[Stoves] Variable Speed Stove Fan

Thu Nov 30 09:43:20 CST 2006

Dear Ken

Thanks for your comments. They really help put things in perspective. It is 
a lot more fun to work with fans because they really bring a fire to life, 
but if the controller costs $10, the fan $1, the battery $1, and the 
recharger $30, it sort of prices the system out of the reach of the $5 stove 
market.

Oops!!, I forgot to allow something for the stove. ;-)

Best wishes,

Kevin
----- Original Message ----- 
From: "ken goyer" <kgoyer at comcast.net>
To: "Discussion of biomass cooking stoves" <stoves at listserv.repp.org>
Sent: Thursday, November 30, 2006 2:22 AM
Subject: Re: [Stoves] Variable Speed Stove Fan

> Dear friends, I think that fans sound like a great idea but when
> thinking about stoves you should consider the following information that
> I just chopped out of google:
> <>
> "The United Nations estimates that more than 2 million villages
> worldwide are without electric power for water supply, refrigeration,
> lighting, and other basic needs, and the cost of extending the utility
> grids is prohibitive,"
>
> <>"85% Africans live in rural communities without electricity."
>
> <>"Worldwide, some 2 billion people are currently without electricity.
> (U.S. Department of Energy)"
>
> "Third World's estimated two billion people who live on less than $1 a
> day and the three billion living without electricity."
>
> <>"BHUBANESWAR: Although Orissa is set to become the country's
> powerhouse, millions of people living in thousands of villages and
> hamlets in the State are still managing without electricity. Of the
> total 47,902 revenue villages in the State, 17,935 villages do not have
> electricity supply at present. The Government is now preparing to
> provide electricity to these villages under the Rajiv Gandhi Gramya
> Vidyut Yojana (RGGVY), Energy Minister Suryanarayan Patro informed the
> State Assembly on Saturday. Apart from 17,935 revenue villages, 38,370
> hamlets too did not have electricity. These hamlets will also be
> provided with electricity under the RGGVY, Mr. Patro said."
>
> Most people can't afford batteries or PV either.
>
> This was the main reason that Larry invented the Rocket Stove :-) .
>
> Best regards, Ken Goyer
>
>
>
> Tom Miles wrote:
>
>>Good explanation and links, including your second note, Thanks.
>>
>>This kind of controller may be best used while developing a fan stove. A
>>simple damper might work better once you determine the fan size and speed
>>range. The object is really to find the best balance of pressure and flow
>>for the application.
>>
>>Tom
>>
>>
>>-----Original Message-----
>>From: stoves-bounces at listserv.repp.org
>>[mailto:stoves-bounces at listserv.repp.org] On Behalf Of William Carr
>>Sent: Wednesday, November 29, 2006 5:01 PM
>>To: Discussion of biomass cooking stoves
>>Subject: Re: [Stoves] Variable Speed Stove Fan
>>
>>
>>On Nov 29, 2006, at 12:46 PM, Tom Miles wrote:
>>
>>
>>
>>>Kyle's comment reminded me of a conversation between Charlie Sellers
>>>and Paul Anderson at Stoves Camp this summer. Charlie was describing
>>>an electronic  "chopper circuit" to adjust the speed of a DC fan. Has
>>>anyone built one? Can anyone provide the circuit, list of components
>>>(and
>>>sources)
>>>or a step by step how-to (with pictures) for building one? Or is there
>>>an internet source?
>>>
>>>
>>
>>This sounds like a "type D" amplifier.
>>
>>It came up in High School, when I was interested in controlling the speed 
>>of
>>small DC motors.
>>
>>
>>(Turns out it's also the only way to 'dim' fluorescent lights.
>>
>>You see, a fluorescent tube won't fire without full voltage.   Lower
>>the voltage, no light at all.)
>>
>>
>>
>>You can control the speed of a DC motor fairly well by dialing down the
>>voltage, that trick works somewhat with an AC motor, but it won't work at
>>all with a fluorescent tube.
>>
>>
>>
>>So instead of turning down the voltage, you want to dial down the wattage
>>instead without affecting the voltage.
>>
>>
>>
>>The only way to do that is with a type D amplifier, by converting the 
>>input
>>signal into a squarewave (AC) or a series of pulses (DC).
>>
>>
>>If you look at the sinewave of standard 60 cycle AC,  you see a trace 
>>going
>>up, and down, up, and down.
>>
>>The circuit is getting peak power at the tops of the wave, of course, but
>>it's still getting SOME power on the way up and on the way down.
>>
>>At any given point you can calculate the amount of power by a process 
>>called
>>"Root-Mean-Square", a term that still triggers my math aversion 24 years
>>later....
>>
>>By generating a squarewave output, you can provide the full voltage at the
>>correct frequency.
>>
>>
>>But if you cleverly reduce the width of the squarewave, you will be still
>>supplying the correct voltage, at the correct frequency, but you'll starve
>>the circuit on wattage.
>>
>>Thus, the motor slows down in a nice linear fashion as you decrease the
>>squarewave width, and a fluorescent tube dims gradually.
>>
>>The method works with DC also, just by making the squarewave a series of 
>>DC
>>pulses.
>>
>>
>>Here's a link to controlling your DC motor:
>>
>>http://www.solorb.com/elect/pwm/index.html
>>
>>William Carr
>>
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>>
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