PC Fan Speed Control

[sundancer87]

I searched first before asking but didn't turn up anything I can use.<p>Here's the project. I have a battery box that has an 80mm muffin fan installed to help vent the battery box. Under normal solar charging very little gases and heat are created, therefore the fan doesn't need to run at full speed. I run the fan at a slower speed to keep the tip noise to a minimum. The battery box is in the bedroom so the fan noise, at night, can be bothersome.<p>I'm needing a circuit that will speed the fan when the battery box becomes warmer than ambient temperature. This temperature rise will occur when heavy charging is taking place. At this point the gases and heat will be needed to be vented.<p>The circuit doesn't need to have a speed/temperature ratio or anything that sophisticated. It just needs to run at maximum until the charging has finished and the box temperature cools.<p>I want to keep it as simple as possible, perhaps with a 'speed up' set point and a minimum speed set point.<p>Thanks

[philba]

Is there a charging active LED? If so you could just use that as input to a relay driver transistor that turns on a relay which turns the fan onto full speed when charging is active. a resistor, transistor and a relay is all you'd need. If its a charging complete LED, you'd need to invert the logic sense. If its a blinking light while charging, then its a little trickier but still doable.<p>Of course you could just use a thermostat to control the fan. The only concern I'd have about a thermostat is that is has a single set point and on a hot summer day it might be tricked into running all the time.<p>to build a true differential temperature controller is more complex and I wonder if its worth the trouble.<p>[ December 22, 2004: Message edited by: philba ]</p>

[Engineer1138]

sundancer, here's a sample circuit. I have not tested it, but it should work. I will shortly have a need for something similar (cooling a heatsink), so I figured it was time to take a first pass at it. If you build it, let me know. <p>D1 and D2 take advantage of the temperature coefficient of a silicon diode (2 mV/K) and behave as temperature sensors. You can also use standard temperature sensors here like LM34/LM335 if you have them. These are cheaper, but more sensitive to adjustment. The trimpot sets the percentage above ambient where the fan will speed up (adjust so with both D1 and D2 at ambient temp, pin 3 has about 20mV or so below pin 2). Oh, note that the schematic doesn't show V+ (pin 4) and GND (pin 11) for the LM324. Any single supply op amp should work fine here.
When the sensors are properly placed and adjusted, if D1 gets appreciably higher than D2, the transistor turns on and shorts out the speed limiting resistor, speeding up the fan. At least that's the theory <p>Any questions let me know
www.veronasoftware.com/embedded/fancontrol.png<p>[ December 23, 2004: Message edited by: Engineer1138 ]</p>

[sundancer87]

Thanks for the curcuit. I like it and it looks like it will do the job.<p>I only have one LM34 in my parts bin so I will use the diodes. I think I have a handful of 324s so, all in all, I have enough to get started today.<p>One question I have, R4, the fan speed resister. Is that up to my discretion as to how fast I want the fan to spin up? Also, do I really need a 2N3055 to switch a muffin fan?<p>I find a little humor in the MN in your sig line. I would think, this time of year, a person would be looking to heat something. <p>[ December 23, 2004: Message edited by: sundancer87 ]</p>

[sundancer87]

Philba, we're talking about charging 1000 amphours of battery capacity. There are 6, 6 volt, deep cycle batteries with a capacity of 350 amphours each.<p>When charging these guys at 45 amps a lot of heat is made and a lot of gases are created.<p>This needs to get out of the box and the box needs to be as cool as possible during the charging process.<p>So, to answer your query, it will definately be worth putting the circuit together.<p>Thanks for your input, that's what the hobby is all about.

[Engineer1138]

Yes, R4 is sized to fan speed. Use whatever you have on hand instead of the 3055, but I figured the fan probably draws more current than a 2N3904 could handle.
I drew the circuit this morning while simultaneously trying to wake up and keeping my 4 year-old from wrestling with the dog, so I was drawing it as fast as possible <p>And yeah! It's -8 degF outside (today's high temp will be around Zero fahrenheit); I could tape that heatsink to the window and not have to worry about needing a fan!<p>
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by sundancer87:
Thanks for the curcuit. I like it and it looks like it will do the job.<p>I only have one LM34 in my parts bin so I will use the diodes. I think I have a handful of 324s so, all in all, I have enough to get started today.<p>One question I have, R4, the fan speed resister. Is that up to my discretion as to how fast I want the fan to spin up? Also, do I really need a 2N3055 to switch a muffin fan?<p>I find a little humor in the MN in your sig line. I would think, this time of year, a person would be looking to heat something. <p>[ December 23, 2004: Message edited by: sundancer87 ]<hr></blockquote>

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by sundancer87:
So, to answer your query, it will definately be worth putting the circuit together.
<hr></blockquote><p>I was referring to the differential part. My point was why not just run the fan when recharging.

