Hi all,
I am in the process of building a dew controller following instructions from here http://www.blackwaterskies.co.uk/201...ew-heater.html
I am also making my own nichrome wire heater straps from the same site http://www.blackwaterskies.co.uk/201...ew-heater.html
Using the online calculator, I estimated that I will need a 12.5w 1.04 amp heater for my ED 80 and 25w 2.09 amp for my C8.
I will also be making Al Sheeney's resistor heater for my 50mm finder (3.85w 0.32 amp).
This bring the total amp draw to just under 3.5 amps.
I also want to make room in the box for my Canon DSLR power. The AC adapter for the battery is rated at 7.8v 2A output.
Now I have a few questions which I hope members can assist me with
1. I should be able to run the entire setup using a 12v 6A laptop power supply like this http://www.ebay.com.au/itm/12V-6A-AU...bbd6dc3&_uhb=1 Please confirm if this is correct.
2. I cannot find a 12v to 7.8v step down converter. I can get a 7.5v 2A module http://www.ebay.com.au/itm/221419126...84.m1423.l2649 Would this be ok? (I cannot find 8v 2A modules)
Thanks for your help in advance!
Bo
1. I find a lot of the ebay powersupplies are overrated. Including those supposedly intended for laptops. I would look at something more solid. The last thing you want to do is end your DSLR on a cheap $15 powersupply. It should be fine for dewheaters though, worst case scenario it burns down. Jaycar has a nice 12V 10A powersupply but it's on the pricier side. That said I'm certain you will want to power more from it soon :-) Dewstraps on camera lenses for widefields perhaps?
2. I would look at LM2596 module based adjustable regulators. There's heaps of variants available on ebay. like this one: http://www.ebay.com.au/itm/Brand-NEW...b428565&_uhb=1
The reason I'd pick something like this is firstly you can get your 7.8V output, and secondly because they are relatively simple single chip solutions with a good reference design they are relatively hard to screw up even for cheap nasty Chinese vendors.
Now as for the design 25w is a lot to be putting through the front of the C8, though someone may correct me. I'm putting around 14w into mine. At first I found it wasn't enough but my key problem was that I simply strapped the wire on the front of my element. It lost a lot of heat to the atmosphere. It wasn't until I put a strip of rubber around it to insulate it that it worked perfectly.
Hi Chris,
Thanks for the suggestion re LM2596 modules, I will look into them and they look like what I am after.
Re the power supply, I understand your concerns about the actual current and output. The way I thought it is that the 12v input will be stepped down to 7.8v output socket to the fake battery into my DSLR. so if anything, the stepper/LM2596 module will be blown first and not fuse in my DSLR.
Re the power output of 25w, I too thought it was on the high side.
I use a 20w rubberised band for my c8, but it ends in a fused cigarette plug. I could rewire the existing heater into an RCA plug as an alternative.
The reason I want to make a new band is I want to keep the bands the same and I have sufficient length of nichrome wire for it. The other way I look at it is that each band will be connected to a potentiometer, and therefore I can always turn the power down.
Happy to hear your views on my train of thought.
Thanks
Bo
Be very careful which units you buy off ebay. Some seem quite OK and appropriately rated, but after one unit catching fire and another breaking down, I tend to go with, you get what you pay for.
Of late I am using two postage stamp size dc-dc converters to power two dew heaters separately. Available from LEDsales in Tasmania.
You can hack up an old ATX psu if youve got one lying around. Its got good clean regulated power with lots of amps to give. By standard you can combine rails to produce 24v, 17v, 15v, 12v, 9v, 7v, 5v and 3.3v. The rails can be split and further stepped down with a buck converter like the LM2569 or a ZXY6005
I use a 300w mATX PSU as a bench supply, it can power all my DC equipment. Gonna make a power panel soon for astro stuff.
Hi,
I have used the e-Bay LED dimmers and have made my own small controller.
I feed it from a SLA battery, the only cable from battery to mount.
Having no 240V out in the field just makes it so much safer.
The SLA is housed in a $17 box and the box has 2 x 12V out and also one LED dimmer with 2 outputs, currently not in use but could heat a eyepiece box.
I have a 12V out from the dew-controler to my DSC to reduce cables.
The controller connects to the Telrad, and a cable gors from the Telrad to the heater strap on the lens.
The Telrad heater and a band for the refractor using resistors, Telrad 2 and Heater band 10.
The lens heater is just 10 resistors (30mm long) soldered across a seperated (by 30mm) speaker cable in 20mm distances , in a plastic sleve and sewn between a 50mm elastic and 50mm velcro.
I have attached some images.
Thanks Peter,
The project I had in mind would be very similar in concept. Having a 12v input would allow me to plug in either a high capacity battery or a regulated 12v DC power supply.
I am hoping to get this project off and running by end of May in ready for the colder nights ahead.
Bo
I have 2x 12v SMPS from Jaycar and they have been reliable. One is spare and happy to part with it - trade? I will check, but I think around 12A. It's open case and will need an enclosure - I use a fan ventilated plastic container with a clippable top. It's mains switched - doesn't have separate switch like the other low ripple unit.
It's the mini buck converters that have been problematic, but the Ledsales units have been OK. I have a good quality adjustable converter as well, if you want - trade?
Let me know. I'll bring them into work if you are interested.
I am the author of the instructions; I'd say that 25W / 2.09A is a bit on the high side for an 8" SCT. Using the calculator the heater I built is more like 19.5W / 1.65A.
