Dew Heater controllers - Kenrick & RF modulation - advice sought

[niko]

It's high time I got my act together with dew control.

The guy at Bintel showed me a Kendrick 2 controller, 4 port heater controller and an Orion 4 port, 4 controller model.

The Kendrick was quite a bit cheaper and he suggested it had RF shielding which would be better for astrophotography.

I've seen a lot of Thousand Oaks models in the field =but not any Kendricks.

Anyone able to offer any advice?

cheers

niko

[mill]

Niko as long as you use shielded cable to the dew heater it will be ok.
If you want to be sure of no RF interference then you make a voltage controller without PWM but it will need a larger cooling block.
If you are on AC power it doesn't matter much but when you use batteries it is a waste of power.
I run my heaters on 12V all the time and that works ok with the refractor type of scopes.
With reflectors it will be different :(
If you make it yourself with LM voltage converters then you can make all the channels you want and expand later.

[Louwai]

I have 4 Kendrick controllers operating on 3 scopes.
1 x Premier, 2 x Digifire 7, & 1 x Digifire 10. collectively they control about 17 heaters + spares.
All work perfectly......

I like Kendrick....:D:bowdown:

[ballaratdragons]

What happened to the 'build your own heater strips and controller' plans I sent to you Nick?

Given up on DIY huh? ;)

[peter_4059]

I've got a Kendrick and had a Thousand Oak - no problem with either but the Kendrick has a pc interface and I love toys!

[tlgerdes]

I have one of the 2 port Kendricks, they just work!

[erick]

But, do you take photos through your scopes, Bryan? If I understand correctly, this is the essence of the Nick's concern - interference with electronic photography.

My experience with Kendrick controllers has been that the older controllers blow up and have to be repaired and I saw a brand new one at Snake Valley camp cease to work after an hour or so? :confused2:

[alistairsam]

Martin,

slightly different question, but why exactly do we need to avoid RF interference for astrophotography? what is the effect of RF interference on any equipment we'd use in the field?

Edit: just saw eric's post as well. eric, comments? how does rf interference affect cameras?
i had started a thread for this here http://www.iceinspace.com.au/forum/showthread.php?t=71687

didn't mean to digress niko.

[ballaratdragons]

And Bryan, who's heater controller caught on fire at Snake Valley one club night ;) :poke: :lol:

[barx1963]

I have a Digifire 7 and a dual channel, 4 output controller. The Digifire I have had for about 18 months while the other is only a month or so. They are both excellent, the digifire can be set to a percentage of output on 4 output and has full output on another 2. I use this primarily as I know once they are set they won't change. The other has knobs so there is always the risk that I will brush against them and change their settings.
Cannot comment on RF issue as I only use for visual, but I am happy with them so far.

[erick]

Not a digression, Alistair - I think this is exactly the point Nick wants to clarify (but tell me if I am wrong, Nick, please). I have no direct experience but I have seen mention of this matter from time to time here. I'm sure those with experience will comment soon.

[niko]

Thanks everyone. Yes, Eric, guess that's my real question as I hadn't heard it ever mentioned.

Ken - I feel ashamed now! I had a long discussion with an electronics mate over drinks the other night where we discussed making your setup. I even priced Nichrome wire at Jaycar!

And then today I was driving to the accountant to do my last year's tax (long overdue) and happened to be passing Bintel. Confident I would get a tax return I thought I'd just pop in and check a few prices. He even offered to hide the sale on Doug's account if I need to keep it a secret!!! :rofl:

When he raised the RF issue I got all nervous but I'll be a good lad and get the soldering iron out!!!!

cheers everyone

niko

[ballaratdragons]

:lol: I expect photos posted in here very soon of your home-made heater straps and controller :D

:rofl:

[tlgerdes]

The issue with RF interference is around Pulse Width Modulation (PWM) used to drive power in the heater straps. As you are toggling power on and off, every time you switch power if creates a small power spike that also create an RF spike with multiple RF harmonics. This RF came induce RF noise into USB and other cables if they are in close proximity. The solutions to this are 1) Dont run your heater cables near your USB cables 2) Dont run your camera power and heater power from the same power source.

It affected earlier cameras and cables more than they do now. if you notice lines or bands through your images, then RF interference from your dew heaters could be one source. If you image dont have patterned artifacts through them then dont worry.

[Barrykgerdes]

In actual fact the Kendrick PWM supply does not produce a great amount of interference at the higher frequencies. It is quite well damped by its RC filter on the output and by an RF choke in the input coupled to the low impedance of a power supply.

If you look at the output of the pulse on a CRO you will see it has its rise and fall times considerably modified by the sharp fall off of the high frequency components.

Stray radiation from PC's is a far more likely source of interference.

Good single point grounding, cable separation and shielding of equipment and cables that are sensitive is the best solution.

Barry

PS in regard to reliability I have repaired Kendrick Units and the weak point is the 555 pulse generator it doesn't seem to like voltage overloads.

BG

[ballaratdragons]

Simple fix for the pulse generation problem:

Build your own like I did and it doesn't pulse. Problem solved :thumbsup: :lol: :poke:

[Barrykgerdes]

That's too much like hard work for a person who has spent most of his life building electronic equipment for fun. Now I would rather do something else and buy those items.

Barry:P:thumbsup::):)

[peter_4059]

I've got the Premier Kendrick - no reliability problems and no RF issues.

[Tandum]

A few people have built their own using these hot wire controllers (http://secure.oatleyelectronics.com//product_info.php?cPath=100_75&products_id=625&osCsid=970a2b794983fa293138e6550ae0 98ff)from oatley electronics as dew controllers and they work fine. The box and sockets etc to mount them are the expensive bit :)

[Louwai]

Yes Ken.... But that was MY fault.... I had the controller on & running & I'd forgotton to plug in one of the straps on the scope end. The "active" extension lead shorted out on the metal leg of the tripod....

See... I've got an excuse >...:P

[ballaratdragons]

OK, you are excused :lol: