Hi,
I've read up about using a vellman 8004 kit as a dew heater controller, looks like it only needs a VR, box and cables to make it astro compatible, not bad for £10, probably £15 in total with all the bits.
Chris
http://www.rapidonline.com/productinfo.aspx?tier1=Educational+Products&tier2=Projects+%26+Robotics&tier3=Project+Kits&tier4=DC+to+pulse+width+modulator&moduleno=73984#
Yeah that would do the trick. You'd just need to add a box and the heating element.
not too dissimilar to one I put together for Tony a while back.
Did you have any success with it Tony? It might need some tweaking if not...
I made one a while ago with an IC555 timer, it all works ok, but I'd like to do some more soldering so I'll give this a go, will give you an update.
I also made a dew strip for my 8" SCT yesterday, MK2 version much has insulation on the outside of the band and it feels a lot better than the MK1 version.
Chris
Looks ideal, it's smaller and much cheaper than the maplin version too.
Chris,
Did you use resistor ladders for your dew band of nichrome wire? I have always used nichrome but its a pain to insulate the 2.5m needed to get the right resistance.
Duncan
Duncan, you can get different thickness of nichrome which are obviously different resistances. Did you try shrink wrap tubing?
I just haven't shopped around for different gauges, just got what Maplin had on the shelf (a while ago now).
Heatshrink is good but bulky. My last design was to create a dewshield 'liner' for my SKyWatcher 80mm which meant I could wind the nichrome around the plastic former I used and cover it with another layer of plastic. Welded the sheets together with a few soldering iron spot welds. Works nicely.
eBay is the best place for nichrome wire.
Heat shrink can be purchased in really small diameters too.
Hi Dunc,
I use 330ohm 1/4 watt resisters in a ladder approx 20mm appart around the scope. This really kicks off heat, on the MK2 version I have used double sided number plate foam on the back to act as insulation so less of the heat goes out side the tube, the dew heater is also positioned the heater behind the corrector and not on it, or in front of it, this way a) I use less heat and b) it causes less heat turbulance. I shortened and put my mk1 strip on the ED80 and its allways clear with only a 15% power setting on the heater controller.
This is where I got the design from.
http://www.dewbuster.com
http://www.dewbuster.com/faq/3_heaters-sensors.htm
Chris
P.S. Tesco are selling 5mm thin black (with silver coating on one side) roll matts, these would make a nice dew sheild.
QuoteP.S. Tesco are selling 5mm thin black (with silver coating on one side) roll matts, these would make a nice dew sheild.
I'm after a couple of dew shields. Have you used one of these Tescos mats?
I used a Maplin drill controller (http://www.maplin.co.uk/Module.aspx?ModuleNo=30310) but it cost 15 quid and only goes to 3A - works really well for dew strips and Peltiers. Would definitely go for the Vellman next time.
For some time I used a silver coated roll mat on my C11 (silver side out). Worked really well but eventually wanted something a bit blacker on the inside so I ended up buying a dedicated one.
Quote from: RobertM on May 03, 2010, 21:48:34
I'm after a couple of dew shields. Have you used one of these Tescos mats?
No, but I would not put one on a C11 or something large but if its a refractor or camera lens then yes they would be good.
Chris
This is how you make nice flexible strips :-
http://www.myastrospace.com/DIY_Dew_Heater.htm
That's what I did using solder braid but you have to be really quick making the joints. The solder braid is rather too good at what it's designed for...
You could just strip off a lump of old flex
Flexible speaker wire would also work.
I'm wondering if it would be any good for controlling a hot wire cutter.
Quote from: Mike
I'm wondering if it would be any good for controlling a hot wire cutter.
It'll be fine as long as the current is within the specified limit.
Might have stability issues. Depending on the design the load forms part of the control. The wire won't be significantly inductive, but it's resistance may be too low. It'd be worth taking a close look at the spec sheet.
For that price I've got to have a go. Placed an order with Rapid today. I'll post the results when available.
Kit arrived yesterday.
Today I went from this:
(http://gallery.orpington-astronomy.org.uk/albums/userpics/10053/thumb_DC_PulseWidthConv1.jpg) (http://gallery.orpington-astronomy.org.uk/albums/userpics/10053/DC_PulseWidthConv1.jpg)
to this:
(http://gallery.orpington-astronomy.org.uk/albums/userpics/10053/thumb_DC_PulseWidthConv2.jpg) (http://gallery.orpington-astronomy.org.uk/albums/userpics/10053/DC_PulseWidthConv2.jpg)
to this:
(http://gallery.orpington-astronomy.org.uk/albums/userpics/10053/thumb_DC_PulseWidthConv3.jpg) (http://gallery.orpington-astronomy.org.uk/albums/userpics/10053/DC_PulseWidthConv3.jpg)
in just under an hour.
