build a thermostat controlled fan speed unit, CALLING ALL SPARKYS!!!!! Options

[Detritus]

Guys,

I've been thinking about temperature control for my growbox in my attic.
As the temperature varies massively in the attic I would like to be able to have my fan speed controlled so that it (tries to) maintains the temperature within a set range by altering the fan speed (not a lot to ask I know!)

I've drawn up a rough plan but I need someone with electrical expertise (themadhippie? anyone?) to help me finish it. I may even be barking up the wrong tree completely.

well, here goes, follow me if you can!:

The system will be controlled by two thermostats which are used to set the upper and lower ends of the desired temperature band (I thought 22 deg c lowest and 28 deg highest?). Each of these will be wired to a relay (or a pair of relays - see diagram).

When the temperature drops below the low mark it will trip the thermostat which in turn operates the relay. This diverts the power to the fan so that it goes through a transformer (?80v I thought) which puts the fan on it's slowest speed so that enough air is brought in to replace that used but not enough to remove the heat generated by the lamp (a 600w hps).

The temperature will then increase until it is back into the desired range, causing the thermostat to switch back and the relay. The power to the fan is then going through a different transformer (160v?) which runs the fan at a speed that removes enough air to maintain the temperature but not enough to cool it down.

If the temperature rises above the upper limit of the range this will trip the other thermostat which operates it's relays and diverts the power so that it now flows directly to the fan and is therefore at 240v - runs the fan at maximum speed which will remove sufficient air to reduce the temperature.

I have attached a diagram to try and help explain what I have in mind.

I see Maplin's sell transformer kits which allow you to wind the secondary coil yourself so this would allow me to experiment with the voltages/speeds. Are there any better ways to do this. I've seen people talk about using thyristors to control fan speed - what are they and how much do they cost? I'm looking to do this as cheaply as possible.

Any comments, advice, complete working solutions( ) would be great.

Det

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[Thriver]

Hi m8 check this out.i hope it helps.i think that 1 thrmostat is sufficient.but it will give you something to work from

http://www.ukcultivator.biz/showthread.php?t=89

Thriver

This post has been edited by Thriver: Sep 14 2003, 01:44 AM

[Kafka]

Ello folks

No real advice on your creation / idea but I think that you could adapt Fazered's existing system to accommodate the need for a minimum temp.
To be honest though I think that you only really need a maximum temp which; when reached allows the fan to run at full pelt. All other temps your fan runs at whatever speed you set your fan speed controller at.

This is a topic which has interested me greatly since seeing the practical uses of thermostatic fan speed controllers. I think that building your own would save alot of cash over purchasing one. The thread poster on ukcultivator "Fazered" seems to be on the money. Also seems to be a qualified electrician.

Only thing I haven’t seen though is a solution for running 2 fans from the one controller unit. I’m assuming it would be possible to just wire in the other fan at the same place as the first one; thus both would switch at the same time.

- Kafka

[Thriver]

post on the thread and ask fazered

Peace

Thriver

[Themadhippy]

seems a bit complicated detrius,how you wire the thermostat depeneds on the type of fan your useing,normally you switch in another winding
heres one way of doing it.If youve olny a single speed fan then easiest and possible cheapest option is to buy a new fan

This post has been edited by Themadhippy: Sep 14 2003, 12:32 PM

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[oldtimer1]

Kafka you could run any number of fans wired in parallel as long as you did not exceed the rating of the fan controller.

[oldtimer1]

Themadhippy you can control the speed of single speed fans with solid state dimmers suitable for controlling fluorescents and transformers, basically that is what the TL FC1 fan controller is I think, although they don’t give a spec to be totally sure..

[Themadhippy]

i thought the fan motor had to be designed for varible speed use then again its been a few years since collage

This post has been edited by Themadhippy: Sep 14 2003, 01:24 PM

[Detritus]

cheers guys, thats MAGIC

Thriver, that post is superb mate - just what I needed.

I'm still keen on having 3 fan speeds (just like the idea - now I've thought of it I've got to give it a go and see if I can make it work!

Using the dimmer switch to vary the voltage is much simpler and will enable me to tinker with the two lower speeds without the need to re-wind the secondary coils! Much simpler.

I didn't realise I would be able to use a thermostat on it's own to switch the current - that's why I was using the relays.

I'm gonna go and have a look at this again now and see if I can't finish it off - I may have a completed design by tonight! If you come up with any ideas in the meantime then let me know guys - I'm sure this is a project that would be of benefit/interest to most of the people on this forum.

cheers again for your input guys, I'll let you know what I come up with.

I think I may have to change my name to Igor.

[Detritus]

Mad, just seen your latest post mate.

As far as I understand it, RVK fans are designed to be speed controlled by varying the voltage between 0-100% - this is much superior to so called "multi-speed" fans that use different secondary coils to alter the speed as it gives you infinite variation of the speed(theoretically) rather than preset speeds (none of which may be quite what you need).

I've attached a PDF on the RVK fans that I got off a link here somewhere - this place has everything you need!

Hope that helps and thanks again - I'll be needing you to look over the next version of the plan if you don't mind? It's taking shape at the moment.

Det

[oldtimer1]

its got to be a dam site longer since I was at collage. You cant use solid state controllers for cap start single phase motors.

Here is a simple diagram showing live only wiring to do what was originally asked, but using speed controllers not transformers.

Detritus, if you have no eaves insulation you may need a third cold stat to control a heater, you don’t want your box going below 60f in dark periods. Long run eves insulation of the whole loft is the answer.

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[oldtimer1]

I should add the change over stat can be 2amp, the ones made by Honeywell are the most accurate of the mechanical types, ie the smallest switching swing. They also have a long life when controlling inductive loads like pumps and zone valves.

[Detritus]

thanks oldtimer! I've just drawn almost exactly the same picture as I've just found a changeover thermostat on TLC - I didn't realise you can get them!

I didn't get the part about the controllers - did you mean that the one I was gonna use:
http://www.tlc-direct.co.uk/Products/VLFC1.html
isn't suitable? if so, then I presume this one sold is ok?:
http://www.growell.co.uk/p/1541/Fan_Speed_...ontrollers.html

thanks for the help mate,

Det

p.s. - I've got an even better invention in the pipeline that would ideal for all those overanxious fathers - but I'll save that for once this is completed. It's gonna take a lot more work but it'll be worth it! I can't wait!

[oldtimer1]

I would use the tlc ones they are on a standard single plate type, mount them on a surface box made to take two single plates.

Honeywell stats are better than the ones sold at tlc.

You may be able to find units cheaper still at a local wholesaler, its worth asking around.

If you want to be really pucker you could parallel the high speed stat with a humidity stat!

Only joking, but I was going to do it once, I do like toys.

That coalface he's a bad troll!!!!!

[Detritus]

It must be fucking cold in here 'cos my brains working overtime - silicon-absolutezero-superconductivity does that for you! Better stop smoking this ICE!

guys, I've drawn up a shopping list for the system now:

from www.tlc-direct.co.uk:
VLFC1 mulit-speed fan control x 2 @ £11.70(inc vat) = £23.40
AA225MB 2 gang 25mm surface box white x 1 @ £1.06(inc vat) = £1.06
AAJB20 20Amp 4 terminal junction box x 1 @ £0.76(inc vat) = £0.76

from www.discountedheating.co.uk:
T6360B 1028 2Amps thermostat x 2 @ £14.22(inc vat) = £28.44

so the total cost is £53.66 plus delivery!
not bad - let me know if you find any of these bits cheaper anywhere! I won't be able to put it together for a while - if anyone else does then let me know how brilliantly it works!

thanks again for all your help guys,

Det