That is perfectly adequate for UK conditions - it keeps the corrector dew free all night without a dew shield. I insulated the outside of the band with some rubber window draftproofing strip. It is not particularly thick so you might well get away with a lower power output if you have better insulation and/or a dew shield as well. Bear in mind you're just trying to keep the corrector above the dew point, not heat it so it is warm to the touch.
For my ED80 I actually wrap the same band around the outside of the metal dew-shield (goes around twice) and set the dew controller to roughly 1/3 to 1/2 power. Radiating the heat from the metal shield is actually more efficient than trying to conduct it through the front ring and corrector in the SCT. Your mileage will vary depending on your local climate of course.
240V definitely presents hazards in outside - make sure you use an RCD and have appropriate fuses in the right places to protect the equipment. I really wouldn't try to run a cheap eBay supply at maximum rating full time - either buy a better supply or use more than one (but read up about ground loops in either case which can be a hazard).
12V batteries are not as safe as you'd imagine though. No danger of electrocution, but there is a real risk of fire in case of a short-circuit. With a power supply a fuse or other component will blow if you get a short in the band or elsewhere, whereas with a battery you will get al the amps you need to cook your scope or fingers, so make sure you put a fuse inline between the battery and the load.
Hope this helps and feel free to ask any more questions you like.
Should just mention to anyone thinking of using an ATX PSU, I highly suggest mounting an in-line fuse as close to the powersupply as possible. Reason being that the incredible amount of power these things can put out (40A+) and the lack of output fusing means that if you end up with an equipment short which can often be damage free you may find your connectors and cables simply melting.
Computer powersupplies, especially larger ones will often keep humming away when you have a dead short on the other end.
Thanks Chris,
Yes, I do intend to hook up some fuses (more likely 10A) at the 12V outlets (I am hoping to get a newer PSU with 2 12V rails) to make sure they don't cook the electronics down the line. I am looking at either an inline fuse or a small fuse box with blade fuses.
Ian, welcome to IIS and thanks for the write up of your project. I have built the controllers now, will be testing it shortly to make sure all is ok. Then I will be making the heater straps. I am now leaning towards using the 20W SCT heater with the cig plug and just hook up a power distribution board powering a couple of cig sockets.
Will post some pics once I am satisfied with the results.
Bo
Cig plugs will usually have a cartridge fuse on the tip, depending on the device its for. Just twist the top and you can change the fuses for different amperage.
Thanks Ed,
Yes, I am aware of the screw in plug fuses. There are also 1 to 4 cig outlets from Jaycar that has a built in blade fuse, so lots of choices.
Bo
For the record I HATE cig plugs. I'd like to find the person who decided a plug with a spring loaded tip that basically attempts to force its way out of its socket is a good idea.
I find it funny that in this hobby of sensitive electronics and systems where having stable and continuous power for many hours at a time is imperative that so many people rely on the wretched things.
I highly recommend the smallest of the Anderson Powerpole series if you need something sturdy with a high current rating.
For the record I HATE cig plugs. I'd like to find the person who decided a plug with a spring loaded tip that basically attempts to force its way out of its socket is a good idea.
I find it funny that in this hobby of sensitive electronics and systems where having stable and continuous power for many hours at a time is imperative that so many people rely on the wretched things.
I highly recommend the smallest of the Anderson Powerpole series if you need something sturdy with a high current rating.
I have to agree, although the original design of the Cig plug and socket was different and latch better. As the cheap import became more available then the designs changed.
The CIG plug was designed only for the cigarette lighter which used the bimetal temp sensor to spring out. Someone decided to try and adapt it for non smokers and left us with frustrations.
On my last attempt I discarded and went for XLR connectors for mid current rating. Andersons are designed for very high currents and I use them for the main battery terminals.
When I was working for Jaycar I often had customers come in for a replacement plug because theirs had melted.
The spring in the tip makes a very good heater element at high currents!
On my last attempt I discarded and went for XLR connectors for mid current rating. Andersons are designed for very high currents and I use them for the main battery terminals.
Audio connectors are quite useful for signals though I've kept them away from power because of lack of standards regarding current handling (the exception being speaker terminals). I.e. different brands of XLRs have different power ratings. Just a case of making sure you get the right datasheets if you're going to push it :-)
I used to think of Anderson connectors for high currents and camper vans, electric buggies etc, but their smallest set are 15A and you can fit 4 of them in the same space as an XLR connector making them surprisingly space efficient. They are expensive though. Mind you that suits this hobby quite well doesn't it.
Audio connectors are quite useful for signals though I've kept them away from power because of lack of standards regarding current handling (the exception being speaker terminals). I.e. different brands of XLRs have different power ratings. Just a case of making sure you get the right datasheets if you're going to push it :-)
I used to think of Anderson connectors for high currents and camper vans, electric buggies etc, but their smallest set are 15A and you can fit 4 of them in the same space as an XLR connector making them surprisingly space efficient. They are expensive though. Mind you that suits this hobby quite well doesn't it.
You are correct, they are audio connectors, fortunately I had tested the ones I already have and they worked a treat with no noticeable loss in current consumption on my EQ5. There is enough metal on the contacts to allow reasonable current through. I used them because I had a lot available from a previous job which I no longer deal with any more.
There is a new CIG lighter connector, I think mention above that could be useful but they are not used much in vehicles at this stage. I believe some manufacturers are using them as accessory 12V connectors realising they are quite a good and positive connector, but they are more expensive than XLR.
With my new obs set-up I plan to investigate all my options again anyway.
