Reply #18 on:** August 06, 2008, 08:35:14 AM »

Thanks a lot

I'll dig around a bit and let you know if I can't find anything locally

Owen

la7qz · « **Reply #19 on:** August 06, 2008, 09:13:13 AM »

OOps

In the post above, I wrote:

"It breaks even at around 340 - 350A and 2A."

That SHOULD read:

"It breaks even at around 340 - 350rpm and 2A."

If I was getting 340 - 350A out of a 5 foot diameter turbine, I could probably retire VERY RICH....

Owen

tecker · « **Reply #20 on:** August 06, 2008, 09:18:38 AM »

No dumper . It says it boosts too but from looking at the circuit the reference voltage is tied to a 7812 . The boost reference would come from the battery bank .No protection I can see this circuit go with a little static .

la7qz · « **Reply #21 on:** August 06, 2008, 11:33:39 AM »

I have one in my hand!

I knew we stock some stuff from Grainger at work, so I printed the page from their site and took it to Titus who restocks stuff and asked him to get me one (after I'd searched the whole shop). He said "follow me", and pulled one out from the back of a shelf. We didn't get it from Grainger, but from, "Alaska Diesel Electric".

I am now a happy bunny

I'll install it an let y'all know how it works out. Just need enough wind to heat those rectifiers up a bit...

(I don't work in the store. I'm just a technician. I just fix things ..)

Owen

s4w2099 · « **Reply #22 on:** August 06, 2008, 12:14:07 PM »

hmm tecker,

There is no reference connected to 7812. The reference is taken from the VREF pin generated from the tl494 itself. I think you have it all wrong. This is not supposed to boost based on voltage read from the battery.

It should boost based on the current seen into the batteries.

Read this: to clear it out a bit: http://s4wsbox.com/?q=node/32

I attempted to explain there how it works.

tecker · « **Reply #23 on:** August 06, 2008, 02:05:42 PM »

I'll do that. http://s4wsbox.com/?q=node/32 crashes

tecker · « **Reply #24 on:** August 06, 2008, 02:06:45 PM »

Ok I got it to work

Ungrounded Lightning Rod · « **Reply #25 on:** August 06, 2008, 02:12:55 PM »

Your local travel-trailer supply (or its online catalog) should have a little gadget for boosting the efficiency of an ammonia-cycle refrigerator.

It's a thermostatic snap switch and a small, low-drain, fan with a 12-volt brush-type motor, to be mounted in the back of the fridge space and help the airflow past the coils. Not sure what the setpoint is but I suspect it's about right to cool your diodes. Intended for coming on when the day is hot enough that convection cooling with a 4-foot chimney is inadequate.

Don't know how long the motor will last. (Mine outlasted the cooling coils, which failed a couple weeks ago and gave me a couple lungfulls of ammonia before I made it out the door. B-( Probably had at least a years worth of run time so far.) But if the motor goes out (or if you don't like it) you can always use the snap switch with something you trust better. Or use two of 'em for redundancy.

la7qz · « **Reply #26 on:** August 06, 2008, 02:39:24 PM »

Hmmmm....

I can't remember ever seeing a travel trailer (or mobile home) on this island. I'll have to keep my eyes open for one. There probably isn't much market for them on an island the size of a postage stamp.

Anyway, I've found a snap switch now (see above), so I'm a happy camper.

Owen

RUFUS · « **Reply #27 on:** August 06, 2008, 07:30:33 PM »

ALL RIGHT TITUS

man knows his stuff

RUFUS

tecker · « **Reply #28 on:** August 06, 2008, 08:11:46 PM »

Vcc is the voltage reference no doubt there . Your error comparing that to the voltage from the allegro .That's a nice choice there . I like lean circuit designs . I'll buy one and run it through it's paces . Rather than go on as negitive input .

s4w2099 · « **Reply #29 on:** August 06, 2008, 09:29:32 PM »

Tecker, I ran out of them a while ago, here is a cache from google of that page with the message dated July 10th.

http://74.125.45.104/search?q=cache:m6Z7WI0vCU4J:www.s4wsbox.com/%3Fq%3Dnode/33+site:http://www.s4ws
box.com/&hl=en&ct=clnk&cd=15&gl=us&client=firefox-a

If you think its so bad I invite you to put it together properly (good layout) and test it. I dont force ppl to buy it or try to convince them about it, thats the reason I give schematics. You dont want to buy it or skeptical you have the map to build it and test for yourself. I have no plans to make a business out of it either, I posted it free for all.

tecker · « **Reply #30 on:** August 07, 2008, 05:33:55 AM »

I understand I like the idea .I'm not tring to be an a hole . I 'd like to expand this if the loops are sound .

s4w2099 · « **Reply #31 on:** August 07, 2008, 06:53:32 AM »

I see,

This works fine but its not MPPT it was not my idea actually but Flux's. I was just the one that actually implemented the idea and got it to work after Flux.

I wont be making this one anymore, I will be replacing the tl494 with a small PIC and go MPPT all the way. Sure it will have to be more expensive as there would have to be much more protection for the micro, the 494 is a tough IC.

I have to finish older projects though.

SparWeb · « **Reply #32 on:** August 10, 2008, 11:41:06 PM »

I'm a bit late... ... I see you have the snap switch.

I was going to suggest using a simple house-hold furnace thermostat. A snap-switch is not adjustable, and the furnace thermostats are adjustable in more ways than you might expect.

I rigged one up last winter to turn on a heater when it went below -20C in the battery box. The thermostat of course can't normally be adjusted to that range, but all you have to do is mount it diagonally on the wall, and then it will work at some different temparature range altogether.

If it has to switch a lot of current, you can use a relay. If it's just a tiny heat-sink fan (<1Amp), the thermostat switch can handle it.

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Author Topic: Temperature control of small 12V fan (Read 11304 times)