[sundancer87]

Philba, during normal use I want the fan to just move air through the battery box. I don't want to hear the fan while I'm trying to sleep. <p>During heavy charge time I don't care how fast it runs or how much noise it makes. The heavy charging takes place in the day time. The charger is growling while pushing the amps out, the generator is running supplying the charger, and I'm not trying to sleep. This is when I need to speed the fan to have a rapid exchange of air through the box.<p>Besides, where would be the hobbyist's fun if one just didn't have something a little 'off the shelf' for a little automation?

[jwax]

sundancer87 - Couple of questions: What make and size of solar arrays are you using, and which coast are you on?
Also, any comments on your choice of solar arrays? Would you recommend them?
Thanks, I'm becoming a solar nut!

John

[sundancer87]

Hey John, I'm located on the west coast of Mexico, about 250 miles and 5 hours from Tucson.<p>In the afternoon I can see the Baja of California 60/70 miles away.<p>I've had 8 Hoxan, 45 watt modules in service for 12 or so years. Last year I added 4 more BP's to the array. These guys are 75 watts each.<p>I would stay away from the 'Johnny come lately' manufacturers and go with brand name.<p>The price per watt was supposed to fall over the years but there hasn't been a significant drop. Something is keeping the price elevated, most likely from the lobbyists from the oil and energy sector.<p>Google for solar modules and you will find a ton. The best price I've found lately is the outfit in Flagstaff, Arizona. They have good prices and ship quick.<p>Shop around for your solar stuff. The prices are all over the place. Some suppliers treat solar items as if they are gold and so very special. For others, it's just another thing that makes them money. That's where you want to shop, with the guy that doesn't have a deep affection for his product.<p>I was thinking last night how much I enjoy having a 12 volt house. I can do all kinds of projects and can have all kinds of strange stuff doing strange things. Everyone should have a 12 volt room in their house. Of course, I have an inverter that makes my 110VAC and an air conditioner for when it gets to0 hot to sleep.
I have a wind generator and a Honda motorhome generator for backup amd those three days the sun doesn't shine down here.<p>I hope this has been helpful to you. If you need or want more info I'll be happy to do what I can.<p>
<p>[ December 24, 2004: Message edited by: sundancer87 ]</p>

[terri]

These batteries are "venting gases" indoors, AND in your bedroom?<p>Holy cow!<p>I am sometimes surprised at some of the more risky things I've seen on the board.<p>[ December 24, 2004: Message edited by: terri ]</p>

[jwax]

Thanks sundance!
I know the "newer, cheaper" solar cell has yet to hit the market, but we're all still hoping, aren't we?
I'll research your mfg's, as well as others, since as of next year, I'll be in the solar cell manufacturing business!
Perhaps I'll get a business trip this winter to "research" your installation in sunny Mexico!

Stay cool!
John

[sundancer87]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by terri:
These batteries are "venting gases" indoors, AND in your bedroom?<p>Holy cow!<p>I am sometimes surprised at some of the more risky things I've seen on the board.<p>[ December 24, 2004: Message edited by: terri ]<hr></blockquote><p>Guess what? All six of them are in an Igloo ice chest. However, don't be surprised at what you've seen in this thread because you haven't heard the rest of the story.<p>I am retired fireman so I have a little knowledge of safety aspects. I'm dangerous with electricity, electronics and batteries. All that aside, (the rest of the story), the battery box doesn't vent in the bedroom. There is a 2" PVC vent pipe that goes from the battery box, through the wall and to the outdoors where it vents. The fan just helps the box be cooler and less gassy during charging times.

[sundancer87]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by jwax:
Thanks sundance!
I know the "newer, cheaper" solar cell has yet to hit the market, but we're all still hoping, aren't we?
I'll research your mfg's, as well as others, since as of next year, I'll be in the solar cell manufacturing business!
Perhaps I'll get a business trip this winter to "research" your installation in sunny Mexico!

Stay cool!<p>John<hr></blockquote><p>Well yeah, come on down and bring some of your product. We'll field test it here in the number 6, sun insolation zone.<p>I'm still waiting for a satellite to fall in the front yard. Now there's a pile of solar modules!<p>[ December 24, 2004: Message edited by: sundancer87 ]</p>

[jwax]

That's a deal, sundancer87!
Our insolation is about half of yours, so I guess my goal is to build an array that gets the same output/sq ft as yours! AND affordable.
Are your arrays tracking, or fixed? Correct me if I'm wrong, but wouldn't the dollars spent be better put into a larger fixed installation, than a smaller, movable one?
Also, do you "sell back" any power to the grid, or are you not part of "the grid"?
Shine on!
John