6 Channel Dew Heater Controller

[malc-c]

I've been looking at installing a dew control system to the observatory, but was shocked at the cost of commercially available multi-channel controllers. I didn't want to dabble in a complete self build from discrete components, so looked at other PWM options, such as 12v drill speed controllers, but then the cost of six of those worked out more expensive than a 4 channel commercial unit.

I was browsing for a few computer upgrades and by chance stumbled on a PC modding site where the guy used a 6 channel speed controller for the fans in the case. A bit more research and I located a suitable unit which will form the basis of my experiments.

I ordered from Scan Computers at 4pm yesterday and it arrived at 2pm today - very impressed and for only £3.99 delivery.

The specification is that each output is rated at 30w which should be ample for the heaters I intend to use.

OK onto the initial testing:

I plugged a spare fan in to one of the outputs and connected the unit to the PC - The fan could be spooled up from off to full speed - so it worked as intended. I then used an old molex connector to fabricate a test lead to power it from just the 13.8v bench supply, hoping that the unit would derive any 5v it needs from the 12v supply rail - No such luck So the first modification will be to use a 7805 1amp regulator to provide the 5v supply from the incoming 12v supply.

The unit came with six fly leads to hook up various fans, these will have their ends removed and terminated in tradition phono sockets.

The best bit is the cost - Less than £24 delivered

[Reggie]

any pictures of the circuit board attached to that? Or is it simply relying on the resistance of the pots to lower current/voltage going to the heaters? I wonder if it's actually doing PWM or whether it relies on the motherboard/fans to have the speed control circuit?

2x 556 timers would give you 4x independent pwm ports, it's a pretty simple circuit too.

lastly, was it £4 or £24 delivered?

[malc-c]

Reggie,

I'll post some pictures later, but basically there is a large chip on the PCB and it's quite heavily populated with surface mount components. The spec states that it's 6 x PWM outputs, and when I tested with a fan you could hear the pulses in the fan windings at the lowest setting.

I've now added a 5V regulator and had it driving a 52 ohm power resistor. At the low setting it was warm, but I could still hold the resistor comfortably in my hand. I then cranked it up and and felt it getting hotter, so turned it down and the heat dissipated. No a scientific test I know, but at least it proved it would work with more load than PC fan.

Yes I know about the schematic that uses an NE555 / 556, but as I said, I wasn't really looking at making something up on stripboard, and this looked the ideal solution.

The unit was £20.78 in VAT with delivery being £3.99

Here's a link to the manufactures site http://www.akasa.co.uk/update.php?tpl=product/product.detail.tpl&no=181&type=Fans&type_sub=Fan%20Controller&model=AK-FC-08BK

[Reggie]

Thanks malc, no worries, I wasn't sure what the akasa featured, wasn't sure if it was just pots controlling it or some kind of pwm, so I suggested the 555/556 circuit just in case. I found your controller on the akasa site this afternoon but couldn't find any pictures of the guts.

[malc-c]

OK, even though I'm recovering from a chest infection I wrapped up warm and stuck the heaters on in the warm room and went out for an hour - Bad mistake and now suffering for it So I've come back inside and have taken a picture.

This is how far I got.

[Reggie]

Sorry to hear that you're not well Malc, I can see a header on that board, with SDA,SCK on it, I wonder if that's an i2c header for something, lcd display possibly? Pity the IC is one of those black blob jobs, I wonder if there are any identifiable ICs on the other side of the board.

[malc-c]

Can't see any components on the other side of the board (other than the pots and LEDs)

Here's a close up... would be interesting what the I2C bus is used for ??

[malc-c]

Question...

Is there any disadvantage of having longish (circa 7m) cables between the controller and the heaters. The reason I ask is that I could install the controller in the warm room and then run cables to the heaters. If the voltage drop is going to be that great then I'll have to place the controller on the pillar some way

[Psychobilly]

You could run reasonably thick cable from the unit in the warm room to a break out box on the pier... and leave the extra flex connections on the dewbands should be ok then

[malc-c]

You could run reasonably thick cable from the unit in the warm room to a break out box on the pier... and leave the extra flex connections on the dewbands should be ok then

Uhmmm... So I could run 6 sets of cables with in-line phono sockets from the pier to the controller in the warm room without issue. Then simply connect the dew bands to the sockets... sounds good

[michael8554]

At that price this looks very handy.

Do the outputs come directly from the big chip, or are there seperate output devices on heatsinks for the 180W total it can pump out?

Cheers

Michael

[malc-c]

Michael, the chip in the photo is a standard 7805 5volt regulator. I was hoping that the PCB would derive any 5v line it needed from the 12v supply, but alas it didn't. I therefore had to install the regulator to give me a 5v supply.

I can only presume that the unit uses some form of PWM switching supply as there are no large mosfets or power transistors, unless they are of the SMT type device rather than discrete.