Nice simple and easy to build kit. All I need to do now is build some heaters for the 'scope!
(Edit: Added links to full-sized images -- Rick)
Could you make those images a bit smaller please they are taking up way too much screen space.
Quote from: Mike on May 08, 2010, 23:32:11
Could you make those images a bit smaller please they are taking up way too much screen space.
I've added links to the full-sized imges... ;)
Quote from: Mike on May 08, 2010, 23:32:11Could you make those images a bit smaller please they are taking up way too much screen space.
Quote from: Rick on May 09, 2010, 09:58:34I've added links to the full-sized imges...
Thanks, Rick, I didn't know you could do that.
Mike, I included only small images as I didn't feel they were of overly great interest. My main message was that from taking the board and components out of it's mailing box to a having a soak testable board took less than an hour. I'll post some larger images of the fully completed unit in due course, if you're interested.
Personally I think it's worth buying dew strips instead of making them. They are not that expensive and you do get a nice finished product.
On the other hand I find the controllers to be overpriced - well worth the effort of making your own!
Mark
Which strips are you using, Mark?
Quote from: PhilB on May 09, 2010, 10:31:27
Thanks, Rick, I didn't know you could do that.
If you edit the relevant message you'll be able to see how it's done. ;)
Quote from: PhilB on May 09, 2010, 10:31:27Mike, I included only small images as I didn't feel they were of overly great interest.
Phil, I run an electronics business, of course i'm interested. :)
Ok, looks good, I'll put one together soon.
Marks, I really do not like spending £20-30 for a dew strip because it costs about £3 to make one for the 8" SCT and thats at Maplin prices, I also do not take them off so flexing is not an issue for me. I beleive a cheap dew heater strip for my 8" is about £25 or so. Have a look at the one I built last week, it only took about 30 minutes to do.
Chris
OK £3 vs £30 - point taken!
Quote from: Space Dog on May 09, 2010, 18:51:02
Have a look at the one I built last week, it only took about 30 minutes to do.
Chris, I'd rather like to see this. Did you post it?
Its here Phil, http://www.dewbuster.com/heaters/heaters.html one tip get a piece of wood put 4 nails in it 2 left 2 right spaced as per the spacing you want for the + & - pull the wire between the left and right sides and this gives you a nice template to solder the resisters onto.
For the insulation I use gaffer tape and double sided number plate tape (foamy stuff) the foamy tape on the outside. The wire I used is nickle covered copper wire from maplis its solid and about 1mm thick.
The resisters I used are M330ohm from Maplin, they seems to have gone upto 17p each now, I'm positive they were 8p when I bought a load.
My 8" SCT tool 24 of these, some wire and a connector to the dew heater.
Chris
I used the same construction as Chris for two small tapes and they work a treat. Whether you use resistors or Nichrome wire I'd strongly suggest you use very flexible cable so it stays like that in low temperatures.
Robert
PS. It's 330 ohm resistors....
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0132371 (http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0132371)
(http://img-europe.electrocomponents.com/largeimages/R132012-02.jpg)
2p each
1.4 if you get a thousand.
Radio spares.
Mac.
Yeah don't use Maplins, they are at least 10 times more expensive than anywhere else.
Thanks everyone, I'll give building a heater strip a try. One point though, what type of connectors do you use when connecting the strip to the power supply?
however, if you use Maplins then they'll be there when you need something for a project, *right now*...
Male phono plugs are standard for the leads - yes I know. Known for their superior current carrying capacity and reliable connection - not!!!
In other words, choose whatever connector you like. if you are making your own controller and strips then choose something suitable, you don't need to use the standard type connector.
I like Banana plugs myself. Nice and reliable.
Yellow banana plugs would match the scope nicely ...
Quotehowever, if you use Maplins then they'll be there when you need something for a project, *right now*...
RS is the same, they have direct access trade counters.
Quote from: RobertM
Yellow banana plugs would match the scope nicely ...
They would match my banana scope VERY nicely :cheesy:
Ok, its probably £2 for a dew strip then, :-)
Thats means the controller and strip would probably be £13, bargain. The cheapest pro made one I found for the controller was £29.00.
Home made rules..
Trouble is that a case for this project could easily cost as much as the project itself. :oops:
Guys i'd just like to remind you that I run a little electronics business. If you need resistors or any other components then contact me and i'll do my best to beat the price you've found elsewhere. Also, if you don't see what you want on the store, again, just ask as I might be able to get it.