Controlling ac blower output - variac?

[julianf]

I have a blower here - probably off a bouncy castle, of similar.

Id like to control its output. I have a variac somewhere, but i suspect this is not the thing to use?

(my variac is a simple transformer with a screw that, i assume, lifts the core, or offsets the windings?)


Im thinking that the fan will be a brushed motor - i dont know much about motors, but im thinking that rotational speed is a function of the frequency of the AC, and not the voltage?

Controlling the voltage would affect the torque, but not the speed, right?


Basically, the fan is attached to a DIY burner, and, on full whack, its a bit much, especially trying to get it lit. Having a simple control would make things easier.

 

[julianf]

Yeah, at present, im just crushing the pipe, but operation requires more hands than i have really.

I was thinking about some sort of sliding cover, like you get on a hoover hose handle, but, in this case, to let out excess air, but an electronic solution would, if it were easy, probably require less work for an elegant result.

 

[julianf]

I think its only about 400w - not massive at all.

 

[rtbcomp]

If it's a brushed motor a variac may work, the drill trigger or a pulse width modulator (PWM) would be better.

A variac is not suitable for an induction motor, which is frequency dependent.

 

[brightspark]

a gate valve in outlet just restrict the flow . no need to vent it off as the motor runs with less power as the fan is only spinning round in the case not actually pushing the air along using more power to do it

 

[julianf]

A gate valve would be fine with me, but id have to make it. The flexible ducting between the blower and the furnace is 100mm. I have not looked, but i doubt there's an off-the-shelf gate valve of that sort of diameter that would be in any way comparable in price to a cheap PWM kit?

 

[julianf]

If it's a brushed motor a variac may work, the drill trigger or a pulse width modulator (PWM) would be better.

A variac is not suitable for an induction motor, which is frequency dependent.

"may work" as in should i just try, or is the magic smoke likely to escape?

 

[rtbcomp]

A gate valve would be fine with me, but id have to make it. The flexible ducting between the blower and the furnace is 100mm. I have not looked, but i doubt there's an off-the-shelf gate valve of that sort of diameter that would be in any way comparable in price to a cheap PWM kit?

Look for ducting products, there's a type of valve who's name escapes me that is a flap that you can control from the outside of a tube. Butterfly valve?

"may work" as in should i just try, or is the magic smoke likely to escape?

Are you it's a commutator-type (universal) motor?

 

[julianf]

Ill take a photo of the plate...

 

[the artfull-codger]

If it's a bouncy castle blower [the big yellow snail fan type] it'll be an induction motor probably made in china,they're good blowers, just cut a 3mm circular disk of alloy with a lug to cover the inlet fixed with a bolt & spring so you can completely close it then gradually open it to the volume you want, & as BS says the more it's closed the less work it's doing you won't overheat it, no need to mess on with valves etc.I have mine on a furnace.

 

[WorkshopChris]

Search ducting blast gate. Often used in woodwork dust extraction.

 

[rtbcomp]

^^ "Blast gate", that's the word I was looking for (#10)

 

[Wightsparks]

If its the snail type I have one I controlled with a £5 2kw controller off ebay, triac based I think. I just mounted it in a box. Like this one http://www.ebay.co.uk/itm/Adjustabl...487791?hash=item1a2d8edfaf:g:KcAAAOSwgQ9VkXMs

 

[wookie]

Look for ducting products, there's a type of valve who's name escapes me that is a flap that you can control from the outside of a tube. Butterfly valve?

Yeah butterfly valve, think of the type you get in the inlet of a car's induction system, in fact one off a scraper might be suitable....

 

[BarrieJ]

Professional blacksmith's forges frequently have an adjustable speed blower and a gate valve. The gate valve allows you to cut all air to the fire pit/pot whilst forging and then open it again to return air flow when taking the next heat. Considerable saving on fuel over the course of a working week.
Volume of supplied air is more important than pressure.

 

[puffernutter]

There's quite a range of (cheap) electronic speed controls on various sites, but that may overheat the motor. Better to either throttle or divert some of the air (like a turbo waste gate).

Cheers

Peter

 

[rtbcomp]

^^ You need the correct type of controller for the motor, the shape of the fan cowl doesn't determine the motor type.

 

[gaz1]

here you are

it was done but id advise reading the info on youtube as it failed

i kinda looked a long time ago it worked out a squirel fan was better

 

[magnet]

I made a version of this

for my forge its more of a diverter than a valve and allows the fan to move its correct flow of air mine works a treat