A Weird project I know... help needed!

[obmitty]

Hi guys, I have a crazy Idea that I want to build a forced induction bbq.

The plan is to use an old dyson motor on the other side of a wall to blow
air into an enclosed space below my brick bbq with holes allowing air entry into the fire pit.



Problem is, I really want the motor to be variable in speed.

It is 1200 Watts, so normal dimmer switches (400watts limit) are not enough.

Question is, where can I get or how can I make a 1200 Watt dimmer/pot.

For example would connecting dimmer switches in parallel work? Ideally would rather have just one knob to control it, but anyway...

Any ideas?

Tim

 

[industryspark]

You cannot use dimmer switches for such an application so forget that.

The way to control a motor speed is by using a suitable inverter or variable speed drive.

 

[bernardgreen]

With that size motor you will create a black-smiths forge and be able to soften iron............or blast red hot material into the cooks face.

The idea is good and will work extremely well with the gentle air movement of a bath room extractor fan. Leave the fan full speed and simply control the air flow into the fire bed by opening or closing an escape route for the air on route to the fire bed.

 

[obmitty]

The way to control a motor speed is by using a suitable inverter or variable speed drive.

Inverter? Those seem to covert AC to DC. I presume I need to stay in AC for my motor to work well?


What's a variable speed drive?


BTW, I know this is excessive, and I know it will be capable of melting steel. haha

It's going to be awesomely pointless! Will post pics of white hot coals when it's done.

 

[obmitty]

......or blast red hot material into the cooks face.

Hence the need for a rheostat!

If you crank it up slowly, should be safe and excessive at the same time.

 

[ColJack]

inverters do change AC to DC, but they then electronically controll that DC and chop it into something that approximates a sine wave as far as the motor is concerned..

the frequency and characteristics of this "sine wave" can then be controlled to change the speed and / or torque of a motor..

so instead of running at 50Hz, you slow it down to say 25Hz, and the motor is only going half as fast..

 

[Spark123]

The way to control a motor speed is by using a suitable inverter or variable speed drive.

Inverter? Those seem to covert AC to DC.

A Rectifier is used to convert AC to DC, an inverter is used to convert DC back to AC. You'll probably find the motor you have is a universal motor i.e. wound stator, rotor and has a commutator. These will run on AC or DC.
If it is a universal motor then some sort of thyristor device should be able to slow it down (i.e. a normal dimmer switch of sufficient rating)

What's a variable speed drive?

A VSD is a device used to alter the frequency of the current flowing to a motor to adjust its speed.

 

[TicklyT]

A 1200 Watt vacuum cleaner motor sounds totally OTT!

Some years ago I used an old 500 Watt cylinder vacuum cleaner to provide the air blast for a furnace for melting about 20 pounds of cast iron. When it was working it produced about a four foot jet of blue flame above the top of the cupola like a giant bunsen burner.

That's just a trifle too fierce for grilling a few sausages!

Something like a PC power unit cooling fan would probably be more appropriate

 

[powersurge]

Hell yess its wierd and OTT (but I like wierd and OTT) so :

Its a drill speed controller you need, Maplin used to do one, but I just looked on their www and its not there anymore, but I did find this:
http://cgi.ebay.co.uk/POWER-CONTROL...PS/DRILLS_W0QQitemZ110375639016QQcmdZViewItem

I have a similar one inline in an extension lead and it works well with my big drill (especially with the paint mixer in - stops me going to fast and making a big mess!!) and the workshop vacuum cleaner (still sucks OK but runs much quieter)

Just check 'cos they usually only work with series-wound induction motors (thats usually motors with brushes) check if your Dyson is of this type.

 

[aptsys]

If you're stuck on using the vacuum cleaner motor, your easiest way of controlling the airflow would probably be to control the airflow from the motor by restricting the airflow into the fire pit, and diverting the unwanted airflow away from the fire pit.

 

[DCC]

A 1200 Watt vacuum cleaner motor sounds totally OTT!

Some years ago I used an old 500 Watt cylinder vacuum cleaner to provide the air blast for a furnace for melting about 20 pounds of cast iron. When it was working it produced about a four foot jet of blue flame above the top of the cupola like a giant bunsen burner.

That's just a trifle too fierce for grilling a few sausages!

Something like a PC power unit cooling fan would probably be more appropriate

Was just going to suggest the same. Get a bunch of 12v fans maybe 6 inch or 8 inch on a panel, buy one of the fan speed controllers they sell find a suitable outdoor low voltage transformer and bobs your uncle.

On the other hand if the OP *really* wants the blacksmiths forge effect then by all means use the Dyson motor - if you're not sure about motor control you could always knock up some sort of mechanical bypass to divert some or all of the airflow away from the BBQ.

 

[ban-all-sheds]

Hi guys, I have a crazy Idea and no matter how many people tell me that it's so crazy it could easily maim or kill people, I'm so stupid that I'm going to go ahead with it.

 

[electronicsuk]

Hi guys, I have a crazy Idea and no matter how many people tell me that it's so crazy it could easily maim or kill people, I'm so stupid that I'm going to go ahead with it.

You've gotta admit though, it does sound like fun. OP - if you do build this, come back to us and let us know how it went. I'd be interested to see if something as powerful as a vacuum cleaner fan will simply blow the flames out.

 

[ban-all-sheds]

You've gotta admit though, it does sound like fun.

Fireworks are fun too, but I wouldn't use them a few feet from my face/inches from my hands to cook food.

OP - if you do build this, come back to us and let us know how it went. I'd be interested to see if something as powerful as a vacuum cleaner fan will simply blow the flames out.

Once charcoal is burning you can't blow it out.

 

[bernardgreen]

Using a heat gun to light a barbecue.......

Power input 1500 watts, two heat settings 300°C at 480 litres of air per minute or 500°C at 280 litres per minute.

No danger while the charcoal is not burning but once burning there are red hot fragments of disintegrating charcoal flying everywhere.

Turning to cold air blow and the ferocity of burning and flying fragments is reduced but still enough to be dangerous.

Using a length of 22mm copper pipe to feed cold air from gun into charcoal ( to protect the gun from being cooked ) resulted in white hot charcoal and melting of some cast iron fragments placed on the charcoal.

The steaks dis-appeared.......