[Reggie]

seems to be a lot of power handled but nothing in the way of heatsinking? Apart from what I assume is your 7805 bolted to the side of the unit?

[malc-c]

true... been doing further googling to see if this has been done before and came across one similar project in the states, around 18 months old. The controller he used had rows of TO22 devices bolted to heatsinks... which made me a bit shocked when I got the Akasa unit as there is nothing like that in the unit. But it claims 2.5A output from each channel - other than placing a 5ohm 50w resistor on each output to test there is no way of proving or denouncing the manufactures specs

[Reggie]

you could always email akasa, they might play ball and give you some info?

[malc-c]

you could always email akasa, they might play ball and give you some info?

Might just give that a whirl.

OK picked up some phono sockets from Maplin this afternoon and spent a few hours fabricating a rear panel. Pleased to say it all works

I've added three additional phono sockets off the input to act as a power distribution box as well. Hoping to fix it to the pillar tomorrow and then re-wire the supply to the mount and USB focuser which will make for a neater installation.

Now just need to sort out some heaters, either DIY or buy some commercial bands....

Here's a picture - with the cover removed

[kirkster501]

Malc, Can you put together a procedure for building this please mate? I have exactly that fan controller in my PC spares box and I was thinking along very similar lines to you in building such a dew box - great minds think alike!

Right heading out to see some stars......

[malc-c]

Malc, Can you put together a procedure for building this please mate? I have exactly that fan controller in my PC spares box and I was thinking along very similar lines to you in building such a dew box - great minds think alike!

Right heading out to see some stars......

It's fairly simple. To use the controller as is (ie without taking it all apart and putting it in a new box) I used the following:

1 x 7805 1A 5v regulator

1 x 2mm sheet of plasticard (available from any good model shop)

1 x 28ml bottle of liquid poly weld (solvent adhesive for the plasicard)

Multi-Phono sockets to suit Multi - Phono Sockets : Loudspeaker & Speakon Connectors : Maplin Electronics (either 2 x 4 square or an 8 way square cut down)

couple of M3 x 10mm nuts and bolts

Simply cut the plasicard to fit the rear panel, add some side tabs to support the panel, weld them together and then cut out the rear panel to accept the phono sockets. Then its a case of doing the wiring.

The unit needs a 5v supply which is derived from the 12v supply using the 7805 regulator. I'll see if I can draw something up, but its well documented on the web. For the outputs I used the supplied cables, simply remove the yellow RPM data wire then connect the RED as the supply and common the BLACK wires

[Psychobilly]

This got me thinking... while it would add £12 to the cost you could get a cheap 5.25" external drive bay case of ebay.. this would already have the 12V to 5V adpator inside it.. you would still need to beef up the 12V supply connection though as typically they only good for a couple of amps from the rear power supply input...

5.25" Dual SATA/IDE to USB 2.0 External DVD CD HDD Drive PC Case Enclosure Caddy | eBay

Peter...

[malc-c]

Peter, that's a neat idea... the only drawback I can see is the depth.

[Psychobilly]

If you can find one that an extrusion then they can be cut back to any length... Ok it's not a 2 minute job... but...

[malc-c]

If you can find one that an extrusion then they can be cut back to any length... Ok it's not a 2 minute job... but...

Like this 5.25" IDE CD/DVD/RW USB 2.0 IDE Enclosure Caddy | eBay

[Psychobilly]

Yep... Depends how easy it is to remove one of the ends ...

[Reggie]

Just a thought, why not gut an old optical drive? would be shorter than the caddy as it's not got to accomodate cables, fans and sockets for the drive to plug into.

[kirkster501]

It's fairly simple. To use the controller as is (ie without taking it all apart and putting it in a new box) I used the following:

1 x 7805 1A 5v regulator

1 x 2mm sheet of plasticard (available from any good model shop)

1 x 28ml bottle of liquid poly weld (solvent adhesive for the plasicard)

Multi-Phono sockets to suit Multi - Phono Sockets : Loudspeaker & Speakon Connectors : Maplin Electronics (either 2 x 4 square or an 8 way square cut down)

couple of M3 x 10mm nuts and bolts

Simply cut the plasicard to fit the rear panel, add some side tabs to support the panel, weld them together and then cut out the rear panel to accept the phono sockets. Then its a case of doing the wiring.

The unit needs a 5v supply which is derived from the 12v supply using the 7805 regulator. I'll see if I can draw something up, but its well documented on the web. For the outputs I used the supplied cables, simply remove the yellow RPM data wire then connect the RED as the supply and common the BLACK wires

Thanks, so to confirm the heaters will have a 5v potential cross them right? You are using the 7805 to drop the incoming 12v down to 5v in order to provide that potential? If so, and at 5v, that's quite a current that'll be drawn for the same power...

Did you just wire the 7805 in line with the 12v incoming?

Thanks, Steve