Here is my design for an inductive load fan dimmer that can handle mutiple rvk/capacitor start fans up to 8A.

Please feel free to ask any questions

Click to view attachment

SL....

Does it work cos there are loads of designs but few actually work have you built it and tested it

i have been using the exact same design for the last 5 years continusly running a 10" and 2 x 6" RVK and it has worked faultlessly,infact i lost the shematic and got this from the one i am using right now,(hence a quick veroboard layout) i am an electronic engineer who used to design power control circuits all the time, the only thing i will say is you may need to experiment with vr1 value as some fans may switch off completly in half a turn, so try a 47kohm instead or use a 15kohm and 100kohm in series to get a rough and fine dual control, or 2 of the same pots and a room thermostat with a changeover contact and there you have it seperate day and night time fan speeds

SL..

Thanks for that SativaLover,much appreesh.

It's good that you've shown the circuit on Veroboard as well.

Easy peasy for less tech minded peeps.

So this is a design that places no undue load on the fan motor,unlike some designs that buzz?

Electronics is not my strongest point but do you build in a feature to prevent the user setting it too low and burning out the windings because of the effects of the capacitive component its certainly risky business playing with this stuff

It sounds good man this site could really do with an electronics expert well done

My only concern is the voltage/current rating of vero board,id be tempted to use tag strip instead.Another idea why not add a thermistor so the speed varies with tempreture

Hi
Nice drawing thanks for adding it, i can see it will work just fine, i have something very similar using triacs and coils,
i like your idea of switching the pots with a thermo for dual control, i use two controlers to do that, and now you have me thinking
im gonna have to get out my soldering station and try that now.
JS

Hi all , yes the fan should not be run so low that it sits there buzzing you can get round that by playing with the pot value or adding resistors in series with a lower value pot so that it can never reach zero (a preset would work well here). veroboard does have its limitations for current and high voltage on the one i am using now i have soldered wire on top of the power rails and direct to the triac on reverse of board for peace of mind (i will redraw a shematic if anyone wants it for their own design).i will post some pics of the one i am using in the next few days for an example.
i like the thermistor idea, the only prob is most thermistors rise in resistance with temp which would slow the fan down, but this could be redesigned

thnx for all the comments, i just think the shops rip people off sometimes for something so simple and cheap to build and thought i would share it with fellow growers..

SL..

Now I could be wrong here but with this type of thing don't we need a snubber circuit to reduce transients, don't these cause radio interference due to the sharp surges caused by the triac.

EM2

Would it not be advisable for radio interference suppression or is the snubber reducing this effect due to it absorbing the transients

You are very good with electronics both sativa lover and whazzup

Do you know how to build a practical frequency controller whazzup or sativa I hve looked into this but my knowledge limits me

Thanks

Your right whazzup its just a light dimmer, not good news I thought they used two triacs back to back

EM2

C3 and R3 are snubber as wazzup says, unfortunatly when using any of this style of power controller you will always get hum at low speeds its inherent with triacs. the only way to get round this would be as mentioned a frequency controller or hertz drive, but these can run into hundreds of pounds to build.


Sativalover

Good point i agree, this circuit was used to power 4 x huge box squirrell cage fans(6000m3) that were drawing i think about 2 amps each and the hum was alot less noticable than with just a rvk.

as i never run my fans less than 50 -60% power i find i don't get hardly any hum.

one good point is that this is the very same circuit prob that you will find in fan controllers in hydro shops selling for anywhere from 40 to over 100 quid its a good saving and you will learn something from building it

sl

completely diy speed controller, this is awsome... I really want to try some of this electronics... ur diagrams look simple enough to follow too. i really want to do the maplins temp control module wth hi and lo out put settings and remote sensor(like madhippy helped with in detritus's thread) but havent bothered yet becuase i dont understand proper electronic diagrams with symbols representing components and would hate to waste the bits.... Thats combined with ur dy speedo would be really cool, and i know id be be super smug in the growroom . I bet it would be cheaper than buying variacs(my current plan includes them being bypassed by a remote sensor themorstat at a set temp) especally when maplins only have 0.75 amp ones for 32 quid a'piece. I may buy an electronics book and have a go at this.
Great thread man...

Can you do a circuit that will adjust the fan speed proportional to an input from a basic thermocouple device over a fixed temperature range? (or preferably, an adjustable range via a pair of pots)

Me too, i am working out a reliable way with a thermistor over a pre set temp, i will post a new board layout in next few days, unless wazzup beats me to it

First post! I know its a very old thread but did anyone ever use this design?

Will it work as a cheap alternative to Variac based diy controllers?

you could build this for around 5 quid, or you could buy a b&q fan dimmer ready built, for about 10 quid. edit: you could do a different design with an LM35 chip for a temperature sensor for auto control, not right now, heads not in quite the right place

Is this the just the same thing as a dimmer?
Would a B&Q dimmer be OK on an RVK/capacitor start fan?

yeah, that's all it is. you have to make sure you use a fan dimmer, and not a light dimmer. not all b&qs stock them, eay enough to get one off the net. not a hydro shop though or you'll be paying through the nose

thanks for the quick replies but i cant find any fan dimmers online (b&q or otherwise). I'll pop in tomorrow and ask someone instore.

Interesting idea (the original triac + diac design). I wonder how much it would cost, all told.

I've also seen this* on fleabay - a bit expensive, but it's controlled by a pot, so you could use a digital pot too, if you want to control remotely.

The main advantage though, is that it handle up to 25 Amps, which is a lot of motors.
The variac I'm using at the moment (quite happy with it BTW, see my thread) can only handle 0.75 Amps and cost me more (around 35 quid). V.G. results but you have to set it manually, no chance for automation.

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*Hm, I see that the usual "enlightened" policy of UK420 does not allow me to link to anything that may actually be of use to DIYers or anyone else.
Try searching on "POWER VOLTAGE SPEED CONTROLLER, Rheostat - 25Amp" in fleabay and good luck to you, if some loopy mod don't delete it first.

Me, I'm fed up of the moronic, paranoid, anti-any-link of this site, so this is my last post - period.

you could automate a variac with a stepper motor, or a servo from say a model airplane or whatever. easy

Yeah get the one called a halogen dimmer, that one will work with a fan no probs about a tenner in b & q.

Just to let you know this circuit is still working well in my room been running nearly 9 years now so has stood the test of time although i may revise my circuit and build myself another better version.

would it be easy to do one with an lm35 for temp control? needs a dc supply though, thought maybe just a little bridge rectum frier, with a resistor to get the right voltage drop across it, and 12v regulator would do, haven't really looked into how you'd go about injecting the signal in for the control though